The Development of Warm Gas Cleanup Technologies for the Removal of Sulfur Containing Species from Steam Hydrogasification
The steam hydrogasification reaction (SHR) refers to the thermochemical conversion of carbonaceous materials into synthetic gas in a steam and hydrogen environment. The formation of gaseous sulfur species from the solid sulfur in the feedstock is commonplace in thermochemical processes. It requires the cleaning of the output gas to protect the operation of downstream processes and catalysts. This thesis presents the results of an experimental study to determine the effect of temperature, steam and H2 partial pressure has on the distribution of the various gaseous sulfur species in the outlet gas of the SHR. Experiment results showed that sulfur in the feedstock is mainly converted to H2S in the SHR process. COS and CS2 were undetectable. The H2 and steam rich environment in the SHR process are favorable for the formation of H2S and suppress the COS and CS2 formation. An increase of H2S concentration was observed with the rise in temperature from 700oC to 800oC. An increase in the partial pressure of H2 decreased the H2S concentration released in the gas phase.
A lab-scale warm gas cleanup system was developed by using commercial ZnO sorbents based above results. A mixture gas simulated the composition of syngas from steam hydrogasification reaction was used as the feed gas. The effect of space velocity and gas composition on H2S breakthrough time was studied. It was found that H2S breakthrough time and sulfur capture capacity increased as the space velocity decreased. Moreover, addition of H2 or CH4 to the inlet gas stream has the positive effect on H2S breakthrough time. However, Addition of CO to the inlet gas stream decreased H2S breakthrough time. And addition of low content of CO2 to the inlet gas stream almost has no influence on H2S breakthrough time.
Techno-economic analysis was performed based on experimental and Aspen Plus simulation results in order to design warm gas cleanup system for CE-CERT process. Warm gas cleanup process by using regenerable sorbent is feasible for high capacity plant (syngas feed >=1000 tonne/day). And warm gas cleanup process by using disposable sorbent is more feasible for low capacity plant (syngas feed <1000 tonne/day). Economic sensitivity results showed that H2 availability and price is the most influential parameter affecting the cost for warm gas cleanup process by using regenerable sorbent, while ZnO sorbent price is the most influential parameters affecting the cost for warm gas cleanup process by using disposable sorbent.