Sergio Rapagnà

Gas cleaning, gas conditioning and tar abatement by means of a catalytic filter candle in a biomass fluidized-bed gasifier

A bench-scale fluidized-bed biomass gasification plant, operating at atmospheric pressure and temperature within the range 800-820 degrees C, has been used to test an innovative gas cleaning device: a catalytic filter candle fitted into the bed freeboard. This housing of the gas conditioning system within the gasifier itself results in a very compact unit and greatly reduced thermal losses. Long term (22h) tests were performed on the gasifier both with and without the catalytic candle filter, under otherwise identical conditions. Analysis of the product gas for the two cases showed the catalytic filtration to give rise to notable improvements in both gas quality and gas yield: an increase in hydrogen yield of 130% and an overall increase in gas yield of 69% - with corresponding decreases in methane and tar content of 20% and 79%, respectively. HPLC/UV analysis was used to characterize the tar compounds.

Olivine, dolomite and ceramic filters in one vessel to produce clean gas from biomass

Heavy organic compounds produced during almond shells gasification in a steam and/or air atmosphere, usually called tar, are drastically reduced in the product gas by using simultaneously in one vessel a ceramic filter placed in the freeboard and a mixture of olivine and dolomite particles in the fluidized bed of the gasifier. The content of tar in the product gas during a reference gasification test with air, in presence of fresh olivine particles only, was 8600mg/Nm3 of dry gas. By gasifying biomass with steam at the same temperature level of 820°C in a bed of olivine and dolomite (20% by weight), and in the presence of a catalytic ceramic filter inserted in the freeboard of the fluidized bed gasifier, the level of tar was brought down to 57mg/Nm3 of dry producct gas, with a decrease of more than two orders of magnitude.

Characterisation of Tar produced in the Gasification of Biomass with in situ Catalytic Reforming

This paper concerns the cleaning of the hot gas produced by steam gasification of biomass in a fluidized bed. The cleaning takes place in a catalytic filter candle device placed directly in the freeboard of the bed. Such integration results in a compact processing unit and increased thermal efficiency; the result of the cleaning being carried out directly at the reactor outlet temperature. It thus lends itself to exploitation in distributed power generation systems utilizing renewable energy sources. Results are reported for runs performed in a bench scale fluidized bed steam gasifier fitted with a single full-size catalytic candle filter. Tar and particulates in the product gas were sampled in accord with technical specification CEN/TS 15439 with analysis by UV and fluorescence spectroscopy.