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Absorption of Carbon Dioxide from Gases For the leaching of carbon dioxide from gases by means of aqueous ammonia, which process is particularly advantageous for the processing of coke oven gas for ammonia synthesis, only relatively low-ammonia solutions can be used, since the heat of reaction occurring during the absorption of the carbonic acid is quite considerable and the resulting increase in temperature of the solution makes the absorption incomplete. the more dilute the solution used, the higher the steam consumption for the necessary regeneration of the ammonia from the resulting ammonium carbonate solution.

The present invention allows to obtain highly concentrated ammonium carbonate solutions, without the absorption of carbon dioxide is impaired by inadmissible increase in temperature of the washing liquid. It is based on the observation that the rate of absorption of carbon dioxide by ammonia-containing solutions is not substantially diminished when, in addition to the free ammonia, a relatively large amount of ammonium carbonate is present. The idea of ​​the invention consists in diluting the freshly supplied high-percentage ammonia instead of water with an ammonium carbonate solution, and thus also using a wash liquor which contains relatively little free ammonia and, as a result, heats up only slightly when taking up carbon dioxide. but in addition contains a high percentage of already bound ammonia in the form of ammonium carbonate. This solution is obtained by recycling part of the carbonate solution obtained at the bottom of the scrubbing tower in the tower and adding only as much fresh ammonia as is required to absorb the carbonic acid from the gas. In order to achieve a complete absorption, the gas after washing with the aforementioned solution may be subjected to a post-washing with the fresh ammonia water required as an additive. Although processes have already become known in which the amount of ammonia required for carbon dioxide absorption is returned to the process, the recycling of the ammonia from the spent ammonium carbonate solutions always takes place after prior regeneration, so that the washing liquid introduced into the process no longer contains ammonia contains in bound form.

The implementation of the method is explained with reference to the figure. The gas to be liberated enters into a scrubbing tower a at r and is washed by ammonia water, which is fed at 5 and flows countercurrently downwards, and freed from carbon dioxide. Part of the C02-containing liquid is at; removed from the lower end of the wash tower and returned by means of a pump 8 in the wash tower at 6. The heat of reaction can be dissipated in a cooler 9 by cooling water. The excess of the absorption liquid is removed at io. The arrangement achieves: r. in that in the part of the absorption tower serving for the absorption of the carbonic acid, a larger amount of absorption liquid flows towards the gas, so that favorable conditions for a substantial absorption of the carbon dioxide are present. Without the given cycle, for example, for a gas with a z% CO "content and a 40 /" wash ammonia, the amount of liquid would be only o.8% of the gas volume, and it is difficult to achieve sufficient liquid to gas contact; z. For example, the heat of reaction can be readily removed as a result of the large volumes of washing fluid used; Third can withdraw a solution due to the circulation of the washing liquid at io, which is arbitrarily strong at ammonia and the whole ammonia bound to carbonic acid, with even a fraction may be present as ammonium bicarbonate. As a result, requires a very extensive use of ammonia, possibly. Regeneration, the ammonia from this solution only a fraction of the heat, which had to be expended in previously dilutable dilute solutions.

q. By optionally introducing the fresh ammonia water at a corresponding higher point in the scrubbing tower, it is achieved that the gas washed with the ammonium carbonate solution, which still contains small amounts of CO, in the tower section above 6 of the residues CO, is released. In order to reduce the ammonia content of the gas as far as possible, a part of the water to be supplied continuously at the highest point of the tower at q. introduce while at the same time giving up 5 a correspondingly stronger ammonia solution. As a result, the entrained with the gas ammonia is largely washed out again.

5th Another advantage of the method is that it is completely continuous and requires only simple means of equipment (a washing tower and a circulation pump).

The filling of the wash tower can be done with any material that ensures a good contact between liquid and vapor. Conveniently, you can in the lower part of the tower, where a relatively large amount of liquid circulates Raschigringe use for filling, while providing in the upper part of soils, as is usual in rectification columns. Instead of using a tower of the appropriate height, it is of course also possible to subdivide the tower into several towers connected in series in the gas flow direction.