Equipment and process for preparing sulfuric acid by wet method and recovering waste heat in preparation process

Abstract

The invention belongs to the technical field of wet-process acid preparation, and particularly relates to equipment and a process for wet-process sulfuric acid preparation and waste heat recovery in the preparation process. The system comprises: a flue gas purification section comprising a flue gas inlet and a flue gas outlet; the flue gas acid making section comprises a combined converter and a combined absorption tower, the combined absorption tower is provided with a condensation gas inlet, a condensation gas outlet and a conversion gas inlet, the condensation gas inlet is communicated with the flue gas outlet, the combined converter is provided with a process gas inlet and a conversion gas outlet, the process gas inlet is communicated with the condensation gas outlet, and the conversion gas outlet is communicated with the conversion gas outlet. The converted gas outlet is communicated with the converted gas inlet; and the waste heat recovery section comprises an evaporator which is communicated with an acid circulation tank at the bottom of the combined absorption tower. The invention is used for solving the technical problem of low waste heat recovery utilization rate of wet-process sulfuric acid preparation equipment and process in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of wet-process sulfuric acid production, and particularly relates to an apparatus and process for wet-preparing sulfuric acid and recovering waste heat during the preparation process. Background Art

[0002] During the production process of wet-process sulfuric acid, a large amount of heat is generated. The sources of this heat are divided into three parts: the combustion of sulfur-containing raw materials, the conversion of sulfur dioxide, and the absorption (or condensation into acid) of sulfur dioxide. In the wet-process sulfuric acid process, the purified process flue gas is preheated through 2 - 3 stages, and the process flue gas needs to be heated to a temperature of 400 - 420 °C before entering the combined reactor for conversion (when the volume ratio concentration of SO2 in the flue gas is 0 - 2.5%, it is a two-stage process; when the volume ratio concentration > 2.5%, it is a three-stage process). The heat at this time is called high-temperature waste heat; the heat of the flue gas after conversion drops to a temperature of about 280 ± 5 °C (higher than the dew point temperature of the flue gas, and generally the dew point temperature of saturated acidic gas is about 252 ± 4 °C) is called medium-temperature waste heat; the heat during the process of condensing into acid from 240 °C to about 105 °C is called low-temperature waste heat.

[0003] Among them, the high-temperature waste heat accounts for about 57% of the total waste heat, the medium-temperature waste heat accounts for about 8% of the total waste heat, and the low-temperature waste heat accounts for about 58% of the total waste heat. If these heats can be fully recovered, not only can energy be saved and consumption reduced, but also economic and social benefits can be improved.

[0004] In addition, the tower trough of the existing heat recovery tower has an integrated through structure, with a liquid accumulation trough at the bottom, and the liquid accumulation trough and the circulation trough are connected by a connecting pipe; the middle part is the absorption section, which has two sections. The first section below is the high-temperature absorption section, and the second section above is the low-temperature absorption section. The high-temperature absorption section and the low-temperature absorption section are directly connected in the middle. The low-temperature and low-concentration sulfuric acid in the low-temperature absorption section directly mixes into the high-temperature and high-concentration sulfuric acid in the high-temperature absorption section, reducing the temperature and concentration of the high-temperature and high-concentration sulfuric acid, reducing the output of low-pressure steam of the evaporator, increasing the flow rate of the high-temperature and high-concentration sulfuric acid, increasing the power consumption of the equipment and the heat exchange area of the heat exchanger. Summary of the Invention

[0005] The present invention provides an apparatus and process for wet-preparing sulfuric acid and recovering waste heat during the preparation process, which is used to solve the technical problem of low waste heat recovery and utilization rate of the existing wet-process sulfuric acid equipment and process. An apparatus for wet-preparing sulfuric acid and recovering waste heat during the preparation process according to the present invention includes: A flue gas purification section, including a flue gas inlet and a flue gas outlet; The sulfuric acid production section from flue gas includes a combined converter and a combined absorber. The combined absorber is provided with a condensate inlet, a condensate outlet, and a converted gas inlet. The condensate inlet is communicated with the flue gas outlet. The combined converter is provided with a process gas inlet and a converted gas outlet. The process gas inlet is communicated with the condensate outlet. The converted gas outlet is communicated with the converted gas inlet; The waste heat recovery section includes an evaporator, and the evaporator is communicated with the acid circulation tank at the bottom of the combined absorber.

