RETORT-BENCH APPURTENANCES
273
THE PITCHING-UP OF MAINS, ETC.
The pipes which are used for conveying the tar and liquor from the liydraulic mains to the storage well are often a source of trouble owing to the adherence of pitchy matter to the inside, thereby causing blockage. This is particularly the case where the pipes are subjected to radiated heat from the retort bench. The most eflective means of collecting liquor, and at the same time furnishing a flushing system for the draw-off pipes and hydraulic, is to provide a tank into which all liquor running from the foul main, hydraulic mains, or tar towers, is taken. This liquor is tlien raised by means of a pump to an upper tank a few feet above the retort bench, and provides the constant feed to the tar towers as already explained. One function of the pump, however, is that of periodically flushing out the tar pipes. This is effected by fitting a connection from the delivery of the pump to the run-off pipes of eacli
g Fig. 191.—Smith & Pearson’s Arrangement rojt absokbing
“ Ammonium Chlokidb.
individual tar-tower system. Accordingly a.flush. of liquor at considerable pressure can be pumped backwards through the pipes and into the hydraulics. A short period of such flushing carried out once a day, or even once during each stift, assists in the prevention of stoppage. The system of liquor tanks, moreover, has other advantages, in that the warm liquor coming straight from the towers and foul main is permitted time to cool down before being discharged into the storage well, thus curtailing loss of ammonia. A further advantage is that the liquor run into the towers or mains can. be kept in continuous circulation (only the surplus being allowed to drain o ff to the well through an overflow in the lower tank), which results in a greatly increased strengtli being obtained. When liquor is circulated in this manner it will usually be found that the proportion of “ fixed ” ammonia is appreciably greater than when ordinary methods are employed.
Smith and Pearson, in the course of their researches carried out with the Birmingham coal-testing plant, found that, so far as the pitchy deposits in the liydraulic main were concerned, the chict binding material in the pitch appeared to be ammonium chloride taken up from the gas in the liydraulic main. In order to eliminate this