Chemical Looping Gasification Process Research Articles

Coal chemical-looping gasification of Ca-based oxygen carriers decorated by CaO

Chemical-looping gasification (CLG) for reacting coal with oxygen carriers to yield syngas is a clean and effective coal gasification technology. In the present investigation, a mechanical mixing-impregnation method was used to prepare a CaSO4–CaO/bentonite (CaSO4–CaO/Ben) compound oxygen carrier with excellent catalytic reactivity and stabilizing ability. An investigation on the reaction performance, cyclability and sulfur release of CaSO4–CaO/Ben was performed in a batch fluidized-bed reactor with steam as the gasification–fluidization medium. The results of this study demonstrate that the CaSO4–CaO/Ben compound oxygen carrier has excellent catalytic reactivity. At 900°C, the carbon conversion rate, cold gas efficiency and syngas content reached 96.84%, 84.28% and 66.98%, respectively. Furthermore, the addition of CaO can inhibit CaSO4 side reactions to improve the stability of the oxygen carrier. The cold gas efficiency, carbon conversion efficiency and syngas content exhibited slight changes during ten redox cycles, which indicates that the CaSO4–CaO/Ben oxygen carrier has excellent reactive stability. SEM images of the oxygen carrier after being recycled in ten redox reactions indicated that the surface of the oxygen carrier became porous, which favored CLG. The coal CLG kinetics could be well explained by an active site extending model, and the synergy of CaSO4 and CaO was verified during the coal CLG process.

Effect of Gasifying Medium on the Coal Chemical Looping Gasification with CaSO4 as Oxygen Carrier

The chemical looping gasification uses an oxygen carrier for solid fuel gasification by supplying insufficient lattice oxygen. The effect of gasifying medium on the coal chemical looping gasification with CaSO4 as oxygen carrier is investigated in this paper. The thermodynamical analysis indicates that the addition of steam and CO2 into the system can reduce the reaction temperature, at which the concentration of syngas reaches its maximum value. Experimental result in thermogravimetric analyzer and a fixed-bed reactor shows that the mixture sample goes through three stages, drying stage, pyrolysis stage and chemical looping gasification stage, with the temperature for three different gaseous media. The peak fitting and isoconversional methods are used to determine the reaction mechanism of the complex reactions in the chemical looping gasification process. It demonstrates that the gasifying medium (steam or CO2) boosts the chemical looping process by reducing the activation energy in the overall reaction and gasification reactions of coal char. However, the mechanism using steam as the gasifying medium differs from that using CO2. With steam as the gasifying medium, parallel reactions occur in the beginning stage, followed by a limiting stage shifting from a kinetic to a diffusion regime. It is opposite to the reaction mechanism with CO2 as the gasifying medium.

Investigation into Syngas Generation from Solid Fuel Using CaSO4-based Chemical Looping Gasification Process

Chemical-looping gasification (CLG) is a novel process for syngas generation from solid fuels, sharing the same basic principles as chemical-looping combustion (CLC). It also uses oxygen carriers (mainly metal oxide and calcium sulfate) to transfer heat and oxygen to the fuel. In this paper, the primary investigation into the CLG process with CaSO4 as oxygen carrier was carried out by thermodynamic analysis and experiments in the tube reactor. Sulfur-contained gas emission was mainly H2S rather than SO2 in the CLG process, showing some different features from the CLC. The mass and heat balance of CLG processes were calculated thermodynamically to determinate the auto-thermal operating conditions with different CaSO4/C and steam/C molar ratios. It was found that the CaSO4/C molar ratio should be higher than 0.2 to reach auto-thermal balance. The effect of temperature on the reactions between oxygen carrier and coal was investigated based on Gibbs free energy minimum method and experimental results. It indicated that high temperature favored the CLG process in the fuel reactor and part of syngas was consumed to compensate for auto-thermal system.

Syngas chemical looping gasification process: Bench‐scale studies and reactor simulations

AbstractThe syngas chemical looping process co‐produces hydrogen and electricity from syngas through the cyclic reduction and regeneration of an iron oxide based oxygen carrier. In this article, the reducer, which reduces the oxygen carrier with syngas, is investigated through thermodynamic analysis, experiments, and ASPEN Plus® simulation. The thermodynamic analysis indicates that the countercurrent moving‐bed reducer offers better gas and solids conversions when compared to the fluidized‐bed reducer. The reducer is continuously operated for 15 h in a bench scale moving‐bed reactor. A syngas conversion in excess of 99.5% and an oxygen carrier conversion of nearly 50% are obtained. An ASPEN Plus® model is developed which simulates the reducer performance. The results of simulation are consistent with those obtained from both the thermodynamic analysis and experiments. Both the experiments and simulation indicate that the proposed SCL reducer concept is feasible. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Utilization of chemical looping strategy in coal gasification processes

Three chemical looping gasification processes, i.e. Syngas Chemical Looping (SCL) process, Coal Direct Chemical Looping (CDCL) process, and Calcium Looping process (CLP), are being developed at the Ohio State University (OSU). These processes utilize simple reaction schemes to convert carbonaceous fuels into products such as hydrogen, electricity, and synthetic fuels through the transformation of a highly reactive, highly recyclable chemical intermediate. In this paper, these novel chemical looping gasification processes are described and their advantages and potential challenges for commercialization are discussed.