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Coal Refining Chemical-Looping Systems with CO2 as a Co-Feedstock for Chemicals Syntheses Mandar Vinod Kathe, Peter Olaf Sandvik, Charles Fryer, Fanhe Kong, Yitao Zhang, Gabrielle Grigonis, and Liang-Shih Fan Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02742 • Publication Date (Web): 26 Dec 2017 Downloaded from http://pubs.acs.org on December 31, 2017
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Energy & Fuels
Coal Refining Chemical-Looping Systems with CO2 as a Co-Feedstock for Chemicals Syntheses Mandar Kathe*, Peter Sandvik*, Charles Fryer, Fanhe Kong, Yitao Zhang, Gabrielle Grigonis, Liang-Shih Fan** Department of Chemical and Biomolecular Engineering The Ohio State University Columbus, Ohio 43210 U.S.A.
*Co-first author **To whom the correspondence should be addressed
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Abstract This study quantifies the advantages of a chemical looping reducer reactor modularization strategy that leverages two or more reducer reactors operating in parallel to enhance syngas production beyond what is achievable by a single reducer reactor or conventional processes. The modularized system incorporates CO2 capture and utilization as a feedstock in an iron-titanium composite metal oxide based chemical looping system to enhance coal based chemical production. Simulations conducted in ASPEN Plus software suggest that adopting a cocurrent moving bed reducer reactor based modularization strategy can improve syngas yield by greater than 11% over a single chemical looping reducer reactor. Experiments conducted on a bench scale reducer reactor confirm the findings of the simulations. The modularization simulation was scaled up and incorporated into commercial sized methanol and acetic acid production plants. Chemical looping modularization demonstrates the ability to reduce coal consumption by 25% over a baseline coal gasification process, compared to 15% reduction if a single chemical looping reducer reactor is used instead of the modular strategy, for 10,000 ton per day methanol production. Integration into a commercial scale acetic acid plant shows conditions in which the process can operate as a CO2 neutral or negative system, where the process was consuming more CO2 than it produces. These results indicate the potential for significant feedstock reduction in large-scale coal to chemical processes.
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Energy & Fuels
1. Introduction In 2016, coal was responsible for 29% of the world’s energy demand, continuously making it an important fuel source for industrial production and everyday livelihood1. Despite the declining coal production (-10% in 2016) and consumption (-12 % in 2016) in the United States (US), coal is projected to still play a significant role in catering to the world energy demand in the near future1,2. For example, coal is projected to provide 24% of the world energy demand and 18 % of the US energy demand in 2040.1-4 Coal has nearly twice the proved reserves to production ratio as natural gas and oil making it immediately apparent that, in the future (next 100 years), the elimination or reduction of dependence on coal as a primary energy source is not feasible. The importance of coal has directed energy research investment towards improving energy conversion efficiencies associated with chemical production from coal and research in carbon capture, utilization and sequestration (CCUS). CCUS research aims to reduce the costs associated with CO2 emissions into the atmosphere and offer solutions to the factors deterring CCUS which include high costs of implementation and limitations in sequestration, utilization technology5-9. Novel research approaches in the CCUS field focus on the development of synergistic technologies that combine at least two of the three functions associated with CCUS5,7,10-12. In principle, the concept of reutilizing CO2 is attractive and allows for the development of rational flowsheets based on thermodynamic investigation that can propose to produce products from fossil fuels with minimal, zero or even negative CO2 emissions. Coal gasification to produce syngas, an intermediate in a variety of chemical products, is considered an important component of coal utilization strategies13. Research in reducing costs associated with a coal to chemicals/liquid
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fuels plant has several focus areas including heat integration for coal gasification, gas clean-up and conditioning equipment, improving pollutant control strategies, amongst others13-25. Chemical looping uses lattice oxygen from a metal-oxide oxygen carrier for coal gasification and is considered a potential high efficiency alternative to conventional coal gasification technology26-29. The concept of chemical looping coal gasification has been investigated using metal-oxides based on copper, calcium, iron, nickel, amongst others30-36. Previous research on chemical looping coal gasification has focused on quantifying reactivity with different coal types, performance of different supports for primary metal-oxides, effect of enhancing gasification agents like CO2 or steam and reaction-engineering aspects based on fluidized beds3740
. The OSU system utilizes a co-current moving bed fuel-metal contact pattern coupled with
iron-titanium composite metal oxide that enables precise control of metal-oxide oxidation and high syngas selectivity27-29, 41. This paper initially identifies the thermodynamic behavior of the conventional system and the OSU chemical looping based coal to syngas (CTS) gasification system. A non-linear relationship is observed between the co-injection of CO2 and H2O with coal and its syngas yield and H2:CO molar ratio. A dual-modularization strategy is developed that proposes to leverage the non-linearity of thermodynamic behavior for syngas generation, which approaches the stoichiometric limit. Experimental studies, which validate the thermodynamic simulation of CO2 injection and the advantages associated with the dual modularization strategy, are presented. ASPEN Plus (v8.8) software based simulations are generated to observe the efficiency improvements provided by a dual-modularization strategy and CO2 utilization on a commercial scale for both methanol and acetic acid production.
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Energy & Fuels
2. Thermodynamic Analysis for a Coal Gasification System Coal gasification produces syngas using different hydrodynamic flow patterns of coal, including a moving bed flow, a fluidized bed flow or an entrained bed flow. Entrained bed gasifiers are the most widely used. They operate in a cocurrent contact mode between coal and molecular oxygen13,14. This study uses a specific entrained bed gasifier, the oxygen blown Shell gasifier, as the baseline case as shown in Figure 1a. The baseline oxygen blown gasifier uses a dry fed coal stream that operates at high coal carbon conversion efficiencies (> 98%). A novel alternative to the baseline oxygen blown gasification system is a chemical looping gasification scheme, as shown in Figure 1b. The chemical looping system is comprised of two main reactors, the reducer reactor and the combustor reactor27-29,41. The reducer reacts solid iron-titanium composite metal oxide (ITCMO) particles with coal in a cocurrent moving bed reactor. Operating the reducer in a cocurrent contact mode promotes phase change under greater thermodynamic control for coal partial oxidation. The desired partial oxidation chemistry of coal with ITCMO in the reducer reactor follows Equation (1). CH0.8O0.1668+FeTiyOx→ FeTiyOz + CO + 0.4 H2 (z
