Modern Gasworks Practice

 I per cent. 6 1 63 64 MODERN GASWORKS PRACTICE gen; for, owing to the modern use of a small supply of steam, also to the impossi-bility of ensuring the entire “ burning-off ” of all coke charged from the retort into the fumace, a certain quantity of hydrogen and methane is invariably present. The following, in fact, is the average composition under good conditions :— Carbon monoxide Carbon dioxide Hydrogen Methane Nitrogen Witli regard to the regulation of the weight of the combustion products, th.e gas engineer keeps the weight to a minimum by manipulation of the fumace dampers in conjunction with analyses of the waste gases. In order to allow for variation in the composition of the producer gas no attempt is made to admit the exact quantity of air required, but the waste of fuel is curtailed by ensuring a slight excess of air— in other words, by admitting sufficient air until oxygen is present in the waste-flue gases. The absence of oxygen in these gases is a fairly sure indication of the presence of carbon monoxide—the latter being a useful combustible product, and accounting for the blue flame so frequently to be seen emerging from the chimney skafts of improperly worked settings. An analysis of the gas drawn from the waste flues of a retort setting should approximate very closely to— Carbon dioxide.........................................190 per cent .............................................. .............................................. Oxygen.................................................0-4 „ Nitrogen..............................................._ ” If oxygen is absent, then CO will almost surely be present, and the secondary air should be increased until th.e required conditions are obtamed. At the sanic time, the above percentage of oxygen is quite within. the limits of practical adjustment, and any excess should be curtailed by a reduction of the secondary-air supply. THE EFFECT OF REGENERATION It has been pointed out that the ultimate combustion temperature is governed in part by the temperature of the mixture before ignition takes place. This being the case, the quantity of heat in the gases before combustion can be added to the heat of combustion ; th.us the total quantity of heat available for raising th.e temperature of the waste products is increased in proportion to the intensity of the pre-liminary heating. Before the introduction of the regenerator, one of the chief causes of loss arose from the escape of the waste products from the retort settings at unnecessarily high, temperatures, this occurring in both. “ direct-fired ” and generator settings. In the latter type the secondary air is certainly heated up, but merely at the expense of the producer; and the system owes its greater efficiency mainly to the reduction of losses by radiation, to its flexibility, and to increased facili-ties for the regulation of the air supply. In such, cases the normal temperature at which. the gases are allowed to leave the setting is in the neighbourhood of 950° C.; but by the transference of sensible heat from these gases to the inflowing secondary air _____________