[0006] Furthermore: The combined converter includes a preheater and an interlayer heat exchanger. The preheater includes the process gas inlet, the process gas outlet, the converted gas outlet, and the converted gas preheating inlet; The inlet of the interlayer heat exchanger is communicated with the process gas outlet, and the outlet of the interlayer heat exchanger is communicated with the converted gas preheating inlet. The beneficial effect of this step is that the SO2 flue gas enters from the preheater, then enters the interlayer heat exchanger for reaction to generate SO3 flue gas. Then the SO3 flue gas enters the preheater again. The preheater preheats the SO2 flue gas, increases the temperature of the SO2 flue gas, which can not only promote the conversion of SO2 flue gas into SO3 flue gas, but also utilize the heat generated by the conversion of SO3 flue gas to reduce the temperature of the SO3 flue gas, avoiding the temperature of the circulating acid in the combined absorber from rising too high, resulting in overheating and failure of the acid circulation pump.

[0007] Furthermore: An electric furnace is also provided between the preheater and the interlayer heat exchanger. The beneficial effect of this step is that the electric furnace is used as a heat compensation tool. When the application starts initially and there is no already converted SO3 flue gas to preheat the SO2 flue gas, the temperature of the SO2 flue gas can be increased by the electric furnace.

[0008] Furthermore: The combined absorber is successively provided with a liquid accumulation section, a circulating acid heat removal section, a condenser acid production section, and a demisting section from bottom to top; The demisting section includes several groups of tube - type fiber demisters; The condenser acid production section includes glass condenser tubes. The condensate inlet and the condensate outlet correspond to the condenser acid production section. The condenser acid production section is also provided with an acid outlet; The circulating acid heat removal section includes a packing area and a distributor located above the packing area. A riser cap is provided between the circulating acid heat removal section and the condenser acid production section. The circulating acid heat removal section also corresponds to the converted gas inlet; The liquid accumulation section includes an acid circulation pump and the acid circulation tank. The acid circulation pump transports the acid in the acid circulation tank to the evaporator. The beneficial effect of this step is as follows: The SO3 flue gas enters from the circulating acid heat transfer section of the combined absorption tower. SO3 in the SO3 flue gas reacts with H2O to generate sulfuric acid vapor. Part of the heat is transferred into the circulating acid, and the circulating acid then enters the evaporator to heat the water in the evaporator into water vapor, realizing the utilization of low-temperature waste heat. Another part of the heat enters the acid production section of the condenser along with the sulfuric acid vapor and condenses into sulfuric acid liquid in the glass condenser tube, and can also heat up the SO2 flue gas flowing through the acid production section of the condenser, realizing the utilization of medium-temperature waste heat.

[0009] Furthermore: There are two branches at the circulating acid outlet of the evaporator. The first branch returns to the combined absorption tower, and the second branch enters the acid storage tank. The acid outlet is connected to the acid storage tank. The acid circulation tank is also connected to the acid storage tank. The beneficial effect of this step is as follows: As the acid production section of the condenser continuously produces acid, the liquid accumulation section will also slightly increase to form sulfuric acid liquid, and the produced acid and the excess acid are both transported to the acid storage tank.

[0010] Furthermore: The flue gas purification section includes a Venturi scrubber, a packed cooling tower, a re-cooling tower, an electrostatic demister, and a booster fan connected in sequence. A refrigeration unit is also connected in parallel to the re-cooling tower. The flue gas inlet is the inlet of the Venturi scrubber, and the flue gas outlet is the outlet of the booster fan. The beneficial effect of this step is as follows: The impurities in the SO2 flue gas are removed by water washing, and the excessive moisture, acid mist, etc. in the SO2 flue gas are removed by the packed cooling tower, the re-cooling tower, the electrostatic demister, and the refrigeration unit, etc., to avoid the adverse effects on the wet catalyst caused by insufficient flue gas purification.

