The Low Temperature CFB Gasifier - Further Test Results and Possible Applications

The novel "Low Temperature Circulating Fluidised Bed" (LT-CFB) gasification process is described together with the most recent results from the 50 kW LT-CFB test plant located at the Technical University of Denmark. The LT-CFB concept aims at avoiding problems due to ash sintering/agglomeration and corrosion when using difficult fuels such as agricultural biomass and many waste materials. This is achieved by pyrolysing the fuel at around 650°C in a circulating fluidised bed (CFB) chamber and subsequently gasifying the char down to only around 730°C in a slowly fluidised bubbling bed (BFB) chamber located in the CFB particle re-circulation path. The 50 kW test plant was built and commissioned during 1999 and since then experiences have been gained from more than 80 hours of operation. Nearly all of the test work has been performed on fuel that is expected to be worst-case conditions, i.e. the fuel has mainly been Danish wheat straw containing 1,8 % potassium and 0,8 % chlorine (dry basis) and the bed material has been ordinary silica sand with no additives.The test results have showed a high retention of potassium (73-98%) and chlorine (23-75%) in the ash. At the same time the char loss was approx. 3,5 mass% of supplied amount of fuel, and the content of PAH in the ash was only around 2 mg/kg. The most recent test results and anticipated applications are described in this paper. Keywords: gasification, biomass conversion, circulating fluidised bed (CFB)