THE CONDENSATION OF COAL GAS
05
K5
THE EXTRACTION OF TAR
On coke-oven works it is customary in some cases to wash the gas for the removal of the sus-pended tar. In the Otto-Hilgenstock system the vesicles a r e actually thrown down by spraying the gas coming from the foul main with. more tar, as shown in Fig. 279. It is understood, however, that the tar spray has now been abandoned in favour of a mixed spray of tar and liquor. In spite of the many
mechanical appliances now to be had, the complete removal of all traces of tar from coal gas is rarely efiected before the wet purification plant is reached, and the most successful means for attaining this end would still seem to bethat of bubbling the cooled gas through, a bath of liquid, rather than by the introduction of apparatus embodying the principle of “ wire-drawing ” orfriction. Of the tar extrac-tors operating on the latter principle, the Pelouze and Audouin is probably the most generally utilized. The machine consists of an outer cylindrical casing with. the gas - inlet entering through the centre of the base. A bell, suspended from an overhead pulley (or in later designs from a central shaft, as shown in Fig. 280), passes over the inlet pipe and has its base sealed in liquor. The weight