[0011] Furthermore: The preheater is a gas-gas heat exchanger. The beneficial effect of this step is as follows: The heat exchange effect of the gas-gas heat exchanger is better, and it is more suitable for heat exchange between gases.

[0012] Furthermore: A tail gas treatment section is also connected to the top of the combined absorption tower. The beneficial effect of this step is as follows: The excess sulfur oxides in the tail gas are removed through the tail gas treatment section, so that the tail gas meets the emission standards.

[0013] The present invention also provides a process for wet preparation of sulfuric acid and waste heat recovery during the preparation process. The wet preparation of sulfuric acid and waste heat recovery equipment described above is used for wet sulfuric acid production and waste heat recovery, including the following steps: S1. The SO2 flue gas with a volume ratio concentration less than 2.5% is sent into the acid production section of the condenser in the combined absorption tower for internal circulation after being washed, cooled, dust-removed, and demisted, and then the SO2 flue gas with a volume ratio concentration less than 2.5% is sent into the combined reactor. S2. In the combined reactor, SO2 flue gas with a volume ratio concentration less than 2.5% reacts catalytically, and SO2 in the SO2 flue gas reacts with O2 to form SO3 flue gas. S3. Feed the SO3 flue gas into the circulating acid heat removal section of the combined absorption tower. The SO3 flue gas contains SO3 and H2O. SO3 combines with H2O to form sulfuric acid vapor, and the heat generated by its own reaction is absorbed by concentrated sulfuric acid with a mass ratio concentration of 99.2% - 99.8%. The sulfuric acid vapor is cooled by the SO2 flue gas with a volume ratio concentration less than 2.5% in the acid production section of the condenser, and the sulfuric acid vapor condenses into sulfuric acid liquid and is discharged. S4. The concentrated sulfuric acid with a mass ratio concentration of 99.2% - 99.8% after absorbing heat is pumped by the acid circulation pump of the acid circulation tank and transported to the evaporator to transfer the heat to the water in the evaporator.

[0014] Furthermore: It is necessary to control the volume ratio of SO2 to H2O in the SO2 flue gas with a volume ratio concentration less than 2.5% in step S2 to be 1:1 - 4, and control the temperature of the generated SO3 flue gas to be 240 - 280 °C, so that the partial pressure of H2O in the SO3 flue gas in step S3 is less than the vapor pressure of H2O in the concentrated sulfuric acid with a mass ratio concentration of 99.2% - 99.8%, and the partial pressure of SO3 in the SO3 flue gas in step S3 is less than the vapor pressure of SO3 in the concentrated sulfuric acid with a mass ratio concentration of 99.2% - 99.8%, so as to ensure that the circulating acid does not absorb SO3 and H2O and only serves as a heat removal medium.

[0015] The beneficial effects of the present invention are as follows: In this application, the preheater is used to increase the temperature of the SO2 flue gas coming out of the acid production section of the condenser. The acid production section of the condenser is used to increase the temperature of the SO2 flue gas entering the acid production section of the condenser by using the medium-temperature waste heat of the sulfuric acid vapor. Finally, the circulating acid is used to transfer the low-temperature waste heat generated by the SO3 flue gas to water vapor through the evaporator, and finally the water vapor is sent to the pipe network for reuse, which can make full use of the waste heat generated in each stage of wet sulfuric acid production and achieve the effect of saving energy. Description of the Drawings

[0016] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is a schematic flow chart of a device for wet preparation of sulfuric acid and waste heat recovery during the preparation process provided by the present invention. Figure 2A process flow diagram of the flue gas sulfuric acid production section of the equipment for wet preparation of sulfuric acid with waste heat recovery during the preparation process provided by the present invention; Figure 3 A process flow diagram of the waste heat recovery section of the equipment for wet preparation of sulfuric acid with waste heat recovery during the preparation process provided by the present invention.

