Up-to-date CO2 Capture in Thermal Power Plants - ScienceDirect

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ScienceDirect Energy Procedia 114 (2017) 95 – 103

13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, 14-18 November 2016, Lausanne, Switzerland

Up-to-date CO2 capture in thermal power plants Mohamed Kanniche*, Yann Le Moullec, Olivier Authier, Hayato Hagi, Domitille Bontemps, Thibaut Neveux, Myriam Louis-Louisy EDF R&D, 6 Quai Watier, F-78401 Chatou, France

Abstract An up-to-date review of CO2 capture technologies for coal-fired power plants is presented. This study is based on EDF experience on CO2 capture build through collaborative projects and pilot plants operation follow up. This review focuses mostly on most mature technologies and provides insight on the interest of least developed technology with high potential. Technologies are compared and assessed based on energy performance, maturity and economic criteria. A specific method for assessing uncertainties in this process is proposed. Amine based post-combustion technology remains the best reference for short and medium terms with a tight competition with cryogenic oxy-combustion. Both share the highest maturity and similar energy performance in their most advanced embodiments. At the moment IGGC based capture looks less promising for power generation due to the high cost of the plant even without CO2 capture. Regarding more innovative technology, promising candidates, such as inertial extraction, chemical looping combustion or oxy-fired CO2 cycle, are highlighted but their effective development up to industrial ground is not guaranteed due to the constant improvement of reference technology and their difficulty to be retrofitted. © Published by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license © 2017 2017The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of GHGT-13. Peer-review under responsibility of the organizing committee of GHGT-13. Keywords: post-combustion, oxy-combustion, pre-combustion, chemical looping combustion, technico-economic analysis, cost uncertainties propagation.

*

Corresponding author. Tel.: +33 130877093 Email: [email protected]

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of GHGT-13. doi:10.1016/j.egypro.2017.03.1152

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Mohamed Kanniche et al. / Energy Procedia 114 (2017) 95 – 103

1. Context and objective Power generation represents 40% of global greenhouse gas emissions related to energy (transport, heating and industries) and 78% of emissions from fixed sources. Coal-fired power plants emit more than 75% of CO2 emissions of the power generation sector, i.e. they emit 30% of the anthropogenic CO2. The generated electricity supplies residential houses as well as the tertiary sector or industries. Rapid economic growth of countries such as China and India has led to a substantial global CO2 emissions raise, China having become now the world largest CO2 emitter. While future coal power plants will go into service in China and India and existing power plants will continue to be operated in US, Australia and Europe, reducing global CO2 emissions in the next decades remains an important challenge.. In this context, CO2 capture and geological storage is an interesting technology that could help mitigate the impact of fossil fuel continuous use on global climate change. The aim of this paper is to provide a state-of-the-art analysis of CO2 capture technologies for coal-fired power plants. This report updates the previous synthesis [1] and has been performed within the framework of the EDF R&D project “Toward zero emission power plants”. This review focuses mostly on most mature technologies and provides insight on the interest of least developed technology with high potential.

2. Evaluation method The three main technological pathways: post-combustion using chemical absorption, oxy-combustion with cryogenic air separation and pre-combustion with physical absorption, are studied regarding several evaluation criteria. The most mature processes are particularly assessed, innovative capture processes studied within the project are also evaluated in terms of foreseen performances. The objective is also to provide a synthesis of possible future development for these technologies. 2.1. Criteria definition The following evaluation criteria have been retained to evaluate and compare the capture processes, including quantitative (mostly technical indicators) and qualitative criteria: - Technology Maturity Level (TRL), - Net efficiency loss, i.e. the difference between the power-plant net efficiency with and without CCS, - Levelized cost of avoided CO2 (LCACO2), - Operability, flexibility and risk levels (qualitative), - Market (retrofit and/or new built), - Technology interest, - Technological gap, - Environmental issues. 2.2. Maturity and efficiency loss evaluation Technological maturity and energy performance evaluations are based on technological watch, EDF participation in collaborative projects and the utilization of pilot plants results reported in literature and pilot plants operated by EDF, e.g. Alstom AAP pilot plant in EDF’s Le Havre power plant or Skid ANSU (ANti-SUblimation or frostingdefrosting of CO2, in EDF’s Vitry power plant). Investigated technological options include post-combustion capture processes using amine and ammonia absorption [e.g. 2-10], activated carbon adsorption [e.g. 11-13], solid CO2 deposition [e.g. 14-16]; oxycombustion with cryogenic air-separation [e.g. 17-21], chemical looping combustion [e.g. 22-25]; and pre-combustion with physical absorption [e.g. 26, 27].


