. Applied thermodynamics for engineers. grate is a decided advan-tage with many types of boilers. The smoke is distilled off at the coking underfeed stoker feeds the coal by means of a worm to the under side of the fire,and the smoke passes through the incandescent fuel. All stokers have the advantageof making firing continuous, avoiding the chilhng effect of an open fire door. Amongsoft coal furnaces not associated with stokers, one of the best known is the Hawleydown draft. In this, there are two grates, coal being fired on the upper, throughwhich the draft is downward. Partially c
. Applied thermodynamics for engineers. grate is a decided advan-tage with many types of boilers. The smoke is distilled off at the coking underfeed stoker feeds the coal by means of a worm to the under side of the fire,and the smoke passes through the incandescent fuel. All stokers have the advantageof making firing continuous, avoiding the chilhng effect of an open fire door. Amongsoft coal furnaces not associated with stokers, one of the best known is the Hawleydown draft. In this, there are two grates, coal being fired on the upper, throughwhich the draft is downward. Partially consumed particles of coal (coke) fallthrough the bars to the lower gate, where they maintain a steady high temperaturezone through which the smoking gases from the upper grate must pass on theirway to the flue, 579. Superheaters ; Types. Superheating was proposed at an early date, andgiven a decided impetus by Hirn. After 1870, as higher steam pressures wereintroduced, superheating was partially abandoned. Lately, it has been reintro-. FlG. 279. Art. 579. — Cole Superheater. (American Locomotive Company.) duced, and the use of superheat is now standard practice in France and Germany,while being quite widely approved in this country. Superheaters may be sepa-rately fired, steam from a boiler being passed through an entirely separate machine,or, as is more common, steam may be carried away from the water to some space 428 APPLIED THERMODYNAMICS provided for it within the boiler setting or flue, and there heated by the partiallyspent gases. When it is merely desired to dry the steam, the superheater maybe located in the flue, using waste heat only. When any considerable increaseof temperature is desired, the superheater should be placed in a zone of thefurnace where the temperature is not less than 1000° F. With a difference inmean temperature between gases and steam of 400° F., from 4 to 5 B. t. u. may betransmitted per degree of mean temperature difference per square foot of
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