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the gas manufacture; but in works where shale and rich | with ease be pushed in and overturned within the retort. cannel coals are distilled, common coal must be used in the The scoop deposits the coal neatly over the sole of the furnaces. At the Ivry Gas Works of the Compugnie 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 satisfactory 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, and for coal with a high percentage of volatile matter a higher temperature is requisite than is needed for coal less rich in gas. As the retorts in one setting are necessarily subject to somewhat 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 proportion 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 into 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 FIG. 6.-Section of Rotort Bed on line A A of fig. 6. the sides of the retorts, which requires to be periodically Parisienne d'Eclairage et de Chauffage par le Gaz, the removed by. " scurfing” with chisels, or burning it off with retorts are heated by gas on a method modified from the free admission of air or steam. Siemens regenerative gas furnace. Sectional illustra

The Hydraulic Main.-From the retorts the gas, after its production, ascends by means of pipes called ascensionpipes B (figg. 5 and 6) into what is termed the condensing or hydraulic main HH, which is a large pipe or long reservoir placed in a horizontal position, and supported by columns in front of the brick-work which contains the retorts 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 produced 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 connected by a flange with a dip-pipe C, arising from the upper side of the coudensing 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 Fig. 7.-Retort Setiing in Hislop's Furnace.

mouthpiece on the retort is removed, until it has forced the

liquid matter over the bend, a result which is easily pretions of a retort setting on this plan, and a description of vented by making it of a suitable length. The tar which the various arrangements connected with the regenerators is deposited in the hydraulic main overflows at the partition, and the controlling of the air and gas currents, will be and is carried by a pipe to the tar well. found in the article FURNACE, vol. ix. pp. 846, 847.

Condensation.

—The gas as it passes on from the hydraulic Ordinarily the work of charging and drawing the main is still of a temperature from 130° to 140° Fahr., and retorts is accomplished by manual labour, by means simply consequently carries with it heavy hydrocarbons, which, as of shovels for charging, and long iron rakes for drawing the its temperature falls, would be deposited. It is therefore spent charge. In the larger works it is usual to charge the a first consideration in ordinary working to have these retorts with a scoop semi-cylindrical in form, made a little condensable vapours at once separated, and the object of shorter than the retort, and of such a diameter that it can the condenser is to cool the gas down to a temperature

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Bearly that of the surrounding atmosphere. The first con- The practice of condensation and separation of tarry trivances employed for the purpose of condensation were matter by rapid cooling is condemned by Mr Bowditch and all constructed on the supposition that the object would be many eminent authorities, on the ground that thereby a best attained by causing the gas to travel through a great proportion of light hydrocarbons are thrown down with the extent of pipes surrounded by. cold water, and winding heavier deposit, which on another method of treatment through it like the worm of a still, or ascending upwards would form part of the permanent gas and materially enrich and downwards in a' circuitous manner. An improvement its quality. A system of treating gas has accordingly on this form of condenser, and one now in general use, is been introduced by Messrs Aitken & Young, in which the represented in fig. 8. It consists of a series of upright gas, kept at a high temperature, is carried from the retorts

into an apparatus termed an analyser, which consists of an enclosed series of trays and chambers arranged in vertical series, in principle like a Coffey still, the lower portion of which is artificially heated. In action the analyser separates the heavier carbonaceous part of the tarry matter in the lower part or chambers, and as the gas gradually ascends from one tray or tier to another, it is at once cool. ing and depositing increasingly lighter fuids, while it is meeting and being subjected to the purifying action of the light hydrocarbons already deposited. Thus on entering the analyser it meets, at a high temperature, heavy tar deposits, and it passes out of the apparatus cooled down to nearly atmospheric temperature after being in contact with the lightest fluid hydrocarbons.