Energetic performance evaluation were carried out using Aspen Plus™, a process simulation software, with inhouse development when it was necessary, and checked against literature review. The reference coal-fired power plant is an ultra-supercritical single reheat Hirn steam cycle with steam conditions of 300 bar/600°C/620°C and is further described in a previous communication [28]. 2.3. Economic performance Technical-economic evaluations were carried out through a simplified equipment sizing and a preliminary cost estimation made by an internal EDF economic evaluation tool. In these evaluations, only the CO2 capture unit and compression process equipment are assessed; cost of reference power plants is based on EDF internal feedback on these technologies. Technical-economic calculations are provided for an assumed Nth of a Kind cases build in 2015, at base-load operation, with 90% plant availability and with the capture technologies taken into account among technologies demonstrated at Technology Readiness Level (TRL) 6-7. 2.4. Environmental issues The CO2 capture processes have to be not only acceptable economically but also environmentally and socially. Almost all CO2 capture technologies are facing environmental issues with more or less increased pollutants emissions comparatively to the reference power plant without CO2 capture. Concerning the oxy-combustion technologies, there is a priori no added pollutants comparatively to reference power plant without CO2 capture as these emissions concern nitric oxides (NOX), sulfur oxides (SOx), particulates, volatile organic compounds (VOCs) and heavy metals like mercury. However, the normalization of these emissions when reported as concentration need to be clarified as we don’t have any more the same amount of diluent. The classical dilution with nitrogen of combustion air in reference power plants is replaced by the dilution with recycled CO2 with however relatively lower ratio CO2/O2 than N2/O2 in the combustion air. This lower concentration is necessary to maintain similar flame temperature in the boiler because of the higher heat capacity of CO2 over N2 one. In the nibliography it is not clear whether the NOx and SOx emissions are higher or lower than the reference power plant without CO2 capture. More work is needed to clarify these emissions as well as the emissions of the other pollutants. The same problem as above is encountered in chemical looping technology for which there is almost no dilution as this technology is operating at lower temperatures quite similar to fluidized bed technologies. However, unlike above, for chemical looping technologies, there could be added pollutants in the form of oxygen-carrier metal which could undergo attrition phenomena leading to very fine particles. Concerning post-combustion, even if ash particles emissions are supposed to decrease because of additional flue gas washing by the solvent and water, the process based on amines could lead to gaseous, solid and liquid emissions which are potentially toxic for human being and environment. Three major sources of emissions have been listed from the literature which doesn’t seem quite exhaustive at the moment. The first one is a potential leakage of the solvent and degradation products, the second one is an emission to the atmosphere of amines traces and other degradation products within the treated flue gas, the last one is the waste production in the solvent reclaimer. The most challenging emission issues concern the second risk, i.e. emission in gaseous form. Indeed the treated flue gas can contain amines traces as a gas or an aerosols which could be not trapped by the flue gas water wash downstream the absorption columns. Treated flue gas can also contain some amine degradation products. The emitted amine and degraded amine products may react in the atmosphere according to a complex mechanisms (photolysis, degradation…) leading to additional number of degradation products, like nitrosamines which are highly toxic for health and environment [31], [32], [33]. Indeed a main problem associated with chemical absorption

