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 passes through a sheet-iron shell 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 passage through an annular piece arranged in the ash-pit of the generator.
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 partition. The upper compartment up to a certain level contains either coke, glass balls, 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 passed 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 passed 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 passes through the grate or partition which supports the material filling the tower, and travels