NAPHTHALENE IN COAL GAS 471
Naphthalene, grains per 100 cubic feet of gas. Löss per cent.
Before scrubbing. After scrubbing.
Coke-oven gas (590 B.Th.U.) . 24-6 8-8 64-2
Coke-oven gas (508- B.Th.U.) . 27-1 6-9 74-6
Coal gas (544 B.Th.U.) 7-8 1-6 80-0
The effect of temperature upon naphthalene extraction is shown by the follow-ing figures which refer to a stream of coal gas of two million cubic feet per day, treated in a rotary washer-scrubber with. green oil:—
Naphthalene, grains per 100 cubic feet.
Temperature of Wash-oil. ° Fahr. Before washing. After washing.
75 16-2 6 9
76 11-2 7-9
77 190 10-8
General experience shows that the naphthalene content of the gas is reduced by 75 per cent, when the latter is thoroughly scrubbed with an oil containing practically no naphthalene.
Many benzol plants are now fitted with a primary or vapour condenser, through which the hot still-vapours pass in counter-current to the benzolized washing oil. If an outlet is provided at the base of this primary condenser, and the high-boiling condensates are run off to a separator tank, it will be found that th.ey consist essen-tially of water, naphthalene, and naphthas. The water and naphthalene may be separated direct, or, to carry the process a stage further, it is profitable to erect a small secondary still in which the naphtha portion may be dealt with. If the dis-tillate is collected, cooled, and run to a shallow settling-tank, the remainder of the naphthalene may be recovered, while the liquid portion will consist largely of naphtha, which may be sold direct as such or returned to the debenzolized oil-tank. Such a process förms, in the airthor’s opinion, the nucleus of what may become a recognized nietliod for naphthalene removal and recovery in the future.
The Use of Solvent«
One of the most effektive means of eliminating naphthalene trouble in the-district mains and services is to ensure that the gas distributed contains a sufficient proportion of suitable solvents. The solvents may be present as a fine atomized mist which is carried forward in rnechanical suspension by the gas, or tliey may be present as vapours produced from suitable spirit or light oil treated in. a special form of carburettor.
There are a number of liquids which may be employed for the purpose of