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using amines is the solvent degradation trough irreversible reactions mainly with CO2 and O2 but also with NOx [34] and SOx [36] leading to the formation of volatile compounds potentially harmful for the environment [37]. Actually, emissions measurements are complex: there is no standard normalization for most of emitted species, the sampling are difficult, reproducibility (comparison inter-laboratories) is not always satisfied, analysis methods exist but these competences are not widely applied in the context of CO2 capture [35]. Concerning the pre-combustion, it faces the same problem as post-combustion depending on the used solvent. However, unlike post-combustion, the treated syngas undergoes further on combustion in the gas turbine. The issues of the combustion of the pollutants added by pre-combustion are not yet studied. 2.5. Comparing processes with several maturities and level of project definition Depending on the technical and project definition level, methods used for cost estimation are associated with a broad variability in accuracy ranges. In early stages of a given project, such as concept screening (prefeasibility), accuracy ranges are low (over 30% error) due to the simplified estimating method, while higher accuracy ranges are expected only in the latter stages of project when detailed informations become available for unit and plant design. Similarly, the estimation accuracy increases with the TRL and the process level of knowledge: new concept, benchscale unit, pilot-plant, first full-scale units, commercial installation, return of experience. These project contingencies (due to the estimation method) and process contingencies (due to the process Technology Maturity Level) directly affect the cost estimation. For instance, an innovative process could appear less expensive than a mature process but its estimated cost could also have a higher uncertainty and there will be some probability that the estimated cost would be higher than a mean value. A methodology is therefore used based on the propagation of project and process contingencies on the cost of CCS. The purpose here is not to favor mature or innovative processes, but to quantify level of confidence in each process evaluation in order to conclude on the potential of each capture technology. The Association for the Advancement of Cost Engineering (AACE) provides 50% level of confidence in accuracy ranges (i.e. the 25th and 75th percentiles) for each cost estimation class [29] as well as for each maturity level [30]. Log-normal distributions are affected for each contingency based on AACE data, and Monte-Carlo simulations are performed in order to obtain a probability density for the estimated cost of each process. Several thousands of simulations are indeed performed using random contingencies from the probability distributions, resulting in a cost distribution instead of a single value.

3. Results Amine based post-combustion –i.e. flue gases treatment downstream the combustion, using chemical absorption– remains the preferred CO2 capture technology for the short and medium terms (2030). The only real competitor, oxy-combustion with cryogenic air separation, shows a higher investment cost and is much less suited for retrofitting. Oxy-combustion therefore seems less likely to be implemented, except that it is complicated to “measure” the negative impact in large inventory of new chemical products (and associated risks) that might have on power utilities acceptance (the oil and gas industry uses amine-based post-combustion technologies for decades). Their TRL is between 6 and 7 with energetic performance in the range of 7.5 - 8%pt loss of efficiency on a state-ofthe-art power plant designed and optimized for CO2 capture. Pre-combustion technologies show lower economic performances. However, these conclusions based on the current paradigm that electricity companies are power plant operators, could be significantly modified if the paradigm would evolve towards electricity companies also as coproducers of chemicals from coal, complementing flexible power generation. For post-combustion, the investment cost is estimated to increase by about 50% relatively to pulverized coal reference power plant without CO2 capture, whereas for oxy-combustion it is estimated to increase by 65%. This difference in investment cost is compensated by the cost of solvent make-up during post-combustion operation. Investment cost of pre-combustion is estimated to be higher by around 90% comparatively to pulverized coal power


plant without CO2 capture but this high increase is almost due to high investment cost of IGCC without CO2 capture. Indeed, the investment cost increase of pre-combustion relatively to IGCC without CO2 capture is around 50%. Fig. 1 presents the economic results for six capture processes. The power plant levelized cost of electricity is presented relatively to pulverized power plant without CO2 capture for each process with its uncertainty. The black dot denotes the median cost, the black line the 50% level of confidence range (i.e. the 25th and 75th percentiles) and the envelope curve represents the probability distribution. Besides chemical looping combustion, all processes are evaluated using the same estimation class (project contingencies) and have the same TRL (process contingencies), hence a similar uncertainty range. For chemical-looping, its lower TRL trends to increase the process contingencies, hence a stretched probability distribution.