[0018] Reference numerals: 1 - Flue gas purification section; 2 - Flue gas sulfuric acid production section; 3 - Waste heat recovery section; 4 - Tail gas treatment section; 11 - Venturi scrubber; 12 - Packed cooling tower; 13 - Re-cooling tower; 14 - First electrostatic demister; 15 - Second electrostatic demister; 16 - Booster fan; 17 - Refrigeration unit; 21 - Combined absorption tower; 22 - Preheater; 23 - Interlayer heat exchanger; 24 - Electric furnace; 31 - First heat exchanger; 32 - Second heat exchanger; 33 - Deaerator; 34 - Evaporator; 35 - Drainage tank; 36 - Mixed acid tank; 37 - Acid storage; 41 - Hydrogen peroxide combined tower; 42 - Tail gas electrostatic demister; 211 - Liquid accumulation section; 212 - Circulating acid heat transfer section; 213 - Condenser acid production section; 214 - Demisting section; 215 - Acid circulation tank; A - SO2 flue gas with a volume ratio concentration less than 2.5%; B - Demineralized water; C - Water vapor; In the figure, the thin line represents the sulfur-containing gas or sulfuric acid, the thick line represents the process water (including demineralized water and water vapor, etc.), and the dotted line represents the scope of each section. Detailed implementation manners

[0019] The embodiments of the technical solution of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, so they are only examples and cannot be used to limit the protection scope of the present invention. It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which the present invention belongs.

[0020] Embodiment In view of the problems of low utilization rate and recovery rate of high-temperature waste heat, medium-temperature waste heat, and low-temperature waste heat generated during the sulfuric acid production process in the existing wet sulfuric acid production equipment and process, the present application proposes improvements, and the specific solutions are as follows: As Figures 1 to 3 shown, the equipment for wet preparation of sulfuric acid with waste heat recovery during the preparation process provided by the present invention includes: Flue gas purification section 1, including a flue gas inlet and a flue gas outlet, introduces SO2 flue gas A with a volume ratio concentration of less than 2.5% through the flue gas inlet, and discharges it from the flue gas outlet after various purification measures; Sulphuric acid production section 2, including a combined converter and a combined absorption tower 21. The combined absorption tower 21 is provided with a condensation inlet, a condensation outlet, and a converted gas inlet. The condensation inlet is communicated with the flue gas outlet. The combined converter is provided with a process gas inlet and a converted gas outlet. The process gas inlet is communicated with the condensation outlet. The converted gas outlet is communicated with the converted gas inlet. SO2 flue gas A with a volume ratio concentration of less than 2.5% enters from the condensation inlet of the combined absorption tower 21, then exits from the condensation outlet, reaches the process gas inlet of the combined converter, is converted into SO3 flue gas after conversion, and then exits from the converted gas outlet, reaches the converted gas inlet of the combined absorption tower 21. The SO3 flue gas is absorbed into sulfuric acid and discharged in the combined absorption tower 21, and the remaining tail gas is discharged from the top of the combined absorption tower 21. In order to meet the waste gas emission standards, a tail gas treatment section 4 is provided at the rear end of the combined absorption tower 21; Waste heat recovery section 3, including an evaporator 34, which is communicated with the acid circulation tank 215 at the bottom of the combined absorption tower 21. Through the heat exchange between water and sulfuric acid, the heat in the sulfuric acid is transferred to the water for reuse.

[0021] In the above-mentioned sections, the chemical reactions involved have the following four processes: SO2 + ½O2 → SO3 + reaction heat (96.1 KJ / mol); (1) SO3 (gas) + H2O (gas) = H2SO4 (gas) + reaction heat (124.8 KJ / mol); (2) H2SO4 (gas) = H2SO4 (liquid) + reaction heat (50.1 KJ / mol); (3) H2O2 + SO2 = H2SO4 + reaction heat (neglected); (4) In the above reaction process, the temperature of SO2 flue gas A with a volume ratio concentration of less than 2.5% is about 40°C before entering the combined absorption tower 21, and about 215°C when exiting the combined absorption tower 21; when entering the combined converter for conversion, the temperature needs to be further raised to about 400 - 420°C. The generated SO3 flue gas enters the combined absorption tower 21, where SO3 and H2O generate sulfuric acid vapor, and then the heat is transferred to the water for reuse through the circulating sulfuric acid.

