THE COLLIERY GUARDIAN AND JOURNAL OP THE COAL AND IRON TRADES. Vol. CIX. FRIDAY, FEBRUARY 5, 1915. No. ». MECHANICAL STOKING.* By EDWIN Hand Firing .—Long before steam raising received the scientific attention it now commands, the coal bill usurped every other consideration. Periodical enquiry, however, led to the discovery of variations in fuel con- sumption, more noticeable when changes took place in the engagement of firemen. One somehow managed to keep up the steam without over-exertion; while another made the task both constant and laborious. Compari- sons of this kind had the effect, in some manufacturing districts, of fixing a standard of coal consumption; any saving upon which was distributed by way of bonus to the engineering department, at such rate per ton as might.be mutually agreed upon. As may be imagined, these emoluments, added to the then permissible calls upon the supply agency, elevated engine and boiler house duties to an enviable position in the. labour market of those days. These investigations did more : they encouraged a spirit of emulation, and led to inter- changes of ideas amongst the faculty, which in turn brought about economies in hand firing. Fig 1. The knowledge now acquired by chemical analysis, then.came—but.not with.the same exactitude—as the result of careful. observation when handling various classes of coal. Thus the intelligent fireman became quite an adept in assessing comparative values, and in aiding combustion by prejudging the laying on of fuel according to its kind, or in gauging the effective admis- sion of uir, as structural arrangements dictated. As the result of laboratory tests, exact calorific values are now ascertainable. Our scientific conclusions would, however, prove of little practical value without the intelligence behind the fire shovel. This must therefore of necesity decide the issue between calori- metric indications and the heat .energy obtainable under actual working conditions. For example, according to laboratory tests, the correct admission of air for certain specified grades varies from 9’86 to 12 lb. per pound of coal. But if these- figures are-compared with actual working differences, which range from, say, 18 to 501b., we shall.the more readily understand why so much, * From a paper published in the Proceedings of the South Wales Institute of Engineers, January 21, 1915. KENYON. after all, must be left to the discretion of the aforesaid intelligent fireman. Whatever its limitations, hand firing most assuredly provides the best opportunities for critical observation, and for directing our efforts towards realising the larger possibilities of mechanical stoking. ■. Smoke Abatement.—'Inseparably associated with our present enquiry is the vexed question of smoke abate- ment, to consider which the President of the Local Government Board has appointed a Departmental Committee. Many and varied are the propositions submitted with the object of effecting such complete combustion that no particles of consumable matter shall escape. In a paper on “ Smoke Abatement,” Mr. George Gemmel draws interesting comparisons between the domestic and industrial smoke of Glasgow. According to his estimate, the city contains 1,150 factory chimneys, each discharging 672,000 cu. ft. of waste gases per hour, or a total equal to 46,000 household fires—of which, however, there are no less than 195,000 (reckoned at 17,500 cu. ft. each). At this rate air pollution from domestic hearths must be four times greater.than that' attributable to the smoke stacks of commerce. Scientific investigation goes to prove that the evapor- ative power of HE of average English coal is 15*2. But if the volatile parts are allowed to go unconsumed in the form of smoke, the fixed carbon left would only Fig. 2. be equal to an evaporation of one-half its estimated value.. Since smoke, then, is merely the outward and visible sign of inward prodigality, there is more in its sup- pression than meets the eye of the casual observer. A new body, known as the London Coke Committee, is making desperate efforts to induce factory owners to use coke or other smokeless fuel. This committee reports that, through the influence of their experts, users of coal, aggregating 50,000 tons per year, have been persuaded to adopt their suggestions. Suppose, however, the system thus advocated won anything like universal favour. The consumption of coal (almost entirely bituminous) will be somewhere in the neigh- bourhood of 60,000 tons per week for the Lancashire cotton spinning mills alone—reckoned at the usual spindlage rate. Then, again, there is the well-known difficulty attending the ignition of coke or coke breeze, without intensifying the draught to the extent of carry- ing off minute crystals as they break away from the crackling fire—such as gleam on the pavement and we grind under our feet in any district where there happens to be blast furnaces. . The Coking Method of Firing.—Allowing the super- lative advantage claimed for coke as a smoke preventer over other classes of fuel, similar, but far more economical, results may be obtained by what is known as the coking method of firing. This consists of piling ■every fresh charge of coal near the dead plate, where ignition - takes place and. the hydrocarbon gases: are given off. These are distilled while passing over the already incandescent fire. In this manner the coal is reduced to coke, which, in its red, hot state, is gradually pushed forward; so that by the time it reaches the far end of the grate its combustion is complete, leaving only ashes and . clinkers by way of residual. With side firing—so-called because the coal , is thrown alternately to right and left—each side in turn becomes incandescent, and partially consumes the smoke of the other. As may be imagined; this system is not so readily manipulated. Nor can it be quite so effective as the steady push from the front, seeing that the flames must follow the direct pull of the draught, thereby losing some of the benefits afforded even by a restricted •area of incandescence. On the other hand, expert opinion goes to prove that, while evaporation more readily responds to the spread- ing or sprinkling of fuel over the entire grate, steam pressure is not so readily maintained, and smoke •emission is not held in check to the same extent as by either of the methods just mentioned. The Menace of the Open Door.—Whatever system of hand ■ firing may be adopted, the inrush of cold air, consequent upon the open door, when re-charging or clearing the grate—against which closed dampers afford •but indifferent protection — must prove a constant menace to our advancement in the direction of absolute efficiency. And when the generally accepted principle is carried into practice, viz., that light charges, frequently applied, are more effective than overloading Fig. 3. at longer intervals, we- may reasonably presume upon such irregularities as decomposition of the highly sensitive gases and formation of soot, following a drop in temperature. ' Inferior Coal.—If tabulated analyses of fuel values are to be relied upon, there must be considerable differences even in Welsh coal, seeing that the cash equivalents represent a fall of at least 30 per cent, between the highest and lowest grades. Carry the comparison still farther, so . as to. include the. commonest “ slack” of other districts—practically valueless, for steam raising without artificial aids—and the difference widens to fully 70 per cent. The chief functions, then, of the mechanical stoker are those of relieving the innate poverty of baser sorts, by regulating otherwise erratic supplies, and accelerating laggard combustion by precision in air feeding. Mechanical stokers are almost as diverse in structural detail as methods of hand firing. ' The , choice may,, however, be said to rest between the two main principles •embodied in the “ coking ” and “ spreading ” methods already discussed. An Automatic Coking Stoker.—All mechanical stokers, it will be observed, are provided with coal hoppers, and these are fed either by hand or by means of elevators connected with the bunkers. It will also be observed that furnace doors are specially arranged to meet the