Part 15 (2/2)
[Ill.u.s.tration: FIG. 132.--Pintsch regulating-bell.]
In order to save floor s.p.a.ce the gas-holder may be placed in the bas.e.m.e.nt. Preferably the capacity of the holder should be at least from 3 to 4 times the volume of the engine-cylinder. The holder should also be provided with a drain-c.o.c.k and with a hand-hole located at some accessible point, so that the slimes and pitch which tend to acc.u.mulate in the holder can be removed. In some cases the gas-holder is formed by a small regulating bell, the function of which is to insure a uniform pressure. This bell is emptied during the suction period and is filled during the three succeeding periods of compression, explosion, and exhaust (Pintsch, Fig. 132).
[Ill.u.s.tration: FIG. 133.--Types of gas-driers.]
=Drier.=--Sometimes, toward the end of a producer-gas pipe, a drier is located for the purpose of keeping back the water carried along, the drier being similar to that employed in steam conduits. It will, of course, be understood that such driers are useful only in plants having no purifiers (Fig. 133). The employment of the drier is advisable to prevent the entrance of moist gas into the cylinder and the condensation of moisture on the electric igniter.
[Ill.u.s.tration: FIG. 134.--Elbow with closure.]
=Pipes.=--The pipes connecting the several parts of a gas-producing plant should be disposed with particular care to insure tightness and cleanliness. It should be borne in mind that the gas is under a pressure below that of the atmosphere, and that the least leakage will cause the entrance of air, which will impair the quality of the gas. The greatest care should therefore be taken in fitting the joints. These joints are numerous, because there are joints wherever tubes are connected with each other and with the apparatus. Furthermore, all elbows should be provided with covers held in place by a yoke and compression screw, this being done for the purpose of providing for the introduction of a brush or other implement to remove the dust and pitch (Fig. 134).
For conduits of small diameter the elbows with covers may be replaced with =T= connections, or connections provided with plugs.
Gas piping in the immediate neighborhood of the c.o.c.k for admitting gas to the motor should be provided with a conduit of proper diameter leading to the open air and serving to clean the apparatus and to fill them, during the operation of the fan, with gas suitable for combustion.
This conduit should be provided with a stop-c.o.c.k. Test-c.o.c.ks for the gas should be placed on the piping immediately beyond the vaporizers, the scrubber, and near the engine.
It will also be well to provide water-pressure gages before and after the scrubber to enable the attendant to ascertain the vacuum in the conduits and to adjust the running of the apparatus.
=Purifying-Brush.=--As an additional precaution against the carrying of tar to the engine, metallic brushes are often employed, these brushes being spiral in form and enclosed in a cast-iron box interposed in the gas-supply pipe immediately after the engine. The gas will be broken up into streams by the obstacles formed by these brushes and will be freed of the suspended tar (Fig. 135). These brushes should be carefully cleaned at regular intervals. The best way of doing this is to drop them into kerosene or some other suitable solvent.
[Ill.u.s.tration: FIG. 135.--Metal purifying-brush.]
CONDITIONS OF PERFECT OPERATION OF GAS-PRODUCERS
These conditions depend upon the workmans.h.i.+p or upon the system of the plant, on the care with which it has been erected, on the nature of the fuel, on the condition of preservation of the apparatus, and upon the manner in which the producers have been working.
=Workmans.h.i.+p and System.=--The workmans.h.i.+p itself, which term is meant to include the choice of materials and the way they have been worked, presents no difficulty. The producers which we have discussed are very simple and offer absolutely no difficulties in their mechanical execution. As regards the system, however, especially with respect to the relative dimensions of the elements, it does not seem so far that it is possible to indicate any principle or rule capable of a rigid general application. It must be taken into account that the use of suction gas-generators has become general only in the last three or four years; the problem has therefore scarcely been adequately solved. However, some hints may be given on this subject.
=Generator.=--In regard to the generator, it is possible to deduce from the best existing plants the dimensions to be given to the generator relatively to those of the engine to be supplied, upon the a.s.sumption that the engine is single-acting and runs at a normal speed of from 160 to 230 revolutions per minute. The essential portion of the generator which contributes to the production of a proper gas is that which corresponds with the combustion zone. To this portion a cross-section is given varying in size between one-half and one-quarter of the surface of the engine-piston, sometimes between one-half and nine-tenths of this surface, according to the nature and the size of the fuel that is used.
With small apparatus, however, ranging from 5 to 15 horse-power, the size of the base cannot be reduced below a certain limit, since otherwise the sinking of the fuel will be prevented. This danger always exists in small generators and renders their operation rather uncertain, such uncertainty being also due to the influence of the walls. It is to be noted that most modern generators are rather too large than otherwise.
Many manufacturers of no wide experience have been led to make their apparatus rather large so as to insure a more plentiful production of gas. As a matter of fact, the fire in such apparatus is liable to be extinguished when the combustion is not very active. If the principles of the formation of gas in suction-generators be kept in mind, it is evident that the gas developed is the richer the ”hotter” the operation of the apparatus. Such operation also permits the decomposition of the hydrogen and carbon monoxide.
The ”hot” operation of a generator is accomplished best with active combustion; and since this is a function of the rapidity with which the air is fed, it obviously is advantageous to reduce the area of the air-pa.s.sage to a minimum as far as allowed by the amount of fuel to be treated. As to the height of the fuel in use in the apparatus, this varies as a rule between 4 and 5 times the diameter at the base.
=Vaporizer.=--The size of the vaporizer varies materially according to its type. No hard-and-fast rule can therefore be adopted for determining its heating surface; but this surface should in all cases be sufficient to vaporize under atmospheric pressure from .66 to .83 pounds of water per pound of anthracite coal consumed in the generator.
=Scrubber.=--For the scrubbers, the following dimensions may be deduced from constructions now used by standard manufacturers.
The volume of a scrubber is generally from six to eight times the anthracite capacity of the generator. A height of from three to four times the diameter is considered sufficient in most cases. It should be understood that in this height is included the water-pan chamber located below the part.i.tion or grate, and the upper chamber through which the gas escapes. The height of these two chambers depends necessarily upon the arrangement used for leading the gas to the lower portion of the washer and for the distribution of wash-water at the top.
=a.s.sembling the Plant.=--The author has insisted strongly on the necessity of having all the apparatus and pipe connections perfectly tight. In order to ascertain if there is any leakage, the following procedure may be adopted:
When starting the fire by means of wood, straw, or other fuel producing smoke, instead of allowing this smoke to escape through the flue during the operation of the fan, it may be caused to escape through the c.o.c.k which generally admits the gas to the motor, the c.o.c.k being opened for this purpose. The damper in the outlet flue is closed. In this manner the smoke will fill all the apparatus and connecting pipes under a certain pressure and will escape through any cracks, the presence of which will thus be revealed.
Another test, which is made during the ordinary operation of the generator, consists in pa.s.sing a lighted candle along the joints; if there is any leakage, this will be shown by a deviation of the flame from a vertical position.
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