estado de la tecnología de la captura y almacenamiento de...
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eEquation Chapter 1 Section 1
Trabajo Fin de Grado
Grado en Ingeniería de Organización Industrial
Estado de la tecnología de la captura y
almacenamiento de CO2. Modelado y
optimización del proceso “Calcium
Looping”.
Dep. Ingeniería de Sistemas y Automática
Escuela Técnica Superior de Ingeniería
Universidad de Sevilla
Autor: Gonzalo Muñoz Romero
Tutora: Ascensión Zafra Cabeza
Sevilla, 2017
Trabajo Fin de Grado
Grado en Ingeniería de Organización Industrial
Estado de la tecnología de la captura y
almacenamiento de CO2. Modelado y
optimización del proceso “Calcium Looping”.
Autor:
Gonzalo Muñoz Romero
Tutora:
Ascensión Zafra Cabeza
Profesora titular
Dep. de Ingeniería de Sistemas y Automática
Escuela Técnica Superior de Ingeniería
Universidad de Sevilla
Sevilla, 2017
TRABAJO FIN DE GRADO ESTADO DE LA TECNOLOGÍA DE LA CAPTURA Y ALMACENAMIENTO DE CO2.
MODELADO Y OPTIMIZACIÓN DEL PROCESO “CALCIUM LOOPING”.
Autor: Gonzalo Muñoz Romero
Tutor: Ascensión Zafra Cabeza
El tribunal nombrado para juzgar el Proyecto arriba indicado, compuesto por los siguientes miembros:
Presidente:
Vocales:
Secretario:
Acuerdan otorgarle la calificación de:
Sevilla, 2017
El Secretario del Tribunal
A mi familia
A mis maestros.
¿Qué mayor rechazo a aquellos que
quisieran acabar con nuestro mundo que unir nuestros mejores esfuerzos para salvarlo?
“Barack Obama’’
i
Agradecimientos
Una vez llegado a este punto de mis estudios, me gustaría dar las gracias a las siguients personas por lo contribuido en estos cuatro años:
Gracias a mi familia, a todos por aguantar mis quejidos y mis tonterías en este período y darme el ánimo y las ganas para seguir que en ocasiones faltaba. Gracias a mi madre por darme el cariño que sólo ella sabe dar y a mi padre por ser el acicate que siempre es necesario.
Gracias a la familia que se elige, los amigos. Gracias por escucharme, aliviar las penas y celebrar los triunfos. Gracias por ser una influencia tan positiva en la vida y ejemplo de verdadera amistad.
Gracias a aquellos profesores que me han formado como ingeniero, alecionado sobre la vida, y hacer que hoy en día sea una persona de provecho.
Finalmente agradecer a mis tutoras María y Ascensión, por su amabilidad y estar siempre con una sonrisa cuando las necesitaba.
A todos ellos, gracias de corazón.
Gonzalo Muñoz Romero
Sevilla, 2017
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iii
Contents
Agradecimientos i
Contents iii
List of Tables vii
List of Figures ix
Resumen xi
Abstract xxiii
1 Introduction 1
1.1 Context 1
1.2 Objetive of this work 3
2 Precedent 4
3 Options for CO2 capture 7
3.1 Pre-combustion capture 8
3.1.1 Concept 8
3.1.2 Advantages & Disadvantages 9
3.2 Post-combustion capture 10
3.2.1 Concept 10
3.3 Oxyfuel combustion 10
3.3.1 Concept 10
3.3.2 Advantages & Disadvantages 11
4 Technologies for post-combustion capture 13
4.1 Absorption process 13
4.1.1 Concept 13
4.1.2 Advantages & Disadvantages 15
4.2 Adsoprtion process 16
4.2.1 Concept 16
4.2.2 Advantages & Disadvantages 16
iv
4.3 Ionic liquid membranes 17
4.3.1 Concept 17
4.3.2 Advantages & Disadvantages 19
4.4 Mixed matrix membranes (MMM) 20
4.4.1 Concept 20
4.4.2 Advantages & Disadvantages 21
4.5 Enzyme based separation 22
4.5.1 Concept 22
4.5.2 Advantages & Disadvantages 22
4.6 Hydrate based separation 23
4.6.1 Concept 23
4.6.2 Advantages & Disadvantages 24
4.7 Calcium looping CO2 capture 24
4.7.1 Concept 24
4.7.2 Advantages & Disadvantages 25
4.8 Summary made in Excel of the CO2 capture processes 26
5 Model 29
5.1 Introduction 29
5.2 Description of the model 31
5.3 Inputs & Outputs 38
5.4 Economic Study 38
5.4.1 Coal & Oxygen 38
5.4.2 Costs 41
5.5 Future trends 43
5.6 Conclusions 45
6 Storage 47
6.1 Geological storage 47
6.1.1 CO2 storage mechanisms in geological formations 48
6.2.1 Risk & Environmental impact 50
6.2 Industrial CO2 utilization 52
6.2.1 Biofuel production from CO2 53
v
7 Legislation 57
7.1 Subsurface 57
7.2 Kyoto Protocol 57
7.2.1 The International Emissions Trading System 58
7.3 The Paris Agreement 59
7.4 Legal main developments of geological CO2 capture in the developed countries 60
7.5 Current state of CCS policy 61
7.6 Public perception of CCS 62
8 Conclusion 63
Apendix 67
Bibliography 72
vi
vii
LIST OF TABLES
Table 1. Table of CO2 capture technologies. Pg. 27
Table 2. Comparation of Spanish and South African coal. Pg. 39
Table 3. Comparation of costs in both situations. Pg. 40
Table 4. Capital cost of the Ca-l model. Pg. 42
Table 5. Operation & Maintenance cost. Pg. 42
Table 6. Cost of mineralization and energy required. Pg. 50
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ix
LIST OF FIGURES
Figura 1. Emisiones de CO2 en 2015. Pg. xii
Figura 2. Opciones para la captura de CO2. Pg. xiii
Figura 3. Diagrama de la absorción química. Pg. xv
Figura 4. Funcionamiento de membranas. Pg. xv
Figura 5. Esquema captura CO2 mediante ciclos carbonatación. Pg. xvi
Figura 6. Esquema de la oxicombustión. Pg. xvii
Figura 7. Potencial mundial de almacenamiento de CO2 en cuencas sedimentarias. Pg. xix
Figura 8. Ciclo de la mineralización del CO2. Pg. xx
Figura 9. Diagrama de la conversión de CO2 en hidrocarburos. Pg. xxi
Figure 10. Evolution of energy consumption in USA. Pg. 1
Figure 11. Number of CCS related publications from 1970 to 2012. Pg. 5
Figure 12. Progess of CCS proyects capacity from 2012 to 2020Options For CO2 Capture Pg. 5
Figire 13. Options for CCS capture. Pg. 7
FIgure 14. Diagram of pre-combustion capture. Pg. 8
Figure 15. Gasification plant in USA. Pg. 9
Figure 16. Diagram of oxyfuel combustion. Pg. 11
Figure 17. Diagram of absprtion CO2 capture process. Pg. 13
Figure 18. CO2 absoprtion mechanism. Pg. 14
Figure 19. Absorption CO2 capture plant in Malasia. Pg. 15
Figure 20. Principle of gas separation membrane. Pg. 17
Figure 21. Principle of gas absoprtion membrane. Pg. 18
Figure 22. Commonly used anions and cations. Pg. 18
Figure 23. Ilustration of facilited transport of CO2 in a membrane. Pg. 19
Figure 24. Robenson upper bound correlation for CO2 CH4 separation. Pg. 21
FIgure 25. Memzyme operation diagram. Pg. 22
Figure 26. Formation of hydrates. Pg. 24
Figure 27. Diagram of calcium loopin CO2 capture. Pg. 25
Figure 28. Diagram of calcium looping looping CO2 capture. Pg. 29
Figure 29. Variaton of parameters with sulfation level. Pg. 34
Figure 30. CO2 capture efficiencyr vs. active space time for 3 different reactor sizes Pg. 35
x
Figure 31. Spanish coal vs South African coal. Pg. 40
Figure 32. O2 introduced depending of the efficiency. Pg. 44
Figure 33. Integration of calcium looping in the cement industry. Pg. 44
Figure 34. Ca-L without recarbonator. Pg. 44
Figure 35. Ca-L with recarbonator. Pg. 44
Figure 36. Ca-L with three fluidized beds. Pg. 45
Figure 37. Shematic of the trapping mechanism and their evolution over a 10000 year
period, expressed as a percentage of the total trapping. Pg. 47
Figure 38. Shematic of geological storage options. Pg.49
Figure 39. Possible escape routes and possible solutions for co2 injected into saline
formations. Pg. 51
Figure 40. A shematic of CO2 movement after injection. Pg. 52
Figure 41. Diagram of the convetion of CO2 into hidrocarbons. Pg. 54
Figure 42. Projection of use of biofuel as global energy source. Pg. 55
Figure 43. Shematic of CO2 trading emissions mechanism. Pg. 59
Figure 44. Contribution of different options to mitigate Co2 for the 450 scenario. Pg. 63
Figure 45. Educating game for ilustrate a CO2 capture plant in Japan. Pg. 64
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Resumen
El presente trabajo tiene como temática la revisión de las diferentes técnicas actuales de
captura de CO2, además de ofrecer una breve visión sobre el ámbito legal sobre este aspecto.
Además, también se presenta un apartado introductorio sobre el almacenaje del CO2
previamente obtenido con los métodos de captura a explicar. Finalmente se muestra un
pequeño modelado en el lenguaje de programación C sobre la técnica de captura denominada
‘’Calcium Looping’’. Se ha realizado un algoritmo para calcular la cantidad de masa de cal viva
(CaO) y caliza (CaCO3) necesarias para una determinada eficiencia y flujo de gases de entrada.
Además, se realizará una aproximación de los costes del proceso y las posibles mejoras del
mismo.
Desde el siglo pasado los países desarrollados de nuestra sociedad han experimentado un
crecimiento exponencial junto a un gran incremento del consumo energético. Se ha debido a
un modelo energético centrado en el uso de combustibles fósiles, llevando a un aumento
considerable de las emisiones de los gases de efecto invernadero (GEI). Esto ha conllevado a la
situación crítica actual donde el aumento de CO2 en la atmósfera, principal causante del efecto
invernadero que ha obligado a tomar iniciativas para tratar de reducir o evitar que emisiones
antropogénicas de los grandes centros de combustión alcancen la atmósfera.
Son varias las opciones tecnológicas para reducir las emisiones de GEI; reducción del consumo
de energía, uso eficaz de la energía (tanto en la utilización como en la conversión energética),
uso de combustibles con menores contenidos en carbono (como el gas natural frente al
carbón), promoción de los sumideros naturales de CO2 (como los bosques, suelos u océanos),
uso de fuentes de energía con bajos niveles de emisión de CO2 (como las energías renovables
o la nuclear) y la Captura y Almacenamiento Geológico de CO2 (CAC). Según el Informe del
Panel Intergubernamental para el Cambio Climático de Naciones Unidas (IPCC) la Captura y
Almacenamiento de CO2 contribuiría entre el 15% y el 55% al esfuerzo mundial de mitigación
acumulativo hasta el 2100, presentándose, por tanto, como una tecnología de transición que
contribuirá a mitigar el cambio climático.
El Cambio Climático es un fenómeno global que requiere una respuesta multilateral y
colaboración de todos los países. Tras la ratificación del Protocolo de Kioto, la Unión Europea
ha modificado e incluido nuevas Directivas Medio Ambientales que regulan y limitan las
emisiones de Gases de Efecto Invernadero en ciertos sectores industriales: generación de
electricidad, refino del petróleo, fabricación del cemento, vidrio, papel y cerámica (Directivas
2003/87/CE y 2004/101/CE). Recientemente se ha incluido un sector adicional, el sector del
transporte aéreo (Directivas 2009/29/CE), fijando además un nuevo objetivo europeo para
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limitar las emisiones: reducción de un 21% en el año 2020, con respecto a los niveles notificados
del 2005.
Para hacernos una idea de como son las emisiones de CO2 en cada país, se presenta una imagen
que muestra las emisiones de CO2 en en 2015.
Figura 1. Emisiones de CO2 en 2015.
La CAC ha experimentado un expencial crecimiento desde sus inicios, especialmente en esta
última década. El primer proyecto de este tipo en realizarse fue en Estados Unidos en 1972, con
el llamado ‘’Terrell Natural Gas Processing Plant’’. Pertenecía a la industria del procesamiento
del gas, tenía una capacidad de captura de 0,4-0,5 MTPA (millones de toneladas por año) y se
almacenaba medicante la técnica EOR (Enhanced Oil Recovery). Actualmente hay más de una
decenea de proyectos en construcción, con una capacidad media de captura de 2 MTPA.
Tecnologías para la captura de CO2
En lo referente a la captura de CO2, se ha evolucionado desde las técnicas de captura en la
precombustión hasta la actual línea de investigación del oxicombustión (captura usando una
combustión con oxígeno puro).
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Figura 2. Opciones para la captura de CO2.
Existen diferentes técnicas de captura de CO2 dependiendo de si se produce antes o después
de la combustión del combustible que lo produce.
1. Precombustión
En los sistemas de pre-combustión, el combustible primario se transforma primero en gas
mediante su calentamiento con vapor, aire u oxígeno. Esta transformación produce un gas
compuesto esencialmente de H2 y CO2, que pueden ser fácilmente separados. El hidrógeno
puede entonces utilizarse para la producción de energía o calefacción. Un ejemplo tipo de este
mecanismo en España se encontraba en Puertollano (Castilla-La Mancha), con la central de
precombustión de la empresa ELCOGAS, la cual tuvo que cerrar por la ausencia de las ayudas
públicas al carbón, mostrando la carencia de iniciativas por parte del gobierno respecto a las
CAC.
