Wood pyrolysis isn't just fueling
15 Jan 2000
Wood was probably humanity's first fuel, and it's shaping up as a fuel of the future, as well as a possible source for new chemical products. Chemical engineers at Aston University's energy research unit are currently devising a system that will convert wood, agricultural waste and other 'biomass' into a hydrocarbon liquid that can be stored and transported to power station; or used for recovery or production of speciality chemicals or fertilisers.
The system, known as a fast pyrolysis unit, works by breaking down the three major constituents of biomass cellulose, which is a polymer of anhydroglucose; hemicelluloses, which are also sugar polymers; and lignin, a three-dimensional polymer of phenol units.
Pyrolysis involves the degradation of these substances using heat, but in the absence of oxygen, the team explains. The fast pyrolysis technique tweaks the parameters of the process to maximise the yield of organic liquids at the expense of solids and non-condensible gases. It uses biomass ground into particles of 2mm diameter or smaller, and with less than 10% moisture; a reactor temperature of around 450 C (see charts); reactor residence times of less than 2sec; and product temperature no greater than 500 C.
The biomass doesn't burn, the researchers say, but decomposes into a liquid intermediate which, itself, rapidly decomposes into a condensible aerosol of volatile materials; non-condensible gases; and solid 'char', mostly inorganic minerals.
