Modern Gasworks Practice

 THE DRY PURIFICATION OF COAL GAS 597 mat to distribute the pressure. The secondary beams are 21 inches deep, the floor slab 5 inches thick, the sides 7 inches thick, and the decks and gangways 6 inches thick. Only five pillars, 10 inches square, are used internally to support the gangways. These pillars form ties between the floor and top when the puriflers are closed and under pressure. The mixture used was one of 4 : 2 : : 1, but for the columns a slightly richer mixture was used, as they were made horizontally and elevated into position when set. To render the concrete gas-tight the puriflers were treated on the inside with “ Ironite.” Special provision was made to keep the weight of the massive 24 inches diameter pipes, forming the gas mains, from coming on to the floor of the puriflers. There are also four discharge outlets provided for emptying each purifier. THE SIZE OF PURIFIERS It is essential that purifiers should be of ampie capacity for the work they are called upon to perform. Nothing is more detrimental to working efficiency than an overloaded series of purifiers, and the cost of an additional unit can soon be expended in labour charges owing to the skorter life of the material when capacity is inadequate. For oxide purification alone it will suffi.ee if the following allowance is adhered to:— Set of four purifiers : Allow, as a minimum, an area of 0-5 square foot per 1,000 cubic feet of gas to be purified per day. This is the allowance for each box, and not the total area of all boxes. If lime is to be used for the removal of sulphur com-pounds, the figure should be inereased to 0-6 square foot, or 0-65 to 0-7 square foot if no “ catch-boxes ” are available. So far as the total area of all boxes is concernecl, Hunt states that for lime and oxide purification combined 20 to 30 square feet per ton of coal carbonized per day should be allowed. As has already been pointed out in Chapter I, it is essential to make provision for future requirements, and so far as a new works is concerned it is preferable to erect only three boxes to each unit, provision being made for the easy addition of the fomtli when it is required. In such, cases the three boxes should be constructed with a capacity 50 to 60 per cent, larger than that necessary in a group of four; that is, an allowance for each box of 0-8 to 0-85 square foot per 1,000 cubic feet of gas passing per day. Considering the case of a very small works with. prospects, it would be advantageous to provide only two boxes at the outset. Each box, liow-ever, should be of large capacity, say 1-5 to 1-7 square feet per 1,000 cubic feet per day. In this way there will be very little inerease in first cost (as compared with. a system of three small purifiers), and money will be saved when. extensions are carried out. Within certain high and low limits purifiers may be constructed of almost any dimensions. They are invariably square or rectangular in shape. The minimum size is usually 4 feet square by 3 feet in depth, whilst the maximum size will not, except in abnormal cases, exceed 1,600 superficial feet, i.e. boxes Iiaving sides of 40