Modern Gasworks Practice

142 MODERN GASWORKS PRACTICE 2. Incomplete combustion of CO to CO2. 3. Too rapid travel of primary air through, fuel-bed. 4. Too rapid travel of hot gases through setting, or too much chimney draught. 5. Losses due to fuel falling through firebars into ashpit or remo ved with clinker. 6. Radiation and convection losses. 7. Extensive variation in composition of producer gas. 8. Insufficiency of gas. The main sources which account for loss of heat have been fully dealt with in Chapter III. With regard to the first two items, tliese are, of course, avoidable, providing that no faults have been introduced in the design of the producer; and they are best remedied by systematic analysis of both the producer and waste gases. It is necessary, however, to emphasize the faet that satisfactory gas tests do not in any sen.se ensure good heats; for, although the combustibles may be present in ideal proportions, it is quite possible that they may not be present in sufficient quantities. The third item in the list lends itself to adjustment, providing, again, that the construction of the producer is not to blame. If this is the case the trouble can usually be traced to an insufficiency of grate area, the importance of providing adequately for this having been somewhat underestimated by designers in the past. Slow travel of the primary air through the fuel-bed is ensured with abundant grate area (see Chapter III, p. 82); whilst there will be less “ slip ” up the sides of the furnace, and a shallower bed of clinker will be formed. Owing to the extended contact of primary air and coke, the quality of the gas will be materially improved. On no account should the velocity of draught be so great as to draw ofi the gases from the setting before they have been cooled down in the regenerators by at least 375° C., and the base of the waste-gas oharmel should be almost devoid of colour. This question of draught may affeet the formation of the producer gas in two ways. First, the rate of travel of air through the fuel-bed may be sufficiently slow for the formation of carbon dioxide in the lower portions of the furnace, but the time of contact may not be sufficiently long for the reduction of this gas to carbomc oxide— hence an excessive proportion of incombustibles in the furnace gas may result. So far as the draught is concerned, it is the chimney height and flue area which are of importance in this respect (see p. 86). CLINKER AND ASH A word is necessary here with regard to the troublesome formation of clinker with some types of producer. When clinker difficulties set in, it is, perhaps, the natural inclination of the man charged with its removal to make disparaging reference to the coke supplied to the producers at the time. A coal with a heavy ash conten.t must necessarily inerease the amount of inert matter to be cleaned from the producer; but the secret of long periods without clinkering is due to the physical condition of the non-combustible portions of the fuel after passing through the producer. With a strong draught a large proportion of the ash in the fuel is fluxed, with. the con-sequent formation of clinker ; whilst with a slow draught the heat of the fuel-bed is