Chemical looping combustion

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Fig 1. Diagram of CLC reactor system CLC basic concept1.png
Fig 1. Diagram of CLC reactor system
Fig 2. (Left) Dual fluidized bed design, the Darmstadt chemical looping combustion pilot plant and (Right) interconnected moving bed-fluidized bed design, the Ohio State University Coal Direct Chemical Looping pilot plant CLC examples.jpg
Fig 2. (Left) Dual fluidized bed design, the Darmstadt chemical looping combustion pilot plant and (Right) interconnected moving bed-fluidized bed design, the Ohio State University Coal Direct Chemical Looping pilot plant

Chemical looping combustion (CLC) is a technological process typically employing a dual fluidized bed system. CLC operated with an interconnected moving bed with a fluidized bed system, has also been employed as a technology process. In CLC, a metal oxide is employed as a bed material providing the oxygen for combustion in the fuel reactor. The reduced metal is then transferred to the second bed (air reactor) and re-oxidized before being reintroduced back to the fuel reactor completing the loop. Fig 1 shows a simplified diagram of the CLC process. Fig 2 shows an example of a dual fluidized bed circulating reactor system and a moving bed-fluidized bed circulating reactor system.

Contents

Isolation of the fuel from air simplifies the number of chemical reactions in combustion. Employing oxygen without nitrogen and the trace gases found in air eliminates the primary source for the formation of nitrogen oxide (NOx), produces a flue gas composed primarily of carbon dioxide and water vapor; other trace pollutants depend on the fuel selected.

Description

Chemical looping combustion (CLC) uses two or more reactions to perform the oxidation of hydrocarbon-based fuels. In its simplest form, an oxygen-carrying species (normally a metal) is first oxidized in the air forming an oxide. This oxide is then reduced using a hydrocarbon as a reducer in a second reaction. As an example, an iron based system burning pure carbon would involve the two redox reactions:

C(s) + Fe
2O
3(s) → Fe
3O
4(s) + CO
2(g)

 

 

 

 

(1)

Fe
3O
4(s) + O2(g) → Fe
2O
3(s)

 

 

 

 

(2)

If ( 1 ) and ( 2 ) are added together, the reaction set reduces to straight carbon oxidation i.e.:

C(s) + O
2(g) → CO2(g)

 

 

 

 

(3)

CLC was first studied as a way to produce CO2 from fossil fuels, using two interconnected fluidized beds. [3] Later it was proposed as a system for increasing power station efficiency. [4] The gain in efficiency is possible due to the enhanced reversibility of the two redox reactions; in traditional single stage combustion, the release of a fuel's energy occurs in a highly irreversible manner - departing considerably from equilibrium. In CLC, if an appropriate oxygen carrier is chosen, both redox reactions can be made to occur almost reversibly and at relatively low temperatures. Theoretically, this allows a power station using CLC to approach the ideal work output for an internal combustion engine without exposing components to excessive working temperatures.

Thermodynamics

Fig 3. Sankey diagram of energy fluxes in a reversible CLC system. CLC MCG.png
Fig 3. Sankey diagram of energy fluxes in a reversible CLC system.

Fig 3 illustrates the energy exchanges in a CLC system graphically and shows a Sankey diagram of the energy fluxes occurring in a reversible CLC based engine. Studying Fig 1, a heat engine is arranged to receive heat at high temperatures from the exothermic oxidation reaction. After converting part of this energy to work, the heat engine rejects the remaining energy as heat. Almost all of this heat rejection can be absorbed by the endothermic reduction reaction occurring in the reducer. This arrangement requires the redox reactions to be exothermic and endothermic respectively, but this is normally the case for most metals. [5] Some additional heat exchange with the environment is required to satisfy the second law; theoretically, for a reversible process, the heat exchange is related to the standard state entropy change, ΔSo, of the primary hydrocarbon oxidation reaction as follows:

Qo = ToΔSo

However, for most hydrocarbons, ΔSo is a small value and, as a result, an engine of high overall efficiency is theoretically possible. [6]