Exhaustion.—To the subsequent progress of the gas considerable obstructions are interposed in connexion with its further purification and storing in the gas-holders, and the result of which would be that, were it not artificially propelled, there would be a pressure in the retort equal to the amount of the resistance the gas meets with in its onward progress. The relief of this back pressure not only improves the quality of the gas, but also increases its amount by about 10 per cent. Among the numerous methods of exhaustion which have been proposed since the operation was first introduced in 1839, there are several rotary exhausters, hav. ing more or less of a fan action, and recently an apparatus on the principle of a Giffard's injector has been introduced, chiefly in Continental works. A most efficient form is found in the piston exhauster, a kind of pumping engine with slide valves, which exhausts the gas in both the

upward and the downward strokes of its piston. The action of z u

the exhauster is controlled by a governor, which passes back

a proportion of the gas when the apparatus is working too E

fast for the rate of production in the retorts; and “pass

by" valves are arranged to carry the gas onward without Fig. 8.

passing through the exhauster should it cease to work from pipes connected in pairs at the top by semicircular pipes accident or any other cause. e, e, and terminating at the bottom in a trough X Y con

Purification.—The operations embraced under this head caining water, and divided by means of partitions in such a have for their cbject the removal from the gas of am. way that, as the gas enters the trough from one pipe, it monia, sulphuretted hydrogen, and carbonic acid as the passes up the next pipe and down into the next partition, main impurities, with smaller proportions of other sulphuric and so on to the end of the condenser. The cooling power and of cyanogen compounds. of this air condenser, as it is called, is sometimes assisted

The agencies adopted are partly mechanical and partly by allowing cold water to trickle over the outer surface of chemical, the separation of the ammónia being first effected the pipes. Annulur tubes for condensing are also used, in in the "scrubber," from which the gas passes on to completo which the gas is exposed to a much greater cooling surface, much greater cooling surface, its purification in the "purifiers.'

its purification in the “purifiers.' 'n early times the purify and in some large works the condensers are cooled by a ing was performed in a single operation by the use of milk current of water. In passing through the pipes the gas is of lime in the wet purifier, a form of apparatus still in use considerably reduced in temperature, and the tar and am- where wet purifying is permissible. moniacal liquor condense, the tar subsiding to the bottom of The Wet Purifier. This apparatus was supplied with a the troughs, and the ammoniacal liquorfloating on thesurface. cream of lime and water, but, although it was a most In course of time the water in the trough is entirely displaced efficient purifying agent, the ammonia now of so much value by these two gaseous products, and as they accumulate they was lost by its use, and the “ blue billy," as the saturated pass off into the tar-tank, from which either liquor can be liquid holding the impurities was termed, created an intolremoved by means of a pamp adapted to the purpose. The erable nuisance, and could be in no harmless way got rid New York Gas Lighting Company employ a multitubular of. Except in small works, wet purifying is not now condenser, consisting of two sets of eight boxes, each con- practised. taining 100 tubes 3 inches diameter by 15 feet long. The Scrubber.-The object sought in an ordinary Through each set of tubes, up one and down another, the scrubber is to cause a large amount of gas to come in congas travels, cooled by an external stream of water, while it tact with the smallest possible quantity of water, Bu as at traverses the 240 feet of piping in the condenser.

once to dissolve out ammoniacai gases, which are exceeii...gly

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soluble in water, to obtain a strong ammoniacal liquor from and down the other, and from the top a constant small the scrubber, and at the same time, as far as possible, to stream of weak ammoniacal liquor trickles down. Such a

sorubber, it is stated, is subject to clogging by deposits of tar, and equally efficieut work is done without that draw. back by an apparatus in which perforated iron plates occupy the place of the coke, and in the Livesey scrubber layers of thiu deal boards are employed. These boards are set in tiers perpendicularly, slightly crossing each other, with about f of an inch between each tier. Anderson's washer is a form of scrubber recently introduced, in which the interior is occupied with a series of rotating whalebone brushes, which dip into troughs of ammoniacal liquor, and in their revolution meet and agitate the gas in its passage upwards through the tower or column. The scrubber shown in section and plan in figs. 9 and 10 is a form introduced by Mr James Hislop. It contains 10 tiers of

trays of cast iron, perforated with 2-inch holes at a distance of 2 inches from centre to centre. The gas passes upwards through these, meeting in its course a shower of ammoniacal liquor pumped up and distributed by the rose arrangement shown in fig. 9. The bottom part of the scrubber, to the height of the first course of plates, is Gilled with liquor, which is repumped till it reaches the strength de sired for the manufacturer of ammonia sulphate.

