of the producer gas into the cylinder of the engine, are effected by the suction or aspiration caused by the forward stroke of the piston.
Although the pressure system is composed, usually, of more cumbrous apparatus, and re quires more space, it possesses greater elas ticity than the suction system for meeting varia tions in the quality of fuel and greater capa bility for utilizing different kinds and cheaper grades of fuel. It is also the better for use with large power-producing units, or where several gas engines receive gas from the same pro ducer plant.
On the other hand, for isolated plants of small capacity, or where only a single gas en gine is used intermittently, the application of the suction system not only simplifies the bulk and reduces the cost of the plant, but what is more important, it makes the demand of the engine for gas the controlling factor of its generation from solid fuel.
Pressure Gas Producer System.— Fig. 3 shows the general arrangement of a pressure gas producer system. Usually it consists of a The following table gives the average anal yses by volume of the gas produced by the two types of producers: Gas Producer Systems.— Through the methods of operating gas producers of all types have sprang two general but well-defined sys tems of gas production for power purposes the pressure system and the suction system.
In the pressure system, the air required for combustion and for the generation of the gas is supplied to the gas producer tinder pressure, and the gas generated is delivered under pres sure to the engine using it.
In the suction system, both the passage of the air through the producer, and the introduction small steam boiler A, for making steam, or pro ducing the necessary air pressure; a gas pro ducer B, with a continuous-feed arrangement; an economizer C, with superheater and wash box; a scrubber D; a purifier E; a gas holder F, consisting of a steel tank; and suitable drips and connections.
The details of the several organs may be modified to adapt them to varying conditions. For example, the boiler may be omitted where steam can be obtained from some other con venient source of supply, and in some cases a i separate steam generator is not absolutely neces sary.
For smaller equipments, or those employed for operating engines up to 500 horse power, single producers are generally considered suf ficient, but the larger equipments require two or more producers, which may be varied in de sign and arrangement.
In the operation of a plant of this type, the gases generated in the producer enter the superheater and economizer. In the latter, the air blast of the producer travels in a direction opposite to that of the blower, and the gas passing through the wash-box deposits a large portion of its extraneous matter. The econo mizer also contains the seal arrangement against the gases stored in the holder and present in the other organs of the plant. From the wash box the gas passes into the scrubber, the com partments of which are filled with coke. Here the gas is showered by water sprays, and still further purified by the removal of any tar, sulphur or ammonia that may be present prior to its introduction into the purifier where the final purifying operations are performed. From the purifier the gas passes into the holder, which stores a supply sufficient to start and run the plant for several minutes, but the main function of the holder is to regulate the pressure, and care for variations in the consumption and mix ture of the gases.
The drip pots and drainage pipes are very essential parts of the plant and are suitably the tar is thus split up into its gaseous constitu ents. The gas outlet for producers of this type is near the grate. Another device to accom plish the same result conducts the tarry gases from the top of the producer by an outside pipe downward to the base of the producer whence they pass again through the fire. A still more successful type has two fire zones, one at the top of the fuel mass and the other at the bot tom, the gas outlet being between the two. Doubling the producer is also effective, one of the two being fired with anthracite, and the gases from the low-grade fuel in the other be ing passed through its fire.