CO2 capture

Although proposed as a means of increasing efficiency, in recent years, interest has been shown in CLC as a carbon capture technique. [7] [8] Carbon capture is facilitated by CLC because the two redox reactions generate two intrinsically separated flue gas streams: a stream from the air reactor, consisting of atmospheric N
2 and residual O
2, but sensibly free of CO2; and a stream from the fuel reactor predominately containing CO2 and H
2O with very little diluent nitrogen. The air reactor flue gas can be discharged to the atmosphere causing minimal CO2 pollution. The reducer exit gas contains almost all of the CO2 generated by the system and CLC therefore can be said to exhibit 'inherent carbon capture', as water vapor can easily be removed from the second flue gas via condensation, leading to a stream of almost pure CO2. This gives CLC clear benefits when compared with competing carbon capture technologies, as the latter generally involve a significant energy penalty associated with either post combustion scrubbing systems or the work input required for air separation plants. This has led to CLC being proposed as an energy efficient carbon capture technology, [9] [10] able to capture nearly all of the CO2, for example, from a Coal Direct Chemical Looping (CDCL) plant. [11] [12] A continuous 200-hour demonstration results of a 25 kWth CDCL sub-pilot unit indicated nearly 100% coal conversion to CO2 with no carbon carryover to the air reactor. [13] [14]

Technology development

First operation of chemical-looping combustion with gaseous fuels was demonstrated in 2003, [15] and later with solid fuels in 2006. [16] Total operational experience in 34 pilots of 0.3 to 3 MW is more than 9000 h. [17] [18] [19] Oxygen carrier materials used in operation include monometallic oxides of nickel, copper, manganese and iron, as well as various combined oxides including manganese oxides.combined with calcium, iron and silica. Also natural ores have been in use, especially for solid fuels, including iron ores, manganese ores and ilmenite.

Cost and energy penalty

A detailed technology assessment of chemical-looping combustion of solid fuel, i.e. coal, for a 1000 MWth power plant shows that the added CLC reactor costs as compared to a normal circulating fluidized bed boiler are small, because of the similarities of the technologies. Major costs are instead CO2 compression, needed in all CO2 capture technologies, and oxygen production. Molecular oxygen production may also be needed in certain CLC configuration for polishing the product gas from the fuel reactor. In all the added costs were estimated to 20 €/tonne of CO2 whereas the energy penalty was 4%. [20]

A variant of CLC is Chemical-Looping Combustion with Oxygen Uncoupling (CLOU) where an oxygen carrier is used that releases gas-phase oxygen in the fuel reactor, e.g. CuO/Cu
2O. [21] This is helpful for achieving high gas conversion, and especially when using solid fuels, where slow steam gasification of char can be avoided. CLOU operation with solid fuels shows high performance [22] [23]

Chemical Looping can also be used to produce hydrogen in Chemical-Looping Reforming (CLR) processes. [24] [25] In one configuration of the CLR process, hydrogen is produced from coal and/or natural gas using a moving bed fuel reactor integrated with a steam reactor and a fluidized bed air reactor. This configuration of CLR can produce greater than 99% purity H2 without the need for CO2 separation. [19] [26]

Comprehensive overviews of the field are given in recent reviews on chemical looping technologies. [7] [27] [28]

In summary, CLC can achieve both an increase in power station efficiency simultaneously with low energy penalty carbon capture. Challenges with CLC include the operation of dual fluidized bed (maintaining carrier fluidization while avoiding crushing and attrition [29] ), and maintaining carrier stability over many cycles.

See also

Related Research Articles

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<span class="mw-page-title-main">Pyrolysis</span> Thermal decomposition of materials at elevated temperatures in an inert atmosphere

The pyrolysis process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. The word is coined from the Greek-derived elements pyro "fire", "heat", "fever" and lysis "separating".

<span class="mw-page-title-main">Gasification</span> Form of energy conversion

Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.

<span class="mw-page-title-main">Fluidized bed combustion</span> Technology used to burn solid fuels

Fluidized bed combustion (FBC) is a combustion technology used to burn solid fuels.

<span class="mw-page-title-main">Fluidization</span> Conversion of a granular material from a solid-like to liquid-like state

Fluidization is a process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid is passed up through the granular material.