The Purifiers. The ordinary lime purifier, bị sbich sulphuretted-hydrogen and carbonic acid are 'abstracted from the gas, consists of a large rectangular vessel seen in section in fig. 11. Internally it is occupied with ranges

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Fig. 9.--Hislop's Scrubber-Sectional Elevation. prevent the heavy hydrocarbons from being acted on-they

FIG. 11.-Section of Lime Purifier. being also soluble in water. The ordinary form of scrubber

of wooden trays or sieves A, made in the form of grids of 4-inch wood, with about half an inch between the bars, These are covered with slightly moistened slaked lime B to the depth of about 6 inches, and from three to six tiars of such sieves are sanged in each purifier. The gas enters at the bottom by a tube C, the mouth or inlet being protected from lime falling into it by a cover D, and it forces its way upward through all the trays till, reaching the lid or cover E, it descends by an internal pocket F to the exit tube G, which leads to the next purifier. The edges of the lid dip into an external water seal or lute H whereby the gas is prevented from escaping. The purifiera are generally arranged in sets of four, three being in use, through which the gas passes in succession while the fourth is being renewed ; and to control the course of the gas current among the purifiers, the following ingenious arrangement of centre valves and pipes was devised by Mr Malang (fig. 12).

It has a cover fitting within it in such a way as to communicate with the pipe a and either of the four inlet pipes, and also to com. municate between' one of the outlet pipes and the pipe h, which carries off the purified gas. The inlet pipes, b, d, f, admit the gas from the central case to the bottom of the purifiers; and the outlet pipes, c, e, g, return the gas from the purifiers back to the case,

after it has passed up through the layers of lime, and descended at 1260

the back of a partition plato in each purifier to the outlet pipes at

the bottom. a is the main inlet pipe for conveying the gas from Fig. 10.-Hislop's Scrubber-Plan.

the scrubber or the condenser, and h is the main outlet pipe for consists of a tower or hollow column, vertically divided into

conveying the gas to the gasholder. The central cylinder contains

water to the depth of 10 inches, and the ten pipes rise up through two, and filled with coke, &c. The gas passes up one side I the bottom to the height of 12 inches, so that the mouth of each is

WATER

VALVE

PIPE

8 WAY COCK

VALVE

TO
EXHAUSTER

AND
PURIFIERS

TO PUMP

FROM PUNPE

FROM
CONDENSER

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2 inches above the surface of the water. The cover which fits into separated in an uncombined form, 2Fe8 +39 = Fe,0, +2S the cylinder is 4 feet 3 inches

in diameter, and is divided into five The mixed material can be again employed in the purifica parts, the first of which, 1, fits over the inlet pipe a, and over either of the inlet pipes leading to the purifiers. The partitions 2, tion of the gas, and the process may be repeated until the

accumulation of sulphur mechanically impairs the absorbent powers of the mixture. The sulphocyanogen which accompanies the gas is retained by the oxide of iron, and gradually accumulates in the mixtare. For the separation of the carbonic acid, which is unaffected by this treatment,

the gas next passes on to a dry lime purifier, D

A

'The gas is now ready for use, and it is passed on through the station meter to register the amount made and

stored in the gas-bolders. At this stage it may be interest M

ing to compare the composition of the gas as it exists at different stages of the manufacture, as these show the result of the successive purifying processes. Taking 1000 cubic feet, the figures are

From Purifiers

DA

a

From From
Condenser. Scrubber.

4

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Fig. 12.

STORING AND DISTRIBUTION. 3, and 5 fit each over an inlet and an outlet pipe, while one parti. The Gas-holder.—This, which is frequently designated tion, 4, its over one outlet pipe from one parifier, and over the the gasometer, though incorrectly, since it does not in any pipe h, which leads to the gas-holder. In fig. 12 the arrangement is such as to open a communication between the inlet pipe a and way measure gas, but simply stores

