TH1472A - Sulfuric acid production process - Google Patents

Abstract

This invention relates to a process for producing sulfuric acid from filtered SO2-containing gas. The process involves a multi-step chemical reaction of SO2 to SO3, with subsequent SO3 absorption from the final step of each process. The humid SO2-containing gas, with water content not exceeding the equilibrium water ratio, is dried with concentrated sulfuric acid before entering the first step. The water absorbed by the dry acid is then transferred to the absorbent acid, which then absorbs SO3. The absorbed acid is then recirculated at a rate consistent with the drying step. All absorption occurs at high temperatures, and excess heat generated during the process is utilized.

Claims (12)

1. The process of producing sulfuric acid from filtered SO2 gas mixture involves a chemical reaction between SO2 and SO3, followed by the absorption of SO3 in a middle absorption unit and final absorption of SO3 in a final absorption unit after the final contact process. The humid gas containing water at a ratio not exceeding the equilibrium ratio is dried with concentrated sulfuric acid before entering the first stage of the contact process. Water absorbed by the drying acid is then transferred along with the drying acid to the absorption acid that absorbed SO3. This absorption acid is returned at the same rate as used in the drying step. The middle absorption stage is performed at high temperatures, utilizing excess heat. A unique characteristic of this process is that the gas is first dried with diluted sulfuric acid (approximately 40 to 80% by weight) to separate the water from the gas before being further dried with concentrated sulfuric acid. At least a portion of the water absorbed by the acid in the first drying unit is retained. The acid is sent along with the absorption unit, which absorbs SO3. The absorbed acid used to absorb SO3 is then recirculated for reuse at a rate consistent with the operation of the first drying unit. 2. The process described in claim 1 is characterized by the separation of water mixed in the gas by a first drying unit at a rate of 50 to 98%. 3. The process under claim 1 or 2, which is characterized by drying, can be accomplished using concentrated sulfuric acid without the need for cooling the acid drying system. 4. Any process under claims 1 through 3 that has a special characteristic of using air mixed with SO3 gas during the initial drying stage and the main drying stage. 5. Any process under claims 1 through 4, characterized by the fact that all or part of the adsorption acid used for SO3 adsorption is delivered into the acid drying system at a rate required by the first drying unit before being returned from the acid drying system. 6. Any process under claims 1 through 5, which is characterized by the separation of a portion of the acid used in the first drying step into a product acid along with water at a rate in which the water injected with the acid is added to the SO3 absorption system. 7. Any process under claims 1 through 6 that has a special characteristic of adding water to the SO3 absorption system when the gas flowing into the first and main drying units has a water content lower than the equilibrium rate. 8. Any process under claims 1 through 7, characterized by the acid separated from the first drying unit being introduced into the intermediate SO3 absorption system. 9. Any of the processes described in claims 1 through 8, which have a special characteristic in that a portion of the SO3 mixture gas obtained from the first process is passed through an obium production unit before being sent to the central absorption unit. This gas, before being sent to the oleum production unit, must be cooled by indirect heat switching with the portion flowing out of the oleum production unit. This portion flowing out of the oleum production unit must have been preheated. It is then mixed with the remaining gas, and the mixture is then sent to the central absorption unit. 10. The process under claim 9, which is unique in that the gas portion is cooled to approximately 120 to 160°C before being sent to the oleum production unit, and the gas flowing out from the oleum production unit is further heated to approximately 100 to 150°C. 11. The process under claim 9 or 10, which is characterized by the presence of residual SO3 gas not being fed into the oleum production unit, is further heated by indirect heat alternation with the gas flowing out of the oleum production unit, and after being further heated, is mixed with the residual gas. 12. Any of the processes described in claims 1 through 11, which are characterized by the initial drying and/or primary drying and/or SO3 absorption being internal production steps that can be performed in a redundant manner, with approximately 50 to 80% of the acid being fed into the first stage of the gas flow and the remainder into subsequent stages (12 claims, 3 pages, 6 figures).