474
MODERN GASWORKS PRACTICE
vapour pressure, and remain, therefore, as a permanent vapour in the gas. Higher boiling solvent» such as paraffin may be employed in vaporizers ; but, as pointed. out above, atomization in such cases is to be preferred. When paraffin is utilized in a vaporizer it will be found that some of the higher-boiling constituents do not evaporate, and they flow away from the apparatus.
One type of carburettor which. has been employed is shown in Fig. 288. The carburettor is connected with the gas main at the outlet of the works, the main being provided with a throttle valve so that about 10 per cent, of the gas distributed can be passed through the vaporizing chamber. The illustration shows the solvent storage drum, the overhead supply tank, and the vaporizing chamber in cross-
T'ig. 288.—Atpabatus fok Cakbubation of District Gas.
section. It will be noted that water pressure is employed for transferring the solvent from the drum to the overhead tank. When solvents, such, as paraffin, of moder-ately high, boiling-point are used, the distance from the outlet of vaporizing chamber to the gas main sh.ou.ld be as short as possible, for the character of the oil mist pro-duced is favourably influenced by a moderately sudden temperature drop of the hot by-passed gas. The introduction of carburetted water gas undoubtedly went some considerable way towards lessening the naphthalene evil, although. opinions difier considerably as to its utility in this direction. A great deal, however, depends upon the method of rnanufacture of the water gas, and more particularly upon the temperature to which. it is subjected during its passage through the superlieater. If the superheater is maintained at temperatures much above the normal the gas will