Se pueden distinguir tres pasos principales en el aprovechamiento de combustibles primarios
con captura en precombustión:
1. Reacción de producción de gas de síntesis. Procesos que llevan a la generación de una
corriente compuesta principalmente por hidrógeno y monóxido de carbono a partir
del combustible primario. Existen dos vías
Reformado con vapor de agua
•𝐶𝑥𝐻𝑦 + 𝑥𝐻2𝑂 → 𝑥𝐶𝑂 + 𝑥 +𝑦
2𝐻2
Reacción con oxígeno
•𝐶𝑥𝐻𝑦 +𝑥
2𝑂2 → 𝑥𝐶𝑂 +
𝑦
2𝐻2
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2. Reacción shift para convertir el CO del gas de síntesis a CO2. Esta reacción aporta
más hidrógeno a la corriente de gases de la fase anterior. La reacción se conoce como
reacción shift de gas - agua:
𝐶𝑂 + 𝐻2𝑂 → 𝐶𝑂2 + 𝐻2
3. Separación del CO2. Existen diversos procedimientos para separar el CO2 de la
corriente CO2/H2. La concentración de CO2 en la corriente de entrada al separador
puede estar comprendida entre el 15-60% en base seca y la presión de la corriente
entre 2-7 MPa. El CO separado está disponible para su almacenamiento.
• Reformado con vapor de gas natural e hidrocarburos ligeros
Es la tecnología dominante actualmente para la producción de hidrógeno. Existen
plantas que producen hasta 480 t/día de H2. El combustible de alimentaciónsuele ser
gas natural, por lo que el proceso se conoce como reformado de metano con vapor de
agua (en inglés SMR), aunque podrían ser también hidrocarburos ligeros. Es
fundamental una previa eliminación del azufre del combustible de alimentación, ya que
es muy perjudicial para el catalizador de níquel usado.
• Centrales eléctricas de gasificación integrada en ciclo combinado (GICC)
Son un caso particular relativo a la gasificación. En el gasificador se produce la
oxidación parcial a presión del combustible, aportando la propia reacción el calor
necesario. La corriente de gas de salida del gasificador se enfría en intercambiadores
cediendo calor al vapor que alimentará a las turbinas de vapor de ciclo combinado.
2. Postcombustión
La idea principal de esta tecnología es trabajar con los gases de combustión de grandes focos
emisores de CO2, de tal forma que se aumente la concentración de CO2 en la corriente
principal de los gases, pasando de una concentración de un 12% - 15% a una concentración
próxima al 100% de CO2. El principal escollo de este tipo de tecnologías es el consumo de
energía que repercute en una pérdida de eficiencia muy relevante y en el alto coste de la
inversión requerida para separación de CO2 en comparación al resto de la planta.
• Absorción química
Este proceso es el más relevante y ampliamente usado para la separación de CO2 de un
flujo de gases, siendo una tecnología madura para la purificación de gas natural y la
xv
producción de CO2 para usos industriales. La base de todos estos procesos es la
reacción de una base alcalina, normalmente aminas (MEA), en medio acuoso con un
gas ácido.
Figura 3. Diagrama de la absorción química.
• Adsorción
En estos procesos se utilizan tamices moleculares o carbón activo para adsorber el CO2.
La desorción del CO2 se realiza variando las condiciones de temperatura, pero
fundamentalmente las de presión. Se usa principalmente para la eliminación de CO2
del gas síntesis y producción de H2, aunque aún no se ha alcanzado una etapa comercial
como con la tecnología de absorción.
• Membranas
Consiste en hacer pasar por una membrana un flujo con alto contenido de CO2 y
elevada presión, absorbiendo esta el CO2 del flujo o separándolo en otra corriente de
alto contenido de CO2. Se suelen usar membranas de polímeros, pero se han mostrado
insuficientes debado a al gran consumo de energía y bajo nivel de recuperación de CO2.
Se están investigando en líneas innovadoras como el uso de líquidos iónicos para
mejorar estos parámetros.
Figura 4. Funcionamiento de membranas.
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• Captura con enzimas
Con esta tecnología se pretende crear rutas biosintéicas para la fijación del CO2. Existen
alternativas como el anhídrido carbónico o en enzimas parecidas a las usadas por las
plantas en su fotosíntesis.
• Captura basada en hidratación
Se basa en el uso de un gas compuesto por tetrahidrofurano y agua para capturar CO2
mediante la formación de pequeños cristales donde el CO2 queda atrapado. Permite la
captura de grandes cantidades en condiciones de baja temperatura y presión, con lo
que últimamente ha llamado mucho la atención
• Captura mediante ciclos de carbonatación
Por el interés que está generando y posible implantación el un futuro próximo, esta
tecnología será vista con mas detenimiento en el trabajo. Dicha tecnología se basa en
la reacción del CaO (cal viva) con el CO2 para formar CaCO3 (caliza) denominada
“carbonatación”, y su posterior reacción de descomposición a alta temperatura
denominada “calcinación” para liberar el CO2 capturado para su posterior
almacenamiento. Está formado por dos reactores, carbonatador y calcinador, y entre
ellos circula una corriente con CaO y CaCO3 que está recirculando constantemente. La
caliza se degrada con cada ciclo, con lo que se va añadiendo una corriente de caliza
freca para mantener la relación de recirculación constante.
Es aún una tecnología en fase de desarrollo, pero ya se están investigando nuevas líneas
de mejoras al esquema general, como su implantación en la industria cementera o la
adición de otro carbonatador.
Figura 5. Esquema captura CO2 mediante ciclos carbonatación.
3. Oxicombustión
Esta tecnología se basa esencialmente en realizar el proceso de combustión en una atmósfera
rica en O2, con el fin de obtener una corriente de gases de combustión con un alto porcentaje
de CO2 para facilitar así su captura.
xvii
El principal problema asociado a la combustión con oxígeno puro es la altísima temperatura
que se alcanza, ya que la temperatura en la llama es del orden de 3000 K, haciendo inadmisible
su puesta en funcionamiento ya que no hay materiales que soporten estas temperaturas. Para
solventar este problema se hacen recircular los gases de escape o inyectando agua, de manera
que la temperatura desciende hasta los 1300-1400 ºC.
Por último, la tecnología de la oxi-combustión se usa en industrias como la del aluminio, vidrio
y acero, aunque para la implantación comercial de la tecnología en los procesos de captura de
CO2 aún se necesita bastante desarrollo.
Figura 6. Esquema de la oxicombustión.
Modelado “calcium looping’’
En la siguiente parte del trabajo se presenta el modelado del sistema de carbonatación-
calcinación. El modelo a seguir es el propuesto por Matteo C. Romano en la página 269 del
artículo ‘’Modeling the carbonator of a Ca-looping process for CO2 capture from power plant flue
gas’’.
Mediante este modelo, se pretende calcular la cantidad de materia a introducir en el sistema
para una determinada eficiencia deseada y una altura de carbonatador de 40 m. Tras la
resolución del modelo, añadimos nuevas ecuaciones para obtener una información mas
completa de este, para así poder realiar luego una aproximación de los costes de capital y de
operación (los más representativos del proceso).
Como entrada principal destacamos el volumen de CO2 que entra en el sistema y la eficiencia
deseada. Como salidas tenemos la cantidad de masa a introducir, las cenizas generadas, masa
de carbón a introducir para la combustión en el carbonatador y el oxígeno necesario para la
oxicombustón requerida. Este ultimo dato es de especial importancia ya que la separación del
oxígeno mediante un ASU (Air Separation Unit) es un proceso muy caro y tendrá relevancia
en el cálculo de los costes.
xviii
Tras realizar el modelado, se presentarán unas gráficas y análisis comparativo entre el carbón
español y el sudafricano, los más habituales en las centrales térmicas españolas. Pese a ser el
carbón español mas barato, finalmente es mucho más caro que la otra opción ya que posee un
poder calorífico muy inferior al sudafricano y por consiguiente hará falta más carbón y mas
oxígeno procediente del ASU.
Con este ejercicio práctico, se intenta mostrar en líneas generales los elementos, costes y
problemas a la hora de abarcar la implantación de este proceso de captura de carbono como
alternativa a las actuales, dando unas pequeñas pinceladas de la situación y perspectiva de
futuro de esta tecnología.
Almacenamiento de CO2
Una vez capturado el CO2 mediante algunas de las técnicas anteriores, es necesario almacenar
el CO2. Este tema ha provocado incluso mayores quebraderos de cabeza que la captura del gas,
ya que además de las dificultades técnicas para su almacenaje, existen otros factores de carácter
político y social que añaden complicaciones a la hora de pensar dónde y cómo almacenar el
CO2.
Numerosas opciones para almacenarlo se han ideado, como la mineralización ex-situ, la
inyección de CO2 en las profundidades oceánicas o el almacenamiento geológico. De todas
estas, sólo la última opción es considerada factible hoy en día y además posee suficiente
capacidad para almacenar todo el CO2. Se considera que nuestro planeta tiene una capacidad
de almacenamiento total de CO2 de 236 Gt, siendo la teórica 2000 Gt, mientras que las
emisones por año en 2020 se esperan de 8-12 Gt. A continuación, se muestra un mapa global
con las zonas con mayor capacidad de almacenamiento. En las cuencas sedimentarias pueden
encontrarse formaciones salinas, yacimientos de petróleo, gas, o capas de carbón apropiados.
xix
Figura 7. Potencial mundial de almacenamiento de CO2 en cuencas sedimentarias.
• Los mecanismos de almacenamiento geológico de CO2 son los siguientes :
• 700-3000m donde la roca es mucho impermeable. Mayor capacidad que otros
• Facil control y riesgo mínimo. EstabilidadAcuíferos salinos
• Bajo coste debido a la recuperación del petroleo.
• Una vez extraido el petróleo, el 75% CO2 permanece.
Recuperación mejorada del
petróleo
• Bajo coste ya que se recupera el metano adherido en los micro-poros del carbón.
• Bajo nivel de investigación aún
Recuperación de metano
xx
• Mineralización
La carbonatación mineral se refiere a la fijación de CO2 mediante el uso de óxidos
alcalinos y alcalinotérreos, como el óxido de magnesio (MgO) y el óxido de calcio
(CaO), que están presentes en las rocas de silicatos de formación natural como la
serpentina y el olivino. Las reacciones químicas entre estos materiales y el CO2
producen compuestos como el carbonato de magnesio (MgCO3) y el carbonato cálcico.
La carbonatación mineral produce sílice y carbonatos que se mantienen estables
durante largos períodos de tiempo y que, por tanto, pueden eliminarse en zonas como
las minas de silicato o pueden reutilizarse con fines de construcción.
Figura 8. Ciclo de la mineralización del CO2.
• Usos industriales
Los usos industriales del CO2 comprenden los procesos químicos y biológicos en que
el CO2 actúa como reactivo, por ejemplo, los que se utilizan para la producción de urea
y metanol, así como diversas aplicaciones tecnológicas que usan directamente el CO2,
como en el sector hortícola, la refrigeración, el envasado de alimentos, la soldadura, las
bebidas y los extintores de incendios. En la actualidad, la tasa aproximada de utilización
de CO2 es de 120 Mt al año en todo el mundo.
• Conversión en biocombustibles
Mediante esta innvodaora solución, el CO2 pasa de ser de un gas dañino a una fuente
de energía energética y con valor, más aún si tenemos en cuenta el ritmo de
desaparición de los combustibles fósiles. Principalmente se pueden transformar en los
siguientes biocombustibles:
xxi
Methanol 𝐶𝑂2 + 3𝐻2 ↔ 𝐶𝐻3𝑂𝐻 + 𝐻2𝑂
Dimethyl Ether Síntesis del metanol: 𝐶𝑂 + 2𝐻2 ↔ 𝐶𝐻3𝑂𝐻
Deshidratación del metanol: 2𝐶𝐻3𝑂𝐻 ↔ 𝐶𝐻3𝑂𝐶𝐻3 + 𝐻2𝑂
Figura 9. Diagrama de la conversión de CO2 en hidrocarburos
Aspectos legales
Debido a la peligrosidad e interés público, los pasos dados en materia legal se referieren
fundamentalmente al almacenamiento de CO2 no a su caputra, ya que la captura de este
apenas tiene implicaciones para la sociedad o peligrosidad alguna.
Las medidad para regular el almacenaje son muy diversas a lo largo del planeta debido a los
diferentes marcos legales, industrias predominantes del país y cultura.
Un término imprescindible es la propiedad del subsuelo, ya que mientras en la mayoría del
planeta es propiedad del estado, en Estados Unidos pertence al propietario de la superficie.
Debido a esto las leyes son muy variadas respecto al resto del planeta, ya que en este último
país el estado solo es encargado de los elementos medioambientales y de seguridad. Debido a
este marco legal, los avances en Estados Unidos, país remarcable en la captura de CO2 debido
a la cantidad de este gas que emite y proyectos llevados a cabo, se han fundamentado en el
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desarrollo de préstamos y condiciones favorables para la iniciativa privada, dando lugar a
numerosas líneas de investigación como la del Laboratorio Nacional de Sandia, referente en la
investigación de captura de CO2 con membranas.
Sin embargo, para conocer el origen de la regulación sobre CAC, debemos remontarnos al
Protocolo de Kioto firmado en 1997. Este es el acuerdo internacional más importante sobre el
cambio climático ya que impone obligaciones legales a los países firmantes, y establece una
reducción de los gases de efecto invernadoro de al menos un 5% desde 1990 hasta 2012. Además
establece un valor monetario sobre la atmósfera compartida por los países de Naciones Unidas
y se genera un mecanismo llamado ‘’Comercio Internacional de Emisiones’’ a través del cual se
le asgina un cupo de emisiones a cada país, existiendo la posibilidad de compra-venta de dichos
cupos.
Finalmente, la percepción de la sociedad respecto al almacenamiento de CO2 es algo que cada
vez tiene más importancia, ya que la negativa a esta tecnología es cada vez mayor, como se
puedo ver en Alemania tras la cancelación de un proyeto europeo de demostración en
Jänschwalde.
xxiii
ABSTRACT
This work presents the current alternatives for the capture of carbon dioxide, which I consider
to be more important and more likely to be implanted in the next decades.
In addition, some of the current and future trends for the storage of carbon dioxide are
presented, to complement the review of different capture technologies. The diverse ways to
storage it and the possible uses for CO2 are also descripted. Ending with this part of the work,
I will write about the policy regarding the Carbon Capture and Storage (CCS) issue, focusing
in the main developments in this field and its public perception.
In the practical part I focus on the technology called ‘’Calcium Looping’’. I build an algorithm
to calculate the measures that must have the reactors and the amount of matter circulating
between them based in a desired efficiency. Also, a brief technoeconomic balance is proposed
in order to give a vision of how much could the launch of this technology cost.
