Modern Gasworks Practice

90 MODERN GASWORKS PRACTICE that the analysis of the waste products by weight is:—Carbon dioxide, 26-9 per cent.; oxygen, 0-4 per cent.; and nitrogen, 72-7 per cent. The only constituent derived from carbon is the carbon dioxide, and a simple calculation shows that the amount of coke (10 per cent, ash) which. yields 100 1b. of waste gases is 8-16 1b. In other words, 1 Ib. of coke gives 12-26 1b. of dry gases, a figure which. is inclusive of the excess air, but exclusive of steam. It must be bome in mind, however, that to-day it is customary to admit a certain amount of live or exhaüst steam to the fuel-bed, and from recent trials the writer finds that in some instances the quantity may amount to nearly 100 1b. per producer per hour. Inclusive of the steam, therefore, the weight of the waste products amounts to 12-76 1b. per Ib. of coke consumed. Accordingly, 1 lb. of ch.imn.ey gases consists of the following :— Carbon dioxide ......................... O-’öS lb ............................................ 0-004 lb. _____________________________________________ 0-699 lb. ............................................ 0-039 lb. Oxygen Nitrogen Steam ________ 1-000 lb. The specific heats, at constant pressure, of the above gases may be taken as :__ Carbon dioxide_____________________.... n oi r Oxygen...................................................................0-218 ............................................................... Nitrogen...............................................................0-244 ............................................................... Steam....................................................................0-480 Hence, the mean specific heat of the waste gases is :__ Weight of CoJ x -216 = 0-0557 „ O2 x -218 = 0-0009 „ N2 x -244 = 0-1705 „ Steam x -480 = 0-0187 ______ Total — 0-2458 or, say, 0-246 praotically. Betört Bench Possibilities. If consideratioa is given to a standard, regenerative horizontal retort setting containing ten 20-feet retorts, then the fuel fed into the producer per hour will be in the neighbourhood of 1-6 cwt. This is based on the assumption th.at 12-h.our retort charges of 12 cwt. each. are employed, and that carbonization demands 3-3 cwt. of coke per ton of coal. The temperature of the waste gases as they leave the regenerator varies between 1,000° and 1,200° F., more often th.an not the latter figure prevailing, although tlieoretically it is higher than is desirable. Accordingly, if the temperature of the available products is taken at 1,200° F., then H= W X S (T — 0, where H is the available heat in waste products in B.Th.U., W the total weight of products in. lb.,S th.e mean specific heat = 0-246, and T and t are tlie temperatures F. of the gases before and. after passing boiler. Hence from 1 lb. of coke containing 10 per cent, of ash:__