Reduction of Chimney Emissions

Abstract

THE Technical Committee appointed by the Electricity Commissioners in 1930 to consider the methods that should be taken to prevent the emission of soot, ash and grit from the chimneys of electric power stations has now published its report (London: H.M. Stationery Office, 5s.). A sub-committee made a thorough investigation, visiting many foreign stations which have adopted preventive measures. In 46 of the 111 British selected stations no grit extraction plant has yet been installed. The subcommittee regards grading by sieves as unsatisfactory, as it is impossible when the mesh is too small and untrustworthy for larger values. Particles below 20 microns (1 micron is a thousandth part of a millimetre) when discharged into an air stream are sufficiently diffused to avoid creating a nuisance. The only satisfactory way of testing the efficiency of dust extraction plant is to weigh the dust in unit volume of the gases at as high a point in the chimney as practicable. In Germany, where the power stations are generally larger than in Great Britain, electrostatic precipitation together with very high chimneys is favoured. The main conclusions arrived at by the Committee are that dust nuisance is avoidable with new stations, but the application of means for its prevention to all existing stations may not be practicable. There is an urgent need for standardisation of good methods of testing dust extraction plant. For pulverised fuel installations the electrostatic precipitator is the most suitable type to use. Water for dust extraction is not to be commended. The minimum height of chimneys should be at least two and a half times that of the highest point of the generator station buildings. Photographs are given of the filters used for separating ash and grit particles and of plant for multiple-cyclone dust extraction.