Abstract
Chemical Looping Combustion (CLC) has been considered as one of the most promising technologies to implement CO2 capture with low energy penalty. A comprehensive three-dimensional numerical model integrating gas–solid flow and reactions, based on the authors’ previous work (Energy Fuels 2013, 27, 2173–2184), is applied to simulate the in-situ Gasification Chemical Looping Combustion (iG-CLC) process in a circulating fluidized bed (CFB) riser fuel reactor. Extending from the previous work, the present study further validates the model and investigates the effects of several important operating conditions, i.e., solids flux, steam flow and operating pressure, on the gas–solid flow behaviors, CO2 concentration and fuel conversion, comprehensively. The simulated fuel reactor has a height of 5 m and an internal diameter of 60 mm. The simulated oxygen carrier is a Norwegian ilmenite and the simulated fuel is a Colombian bituminous coal. The results of this simulation work have shown that an increase in the solids flux can promote CO2 concentration, but may also have a negative effect on carbon conversion. A decrease in the steam flow leads to positive effects on not only the CO2 concentration but also the carbon conversion. However, the reduction of steam flow is limited by the CFB operation process. An increase in the operating pressure can improve both the CO2 concentration and carbon conversion and therefore, the CFB riser fuel reactor of a practical iG-CLC system is recommended to be designed and operated under a certain pressurized conditions.
Highlights
Chemical Looping Combustion (CLC) is one of the most promising technologies to implementCO2 capture with low energy penalty [1,2,3]
The first approach is the so-called in-situ Gasification Chemical Looping Combustion which is usually based on the concept of Dual Interconnected Fluidized Bed (DIFB), as shown in Figure 1 [16,17]
Nine different cases were simulated to study the effects of operating conditions including solids flux, steam flow and operating pressure on the flow behavior and reaction performance in the fuel reactor
Summary
Chemical Looping Combustion (CLC) is one of the most promising technologies to implementCO2 capture with low energy penalty [1,2,3]. The more abundant reserves and higher carbon intensity of coal compared to gaseous fuels make the adoption of coal in the CLC system more attractive [12,13,14,15,16,17]. In the fuel reactor, the particles of the oxygen carrier are mixed with the coal particles and react with the gas products from coal pyrolysis and gasification. With a high conversion of combustion gases, the flue gas leaving the fuel reactor would mainly contain CO2 and H2 O. For the particles (i.e., reduced oxygen carrier and unreacted char) entrained by the flue gas, they are directed into the separation system (including separators and a carbon stripper) to achieve the solid–solid and gas–solid separations. The char particles are sent back to the fuel
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