I particularly chose this topic because global warming is an issue that concerns me, and I
though this project could be an excellent opportunity to delve into this topic, specifically CCS
technology, a technology field that caught my attention many time ago
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1
1 INTRODUCTION
1.1 Context
Rapid economic growth has contributed to today’s ever increasing demand of energy. A
consequence of this is an increase in the use of fuels, particularly fossil fuels like oil, coal and
natural gas. Since the Industrial Revolution those sources of energy have been exponentially
demanded. As proof of this the following figure represents how energy consumption has
changed in the United States since the Industrial Revolution.
Figure 10. Evolution of energy consumption in USA.
However, the excessive use of fossil fuels has become a cause of concern due to their adverse
effects on the environment, particularly related to the emission of CO2, a major antropogenic
greenhouse gas (GHG). CO2 is the major contributor for global waming, and it has the greatest
adverse impact which accounts approximately 55% of the observed global warming.
This global warming is created by the greenhouse effect. The greenhouse effect is the
phenomenom where GHGs absorb outgoing infrared radiation causing an increase of Earth’s
temperature. This phenomenom is responsible for various environmental problems like the
rise of water-level in sea, the increasing number of ocean storms, floods, etc.
Over the past century, CO2 level in the atmosphere has increased more than 39% from 280
ppm during pre-industrial time to the record level of 406 ppm in the Spring 2016, with an
2
increase of global surface temperature of about 0.8 Cº. The concencration is expected to rise,
growing to as much as 600-1550 ppm, bringing disastrous consequences.
To solve this problem, one of the solutions is CO2 capture and storage (CCS). CCS is a process
consisting on the separation of CO2 from industrial and energy-related sources, transport to a
storage location and long-term isolation from the atmosphere.
When thinking about a technology for capture CO2, three factors are crucial for its
development in industry; efficiency, cost, and level of contamination. Unfortunately, most of
the investigated technologies have deficiencies in some of these factors but recently there are
new researches which bring some hope in these aspects. In terms of effiency new reactions are
being developed, bringing for example higher rates of reaction. When talking about cost new
models of Air Separation Unit (an essential element in some technologies) are being designed
with much lower costs, and also, related with level of contamination, new environmentally
friendly catalysts are being tested.
In the early 2000s, CCS emerged as a promising option to contribute to global warming
mitigation. Within a few years, from 1996 to 2004, four industrial-scale projects were initiated,
leading to an optimistic perpective about the speed and short-term impact of CCS technology.
However, that pace of deployment of new project has slowed. Although government and
private-sector investments continue to build a strong and broad foundation for it, similar
progress has not been made in the legal, social and financial dimensions of CCS.
Once we have captured CO2, we have two options; recycling it or storage it. Storage of the CO2
is envisaged either in deep geological formations, or in the form of mineral carbonates. Deep
ocean storage is not currently considered feasible due to the associated effect of ocean
acidification. Geological formations are currently considered the most promising
sequestration sites. The National Energy Technology Laboratory (NETL) reported that North
America has enough storage capacity for more than 900 years worth of carbon dioxide at
current production rates. A general problem is that long term predictions about submarine or
underground storage security are very difficult and uncertain, and there is still the risk that
CO2 might leak into the atmosphere.
Besides CO2 storage, CO2 utilization may also offer a response to mitigate CO2 in the
atmoshphere in the near to medium term, but is usually considered a different technological
category from CCS. In this category, the promising technology Bio CCS Algal Synthesis is under
deveploment but has attracted a great attention. It uses CO2 from sources like coal-fired power
station as a useful feedstock input to the production of oil-rich algae in solar membranes to
produce oil for plastics and transport fuel (including aviation fuel), and nutritious stock-feed
for farm animal production. Another potentially useful way of dealing with industrial sources
of CO2 is to convert it into hydrocarbons where it can be stored or reused as fuel or to make
plastics.
3
1.2 Objetive of this work
This work will present a summary of the actual technologies for CO2 capture, wich lead to
mitigate the growth of CO2, and the most promising options of storage it. I will focus on the
concept, advantages and disadvantages of these technologies.
The main objective of this project is to know and understand the CO2 capture technologies in
deveploment, and trying to analyze the operation feasibility in the power plants. I particulary
took this work because I consider that nowadays people only think in renewable energies when
talking about mitigate climate change. Most of them don’t know about CCS, and in my
opinion, that’s one of the key issues of CCS to be solved, in order to implement and develop it,
firstly society has to know, understand and be concerned about it.
4
2 PRECEDENT
Since CCS is gaining more and more importance, the number of publications related to it has
increased at the same time. Also, several institutions were founded to address the CCS topic,
giving continuous publications with a scientific and politic view of the issue. Among them
there are two international relevant institutions:
• The Intergovernmental Panel on Climate Change is the leading international body for
the assesstment of climate change and thus CCS. It was established by the United
Nations Environment Programme (UNEP) in 1988 to provide the world a clear
scientific view on the current state of climate change, its potential impacts and the
options for mitigate it.
• The Global CCS Institute was established in 2009, by the Australian Govenment. It is
an international membership organization, whose mission is to accelerate the
development, demonstration and deployment of CCS. It is the most active CCS
institution, with the largest number of publications, with special importance of the
Global Status of CCS annual publication.
In a regional level, there are two big institution with publications about CCS.
• US Agency of Energy: This National US Agency carries out research and development
activities about CCS, publicating many works per year which are of great importance
for the scientific community.
• Joint Research Centre, European Comission: Its mission is to support EU policies, and
it has a key player in the research on CCS with an investmen in knowledge and
innovation foreseen by Horizon 2020. Their workshops about CCS are the main
reference in Europe.
At the same time, the scientific community has also a great interest in CCS. The number of
publications has rapidly increased through the years, as it can be seen in the next figure.
5
Figure 11. Number of CCS related publications from 1970 to 2012.
On the side of the projects and numbers of CO2 capture technogies applied, the rapid increase
is also a fact. The first technologies to be implanted were related with post-combustion
capture, specifically amine absorption and oxyfuel combustion. In Europe, the german
company “The Linde Group Company’’ is the leader in the application of this technologies, with
many projects from oxyfuel combustion to amine based CO2 capture.
The CCS technology is proven and in use around the world from 2010 to end of 2017. The
number of operational large-scale projects is set to rise from 10 to more than 20. Nowadays
there are 22 large-scale projects in operation or under construction globally. The combined
CO2 capacity of these 22 projects is around 40 million tonnes per annum. To have a detailed
vision of how the capacity has increased, the following figure represents how the capacity of
CCS proyects have progessed.
Figure 12. Progress of CCS projects capacity from 2012 to 2020
6
7
3 OPTIONS FOR CO2 CAPTURE
Several technological options are available for separating CO2 from a gas stream. The optimal
choice depends on the type of source, cost, and the ease of deployment. In particular, this
choice depends on CO2 composition in gas, which ranges from 3-4% for natural gas turbines
to 10-15% for pulverized coal plants and up to 40-60% for integrated gasification combined
cycle (IGCC) plants.
In order to apply the best technology, the most important factor is the energy required for CO2
capture. The minimum energy required, from a thermodynamic perspective, depends on the
concentration of CO2 and ranges from 3-6kJ/mol CO2 for coal plants to 7-9 kJ/mol CO2 for a
natural gas plant. The fact is that in practice the total energy penaly is much greater, about 5
to 10 times the minimum energy requirement. Compression of CO2 to be storage-ready at
approximately 150 bar represenst a significant cost too.
Depending upon different plant configurations, CO2 emissions from thermal power plant flue
gas can be reduced by using one of the following methods:
• Pre-combustion capture
• Post-combustion capture
• Oxyfuel combustión
Figure 13. Options for CCS capture.
8
3.1 Pre-combustion capture
3.1.1 Concept
This technology refers to removing CO2 from fossil fuels before the combustion is completed.
To begin, the fossil fuel is gasified with oxygen at elevated pressures typically in the range of
30-70 atm to produce syngas predominantly CO and H2 and mainly free from other pollutant
gases. Thereafter, steam is added to syngas and passed through the bed packed with catalysts,
onto which water gas shift reaction takes place that convert CO in CO2 through this reaction:
CO2+H2 O↔H2+CO2. The separation process normally uses a physical solvent such as rectisol
or selexol, which are available at low cost.
From CO2 and H2 bearing steam, CO2 is separated and sent to the compression unit and pure
H2 is further used as an input to a combined cycle to produce electricity. Another option is to
use the H2 to power cells, raising the overall plant efficiency. In future, H2 could also be used
as a transportation fuel. The integration of this technology in Integrated Gasification
Combined Cycle (IGCC) is being a tendency due to the easy integration and low penalty loss
of the process.
Another line for pre-combustion process is the use of natural gas instead of coal. This natural
gas mainly contains CH4 and can be reformed to syngas containing H2 and CO. Natural gas
also contains Hydrogen Sulfide (H2S) which has to be removed too. After, the content of H2
can be increased by the water gas shift reaction and by dissociating H2S and the rest of the
process is similar to that described above for coal. Using natural gas, a CO2 capture efficiency
of 80% can be obtained.
The following figure gives an idea of the general process.
Figure 14. Diagram of pre-combustion capture.
9
For coal-fired it has a thermal efficiency (% LHV) of 31,5, and for gas-fired plants 41,5. As
expected, a higher 𝐶𝑂2 concentration enhance sorption efficiency.
The costs for conventional coal plants range from 29 €/tn of 𝐶𝑂2 (for an advanced design
concept) to 50 €/tn of 𝐶𝑂2. The capital costs are 1820 $ per kW produced for coal-fired plants
and 1180 $ per kW produced in gas-fired plants.
3.1.2 Advantages & Disadvantages
There are 5 main advantages regarding this techonolgy:
1. High concentration of 𝐶𝑂2 in the syngas enhance sorption efficiency.
2. Utilization of physical solvent which are available at low cost and require low energy
for regeneration.
3. Separation of H2 for different uses, like power cells or fuel. Its expected to be demanded
in the future.
4. Developed technology, commercially deployed at the required scale in some industrial
sectors.
5. Oportunity for retrofit to existing plant.
However, there it has many disadvantanges which lead to investigate other options for 𝐶𝑂2
capture. These are:
1. Non-gaseous feed stocks.
2. Requirement of the cleaned gas stream, considerably raising the capital costs.
3. NOx emission control.
4. High parasitic power requirement for sorbent regeneration.
5. Bad experience due to the plants currently operating in the market.
Finally, figure 15 shows a pre-combustion CO2 capture plant. It is a gasification plant in
United States which separates 3.3 Mt of CO2 per year.
Figure 15. Gasification plant in USA.
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3.2 Post-combustion capture
3.2.1 Concept
Post-combustion capture involves removal of 𝐶𝑂2 from flue gas, which comes from the
thermal power plant combustion chamber. Regarding this technology, there are different
technologies for 𝐶𝑂2 capture:
• Absorption.
• Adsorption.
• Membranes: Ionic Liquid Membranes & Mixed Matrix Membranes.
• Enzyme based separation.
• Hydrate based separation.
• Calcium looping.
The main issue to be solved in post-combustion capture is the parasitic load. Since the CO2
level in combustion flue gas is normally low (7-14% for coal-fired plants and 4% for gas-fired),
the energy penalty and associated costs for the capture unit to reach the CO2 concentration
of 95% are elevated.
Post-combustion capture is the main line of deveploment, because of its big ease of expansion
and multiple forms that can fit with serval conditions. For each one of the post-combustion
technologies, I will make a brief summary of the most important aspects in the section
number 5.
3.3 Oxyfuel combustion
3.3.1 Concept
It is a technology that consists in modifying the combustion process so that the flue gas has
high concentration of CO2 (>95%) for easy separation.
In this process, fuel is burned in combustion chamber in the enviroment of pure O2 mixed
with recycled flue gas (RFG). A criogenic air separation unit is used to supply high purity
oxigen. This O2 is mixed with RFG because currently available materials of construction
cannot withstand at elevated temperatures resulting from coal combustion in pure oxygen.
Flue gas stream from this system contains mainly CO2 and H2O wich are easy and cheap to
remove.
The CO2 content of the flue gas varies in the range of 70-95% and the cost per tn of CO2
removed is around 36$/tn of CO2 for coal fired plants and 102$/tn of CO2 for gas fired plants.
The major units for oxyfuel combustion for power generation are the following;
• Air Separation Unit: For oxygen production.
• Boiler or Gas Turbine: For combustion of fuel & generation of heat.
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• Flue Gas Processing Unit: Flue gas cleaning or gas quality control system.
• CO2 processing Unit: Final purification of CO2 for transport & storage.
Figure 16. Diagram of oxyfuel combustion.
3.3.2 Advantages & Disadvantages
Talking abour advantages, the most significant are:
1. 60-70% NOx emission is reduced compared to air-fired combustion.
2. Less CO2 compression energy is required than conventionals methods because it has
potential to be operated at high pressure.
3. It can be used in the cement industry, which gives more economic potential.
Regarding the disadvantages, these are the most important:
1. The material of construction can not withstand at the high temperatures needed.
Currently this is one of the principal issues about oxyfuel combustion, and the available
materials are very expensive.
2. The auxiliary power consumption of a cryogenic air separation unit is high and has a
major impact on the overall efficiency of the power plant.
3. High efficiency drop and energy penalty
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13
4 TECHNOLOGIES FOR POST-COMBUSTION
CAPTURE
As I mentioned above, there are different technologies for post-combustion 𝐶𝑂2 capture. Some
are emerging and being tested in laboratories as new and promising solutions and some others
have been implemented for a while. The following list represents the technologies, which from
all, membranes and calcium looping capture are the most remarkable
4.1 Absorption process
4.1.1 Concept
It is based in the reaction between the CO2 and a liquid chemical solvent, normally an amine.
Flue gas stream containing CO2 is introduced from the bottom of the column that leads
counter current contact between flue gas and solvent and selective absorption of CO2 takes
place. Then CO2 rich stream is fed to the regenerator, where desorption of CO2 occurs and the
sorbent is regenerated by heating and depressurization, for further use. Desorbed CO2 is
compressed and sent to storage.
Figure 17. Diagram of absprtion CO2 capture process.
