Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/102

Rh 92 the gas manufacture; but in works where shale and rich cannel coals are distilled, common coal must be used in the furnaces. At the Ivry Gas Works of the Conzpztgrzie r a ,'I 4 I, /. ‘ ~ .,  " /I/4,” ‘ ,, 2% 5 -, 5 s 7 e T; —- --L 7.17 -1. ft» —. 1 FIG. 6.—Section of Retort Bed on line A A of ﬁg. 5. .u Is: n 1 B l?FI _l l‘‘—7 * i Parisielme (l'E'claz'7-age et de Chazzﬂtzge par le Gas, the retorts are heated by gas on a method modiﬁed from the Siemens regenerative gas furnace. Sectional illustra- BLOCK FIG. 7.—Retort Setting in Ilislop’s Furnace. tions of a retort setting on this plan, and a description of the various arrangements connected with the regenerators and the controlling of the air and gas currents, will be found in the article FURNACE, vol. ix. pp. 846, 847. Ordinarily the work of charging and drawing the retorts is accomplished by manual labour, by means simply of shovels for charging, and long iron rakes for drawing the spent charge. In the larger works it is usual to charge the retorts with a scoop semi-cylindrical in form, made a little shorter than the retort, and of such a diameter that it can GAS with case be pushed in and overturned within the retort. The scoop deposits the coal neatly over the sole of the retort, and of course the lid is much more quickly replaced than can be done with shovel charging. Numerous attempts have been made to introduce purely mechanical means of feeding retorts, hitherto with indifferent success,— such devices as a travelling endless sole and a rotating sole having been tried without good effect. A charging machine and a drawing machine, worked by hydraulic power, have been introduced by Mr Foulis, the engineer of the Glasgow Corporation Gas Works, but after prolonged trial both in Glasgow and in Manchester, these have not yet proved satis- factory in action. In West's patent the charging is effected by the introduction of a small waggon within the retort, which distributes the charge evenly and uniformly Neither has it, however, met general acceptance. The retorts are kept at a bright red heat, a11d for coal with a high percentage of volatile matter ahigher tempera- ture is requisite than is needed for coal less rich in gas. As the retorts in one setting are necessarily subject to some- what different amounts of heat, the charges in those nearest the furnace ﬁre, and consequently most highly heated, must be drawn more frequently than the others, as otherwise the quality of the gas would be deteriorated, and a large pro- portion of sulphur‘ compounds would be given off from the overburnt coke. In drawing a charge the lid is first slightly opened and the escaping gas lighted, to prevent an explosion or “ rap" that would otherwise ensue. The gas is prevented from escaping outward by the ascension pipe dipping i11to the hydraulic main as afterwards explained ; but in some cases special valves are ﬁtted on the ascension pipe to prevent a back rushing of the gas. A carbonaceous deposit forms on the sides of the retorts, which requires to be periodically removed by “ scurﬁng ” with chisels, or burning it off with free admission of air or steam. The II3/draulic 1l[ain..—From the retorts the gas, after its production, ascends by means of pipes called ascension- pipes B (ﬁgs. .5 and (3) into what is termed the condens- ing or hydraulic mai11 HH, which is a large pipe or long reservoir placed in a horizontal position, a11d supported by columns in front of the brick-work which contains the re- torts A. This part of a gas apparatus is intended to serve a twofold purpose :—ﬁrst, to condense the tar and some ammoniacal liquor, and secondly, to allow each of the re- torts to be charged singly without permitting the gas pro- duced from the others, at the time that operation is going on, to make its escape. To accomplish these objects one end of the hydraulic main is closed by a ﬂange ; and the other, where it is connected with the pipes for conducting the gas towards the tar vessel and purifying apparatus, has, crossing it in the inside, a partition occupying the lower half of the area of the section, by which the condensing vessel is always kept half full of liquid matter. The stand-pipes are con- nected by a ﬂange with a dip-pipe C, arising from the upper side of the condensing main HH, and as the lower end of it dips about 2 inches below the level of the liquid matter, it is evident that no gas can return and escape when the mouthpiece on the retort is removed, until it has forced the liquid niatter over the bend, a result which is easily pre- vented by making it of a suitable length. The tar which is deposited in the hydraulic main overﬂows at the partition, and is carried by a pipe to the tar well. C'onden.sation.——T he gas as it passes on from the hydraulic main is still of a temperature from 130° to 140° Fahr., and consequently carries with it heavy hydrocarbons, which, as its temperature falls, would be deposited. It is therefore a ﬁrst consideration in ordinary working to have these condensable vapours at once separated, and the object of the condenser is to cool the gas down to a temperature