Removal of NH3 and H2S from producer gas in a dual fluidised bed steam gasifier by optimisation of operation conditions and application of bed materials

Abstract

In the present study, in situ removal of ammonia (NH3) and hydrogen sulphide (H2S) in the producer gas has been investigated for steam gasification of woody biomass in a 100 kW dual fluidised bed (DFB) gasifier. The removal measures consist of optimisation of operation conditions and application of catalytic bed materials. The operation conditions investigated were gasification temperature in a range of 750 to 850 °C, steam to fuel ratio from 0.6 to 1.4 kg/kgdry, and mean gas residence time from 0.19 to 0.25 s. The catalytic bed materials tested included silica, ilmenite and calcined olivine sands which were applied in the DFB steam gasifier. The concentrations of NH3 and H2S in the producer gas were measured and the conversions of fuel nitrogen (N) and sulphur (S) to form NH3 and H2S were calculated based on the experimental results. The results showed that NH3 and H2S concentrations and conversions increased with the gasification temperature and the steam to fuel ratio. However, with increase in the mean gas residence time, the NH3 concentration and conversion increased whereas the H2S concentration and conversion slightly decreased. In addition, ilmenite sand and calcined olivine sand as the bed materials showed stronger influence on reduction of NH3 and H2S concentrations as well as fuel-N and fuel-S conversions in comparison with silica sand.