Desulfurization of hot syngas containing hydrogen chloride vapors using zinc titanate sorbents

There is a primary need to increase the use of Illinois coal resources by d eveloping new methods of converting the coal into electricity with highly e fficient and environmentally acceptable systems. New coal gasification proc esses that can generate electricity with high thermal efficiency either in a combined gas-turbine, a steam-turbine cycle (IGCC), or in a fuel cell (MC FC) are being developed. Both of these new coal-to-electricity pathways req uire that the coal-derived fuel gas be at a high temperature and free of po tential pollutants, such as sulfur compounds. Unfortunately, some high-sulf ur Illinois coals also contain a significant amount of chlorine, which conv erts into hydrogen chloride (HCl) in the coal gas. In this study, two simul ated gasifier-product streams were contacted with the zinc titanate desulfu rization sorbent in a bench-scale atmospheric fluidized-bed reactor at temp eratures ranging from 538 to 750 degrees C (1000-1382 degrees F). The first set of experiments involved treating a medium-Btu fuel gas (simulating tha t of a "Texaco" oxygen-blown, entrained-bed gasifier) containing 1.4% H2S a nd HCl concentrations of 0, 200, and 1500 ppmv. The second set of experimen ts evaluated the hat-gas desulfurization of a low-Btu fuel gas (simulating the product of the "U-Gas" air-blown gasifier), which had a 0.5% H2S conten t and with HCl concentrations of 0, 200, and 800 ppmv. These operating cond itions were typical of the gas-treatment requirements of gasifier systems f ueled by Illinois basin coals containing up to 0.6% chlorine. The results o f the experiments at 538 and 650 degrees C at all the HCl concentrations re vealed no deleterious effects on the capability of the sorbent to remove H2 S from the fuel-gas mixtures. In most cases, the presence of the HCl signif icantly enhanced the desulfurization reaction rate. Some zinc loss, however , was encountered in certain situations at 750 degrees C when low-steam ope rating conditions were present. Also of interest, a portion of the incoming HCl was removed from the gas stream and was retained permanently by the so rbent.