Part 4 (2/2)

Recently, however, a new type of governor, for application to burners, has been brought out by the same manufacturer, the construction of which is very different to that of the instrument referred to above; and as it is somewhat simpler in its details, and withal appears to be cheaper in construction, it seems destined to supersede the former instrument. In this new governor, instead of a leather diaphragm, there is a bell (or float) of steat.i.te, which is free to move, in the manner of a piston, within an inner cylindrical chamber contained within the outer case of the instrument. Attached to the centre of the float, and on its upper surface, is a tube sliding within another tube of somewhat larger area; the latter forming a continuation of the inner cylindrical chamber. The smaller tube is open at both ends, and thus communicates from below to above the float; the outer tube is closed at the top, but has an orifice in its side. The action of the instrument is as follows:--The gas, entering below the float, pa.s.ses through the inner tube to the upper part of the cylindrical chamber, and thence, through the orifice in the outer tube, to the burner. As the pressure of the entering gas exceeds that required to overcome the weight of the float, the latter is raised; the tube which is attached to it being propelled farther into the outer tube in which it slides, and, in so doing, partially closes the orifice in the side of the latter. In this way, according to the pressure of the gas acting upon the under side of the float, the area of the opening through which it must flow to get to the burner is reduced; and so the quant.i.ty of gas which issues from the burner remains the same under all pressures above that required to actuate the float. The instrument appears to be as reliable as it is simple, and to contain few parts calculated to get out of order; but, of course, whether or not it will retain its good qualities after long-continued use can only be proved by experience.

[Ill.u.s.tration: FIG. 17.--SUGG'S STEAt.i.tE-FLOAT GOVERNOR.]

[Sidenote: Peebles's needle governor-burner.]

[Sidenote: Efficiency of the needle governor-burner.]

Another instrument of this cla.s.s--the last which I shall notice--is Peebles's needle governor-burner. For simplicity combined with remarkable efficiency, it is undoubtedly ahead of all its compeers.

Somewhat similar in principle to Giroud's rheometer, it differs from that instrument in many of the details of its construction; and while dispensing with the use of liquid, maintains equal efficiency in operation. It was described as follows by Dr. W. Wallace, in a lecture on ”Gas Illumination,” delivered before the Society of Arts in January, 1879:[13]--”In a little cylinder stands a so-called needle, on the point of which rests a f.l.a.n.g.ed cone of exceedingly thin metal. At one side of the cylinder there is a small tube leading away the gas, and the orifice of which is influenced in area by the action of the cone. The instrument, by means of a screw leading into the side tube, can be made to deliver any desired number of cubic feet, which it does with surprising accuracy, provided that the pressure of the gas is not less than 6-10ths of an inch.” As to the efficiency of the instrument, Dr. Wallace proceeded to state:--”In trials that I have made, I have not found the variations of volume at different pressures to exceed 1 per cent.” For situations where this extreme nicety of operation is not absolutely essential, or where the rate of consumption is to be invariable, the instrument is constructed in a somewhat modified and simpler form. The small tube on the side of the instrument is dispensed with, and the gas permitted to pa.s.s through perforations in the lower part of the cone. With this alteration there is a nearer approach to the construction of the rheometer; but, as in that instrument, there is no provision for altering the rate of consumption to suit different circ.u.mstances.

[13] See _Journal of Gas Lighting_, Vol. x.x.xIII., p. 162.

[Ill.u.s.tration: FIG. 18.--PEEBLES'S NEEDLE GOVERNOR.]

CHAPTER V.

REGENERATIVE BURNERS.

[Sidenote: Temperature of a gas flame.]

As was remarked in the introduction to this treatise, recent years have witnessed a very considerable advance in the construction of gas-burners, and in the amount of light capable of being developed from each cubic foot of gas consumed. Undoubtedly the most noticeable feature of this advance is the successful application of the regenerative, or, as it would be more appropriately designated, recuperative system. Briefly stated, this consists in utilizing the heat of the products of combustion from the gas flame (which otherwise would be dissipated into the atmosphere) to raise the temperature of the gas before it is ignited; and, likewise, of the air necessary for combustion. The temperature of an illuminating gas flame is usually estimated to be between 2000 and 2400 Fahr.; and as the products of combustion must leave the flame at a temperature little, if at all, inferior to the former figure, it must be evident that there is an ample margin of heat for employment in this direction. A considerable proportion of the large amount of heat conveyed by those products of combustion which, under ordinary circ.u.mstances, is imparted to the surrounding atmosphere--often elevating its temperature to an unnecessary and prejudicial extent--is, by this method, returned to the flame; intensifying the process of combustion, and augmenting, in a remarkable degree, the illuminating power developed from the gas consumed. Thus the ultimate effect of the operation is to produce a concentration of heat in the flame, and the conversion of superfluous heat into beneficial light. Within a comparatively recent period, the utility of this process was strongly disputed; and it was stoutly maintained, by many persons, that as the immediate effect of ignition was to cause a temperature of more than 2000 Fahr. to be attained, the heating of the gas and air prior to their combustion could produce little or no beneficial effect upon the illuminating power of the flame. However, the falsity of this view of the case is conclusively demonstrated by practical experiment; the remarkably high results yielded by burners that have been constructed upon the regenerative system sufficiently attesting the correctness of the principles upon which they are founded.

