Partial oxidation of biomass gasification tar with oxygen transport membranes

Abstract

Dual phase oxygen transport membranes were directly integrated into the producer gas stream of a low temperature circulating fluidized bed (LT-CFB) gasifier for partial oxidation of tar. Ce_0.9Gd_0.1O_1.95–La_0.6Sr_0.4FeO_3-d composite membranes were prepared by extrusion and dip-coating, co-sintered and infiltrated with electro-catalysts. These were investigated in two different set-ups: i) a membrane test rig, and ii) a partial oxidation testing unit connected to a biomass gasifier. The stability and performance of the membrane were tested in two different gas-streams; i) H₂ and ii) producer gas. An oxygen flux of 1.5 Nml∙cm⁻²∙min⁻¹ was measured in an air/H₂ gradient at 850 °C through a 10 cm long membrane with a diameter of 10 mm, whereas a lower oxygen flux of 0.5 Nml∙cm⁻²∙min⁻¹ was measured for the air/producer gas case. The producer gas contained ca. 2000 mg Nm⁻³ of primary tar. Analysis of the gas and the tar composition at the output of the membrane unit demonstrated that it contributed to the partial oxidation of the primary tar, resulting in a twofold increase of H₂, CH₄ and CO in the producer gas. This successful integration of oxygen transport membranes demonstrated that these membranes can reduce the tar content in producer gas from biomass gasifiers.