Modern Gasworks Practice

THE DRY PURIFICATION OF COAL GAS 589 The difference between the two systems is in reality a constructional one, and depends merely upon whether a set of purifiers is arranged around a centre valve, as shown. in Fig. 355, or in a line, with a number of single valves, as seen in Fig. 357. For the operation of the rotation system it is not necessary that the four purifiers should be set one at each corner of a square, although this arrangement is the most convenient. With oxide purification the modus operandi usually adopted is that of ha ving three of the four boxes in action at a time ; that is, gas is passing first through Fig. 355.—Rotation System or Purification. the first box or “ taker,” then through the second, and lastly through the third, by which time it is wholly deprived of sulphuretted hydrogen. After a time the oxide in the first box becomes “ fon] ed ” and useless for the further extraction of H2S until the material is revivified. No. 4 box is then put into action and No. 1 box is shut ofi, so that the original second box now becomes first “ taker.” In the mean-