Coal Direct Chemical Looping Process Research Articles

Numerical simulation of multiphase flow in a full coal-direct chemical looping combustion process

Chemical looping combustion (CLC) is a promising clean combustion technology alternative to conventional oxy-combustion, yet the full loop flow details are not well understood. In this work, a multi-fluid model based on the Eulerian-Eulerian framework is used to study the gas-solid hydrodynamics in a full-loop Coal-direct chemical looping (CDCL) combustion unit with a unique moving-bed fuel reactor. The unique fluidization states are described throughout the full-loop system. Then, the influences of several operating conditions on the solid circulation rate and pressure distribution are investigated. It is shown that the solids circulation rate is dominantly controlled by the gas flow rate on the standpipe of the L-valve. Meanwhile, a higher combustor gas velocity reduces the pressure of the whole system and an increased L-valve gas velocity influences the pressure distribution slightly but increases the local pressure at the L-valve. This work provides a cost-effective tool for understanding and optimizing the CDCL process.

Coal-Direct Chemical Looping Process with In Situ Sulfur Capture for Energy Generation Using Ca–Cu Oxygen Carriers

Coal-Direct Chemical Looping Process with <i>In Situ</i> Sulfur Capture for Energy Generation Using Ca–Cu Oxygen Carriers

Coal direct chemical looping process: 250 kW pilot-scale testing for power generation and carbon capture

Chemical looping combustion (CLC) is an energy conversion technology that can produce concentrated CO2 stream without the need for a gas separation step, and thus, has the potential to drastically reduce the energy consumption and cost associated with CO2 capture in power generation. The coal-direct chemical looping (CDCL) process is a CLC technology that uses a moving bed reducer configuration that can directly consume coal as a feedstock without requiring an upstream gasification step. An integrated 250 kWth CDCL pilot unit using iron-based oxygen carriers was constructed and demonstrated for over 1000 h of testing. The principles for the CDCL pilot unit design and operation are summarized in this article. During the 288-hour continuous operation testing, the CDCL pilot unit achieved >96% coal conversion with a CO2 purity of >97%. Low carbon carryover into the combustor, i.e. <2%, was also confirmed during the test, which shows the capability of the moving bed reactor to retain and convert coal using the oxygen available on the iron-based oxygen carrier. The results from the pilot unit testing confirms the CDCL concept as a promising coal combustion technology for heat and power generation with CO2 capture.

Numerical study of gas-solid flow behaviors in the air reactor of coal-direct chemical looping combustion with Geldart D particles

Chemical Looping Combustion (CLC) is a promising clean combustion technology alternative to conventional oxy-combustion because of its technical feasibility to achieve intrinsic separation of CO2. In a typical Coal-Direct Chemical Looping (CDCL) process, iron-based oxygen carriers belonging to Geldart D particles are used. Such system has been seldom studied. In this work, a two-fluid model (TFM) is adopted for describing the gas-solid flows in a bottom-enlarged air reactor of CDCL process. The model is qualitatively and quantitatively validated. The simulation results indicate that the oxygen carrier particles show a slugging flow pattern in the bottom section of the air reactor, an anti-core-annulus structure in the riser and a periodic fluctuation in the whole air reactor. Besides, the effects of several variables on the gas-solid flow in CDCL air reactor are also studied including gas velocity, specularity coefficient and different drag models. The simulation results indicate that the higher gas inlet velocity can increase the pressure drop over the air reactor and show a significant influence on solid allocation in the bottom section and the riser. Specularity coefficient of zero and Syamlal-O’Brien drag model give the closest mass flow rate by comparing with experimental values, indicating that they are suitable for the three-dimensional air reactor modelling. This model provides a cost-effective tool for better understanding of gas-solid flows in the air reactor of CDCL systems.

