Modern Gasworks Practice

00 01 MODERN GASWORKS PRACTICE the majority of carburetting plants a device is in use whereby the oil, before being passed into the carburettor, is preheated by the hot gas leaving the plant. The heater is usually placed in the down pipe leading from the superheater, and raises the temperature of the oil to about 110° C. In this way the “ candles per gallon ” are appreciably enhanced ; but the author would point out that in some insta.ne.es he has found that the removal of the oil heater has been followed by a general im-provement in results. This faet is ascribed to the reason that the heater appro-priates a considerable portion, of the area of the main gas outlet, with the result that the latter is insufficiently large for the gas to get away with the ease it should do. A point which is patent to all users of water-gas plant is the necessity for seavenging the apparatus prior to commencing the “ blow.” When the steam is sliut ofE at the end of the “ run ” the vessels, the cubic capacity of which is fairly considerable, remain full of water gas. To open the stack valve at once and to com-mence with the “ blow ” would be to discharge this water gas into the air. To pre-clude this, after the steam is shiit o ff the etack valve should remain closed, not being opened. until the air biast has been passing through for a few seconds. In this way, the gas will be driven forward to the holder, and the plant will be effectively cleared out. In the early days of carburetted water gas in this country the enriching medium employed was almost solely a Russian Solar distillate. At the present day, however, the centre of supply has moved to America, from which country the residual petroleum, having a specific gravity of about 0-85, is obtained in large quantities. The gas engineer, so long as he can obtain his oil for a reasonable price, does not trouble very rnuch about its quality, although an inferior product will soon make its mark on the working results of the plant. It has been more or less conclusively proved that the laboratory analysis of gas oil is of little avail in determining the suitability of the oil for carburetting purposes. On this account it is umisual to subject consignments of the oil to anything more than the erudest tests. It is general for the gasworks’ chemist to draw off his sample carefully and to note the specific gravity of the oil; but the result aflords him no indication of the gasmaking qualities, and is merely a guide as to the origin, upon which this property to a large extent depends. So far as the origin of gas oil is concerned, it has already been pointed out that practically all of that imported now comes from America. The other suitable types, Russian Solår distillate, also Galician—these being high-grade oils—have not been imported for some years. Rumanian oils are of a poorer character and rarely reach this country. An average sample of present-day American gas oil will show on distillation approximately the following fractions :—