Modern Gasworks Practice

20 MODERN GASWORKS PRACTICE leaving sufficient margin, and unless stated otherwise by the purchaser, this standard size will be supplied. Wet Purification Plant This may include one, two, or three of the following types of plant Tower scrubber. Livesey type washer. Mechanical washer. Washer-scrubber. Purifying machine. The last mentioned includes one or two makes of mechanical apparatus which remove both. tar and ammonia. The washer-scrubber is mechanical, and the many different patterns conform to one general type. Livesey washers, made by many firms, are not .mechanical; and the first mentioned in the list is usually fed with water or liquor by mechanical means. In many cases two pieces of plant in the above list are associated with a tar extractor of the Pelouze pattern. By far the most common combination is a mechanical washer-scrubber followed by one or more tower scrubbers. If two are adopted, the last is fed with. clean water, which. should, if desired, remove the whole of the ammonia. In small works, it is common to have only one or two tower scrubbers, with no mechanical washing apparatus whatever. When associated with a mechanical apparatus, the scrubber allowance should be at least equal to 5 or 6 cubic feet per 1,000 cubic feet of gas per day. Newbigging and Herring recommend 9 cubic feet. In cases where no washer-scrubber is employed, the aggregate capacity of ordinary washers and scrubbers must be increased to 10 cubip feet per 1,000. In very small works where only one tower scrubber is used, this figure might with advantage be increased to 12 cubic feet. The ratio of the height of a scrubber to its diameter varies in normal cases from 2| to 5. With regard to the otter forms of apparatus mentioned, each manufacturer has his own standard sizes of plates for varying capacities, but as a general guide the following figures will be found useful:— Livesey washers . ... |-i. cubic feet per 1,000 cubic feet per day. Washer-serubbers .... BH Dry Purification Plant If it is necessary or desirable to remove sulphur compounds otter than sul-phuretted hydrogen, the purifier capacity is increased, this frequently calling for the use of lime in addition to oxide of iron (or its equivalent). Under such circum-stances it is advisable to increase slightly the size of the vessels, as well as further increasing the capacity by means of catch boxes. It sh.ou.ld be remembered that if more area can be given than in. the following rules, it is never wasteful, purification charges undergoing reduction, whilst the first oost of the plant increases slowly as compared with the capacity. In other words, the smaller the boxes the more expensive do they become per unit of purifying capacity. For oxide purification