Reduction of tars by dolomite cracking during two-stage gasification of olive cake

The effective implementation of biomass gasification has to overcome some difficulties such as the minimization of tars. On the other hand, with a proper design of experimental conditions, biomass gasification can be directed towards the production of hydrogen. The aim of the present study was to investigate the use of dolomite as catalyst to improve tar removal and hydrogen production by a two-stage steam gasification process, using olive cake as raw material. Fixing the olive cake gasification conditions on the first reactor (900 °C, steam flow rate of 190 mg min−1, O2 flow rate of 7.5 cm3 min−1), the cracking of tars was prompted by: a) steam gasification (steam flow rate in the range 40–190 mg min−1) at 1000 °C, b) catalytic gasification, using dolomite (5% wt.). It was found that increasing steam flow rate up to 110 mg min−1 involves an increase in hydrogen fraction due to the enhancement of water gas and water gas shift reactions. Also, the influence of dolomite was studied at 800 and 900 °C in a second reactor, finding better results at 800 °C, which gave an hydrogen fraction of 0.51.

► The use of dolomite for tar cracking during olive cake steam gasification was studied.
► Two reactors in series were used, and the second one was provided with a dolomite bed.
► Increasing the steam flow rate above 40mg min-1 in reactor 2, favours H2 production.
► Using dolomite promotes tar cracking increasing H2 production, especially at 800 °C.