MXPA99000665A - PROCEDURE FOR THE ELIMINATION OF NITROSILSULFUR ACID NOx CONTENT - Google Patents

Abstract

Nitrosyl sulfuric acid is mixed in a mixing reactor with sulfuric acid saturated with S02. The mixture is passed to a saturation reactor to the bottom of which water is introduced and a gas containing SO2. The gas partially serves as a wash gas inside the saturation reactor. Sulfuric acid saturated with SO2, free of NOx and with 5 to 60% of H2SO4 is removed from the bottom region of the saturation reactor and part of it is mixed with acid. nitrosylsulfuric in the mixing reactor

Description

PROCEDURE FOR THE ELIMINATION OF THE CONTENT OF NITROSILSULFURIC ACID NOx.

The invention presents a process for eliminating nitrosyl sulfuric acid by mixing the nitrosylsulfuric acid in a mixing reactor with sulfuric acid which is saturated with S02 / whereby a sulfuric acid containing N203 / and through the sulfuric acid is evacuated from the mixing reactor. evacuated a washing gas is conducted. A process of this nature is known from GB-A-0348866. There it is conducted, to remove the nitrogen oxide remaining from the exhaust gas, sulfuric acid or an inert gas through the sulfuric acid, in which the temperature is in the range of 100-200 ° C. In the PI database, AN91-108 779 it is described that sulfuric acid containing Nox (waste acid) is mixed with recirculating acid and fed a second column. In the bottom region of the second column, S02 gas is introduced, which comes from a first column. A portion of the recirculation acid discharged from the second column is fed * to the first column, which reaches S02 in excess. The waste gas from the second column does not contain S02, and the sulfuric acid evacuated from the first column, which is free of NOx, contains 75% by weight of H2SO4. In the known processes, a mixture of waste acid of saturated sulfuric acid with S02 is not carried out. The invention proposes the task of eliminating NOx from nitrosylsulfuric acid easily and economically. According to the invention this is solved by the aforementioned process, in which the sulfuric acid containing N203 obtained from the mixing reactor feeds a saturation reactor, whereby at the same time a saturation reactor is introduced into the lower part of the saturation reactor. gas containing S02, which at least partially rises through the stream of sulfuric acid containing N203, in which water is introduced into the saturation reactor and which is obtained from the mime practically NOx-free sulfuric acid with a concentration of H2SO4 from 5 to 60% by weight, of which one part is fed to the mixing reactor, whereupon this SO2 is fed in a stoichiometric excess of at least 2% by weight, calculated on the basis of the N0X content of the acid nitrosylsulfuric. The expression "NOx" refers, in the sense of the invention, to a mixture of NO and N02. N0X is found in sulfuric acid in the form of dissolved nitrosylsulfuric acid. Nitrosilylsulfuric acid is formed from the NO that is included in gas containing S02. The gas containing S02 comes, for example, from the process of roasting, sulfur combustion, sulphate dissociation or a metallurgical process. NO is oxidized to N02 by up to 50% in the oxidation catalyst of the sulfuric acid production facility. The mixture of NO and N02 is transformed with sulfuric acid into nitrosylsulfuric acid, in the following way: NO + N02 + 2S04H2 - 2S04NOH + H20 It is known that S02 reacts with nitrosylsulfuric acid with the formation of sulfuric acid and nitrogen oxides: S02 + 2S04NOH + 2H20 - 3S04H2 + 2N0. In the production of sulfuric acid, nitrosylsulfuric acid, with a NOx content in > 2.5%, it is separated as condensate. In the condensate, the NOx content is in the form of nitrosylsulfuric acid, together with the sulfuric acid. Formally, nitrosylsulfuric acid is transformed with S02 and water into sulfuric acid and N2. The redox reaction takes place between the dissolved S02, in the form of S032", and the N203 originated by the hydrolysis of nitrosylsulfuric acid, in the form of N02 The reduction of the nitrogen oxides of NO and N02 elemental nitrogen in the hydrolysis of the acid Nitrosylsulfuric acid with dilute sulfuric acid saturated with S02 is favored by having a reducing agent in the dilution solution, in the form of S032", in a higher proportion than stoichiometric and moving the equilibrium in the direction of N2 formation. An advantage of the present invention is that the sulfuric acid fraction of the condensate containing nitrosylsulfuric acid is recirculated free of N0X to the circulating stream in the production of sulfuric acid. According to the usual procedure, the condensate is extracted from the process and must be treated or discarded. A special advantage of the process according to the invention is that nitrogen is formed from the noxious substance NOx and nitrogen is removed with the fumes. A preferred embodiment of the invention consists in using S02 in a minimum excess of 5% by weight on the stoichiometric, based on the content of N0X in the acidic acid. With this excess of S02 a good result in the reduction of the NOx content is achieved. S02 is not lost by reducing NOx to N2, but is oxidized to S04 ~ "The excess S02 can be conducted to a sulfuric acid production plant, so that no further treatment is needed. of the invention is that after the addition of S02 the concentration of the sulfuric acid rises to 5 to 30% In this concentration range of sulfuric acid especially good results are achieved in the reduction of N0X to N2.

