Investigation of Adsorbent - based Warm Carbon Dioxide Capture Technology for IGCC System

Integrated gasification combined cycle with CO 2 capture and sequestration (IGCC-CCS) emerges as one of the most promising technologies for reducing CO 2 emission from coal power plant without reducing thermal efficiency significantly. However the high capital cost of these plants has limited their deployment. The current solvent-based low-temperature CO 2 capture process (Selexol process) is energy and capital intensive contributing to the problem. Sorbent-based warm CO 2 capture has been predicted to be a key enabling technology for lowering down the costs of IGCC-CCS. However, no commercial adsorbents or processes exist for these warm CO 2 separations. My thesis work has been devoted to developing a solid sorbent and CO 2 capture process which can capture CO 2 at an elevated temperature in IGCC system. By combining experimental methods and quantum calculation, I have successfully identified and invented one new sorbent material. The sorbent for warm CO 2 capture containing magnesium oxide was developed using incipient wetness impregnation. The reversible adsorption isotherm, cyclic stability, and sorption rate were measured using a custom-built high pressure microbalance system and a thermogravimetric analyzer. Experimental data indicate the sorbent has a fairly large regenerable capacity in 180-240 *C temperature range, fast kinetics, low heat of adsorption, and stable working capacity for at least 84 cycles. The new sorbent performs better than synthetic hydrotalcite and K 2 CO 3-promoted hydrotalcite in the temperature range of interest. To assess the applicability of CO 2 removal technology to IGCC via a warm pressure swing adsorption (PSA) process based on our newly invented sorbent which has good cyclic sorption-desorption performance at an elevated temperature, a 16-step warm PSA process was simulated using Aspen Adsorption based on the real sorbent properties. I used the model to fully explore the intercorrelation between hydrogen recovery, CO 2 capture percentage, regeneration pressure of sorbent, and steam requirement. Their trade-off effects on IGCC efficiency were investigated by integrating the PSA process into the plant-wide IGCC simulation using Aspen Plus. On the basis of our analysis, IGCC/warm PSA using our new sorbent can produce slightly higher thermal efficiencies than IGCC/cold Selexol. In order to achieve this, warm PSA needs a narrow range of process parameters to have a good balance between the hydrogen loss, steam consumption and work requirement for CO 2 compression. 3 Sensitivity analysis is finally conducted to point out the future direction for making warm syngas cleanup more applicable. Further …