<span class="mw-page-title-main">Sabatier reaction</span> Methanation process of carbon dioxide with hydrogen

The Sabatier reaction or Sabatier process produces methane and water from a reaction of hydrogen with carbon dioxide at elevated temperatures and pressures in the presence of a nickel catalyst. It was discovered by the French chemists Paul Sabatier and Jean-Baptiste Senderens in 1897. Optionally, ruthenium on alumina makes a more efficient catalyst. It is described by the following exothermic reaction:

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<span class="mw-page-title-main">Supercritical carbon dioxide</span> Carbon dioxide above its critical point

Supercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.

<span class="mw-page-title-main">Carbon capture and storage</span> Collecting carbon dioxide from industrial emissions

Carbon capture and storage (CCS) is a process in which a relatively pure stream of carbon dioxide (CO2) from industrial sources is separated, treated and transported to a long-term storage location. For example, the carbon dioxide stream that is to be captured can result from burning fossil fuels or biomass. Usually the CO2 is captured from large point sources, such as a chemical plant or biomass plant, and then stored in an underground geological formation. The aim is to reduce greenhouse gas emissions and thus mitigate climate change. The IPCC's most recent report on mitigating climate change describes CCS retrofits for existing power plants as one of the ways to limit emissions from the electricity sector and meet Paris Agreement goals.

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<span class="mw-page-title-main">Oxy-fuel combustion process</span> Burning of fuel with pure oxygen

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<span class="mw-page-title-main">Carbon dioxide scrubber</span> Device which absorbs carbon dioxide from circulated gas

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The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but a few.

Hydromethanation, [hahy-droh- meth-uh-ney-shuhn] is the process by which methane is produced through the combination of steam, carbonaceous solids and a catalyst in a fluidized bed reactor. The process, developed over the past 60 years by multiple research groups, enables the highly efficient conversion of coal, petroleum coke and biomass into clean, pipeline quality methane.

The circulating fluidized bed (CFB) is a type of Fluidized bed combustion that utilizes a recirculating loop for even greater efficiency of combustion. while achieving lower emission of pollutants. Reports suggest that up to 95% of pollutants can be absorbed before being emitted into the atmosphere. The technology is limited in scale however, due to its extensive use of limestone, and the fact that it produces waste byproducts.

Calcium looping (CaL), or the regenerative calcium cycle (RCC), is a second-generation carbon capture technology. It is the most developed form of carbonate looping, where a metal (M) is reversibly reacted between its carbonate form (MCO3) and its oxide form (MO) to separate carbon dioxide from other gases coming from either power generation or an industrial plant. In the calcium looping process, the two species are calcium carbonate (CaCO3) and calcium oxide (CaO). The captured carbon dioxide can then be transported to a storage site, used in enhanced oil recovery or used as a chemical feedstock. Calcium oxide is often referred to as the sorbent.

Chemical looping reforming (CLR) and gasification (CLG) are the operations that involve the use of gaseous carbonaceous feedstock and solid carbonaceous feedstock, respectively, in their conversion to syngas in the chemical looping scheme. The typical gaseous carbonaceous feedstocks used are natural gas and reducing tail gas, while the typical solid carbonaceous feedstocks used are coal and biomass. The feedstocks are partially oxidized to generate syngas using metal oxide oxygen carriers as the oxidant. The reduced metal oxide is then oxidized in the regeneration step using air. The syngas is an important intermediate for generation of such diverse products as electricity, chemicals, hydrogen, and liquid fuels.

Sorption enhanced water gas shift (SEWGS) is a technology that combines a pre-combustion carbon capture process with the water gas shift reaction (WGS) in order to produce a hydrogen rich stream from the syngas fed to the SEWGS reactor.

