Desulfurization Of Hot Coal Gas

Economic and environmental requirements for advanced power generating systems demand the removal of corrosive and other sulfurous compounds from hot coal gas. After a brief account of the world energy resources and an overview of clean coal technologies, a review of regenerable metal oxide sorbents for cleaning the hot gas is provided. Zinc oxide, copper oxide, calcium oxide, manganese oxide based as well as supported and mixed metal oxide sorbents are treated. Performance analysis of these sorbents, effects of various parameters on the desulfurization efficiency, kinetics of sulfidation and regeneration reactions, sulfiding and regeneration mechanisms are discussed. Two chapters present recent results in the direct production of elemental sulfur from regeneration or SO2-rich gases.

New coal gasification processes are now being developed which can generate electricity with high thermal efficiency either in a combined gas-turbine, steam-turbine cycle or in a fuel cell. Both of these coal-to-electricity pathways require that the coal-derived fuel gas be at a high temperature and be free of potential pollutants, such as sulfur compounds. Unfortunately, some high-sulfur Illinois coals also contain significant chlorine which converts into hydrogen chloride (HC1) in the coal-gas. This project investigates the effect of HC1, in concentrations typical of a gasifier fed by high-chlorine Illinois coals, on zinc-titanate sorbents that are currently being developed for H2S and COS removal from hot coal-gas. This study is designed to identify any deleterious changes in the sorbent caused by the HC1, both in adsorptive operation and in the regeneration cycle, and will pave the way to modify the sorbent formulation or the process operating procedure to remove HC1 along with the H2S and COS from the coal-gas. This will negate any harmful consequences of utilizing high-chlorine Illinois in these processes. The bench- scale fluidized bed has been modified to prevent potential HC1 corrosion and startup experiments have proven the reactor system operable and capable of yielding reliable experimental results. The first of the planned experiments in the project are now being performed. 1 fig.

The primary major deposit of manganese in the US which can be readily mined by an in situ process is located in the Emily district of Minnesota. The US Bureau of Mines Research Centers at both the Twin Cities and Salt Lake City have developed a process for extracting and refining manganese in the form of a high-purity carbonate product. This product has been formulated into pellets by a multi-step process of drying, calcination, and induration to produce relatively high-strength formulations which are capable of being used for hot fuel gas desulfurization. These pellets, which have been developed at the University of Minnesota under joint sponsorship of the US Department of Energy and the US Bureau of Mines, appear superior to other, more expensive, formulations of zinc titanate and zinc ferrite which have previously been studied for multi-cycle loading (desulfurization) and regeneration (evolution of high-strength SO2 and restoration of pellet reactivity). Although these other formulations have been under development for the past twelve years, their prices still exceed $7 per pound. If manganese pellets perform as predicted in fixed bed testing, and if a significant number of utilities which burn high-sulfur coals incorporate combined-cycle gasification with hot coal gas desulfurization as a viable means of increasing conversion efficiencies, then the potential market for manganese pellets may be as high as 200,000 tons per year at a price not less than $3 per pound. This paper discusses the role of manganese pellets in the desulfurization process with respect to the integrated gasification combined-cycle (IGCC) for power generation.

New coal gasification processes are now being developed which can generate electricity with high thermal efficiency either in an integrated gasification combined cycle (IGCC) or in a fuel cell (MCFC). Both of these new coal-to-electricity pathways require that the coal-derived fuel gas be at a high temperature and be free of potential pollutants, such as sulfur compounds. Unfortunately, some high-sulfur Illinois coals also contain significant chlorine which converts into hydrogen chloride (HCl) in the coal-gas. This project investigates the effect of HCl, in concentrations typical of a gasifier fed by high-chlorine Illinois coals, on zinc-titanate sorbents that are currently being developed for H2S and COS removal from hot coal gas. This study is designed to identify any deleterious changes in the sorbent caused by the HCI, both in absorptive operation and in the regeneration cycle, and will pave the way to modify the sorbent formulation or the process operating procedure to remove HCl along with the H2S and COS from hot coal gas. This will negate any harmful consequences of utilizing high-chlorine Illinois coal in these processes. The work activity during the third quarter of this project involved the performance of the second block-set of experiments in the bench-scale fluidized-bed reactor. These experiments were designed to study the effect of HCl in the desulfurization of a low-Btu fuel gas. Nine single-cycle experiments were performed, at operating temperature of 538, 650, and 750°C, with HCl concentrations of 0, 200, and 800 ppMv. The presence of HCl in the coal gas significantly enhanced the desulfurization efficacy of the sorbent. A 10-cycle sulfidation-regeneration sequence is currently being performed at 650°C with 800 ppMv HCl in the simulated fuel gas to determine any adverse effects on the sorbent structure or its desulfurization capability.

New coal gasification processes are now being developed which can generate electricity with high thermal efficiency either in a combined gas-turbine, steam-turbine cycle or in a fuel cell. Both of these coal-to-electricity pathways require that the coal-derived fuel gas be at a high temperature and be free of potential pollutants, such as sulfur compounds. Unfortunately, some high-sulfur Illinois coals also contain significant chlorine which converts into hydrogen chloride (HC1) in the coal-gas. This project investigates the effect of HC1, in concentrations typical of a gasifier fed by high-chlorine Illinois coals, on zinc-titanate sorbents that are currently being developed for H2S and COS removal from hot coal-gas. This study is designed to identify any deleterious changes in the sorbent caused by the HC1, both in adsorptive operation and in the regeneration cycle, and will pave the way to modify the sorbent formulation or the process operating procedure to remove HC1 along with the H2S and COS from the coal-gas. This will negate any harmful consequences of utilizing high-chlorine Illinois in these processes. The bench- scale fluidized bed has been modified to prevent potential HC1 corrosion and startup experiments have proven the reactor system operable and capable of yielding reliable experimental results. The first of the planned experiments in the project are now being performed. 1 fig.