Modern Gasworks Practice

268 MODERN GASWORKS PRACTICE the ordinary way the liquid products flow from the hydraulic to the tower by way of the tar main (A), the outlet from each. hydraulic being fitted with a valve (B). If stoppages occur in the main the valves (£>) are closed, and liquor under pressure from a pump is forced along the main into the tower, thus clearing away the obstruction, without upsetting the seal conditions in the hydraulic. A supplementary tar and liquor main (C) is provided, so that any excess liquor deposited during the flushing period is constantly drawn off, travelling to a seal-pot, and maintaining the normal seal. Once tlie obstruction is removed the valves (5) are again opeiied, and tlie tar tower is brought into action. THE REFLUX PRESSURE SYSTEM The operation of this system,1 which. was recently introduced by the author, will be readily understood by reference to Fig. 187, which shows the general arrangement of the retort bench, hydraulic mains, tar and liquor overflow, etc. The hydraulic mains are made throughout from mild steel. Tar and liquor flow from the hydraulics to a common 6-inch main which runs direct to a pressure box, the overflow in which. is some 10 to 18 inches below the level of the bottom of the dip pipes. Thus both. tar and liquor are always flowing down hill. The difference in level between the overflow in th.e pressure box and the height of liquor in the hydraulics is maintained by gas pressure commuiiicated to the pressure box. The pressure required for this purpose varies between 10 and 18 inches of water, and is supplied by bringing back a f-inch service from the outlet of the serubbers, where on. many works the pressure is 25 inches and frequently more. The pressure gas from the serubbers is taken, prior to its passage to the pressure box, through, a specially designed controller, so constructed that, whatever the fluctuations of pressure at the outlet of the serubbers, a coustant pressure is mamtamed in the box. The governor is so constructed that it is entirely unaffeeted by sulphuretted hydrogen in the gas. It is also fitted with a special regulator, so that, by the turn of a milled head, the outlet pressure may be adjusted within ex-tremely fine limits to give any desired depth. of seal, or the dip pipes may be worked without a seal. After lea ving the pressure box, both tar and liquor pass to a separator where they are completely separated while in the hot state, the hot liquor being pumped up and retæmed to the hydraulics, thus ensuring continuous circulation. Tn this way the quality of the tar is improved, and it has a particularly low “ water content.” On. the other hånd, the re-circulation of h.ot liquor has a substantial purifyiug effeet on the gas, and its ounces strength is considerably enhanced. In Fig. 187 an arrangement is shown whereby the liquor is raised for re-circulation by means of a compressed gas lift. This is a decided improvement upon tlie ordinary stearn pump, for tlie considøra/ble loss. of amnioni<i at tli.c glauds of the ord.ma.ry pump is thereby avoided. The gas lift, however, is a refinement which can be employed or not, and depends upon the taste of the engineer. Fig. 188 illustrates the battery of gauges and the controller, which. may be fitted in the engineer’s office, so that regulation of the quality of the gas may be effeeted 1 Pat. No. 165,581.