Chemical absorption holds good results in terms of removal efficiency using MEA amine, with
a CO2 recovery of 90-98% and an energy requirement of 4-6 MJ/kg CO2. The cost is quite
elevated (52$/tn of CO2).
Recently blends of alkanolamines are preferred for absorption of CO2. The process involves
passing of gaseous CO2 through an amine solution until equilibrium is reached. The reaction
of CO2 with aqueous amine is as follows:
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1. CO2+R1+R2NH ↔ R1 R2N𝐶𝑂𝑂− + 𝐻+ Carbamate formation
2. R1R2NH + 𝐻+ ↔ R1 R2N𝐻2+ Protonated alkanolamine formation
The ecuations above represents the following steps:
• Dissolution of the gaseous CO2:
Initially, diffusion of CO2 occurs from gas to liquid phase. It’s a purely physical step and must
occur prior to further reaction of CO2 in the liquid phase.
• Formation of bicarbonate and carbonate:
The amine behaves like a base and reacts with carbonic acid formed in the previous step, with
a CO2 to amine ratio of unity, forming bicarbonate, which also exists in equilibrium with
carbonate and carbonic acid.
The second reaction is the carbamate formation. This occurs at a CO2 amine ratio of 0.5, which
means one molecule of CO2 is absorbed by two molecules of amine. The low CO2 to amine
ratio results in a lower efficiency and lower CO2 capacity than that for the acid path. Another
bad point of this reaction is the high enthalpy of reaction. This means that reversing this
reaction in the stripper requires the addition of large amount of energy, making the entire
process energy intensive Costly
Figure 18. CO2 absoprtion mechanism.
15
4.1.2 Advantages & Disadvantages
Through the time, it has been revealed that this technology has more disadvantages than
advantages, making it less interesting for companies.
Advantages:
1. Suitable for retrofitting of the existing power plants.
2. Low solvent cost.
3. Most reliable option for CO2 capture.
Disadvantages:
1. Low CO2 loading capacity (0,5 mol CO2/mol amine)
2. High equipment corrosion rate.
3. High amine degradation.
4. High energy consumption during high temperatures absorbent regeneration.
In order to show how these plants are, the following image shows a post-combustion plant
in Malasia which uses absorption to separate o.2 Mt/year of CO2 from an electric power
plant.
Figure 19. Absorption CO2 capture plant in Malasia.
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4.2 Adsorption process
4.2.1 Concept
A packed column is mainly filled by spherical adsorbent and CO2 bearing steam is passed
through the column. CO2 is attracted towards the adsorbent and adheres on the surface of
adsorbent. After achieving the equilibrium, desorption takes place to get CO2 in pure form
and regenerated adsorbent can be utilized for further cycle. The adsorption process can be
carry out in different manners as I will describe.
• Pressure swing adsorption (PSA): In this process, the gas mixture flows through a bed
at elevated pressure and temperature until the adsorption of CO2 approaches to
equilibrium conditions at the exit of bed. The beds are then regenerated by stopping
the flow of the feed mixture, reducing the pressure and elutriating the adsorbed
constituents with a gas having low adsorptivity. Once regenerated, the beds are ready
for another adsorption cycle.
• Temperature swing adsorption (TSA). Firstly, the flue gas is passed over the bed. Then
selective adsorption takes place on the adsorbent until equilibrium is reached. The
desorption of gas can be done at elevated temperature by supplying additional heat.
This additional supply of heat makes this process costly.
• Electrical swing adsorption (ESA). The difference with other methods is that low voltage
electric current is passed through the adsorbent. This method has the potential to
reduce cost of CO2 capture, thus becoming more cost-effective than TSA and PSA.
In terms of efficiency, it is not as good as the other options. The CO2 recovery is around 80-
95% but it has an energy requirement of 2-3 MJ/kg CO2, with the cost around 80-150$/tn of
CO2.
It is a mature technology because solid adsorbents have been extensively used for gas
separation. The use of residues from industrial and agricultural operations to develop sorbents
for CO2 capture, has attracted significant attention to reduce the total costs of capture.
4.2.2 Advantages & Disadvantages
Advantages:
1. It has no by-product such wastewater (as it has in absorption).
2. It requires low energy compared to cryogenic and absorption.
Disadvantages:
1. Low selectivity and capacity of available adsorbent for CO2.
2. Lower removal capacity as compared to other technologies.
3. Regeneration and reusability of adsorbent.
4. Elevated pressures.
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4.3 Ionic liquid membranes
4.3.1 Concept
Nowdays, membrane separation is considered an emerging technology, with the potentital to
be more environmentally friendly and energy saving, but its not as mature as compared to the
currently technology, for example the amine absorption, wich occupies the 90% of the market,
while membranes only the 10% mainly in the natural gas sweetening and biogas upgrading
processes.
The main issue in membrane separation is the cost of separation and the operation in real scale
plants, due to the limited membrane separation performance when using conventional
membrane materials. In order to solve this problem, innovative membranes are one of the
promising alternatives to meet the challenges, providing high CO2 permeance and selectivity.
Only then will membrane become economically competive.
Before talking about the two major membrane tecnologies, Ionic liquid Membranes and
Mixmed Matrix Membranes, it is necessary a brief explanation of the two types of membrane,
the gas separation membrane and gas absorption membrane:
• Gas separation membrane: In this process the gas stream containing CO2 is introduced
at elevated pressure into the membrane separator wich consists typically in a large
number of hollow cylindrical membranes arranged in parallel. CO2 selectively
permeates through membrane and is recovered at reduced pressure on the shell side of
the separator as it is indicated in the next figure. Mixed matrix membranes are a
example of this membrane process.
FIgure 20. Principle of gas separation membrane.
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• Gas absorption membrane: It consists of micro porous solid membrane which is used
as contacting device between the gas and liquid flow. CO2 is diffused through
membrane and then is recovered by liquid sorbent by absorption. This process gives
higher removal rate than gas separation membrane due to high driving force at any
instant. Ionic liquid membranes are the best example for this membrane process.
One of the promising alternatives is the Ionic Liquid Membranes. An Ionic liquid (IL) is a salt
with an organic cation and an inorganic or organic anion. Ils have great properties such as high
CO2 solubility, low volatility and designable structure to adjust chemical/physical propierties,
which in combination increase the performance of the membrane.
The following image shows the commonly used anions and cations.
Figure 22. Commonly used anions and cations.
Figure 21. Principle of gas absoprtion membrane.
19
Among the differents types of IL membranes (Poly ionic (PIL), Homo-PIL, Room Temperature
Il), and the Functionalized IL-based SILMs (Supported IL Membrane), the last one is the most
interesting.
In this membrane, a facilitated transport mechanism is also normally involved for gas
transportation. Firstly, the CO2 molecules that dissolve on the feed side can reversible react
with the facilited transport carrier (normally amino groups in TSILs), forming CO2 complexes
(bicarbonates and carbonates). Then these complexes diffuse through the membrane and
eventually CO2 is dissociated and released on the permeate side of the membrane. In this
process, it has been noted that water is needed when using amines in the IL membranes as a
facilitated transport.
However, this kind of membrane shows moderate enhancement in permeability/selectivity at
high temperatures.
Figure 23. Ilustration of facilited transport of CO2 in a membrane.
4.3.2 Advantages & Disadvantages
Advantages
1. High interfacial area per unit volume for mass transfer, especially for hollow fiber supported membranes
2. Low solvent holding (An expensive but effective liquid can be used).
3. More efficient in application over other liquid membrane techniques.
4. The combinations of cations and anions lake possible to design Ils with desired properties.
5. Simplicity in concept and operation.
20
6. Low energy consumption.
7. Environmentally friendly.
Disadvantages:
1. Cost of separation higher than absorption due to the limited membrane separation capacity.
2. Over time the liquid phase evaporates or is pushed out of the membrane pores.
3. The ionic liquid is expensive.
4.4 Mixed matrix membranes (MMM)
4.4.1 Concept
Many factors have a crucial impact on gas separation membrane’s performance, but among
others membrane material and structures have the strongest effect on membrane
performance. This is what MMM plays with, in order to achieve the best membrane
composition. The materials often used have distinct propierties such as
• Different chemical structure.
• Containing a separating layer made of a continuous phase (usually a polymer).
• Embedding a second dispersed phase.
• Different selectivity and permeation flux.
Normally they are made by the implementation of inorganic material (molecular sieves) into
polymer matrices. Its efficiency is quite good, but improvements are still needed to implement
them in the industry scale.
Firstly, MMM were made all of molecular sieves. Molecular sieve membranes provide
considerable discrimination based on the size or shape of gas molecules by letting some of the
component gases to preferentially pass through, that’s why they are good for gas separation.
The properties of molecular sieve membranes such as high thermal and chemical stability,
high mechanical strength as well as their high separation performances, make them
excepcionally good for harsh operational conditions, which are the normal conditions in a
power plant. However fabricating molecular sieve membranes of large surface areas for
commercial explotation is laborious and costly.
Later academic investigators used organic polymers as asymmetric nonporous membranes
that offer many of the desired properties, including low operation cost. A drawback of this
material is that due to the trade-off relationship between selectivities and permeability, it
makes polymeric membranes undergo an upper bound limitation (different for various binary
21
gas pairs) as it is shown in the next figure. This upper bound for various binary gas pairs was
first suggested by Robenson in 1991.
Figure 24. Robenson upper bound correlation for CO2 CH4 separation.
4.4.2 Advantages & Disadvantages
They are similar than ILs membranes, but if we apply an IL in a MMM, the increase of the
advantages is remarkable. These advangages are:
1. High mechanical strength.
2. High separation performances.
3. Simplicity in concept and operation. Modular design and ease of scale up.
4. Low energy consumption.
5. Environmentally friendly.
The main diference in the disadvantages is the fabrication process, because fabricating large
surface areas for commercial explotation is laborious and costly. In addition, the difficulty to
prepare a defect-free membrane is very high.
22
4.5 Enzyme based separation
4.5.1 Concept
In this process, CO2 is removed from gas by naturally occurring reaction of CO2 in living
organism (enzyme). The use of carbonic anhydrase (CA) as an enzyme, in a hollow fiber with
liquid membrane has demonstrated the potential for 90% CO2 capture.
This process has been shown a little heat of absoption that reduces the energy penalty typically
associated with absorption processes. If it is optimized, it could be the best candidate to
replace current methods of CO2 capture. As an example of its performance, CA has the ability
to catalyse the hydration of 600,000 molecules of CO2 per molecule of CA per second. This
fast turnover rate minimizes the amount of enzyme required. Finally, the process must
incorporate a mechanism by which CO2 can be released from the system as a concentrated
stream, by pressure-swing desorption solid carbonate precipitation or some other means.
In 2016, Sandia National Laboratories have patented one process using CA. Its product is called
Memzyme. It has this name because it membrane’s active layer has the CA enzyme dissolved
in water. A very high efficiency was reached, making the selectivity of this membranes 10 times
more than current membranes, and a super-high flux, 100 times more than current
membranes. Also, it can withstand high temperatures typically from power plants flues.
Despite these charasteristics, it is surprising that the fabrication process is simple, and its
estimated that they could reach a cost 40$/tn CO2.
Figure 25. Memzyme operation diagram.
4.5.2 Advantages & Disadvantages
Advantages:
1 Small amount of enzyme required and life around 6 months
2 No toxic chemical is used.
3 No extra energy is used in the process.
23
4 It can stand under high temperatures when placed in a power plant.
5 Highly adaptable for separating other gases. For example, methane from a mixture of gases.
The main disadvantage is the doubts of how it will behave in real industry processes, because
there is still no simulation in an industrial scale. It has also been noticed deficiencies related
to the surface loss of enzyme activity and the key role of watter in the pores, which makes the
fabrication process more difficult.
4.6 Hydrate based separation
4.6.1 Concept
Gas hydrates are crystalline composed of water and gas under suitable conditions of low
temperature and high pressure. Hydrates have the capacity to store large amount and to
separate gas mixture, thus this technology has attracted the attention for capturing CO2.
The fed gas is exposed to water under pressure to form hydrate, which capture CO2. The
hydrate is then separated and dissociated by releasing CO2 in pure form. The water has
additives like TBAB or TBAF are used to reduce the operating pressure and enhance the kinetic
rate. Also, these two additives are much more environmentally friendly than the current used
additive, THF.
The theoretical CO2 storage capacity for stoichiometric TBAB semiclathrate is 193 mg of CO2/g
of water. Giving another example of the storage capacity, upon dissociation, one volume of
CO2 hydrates can release 175 volumes of CO2 gas at standar temperature and pressure
conditions, making it usefull for CO2 separation. The efficiency of the process is driven by the
difference in the operation temperature or pressure from equilibrium condition. It is verified
that the process makes it possible to recover more than 99% of CO2 from flue gas.
Finally, it has been tested that the presence of surfactants like sodium dodecyl sulphate (SDS)
can effectively improve the hydration kinetics by reducing the water surface tension. It
improves the gas diffusion through the gas/water and gas/hydrates interfaces, leading to
enhanced inward and outward growth of hydrates as shown in figure 26.
24
Figure 26. Formation of hydrates.
4.6.2 Advantages & Disadvantages
This technology has three main advantages:
1 Big storage capacity.
2 Less energy consumption than other alternatives.
3 Its capability for continuous operation, which allows large scale treatment (with the
potential to achieve 8 000 ton/day CO2).
Nevertheless, there are some important disadvantages that make this technology still not
ready to be implanted in real scale industry.
1 The current used additive contaminant the environment.
2 The hydrate formation rate is low, but with TBAB it has significantly increased.
3 Large energy penalty, 15.8%. Much higher than conventional technologies such as
amine absorption with a energy penalty of 7-10%.
4 High pressure operating condition.
4.7 Calcium looping CO2 capture
4.7.1 Concept
Since this technology will be more detailed in the next pages with a simulation case, I will give
a deeper introduction and focus more on this technology.
