Modern Gasworks Practice

THE DRY PURIFICATION OF COAL GAS 595 possible, be maintained at about 10° C. (50° F.), although. this will not always be possible during winter. An inactive purifier may frequently be revivified by the injection of a small quantity of air, the oxygen probably reacting with the hydrosul-phide and oxidizing it to hydroxyhydrosulphide, as shown in the above equation. THE CONSTRUCTION OF PURIFIERS Purifiers, as used in gasworks, are generally constructed of cast iron (ferro-concrete has lately been employed), and may be classified into three distinet, groups — («) Water-lute vessels, the type originally employed and still largely made use of, the lute varying from 15 inches to 40 inches deep. (&) Dry-lute purifiers, a modification of the above, in which the use of a hydraulic joint is dispensed with. (c) Purifiers, such as Green’s well-known type, in which small sections of the cover are alone removable. These are fitted with dry joints. All the above groups may be erected— (d) At ground level, or partially buried. (e) Above ground level, i.e. overhead types. So far as the arrangement of the purification plant is concerned, irrespective of the design of the actual vessels, it is essential to provide facilities for rapid and economical discharging and charging. It will be seen at once that where ground space is a con-sideration the overhead system should be decided upon, as in this way a floor space for mixing and revivification is provided beneath the vessels. With the ground-level system a special preparing floor must be arranged for alongside the boxes. When ground-level or sunk purifiers are employed they usually rest on a plain, flat slab of concrete. The nature of the subsoil should, however, be carefully ascertained, as piling or other methods may be necessary (see page 42). Overhead types are supported, usually from 8 to 12 feet above the lower floor, on cast-iron columns or Steel stanchions braced together by cross gilders, which. provide a seating for the boxes. In large works the purification plaht is comparatively costly, but some outlay may be saved by arranging the vessels so that they butt one on to another, with one division plate, thus saving a side plate between. each pair. This arrangement applies to dry-lute purifiers alone. With overhead purifiers the gas outlets are of ten constructed in such a manner as to form a discharging shoot to the floor below; in this way the spent material may be easily shot to the lower level and spread out in layers to undergo revivifi-cation. After revivification. the material is carried up to the tipper floor, in the smaller works by manual labour, and in larger works by some form of lift, elevator, or crane. With overhead purifiers the operation of discharging and recharging may be carried out in a half or a third of the time required with. ground-level systems, where a considerable amount of wheeling to and fro has to be done. Otter advantages of the overhead types are that they are very mueh more accessible for painting and repairs, whilst there is less Capital outlay on land. The outstanding merit of the ground-level purifiers is their comparatively moderate cost, whilst maintenance