Modern Gasworks Practice

WATER GAS 691 trolling influence over the coke market, and large Stocks of this by-product may to some extent be avoided. 7. The faet that a considerable proportion of the gas may be manufactured from coke in lieu of coal places the works in a position of rather greater independence so far as coal supplies are concerned. 8. In these days of labour upheavals the small amount of manual work required witli a water-gas plant is a prominent consideration. The item of wear and tear, both in the direction of labour and materials, is low in comparison with the ordinary machine-charged horizontal retorts. 9. The sulphur impurities in the gas are low in comparison. with. the same impurities in crude coal gas. As regards sulphuretted hydrogen, crude coal gas contains on an average 500 to 800 grains per 100 cubic' feet, and crude water gas 120 grains. Of carbon disulphide and otlier sulphur Compounds coal gas contains from 35 to 50 grains, and carburetted water gas 10 to 15 grains per 100 cubic feet. 10. In many instances carburetted water gas has proved itself efEective in diminisliing trouble from naphthalene deposita. It is said that the carburetted gas acts as a solvent vehicle for naphthalene and, accordingly, prevents its precipi-tation from the coal gas. Much, however, would appear to depend upon the temperature at whicli the carburettor and superheater are operated, for if the light oil vapours are submitted to too great a temperature, over-cracking will occut and the virtue of the gas as a naphthalene sedative is likely to be lost. Again, of course, müch will depend upon the proportion in which the carburetted gas is present. At any rate, water gas as a naphthalene eradicator must not by any means be looked upon as infallible. Moreover, as blue gas is most commonly made to-day the effect is more likely to aggravate rather than diminish. trouble in this direction. As regards the inherent disadvantages of water gas, it is not possible to compile a very formidable list; but_. first, mention must be made of the very high per-centage of noxious gas, carbon monoxide, whicli it contains, the proportion amount-ing to three or four times as much as that to be found in coal gas. The objection is, no doubt, one which is largely discounted in the present day, for the many years’ experi-ence of water gas shows no tendency towards any increase in the number of deaths from asphyxiation. A further disadvantage lies in the faet that, at the time of writing, the expense of manufacture of carburetted gas is greater than that of coal gas owing to the very considerable increase in the cost of oil. The smooth. operation of a water-gas plant may be quickly upset by the intro-duction of an inferior coke, and its somewhat sensitive nature in this respect is liable to give trouble in those works where a high-class coal, with a low asli-content, is not always procurable. In some works it is customary to set aside the coke from the higher quality coals for the exclusive use of the water-gas plant. It is frequently urged as a merit of carburetted water gas that its permanence is a great recommenda-tion in preventing any deterioration of or deposition from the district gas as it passes through the street maius. On the other band, the author’s experien.ee goes to show that any slight imperfection in thefixing chambers, ot any insufficiency of condensa-tion, may be followed by a very appreciable drop in quality during the passage of