468
MODERN GASWORKS PRACTICE
mains. Naphthalene troubles are, however, in no small measure due to old deposita in the mains, so that the most thorough removal at the works does not in any way guarantee immnnity. For this reason many engineers prefer to treat the gas in the mains, while a combination of both. processes is certainly ideal.
There are many substances w.hich are suitable solvents for naphthalene, although the majority of those which. absorb naphthalene also absorb the aromatic hydro-carbons. Bayer 1 has given the following figures which he obtained as the results of using a light oil for the purpose
Composition of Wash-oil, Pek Cent. by Weicht
Before use. After use
Water . 0-0 5-2
Benzol 0-4 14-9
Light oils 67-6 2-7
Middle oils . 25-0 15-4
Naphthalene . 3-9 191
Heavy oils . 3-1 42-7
As regards the naphthalene solvent power of the most readily available substances for the purpose the following figures have been given:—
Per cent, of naphthalene absorbed.
Creosote oil æl
Gas oil 5-8
Tar oil • 9-74
Water gas tar ....■■■■■■■ 23-50
Benzol 24-90
Some interesting results obtained on a large scale in connection with gas washing for naphthalene removal have been given by Macleod and Henderson.2 In this case the solvent employed was a coal tar distillate which yielded the following fractions on distillation :—
Below 100° C...................................................23-5 per cent.
100°-170°......................................................4-5
170°-185°......................................................63-5
Residue and loss . . . . . • • • . 8-5 „
Specific gravity at 15° ........ 1-000
The effect of treating the gas with this oil is sliown below:—
Naphthalene. Grains per 100 cubic feet. Make of gas per ton of coal. Condenser Temperatures ° C.
Inlet of washer. Outlet of washer. Inlet. Outlet.
I 19-7 6-7 10,498 cubic feet 43 18
II 15-2 6-7 10,352 „ 49 18
Average 17-45 6-7 10,425 „ 46 18
1 J. für Gasbeleuchtung, 1911, p. 496.
2 J. Soc. Chem. Industry, November, 1913.