Modern Gasworks Practice

CO CO MODERN GASWORKS PRACTICE reliance must not be placed in a name. There are many methods of arriving at an approximate comparison between the suitability of different coals for gas-making purposes, the chief being the following:— (a) Proximate analysis. That is to determine, chiefly, the volatile content. This gives some gauge of the gas-yielding and coking properties of the coal. The test is best carried out by Lessing’s method, in which electrical heating is employed. (b) The calculation of pounds of sperm per ton, or the pounds of sperm which •can be purchased for a shilling. This is a time-honoured method which. has proved of some valne in the past, but which has entirely lost its significance at the present ■day. To obtain the value of a coal in pounds of sperm per ton. the make of gas per ton is divided by 5 (which is the cubic feet of gas consumed by the standard test bumer per hour); the result is tlien multiplied by the illuminating power and by 120 (120 being the number of grains consumed per hour by the standard sperm ■candle). Finally, it is necessary to divide by 7.000, which is the number of grains in 1 Ib. Put briefly:— Pounds of sperm per ton = make X illuminating power X -003428. (c) Calculation at current prices of total yields of gas, coke, etc., obtained from a ton of the coal. The figure obtained is then balanced against the cost of the coal, and comparison between various coals is made on these lines. This method cannot be applied with. accuracy, and is not to be recommended. (d) The use of a coal-testing plant. On the larger works it is still customary to submit small samples taken from fresh. consignments of coal to a laboratory experimental plant. The total gas evolved, in addition to the main by-products, is then carefully collected and measured. The usual procedure is to take part of a ton of coal (2-24 Ib.), which is carbonized in a small cast-iron retort. The coal-testing plant of the Birmingham Corporation gasworks is probably the most elaborately equipped of those now in use. It is on an exceedingly large scale, and in reality forms a complete gasworks in itself. Various types of retort settings are in use, including regenerative horizontal beds, and both intermittent and continuous vertical systems. The horizontal test bench is capable of dealing with. 31 tons of coal per diem, and consists of four beds of full-sized through, retorts. The intermittent vertical installation has a capacity of 14 tons a day, and the con-tinuous bench. is capable of dealing with 20 tons per diem. Elaborate apparatus is installed for the purpose of arriving at an accurate knowledge of the capabilities ■of the various coals tested, and their behaviour under different systems of car-bonization. (e) Comparison by “ gas multiple.” This is one of the most recent methods, .and can be looked upon as affording the most satisfactory means of comparing the gas-yielding proclivities of various coals. The yield per ton is obtained by careful ■experiments in the test plant, and the illuminating power and calorific valne of the gas evolved is noted. The “ make ” of gas is then multiplied by tlie candle power, .and the result gives the “ gas multiple.” For example, two coals (a) and (&) might be tested with the following results : —