View Online / Journal Homepage Energy & Environmental Science Accepted Manuscript Volume 3 Volume | Number 12 | 2010 This is an Accepted Manuscript, which has been through the RSC Publishing peer Energy& review process and has been accepted for publication. To our referees: Environmental Science Accepted Manuscripts are published online shortly after acceptance, which is prior www.rsc.org/ees Volume 3 | Number 12 | December 2010 | Pages 1813–2020 Energy & Environmental Science Science Energy & Environmental to technical editing, formatting and proof reading. This free service from RSC Dank u wel kiitos takk fyrir Publishing allows authors to make their results available to the community, in Downloaded by Carnegie Mellon University on 12 July 2012 aitäh děkuji D’akujem Благодаря citable form, before publication of the edited article. 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In no event shall the RSC be held responsible for any errors or omissions in these Accepted Manuscript manuscripts or any consequences arising from the use of any information contained in them. www.rsc.org/ees Registered Charity Number 207890 Page 1 of 13Energy & EnvironmentalEnergy & Environmental Science Dynamic Article Links ► Science View Online Cite this: DOI: 10.1039/c0xx00000x Article www.rsc.org/xxxxxx Molten catalytic coal gasification with in situ carbon and sulphur capture Nicholas Siefert,a Dushyant Shekhawat b Shawn Litster c and David Berry b Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x 5 A molten catalytic process has been demonstrated for converting coal into a synthesis gas consisting of roughly 20% methane and 80% hydrogen using alkali hydroxides as both catalysts and in situ CO 2 capture agents. Baselines studies were also conducted using no catalyst, weak capture agents (CaSiO 3) and strong in situ capture agent for acid gases (CaO). While a similar gas composition can be achieved using CaO rather than alkali hydroxides, the rate of syngas production is greater when using molten alkali hydroxides than when using CaO as the in situ capture agent for acid gases, such as HCl, H 2S and CO 2. Parametric studies were conducted to understand the effects of temperature, pressure, catalyst composition, steam flow rate and the ratio of coal to 10 alkali hydroxide on the performance of the molten catalytic gasifier in terms of kinetics and syngas composition. To measure the amount and the rate of coal conversion, we have developed a method for quantifying the coal conversion as the reduction charge remaining, which is related to the chemical oxygen demand remaining in the coal. At temperatures between 800 oC and 900 oC, we measured first-order steam-coal gasification rates using sub- -1 bituminous coal of 2 hr in a fixed bed reactor while capturing significant quantities of both H 2S and CO 2, and while also generating 20% methane plus ethane in the syngas on a dry volume basis. 15 Broadened Perspective Gasification of solid fuels with in situ capture of carbon dioxide, hydrogen sulphide, and hydrogen chloride provides a simple means of converting coal or municipal solid waste into a gaseous fuel that is capable of being oxidized to generate electricity such that it c an meet current and possible future regulations regarding both acid and greenhouse gas emissions. The gaseous fuel can be converted into synthetic natural gas (SNG ). It can also be sent to Downloaded by Carnegie Mellon University on 12 July 2012 either the combustor of a gas turbine or to the anode of a high temperature fuel cell. Recent system studies 1-3 indicate that the system efficiencies of Published on 02 July 2012 http://pubs.rsc.org | doi:10.1039/C2EE21989A advanced fuel cell power plants can approach 60% while capturing >95% carbon dioxide, minimizing water consumption, and lowering the cost of electricity compared to pulverized coal combustion with carbon capture and sequestration (PCC-CCS) and integrated gasification combined cycl e with CCS (IGCC-CCS) power plants. One of the keys to achieving this target is the production of a high methane synthesis gas (>20% dry vol. basis) in a coal gasifier that consumes little to no oxygen. This gasifier can operate without oxygen because the endothermic steam gasification reactions can be offset by the exothermic carbon dioxide capture and methanation reactions. Operating without oxygen enhances the cold gas efficiency of the gasifier and also reduces the cooling load within the solid oxide fu el cell. By accomplishing what normally requires multiple distinct reactors and by eliminating the need for pure oxygen, a molten catalytic coal or waste gasifier with in situ carbon and sulphur capture has the potential to lower the cost of generating electricity and SNG while producing minimal to near zero emissions of acid and greenhouse gases. an economically viable manner and building power plants that 1. Introduction co-generate fuels/chemicals during times of low electricity demand are pressing goals for research in the energy industry. It Over the last decade, coal-fired power plants have generated appears that one of the ways to achieve both of these goals in an approximately 40% of total electricity across the globe.4 In the 30 economically viable power plant is through the use of a catalytic 20 United States, coal power plants supply approximately 40-50% of gasifier that turns coal or waste into a methane-rich syngas. The Science Energy&Environmental AcceptedManuscript the demand for electricity 5 and municipal solid waste power 6 methane-rich syngas then could be converted into pipeline quality plants supply approximately 0.3% of electricity demand. Current natural gas, could be combusted on site in a gas turbine, or could pulverized coal power plants generate acid gases (NO , SO , and x x directly generate electricity within a solid oxide fuel cell. In the weakly CO 2), greenhouse gases (CO 2), and entrained particulates. 35 fuel cell case, several research groups have shown that one can 25 Reducing the pollution emitted by coal and waste power plants in This journal is © The Royal Society of Chemistry 2012 Energy & Environmental Science , [year], [vol] , 00–00 | 1 Energy & Environmental Science Page 2 of 13 View Online achieve overall system efficiencies near or above 60% on a gasification catalyst is calcium oxide. Calcium oxide acts as both 1-3 higher heating value basis. Methane in the syngas is crucial to 60 a gasification catalyst and as a capture agent for acid gases, such achieving high system efficiency because internal reforming of as H 2S and CO 2. Gasification processes using lime include the the methane into hydrogen can reduce the parasitic loading that CaO acceptor process by Consol Energy,19 which is similar to 5 would be required to maintain the temperature of the solid oxide chemical looping fluidized bed gasifiers such as the HyPr- fuel cell.7, 8 RING.20 One advantage of calcium oxide as a catalyst is that it Conventional entrained flow gasifiers, such as Shell-Texaco 65 remains in the solid phase and does not strongly interact with gasifier, operate around 1400 oC, produce little methane and are ceramic or steel walls of the gasifier. Though, the fact that lime virtually free of any other hydrocarbons.9 From an equilibrium and limestone are solids at typical gasifier temperatures is part of 10 thermodynamics point of view, the temperature of the gasifier the reason that they are not as good catalysts as alkali catalysts. must be lowered in order to increase the composition of methane To achieve similar rates of reaction, often transition metal in the syngas. However, in order to maintain sufficient kinetics at 70 catalysts are used in combination with calcium oxide in order to these reduced temperatures, and hence to minimize gasifier costs, achieve required reaction rates.21 a catalyst is required.10 Potassium carbonate, hydroxide, and One way of achieving fast kinetics is to operate with a molten 15 sulphide were found to catalyze both the steam-carbon reaction bed of catalysts, such as molten alkali carbonates or hydroxides, (C+H 2O ↔ CO+H 2) and the methanation reaction (CO + 3H 2 ↔ which provide for high mass and heat transfer. Previous research 11-13 CH 4 + H 2O). The following are the main gasification 75 into molten bed gasification includes research by Kellogg and reactions and capture reactions inside of gasifier when the Rockwell International 22-25 in the 1970s as well as recent research catalyst is alkali hydroxides, calcium carbonate, or calcium by Tokyo Institute and Nagoya University.26, 27 At the time that 20 silicate. Also included are the changes in the Gibbs free energy most of the original research on catalytic gasification was between reactants and products for each reaction at 1000K.