. Electric railway journal . y Effected by Control of Excess Airand Combustible in Refuse BY H. F. LAWRENCE Test Engineer American Engineering Company, Philadelphia, Pa. In steam generating plant operation the heat lossesdue to excess air are the most important of any of theheat losses that can be controlled to any extent. Theupper set of curves in the accompanying illustrationshows the percentage of heat or percentage of coal whichis lost through the stack for different temperatures ofexcess gases and percentages of CO,. The straight lineslabeled Loss to stack at 450 deg., 500 deg. and 600 de
. Electric railway journal . y Effected by Control of Excess Airand Combustible in Refuse BY H. F. LAWRENCE Test Engineer American Engineering Company, Philadelphia, Pa. In steam generating plant operation the heat lossesdue to excess air are the most important of any of theheat losses that can be controlled to any extent. Theupper set of curves in the accompanying illustrationshows the percentage of heat or percentage of coal whichis lost through the stack for different temperatures ofexcess gases and percentages of CO,. The straight lineslabeled Loss to stack at 450 deg., 500 deg. and 600 atmosphere due to theoretical air show the per-centage of coal required for heating the furnace gasesfrom atmospheric temperature up to the stack tempera-ture. With no excess air, and perfect combustion theselines represent the heat lost through the stack for vari-ous temperatures. With different amounts of excessair indicated by various percentages of CO, the totalheat loss through the stack is as shown by the upper. 10 15 20 25 3 0 35PerCent Combustible in RefuseCURVES SHOWING BOILER HEAT LOSSES curves. The differences between the lower curves andthe upper curves is the excess air loss. It should be remembered in the interpretation ofthese curves that 16 per cent CO, represents cent excess air, 14 per cent CO, represents 39 percent excess air, 10 per cent CO, represents 87 per centexcess air, and 8 per cent CO, represents 123 per centexcess air. When the CO, is reduced from 16 per centto 10 per cent, the heat loss is increased by approxi-mately 6 per cent of the coal burned, provided, of course,that the exit temperature remains the same. The vol-ume of gases is much greater with 10 per cent CO, thanwith 16 per cent, owing to the greater amount of excessair, and the temperature of combustion is lower; there-fore the heat absorbed by the boiler is less, so that thefinal temperature is higher and the heat loss due to ex-cess air is greater than is really shown by
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