Although, in general, both the gas and air supplies are heated, it is chiefly due to the latter that the beneficial effect noticed is produced; and this for two reasons. First, because the quant.i.ty of air is so much greater than the gas it is required to consume; being, at the nearest approach to theoretical perfection, fully six times its volume. Second, because four-fifths in volume of the air consists of inert nitrogen, which does not contribute anything to the heat of the flame, but, when applied in its normal, cold condition, abstracts no inconsiderable proportion of heat from it. Yet the heating of the gas itself is not without very appreciable influence. In an ordinary gas flame there is always an area of non-illumination around, and extending to a variable distance from the burner head. This is caused partly by the conduction of heat from the flame by the burner; but, in a greater degree, by the cooling action of the issuing stream of cold gas, as is shown by its extending farther from the burner in proportion to the pressure or velocity with which the gas issues. The prejudicial effect due to the former is obviated to a great extent by constructing the burner of steat.i.te, or other non-conducting material.

To remedy the latter, nothing will avail but the heating of the gas supply.

[Sidenote: Effects of heating the gas and air.]

The effect of heating the gas is to enlarge the area of the illuminating portion of the flame, and, in a minor degree, to enhance the intensity of incandescence to which the carbonaceous particles are raised. When the gas issues from the burner at a temperature little inferior to the temperature of ignition, the hydrocarbons it contains are immediately decomposed; the liberated particles of carbon are raised to the temperature of incandescence; and the illuminating area of the flame is extended downwards, even to the surface of the burner.

The heating of the air operates chiefly to produce and maintain a more elevated temperature of the flame; and, in this manner, contributes to the development of a higher illuminating power from the same area of flame. In the case of ordinary gas flames, the cold atmosphere by which they are surrounded, by abstracting heat from the flame, prevents the most favourable conditions for the development of light from being attained. When, however, the air immediately surrounding the flame has been previously heated, the particles of carbon (the incandescence of which furnishes the desired illuminating power) attain to a much more exalted temperature; and, consequently, give out a greater degree of light.

But there is yet another direction in which the prior heating of the air supply contributes to the development of improved illuminating power. Being heated, its density is lowered; so that in any given volume of air there is less weight of oxygen than when cold. The consequence is that as less oxygen is presented to a given surface area of flame, the separated particles of carbon remain for a longer period of time in the incandescent condition before being entirely consumed. Thus there are three distinct results produced by heating the gas and air before combustion--namely, first, the particles of carbon are liberated earlier in the flame; second, they are raised to a more exalted temperature; and, third, they remain for a longer time in the incandescent condition. The combined effect of all three is the improved illuminating power developed from the gas consumed.

[Ill.u.s.tration: FIG. 19.--BOWDITCH'S REGENERATIVE GAS-BURNER.]

[Sidenote: Bowditch's regenerative burner.]

So far back as the year 1854, the principle of heating the air supply to an Argand burner, by means of waste heat from the flame, was partially applied, with some success, by the Rev. W. R. Bowditch, M.A., of Wakefield. Mr. Bowditch's burner, which is shown in the accompanying diagram, contained, in addition to the ordinary chimney, an outer gla.s.s chimney, which extended for some distance below the inner one, and was closed at the bottom; so that all the air needed to support the combustion of the gas was required to pa.s.s down the annular s.p.a.ce between the chimneys, and in its pa.s.sage became intensely heated by contact with the hot surface of the inner chimney, as well as by radiation from the flame itself. This burner contained many defects. Amongst others, the inner chimney could not long withstand the intense heat to which it was subjected, and, in consequence, had to be frequently renewed; the heating of the air was not effected solely by the products of combustion, but, perhaps in a greater degree, by the abstraction of heat from the flame itself; while, at best, this heating was but partial. Yet, these defects notwithstanding, the burner showed very clearly the beneficial results attending even a partial application of the principle; as, in the illuminating power it developed from the gas consumed, a clear gain of 67 per cent. over the ordinary Argand burner was obtained. Although the drawbacks connected with the construction of Mr. Bowditch's burner prevented its ever receiving general, or even extensive adoption, its simplicity has gained for it the distinction of being freely copied by so-called inventors of a later day.

[Sidenote: Invention of the Siemens regenerative burner.]

It was left to Herr Friedrich Siemens, of Dresden, to produce a burner which, while applying the principle of regenerative heating in the most scientific and complete manner, should also be adapted to the ordinary conditions of gas lighting. After much experimenting on the subject, a burner embodying the essential features of the regenerative system was invented by this gentleman in 1879; and so great was the advance which its performances manifested over anything previously attained, so wide the prospect of further achievements which was opened out, that it may fairly be said to have inaugurated a new era in gas illumination. In this burner the products of combustion were made to give up a considerable portion of their heat to the gas and air, as the latter pa.s.sed to the point of ignition; the flame itself not being called upon to contribute in any degree to this result.

Although, as was but natural, the first attempts towards the construction of such a burner were very crude, and but partially successful in their results, the inventor persevered in his endeavours to work out his ideas into practical and thoroughly satisfactory shape. It was not until after it had gone through many modifications that the burner acquired the peculiar form which now distinguishes it, and attained to its present stage of perfection. Before proceeding to describe an example of the burner as now constructed, it is necessary to state that the principles embodied in Herr Siemens's invention are equally well adapted--and, indeed, are applied with equal success--to the construction of flat-flame and Argand burners; but as the distinctive features of the invention are common to both cla.s.ses of burners, it will be quite sufficient to describe in detail one of the latter type.

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