bi
MODERN GASWORKS PRACTICE
efEect, they absorbed the chloride before it could reach the tar by interposing a layer of water, 3 inches deep, on top of the tar. The water was run in hot, so that little free ammonia was taken up, and the chloride in the gas was reduced. Considerable benefit resulted from the arrangement, whicli is diagrammatically illustrated in Fig. 191.
HYDRAULIC MAIN AGITATORS
Where modern methods for the drawing-ofi of tar and the flushing of hydraulic mains are in use, little trouble is experienced from stoppage and erratic working due to “ pitching-up.” The disorganization resulting from the latter, however, has in some cases been sufficiently severe to warrant the use of special agitating devices.
A common type of apparatus for the purpose is illustrated in Fig. 192. It con-sists of an endless Chain passing over two sprocket wheels, situated one towards each
end of the hydraulic main. Projecting arms or scrapers are attached to the chain, which is so arranged that the underside drags along the floor of the main. By means of. a projecting spindle the chain can be set in motion at periodieal intervals. Needless to say, it is strongly inadvisable to en-curnber the hydraulic with apparatus of this type wlien it can possibly be avoided. If flushing or agitation is desired, it should be carried out by liquid and not mechanical means.
be somewhat smaller and more sliallow
Fig. 192.—Hydbaulio Main Agitatob.
Modern hydraulic mains all tend to
■fchan many of the old cast-iron types. The tendency is certainly to be encouraged, for the function of the hydraulic is not that of a storage tank, and the depth of liquor should be as shallow as possible, providing that it satisfactorily performs its primary duty of ensuring a seal. If a considerable volume of liquid is always allowed to remain in the hydraulic, there is a tendency for distillation to take place; and, as tar will inevitably settie out, the formation of pitch is only a matter of time, unless special precautions are taken to preclude it.
THE FOUL MAIN
The foul main may be called upon to perform more duties than one, and amono-st other functions it provides :—
(a) A gas conduit between carbonization and primary purification plant.
(b) A. drain pipe for liquor and tar.
(c) A primary condenser.
So far as the last duty is concerned, the total length of foul main should be given consideration when calculations for condensing capacity are made.