This technology utilizes the reversible reaction between CaO and CO2 to form calcium
carbonate in calcium looping cycle. There are two reactors, carbonator and calciner:
• Carbonator: Here is where the primary fuel combustion takes place. Temperature is
in the range of 650-700º depending on pressure of the system. CaO reacts with CO2
achieving in-situ CO2 capture throught this reaction:
𝐶𝑎𝑂(𝑠) + 𝐶𝑂2(𝑔) → 𝐶𝑎𝐶𝑂3(𝑠)
25
• Calcinator: In this reactor 𝐶𝑎𝐶𝑂3 is regenerated into 𝐶𝑎𝑂 by burning a secondary fuel
such as petroleum coke. 𝐶𝑎𝐶𝑂3(𝑠) → 𝐶𝑎𝑂(𝑠) + 𝐶𝑂2(𝑔) . Once the CO2 is separated,
it is compresed and send to storage or utilization.
Figure 27. Diagram of calcium loopin CO2 capture.
The technology is quite investigated and well known, but there is still further investigation
needed. There are some implementations in real-scale plants. It needs some technical
improvements and to be more mature in the commercial scale to reduce costs. Some solutions
to reduce costs are the use of natural gas instead of coal in the calciner and selling the waste
sorbent for use in cement industry.
When talking about effiency, we can say it has good efficiency. Overall CO2 capture
efficiencies in the combustor-carbonator higher than 90% can be achieved with sufficiently
high solids circulation rates of CaO and solids inventories. The sorption capacity is very
high when compared to other processes. Under ideal conditions, the sorption capacities of
monoethanolamine MEA, silica gel and activated carbon are 60, 13.2 and 88 g of CO2/kg of
sorbent respectively.
In addition, there will be modest efficiency penalties and opportunities for a high degree
of integration in the combustion plant (for example, at atmospheric pressure the heat
required for calcination at temperatures over 900 ºC is recovered in the carbonation step
at 650 ºC).
4.7.2 Advantages & Disadvantages
In my opinion, and that’s why I’m focusing more in this technology, it has several significative
advantages that makes it attractive to be implanted in an industry-scale.
1. The sorbent (limestone) is cheap and available in the market.
2. Cost of 105$/ tn of CO2 (including transport and storage).
26
3. The heat released from exothermic carbonization can be used to run steam cycle.
4. The reaction rates are sufficiently high even at low temperatures, to allow compact
reactor designs for the carbonator.
However, there are some disadvantages which need to be overcome. The two major
disadvantages are the elevated cost (especially the one associate to the air separation unit) and
the need of heat supply to the calciner.
4.8 Summary made in Excel of the CO2 capture processes
The following document attached is a table which resumes all the principal capture processes
in the market. The strucutre of the table is simple, so anyone with a quick look at it can have
an idea of how CO2 capture is clasified and the main propierties of the technologies.
Right after the table, an enumeration is presented with the bibliography of the main data of
the table .
27
Table 1. Table of CO2 capture technologies.
28
29
5 MODEL
5.1 Introduction
In this chapter, I will model a calcium looping system with two reactors, the carbonator and
calcinator. I will follow the model published by Matteo C.Romano in the page 268 of the
publication ‘’Modeling the carbonator of a Ca-looping process for CO2 capture from power plant
flue gas’’, published in 2012 in the Chemical engineering Science (69) 257-269. I particularly
chose the calcium looping process because it has a big potential to be developed and became
a widely implanted option for CCS. Although it is still no developed in the industrial scale, it
has an enormous potential and different ways to optimize it, such as the implantation in the
cement industry, or the one-reactor model where both combustions take place in one reactor.
The goal of this algorithm is to calculate the required amount of mass in the process in order
to achieve an efficiency of CO2 capture of 90%. The mass obtained is the optimal for this
problem. Calculate the mass of solids is crucial for understand the problem and to give an idea
of its operation, because from this resoults, other crucial parameters can be calculated and
then, give an estimation of the direct & indirect costs.
The illustration of our problem is as it is shown in the figure 28.
Figure 28. Diagram of calcium looping CO2 capture.
Now, a diagram of the algorithm is presented. It represents, in a a schematic form, how the
algorith works.
30
31
5.2 Description of the model
Equations
• Chemical reactions in carbonator:
CaO(s) + CO2(g) ↔ CaCO3(s) ∆𝐻 = −178 𝐾𝐽/𝑚𝑜𝑙
CaO(s) + S𝑂2(g) + 1/2𝑂2(g) ⇔ CaC𝑂4(s)
• Chemical ractions in calcinator:
CaCO3(s) ↔ CaO(s) + CO2(g) ∆𝐻 = −178 𝐾𝐽/𝑚𝑜𝑙
C (s)+𝑂2(𝑔) →C𝑂2(g)
• Article’s equations:
This model is based fundamentally in 9 equations which are the following, numbered like in
the article used in the model.
32
(5)
(36)
(37)
(40)
(45)
(46)
(28)
(29)
(39)
It was proposed by Grasa and Abanades (2006) to
express the sorbent capacity after a large number of
complete carbonation-calcination cycles.
Proposed by Rodríquez et al. (2010) express the fraction
𝑟𝑁𝑎𝑔𝑒 of particle which have experienced 𝑁𝑎𝑔𝑒 of
complete cycles as function of the actual 𝑓𝑐𝑎𝑟𝑏 and 𝑓𝑐𝑎𝑙𝑐
Represents the average máximum conversión of the
sorbent 𝑋𝑚𝑎𝑥,𝑎𝑣𝑒 .
Formulated to calculate the average fraction of sorbent
sulfated at each cycle.
Ecuation to calculate 𝑓𝑐𝑎𝑟𝑏 based in the terms above.
𝑛𝑠,𝑎 represents the moles of Ca and CaC𝑂3 in the
circulating fluidized bed.
Molar fraction of CaS𝑂4.
Molar fraction of ash.
Molar fraction of CaCO3
33
Now i will explain how the code works. The objective of the model is to calculate the total
amount of limestone mass (CaCO3) and the CaO needed to achieve a desired efficiency of 90%.
The first part of the code is to calculate the value of the average carbonation level, 𝑓𝑐𝑎𝑟𝑏,
applying an iterative calculation solving the equations (5), (36), (37), (40) and (45). We initiate
the variable 𝑓𝑐𝑎𝑟𝑏 with a value of 0,44 (44%) and we iterate, until we reach a value of
𝑓𝑐𝑎𝑟𝑏 which only a difference of 0,05.
Then we can assume it’s a good approximation. After that, we can calculate the sulfation level
ecuation (40), obtaining the new values of k and 𝑋𝑟 through the figure 29 that shows the %
variation of parameters k and 𝑋𝑟 with sulfation level.
34
Figure 29. Variaton of parameters with sulfation level.
Right after, the parameters mentioned above are used in the equations (37), (5), (36) and (45)
to check if we calculated correctly fcarb, saving the new value in the variable fcarb_nueva.
35
Once we calculated fcarb, we follow with the second part of the algorithm. Here we are going
to determinate the molar composition and mass of the solids in the carbonator. That’s the goal
of the algorithm publiced in the article, but I will go further with the calculation of the fuel
required to dissociate the CaCO3 and the total volume of O2 necessary for the combustion in
the calcinatory and the sulfation in the carbonator. So as I said, we calculate the solid inventory
in the carbonator considering a single 40 m reactor and a residence time (𝜏𝑎) of 38 s, as
indicated in the figure 30 to achieve a 90% of CO2 capture.
Figure 30. CO2 capture efficiency vs. active space time for 3 different reactor sizes.
From ecuation (46) we obtain the moles of CaO and CaCO3 in the carbonator,
and with equations (28), (29) and (39) we obtain the molar fraction of CaSO4, ash and CaCO3.
Finally calculating the molar fraction of CaCO3 with the following equation;
and the moles of total solids in the carbonator, we can
obtain the composition (mol/kg) of the solid inventory.
36
Once we calculate the solid inventory in the carbonator, it’s time to calculate the additional
parameters that I consider important.
➢ Heat and carbon needed to dissociate the amount of CaCO3 in the calciner.
It’s crucial for our model, because with this parameter we can estimate how much
carbon and O2 is needed. We use the thermodynamic ecuation 𝑄 = 𝑚 ∙ 𝐶𝑝 ∙ ∆𝑇 , where
Q (J/s) is the incognit, m (kg) the amount of CaCO3 to burn, ∆𝑇 (K) the difference
between temperatures and 𝐶𝑝 (J/kg) the specific heat coefficient. The model also
calculates the heat produced in the carbonator through CaO(s) + CO2(g)
↔ CaCO3(s) ∆𝐻 = −178 𝐾𝐽/𝑚𝑜𝑙 , that could be used to minimize the amount of
coal needed in the calicinator and thus the costs too. One we know the amount of heat
37
needed, we can calculate the amount of coal through this ecuation. 𝑄 = 𝑚𝑓𝑢𝑒𝑙 ∙ 𝐶𝑐
where 𝐶𝑐 (KJ/kg) is the calorific power.
➢ Oxygen needed to burn the CaCO3
Now we obtain the amount of O2 needed by a mass balance in calcinator and
carbonator.
➢ Impurities
This parameter is important because depending of how much impurities our fuel and
limestone have, the efficiency in the progess will be modified. We estimate a 10% of
impurities in our Spanish coal, and a 7,6 % of impurities in the limestone, as article [11]
suggests.
38
5.3 Inputs & Outputs
➢ Inputs:
1. Mole flow of ash entering in the system through the carbon fuel. 𝐹𝑎𝑠ℎ= 0.016
kmol/s.
2. Mole flow of sulfur in the flue gas entering in the system. 𝐹𝑆 = 0.0096 kmol/s.
3. Mole flow of fresh makeup limestone 𝐹0 = 0.0256 kmol/s.
4. Mole flow of CaO cycling from the calciner to the carbonator 𝐹𝑟 = 19.2 kmol/s.
5. Efficiency = 0.9
6. Mole flow of CO2 in the flue gas entering the carbonator 𝐹𝐶𝑂2 = 1.28 kmol/s
(corresponding to 700 m³/s of flue gas with 14%vol. CO2, at 650 Cº and 1 bar).
7. k = 0.52. Deactivation constant proposed by Grasa and Abanades in 2006.
8. Xr = 0.075. Residual conversion proposed by Grasa and Abanades in 2006.
➢ Outputs:
From the original model
1. Average carbonation level in the carbonator, 𝑓𝑐𝑎𝑟𝑏 = 0.7.
2. Molar composition of the solids population in the carbonator.
• Total mol = 4982,215 mol.
• X_ash = 0.38461, corresponding with 1918,65 mol.
• X_CaSO4 = 0.230769 corresponding with 1145,9 mol.
• X_CaO = 0.3615 corresponding with 1801.07 mol.
• X_CaCO3 = 0.023077 corresponding with 114,5 mol
Additional outputs
1. Required heat in calcinator to dissociate the CaCO3 = 19733598 J
2. Required coal for combustion in calcinator = 697.117 g/s
3. O2 for calcinator = 126,56 mol/s and O2 for carbonator = 1.28 mol/s.
4. Total O2 volume = 2.85 m³/s.
5. Grams per second of CaCO3 impurities coming out from calcinator = 0,1945
g/s
6. Grams per second of ash coming out from calcinator = 139 g/s
7. Total amount of impurities coming out from calcinator = 139,1945
5.4 Economic study
5.4.1 Coal & Oxygen
After obtaining the value of the characteristics of our calcium looping system, a little economic
study will be presented, to give a brief understanding of how the parameters with major impact
in the models have it effects in the economic results. Finally, some improvements are shown
39
and its possible benefits on this process, making it more economic feasible. The parameters I
will focus in this part are the coal and the Air Separation Unit, in order to give a sensitivity
analysis.
1. Coal: In Spain two types of coal are used. The first one is the Spanish coal, with its
origin in Asturias and León. Its calorific power is 14183950 kJ/kg and it cost no more
than 55 €/tn, thus resulting in a bad coal for combustion. The second coal in the model
it’s the South African coal. It is used to compute the model, has a calorific power of
28307,42 kJ/kg and a price of 70.07 €/tn. Its price and calorific power compared to the
Spanish coal makes the best candidate for the model.
2. Air Separation Unit (ASU): The ASU normally represents a considerable cost when
designing a calcium looping system or some process in which is required. The
technology is still no optimized, resulting in elevated costs to separate O2 from air.
Investigating prices for ASUs in the market, I finally estimated that for obtain 4644
Nm³/h, our ASU will cost 2,35 millions €, taking as a reference an ASU which cost 30
million €, with a capacity to separate 60.000 Nm³/h of oxygen.
Firstly, let’s see the differences of Spanish coal and South African coal for a desired efficiency
of 90%.
Table 1. Comparation of Spanish and South African coal.
As I mentioned above, Spanish coal makes this process much more expensive. In addition to
the increase of cost per gram of coal, we have to include the additional cost of the ASU due to
the increment of O2 needed to combust the higher amount of coal.
Now a sensitive analysis is presented. For a number of cycles between carbonator and
calcinator of 550, a table is presented showing the amount of carbon, cost, and O2 needed for
different efficiencies compararing Spanish and South African coal. We can see the cost increase
using Spanish coal, with a coal cost increase of 55% and a increase of O2 needed of 101,95%.
CARBON COST
Origin Price (€/g) Quantity (g/s) Cost (€/s) Cost (€/h)
South Africa 0.00007074 766.82 0.0542448 195.28145
Spain 0.000055 1530.638 0.0841851 303.06632
EFFICIENCY 0.9
40
Table 2. Comparation of costs in both situations.
Here is attached the graphics related to the above table:
Figure 31. Spanish coal vs South African coal.
N=550 cycles Amount of coal Amount of coal (g/s) Cost(€/h) Cost(€/h) O2 O2
Origin South Africa Spain South Africa Spain South Africa Spain
600,12 1197,69 152,82896 237,14262 1,13 2,24 Average coal cost increase
641,8 1280,86 163,443355 253,61028 1,21 2,39 55%
683,47 1364,04 174,055204 270,07992 1,29 2,55 Average increase of O2
725,15 1447,21 184,6696 286,54758 1,37 2,7
766,62 1530,638 195,230516 303,066324 1,44 2,85
Sum 870,227634 1350,44672 6,44 12,73
Dif (Spanish-Affrican) 480,21909 6,29
Toal increase 1,55183158 1,97670807
Increase 0,55183158 0,97670807
0,7
0,75
0,8
0,85
0,9
Efficiency
97,60%
400
600
800
1000
1200
1400
1600
0,6 0,65 0,7 0,75 0,8 0,85 0,9 0,95
Co
al a
mo
un
t g/
s
Efficiency
Spanish coal amount VS South African
Amount of South Africancoal
Amount of Spanish coal
41
Figure 32 O2 introduced depending of the efficiency.