References

  1. ↑ Ströhle, Jochen; Orth, Matthias; Epple, Bernd (January 2014). "Design and operation of a 1MWth chemical looping plant". Applied Energy. 113: 1490–1495. doi:10.1016/j.apenergy.2013.09.008. ISSN   0306-2619.
  2. ↑ Liang-Shih, Fan. Chemical looping partial oxidation : gasification, reforming, and chemical syntheses. Cambridge. ISBN   9781108157841. OCLC   1011516037.
  3. ↑ Lewis, W., Gilliland, E. and Sweeney, M. (1951). "Gasification of carbon". Chemical Engineering Progress. 47: 251–256.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ↑ Richter, H.J.; Knoche, K.F. (1983). "Reversibility of combustion processes, in Efficiency and Costing – Second law analysis of processes". ACS symposium series (235): 71–85.{{cite journal}}: Cite journal requires |journal= (help)
  5. ↑ Jerndal, E., Mattisson, T. and Lyngfelt, A. (2006). "Thermal analysis of chemical-looping combustion". Chemical Engineering Research and Design. 84 (9): 795–806. doi:10.1205/cherd05020.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ↑ McGlashan, N.R. (2008). "Chemical looping combustion – a thermodynamic study". Proc. Inst. Mech. Eng. C. 222 (6): 1005–1019. CiteSeerX   10.1.1.482.5166 . doi:10.1243/09544062JMES790. S2CID   14865943.
  7. 1 2 Liang-Shih., Fan (2010). Chemical looping systems for fossil energy conversions. Hoboken, NJ: Wiley-AIChE. ISBN   9780470872888. OCLC   663464865.
  8. ↑ Fan, Liang-Shih; Zeng, Liang; Wang, William; Luo, Siwei (2012). "Chemical looping processes for CO2 capture and carbonaceous fuel conversion – prospect and opportunity". Energy & Environmental Science. 5 (6): 7254. doi:10.1039/c2ee03198a. ISSN   1754-5692.
  9. ↑ Ishida, M.; Jin, H. (1997). "CO2 Recovery in a power plant with chemical looping combustion". Energy Conv. MGMT. 38: S187–S192. doi:10.1016/S0196-8904(96)00267-1.
  10. ↑ Brandvoll, Ø.; Bolland, O. (2004). "Inherent CO2 Capture Using Chemical Looping Combustion in a Natural Gas Fired Power Cycle". Journal of Engineering for Gas Turbines and Power. 126 (2): 316–321. doi:10.1115/1.1615251.
  11. ↑ Gorder, Pam (February 5, 2013). "New Coal Technology Harnesses Energy Without Burning, Nears Pilot-Scale Development". researchnews.osu.edu. Archived from the original on December 21, 2016. Retrieved 2016-11-04.
  12. ↑ Bayham, Samuel; McGiveron, Omar; Tong, Andrew; Chung, Elena; Kathe, Mandar; Wang, Dawei; Zeng, Liang; Fan, Liang-Shih (May 2015). "Parametric and dynamic studies of an iron-based 25-kW th coal direct chemical looping unit using sub-bituminous coal". Applied Energy. 145: 354–363. doi: 10.1016/j.apenergy.2015.02.026 . ISSN   0306-2619.
  13. ↑ Bayham, Samuel C.; Kim, Hyung R.; Wang, Dawei; Tong, Andrew; Zeng, Liang; McGiveron, Omar; Kathe, Mandar V.; Chung, Elena; Wang, William (2013-03-08). "Iron-Based Coal Direct Chemical Looping Combustion Process: 200-h Continuous Operation of a 25-kWth Subpilot Unit". Energy & Fuels. 27 (3): 1347–1356. doi:10.1021/ef400010s. ISSN   0887-0624.
  14. ↑ Chung, Cheng; Pottimurthy, Yaswanth; Xu, Mingyuan; Hsieh, Tien-Lin; Xu, Dikai; Zhang, Yitao; Chen, Yu-Yen; He, Pengfei; Pickarts, Marshall (December 2017). "Fate of sulfur in coal-direct chemical looping systems". Applied Energy. 208: 678–690. doi:10.1016/j.apenergy.2017.09.079. ISSN   0306-2619.
  15. ↑ Lyngfelt, A. (2004). "A New Combustion Technology". Greenhouse Gas Issues. No.73: 2–3.
  16. ↑ Lyngfelt, A. (2007). "Chemical-looping combustion of solid fuels". Greenhouse Gas Issues. No. 85: 9–10.
