Modern Gasworks Practice

CONTROL OF HORIZONTAL RETORT SETTINGS 127 better practice is to keep a coke bucket burning for some few days at the base of the chimney. A special brick panel or cast-iron door should always be left in the chimney for this purpose. When working medium fires the furnace lid is, of course, sealed up and secondary air admitted. The necessity for exercising a certain amount of vigilance before doing this is dealt with. later. When the “ fast fires ” are com menced, the dampers and air slides may be adjusted to the maximum amount re-quired for -working the setting. GENERAL WORKING POINTS There is little doubt that the trained eye is by far the most effectual jtidge as to the manner in whicli the furnaces are doing their work. Systematic analyses are, no doubt, helpful so far as the prevention of waste is concerned, but their chief drawback is that whilst giving an indication of the quality of the producer gas they entirely neglect the equally important consideration of quantity. This accounts for the somewhat common experience of a scientifically perfect gas giving decidedly indifferent heats. As a preliminary, the most satisfactory metliod of adjusting the slides is to increase the primary supply until the best results are noticed, thus adopt-ing a trial and effect policy. Having hit upon the correct adjustrnent, the secondary slides are regulated until the characteristic blue flame of carbonic oxide is seen burn-ing at the ports connecting the regenerators with. the waste-gas flue. This indicates that the air entering through the inspection plug is burning the unconsumed CO. Such a state of affairs is, of course, wasteful, and the secondary ports must be further opened until the blue flame just disappears. Sufficient quantities of oxygen for the combustion of the carbon monoxide are now entering the setting; but in order to ensure a slight excess the secondary slides should be further opened to a small extent, say about one-tenth. of their amount at the time. In doing this, however, judgment must be exercised; for an additional quantity of secondary air means an increased volume of waste products, hence reduced combustion temperature. Some interesting figures, showing how the efficiency of the setting may be jtidged from the analysis of the waste gases, have been given by W. M. Russell.1 These figures are given in the following table, which provides a very good illustration of the importance of correct air adjustment. Waste ga.ses per cent. Efficiency per cent. Conditions Prevailing. co2. n2. CO. O2. 20 80 ' 61-7 Complete combustion 17-4 78-2 4-4 — 49-3 Air 10 per cent, deficient 18-2 80-0 — 1-8 58-2 Air 10 per cent, excess 18-0 80-0 — 2-0 57-8 18'0 per cent. CO2, excess air 18-0 78-7 3-3 — 55-4 18-0 per cent. CO2, air deficient 1 Operation of Gasworlcs, p. 30.