. it for consumption, conthe purifier A. Now supposing the gas to have passed from the sists of two portions the "tank" T (bg. 13) and the scrubber into the centre of the cylinder, its only means of escape holder" G. The tank is a cylindrical pit, surrounding is to pass down the pique b into the purifier A, where it ascends through the layers of lime, and passing over the top of a dividing a central core, which is usually covered with concrete c at plate, descends and escapes from the bottom of the purifier by the top, and has its sides built of masonry or brick-work, p, b. ripec back to the cylinder. Here its only means of escape is by The tank is water-tight, and is filled to a high level will the pipe d, which conducts it to the purifier B, in which it ascends water, above which project two tubes mm, one being the and descends as before, returning by the pipe e to the cylinder, whence it proceeds by the pipe f into the purifier C, then along the inlet and the other the supply pipe which leads to the main pipe 3, which is shut off from communication with any pipe except governor.

, by which it is conveyed away to the gas-holder. By this Formerly gas-holders were made of leavy plate iron, arrangement the three purifiers A B C are being worked, while a strengthened by angle-iron and stays, and of so great e fourth purifier D is being emptied and recharged with lime. When it is found, on testing the gas, that the lime is upfit for its office, the purifier A is thrown out of work, and D is brought in. The frame is then shifted so as to bring the triangular division 1 over d, by which means B C D will be the working purifiers, and A will be thrown out of use. In this way, by shifting the frame round its centre over each of the four outlet pipes, any three of the purifiers can be brought into action.

G The “oxide" method of purifying the gas, originally introduced by M. Laming, and shortly afterwards patented by Mr Hills, is now largely used in ordinary gas-works. It is based upon the property of the hydrated oxide of iron to decompose sulphuretted hydrogen, a portion of the sulphur forming a sulphide with the iron. Quicklime is also used to separate carbonic acid, and the oxide of iron is mixed with sawdust or cinders (breeze) for the purpose of increasing the surfaces of contact, and this mixture is placed in the purifiers. When a sufficient quantity of gas has passed through it, the purifiers are opened, and the mixture is exposed to the air, under which new condition it combines with oxygen, aud again becomes fitted for use in the purifiers. The chemical changes which occur in these operations are thus stated. The mixture of hydrated oxide of

Fig. 13.-Section of Gas-holder. iron, &a, absorbs sulphuretted hydrogen, forming ferrous weight as to require a complex system of equilibrium chains sulphide and water, and liberating sulphur, thus :- and counterbalancing weights to relieve the gas from the Fe.0, +3H,8 = 2FeS+S+ 34,0. The ferrous sulphide, great pressure to which it would otherwise be subjected. by exposure to the air, absorbs oxygen, and its sulphur is They are now made so light that they require to be loaded

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in oraer to supply the required pressure, and their rise and station governor. In the form invented and manufactured fall are regulated by means of guide-rods i i round the tank. by D. Bruce Peebles, the bell or holder is enclosed in a For economy of space holders in which different segments gas-tight case or chamber, and a small portion of the inlet “ telescope over each other are now mucb employed. gas flows in and out of this chamber above the bolder. This form of holder consists of two or even three separate The pressure of this small quantity of gas is regulated by parts,- the upper having the form of the common gas- passing it through a small separate governor; and, acting on holder, and the other being open at the top as well as the the outer surface of the holder, this, in a very delicate and bottom. They are connected by the recurved upper edge of sensitive manner, performs the duty of weights in the older the lower fitting into a channel which runs round the bottom forms of governor. An arrangement similar in principle is of the upper, whereby the entire structure is rendered air- applied to the district governor by Bruce Peebles, the tight at the line of junction. Holders of great capacity minimum day pressure being secured by means of a stopcock are now erected in connexion with large works. The or screw-valve on the apparatus, and the maximum night Imperial Company in London possesses two, at Bromley pressure is controlled by a small subsidiary governor. The and Hackney, telescopic in form,--the outer segment principle of the small governor, which thus plays an immeasuring 200 feet in diameter by 35 feet deep, and the portant part in regulating large flows of gas, will be exinner 197 feet by 35. These holders are each capable of plained under consumers' governors, the apparatus being storing 2 million cubic feet of gas, which at sp. gr. 480 shown in section in fig. 18 below. would weigb 73 tons. A still larger holder is at the Supply Pipes. The street main and service pipes are Fulham station of the Gas Light Company, it being 223 tubes of malleable or of cast iron, the gauge of which feet in diameter and rising 66 feet, with a capacity equal must be arranged according to the quantity of gas to be to 3 million cubic feet.

