The effects of process conditions on the pyrolysis products of waste and biomass

Abstract

The prolysis of wood, rice husks, RDF and scrap type has been examined in three different reactors during this research. The fixed-bed reactor was employed to pyrolyse the waste samples at the heating rates of 5, 20, 40 and 80 C min-1 up to different ma- ximum temperatures of 300, 420, 600 and 720 C. Generally, it was ob- served that as the heating rate and pyrolysis temperature was increa- sed, the liquid and gas yield increased and char yield decreased. In wood pyrolysis, it was also observed that after 720 C, the liquid yield decreased as it was accompanied by an increased gas yield. The detailed gas analysis showed that from the biomass wastes wood, rice husks and RDF, the main gases evolved were hydrogen, carbon monoxide, carbon dioxide, methane, ethane, propane and propene. Scrap type pyrolysis showed that the main gases were hydrogen, carbon monoxide, carbon dioxide, methane, ethane, propane, propene, but butadiene was also observed. The calorific value of the gases increased as the temperature of pyrolysis was increased. The individual amounts of each gas also increased. The liquid yields from the biomass wastes consisted of oil and aqueous phases. The scrap oil was of a low vis- cosity and negligible water content. The liquid yield reached a maxi- mum of 53% for the biomass and 58% for the scrap tyre pyrolysis. Examination of the fuel properties of the derived pyrolysis oils showed the biomass oils were highly oxygenated, of moderate calorific value and similar distillation range to a kerosene. A fluidised-bed pyrolysis reactor was designed, constructed and tested to investigate the fast pyrolysis of the waste and biomass samples. With the fluidised-bed reactor, it was shown that the liquid yield and also calorific values of the liquid yield and also calorific values of the liquids increased with increased temperature of pyroly- sis. Oils from a commercial scale batch pyrolysis unit were analysed and showed similar fuel properties and compositions to those derived from the fixed-bed reactor.