Co-Combustion of Biomass Pretreated in a Fluid Bed Pyrolysis Unit

Abstract

An atmospheric bubbling fluid bed pyrolysis unit has been developed to convert straw and wood into volatile matter to be combusted in a conventional boiler. This pre-treatment is a means of supplying a major proportion of the biomass energy to the boiler without the corrosive components.

The pyrolysis unit has been tested extensively as a means of pretreating the biomass before co-combusting straw and wood with fossil fuels in power plant boilers. The fluid bed pyrolysis unit converts the biomass into two fractions: a volatile fraction to be combusted in the power plant boiler and a solids fraction to be converted otherwise. The volatile fraction contains up to 90 per cent of the energy from the input biomass. The idea is to avoid feeding the corrosive alkali metals and chlorine present in the biomass into the boiler, as these cause corrosion damage to the superheater, yet still supply the boiler with most of the biomass energy. This principle keeps ash from biomass and ash from the fossil fuels separated, and thereby avoids contamination of residues.