Hot, low-Btu producer gas desulfurization in fixed bed of iron oxide-fly ash. Final report, July 1977-March 1978

Abstract

This work was undertaken to aid DOE in the development of a fixed-bed cyclic process for desulfurizing hot, low-Btu (100 to 140 Btu/SCF) producer gas with iron oxide sorbents. In this process low-Btu producer gas contaminated with hydrogen sulfide passes through a freshly regenerated fixed bed of supported iron oxide at 1200/sup 0/F and 150 psig. Hydrogen sulfide reacts with iron oxide to yield iron sulfide and steam. Absorption from the producer gas continues until the hydrogen sulfide concentration in the exit stream rises to ten percent of the inlet concentration. Most of the iron oxide in the bed is converted to iron sulfide at this breakthrough point. The bed then is regenerated with a mixture of air and diluent gas. The regeneration reactions are highly exothermic, and the diluent gas limits the maximum temperature rise in the bed. During regeneration iron sulfide is converted to iron oxide, and sulfur dioxide is formed. The economics of hot stage desulfurization of low-Btu producer gas in a cyclic fixed bed were evaluated over a wide range of process variables including linear velocity of the producer gas, operating pressure, onstream cycle length, iron oxide content of the sorbent, pellet diameter, sorbent life andmore » sorbent cost. Capital investment for a regenerative fixed-bed desulfurization unit designed to process producer gas for a 500 megawatt generating plant is 22.4 to 26.2 million dollars for typical operating conditions. Nearly 75 percent of the cost is for regeneration facilities, and he compressors account for nearly 50 percent of the major equipment cost. The total processing cost for desulfurizing low-Btu producer gas ranges from 16.5 cents per MM Btu to 28.1 cents per MM Btu for typical operating conditions. Major contributions to the total processing cost are from sorbent cost, finance charges and depreciation.« less