THE PRELIMINARY PURIFICATION OF CO AL GAS 521
whilst the remainder are operated with liquor. The upper chambers should pre-ferably be used for naphthalene removal, and the lower ones for ammonia extraction.
The Dempster-Feld washer (Fig. 326) is similar to that described above in so far as it consists of a number of superimposed chambers, through which passes a vertical skaft rotating at a speed of about 120 revolutions per minute. The spraying device, which is similar in all chambers, and is shown in detail in Fig. 327, is composed of a number of cones, varying from six to twelve, attached to th.e shaft by means of a. cast-iron hub. The lower ends of the cones are so arranged that they dip into the liquor contained in the dish-shaped channel in the base of the chambers. As the shaft
Fig. 325.-—Centrifugal Washbb-Sobubbbr. Details of Sfkayin-g Device.
rotates, the water is drawn up through the spaces between the cones, and is thrown off at a tangent at the upper edge with tremendous velocity, and passes across the gas space. The base of each compartment is provided with four apertures through, which the gas travels from ch amber to chamber, entering at the base and leaving at the apex. A machine dealing with 3 million cubic feet per day is only 5 feet in diameter and 23 feet high, over all, which includes the heiglit of the pier on which the machine stands. A baffle plate is fixed in the outlet compartment of the washer, which ensures the gas passing away in a dry state. The washers are made in sizes varying from 250,000 to 45,000,000 cubic feet of gas per 24 tours.
Horse-Power Required by Washer-Scrubbebs
The power required to drive washer-scrubbers depends upon their size, the speed of running and the washing medium employed, i.e. weak or strong liquor,