Part 34 (1/2)

Total water evaporated, 153,543 pounds

Per cent of moisture in steam, 05 per cent

Heat value per pound of dry coal, 13,516

Heat value per pound of combustible, 15,359

The factor of evaporation for such a set of conditions is 10834 The actual evaporation corrected for moisture in the steam is 152,775 and the equivalent evaporation frorees is, therefore, 165,516 pounds

The total dry fuel will be 17,500 97 = 16,975, and the evaporation per pound of dry fuel frorees will be 165,516 16,975 = 975 pounds The heat absorbed per pound of dry fuel will, therefore, be 975 9704 = 9461 B t u Hence, the efficiency by (31) will be 9461 13,516 = 700 per cent The total combustible burned will be 16,975 - 2396 = 14,579, and the evaporation frorees per pound of combustible will be 165,516 14,579 = 1135 pounds Hence, the efficiency based on combustible from (32) will be (1135 9704) 15,359 = 7179[should be 7171]

For approximate results, a chart may be used to take the place of a co 39 shows such a chart based on the evaporation per pound of dry fuel and the heat value per pound of dry fuel, from which efficiencies may be read directly to within one-half of one per cent It is used as follows: Fro the evaporation per pound of fuel, with the vertical line, representing the heat value per pound, the efficiency is read directly froonal scale of efficiencies This chart may also be used for efficiency based upon corees and the heat values are both given in terms of combustible

[Graph: Evaporation froainst BTU per Pound of Dry Fuel

Fig 39 Efficiency Chart Calculated froonal Lines Represent Per Cent Efficiency]

Boiler efficiencies will vary over a wide range, depending on a great variety of factors and conditions The highest efficiencies that have been secured with coal are in the neighborhood of 82 per cent and from that point efficiencies are found all the way down to below 50 per cent

Table 59[57] of tests of Babcock & Wilcox boilers under varying conditions of fuel and operation will give an idea of whatconditions

The difference between the efficiency secured in any boiler trial and the perfect efficiency, 100 per cent, includes the losses, some of which are unavoidable in the present state of the art, arising in the conversion of the heat energy of the coal to the heat energy in the steam These losses may be classified as follows:

1st Loss due to fuel dropped through the grate

2nd Loss due to unburned fuel which is carried by the draft, as s or up the stack

3rd Loss due to the utilization of a portion of the heat in heating the moisture contained in the fuel frorees; to evaporate it at that temperature and to superheat the steaases This steam, of course, is first heated to the teives up a portion of this heat in passing through the boiler, the superheating to the teree to be considered

4th Loss due to the water foren in the fuel which must be evaporated and superheated as in ite of the moisture in the air supplied froases

6th Loss due to the heating of the dry products of coases

7th Loss due to the incomplete combustion of the fuel when the carbon is not completely consumed but burns to CO instead of CO_{2} The CO passes out of the stack unburned as a volatile gas capable of further combustion

8th Loss due to radiation of heat fros

Obviously a very elaborate test would have to be made were all of the above items to be determined accurately In ordinary practice it has become customary to su the losses being given in each instance by a typical exa of moisture in the fuel frorees, evaporate it at that teases This in reality is the total heat above the temperature of the air in the boiler room, in one pound of superheated steaases, e of moisture in the fuel As the total heat above the temperature of the air would have to be computed in each instance, this loss is best expressed by:

Loss in B t u per pound = W(212-t+9704+47(T-212)) (33)

Where W = per cent of moisture in coal, t = the temperature of air in the boiler rooases, 47 = the specific heat of superheated steaas temperature, (212-t) = B t u necessary to heat one pound of water frorees, 9704 = B t u necessary to evaporate one pound of water at 212 degrees to steam at atmospheric pressure, 47(T-212) = B t u necessary to superheat one pound of stearees to temperature T

[Illustration: Portion of 15,000 Horse-power Installation of Babcock & Wilcox Boilers, Equipped with Babcock & Wilcox Chain Grate Stokers at the Northumberland, Pa, Plant of the Atlas Portland Cement Co This Company Operates a Total of 24,000 Horse Power of Babcock & Wilcox Boilers in its Various Plants]

(B) Loss due to heat carried away in the steaen coen unites with 8 pounds of oxygen to for of item (A), therefore, this loss will be: