From Richard Durrant
In writing about the use of second-generation biomass, such as plant waste and paper, to produce biofuels, Helen Knight did not mention that fermenting the sugars resulting from cellulose hydrolysis produces a less than 15 per cent solution of alcohol in water (29 May, p 22). A great deal of energy is used in concentrating the alcohol to produce a useful fuel additive.
Biomass is difficult to use directly in conventional power stations because of its corrosive and low-melting-point ash. I suggest that the best way to use biomass is to use the hot gases produced by burning it to dry the coal feed to power stations, which could improve their thermal efficiency.
St Albans, Hertfordshire, UK
