Modern Gasworks Practice

PLANNING AND LAYING OUT OF GASWORKS 21 only (for a set of four purifiers) an area of 0'5 square foot per 1,000 cubic feet per day should be provided as a minimum in each box. If lime is used this figure should be increased to 0'6 square foot, or to 0'65—0'7 if no catch, boxes are provided. For the total amount of purification space necessary (i.e. the combined area of all boxes) the rule given by Hunt is useful. This states that for lime and oxide purification 20 to 30 square feet per ton of coal carbonized per day should be allowed. A further rule, based on the amount of oxide in the boxes, is that one ton of oxide may be expected to purify about 2 million cubic feet of gas before becoming finally spent. The maximum figure can only be obtained when air is put into the boxes for revivification. A further rule is that for each. 1,000 cubic feet of gas per day allow 1| to 2 cwts. of oxide in each of four boxes. In designing plant for a growing works, it is necessary to provide for the more or less immediate future, and it is advisable to erect only three boxes, making provision for the easy addition of the fourth. In this case the boxes in th.e set of three should be made 50 or 60 per cent, larger than those necessary in a set of four (say 0’8-0‘85 square foot per 1,000 cubic feet per day for the area of each box). Tn the case of a very small works with. prospect of growth, two boxes with facilities for extension can be put in with advantage, in which. case each box should be made 3-3| times as large as if there were four (1'5 to 1'7 square feet per box per 1,000 cubic feet per day). By adopting this plan the first cost is not increased, and money is saved when extensions are carried out. The size of connections for purifiers may be calculated as follows Diameter of pipes) r------------------#----—--------------------- in inches J = V Area °* eac^ "ox 111 S(luare ^eet- For small purifiers make no deduction from the figure so found, but in large and medium-sized boxes deduct | to 8mall boxes are from 3 to 4 feet deep, and large ones may run from 6 to 8 feet, 6 feet being most common. The intermediate sizes vary from 4 to 6 feet in depth. Purifiers vary in size from 12 square feet in area up to 40 feet square, the latter size being suitable for a to 3 million cubic feet a day unit. For constructional reasons, convenience in working, lifting covers, emptying, etc., when the works is larger than this it becomes necessary to divide the gas into streams, each with its own set of boxes. In works making less than 2| to 3 millions per day this system is also in operation owing to development in. the past, and it is very useful where different sized units are in use, the larger set being operated in summer and both sets in winter. Thus a 3 million a day works would have 35 or 36 feet boxes for its larger unit and 24 feet boxes for the smaller unit. The former unit would probably be sufficient for eight montlis in the year, and both. sets, would be in use for the remaining four months. The larger set would then take 27-inch. connections and the smaller 18-inch to 20-inch. For carburetted water-gas purifiers it is advisable to take 0’8 square foot per 1,000 cubic feet per day for each box, again assuming four boxes to the set.