Process for the continuous reaction of sodium sulphate to give sodium hydrogen carbonate and gypsum by means of flue gas and lime

摘要

The invention relates to a process for the continuous reaction of sodium sulphate to give sodium hydrogen carbonate, by dissolving sodium sulphate in ammoniacal solution and then trickling it in a scrubber countercurrent to cooled flue gas, with sodium hydrogen carbonate partly precipitating because of its low solubility and being able to be separated off. To obtain, in terms of mass balance, an almost 100% yield, it is necessary to circulate the scrubber solution in the appropriate ratio to the fresh solution. The proportion of the solution transferred outwards from the scrubber flows into a degassing plant in which, in a first step, free ammonia and carbon dioxide are driven off, and, in a further step, bound ammonia is driven off after making alkaline with milk of lime (calcium hydroxide suspension). In the second degassing step, gypsum is simultaneously precipitated by reaction with sulphate. The gypsum is separated off, freed of coprecipitated carbonate by means of washing with sulphuric acid and again dewatered and washed. The distillates containing all the ammonia and the bottom product of the degassing plant desaturated of dissolved gypsum by means of carbonation with a substream of flue gas are recirculated via heat exchangers or coolers to the dissolving station for sodium sulphate. To maintain the water balance, a small substream of the bottom product from the degassing plant upstream of carbonation is discarded as effluent.