An advantageous embodiment of the invention consists in bringing the gaseous SO2 to aqueous solution in a filler column and washing it, in the form of an aqueous solution, with the sulfuric acid containing N0x. With this, saturation with S02 is favored by the operation of the saturator at high gas pressure of S02. According to the invention, it is envisaged to reduce the NOx content in a sulfuric acid containing NOx or in a mixture of sulfuric acids containing NOx. The process according to the invention can advantageously be applied with very good results not only to sulfuric acid containing NOx but also to mixtures containing NOx and sulfuric acid, such as, for example, sulfuric acid or sulfuric acid doped with other comps. The present invention is clarified in more detail by virtue of an illustration and examples. The drawing shows a flow diagram of the process. The most important steps of the process are the reactor (X) for the saturation of S02 and the mixing reactor (Y) for hydrolysis 4 redox reaction of nitrosylsulfuric acid with dilute sulfuric acid containing S02. Toasting gas containing S02 is introduced through the pipe (1) and water is introduced through the pipe (4) into the bottom region of the saturation reactor (X). By pipe (3) nitrosylsulfuric acid or its acid-containing condensate is fed to the mixing reactor (Y). At the beginning, it is conducted between the reactors (X) and (Y) diluted sulfuric acid through the pipes (5), (6), (6A), (7) and (8) in recirculation. The sulfuric acid formed is evacuated through the pipe (6B) and the N2 is conducted with the waste gas through the pipe (2). Through the pipe (5) sulfuric acid is evacuated from the saturation reactor (X) and conducted by means of a pump (9). This sulfuric acid is saturated with S02, is practically free of N0X and has a concentration of H2SO4 of 5 to 60% by weight and almost always of maximum 35% by weight. From the pump (9) sulfuric acid is conducted through the pipeline (6) A part of the acid is conducted through the pipe (6A) to the mixing reactor (Y). The acid evacuated from the reactor (Y) in the pipe (7), which still contains N203, is conducted to the indirect cooler (). Cooling water is fed into the cooler through the pipe (10), which is evacuated through the pipe (11). The cooled sulfuric acid is conducted via line (8) to the saturation reactor (X). The reactor (X) contains at least one filling layer. In the reactor (X) rises a stream of gas containing S02 as wash gas to remove remaining nitrogen oxides of the sulfuric acid conducted by the pipe (8). EXAMPLES Example 1: In one of the embodiments of the drawings, the procedure is as follows: Through the pipe (3), the mixing reactor (Y) was fed with 240 kg / h of condensate with a nitrosylsulfuric acid content of 9.5% of S04NOH, equivalent to 6.8 kg / h of N203. The condensate comes from the production of sulfuric acid. Through the pipe (6A) the mixing reactor (Y) was fed with a sulfuric acid with 20% by weight of H2SO4, saturated with SO2. The condensate and sulfuric acid saturated with S02 were mixed. With this, dissolved S02 reacted with nitrosylsulfuric acid, to give sulfuric acid and elemental nitrogen. The mixture was discharged through the pipe (7) and after the cooling block () still exhibited a content of 465 mg of N203 / 1. This corresponds to a content of 2.0 kg of N203 / h. In the saturator (X), the circulating sulfuric acid was saturated with S02, whereby the roasting gases containing S02, containing 0.28 g / h of Nox, are passed through the pipe (1). Concentration at 20% by weight of S04H2 by controlled addition of water through the pipe (4). The roasting gases leaving the reactor (X) through the pipe (2) exhibited a lower content in S02 and were fed back into the gas stream of the sulfuric acid production plant, in the form of a wet gas. The gas containing S02 of the pipe (2) contains 3.125 mg NOx / Nm3, equivalent to 2.0 kg of N203 per hour. In the sulfuric acid of the pipes (6A) and (6B) some N0X was no longer recognizable. The degree of denitration was 71. 75% Example 2: Example 2 was carried out as example 1 with the following differences. The mixing reactor (Y) was fed through the pipe (6A) with sulfuric acid of 16% by weight of H2SO4; saturated with S02 After the cooling block (W), the sulfuric acid in the pipeline (8) contained 400 mg of N203 / l, equivalent to 1.7 kg of N203 / h. In the saturation reactor (X) a sulfuric acid with a concentration of 16% by weight of H2SO4 was produced after the controlled addition of water through the pipe (4), which is eliminated through the pipe (5). The degree of denitration was 71.75%. Example 3: Example 3 was carried out as examples 1 and 2, with the following differences: Through the pipe (3) the mixing reactor (Y) was fed with 190 kg / h of condensate. The condensate exhibited a nitrosylsulfuric acid content of 7.5% S04NOH, equivalent to 4.3 kg of N203 per hour. LEÍ condensed was mixed in the mixing reactor (Y) with a sulfuric acid of 33%, saturated with S02, of the pipe (6A). After the cooling block (), the sulfuric acid in line (8) exhibited 350 mg of N203 / l, equivalent to 1.5 kg of N203 / h. In the saturation reactor, after the controlled addition of water, a sulfuric acid with a concentration of 33% of S04H2 was produced, which was eliminated through the pipeline (5). The acid does not contain N0X the gases of S02 evacuated by the pipeline (2) contained 4,700 mg / NOxNm3, equivalent to 3.0 kg of N203 / h. The degree of denitration was 34.5%. The comparison of examples 1 to 3 shows that there is a dependence between the transformation of N0x and the concentration of circulating sulfuric acid. The higher the concentration of the sulfuric acid maintained in circulation, the smaller the rate of denitration. The advantage of a denitration ratio as high as possible is that the fraction of NOx that is directed to the circulating current is smaller. NOx that is not removed in the denitration plant returns with the main gas stream to the sulfuric acid production facility, where it then re-forms nitrosylsulfuric acid. A smaller denitration rate requires a larger denitration installation.

