Modern Gasworks Practice

GAS-MAKING AND OTHER COALS 361 GAS-MAKING COALS The quantity of coal now used for gas-making purposes in the United Kingdom amounts to about 18,000,000 tons per annum, while some 20,000,000 tons are utilized in coke-ovens. Generally speaking, it may be said that the favourite coals of the gas engineer are those occurring in the Northumberland and Durham districts. Other fields from which. large supplies are drawn are those of West Yorkshire, South Lancashire, Nottingham, and Derbyshire, also Staffordshire and Warwickshire. Owing to the decided variation in quality which occurs in. coals mined in adjacent or even in the same seams it is difficult to distinguish with. accuracy between the products of the different districts ; in fact, it is by no means uncommon to find both steam coal and gas-making types occurriiig in the seams of any one mine. The problem with which the gas engineer is chiefly confronted is that of balancing. gas-making capabilities against expense of delivery. In the majority of cases it will be found most economical to take the coal nearest to the point of consumption, even thougb. the quality is not all that might be desired. In general, the typical analysis of a gasworks coal of good quality will approxi-mate to the folio wing, although as regards ash content it is by no means an uncommon occurrence to find the inert matter even in coals of good reputation mounting up to as much. as 15 per cent. Typical Gas-making Coal Carbon .......... 80 per cent. Hydrogen...................................5-5 Oxygen.....................................8-8 Nitrogen...................................1-5 Sulphur....................................0-8 Ash........................................3-4 Volatile matter.......................30 to 35 Calorific power.................. 14,400 B.Th.U. per 1b. The above analysis is representative of the good quality gas coal such as was obtainable prior to the late war. Many gas engineers will, however, have good cause to remember the abnormal proportion of inert matter which was delivered in the coal during the years 1917, 1918, and 1919, at some periods the amount of ash being as much as 30 per cent. The cause for this exceptional deterioration in quality was mainly to be traced to the discontinuance of the process of picking over the coal at the pit-heads, a situation which arose partly from the shortage of labour. In the following table there are set forth the differences in ultimate analysis of typical coals from the various seams of the country ; but, as already pointed out, it must be recognized that this standard of judgment is not to be relied upon. If used intelligently, however, the Chemical composition of a coal will give some insight into its value for gas-making purposes. Particular attention should be given to the proportions of ash, oxygen, and sulphur. With regard to the last-named, although a certain amount is chemically combined with the chief elements, and forms,