5.4.2 Costs
• Direct capital costs
Direct capital costs are estimated for the carbonator, calcinatory and ASU. Equipment
cost are included in these concepts. Capital cost of carbonator is estimated based on
the cost of a CFB boiler, using the plant size the scaling variable. I take as reference the
data presented in [20], 4 million 2012 USD MW power plant.
Capital cost of calciner is estimated by [21] using the boiler for a 500 MW power plant,
which costed 151700 USD. This cost is lower that the carbonator because of its smaller
size and more simplicity.
Finally, capital costs of equipment are also based in equipment cost in [20], for a power
plant size of 550 MW. Here we can see how the impurities of our fuel and limestone is
an important factor, due to the Fue gas cleanup cost and Solid waste disposal control
cost
• Indirect capital costs
Indirect capital cost are calculated as percentages of direct capital costs. These
percentages are registered in [11]. The indirect capital cost include general facilities
(10%), engineering and home office fees (7%), project contingency (22%), process
contingency (21%), and royalty fees (5%). The project and process contingency cost
00,20,40,60,8
11,21,41,61,8
22,22,42,62,8
3
0,6 0,65 0,7 0,75 0,8 0,85 0,9 0,95
m³
of
O2
Efficiency
O2 introduced
O2 (South African)
O2 (Spanish)
42
factors are in accordance with standard guidelines for cost estimation of new
technologies.
• Operation & Management costs
Here it is included cost of fuel, make-up limestone, waste disposal (ash) and labor cost.
For the last one I supposed three rounds, with two people per round (this kind of
processes are automaticed) with an avaregage annual salary of 25000 €.
Here it is shown the tables for the cost above mentioned:
Table 3. Capital cost of the Ca-l model.
Table 4. Operation & Maintenance cost.
43
5.5 Future trends
As calcium looping is an innovative and promising process for CO2 capture but yet a expensive
process, many deveploments are still required. Most of these are being studied and tested.
Among them, the most remarkable are the inclusion of this process in the cement industry,
the design of a three fluidised beds combustion system, and the recarbonation process.
a) Integrating calcum looping in the cement industry
After the power sector, cement industry is one of the industrial sectors with the highest GHG
emissions globally, accounting for over than 5% of CO2 emissions worldwide. More than half
of the total direct CO2 produced during the cement manufacture process originates from the
limestone calcination, while the remaining arises from the fuel combustion that is required for
the pyro-processing of raw meal to clinker.
Substantial effort has already been paid toward reducing the emissions in the cement industry
such as utilizing alternative fuels with high biogenic content, for example the Solid Recovered
Fuel (SRF), but they have reached the top of GHGs capture level. Therefore, CO2 capture for
storage (CCS) is being considered as alternative to be end-of-pipe options for achieving a
significant CO2 reduction. Some techniques have been tested but without results. However,
calcium looping process is a promising CO2 capture technology with a relatively small
reduction of the total energy efficiency.
There is a consensus that CaL process seems to be the most appropriate technology for CO2
capture in cement industry since:
• Cement industry is already familiar with the management (handling, storage, feeding,
etc.) of CaO-bearing materials.
• It has a low cost of fresh limestone that is required for the enhancement of the
circulating solids capture ability.
• It allows for potential utilization of the purge CaO for the cement production as it is
the chemically compatible with cement raw meal.
• There is room for recovery of the waste heat that is dissipated from the CO2 capture
unit.
The key idea in this intregation is to take advantage of one of the issues in the calcium looping
process. This problem is the degradation of the solvent particules due to the decrease of
porosity in each cycle. This degradated solvent can then be used as raw material in the cement
industry.
To resume the idea, the limestone coming from the quarry is firstly used as solvent and then
for the manufacture of the clinker.
44
Figure 33. Integration of calcium looping in the cement industry.
b) Recarbonation process
M. Elena Diego improved the traditional Ca-looping CO2 capture system by adding a
recarbonator after the original carbonator. Inside the recarbonator, the sorbent particles from
the original carbonator react with a high concentration CO2 gas stream in order to improve
the CO2 carrying capacity of CaO par-ticles. The recarbonator operates at a temperature
around 750-800 C. The results show that the residual activity of the CaO sorbent among all the
cycles increases from 0.07 to 0.16,
Figure 34. Ca-L without recarbonator. Figure 35. Ca-L with recarbonator.
The research made by this scientific shows that the performance of the bench-mark coal-fired
plant integrated with the Ca-looping CO2 capture system with recarbonation process is better
than that of the benchmark coal-fired plant integrated with the traditional Ca-looping CO2
capture system without recarbonation process because the recarbonation process can enhance
the CO2 capture capability of CaO sorbent in the Ca-looping cycle. The net system efficient of
recarbonation is 34.3%, and the efficiency penalty is only 7.27% compared with the benchmark
coal-fired power plant without CO2 capture. In contrast with the original process, the
efficiency penalty of recarbonation process drops around 3.7 percentage points.
45
c) Three fluidised beds combustion system
This new design consists in the regenerating the sorbent using three interconnected fluidised
bed reactors operating at different temperatures. The first fluidised bed reactor will work as a
high temperature fuel combustor, the second as a limestone calciner and the third as a lime
carbonator for CO2 capture. In comparison with other Calcium looping processes, there is no
need of air separation unit neither to perform the fuel combustion, nor to regenerate the
sorbent. Essentially, this process utilises a solid stream mainly comprised of CaO and fuel ashes
as energy carrier to carry out the sorbent calcination. The absence of air separation unit and
the appropriate energy integration makes this process an efficient one compared with the
original process.
It has been proven that the energy penalty of this new system is lower than the energy penalty
in an equivalent oxy-fired system mainly because no air separation unit is needed. The energy
has to be transferred to the steam cycle in several stages, but it is possible to design an
appropriate energy integration that allows high power generation efficiencies.
Figure 36. Ca-L with three fluidized beds.
5.6 Conclusions
Based in the model’s results and the research made, the Ca-L based CO2 process capture is
much expensive than conventional CO2 capture alternatives like MEA-based capture process.
Sypplying the calciner heat requires a big amount of oxycombusted coal in the calciner. Also,
the quantity of solids waste from this process is also significant, increasing the process cost.
Nevertheless, if the technology configuration were mature at a commercial scale, the process
contingency would be much smaller, around 5%, which would bring the capital cost similar,
or even lower than current CO2 capture alternatives. A mature process would also reduce
financial risks, with a lower cost of capital than a firs-of-a-kind project. Another way to improve
46
the economic feasibility of this process is by selling the waste sorbet for industry as I mentioned
above, recirculating the heat originated in the carbonator or using natural gas instead of coal.
Only then, this technology could be feasible for the commercial development.
47
6 STORAGE
6.1 Geological storage
Over the years, several options for CO2 storage have been assessed, including ex situ
mineralization, ocean storage in a dissolved or liquid form, reuse in chemical industry, and
sequestration in deep geological formations. Of these options, today only storage in geological
formations is considered to have the capacity, permanence, and environmental performance
necessary for CO2 storage at the gigatonne (Gt) scale needed to materially reduce CO2
emissions.
The subsurface is the Earth’s largest carbon reservoir, where the vast majority of the world’s
carbon is held in coals, oil, gas organic-rich shales and carbonate rocks. Geological storage of
CO2 has been a natural process in the Earth’s upper crust for hundreds of millions of years
Geological reservoirs worldwide have a potential storage capacity of 236 Gt of CO2, but there
is a technical potential of at least about 2000 Gt of CO2. Global CO2 emissions range from 29
to 44 GtCO2 (8–12 Gt) per year in 2020. These numbers suggest that this technology would be
a feasible solution to mitigate the amount of greenhouse gases in the atmosphere.
The minimum depth limit is 914m where CO2 has a liquid-like density in the range of 500 to
700kg/m3. It ensures high density, low viscosity and good fluidity, minimizing the storage
volume and easily flowing within pores or fractures in rock masses.
In addition to CO2 storage via trapping below a seal, CO2 may be retained through secondary
trapping mechanisms such as solubility, residual gas trapping, and mineral trapping. They act
over decadal to millennial timescales and thus increase storage security over time.
Figure 37. Shematic of the trapping mechanism and their evolution over a 10000-year period, expressed
as a percentage of the total trapping contribution.
48
6.1.1 CO2 storage mechanisms in geological formations
• Storage of CO2 in deep saline aquifers
Deep aquifers are geologic layers of porous rock that are saturated with brine and are located
at 700-3000 m below ground level. Generally, such location's top is a layer of much less
permeable caprock. The capability of an aquifer to store CO2 is controlled by the depositional
environment, structure, stratigraphy and pressure/temperature conditions. Compared with
depleted oil and gas reservoirs, deep saline aquifers possess much larger storage capacities.
They can store about 10.000 billion tons of CO2.
In order to achieve an acceptable level of security and stability, the pumping of saline water
becomes a potential solution. This type of storage is the so-called CO2 storage with deep saline
water recovery (CO2-EWR). Through this technique, pumping water with low salinity, a
process for desalination to achieve drinking-water standards as wells as industrial or
agricultural water requirement.
• Enhanced oil recovery (EOR)
Storage of CO2 with enhanced industrial production has a great potential to enable large-scale
CO2 storage at reasonable cost since it can help to reduce CO2 emissions and enhance
industrial production at the same time.
When CO2 is turned into a supercritical fluid at about 73.8 bar pressure and 31.1 C, it is soluble
in oil. The resulting solution has lower viscosity and density than the parent oil, thus enabling
production of some of the oil in place from depleted reservoirs.
After that, the produced fluids are separated on a platform with CO2 recycled in situ. In
general, 1 t of CO2 injection facilitates the extraction of 1.5 t of oil.
A relatively high percentage (around 75%) of the injected CO2 is safely stored after production
is stopped due to chemical and physical processes.
• Enhanced coalbed methane technology (ECBM)
Methane is predominantly physically adsorbed to the large internal surface area of the micro-
pores in the coal. Because CO2 is adsorbed more strongly than methane, the injection of CO2
will result in expelling methane. This results in the production of methane at the same time as
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the injection of CO2. Also, coal beds are often located in the nearby of a current or future power
plants, so CO2 transportation cost can be reduced.
However, there is still not enough research about the reactivity of CO2 injected in the coal
under situ conditions.
Figure 38. Shematic of geological storage options.
• Mineralization of CO2
It is an important technology due to its scalability for small/medium scale emitters and
offers a non-monitoring and leakage free CO2 storage option, making it very accessible and
reducing the costs. It is based in the reaction of CO2 with rocks rich in magnesium/calcium
oxide of with appropriate industrial solid wastes to produce mineral carbonates.
CO2 mineralization can be divided into below mineralization (injection of CO2 into
geological formation) and above ground mineralization. In the last one, it is fixed with
calcium or magnesium oxide and the reactions are as it follows:
𝐶𝑂2 + 2𝑁𝑎𝑂𝐻 = 𝑁𝑎2 + 𝐻2𝑂
𝑁𝑎2𝐶𝑂3 + 𝐶𝑎(𝑂𝐻)2 = 𝐶𝑎𝐶𝑂3 2𝑁𝑎𝑂𝐻
In order to reduce costs and overcome low efficiency, recyclable solvents are proposed for
the CO2 capture. Solid waste residue (SWR) generated from the large-scale industrial
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processes such as coal-fired power plant, cement plant, oil shale industry, steel are
increasing annually. This industrial SWRs contain substantial alkali and alkali earth metal,
making feasible the mineralization of CO2.
Focusing now in the costs of mineralization, four types of ores are presented in order to
build a table which represent an approximation of how does the mineralization process
cost and how energy does it requires.
Table 5. Cost of mineralization and energy required.
6.1.2 Risk & Environmental impact
This issue is critical for the development of CCS, because if it is not solved, no storage
project could be launch and as consecuence, no capture project. The risks associeated with
the escapes of CO2 can be classified in two categories: global risks and local risks.
The global risks include the release of CO2 that can contribute to climate change if there is a
leakage of the CO2 stored to the atmosphere. In addition, if there is a CO2 leakage from the
storage formation, it can become into risks to humans, ecosystems and Groundwater,
representing local hazards, but fortunately according with technical models and the
experience of actual storage formations, the The fraction retained will be 99% in the next 1000
years.
Regarding with local risks, there are two scenearies in wich a leakage is possible. The first one
is when there are failures in the injection wells or ascending leaks in abandoned wells which
could create a sudden and rapid release of CO2. It is probable that this type of release is
detected promptly and be addressed through the use of techniques available in the present for
the containment of eruptions of wells. The risks related to this type of release mainly affect
workers who are in the vicinity of those leakages when it occurs, or to those who are called to
control the rash. Its is important to know that a concentration in air of CO2 more than 7% can
be deadly for humans.
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In the second scenario, leaks can occur through faults or fractures that have not been detected,
or by means of wells with losses in which surface filtration is more gradual and diffuse. In this
case, the hazards mainly affect drinking water aquifers and ecosystems in which CO2 is
accumulated in the area between the surface and the top of the water table. In this scenario,
there may also be acidification of soils and a displacement of oxygen in soils. Leakage routes
can be identified by various techniques and by the deposit characterization. Some possible
leakage’s rotues are shown in the next figure:
Figure 39. Possible escape routes and possible solutions for co2 injected into saline formations.
In this figure, we can see that all the escape routes are produced by the difference of pressures.
This difference ends in a movement of the gas through the rock, letting it escape. In order to
prevent and solve this, some solutions are presented, but most of them consists in re-inyecting
CO2 or cleaning the aquifers, always with the aim to reduce the CO2 pressure.
So, as i mentioned above, that difference of pressure and thus, difference of dense, produce a
movement of the CO2 under the cap rock. Since the CO2 (as it is shown in the next figure in
purple) is less dense than brine, it moves upwards through the aquifer, under the cap rock. At
the bottom of the injected CO2 plume, brine displaces the CO2. This leaves behind a trail of
trapped CO2 (purple purple). CO2 also dissolves in the brine, and this denser CO2-laden brine
(pale blue) sinks slowly through the aquifer.
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Figure 40. A shematic of CO2 movement after injection.