[0022] Specifically, in one embodiment, the combined converter includes a preheater 22 and an interlayer heat exchanger 23. The preheater 22 includes the process gas inlet and the process gas outlet, as well as the converted gas outlet and the converted gas preheating inlet; The inlet of the interlayer heat exchanger 23 is communicated with the process gas outlet, and the outlet of the interlayer heat exchanger 23 is communicated with the reformed gas preheating inlet. The SO2 flue gas at about 215°C enters from the preheater 22, is heated to about 235°C and then enters the interlayer heat exchanger 23 for reaction to generate SO3 flue gas. Then the SO3 flue gas enters the preheater 22 again. The preheater 22 preheats the SO2 flue gas to increase the temperature of the SO2 flue gas, which can not only promote the conversion of the SO2 flue gas into the SO3 flue gas, but also utilize the heat generated by the conversion of the SO3 flue gas to reduce the temperature of the SO3 flue gas, avoiding the temperature of the circulating acid in the combined absorption tower from rising too high due to the SO3 flue gas, resulting in overheating and failure of the acid circulation pump.

[0023] In addition, the conversion of SO2 flue gas uses oxygen in the air as an oxidant, and SO3 is produced through a catalytic reaction.

[0024] This reaction is an exothermic reaction. Affected by the reaction equilibrium, at a high reaction temperature, the reaction rate is fast and the efficiency is high, but the equilibrium conversion rate is low; if the temperature is higher than the reaction requirement temperature of the catalyst and the need for self-heat balance is met, controlling the reaction temperature as low as possible is beneficial to improving the reaction equilibrium conversion rate and the overall conversion rate. In view of this, this reaction adopts a multi-stage inter-stage heat exchange reaction.

[0025] The wet-process sulfuric acid device uses a proprietary water-resistant catalyst for wet-process sulfuric acid, with V2O5 as the active component, K20 and Na0 salts as additives, and TIO2 or diatomite as the carrier. By doping elements such as Ce and W, the low-temperature activity is improved. And due to possible dust, arsenic and other impurities in the wet process, Mo03 also needs to be introduced. A special preparation process is used to improve the anti-toxicity of the catalyst, which is suitable for wet operating conditions. Ordinary sulfuric acid catalysts cannot be used in the wet-process sulfuric acid device in process gas with a high water content, and their activity decays rapidly.

[0026] In the above technical solution, the reason why the preheater 22 only heats the SO2 flue gas to about 235°C is that during the normal continuous operation of the interlayer heat exchanger 23, this chemical reaction is an exothermic reaction, and the reaction heat has increased its internal temperature to above 420°C. It can not only increase the temperature of the SO2 flue gas to the conversion temperature, but also use the SO2 flue gas to maintain the temperature, so that the internal temperature of the interlayer heat exchanger 23 is in a relatively constant state; however, in the initial state of the equipment, there is no converted SO3 flue gas to preheat the SO2 flue gas, so other means are needed to increase the temperature of the SO2 flue gas to reach the reaction temperature. Therefore, an electric furnace 24 is also provided between the preheater 22 and the interlayer heat exchanger 23. The electric furnace 24 is used as the heating device for the SO2 flue gas in the initial reaction. In addition, the electric furnace 24 can also be used as a heat compensation tool. When the temperature of the SO2 flue gas coming out of the preheater 22 does not reach the set value, the electric furnace 24 can reheat the SO2 flue gas to meet the process requirements.

