Modern Gasworks Practice

 WATER GAS 715 remain running at full speed during the period of the “ run,” when they are performing no useful work. Those having an eye to small items have pointed out the wastefulness of such procedure, with the result that in some instances a cut-out is arranged to reduce the consumption of steam in the blower engine while the “ run ” is proceeding. The arrangement may be easily effected in the case of turbines, but it presents a greater problem with reciprocating engines. There is, moreover, some question as to its advisability, for the amount of throttling which may safely be practised with a turbine is limited, as the latter must not be checked so that its critical speed be passed. In addition, the eflect of the air biast pressing up against the liot-gas valve during the “ run ” is desirable, in that, if the valve is not perfeetly gas-tight, gas from the generator will be prevented by the biast pressure (which is usually greater than the gas pressure in the generator) from leaking back into the biast main, although such an occurrence is unlikely with modem valves and interlocking gear. PRACTICAL CONSIDERATIONS In order to ensure the effeetual and economical operation of a water-gas plant it is essential that frequent attention be given to what to many may be considered only minor features of the process. Exceptional results, however, as in the manu-facture of coal gas, are obtained by observing the utmost care in connection with details rather than by concentrating upon the more apparent items. The following may be considered amongst the chief factors influencing working efficiency :— (1) The Fuel-bed. In the single generator plant (as opposed to the twin variety) it is generally laid down as a golden working rule that the depth of the fuel-bed must always be maintained. If a shallow fuel-bed is employed it must inevitably follow that the reduction of C02 to CO will not take place to the same extent as with a deep fuel-bed—hence, the final product will contain an abnormal proportion of the former gas. At the present day the presence of a small extra quantity of C02 is of material importance; for, as gas is now sold in therms, C02 is a constituent whicli yields nothing in the way of revenue and which occupies valuable space that may be better employed. The author recommends that in no case should the ftiel be permitted to fall below 7 feet in depth. On the other hånd, too great a depth of fuel means a higher proportion of CO in the escaping blow gases which to-day (in view of the general tendency to manufacture blue gas) liave few or no subsidiary duties to perform. By working with a depth of 7 feet the period of biowing may be curtailed (with a corresponding gain in available gasmaking time), and the capacity of the setting will be appreciably inereased. The additional amount of gas obtained will have an important cfl'ect in reducing cost of manufacture. If this depth of fuel is employed the coke should be moderately small, nothing greater than 3-inch pieces being permitted. If a particularly heavy coke is made use of, less of it will be required as compared with the normal gasworks variety, therefore there need be no hesitation in reducing the fuel depth. The purity of the coke is an important factor, a high percentage of ash causing the clinker to arch over and hang up. The most effeetive remedy for troubles of the kind is to arrange for a system of periodical