GB932895A - Improvements in and relating to the treatment of gases - Google Patents

Abstract

A process for treating waste gases of an industrial plant (prior to passing the gases into an electrostatic precipitator) to reduce the electrical resistivity of the dust particles to 1010 ohm. cm. or less comprises the steps of burning fuel having a high sulphur content (i.e. 2% by weight or more) in an auxiliary combustion chamber in the presence of a supply of oxygen in excess of that required to promote complete combustion to promote the formation of 0,025 to 0,050 volume per cent of sulphur trioxide in the combustion gases produced therein, and passing the combustion gases so produced into the waste gas issuing from the industrial plant, so that the dust particles adsorb sulphur trioxide from said combustion gases. In a modification, when the waste gases contain excess dust or when the combustion gases do not contain sufficient sulphur trioxide to permit adsorption of sulphur trioxide by all dust particles, the process is assisted by humidifying the dust. The auxiliary combustion chamber may be an ordinary fire base grate or an oil-fired furnace, but preferably is a coal fired furnace with an automatic travelling grate, an essential feature of all these grates and furnaces being an ample flow of oxygen to the combustion zone. Coal and oil having high sulphur content is burned in the furnace, especially hard coal containing pyrites mixed with any number of high sulphur content materials, e.g. pyrites, impure iron sulphate and elemental sulphur. The combustion gases are then mixed with the waste gases. In the modified process the auxiliary furnace is the heating means for a low pressure boiler. Sufficient steam and atomized water (water at 95 DEG -99 DEG C.) are mixed with the combustion gases passing through the flue and this gas mixture then introduced into the waste gases from the industrial plant. The invention can be applied to electrostatic precipitators associated with cement furnaces or to calcium carbonate, magnesite, dolomite, bauxite and similar calcining plants, to ore-sintering plants, converter plants, and to other industrial wastegas producing plants.