Claims (1)

1. R E I V I N D I C A C I O N E S. Procedure for the elimination of NOx of the mixed nitrosylsulfuric acid of nitrosylsulfuric acid in a mixing reactor with sulfuric acid, which is saturated with S02, whereby a sulfuric acid containing N203 is obtained from the mixing reactor and conducted through the sulfuric acid obtained a washing gas, characterized in that the sulfuric acid containing N203 obtained from the mixing reactor feeds a saturation reactor, whereby at the same time a gas containing S02 is introduced in the lower part of the saturation reactor, which at least partially it rises through the stream of sulfuric acid containing N203, in which water is introduced into the saturation reactor and practically NOx-free sulfuric acid is obtained therefrom with a concentration of H2SO4 of 5 to 60% by weight. weight, of which a part is fed to the mixing reactor, whereupon it is fed to this S02 in a stoichiometric excess and at least 2% by weight, calculated based on the N0X content of the nitrosylsulfuric acid. Process according to claim 1, characterized in that the sulfuric acid evacuated from the mixing reactor, is cooled before being introduced into the saturation reactor. Process according to claim 2, characterized in that the sulfuric acid expelled from the mixing reactor is indirectly cooled with cooling water, whereby cooling water heated from indirect cooling is evacuated. Process according to claim 1 or one of the following, characterized in that the mixing reactor S02 is fed by means of the partial stream of sulfuric acid saturated with S02, in a stoichiometric excess of at least 5% by weight, in based on the N0X content of nitrosylsulfuric acid. Process according to the 1 or one of the following, characterized in that a sulfuric acid saturated with S02 with an H2S04 content of 5 to 35% by weight is evacuated from the saturation reactor. Process according to claims 1-5, characterized in that the nitrosylsulfuric acid comes from a plant producing sulfuric acid from roasting gas containing * S02, and in which roasting gas containing S02 is introduced in the part bottom of the saturation reactor. p K s u M TÜ u Nitrosilylsulfuric acid is mixed in a mixing reactor with sulfuric acid saturated with S02. The acid mixture is conducted to a saturation reactor towards the bottom of which water and a gas containing S02 are introduced. The gas partially serves as a wash gas within the saturation reactor. Saturated sulfuric acid of S02, free of N0X and with 5 to 60% of H2SO4 is removed from the bottom region of the saturation reactor and part of it is mixed with nitrosylsulfuric acid in the mixing reactor.