Methods and apparatus for extracting ammonium bicarbonate from water containing ammonia and carbonic acid, such as gas washing water

摘要

Ammonium bicarbonate is obtained from water containing ammonia and carbonic acid by dividing the water into two parts, passing steam through the first part to distil off the dissolved ammonia and carbonic acid gas, passing the resultant mixture of steam and gases with more steam through the second part at a temperature such as to distil from it the dissolved carbonic acid gas but substantially none of the ammonia, and cooling the final resultant gas mixture to yield crystals of bicarbonate. Gas from the degasification of hard coal or lignite is washed with water in tower 1 and the water containing ammonia and carbonic acid continuously passing from the bottom of the tower is divided into two streams 2, 3. Stream 2 is preheated in exchanger 4 and passes to the top of first separator 5 and flows down therein over spaced platforms, while steam to raise the temperature to about 100 DEG C. is passed over and through it in the opposite direction. Water from the base of separator 5 flows through exchanger 4 to preheat incoming stream 2 and out at 6 to waste. Stream 3 after preheating in exchanger 9 passes to the top of second separator 8 and the mixture of steam, ammonia, and carbon dioxide. driven off in separator 5 and fed through pipe 7, together with additional steam at a lower temperature, e.g. 80-97 DEG C. than that in separator 5 passes upwards over and through it and further carbonic acid gas is driven off. The water still containing ammonia passes from the base of separator 8, through exchanger 9 to preheat incoming stream 3, and then through pipe 10 with a cooler back to washing column 1. The gas mixture from the top of separator 8 passes to crystallizing closed drum 13, the external surface of which is cooled by liquid from nozzles 14. Crystals of bicarbonate are deposited on the walls of drum 13 and are scraped off by rotary spiral screw 15, which delivers them to trough 16, whence they are fed by conveyer 17 to hopper 18, and thence to centrifuge 19 to separate mother liquor. Remaining gases consisting of surplus carbon dioxide, hydrogen sulphide, and hydrogen cyanide are withdrawn at 20. The ratio of the two parts into which the water is divided may be adjusted volumetrically to ensure that the ratio of ammonia from the first part to carbon dioxide from both is approximately equimolecular.