(36b) Demonstration of High Temperature and Pressure Gas-Solid Circulating Chemical Looping Reactor Systems for Syngas and Heat Generation – Particle Reaction Analysis and Pilot Scale Test Results

Researchers are developing chemical looping technologies to convert carbonaceous fuels to high value chemicals and/or electricity with minimal CO₂ emission. These processes use a metal oxide or metal sulphate to partially or fully oxidize the fuel source to a desired product while being regenerated with air and/or steam in a separate reactor. The chemical looping redox reaction pathway is capable of high product yields without the need for molecular oxygen and minimizes gas product separation requirements. The Ohio State University (OSU) has advanced the chemical looping concept in the development of 2 pilot-scale demonstration plants for coal combustion with CO₂ capture and gaseous fuel conversion to high purity H₂ as well as multiple sub-pilot test units for syngas generation from biomass, natural gas, and coal. In each of these processes, a moving bed reducer reactor is used for partial or full conversion of the carbonaceous fuels to CO/H₂ and CO2/H₂O, respectively. A fluidized bed combustor reactor is used to regenerate the oxygen carriers to their original oxidation state. Interconnecting nonmechanical valves between reactors are used to control the solids circulation rate of the system for the mass balance of the redox reaction and heat balance for the system integration. The present paper discusses the unreacted shrinking core model (USCM) developed to simulate the reduction rate of the oxygen carrier particle which was used in the design of the moving bed reducers. This paper also summarizes the key developments of four chemical looping processes – the 250kW_th-3MW_th syngas chemical looping (SCL) pilot plant, the coal direct chemical looping (CDCL) 25 kW_th sub-pilot unit and 250 kW_th pilot plant, and the 15 kW_th coal to syngas (CTS) and shale gas to syngas (STS) sub-pilot unit. Key process design features and experimental results from over 1,500 hours of cumulative operation will be discussed. The counter-current moving bed reducer reactor design the CDCL and SCL process ensure nearly full fuel conversion to CO₂ with minimal solid circulation and capability of producing high purity H₂. The co-current moving bed reducer reactor design in the CTS and STS processes provides a desirable gas-solid contacting pattern that minimizes carbon deposition and maximizes the syngas yield. The syngas produced by the CTS and STS processes can achieve adjustable H₂:CO ratio with optimized value of 2:1 with little CO₂, unconverted hydrocarbons, and steam, which is required for down-stream processes to produce liquid fuels and chemicals. During operation of the pilot plants, sliding mode control theory was adopted for modulating the aeration gas flow rate against the pressure fluctuations caused by the slugging bed combustor in order to maintain a constant solid circulation rate.