Modern Gasworks Practice

THE HORIZONTAL RETORT BENCH 117 ash-r emo ving apparat tis. A “ wet ” air-blast is blown through the fuel-bed by means of Roots’ blowers, and in this way the temperature is maintained at a comparatively low point, so that ash alone, and no clinker, is formed. The quantity of steam introduced with. the air-blast, when ammonia is recovered, amounts to abont 2J tons for every ton of fuel gasified, the low temperature thus ensured preventing the decomposition of the ammonia, and accounting for nearly four times the yield obtained from the ordinary gasworks process of dis-tillation. The supply of steam and air before entering the producer traverses a regenerator (in which it derives heat from the outflowing producer gas), and after-wards the annular space formed round the inner shell of the producer by the external casing. On. leaving the producer and regenerator the gas passes to a medianical washer, where, by means of a water spray formed by quickly rotating dashers, tar and dust are eliminated. The gas leaves the top of the producer at a temperature of about 500° C. It may be used direct; or the ammonia may be recovered by passing the gas through weak sulphuric acid. in an absorber, in which case the temperature is reduced to that of the atmosphere before it can be finally used for heating purposes. It follows, therefore, that the highest heating efficiency is obtained when the gas is used direct from the producer, and under non-recovery conditions; otherwise there is a loss of sensible heat due to cooling, etc. It is said, however, that when the gas is taken direct from the producer, tar and dust troubles ultimately develop. W. Chaney, formerly of the Saltley Gasworks, has stated that in the case of large installations of Mond gas plants about 150,000 cubic feet of gas can be obtained from a ton of coal slack, at a pre-war price of per 1,000 cubic feet. The calorific power of the gas is about 140 B.Th.U. per cubic foot. The same authority has also given the following interesting comparison of costs for heating by Mond gas and by means of the ordinary coke-fired regenerator furnace. It should be noted that the costs all refer to pre-war conditions :— Pre-War Cost of Heating Retokts by Regenerator Furnacbs. Based on a Fuel Con-SUMPTION OF 12 PER CENT. OF THE WbIGHT OF COAL CARBONIZED Coke at 14s. per ton . , , Labour ...... Repairs and depreciation . 20 ■2d', per ton of coal carbonized. • 2-7d. • 10<Z. Total cost of heating ■ 23-9d. (say 2.s.) per ton carbonized. Pbe-War Cost (a) All coal slack. Small coal at 10s. per ton Boiler fuel ..... Labour ..... Repairs and depreciation Oil, etc. ..... Sulphuric acid at 30s. per ton Sulphate bags, packing . of Heating by Mond Gas . 18-O<7. per ton of coal carbonized. . 2-15d. „ 3-84rf. „ . 8-53< „ . 0-34Æ „ l-95rf. „ „ . 0-46<Z. „ Gross cost .... Less sale of sulphate . 35-27rf. per ton of coal carbonized. . 18-8W. „ Net cost of heating. 16-46rf. per ton of coal carbonized.