GB365737A - Process for obtaining ammonia as ammonium sulphate from gases - Google Patents

Abstract

Ammonia; ammonium sulphite; sulphur; sulphur dioxide; sulphur trioxide; iron ferrocyanide.--In obtaining ammonium sulphate from gases containing ammonia but free or freed from sulphuretted hydrogen, ammonium sulphate lye traverses a cyclic path through a first scrubber for absorbing gaseous sulphur dioxide and a second scrubber for taking up ammonia, the lye being oxidized in a separate step in the cyclic path from the ammonia <PICT:0365737/III/1> scrubber to the first scrubber and the ammonia washing being so carried out in countercurrent that the lye on discharge from the ammonia scrubber is in an ammoniacal condition. The gases to be treated may be obtained from the dry distillation or gasefication of solid fuel such as coal, for example coke-oven gas, producer gas or the like, their original content of sulphuretted hydrogen being utilized as a source of sulphur dioxide necessary in the process. Crude gases from distillation furnaces or the like enter through a pipe 1 one or more tubular coolers 2, the tar and ammonia separating being passed through a pipe 3 to a decanter 4 from which the ammonia liquor passes to a container 6. The ammonia liquor proceeds from the container 6 via a pump 9 to a distilling apparatus 11, the resulting vapours passing through a pipe 12 to mix with the cooled gases which have passed from the cooler through a pump 7 to a pipe 8. The gases are washed in a scrubber 13 by an aqueous suspension of iron oxides maintained at 30-40 DEG C. which frees them from sulphuretted hydrogen and cyanogen compounds. The washing liquor from the bottom of the scrubber 13 is forced by a pump 16 into an oxidizing tower 17 comprising a high column of liquid up which compressed air is forced. Crude sulphur also containing Prussian blue floats as a frothy mass on the liquid and passes through a pipe 19 into a separating vessel 20 from which the liquid containing the regenerated iron compounds returns to the scrubber 13. The wet sulphur passes through a pipe 23 to a container 24 and through a pipe 26 to a rotary filter drum 27, the dried sulphur being removed by a scraper 28 and passing through a worm conveyer 29 and a pipe 73 to an externally gas heated continuously operated rotary drum furnace 34. Air enters at 38. In the cooler upper zones of the furnace the prussian blue reacts with traces of water still present to form ammonia while in the hot zone sulphur is roasted to sulphur dioxide containing some sulphur trioxide. The gases pass from the furnace 34 through a cooler 40 and pipe 41 to a vessel 42 where the relatively hot gases are sprinkled with a limited quantity of water or one of the treating liquids free from sulphuretted hydrogen a dilute sulphuric acid solution being obtained. The other gases proceed through a pipe 44 to the lower part of a packed scrubber 45 up which they pass in counter current, initially to water and subsequently to aqueous ammonium sulphate formed in the process. Sulphurous acid and ammonium sulphite are thus formed while the gases freed from ammonia and sulphur dioxide pass out via pipe 47. The sulphurous acid lye from the scrubber 45 collects above a base 48 and pass through a pipe 49, a vessel 50 and a sprinkler 51 to a packed scrubber 52. The gas containing ammonia withdrawn from the scrubber 13 is led by a pipe 53 to the bottom of the scrubber 52 up which it passes in counter current to the sulphurous acid lye. The ammoniacal lye collecting at the bottom of the scrubber 52 is delivered by a pipe 54 and pump 55 to an oxidizing tower 56 containing a high column of liquid through which air at a pressure of 6-8 atmospheres is forced via a distributer 57. The oxidized ammonium sulphate lye is led from the tower 56 through an outlet 60, reducing valve 59 and cooler 62 to the top of the scrubber 45 down which it flows to absorb further sulphur dioxide. A portion of the lye is withdrawn from time to time by a pipe 64 to be evaporated in a fired pan 65 to ammonium sulphate, the excess of ammonia being neutralized by introducing the necessary amount of sulphuric acid from the vessel 42 via a pipe 66. The remaining sulphuric acid is led from the vessel 50 to the scrubber 52. The gas passing from the upper part of the scrubber 52 is led through a pipe 68 to a scrubber 69 where by treatment with water it is freed from the last traces of ammonia and is withdrawn through a pipe 71. The liquor collecting at the bottom of the scrubber 69 is led through a pipe 72 to the bottom of the tower 52, to compensate for liquor withdrawn through the pipe 64. If the sulphur content of the raw gases is insufficient, additional sulphur, pyrites or the like may be roasted in the furnace 34.