SWEET SOLUTION to a sugary problem

Rumpelstiltskin could spin straw into gold, so the fairy story goes. Impressive, but outdated - gold is yesterday's metal. In Vancouver, a company called DynaMotive is bringing this trick up to date - turning agricultural waste into oil.

Working with another Canadian company, Resource Transforms International, DynaMotive has developed a process it calls BioTherm. This takes the waste products from agriculture - bark and wood chips, straw and the crushed remnants of sugar cane, known as bagasse - and subjects them to pyrolysis, fierce heat in the absence of air. The sugars and cellulose which comprise the plant waste break down into a soup of smaller organic molecules, known as BioOil, which has a vast range of potential uses.

The BioTherm process is the culmination of four years' research. The process heats the raw material to 500 degrees C in a deep bubbling fluidised bed reactor, which produces yields comparable to a more traditional short residence time pyrolyser but distributes the heat better and produces no waste. The waste splits into three products: a non-condensable inert gas, a solid inorganic char, and an aerosol of oxygenated hydrocarbons, which condenses to form BioOil.

BioOil is a fuel similar to light and heavy fuels but is clean-burning. It produces no sulphur dioxide emissions, and its NOx emissions are less than half those produced by light fuel oil in gas turbines and heavy fuel oil in boilers. And because it is produced from agricultural waste, it is classed as CO2 neutral.

Straw and bagasse can themselves be used as a fuel, and several powerstations run on them. But according to DynaMotive, BioOil has a major advantage over these materials - it is a liquid, so it can be stored, pumped and transported like hydrocarbon oils.

Currently, DynaMotive is promoting the use of BioOil in power generation, using it as a fuel for large, static diesel engines and gas turbines. DynaMotive's research indicates that BioOil has a lower heating value than fossil fuel, but can generate power at a rate of 1MWhr per 450-475kg of fuel in a small diesel engine - comparable with light fuel oils. It can also compete in cost terms, particularly in countries where fossil fuels are taxed heavily.

Despite the wide choice of possible raw materials, DynaMotive is targeting its technology at only two areas: wood wastes and bagasse. This decision allows the company to concentrate on industries and countries which have both a plentiful supply of raw materials and a real use for the BioOil product.

The timber producers targeted by DynaMotive are mainly in Europe. Here, energy taxes and the prospect of landfilling of organic matter becoming illegal by 2002 will add to the attractiveness of a technology to convert high-volume solids waste into useful low-volume liquids.

Bags of energy

Sugar cane, meanwhile, tends to be grown in less industrialised regions, such as Latin America, India and Southeast Asia, as well as Australia. Sugar production produces large volumes of bagasse, which has no other uses. The BioTherm process will allow producers to transform this waste into cheap electricity, reducing the countries' dependence on imported fossil fuels.

But fuel oil replacement is only a starting point in the development of BioOil. The first step is to develop a refined blend of BioOil which can be used to run mobile diesel engines.

The ultimate goal is to exploit the chemical composition of BioOil. The substance is a mixture of oxygenated hydrocarbons such as acetic acid, formic acid and hydroxyacetaldehyde. DynaMotive and RTI are now looking at methods for refining BioOil to extract these products, and aiming for commercial production of derivatives by 2002. In areas where agricultural wastes are cheap and plentiful, BioOil could prove to be a ticket to the sharp end of the chemical industry. PE