6.2 Industrial CO2 utilization
CO2 capture through industrial processes represent an effective and promising idea to mitigate
the CO2 problem. Among them, refrigeration systems, fire extinguishers, water treatment
processes, horticulture are remarkable, but the steel and cement industry are the ones that
most CO2 requires. For example, in the iron & steel industry, due to the calcium-silicate
content, many types of steel slag like EAF and BOF is produced. These slags have potential to
react with CO2 for production of cementitious material. The main reactions of dicalcium
silicate and tricalcium silicate are:
2(2𝐶𝑎𝑂 ∙ 𝑆𝑖𝑂2) + 𝐶𝑂2 + 3𝐻2𝑂 = 3𝐶𝑎𝑂 ∙ 2𝑆𝑖𝑂2 ∙ 3𝐻2𝑂 + 𝐶𝑎𝐶𝑂3
2(2𝐶𝑎𝑂 ∙ 𝑆𝑖𝑂2) + 3𝐶𝑂2 + 3𝐻2𝑂 = 3𝐶𝑎𝑂 ∙ 2𝑆𝑖𝑂2 ∙ 3𝐻2𝑂 + 3𝐶𝑎𝐶𝑂3
Amounts of stored CO2 increase with increasing time of carbonation curing. These processes
contribute strength development greater than that in ordinary Portland cement.
In the chemical field, CO2 can be used as a feedstock for chemical engineering. In the near
future, it could mitigate 700 megatons of CO2 per year. Furthermore, high purified CO2 can
be very used, because many high added value chemicals can be synthesized for the benefit of
a wide variety of sectors of the chemical industry. At high pressure and temperature, methane
can be synthesized by reaction with CO2 and H2 using metallic catalyst (Ni), while methanol
can be synthesized by reaction of CO2 and H2 using a metallic catalyst (like copper or Al2O3).
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Another interesting applicatin in the thermochemical field s that methane with CO2 and H2
can be used to storage the solar energy. In the operating temperature of 800 Cº, the total energy
efficiency is about 70%.
6.2.1 Biofuel production from CO2
From converting CO2 to a biofuel, CO2 converts from a damaging greenhouse gas into a
valuable and renewable and nearly unlimited carbon source. Moreover, fossil fuels are
expected to disappear in the next centuries, so biofuels are becoming a priority worldwide.
There are some limitations and challenges that biofuels must overtake. Firstly, and the
principal, is the direct competitions with food production. Lands are being used for growing
crops, but not for food but for biofuels. This is controversial for a world with nearly 1000
million people with lack of food for having a healthy life. Additionally, this fields accelerate
deforestation due to the expansion of land usage for the cultivation of suitable feedstock.
Nevertheless, biofuels have great advantages. They are compatible with current combustion
engines, they are produced from renewable sources, produce low CO2 emissions in
combustion and have a positive socio-economic impact.
With all this, the ideal solution would be to produce biofuels with CO2 and this is possible.
There are several biofuel products that can be produced from CO2 including methanol
(CH3OH) and dimethyl ether (CH3OCH3). The key factor in the large-scale use of biofuel
production process is the availability of the raw materials CO2 and H2. Large amounts of CO2
can be obtained from sources such as fossil fuel-burning power plants and industrial
facilities by using CCS technology.
• Methanol
It is obtained by the catalytic hydrogenative conversion of CO2 with hydrogen.
𝐶𝑂2 + 3𝐻2 ↔ 𝐶𝐻3𝑂𝐻 + 𝐻2𝑂
This is a well-known reaction, it has been used for nearly a century by USA for methanol
production as a by-product of other processes such as fermentation. In order to increase the
efficiency of the reaction, catalysts such as Cu or ZnO have been developed.
• Dimethyl Ether
The production of Dimethyl Ether from CO2 and H2 may have a great deal of potential for use
as a clean alternative fuel for diesel engines. Dimethyl ether can be used as a clean, highly
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efficient compression ignition fuel with low NOx, SOx and particulate matter, and it can be
efficiently reformed to hydrogen at low temperatures. The production of DME usually occurs
by two consecutive reactions: methanol synthesis and the de-hydrogenation of methanol. The
first step in DME production is the conversion of the feedstock to syngas. The second step is
methanol synthesis using a copper-based catalyst and the third step is de-hydrogenation of
methanol into DME, as shown in the next equations.
➢ Methanol synthesis: 𝐶𝑂 + 2𝐻2 ↔ 𝐶𝐻3𝑂𝐻
➢ Methanol dehydration: 2𝐶𝐻3𝑂𝐻 ↔ 𝐶𝐻3𝑂𝐶𝐻3 + 𝐻2𝑂
To facilitate methanol synthesis, the CO in syngas can be converted to CO2 through the WGS
reaction to generate additional H2 and form CO2. The CO2 then reacts with hydrogen to
produce methanol
➢ WGS: 𝐶𝑂 + 𝐻2𝑂 ↔ 𝐶𝑂2 + 𝐻2
In addition, DME can also be produced through the direct conversion of syngas using an
appropriate catalyst. By applying direct conversion to DME, the processes can occur
simultaneously in one reactor and the product is the net reaction shown below. The last step
is the purification of the raw product, which may also contain some methanol and water.
➢ 3𝐻2 + 3𝐶𝑂 ↔ 𝐶𝐻3𝑂𝐶𝐻3 + 𝐶𝑂2
The next figure represents a diagram of carbon conversion cycle from source to methanol and
other hydrocarbon products:
Figure 40. Diagram of the conversion of CO2 into hydrocarbons.
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Biofuels will become important in the future because they will most likely be part of a portfolio
of solutions to address the problem of high oil prices and finite fossil fuel resources. It is
expected that due to the limited fossil fuel resources, conservation and the use of other
alternative fuels will become more important. Other advantages associated with biofuel
include equivalent rates of growth in gross domestic product (GDP) and per capita increases
of GDP. In light of the potential of biofuel, the availability of long term CO2 source needs to
be sure to make large-scale biofuel production feasible. Moreover, today's energy system is
unsustainable because of equity issues as well as environmental, economic and geopolitical
concerns that have implications far into the future.
Based on the scenario in the USA and the European Union, the International Energy Agency
indicates that near-term targets of up to 6% displacement of petroleum fuels by biofuels appear
feasible using conventional biofuels. The recent commitment by the US government to
increase bio-energy over 10 years has provided added impetus to the search for feasible
biofuels. It is expected that biofuel will provide low carbon intensity and a reduction of up to
80% of CO2 emissions in 2050 in the USA.
The next figure represents a projection of use of biofuel as a global energy source.
Figure 41. Projection of use of biofuel as global energy source.
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7 LEGISLATION
The legal, regulatory and public perception developments around CCS are diverse across
countries around the world, due to the different legal systems, industries and culture of its
countries. In the following pages, some key concepts relative to climate change & CCS
legislation are discussed in order to give a brief understanding of the legislation level in this
area.
7.1 Subsurface
Focusing in CO2 storage, it is obligatory to talk about the ownership of the subsurface. In most
of the world, the deep underground is owned by the state, which can permit and make rules
about usage. In USA, the subsurface is owned by the surface owner, and the sate manages only
the environmental and safety elements. Furthermore, legislation for other subsurface
industrial activities, such as natural gas storage, acid gas storage, or EOR provides a framework
for regulating CO2 storage. The question of when or under which conditions liability of the
storage site is transferred to the state is a key issue, as storage operators are unlikely to invest
if the conditions of liability transfer are unclear or unfavorable and if climate liability may be
imposed to them. However, the general public and the state are unlikely to accept transfer of
liability unless safety can be warranted. This issue of transfer liability is treated differently
among countries and even among US states.
7.2 Kyoto Protocol
In the world, the most important agreement concerning climate change is the Kyoto Protocol.
It was agreed in 1997 and it main aim is to provide Contracting Parties with legally binding
obligations and targets for the reduction of their greenhouse gas emissions. It required
developed countries to reduce their emissions of greenhouse gases by at least 5% from 1990 in
the period 2008-2012.
The protocol has attached a monetary value to the earth’s shared atmosphere for the United
Nations Framework Convention on Climate Change’’ (UNFCCC) by including restrictions
upon greenhouse gas emissions. The introduction of mandatory emissions targets effectively
assigns a financial cost to greenhouse gas emissions and creates an incentive for the Parties to
the Convention to seek the most cost-effective methods for reducing them. It is this latter
element that is reflected in the creation of the flexible mechanisms which are the ‘’Joint
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Implementation’’ (JI), ’The Clean Development Mechanism’’ (CDM) and the
‘’International Emissions Trading’’.
In order to follow the lines established in the Kyoto Protocol, an annual meeting was proposed
to assess progress in dealing with climate change. The Conference of Parties (COP) serves as
the meeting of the Parties to the Protocol, which is known as the CMP. The meetings of the
CMP are timed to coincide with the meeting of the COP and its functions are similar to those
carried out by the COP. The first CMP was held in Montreal in 2005, and since then 11 more
CMP were held.
7.2.1 The International Emissions Trading
This mechanism has a special relevance due to the legal and economic implication of the
different parties and its impact in the industry development.
The International Emissions Trading is a system where parties that have exceeded their
emission reduction commitments under the Kyoto Protocol may sell excess “assigned amount
units” (AAUs). Other parties may meet their own emissions reductions by purchasing these
AAUs or offset credits from developing countries. The mechanism has resulted in several
national and regional trading schemes, including the European Union Emission Trading
Scheme (EU ETS).
In January 2005, the European Union GHG Emission Trading Scheme (EU ETS) started its
operation as the largest multi-country, multi-sector GHG trading system worldwide. Until
now, it is the world‘s most advanced emissions trading system.
The EU ETS is implemented as a cap-and-trade system. An aggregate limit (cap) on the amount
of a pollutant that can be emitted is established. The cap is represented by emission allowances
which can be transferred (traded) among installations required to hold a number of allowances
equivalent to their emissions. Installations which emit less than their individual cap allows are
able to sell their surplus emission allowances – and vice versa. Thus, the buyer is paying a
charge for polluting, while the seller is being rewarded for having reduced emissions. Plus,
emissions are reduced where it costs least. The cap is lowered over time, aiming towards the
national emissions reduction target. The EU ETS is based on the Emission Trading Directive
(Directive 2003/87/EC), which entered into force in October 2003, and is implemented at an
installation level.
This means that some 11,500 large emitters of carbon dioxide within the EU must monitor and
report their CO2 emissions annually. Furthermore, they are obliged to surrender a number of
emission allowances (EUAs) and CERs/ERUs equal to the total emissions from their
installation during the preceding calendar year by 30 April at the latest. Installations currently
covered by the ETS are collectively responsible for close to half of the EU's emissions of CO2
and 40% of its total greenhouse gas emissions.
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Since January 2008, the EU ETS not only applies to the 27 EU Member States, but also to the
other three members of the European Economic Area (EEA) – Iceland, Liechtenstein and
Norway.
Figure 42. Shematic of CO2 trading emissions mechanism.
7.3 The Paris Agreement
The Paris Agreement was signed by 144 of the 195 countries of the UNFCC in the CMP number
11 (COP 21). It focuses on climate mitigations actions after 2020 and represents a clear and
indisputable commitment from the world’s political leaders to transition to low-carbon
economy. If the ambitions of the Paris Agreement are to be achieved, CCS must enter the
mainstream climate actions to be undertaken by governments and by business. This
agreement provides cause for optimism that the future investment required to accelerate and
widespread deployment of CCS will rise, but much more needs to be done in the next years.
The agreement defines a number of climate goals, in which CCS is an important mitigation
technology.
• A short-term goal is to reach peak emissions as soon as possible.
• A longer-term goal is to limit average global warming to well below 2 degrees Celsius
(2°C) above pre-industrial times, and an aspiration to limit warming to 1.5°C.
• In the second half of this century, a balance between emissions sources and sinks (often
referred to as net-zero emissions) will be needed.
The IPCC Climate Change 2014: Synthesis Report Summary for Policymakers highlights that,
without CCS, the cost of achieving 450 parts per million (ppm) carbon dioxide equivalent by
2100 could be 138 per cent costlier (compared to scenarios that include CCS), and that only a
minority of climate model runs could successfully produce a 450-ppm scenario in the absence
of CCS.
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7.4 Legal main developments of geological CO2 capture in the developed countries
Developed countries have all started legislation on CCS. US, UE and China are the most
important countries regarding this topic, due to their levels of CO2 emissions.
• United States: Federal oversight of CO2 storage involves regulations from the US
Environmental Protection Agency (EPA) and congressional legislation surrounding
safe drinking water and well safety. As I mentioned above, pore-space ownership is
regulated at the state level, leading to different approaches in different states. In order
to enable CCS, United States has opted for funding tax and credits for research,
development, and demonstration, starting with smaller demonstrations, including
EOR.
• EU: In the European Union, a Directive on the Geological Storage of CO2 was agreed
in 2009. This Directive is the 2009/31/Ce, and it contains detailed guidance on how to
handle the contentious issues around CO2 storage, including liability transfer. The EU
Directive was criticized for not resolving all barriers and for not being fully consistent
with other EU legislation. To promote CCS, the European Union started in 2005 a
demonstration program with subsidies (often complemented by funding on the
member state level) and research programs
• China: Although China is the most polluting country, there is still no domestic
regulatory framework to provide oversight of future CCS projects. An environmental
legislation would require an interplay between local, regional and national councils and
institutions. China’s strategy to implement CCS seems set on adopting parts from both
the US and EU strategies on CCS.
• Spain: As it is part of the European Union, Spain has to follow the Directive that are
redacted and agreeded by the Union. To implement it in the spanish territory, the
40/2010 law for the CO2 geological storage was implanted. The purpose of this law is
to incorporate the provisions contained in Directive 2009/31 / EC into Spanish
legislation, adapting them to the industrial, geological and energy reality of our
country, and establishing a legal basis for the geological storage of carbon dioxide, in
safe conditions for the environment, to contribute to the fight against climate change.
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7.5 Current state of CCS policy
Despite of the first steps taken to promote CCS in the past, the present and future of CCS policy
has changed in the different countries of the world. While CCS path has dramatically slowed
in the USA, in Canada It has emerged as a key issue for the future. Here is the current state of
the principal regions of our planet.
