Mexborough & Swinton Times, September 30, 1932
Coal Tar
How it is “Unpacked” at Manvers Main
Infant industry with great future
Coal-tar, not long ago considered an obnoxious by product of coal gas, is now the basis of an enormous industry in the Country and the sole source of many substances of great industrial importance.
The distillation of coal-tar is as interesting to the layman as it is complicated. Several processes are used for the partial separation of the constituents. One is the forcing of the tar in a fine film through a lead bath; another is by the use of pot stills (the most common method), while another process is continuous from still to condenser.
Among the oldest tar distilleries in this country are those of South Yorkshire, the seat of the finest gas coal in the world. The Manvers Main Collieries use it to make gas for the public and domestic lighting and heating of the towns of Wath, Bolton, Goldthorpe, Thurnscoe, West Melton, Swinton, Kilnhurst and Mexborough. It is only natural, therefore, that Manvers Main should have an excellent tar distillery.
During the production of coal gas, tar comes away from the heated coke in liquid and vaporous forms. The old method for condensing the vapour and this must be done to purify the gas was by impinging the “fog” rapidly on metal plates. Research has found a more rapid way: by means of an electrostatic tar precipitator a voltage of about 45,000 rectified alternating current is passed through the mixtures of gas and tar fog, the latter condensing in the process. With the tar at this point is ammonia liquid and separation is generally done by settling, the lighter liquor being easily run off.
Then comes the actual distillation of the tar which is run into wrought-iron still”, each capable of holding 23 tons, and subjected to great heat. The result is a number of crude products. First come the light oils, naphtha and bensol, which are run off to further stills and later condensed by passing through long iron or lead worms immersed in water. Remaining in the first stills are the middle and heavier oils which include carbolic, creosote, naphthalene and anthracene oils. These are passed through the same processes as the lighter oils, namely; they are run off into further stills and later condensed. Those oils are the basis of an enormous number of products. For example, naphthalene oil is the basis of many dye materials and is also sold to the public in the form of moth balls.
To prepare the naphtha in crystalise form it is allowed to settle in large tanks; the thinner oils with which it is mixed to a certain degree are gradually filtered off, leaving naphtha in crystal and thick liquid form; a brownish mess to the untutored eye. This is passed from the tanks to centrifugal electric pump which churns the stuff at a terrific rate and squeezes it through a very fine copper filter or sieve. It is then commercial crystal naphtha.
Creosote is in demand for preserving or pickling timber. Some years ago the demand was exceedingly great from America, but during the past few years the Americans have realised the commercial value of tar distillation with the result that England has found her market reduced by at least half. During the war, too, creosote oil was extensively used by the Navy as fuel oil. For this purpose it was mixed with anthracene oil. The latter oil is connected with one of the romances of tar distillation. It is now the basis of Turkey red which, at one time, was a “natural” product and was one of France’s principal trades: Tar distillation in this and other countries has resulted in France turning over its fields to sugar beet.
The residue of tar distillation is pitch, a highly inflammable substance, especially so if allowed to come into contact with air when hot after the distillation process. It is exported in large quantities for briquette-making. It is also a basis for varnishes and wood-preserving materials. It can, and has been extensively used for rand-making purposes but is now being superseded by tar itself. The tar, when required for tar macadam is not distilled thoroughly, but sufficiently to remove water and lighter oils. It is then made to various consistencies according to specifications laid down by the Ministry of Transport and local highway surveyors. Tar for this purpose is sent by Manvers Main as far as South Wales and into the Midlands.
Though coal by-product works now play a large part in the industrial life of the country, there is yet further scope for development. A very efficient motor spirit, benzol, made from this process is already becoming a strong rival to petrol. Indeed, there is as yet no known limit to the possibilities of tar distillation.
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