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WASTE HEATHeat to electricity techniques

Within the scope of the EPOS project, extensive literature and market research reviews were performed in order to identify different technological, organisational, service and management solutions that could be applied to different industrial sites and clusters. The collected information will aid in establishing on-site and/or cross-sectorial industrial symbiosis opportunities; additionally, to enhance overall sustainability, performance and resource efficiency of different process industry sectors. Through the cooperation of project partners, a longlist of different technological options was created. Resource material for this list included: scientific articles, project reports, manufacturer’s documentation and datasheets.

About the EPOS Technology Focus

WASTE HEATIndustrial processes in different sectors, depending on the process, may either require or generate enormous amounts of thermal energy. Much of the waste heat is disposed of into the environment; meaning heat sources are frequently not optimally utilised.

Utilisation of waste heat is one of the core and generic activities for achieving industrial symbiosis and resource efficiency. When it is utilised, the waste heat is often reused in the process itself (e.g. pre-heating). Waste heat can also be used in other on-site processes, transformed into electrical energy, integrated into district heating networks or used for provision of industrial steam . An alternative option is to sell the waste heat to

energy supply companies, which can transform it into electricity using the appropriate technological process (e.g. Organic Rankine Cycle).

Utilisation of the waste heat is mainly dependent on its quality, i.e. temperature of the waste heat streams. Historically, there was a common belief that the utilisation of waste heat is only (economically) suitable for waste heat streams of moderate temperatures (e.g. more than 500°C) . With the availability of new technological options, valorisation of waste heat streams of lower temperatures is possible (e.g. industrial heat pumps, Organic Rankine Cycle, etc.).

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HEAT TO ELECTRICITY TECHNIQUES

Organic Rankine Cycle (ORC)Supercritical CO2 power cycle (sCO2)Combined cycleSteam turbineKalina cycleThermoelectric generator (TEG)Thermoacoustic heat engineTrilateral flash cycle (TFC)Cooling towerThermocompressor

HEAT TO ELECTRICITY

TECHNIQUES

The organic Rankine cycle (ORC) is a thermodynamic cycle, similar to a Rankine cycle, except that the ORC uses organic (carbon-based) compounds as the working fluid in place of water. The organic fluid used has a higher molecular mass than water, and unlike water, it will not erode the metal components and can be beneficial due to the lower temperatures needed to vaporise the working fluid.At the beginning of the cycle, the working fluid is in a lower temperature and pressure state (liquid). The working fluid passes through a pump, increasing its pressure, towards the evaporator, where the working fluid is converted to a high-pressure vapour, which is used to drive a turbine. Once it is through the turbine, the vapour is sent first through a recuperator, or directly to a condenser in order to return it to the starting low-temperature, low-pressure state (liquid). This completes the circuit. The heat for the evaporator can be provided by a number of sources.

Figure 1 Organic Rankine cycle 5

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Technology 1: Organic Rankine Cycle (ORC)

ApplicabilityORC utilises the low-temperature waste heat originating from biomass, biogas, sewage gas, exhaust gas of gas turbines, waste heat of industrial processes (such as glass and cement industry) and process steam.

Project/product referenceTurboden

MaturityCommercial.

The supercritical CO2 power cycle uses CO2 as the working fluid. Throughout the cycle, the CO2 is kept at supercritical conditions, which reduces the system’s complexity, as the entire cycle takes place in a single phase (no phase changes). Despite only small changes in temperature and pressure there are drastic density changes, allowing for large energy extractions. The main challenges of supercritical CO2 development require the identification of the best materials that can handle the elevated temperatures and pressures, manufacturing turbo machinery, valves, seals, and costs.

Figure 2 sCO2 power cycle 7

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Technology 2: Supercritical CO2 power cycle

ApplicabilityValorisation of low-temperature waste heat through the generation of electrical energy.

Project/product referenceNetPower is building power plant using sCO2 cycle

MaturityFirst demonstration power plant is under development.

Figure 3 Combined cycle

ApplicabilityValorisation of the heat from gas turbine exhaust by the generation of electrical energy.

Project/product referenceEchogen waste heat to power applications

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Power plants that use both a gas and a steam turbine together. Waste heat from the gas turbine is routed to a heat recovery steam generator (HRSG), which creates steam from the gas turbine exhaust heat and delivers it to the steam turbine, which generates extra power.

MaturityCommercial.

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Technology 3: Combined cycle

Steam turbines use water that has been pumped to a high pressure, which is then heated to become steam. Extraction of thermal energy from pressurised steam for use in performing mechanical work on a rotating output shaft. Steam turbines are widely used in electrical power plants and in processes that are using mechanical power, generated from a steam. 10

Figure 4 Steam turbine

ApplicabilityThe extraction of mechanical energy from steam. It is applicable if high-pressure and high-temperature (high enthalpy) waste stream is available.

Project/product referenceSiemens steam turbines

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MaturityCommercial.

Technology 4: Steam turbine

ApplicabilityUsed to recover the waste heat of lower temperatures; is widely used in geothermal stations and waste heat recovery units.

Project/product referenceGlobal Geothermal Ltd Kalina cycle (iron and steel industry)

MaturityCommercial.

Figure 5 Kalina cycle 13

The Kalina cycle is a process of converting thermal energy to mechanical power. It uses a mixture of two fluids as the working fluid, most commonly ammonia and water. Using an alternative working fluid can improve the system’s thermodynamic efficiency, and additionally, increase the adaptability for the operating conditions. The heat addition and heat rejection happen at varying temperatures even during phase change, as the fluid is a mixture. The Kalina cycle can easily match to any source (heat addition) and sink (heat rejection) condition by varying the mixture concentration in the cycle. 12

Technology 5: Kalina cycle

ApplicabilityTEGs are used to convert waste heat into additional electrical energy.

