Modern Gasworks Practice

GAS-MAKING AND OTHER COALS- 377 Deterioration The deterioration of coal due to storage is another vexed question. Though all are agreed that some loss does take place, tlie estimates as to the amount vary con-siderably. The question has probably received far more attention in Germany than in this country. Prenger, engineer of Cologne gasworks, has found that the de-crease in gas-making value of English coal is from 3 to 15 per cent., or an average of 7 per cent., when stored in the open, and from 0 to 10 per cent., or an average of 4 per cent., when stored under cover. Some authorities state that practically no deterioration occurs. No doubt a great deal depends on the dass of coal in question. The loss in calorific value appears to be cjuite slight, although. the heating value of the coke is reduced in some cases. This usually makes itself felt in the percentage of coke used as fuel. The results of some experiments carried out on the coal-testing plant at the Saltley gasworks of the Birmingham Corporation by W. B. Davidson showed that the gas multiples for coals which had been stocked for periods of six months to two years were in every case lower. No definite loss per annum is fixed by the tests, but it would appear to be no more than 2 per cent. The experiments showed that while the gas value decreased the liquor increased very appreciably ; but the coke was markedly inferior. The following figures are those given by a well-known English gas coal which was tested atter the intervals stated :— Make per ton. _ . __ Moisture. Cubic feet. On amval____________________________________2-71 .. 11,818 After 3 months_______________________________ 5-22 .. 10,708 » 5 _______________________________ 5-64 .. 9,780 ” 6 _______________________________ 7-58 .. 9,630 The ideal state of affairs on a gasworks would, of course, be to take in just as much coal as is required for present requirements, so as to avoid any necessity for keeping a stock in hånd. Owing, however, to the fluctuating output of gasworks, and to the faet that collieries turn out an amount which is fairly constant all the year round, these conditions are impossible. Moreover, in some cases a reduction in price may be obtained for coal delivered during the summer months ; and many gas Companies are eager to seize upon this opportunity. In respect to coal deliveries, the United Kingdom is more fortunate than many other countries. In Germany, for instance, some works are obliged to take the whole of their coal during the summer season, owing to waterways being closed by frost throughout the greater part of the winter. In the same country, too, stored coal is liable to deteriorate to a far greater extent, owing to the wider variations of temperature and fluctuations of weather conditions. At the present day far more coal is stacked out in the open than in elaborate stores, such as were erected as part of the retort hou.se on nearly all works in years gone by, There are still, however, many believers in the indoor method ; and there is no doubt that coals deteriorate to a much less extent when sheltered from the weather. The opinion is expressed by some engineers that coals are just as likely to heat up under cover, and when they do so they are far more difficult to get at.