Modern Gasworks Practice

THE CONDENSATION OF COAL GAS 451 bottom of which is connected aninverted conical chamber, having a seal pipe attached to its lower end. The gas inlet is rectangular and enters the cylinder at a tangent. It contains, moreover, a flap valve by means of which the velocity of the gas is regu-lated. A whirling motion is thus set up, so that the tarry vesicles are thrown against the sides of the vessel by centrifugal force, broken up, and run oft to the seal. The gas, meanwhile, flnds its outlet by way of the central vertical pipe. In one instance it was found that in passing through, the separator the gas gave up about 31 gallons of liquid, per 10,000 cubic feet, of which. 60 per cent, was tar and 40 per cent, liquor. This indicates that the amount of tar fog present was 2 gallons per 10,000 cubic feet. It resembled a thin liquid oil tar of the nature of that produced in the man.ufactu.re of water gas. The extractor is made in sizes varying from 3 feet to 10 feet in diameter. The advocates of the retention of the heavy tars in. contact with the gas point out that as the temperature falls the disposition of the tar to absorb naphthalene increases, hence contact at the lower temperatures is desirable. At the same time it must be remembered that there is a corresponding increase in the capacity of the tar for absorbing the low-boiling constituents. In some cases the “ counter-current ” principle has been introduced ; that is to say, the tar thrown down in the condensers is run backwards towards the hydraulic main, so that gas and tar are travelHing one against the otter. In Dr. Carpenter’s system tar is sprayed down the individual condenser tubes ; in addition, more or less abrupt condensation is arranged for, so that the naphthalene is partially removed and washed out of the apparatus by the tar. At Brunswick gasworks a regulär system of tar washing has been instituted for the purpose of removing, not only naphthalene, but a portion of the sulphur com-pounds as well. Tar from an overhead tank, after undergoing filtration, is made to fall in fine streams down the annular space of the condenser limbs. The cold i rifl o wing tar chilis the gas, forming a fog, which is removed by the descending stream together with. almost all the naphtlialene, the greater part of the CS2, and a part of the H2S. The approximate quantity of tar used is 3J gallons per minute, which reduces the temperature of 3,500 cubic feet of gas from 50° to 30° C. It is stated, moreover, that the illuminating and calorific valnes of the gas are affected favourably by the treatment. Whatever methods may be employed in the condensation of coal gas, it must be remembered that illuminating power has in the present day lost almost all of its former significance; hence the retention in the gas of the maximum quantity of low-boiling constituents is not now so imperative. The greater the proportion of th.ese hydrocarbons in the gas, however, the greater will be the latitude afforded for attaining the best results from carbonization.; and from the point of view of economics the valuable constituents should be retained in the gas to as great an extent as possible.