Part 15 (1/2)
[Ill.u.s.tration: FIG. 122.--Winterthur feeders.]
This apparatus--and all those based on the same principle--presents the advantage of proportioning the amount of water to the work of the engine; but in view of its rather sensitive operation it must be kept in perfect repair and carefully watched. Obviously, should the water contain impurities, the needle-valve will bind or the orifices will be obstructed, and thus the feeding of the water will be interrupted. This will not only result in the production of a poorer gas, but will lead to greater wear of the grates, which in this case are not sufficiently cooled by the introduction of steam.
[Ill.u.s.tration: FIG. 123.--Hille producer.]
=Air-Heaters.=--The preliminary heating of the air appears to be of great utility for keeping up a good fire. This heating is very easily accomplished, and is generally effected by utilizing a portion of the waste heat of the gases, a procedure which also has the advantage of cooling the gases before they pa.s.s through the was.h.i.+ng apparatus.
The heating of the air for supporting combustion takes place either before the addition of steam (Hille's generator, Fig. 123), or after the mixture as in Wiedenfeld's apparatus (Fig. 95). In the first case, the air pa.s.ses through a sheet-iron sh.e.l.l concentric with the basin of the generator, is there heated by the radiated heat, and is conveyed to the ash-pit by a tube into which leads the steam-supply pipe extended from the vaporizer. In the second type of heater, the mixture of air and steam is super-heated during its pa.s.sage through an annular piece arranged in the ash-pit of the generator.
[Ill.u.s.tration: FIG. 124.--Benz dust-collector.]
=Dust-Collectors.=--Dust-collectors are generally placed between the generator and the scrubber or washer. They may be formed of baffle-board arrangements against which the gases laden with dust impinge, causing the dust to be thrown down into a box provided with a cleaning opening (Benz, Fig. 124, and Pintsch, Fig. 118).
Some collectors are formed either by the vaporizer itself, terminating at its base in a tube which dips into water and forms a water-seal, as in the Wiedenfeld generator (Fig. 121), or by a water-chamber into which the gas-supply tube slightly dips (Bollinckx, Fig. 111). With this arrangement, the gas will bubble through the water and will be partly freed of the dust suspended in it. These water-chambers are generally fed by the overflow from the spray of the scrubber. There is thus produced a continuous circulation by which the dust, in the form of slime, is carried toward the waste-pipe or sewer.
=Cooler, Washer, Scrubber.=--Some manufacturers cool the gas in a tower with water circulation. Most manufacturers, however, simply cool the gas in the washer or scrubber. This apparatus comprises a cylindrical body of sheet-iron or cast-iron formed of two compartments separated by a wooden or iron grate or perforated part.i.tion. The upper compartment up to a certain level contains either c.o.ke, gla.s.s b.a.l.l.s, stones, pieces of wood, and the like. The top of the compartment is provided with a water supply in the nature of a sprinkler or spray nozzle. The lower compartment of the scrubber serves to collect the wash-water which has pa.s.sed through the substance filling the tower. An overflow in the shape of a siphon, provided with a water seal, carries the water to the waste-pipe either directly or after it has first pa.s.sed through the dust collector.
The gas drawn in enters the washer in the lower compartment either above the water level (Deutz, Fig. 125; Winterthur, Fig. 126), or through an elbow which dips slightly into the water (Benz, Fig. 127; Fichet and Heurtey producer, Fig. 128).
The gas pa.s.ses through the grate or part.i.tion which supports the material filling the tower, and travels through the interstices in a direction opposite to that of the water falling from the top. Under these conditions, the gas is cooled, gives up the ammonia and the dust which it may still contain in suspension, and is conveyed to the engine either directly or after pa.s.sing through certain purifiers. Care should be taken to place the pieces of most regular shape along the walls, so that the unevenness of their surfaces may not form upward channels along the sh.e.l.l, through which channels the gas could pa.s.s without meeting the wash-water.
[Ill.u.s.tration: FIG. 125.--Otto Deutz scrubber.]
[Ill.u.s.tration: FIG. 126.--Winterthur scrubber.]
[Ill.u.s.tration: FIG. 127.--Benz scrubber.]
The material most commonly employed in washers is c.o.ke in pieces of from 2-1/2 to 3-1/2 inches in size. This material is cheap and is very well suited for retaining the impurities of the gas. The largest pieces of c.o.ke should be placed at the bottom of the washer, and smaller pieces should form at the top a layer from 6 to 8 inches deep. In this manner the water is distributed more evenly and the gas is more thoroughly washed. Blast-furnace c.o.ke is best suited for this was.h.i.+ng, as it is more porous and less brittle than gas-works c.o.ke. It is advisable to put a baffle-board in front of the gas outlet to reduce the carrying along of water in the conduits.
[Ill.u.s.tration: FIG. 128.--Fichet-Heurtey scrubber.]
[Ill.u.s.tration: FIG. 129.--Scrubber-doors.]
The tower of the washer should be provided with three openings having air-tight closures, easily fastened by screws (Fig. 129). One of the openings is located in the lower compartment, slightly above the water level, to allow the deposits to be removed and to permit the cleaning of the orifice of the gas-supply tube, which is particularly liable to be obstructed. The second opening is placed above the grating which supports the filtering material. The third opening is provided on the top of the apparatus to permit the examination and cleaning of the water feed device and the gas outlet without the necessity of taking the lid of the washer apart, the joint of which is kept tight with difficulty.
The two openings last mentioned also serve for introducing and removing the filtering material.
=Purifying Apparatus.=--In some cases, where it is necessary to have very clean gas or where coal is employed which is softer than anthracite coal, and which therefore produces an appreciable amount of tar, supplementary purifying means must be employed. The apparatus for this purpose may, like the washers, be based upon a physical action or upon a chemical action. The physical action has for its purpose chiefly to retain the pitch and the dust which may have pa.s.sed through the washer.
This is accomplished by means of sawdust or wood shavings arranged in a thin layer and capable of filtering the gas without opposing too great a resistance to its pa.s.sage. These materials are spread on one or more shelves superposed to form successive compartments in a box closed in an air-tight manner by an ordinary lid or a water seal cover (Pintsch, Fig.
130; Fichet and Heurtey, Fig. 131). It may be well to point out that the presence of the water carried along will, in the end, destroy the efficiency of the precipitated materials, because they swell up and cease to be permeable to the gas. These materials must therefore be renewed rather frequently. To obviate this drawback, vegetable moss may be employed, which is much less affected by moisture than most filters and keeps its spongy condition for a long time.
[Ill.u.s.tration: FIG. 130.--Pintsch purifier.]
The chemical action has for its chief object to rid the gas of the carbonic acid and the hydrogen sulphide which certain fuels give off in appreciable amounts. The purifying material, in this case, is formed either by a mixture of hydrate of lime and natural iron oxide, or by the so-called Laming ma.s.s, which consists of iron sulphide, slaked lime, and sawdust, which last serves the purpose of rendering the material looser and more permeable to the gas. The Laming ma.s.s as well as other purifying materials will become exhausted in the course of chemical reactions. It can be regenerated merely by exposure to the air.
[Ill.u.s.tration: FIG. 131.--Fichet-Heurtey purifier.]
=Gas-Holders.=--The purifiers by themselves const.i.tute, to a certain extent, storage chambers for the gas before it is supplied to the engine; but in plants for the generation of gas without purifiers it is advisable to provide a gas-holder on the suction conduit near the engine.