supplied, the length it has to travel, and the pressure under The Governor.–An efficient control of the pressure of the which it is carried forward. Practical gas-engineers possess gas, along its whole course from the gas-holder to the point elaborated tables of data for the regulation of the size of of consumption, is an object of great importance for the their various supply pipes. Notwithstanding the utmost avoiding of leakage, for equal distribution, and for supply care and accuracy in the laying and fitting of street ing the burners at that pressure which yields the largest mains, leakage at joints is a constant source of annoyance. illuminating effect. Uncontrolled pressure may supply Under the most favourable conditions there is a discrepancy certain levels in & proper manner, but will leave low- of from 7 to 8 per cent. between the gas made and the lying districts insufficiently supplied, while the pressure amount accounted for by consumption, and the greater part in high districts will be excessive. The variations from of that loss is due to leakage in street pipes.

To convey simple difference of level may be very great. Thus, with the gas from the main pipes and distribute it in houses, a pressure of 1.7 inch at the Leith works, the gas would be pipes of lead or of block tin are generally used. delivered in some parts of Edinburgh at a pressure of 4.5 Consumers'Meters.—Of these there are twoforma in actual inches. The varying consumption from dusk onwards also use, the “wet” and the “dry." The former, the invention greatly affects unregulated pressure. To control and correct of Mr Clegg, is represented in the two sections (figs. 15 and these and other irregularities and disturbances governors 16), where cc represents the outside case, having the for are now used, -at the works or station for delivering the gas to the mains, in districts to correct variations owing to level, and beyond the consumers' meters for controlling

d house supply; while in certain forms of burners a regulating apparatus is also inserted. The principle on which all governors are based consists in causing the gas by its own pressure to act on some form of sensitive surface which opens or closes a valve or aperture iu proportion to the variations of pressure exerted on it. Fig. 14 is a dia. grammatic section of the common form of station governor. The course of the gas is indicated by arrows, d being the inlet

d and e the outlet pipe; c is a valve of conical form fitted to the seat i and raised or depressed by the weight f working by a cord over a pulley; bb is the bell or holder,

--a cylindrical vessel of sheet iron which rises and falls in the exterior vessel aa, in which water is

Fig. 15.

Fig. 16. contained to the level represented. The gas, entering at d, passes through the

of a flat cyclinder; a is the inlet tube and b the outlet pipe ; valve, fills the upper part of the inverted

9, g are two pivots, and h a toothed wheel fixed upon the vessel 86, which it thus partially raises,

pivots and connected with a train of wheel-work to register and escapes by e. If the pressure from

its revolutions. The pivots are fixed to and support a the holder be unduly increased or di

cylindrical drum-shaped vessel ddd, having openings e, e, minished, the buoyancy of bb will be increased or diminished in like proportion,

e, e, internal partitions ef, ef, ef, ef, and a centre piece ffff. and the valve being by this means more

The machine is filled with water, which is poured in at h or less closed, the quantity of gas escap

up to the level of i; and, on gas being admitted under a small ing at & will be unaltered. And not only will the governor accommodate

pressure at a, it enters into the upper part of the centre itself to the varying pressure of the

piece, and forces its way through such of the openings f as holder, but also to the varying quantities

are from time to time above the surface of the water, Ву of gas required to escape at @ for the

its aotion upon the partition which curves over the opening supply of the burners. Thus, if it were necessary that less gas should pass through

FIG. 14.-Section of a, a rotatory motion is communicated to the cylinder,-the e, in consequence of the extinction of a

Governor.

gas from the opposite chamber being at the same time exportion of the lights, the increased pressure thus produced at the pelled by one of the openings e, and afterwards escaping at

, holder would raise the governor, and partially shut the valve, b, as already mentioned. Wet moters work easily, and, leaving just sufficient aperture for the requisite supply of gas. when well set and properly supplied with water, measure

Numerous improvements have been mnde on the ordinary | the gas with much accuracy. But excess or deficiency

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