  17. ↑ Lyngfelt, A. (2011). "Oxygen carriers for chemical-looping combustion - 4000 h of operational experience". Oil & Gas Science and Technology. 66 (2): 161–172. doi: 10.2516/ogst/2010038 .
  18. ↑ Lyngfelt, A; Linderholm, C. "Chemical-Looping Combustion of Solid Fuels – status and recent progress". 13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, 14–18 November 2016, Lausanne, Switzerland.
  19. 1 2 Tong, Andrew; Bayham, Samuel; Kathe, Mandar V.; Zeng, Liang; Luo, Siwei; Fan, Liang-Shih (January 2014). "Iron-based syngas chemical looping process and coal-direct chemical looping process development at Ohio State University". Applied Energy. 113: 1836–1845. doi:10.1016/j.apenergy.2013.05.024. ISSN   0306-2619.
  20. ↑ Lyngfelt, Anders; Leckner, Bo (2015-11-01). "A 1000 MWth boiler for chemical-looping combustion of solid fuels – Discussion of design and costs". Applied Energy. 157: 475–487. doi: 10.1016/j.apenergy.2015.04.057 .
  21. ↑ Mattisson, T., Lyngfelt, A. and Leion, H. (2009). "Chemical-Looping with Oxygen Uncoupling for Combustion of Solid Fuels". International Journal of Greenhouse Gas Control. 3: 11–19. doi:10.1016/j.ijggc.2008.06.002.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  22. ↑ Abad, A., Adánez-Rubio, I. Gayán, P. García-Labiano, F. de Diego L. F. and Adánez, J. (2012). "Demonstration of chemical-looping with oxygen uncoupling (CLOU) process in a 1.5kW th continuously operating unit using a Cu-based oxygen-carrier". International Journal of Greenhouse Gas Control. 6: 189–200. doi:10.1016/j.ijggc.2011.10.016. hdl: 10261/75134 .{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ↑ Zhou, Zhiquan; Han, Lu; Nordness, Oscar; Bollas, George M. (2015-05-01). "Continuous regime of chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) reactivity of CuO oxygen carriers". Applied Catalysis B: Environmental. 166–167: 132–144. doi:10.1016/j.apcatb.2014.10.067.
  24. ↑ Rydén, M.; Lyngfelt, A. (2006). "Using steam reforming to produce hydrogen with carbon dioxide capture by chemical-looping combustion". Journal of Hydrogen Energy. 31 (10): 1631–1641. doi:10.1016/j.ijhydene.2005.12.003.
  25. ↑ Rydén, M.; Lyngfelt, A. & Mattisson, T. (2006). "Synthesis gas generation by chemical-looping reforming in a continuously operating laboratory reactor". Fuel. 85 (12–13): 1631–1641. doi:10.1016/j.fuel.2006.02.004.
  26. ↑ Tong, Andrew; Sridhar, Deepak; Sun, Zhenchao; Kim, Hyung R.; Zeng, Liang; Wang, Fei; Wang, Dawei; Kathe, Mandar V.; Luo, Siwei (January 2013). "Continuous high purity hydrogen generation from a syngas chemical looping 25kWth sub-pilot unit with 100% carbon capture". Fuel. 103: 495–505. doi:10.1016/j.fuel.2012.06.088. ISSN   0016-2361.
  27. ↑ Lyngfelt, A. and Mattisson, T. (2011) ”Materials for chemical-looping combustion”, in D. Stolten and V. Scherer, Efficient Carbon Capture for Coal Power Plants, Weinheim, WILEY-VCH Verlag GmbH & Co.. KGaA, 475-504.
  28. ↑ Adánez, J.; Abad, A. Garcia-Labiano; F. Gayan P. & de Diego, L. (2012). "Progress in Chemical-Looping Combustion and Reforming technologies'". Progress in Energy and Combustion Science. 38 (2): 215–282. doi:10.1016/j.pecs.2011.09.001. hdl: 10261/78793 .
  29. ↑ Kim, J.Y., Ellis, N., Lim, C.J. and Grace, J.R. (2019). "Attrition of Binary Mixtures of Solids in a Jet Attrition Unit". Powder Technology. 352: 445–452. doi:10.1016/j.powtec.2019.05.010. S2CID   164585879.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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