Abstract
The concept of using CO_2 as a gasification medium has been investigated both theoretically and experimentally. The theoretical investigation was done using Aspen[○!R] Plus simulations to explore and understand the impact of CO_2 on an integrated gasification combined cycle (IGCC) plant and the gasifier performance. The results show that a steam to carbon ratio of 1.5 provides a hydrogen output from the gasifier of 1.15 kg hr^<-1> while generating about 14 kW of electricity per kmol hr^<-1> of carbon from a SOFC using the portion of the CO generated that was not needed to drive the reforming reactions. However recycling up to 25% of CO_2 into the gasifier produces about 15% more hydrogen, while using 20% less CO for combustion to drive the gasification reactions. The IGCC simulations show that the addition of CO_2, from the high pressure compressor, does not change the CGE. The baseline CGE using steam gasification of Spring Creek coal (9338 BTU lb^<-1>) is 65.0% whereas replacing the steam with CO_2 resulted in a CGE of 65.1%. Moreover, the H_2O/CO was reduced from 4.2 for steam gasification to 2.0 for CO_2 gasification, which is the minimum necessary to enable efficient operation of water gas shift reactors. Validation tests over a CO_2 concentration range from 0% to 100% by volume resulted in a significant enhancement in the CO evolution above 700℃. However the CO_2 introduction suppressed the H_2 production at temperatures above 700℃, indicating a delayed effect on H_2 suppression. All biomass test samples showed similar mass decay behavior and were completely exhausted by 900°-1000℃. Finally, CO_2 gasification of various biomass and municipal solid waste (MSW) feedstocks has yielded similar results to those obtained using coal.
