Modern Gasworks Practice

532 MODERN GASWORKS PRACTICE AMMONIA LOST THROUGH SCRUBBERS Many engineers, nowadays, make a practice of allowing a very small amount of ammonia to travel forward from the scrubbers to the purifiers. In this way the oxide of iron. is maintained in an alkaline condition and fulfils its functions more satisfactorily. The amount of ammonia permitted to travel forward varies from 0-5 to 1 grain. per 100 cubic feet. In making tests for the quantity of ammonia passing through the scrubber it is preferable to calculate the total ammonia loss ratter than to state the quantity in so many grains per 100 cubic feet of gas. Only by considering the total quantity of gas passed can the actual loss, which should be stated in th.e equivalent of so many gallons of 8 oz. or 10 oz. liquor, be gauged. The folio wing is themeth.od of making the calculation :— Total grains of ammonia lost per week _ Gas made for week No. of grains per 100 cubic feet at scrubber outlet. In 1 gallon of 10 oz. liquor there are 1,522 grains of ammonia. . ■. Quantity of 10 oz. liquor lost (in gallons) Total grains of ammonia lost per week = 1J522 ’ CONSERVATION OF AMMONIA Although. the quantity of ammonia recovered from coal is influenced consider-ably by the männer of carbonization, a consideration of even greater importance to the gas engineer is that of curtailing loss by evaporation and leakage. Exposed surfaces or streams of ammoniacal liquor evolve botli ammonia and sulpliuretted hydrogen, the extent of the loss depending largely upon temperature, although the more extensive the exposed surface the more rapidly will the dissolved gases be emitted. It is essential, therefore, that all seal pots or catch sumps should be fitted with. tightly sealed covers, preferably water-luted, while the delivery pipes which convey liquor and tar to the storage well should. be dipped below the lowest level of the liquid in the well. The m'ain contributory causes of low yields of ammonia may be stated as follows :— (c) The indifference frequently displayed at the smaller works. (d) Losses due to evaporation in imperfectly covered storage wells, seal pots, or from falling arid splashing streams of liquor. (e) Abnormally high ammonia content of effluent liquor escaping from sul-phate of ammonia stills. The loss in this case is mainly due to insufficient quan-tities of lime being added, so that the whole of the fixed ammonia is not liberated. As an instance of the manner in which. the ammonia recovered varies at different gasworks the following figures1 may be quoted :— 2 Hollingworth & Fottrell, Gas. J., March 9, 1920, p. 557.