Abstract
Operating records of five pulverized-fuel-firing arrangements and furnace designs show what value lies in each, these depending upon the grade and price of coal used, the plant load factor, and the rate for fixed charges. The design best adapted shows a saving of $0.40 per ton of coal in operating costs and a saving of $2.44 in fixed charges, having been brought about by reduction in coal-preparation costs, general improvement in boiler economy, reduction in furnace maintenance by the use of water walls, elimination of hard slag in furnace by horizontal firing, and increase in ratings by the use of water walls, turbulent firing, and draft equipment. The nature of further improvements will be difficult to forecast. Improvement of mills will probably depend upon development of new types and on present designs, in maintaining the fineness of grind, and greater facility for repairs. The problem of higher rates of heat liberation in the furnace is receiving attention. Water walls have about reached their limit with practically the entire furnace enclosed. The use of radiant superheaters as a part of furnace walls offers possibilities in obtaining a higher and more even superheat. Means for reducing the quantity of fly ash in the flue gases will be important where pollution of air is a severe local disadvantage. All these problems can be discussed to the greatest advantage if considered from a completely economical viewpoint.
