Energy Analysis of Underground Coal Gasification with Simultaneous Storage of Carbon DioxideAli Akbar Eftekhari

Hans Bruining

x

(Enriched) Air

Water (Steam)

CO, CO2, H2, H2O, CH4, N2

C + 2 H2O + CaO CaCO3 + 2 H2 + 87.9 kJ/mol

Exergy Analysis

Exergy Analysis of Energy Recovery Processes

Recovery Process Energy

Consumption

CO2 Capture and Storage

Energy Source

CO2 Capture and Storage

Recovery Process Energy

Consumption

Recovery Process Energy Consumption

CO2 Capture and Storage Energy

Upstream productionRefinery/processingTransport/DistributionCCSSustainable Recovery

Production/ProcessingTransportCCSSustainable Recovery

Zero-emission recovery factor

Coal (56%)

Natural Gas (62%)

Ref: Dellucci, 2003; Except the CCS data

UCG with mineral injection

5

High Temperature:CaCO3 CaO + CO2

Volume Constraint:

Independent reactions

Combustion C + O2 CO2 + 393.77 kJ/mol

Gasification Global reaction

C + 2 H2O + CaO CaCO3 + 2 H2 + 87.9 kJ/mol Boudouard reaction

C + CO2 2 CO – 172.58 kJ/mol Shift reaction

CO + H2O CO2 + H2 – 41.98 kJ/mol Methanation

C + 2 H2 CH4 + 74.90 kJ/mol

Exothermic

Endothermic

Very Slow

Equilibrium relations

j

v

oi

vii K

P

Py

j

ji

,)ˆ(

yi: gas phase mole fraction

P0: standard pressure (1 bar)

P: system pressure

Kj: equilibrium constant of reaction j

vi,j: stoichiometric coefficient of component i in reaction j

Φi: fugacity coefficient of component i in a gas mixture

ji

oiji

KRT

Gv

,

exp

T

T

oP

T

T

oP

oooo

dTRT

CdT

R

C

TRT

H

RT

HG

RT

G

00

10

0

00

o

i

oiji HHv 00,

oP

i

oPji CCv

i ,

1160

1180

1200

1220

1240

1260

1280

1300

1320

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

1 1.5 2 2.5 3 3.5 4

Tem

pe

ratu

re (

K)

volu

me

(cu

bic

me

ter)

water to oxygen ratio

Produced CaCO3 (cubic meter)Consumed Carbon (cubic meter)Product Temperature (K)

1050

1100

1150

1200

1250

1300

1350

00.20.40.60.8

11.21.41.61.8

1 3

cub

ic m

ete

r

water to oxygen ratio

Produced CaCO3 (cubic meter)

Consumed Carbon (cubic meter)

Product Temperature (K)

Temperature constraint at P=80 bar

Volume constraint

Optimum composition (O2 injection)

0

0.1

0.2

0.3

0.4

0.5

0.6

1 2 3 4

mol

e fr

acti

on

water to oxygen ratio

H2 mole fraction

CO2 mole fraction

CO mole fraction

H2O mole fraction

CH4 mole fraction

 Composition (dry

basis)

H2 0.46

CO2 0.08

CO 0.32

CH4 0.14

Higher heating value (MJ/m3) 14.679

Lower heating value (MJ/m3) 13.286

Process flow diagram (1)

Egain

E1

E2

E4

E3

E5

ECCS

η = (Egain - (∑Ei +ECCS ))/ERes

ERes

From theory to practice

Theoretical

Practical

Zero-emission(Sustainable)

Results of PFD (1)

Theoretical Practical Zero-emission

-20.0

0.0

20.0

40.0

60.0

80.0

100.0

Theoretical, practical, and zero-emission recovery of coal energy (water to oxygen molar ratio of 3.2)

Recovery factor (%)

Process flow diagram (2)

Sustainable recovery for other energy conversion processes

Conclusion

In situ introduction of absorbent e.g. CaO is energetically expensive and with the current state of technology is not feasible

Using naturally abundant minerals can improve the exergetic recovery of UCG process

Coal Zero-emission Recovery

Production/ProcessingTransportCCSSustainable Recovery

Natural gas sustainable recovery

Upstream production

Refinery/processing

Transport/Distribution

CCS

Sustainable Recovery

Formulation

Exergy?

Energy = Exergy + Anergy Exergy is a portion of energy that potentially

can be converted to mechanical work

1 kJ of Electricity = 1 kJ of Exergy + 0 kJ of Anergy

1 kJ of energy in hot water at 70oC = 0.13 kJ Exergy + 0.87 Anergy

Energy is conserved; Exergy is consumed

ExergyAnergy

ExergyAnergy