A multiple-gas cleanup process is proposed for the removal of CO2, SOx and NOx from coal combustion flue gas. This cleanup occurs at high temperatures (500-650 °C) in a single-stage gas-solid fluidized-bed reactor. This process – named Cal-C process – utilizes limestone-derived calcium sorbent and inexpensive coal char, and consists of the three-step calcium looping developed at OSU with the addition of char to the carbonator. The calcium sorbent is re-circulated through the system in a closed loop after regeneration and reactivation, while fresh addition of char is warranted due to complete consumption.
The process has been verified experimentally using a lab-scale fluidized-bed reactor setup and the simultaneous removal of all the species of interest has been established. Based on previous studies, lignite coal chars are known to be suitable for this application. In this work, experiments are performed to quantify the consumption of char on the basis of selectivity of char toward NO. Different parameters such as calcium to char loading, O2 concentration and NO concentration are studied for their effect on this selectivity. Further, the fate of gaseous species such as CO and H2, which are likely to be produced in-situ, is investigated and possible process conditions are identified for minimizing unwanted byproducts. Different process configurations with respect to the entry of char in the process loop are also analyzed experimentally. Thermogravimetric analysis of the hydration (reactivation) reaction is also conducted to study the effect of presence of char on the hydration kinetics. Using ASPEN simulations, the process analysis is conducted and different process configurations are evaluated with respect to the opportunities for heat recovery, minimization of excess char requirement, etc.
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