Fig. 1. Example of increase in levelized cost of electricity and associated uncertainties for six capture technologies

The very conservative case of post-combustion capture using the “standard” solvent MEA leads to an increased cost of electricity by about 80% due to capture and storage. A more realistic case with an advanced thermal integration and the process demonstrated in the CESAR European project leads to an increased cost of 67%. In this last case, the cost of avoided and stored CO2 is 57 €/t including 37 €/t for capture and 20 €/t for transport and storage. The two oxy-combustion cases, one conservative and one more innovative, do not exhibit significant cost differences. In the innovative case, an increase cost of electricity of 70% is found, leading to an avoided and stored CO2 cost of 59 €/t. The IGCC case seems less promising with an increased cost of electricity of 97% and a cost of avoided CO2 of 71 €/t. Beyond the techno-economic analysis, Tab. technologies from coal.

1 sums up the main comparison criteria for CO2 capture

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Post-comb.

Oxy-comb.

Oxy-comb.

Pre-comb.

Technology

Amine absorption

Ammonia absorption

Activated carbon adsorption

Inertial extraction

Cryogenic

Chemical Looping Combustion

Chemical absorption

6-7

6-7

3-4

3-4

6-7

4-5

7

7-8 %-pths

7-8 %-pths

6-7 %-pths

3-4 %-pths

7-8 %-pths

4-5 %-pths

6-7 %-pths

?

?

Maturity (TRL)

Net efficiency loss Energy performance Economic performance Operability

Flexibility

Risk

Market

Retrofit New built

Retrofit New built

Retrofit New built

Retrofit New built

(Retrofit) New built

New built

New built

Interest

Maturity

Stable and cheap solvent

No emission

No emission Performance Easy to build

Maturity No chemicals

Performance

Maturity Polygeneration possible

Pollutant emission Solvent degradation

Seasonal variation Precipitation

Complex regeneration Solid ageing

CO2 quality

Start-up duration

Complexity O2 carrier solid

Operability Flexibility

Technological gap


Post-comb.

100

Post-comb.

Fig. 2 shows a potential evolution in terms of efficiencies (power plants with capture compared to the reference power plant without capture). The technological improvement at 2030 may validate on demonstration units the ability to reach 42–45%LHV efficiency for future power plants with CO2 capture. Moreover, breakthrough technologies could appear and become more relevant.

Post-comb.

Tab. 1. Synthesis of comparison criteria for capture technologies from coal

Pathway

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However, the development until the demonstration stage of breakthrough technologies will be very hazardous without strong indication of a significant efficiency improvement with respect to incremental technological improvement. Moreover, most of the time, these breakthrough technologies are not fitted for retrofitting existing plants and will be more difficult to deploy. For these two reasons, technologies based on adsorption and first generation calcium looping will, probably, never be deployed.

54

350bar/740°C/760°C

50 350bar/680°C/700°C

LHVnetefficiency(%)

PulverizedcoalwithoutCO2 capture

46

Gasifier withOTM

Calciumlooping GenIII

300bar/600°C/620°C

Cryogenic Intertial 250bar/580°C/580°C

Pressurized oxyͲcombustion

HydrogenCT

42 Activated carbon adsoprtion

Chemical looping combustion

Calcium looping GenI

38 Chilled ammonia

Cryogenic Desublimation

34

30 2004

2008

2012

2016

2020

2024

2028

2032

Fig. 2. Foreseen evolution of performance for mature CO2 capture pathways (plain lines) and for innovative technologies (dash lines)

4. Conclusion A continuing technological watch on the three mature technologies is necessary, on the one hand to validate the analyses done in this study and on the other hand to be able to identify and assess technological (incremental) innovation linked to these technologies components (square-section column, regeneration promoters, hydrogen turbine, diabatic ASU, ceramic membrane ASU, etc.). Moreover, the performances of these mature technologies are well understood and do not seem high enough† for large scale CO2 capture industrial deployment. It is then necessary to be able to identify and assess innovative processes with significantly higher energetic performance target, able to reduce notably the cost of avoided CO2.

†

We do not anticipate for these mature technologies a reduction of the levelized cost of electricity increase with capture-storage below 50% (the cost of geological storage considered still being 20 €/t CO2) – corresponding, at best, to 6%pt of efficiency loss and an advanced ultra-supercritical power plant (740°C/760°C, efficiency of 52%-LHV)

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