Preliminary Feasibility Study of the Biomass Vacuum Pyrolysis Process

Abstract

A process for the pyrolysis under vacuum of biomass and waste materials has been under development since 1978 in Canada. Background data regarding the yields and qualities of the pyrolysis products derived from materials such as wood, bark, agricultural residues, peat, municipal solid wastes, activated sludges and scrap tires, have been obtained at the bench scale level. A Process Development Unit having a feedthrough capacity of up to 25 kg h^-1 and using a multiple hearth furnace reactor has been designed and built. The objectives of the P.D.U. were twofold. First, the Unit was used to determine engineering data such as the overall thermal efficiency and the heat requirement for the reactions. Second, the configuration and mechanical operation of the reactor had to be tested before its scale-up for the pilot plant phase of the project (150 kg h^-1).

One feature of the process is the production of high yields of pyrolysis oils and a reactive charcoal from wood. The pyrolysis oil can be separated from the aqueous phase using a proper condensation scheme at the outlet of the reactor. Moreover the wood-derived oils can be fractionated in different cuts at the six outlets of the multiple hearth furnace. The characteristics of this oil widely vary from top to bottom of the reactor. The value of these oils has been investigated in terms of heating fuel and as a source of commodity and high-value chemicals. At 10 Can $ t^-1 for the supply of wood feedstock, the process seems to be feasible. The process feasibility significantly improves if commodity and high-value chemicals are extracted from the pyrolysis oils and sold as by-products.