Liquid metal systems for gasification-based power generation

Abstract

A closed-loop liquid metal system is proposed for the simultaneous quenching and desulphurization at elevated temperature of raw fuel gas from commercial gasifiers. Besides its origins in a recently conceived liquid metal transport gasifier, application to the oxygen-blown Shell gasifier and the air-blown Mitsui-Babcock gasifier is discussed. The quenched fuel gas is filtered at relatively low temperature before being reheated to 750 °C or above by direct contact heat exchange with liquid metal in advance of partial precombustion to raise the temperature (1735 and 1194 °C respectively). Ammonia is reduced and equilibrium established prior to massive superheated steam injection, utilizing all available steam, and then rapid transmission to the can-annular combustors of a 1500 °C Class gas turbine at 870 °C, where autoignition of the highly preheated fuel gas is predicted. NO_x emissions as low as 2 ppmv are anticipated. Mercury is projected to be recovered in elemental form, while other air toxics are prevented from discharging into the environment. Water recovery at 99 per cent appears feasible in a low-pressure drop system, and visible plume discharge is avoided by reheating the condenser off-gas in direct contact with a passivated liquid metal surface. Parallels are drawn with the molten tin based float glass process.