boiler incrustation, use of zinc
boiler incrustation, use of zinc defined in 1909 yearboiler incrustation, use of zinc - boiler incrustation, Use of Zinc;
boiler incrustation, use of zinc - This consists in introducing into the boiler some small ingots or clippings of zinc; it is then observed that the usual earthy substances, instead of forming a hard and adherent deposit, form a noncoherent crust, which can be readily removed. If the water be very strongly impregnated with lime salts, the deposit, even if coherent and solid, does not adhere firmly to the boiler plate. The zinc is converted into a white earthy mass, principally oxide of zinc. No trace of zinc can be detected in the water, and there is very little in the ordinary incrustation, as the oxide of zinc forms a separate deposit. Experience has shown that about 2 lb. of zinc per month per horse-power is sufficient. The action of the zinc, being in contact with the iron boiler plate, is probably electrical, and, if hydrogen be evolved in small bubbles, it would be sufficient to account for the deposit being non-adherent and friable.
A boiler with clean plates yielded with 1 lb. coal 7.5 lb. steam, after two months only 6.4 lb. steam, or a decrease of 17 per cent. At the same time the boiler had suffered by continual working. Suppose a boiler free from inside crust would yield a saving of only 5 per cent, in fuel (and this figure is taken very low compared with practical experiments), it would be at the same time a saving of 1½d. per cub. yd. of water. If the cleaning of 1 cub. yd. of water therefore costs less than 1½d., this alone would be an advantage. For a long time, efforts have been made to find some means for this purpose, and we have reached good results with lime and chloride of barium as well as with magnesia preparations. But these preparations have many disadvantages. Corrosion of the boiler iron and muriatic acid gas have been detected. Chloride of calcium, which is formed by using chloride of barium, increases the boiling-point considerably, and diminishes the elasticity of steam; while the sulphate of soda, resulting from the use of carbonate of soda, is completely ineffectual against the boiler iron. It increases the boiling-point of water less than all other salts, and diminishes likewise the elasticity of steam. (Wullner.)
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