Clean syngas from biomass—process development and concept assessment

This paper summarises the long development work done at VTT for gas clean-up for various synthesis applications. The development work has covered the most challenging and costly steps in biomass gasification based processes: high-temperature gas filtration and reforming of hydrocarbon gases and tars. The tar content of product gas is one of the main factors defining the temperature window in which the hot-gas filter can be operated, which in the case of fluidized-bed gasification is at 350–500 °C. Research is ongoing to achieve higher and thus more economical operation temperatures. Optimal operation of a catalytic reformer can be achieved by using a staged reformer where zirconia-based catalysts are used as a pre-reformer layer before nickel and/or precious metal-based catalyst stages. The temperature of the reformer is optimally increased in subsequent stages from 600 up to 1,000 °C. According to the techno-economic analysis, increasing the hot-gas filtration temperature by 300 °C or methane conversion in the reformer from 55 to 95 % both lead to about 5 % reduction the liquid fuel production cost.