• United Sates: The key uncertainty in the United States remains the legal action
brought by 27 states against the US EPA’s implementation of the Clean Power Plan,
which has resulted in a significant delay to the deployment of this flagship initiative.
While some states have continued to develop their state-wide approach to its
implementation, several have suspended all further work pending a decision from the
courts. Fortunately, The US DOE continues with a robust research and development
capture program and its Regional Carbon Sequestration Partnerships. Funding awards
have started to advance selected capture technologies to large pilot scale.
Canada: Canada has recently become one on the most promising countries in the
field of CCS. This country has seen the realization of its long-term policy, legal and
regulatory ambitions, with the recent entry into force of the CO2 performance
standards for coal-fired power plants, which the Federal Government adopted in 2015.
Prime Minister Trudeau recently announced a national ‘floor price’ on carbon that
would require all provinces and territories to have some form of carbon pricing by
2018. Developments at the Canadian federal level in the past year build upon the
accomplishments of the country’s provincial governments in supporting the
deployment of CCS technology.
• EU: Supranational policy development in Europe has continued to build upon
initiatives launched by the European Commission in 2015. The European Union’s
ratification of the Paris Agreement, together with the ongoing reforms to the EU
Emissions Trading System (EU-ETS) and activities under the Strategic Energy
Technology (SET) Plan process, offer a platform for developing further commitments
to CCS deployment and support. The EU approach is a complete vision of CCS, because
it focuses on carbon pricing, and its funding mechanisms, address emissions from a
variety of sectors, not just emissions from power generation where many countries have
historically tended to focus their deployment efforts.
• China: China’s joint announcements with the US, pledging action on climate change,
includes renewed commitments to carbon capture utilization and storage (CCUS).
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7.6 Public perception of CCS
In 2005, when the IPCC SRCSS (Intergovernmental Panel on Climate Change-Special Report
Emissions Scenarios) was published, the literature on the public’s perception of CCS was so
limited so there was no information about it in the document. However, a considerable
literature has emerged since them.
There are two perspectives regarding public engagement around CCS: Some consider
engagement a success when people can make more informed decisions on CCS, whereas other
consider it a success only when resistance to CCS projects is prevented or reduced.
A synthesis provided by Benson highlights lessons from projects and studies that indicate that
communicating early, honestly, transparently, responsively, inclusively, and clearly around a
potential CCS project and framing it in the context of climate change action are essential
elements of effectively engaging the public and reducing the likelihood of resistance. A key
issue is the lack of knowledge of CCS, but another is the difference in risk perception between
the lay public and experts.
Through history, it is shown that public acceptance can make or break a CCS project. The most
visible example of a project canceled because public resistance is the Barendrecht project in
the Netherlands. In Germany, the general view of CCS is quite negative. The view that CCS
diverts efforts away from renewable energy contributed to the parliamentary rejection of CCS
legislation and the canlation of one of the EU’s demonstration projects is Jänschwalde.
Nevertheless, in the United States and Australia the general attitude seems more favorably to
CCS, maybe because of a more positive view of the fossil-fuel industry (due to historical
reasons), but even in these countries resistance has emerged around several CCS projects.
Regulation also plays a role in public engagement around CO2 storage projects. Several
publications point out that the public is unclear whether governments have taken note of the
recommendations and shifted from ‘’decide, announce, defend’’ to ‘’ investigate, adapt,
engage’’.
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8 CONCLUSION
Como se ha mostrado en este trabajo, la temática de la captura y uso del CO2 es un tema que
cada vez está tomando más relevancia en nuestra sociedad. Año tras año, diferentes países
están incluyendo en su agenda el cambio climático como un problema urgente, y como
consecuencia maneras para afrontarlo. Es aquí donde CCS está apareciendo como una gran
alternativa a las dos principales vías para mitigar el aumento de los gases de efecto invernadero.
La primera de ellas es el diseño eficiente de las estructuras de nuestra sociedad, como la
remodelación de las ciudades, con la entrada en escena de las ‘’Smart Cities’’, cuya tecnología
puede disminuir notablemente las emisiones de CO2 a través de la optimización del flujo de
tráfico o la construcción de edificios eficientes con un bajo consumo energético (y por tanto
de CO2). La otra alternativa es la apuesta por las energías bajas en emisión de CO2 como la
nuclear o renovables como la fotovoltaica o eólica, que tanto han avanzado en estos últimos
años.
Sin embargo, hay un gran consenso científico en admitir que ambos métodos mencionados no
podrían cumplir por si solo el objetivo de reducción de CO2 a la atmósfera, sino que requeriría
de una apuesta por CCS para poder alcanzarlo.
La Agencia Internacional de la Energía ha venido realizando, en particular desde la cumbre del
G8 de Gleneagles, varios análisis y estudios sobre cómo lograr el objetivo de no superar en 2ºC
la temperatura media respecto a los niveles pre-industriales (año 1750), lo que resulta ser
equivalente a limitar las emisiones de CO2 a 450 ppm (escenario 450). Como mencioné
anteriormente para lograr el escenario citado de 450, son necesarias reducciones de emisiones
provenientes tanto de la eficiencia, fundamentalmente en los usos finales, como en el
desarrollo de las energías renovables, la nuclear y la captura y almacenamiento.
Figure 43. Contribution of different options to mitigate Co2 for the 450 scenario.
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Respecto a las diferentes tecnologías de captura, es amplia las diferentes posibilidades que
existen. Las primeras tecnologías en ser desarrolladas (absorción con aminas) ya se han
presentado como una alternativa ineficiente, y han dejado paso a nuevas vías como la captura
con membranas o ‘’calcium looping’’ que prometen aumentar la eficiencia de captura y reducir
los costes.
Precisamente estos costes de operación de dichas técnicas son una de las principales trabas a
la hora de considerar CCS como una via factible. La tecnología precisa aún de mucho avance
para poder ser económicamente rentable para aquellos gobiernos y compañías que deseen
aplicarlas. Por ejemplo, en el mencionado ‘’calcium loopin’’ hemos comprobado las
considerables opciones de optimización que existen. Además de esta reducción, se debe
trabajar también para la concienciación ciudadana. Esta actual carencia de sensibilidad por
CCS ralentiza su evolución, y diferentes opiniones en su contra aparecen como:
• ‘’ No hace desaparecer el CO2 de la atmosfera, sólo lo hace 'de la vista’'.
• ‘’Sigue promoviendo la adicción al carbono. Su desarrollo futuro ha sido muy
promovido por el sector del carbón, como justificación para la construcción de nuevas
centrales eléctricas con ese combustible’’.
• ‘’Dudosos beneficios y 'vampiro' de las renovables. Absorberá financiación que debería
dirigirse a renovables’’.
• ‘’Herramienta de mitigación errónea. Primero porque es imposible que pueda
comenzar a tiempo y segundo porque la CAC será ineficiente y extremadamente
costosa’’.
Como ejemplo de estas actividades necesarias para la concienciación ciudadana tenemos la
iniciativa japonesa del proyecto ‘’Tomakomai CCS’’, donde se educa a los más jóvenes con una
demostración del proyecto de captura de CO2 mediante juegos.
Figure 44. Educating game for illustrate a CO2 capture plant in Japan.
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Finalmente, debemos entender que poseer un mix equilibrado en generación eléctrica como
España posee, con renovables, gas, carbón y nuclear es un bien que aporta seguridad,
flexibilidad y competitividad, haciéndolo más estable y sostenible. Para progresar en este
camino la voluntad política es necesaria y en Europa se está comprobando que esto incrementa
el peso de la industria de un país en el PIB, genera conocimiento y empleo. Nuestro país posee
numerosos elementos para estar a la cabeza del grupo europeo, y debería acometer, reforzando
las iniciativas ya tomadas, los pasos necesarios para apoyar el CCS.
66
67
APENDIX
The code used in the model is was written in C, using CodeBlocks.
1 #include <stdio.h>
2 #include <stdlib.h>
3
4 void main()
5 { float n=1;
6 float f_co2=1.28;
7 float fcarb;
8 float fcarb1= 0.44; //valor inicial que suponemos
9 int seguir=1;
10 float Xr=0.075;
11 float k=0.52;
12 float fash=0.016, fs=0.0096, f0=0.0256, fr=19.2;
13 int i,j=0;
14 float eficiencia=0.70;
15
16
17 float x,xave,r,Ax;
18
19 for (i=1; i<1000 && seguir==1; i++)
20 {
21 for(n=1;n<550;n++) //
22 {
23 x=(1/((1/(1-Xr))+k*n))+Xr; // Ec. 5
24 r=((f0/fr)*pow(fcarb1,n-1))/(pow(((f0/fr)+fcarb1),n));// Ec. 36
25 xave=xave+x*r;// Ec. 37
26 }
27
28 printf(" xave es %f \n",xave);
29
30 fcarb=(f_co2*eficiencia)/(fr*xave);
31
32 if (abs(fcarb-fcarb1)>0.05) //condicion para seguir
33 {
34 fcarb1=fcarb;
35 seguir=1;
68
36 x=0;
37 r=0;
38 }
39 else seguir=0;
40
41 printf("fcarb es: %f",fcarb);
42
43 }
44
45 Ax=(fs/(fr*fcarb))*100;
46 printf("\n Ax es%f",Ax);
47 // cálculo de nueva k
48
49 float k_nueva,Xr_nueva;
50 k_nueva=k*(1+0.2962*Ax);
51 printf("\n nueva k es %f",k_nueva);
52 //cálculo nueva Xr
53 if(Ax>0&&Ax<0.5)
54 {
55 Xr_nueva=Xr*(1-1.536*Ax);
56 }
57 else {
58 Xr_nueva=Xr*(1-(0.3076*Ax)-0.4230);
59 }
60 printf("\n nueva Xr es %f",Xr_nueva);
61
62 //calculamos nueva x_ave
63 float x_avenueva=0,x_nueva=0,r_nueva=0;
64 for(j=1;j<550;j++)
65 {
66 x_nueva=(1/((1/(1-Xr_nueva))+k_nueva*j))+Xr_nueva;
67 r_nueva=((f0/fr)*pow(fcarb,j-1))/(pow(((f0/fr)+fcarb),j));
68 x_avenueva=x_avenueva+(x_nueva*r_nueva);
69 }
70 printf("\n x_avenueva es %f",x_avenueva);
71
72 //calculamos de nuevo fcarb para ver si lo hemos estimado bien
73
74 float fcarb_nueva=0;
75 fcarb_nueva=(f_co2*eficiencia)/(fr*x_avenueva);
76 printf("\n nueva comprobacion fcarb %f",fcarb_nueva);
69
77
78 //Calculo nsa
79
80 int tau=38;// ***¿como programamos la gráfica?
81 float n_sa;
82 n_sa=(f_co2*tau)/(((f_co2*eficiencia)/(fr))*((1/fcarb)-1));
83 printf(" moles de caliza y carb. calcico= %f \n",n_sa);
84
85 //calculamos composicion molar del CaSO4 y ceniza
86
87 float x_CaSO4;
88 float x_ash;
89
90 x_CaSO4=fs/(f0+fash);
91 x_ash=fash/(f0+fash);
92
93 printf("x_CaSO4 es %f y x_ash es %f\n",x_CaSO4,x_ash);
94
95 // calculamos composicion molar de CaCO3 y CaO
96 float x_CaCO3;
97 float x_CaO;
98
99 x_CaCO3=x_avenueva*fcarb_nueva*(1-x_CaSO4-x_ash);
100 x_CaO=1-x_CaCO3-x_CaSO4-x_ash;
101
102 printf("x_CaCO3 es %f y x_CaO es %f \n", x_CaCO3,x_CaO);
103
104 // calculamos toneladas totales solidos
105 float molar_mass=80.77;
106 float total_mol;
107 float total_mass;
108
109 total_mol=n_sa/(x_CaCO3+x_CaO);
110 total_mass=total_mol*molar_mass;
111 printf("moles totales son %f\n",total_mol);
112 printf("la masa toal a introducir es %f kg",total_mass);
113
114 //FIN ALGORITMO LIBRO
115
116 //calculamos masa y mol CaCO3 formada en carbonatador
117
70
118 float Mol_formado_CaCO3, M_formado_CaCO3;
119 Mol_formado_CaCO3=(eficiencia*f_co2)*1000;
120 M_formado_CaCO3=Mol_formado_CaCO3*100.9;
121
122 printf("\n mol CaCO3 formado= %f , masa CaCO3 formada=
%f",Mol_formado_CaCO3,M_formado_CaCO3);
123
124 //calor generado para MEJORA
125 float calor_gen_carb;
126 calor_gen_carb=(Mol_formado_CaCO3*178*1000)*0.7;
127 printf("\nel calor generad para MEJORA es %f J",calor_gen_carb);
128
129 //calor necesario para quemar 1,152 kmol CaCO3 que entran en calc cada s
y cabón necesario
130
131 float Cp=0.66432;
132 float T1=923;
133 float T2=1173;
134 float Cc=14183950;
135 float Q=(M_formado_CaCO3+2583.04)*Cp*(T2-T1); //añado CaCO3 que entra en
calcinador
136 float M_carbon=((Q/Cc)*1000)*1.1;// en un 10% mas ya que tiene 10%
compuestos inertes
137 printf("\n calor necesario en calc es %f J y m_carbon es %f
g/s",Q,M_carbon);
138
139 //IMPUREZAS
140 int cenizas_carbon=((Q/Cc)*1000)*0.1;
141 float impureza_CaCO3=f0*(100-92.4);
142
143
144 printf("\n g cenizas que salen por segundo del carbon= %i",cenizas_carbon);
145 printf("\n g impurezas del CaCO3 que salen por segundo=
%f",impureza_CaCO3);
146 float impurezas_totales=cenizas_carbon+impureza_CaCO3;
147 printf("\n g impurezas totales que salen por segundo=
%f",impurezas_totales);
148
149 //cálculo O2 para el sistema
150 float O2_calc=M_carbon/12.11;
151 float O2_carbo=((1.28/0.12)*0.00024)/2*1000;
152 printf("\n O2 para calcinador %f mol y mol O2 para carb %f
",O2_calc,O2_carbo);
71
153 float vol_O2_tot=(O2_calc+O2_carbo)*8.2057*pow(10,-5)*273;
154
155 printf("vol total O2=%f m3",vol_O2_tot);
156 }
72
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