Development of a Catalytic Candle Filter for One-Step Tar and Particle Removal in Biomass Gasification Gas

Abstract

Renewable energy generation from biomass (e.g. wood, agricultural wastes) by gasification is attractive because it can be used for efficient energy production on both small and large scale. Unfortunately, biomass gasification gas contains unwanted impurities, such as condensable tars and ash particles that need to be removed to avoid damaging of the downstream equipment.This work reports on the performance of a novel catalytic candle filter for the integrated high temperature removal of tars and particles from the biomass gasification gas. The catalytic candle filters that are under development are alumina ceramic filters that contain a suitable nickel-based tar cracking catalyst in their pores. This not only avoids mass transfer limitations occurring in packed beds of such catalysts, but also yields a reduced investment cost for the cleanup step.Different nickel-based catalysts have been developed and impregnated in the pores of the alumina support. Nickel is efficient for tar removal, but is sensitive to sulfur poisoning by the biomass gasification gas that typically contains 20-200 ppm H2S. To enhance the resistance to sulfur poisoning CaO or MgO was added to the nickel and also the number of active nickel sites was increased by the deposition of a highly dispersed secondary alumina layer in the large pores of the primary support.Small-scale porous alumina filter discs were tested on their sulfur poisoning resistance under lab conditions using a simulated biomass gasification gas containing benzene and naphthalene as model compounds. At typical conditions, such as a filtration velocity of 2.5 cm/s and a H2S-content of 100 ppm, naphthalene conversions of 99.89% were obtained with a Ni/MgO-activated filter disc with increased surface of the support.