Project/product referenceAlphabet Energy’s E1 thermoelectric generator

MaturityCommercial.

A thermoelectric generator is a solid-state device that converts heat (temperature differences) directly into electrical energy through a phenomenon called the Seebeck’s effect (a form of thermoelectric effect). 14

Figure 6 Thermoelectric generator 15

Technology 6: Thermoelectric generator (TEG)

ApplicabilityCould be used to convert waste heat into electrical energy.

Project/product referenceAster Thermoacoustics

MaturityEmergent.

Figure 7 Thermoacoustic heat engine 16

Thermoacoustic heat engines, without the use of moving parts, convert heat into sound. This acoustic power can then be used for a number of purposes, including cooling applications, gas mixture separation, and with the addition of an electroacoustic transformer, converted into electricity. Depending on the application heat with temperatures between 120°C and 900°C can be used. The heat sources available vary, from radioactive isotopes and fuel combustion, to solar energy and waste heat. 16

Technology 7: Thermoacoustic heat engine

ApplicabilityTFCs could be used to utilise low temperature waste heat through the generation of electrical energy.

Project/product referencePilot demonstration of TFC

MaturityPilot demonstrations.

A trilateral flash cycle is a thermodynamic power cycle whose expansion starts from a saturated liquid rather than a vapour phase. By avoiding boiling, the heat transfer from a heat source to a liquid working fluid is achieved with almost perfect temperature matching. Irreversibilities are thereby minimised. Potential power recovery of TFC could be 14 - 85% more than from ORC or flash steam systems. 17

Figure 8 Trilateral flash cycle 17

Technology 8: Trilateral flash cycle (TFC)

ApplicabilityWidely used to reject (waste) heat, especially in the power generation sector.

Project/product referenceReuse of alternative water sources for cooling tower systems - case study

MaturityCommercial.

Cooling towers are heat rejection devices, which reject waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of closed-circuit dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature. 18

Figure 9 Cooling tower 19

Technology 9: Cooling tower

ApplicabilityFor the utilisation of low-pressure waste heat streams.

Project/product referenceExhaust steam from evaporator in a fruit juice concentrator plant - case example

MaturityCommercial.

Thermocompressors use high-pressure steam to entrain a low-pressure steam, which, after passing through a venturi, is released as a medium-pressure steam. Thermocompressors can be relatively simple in construction and they provide a function for low-pressure steam. 20

Figure 10 Thermocompressor 20

Technology 10: Thermocompressor

REFERENCESC. J. Roos, “An Overview of Industrial Waste Heat Recovery Technologies for Moderate Temperatures Less Than 1000ºF,” U.S. Department of Energy, 2013.

“Roadmap towards a low-carbon economy in 2050,” CGP Energy & Innovation workgroup.

“Organic Rankine Cycles” [Online].

“Organic Rankine Cycles” [Online].

S. Quoilina, M. Van Den Broek, S. Declaye, P. Dewallef, V. Lemort (2013) Techno-economic survey of Organic Rankine Cycle (ORC) systems. Renewable and Sustainable Energy Reviews. 22: 168-186.

Q. Zhu (2017) Innovative power generation systems using supercritical CO2 cycles. Clean Energy. 1 (1): 68-79.

“Supercritical CO2 Tech Team,” [Online].

“Combined cycle power plant – how it works,” [Online].

“Gas Turbine Working Principle,” [Online].

“Steam Turbine,” [Online].

“Steam Turbine/Generator,” [Online].

X. Zhang, M. He, Y. Zhang (2012) A review of research on the Kalina cycle. Renewable and Sustainable Energy Reviews. 16: 5309-5318.

“Heat transfer research and development,” [Online].

“Thermoelectric power generator,” [Online].

“Thermoelectric energy generation,” [Online].

M. I. Konstantin, “Miniature thermoacoustic engine” [Online].

I. K. Smith, N. Stosic, A. Kovacevic (2005) An Improved System for Power Recovery from Higher Enthalpy Liquid-Dominated Fields. Proceedings World Geothermal Congress 2005, Antalya, Turkey

“Cooling tower fundamentals,” [Online].

S.K. Tyagi, A.K. Pandey, P.C. Pant, V.V. Tyagi (2012) Formation, potential and abatement of plume from wet cooling towers: A review. Renewable and Sustainable Energy Reviews. 16: 3409-3429.

“Waste heat recovery,” [Online].

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Date January 2019Authors

Interested in this work?Please contact us at info@project-epos.eu

www.spire2030.eu/epos @projectepos

CONTACT

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 679386. This work was supported by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 15.0217. The opinions expressed and arguments employed herein do not necessarily reflect the official views of the Swiss Government.

CREDITS

Podbregar G.; Strmčnik B., Dodig V., Lagler B., Žertek A., Haddad C., Gélix F., Cacho J., Teixiera G., Borrut D., Taupin B., Maqbool A. S., Zwaenepoel B., Kantor I., Robineau J., all names in correct order (2017), G. Van Eetvelde and F. Maréchal and B.J. De Baets (Eds.) Technology market screen. Longlist of technical, engineering, service and management solutions for Industrial Symbiosis.

Design CimArk

This report is © EPOS. Reproduction is authorised provided the source (EPOS Technology Focus) is acknowledged.

All the EPOS TECHNOLOGY FOCUS Acts could be found on www.spire2030.eu/epos (Section Outcomes/Publications)