Parametric and dynamic studies of an iron-based 25-kWth coal direct chemical looping unit using sub-bituminous coal

The iron-based Coal-Direct Chemical Looping (CDCL) combustion process is an alternative to conventional oxy-combustion technologies, where the oxygen used for fuel conversion in the CDCL process is provided by an iron-oxide based oxygen carrier instead of an air separation unit. The iron oxide is reduced using coal in the reducer reactor, producing highly-pure CO2 in the flue gas, and the reduced iron oxide is regenerated in a separate combustor reactor using air. The CDCL process at Ohio State has been developed and demonstrated in a 25 kWth sub-pilot unit, and it is the first chemical looping demonstration unit with a circulating moving bed reactor for solid fuel conversion. To date, the CDCL sub-pilot unit at OSU has been operated for more than 680 h, with a 200-h continuous operation, providing important data on long term operability as well as parametric optimization. This paper discusses recent parametric operational experience with sub-bituminous coal as the fuel, where dynamic changes in variables were performed to observe the effects on the unit itself. Measurements included temperature, pressure, and gas concentrations from the reducer and combustor. Furthermore, effects of different variables, such as flue gas recycle ratios (enhancer gas flow rates), feed port injection, and temperature, were observed. Tests confirmed high coal conversions with high purity of CO2 achieved in the flue gas. Overall, the moving bed design of the reducer results in nearly full coal conversion with a high purity of CO2, eliminating the need for additional down-stream fuel polishing and/or separation units. The combustor gas contained lean oxygen concentrations with minute amounts of carbonaceous gases detected, indicating proper regeneration of the oxygen carrier as well as good gas sealing between the reducer and combustor.

Conversion of metallurgical coke and coal using a Coal Direct Chemical Looping (CDCL) moving bed reactor

The CLC process has the potential to be a transformative commercial technology for a carbon-constrained economy. The Ohio State University Coal Direct Chemical Looping (CDCL) process directly converts coal, eliminating the need for a coal gasifier oran air separation unit (ASU). Compared to other solid-fuel CLC processes, the CDCL process is unique in that it consists of a countercurrent moving bed reducer reactor. In the proposed process, coal is injected into the middle of the moving bed, whereby the coal quickly heats up and devolatilizes, splitting the reactor roughly into two sections with no axial mixing. The top section consists of gaseous fuel produced from the coal volatiles, and the bottom section consists of the coal char mixed with the oxygen carrier. A bench-scale moving bed reactor was used to study the coal conversion with CO2 as the enhancing gas. Initial tests using metallurgical cokefines as feedstock were conducted to test the effects of operational variables in the bottom section of the moving bed reducer, e.g., reactor temperature, oxygen carrier to char ratio, enhancer gas CO2 flow rate, and oxygen carrier flow rates. Experiments directly using coal as the feedstock were subsequently carried out based on these test results. Powder River Basin (PRB) coal and Illinois #6 coal were tested as representative sub-bituminous and bituminous coals, respectively. Nearly complete coal conversion was achieved using composite iron oxide particles as the oxygen carriers without any flow problems. The operational results demonstrated that a moving bed reactor design is favorable for the CDCL application.

Coal-Direct Chemical Looping Gasification for Hydrogen Production: Reactor Modeling and Process Simulation

A novel process scheme for hydrogen production from coal with in situ CO2 capture, known as the coal-direct chemical looping (CDCL) gasification process, is discussed in this article. The CDCL process utilizes an iron oxide based oxygen carrier as a chemical looping medium to indirectly gasify coal into separate streams of H2 and CO2. ASPEN Plus reactor simulation models based on both thermodynamic equilibrium limitations and kinetic limitations are developed to analyze individual CDCL reactors. Process simulations are subsequently performed to estimate the performance of the CDCL process under various mass and energy management schemes. Reactor modeling results indicate that a moving bed reducer can effectively convert coal while reducing the oxygen carrier. The reduced oxygen carrier can in turn be oxidized by steam to produce hydrogen in a moving bed oxidizer. The fates of pollutants as well as the effects of various process operating parameters such as carbon and iron oxide conversions are also evalua...