[0027] Specifically, in one embodiment, the combined absorption tower 21 is successively provided with a liquid accumulation section 211, a circulating acid heat transfer section 212, a condenser acid production section 213, and a demisting section 214 from bottom to top; The demisting section 214 includes several groups of columnar fiber demisters, generally filled with glass fiber filaments or polytetrafluoroethylene filaments to capture the uncondensed acid mist in the flue gas; The condenser acid production section 213 includes glass condenser tubes. The condensation air inlet and the condensation air outlet correspond to the condenser acid production section 213, and the condenser acid production section 213 is also provided with an acid outlet; the low-temperature process gas (SO2 flue gas at about 40°C) enters from the upper part of the glass condenser tube and exits from the lower part, so that the process gas is preheated and then enters the combined converter for wet sulfuric acid production. Baffle plates are used in the middle of the glass condenser tubes to increase the turbulence of the gas, making the gas evenly heated and prolonging the residence time; The circulating acid heat transfer section 212 includes a packing area and a distributor located above the packing area. The distributor generally uses a spray pipe to spray the circulating acid, which contacts the SO3 flue gas and the sulfuric acid vapor generated by the reaction of the SO3 flue gas, transferring the heat generated by the reaction of SO3 and H2O to the circulating acid. The packing area is to increase the contact area and contact time between SO3, H2O, and sulfuric acid vapor and the circulating acid to increase the heat transfer amount. An air-lifting cap is provided between the circulating acid heat transfer section 212 and the condenser acid production section 213 to separate the two sections. The condensed sulfuric acid in the condenser acid production section 213 does not mix into the high-temperature and high-concentration circulating sulfuric acid in the circulating acid heat transfer section 212 (because the wet process gas has a large water content and it is necessary to control so as not to reduce the temperature and concentration of the high-temperature and high-concentration acid). The circulating acid heat transfer section 212 also corresponds to the converter gas inlet, and a liquid receiving tank is formed on the air-lifting cap, and the condensed product acid flows by gravity to the acid mixing tank 36; The liquid accumulation section 211 includes an acid circulation pump and the acid circulation tank 215. The acid circulation pump transports the acid in the acid circulation tank 215 to the evaporator 34. The SO3 flue gas enters from the circulating acid heat transfer section 212 of the combined absorption tower 21. SO3 in the SO3 flue gas reacts with H2O to generate sulfuric acid vapor. Part of the heat is transferred to the circulating acid, and the circulating acid then enters the evaporator 34 to heat the water in the evaporator 34 into water vapor, realizing the utilization of low-temperature waste heat; another part of the heat enters the condenser acid production section 213 along with the sulfuric acid vapor and condenses into sulfuric acid liquid in the glass condenser tubes, and can also heat up the SO2 flue gas flowing through the condenser acid production section, realizing the utilization of medium-temperature waste heat.

[0028] Note: The cylinder body of the combined absorption tower 21 is made of materials such as Q345 and 316L (Q345 + acid-resistant bricks lined inside for the liquid accumulation section 211 and the circulating acid heat transfer section 212, 304 + PTFE lining for the acid production section 213 of the condenser, and 316L for the demisting section 214). The circulating acid pipeline and the spraying device are made of 310S or high-silicon stainless steel.

[0029] Specifically, in one embodiment, the circulating acid outlet of the evaporator 34 is provided with two branches. The first branch returns to the combined absorption tower 21, and the second branch enters the acid storage tank 37; the acid outlet is connected to the acid storage tank 37; the acid circulation tank 215 is also connected to the acid storage tank 37. As the acid production section 213 of the condenser continuously produces acid, the liquid accumulation section 211 will also slightly increase to form sulfuric acid liquid, and the produced acid and the excess acid are both transported into the acid storage tank 37.

[0030] In addition, for better heat exchange effect and extended service life of the equipment, the water for transferring heat is preferably demineralized water B. Demineralized water B passes through the first heat exchanger 31 and the second heat exchanger 32 in sequence, then passes through the deaerator 33, enters the evaporator 34, forms steam C with a pressure value of about 3 MPa when heated in the evaporator 34, and finally enters the pipe network for reuse; the second branch of the circulating acid coming out of the evaporator 34 can enter the second heat exchanger 32, then enter the first heat exchanger 31, and finally enter the acid storage tank 37 before entering the acid storage tank 37; and the excess circulating acid in the acid circulation tank 215 after long-term use (the circulating acid will still absorb a small amount of SO 3， affected by the reaction equilibrium) will enter the mixed acid tank 36 together with the acid produced by the acid production section 213 of the condenser, then come out from the mixed acid tank 6, enter the second heat exchanger 32 together with the circulating acid coming out of the first heat exchanger 31, and finally enter the acid storage tank 37. The above structure is designed based on the fact that in the actual production process, the circulating acid will increase, and multiple heat exchanges are required to fully utilize the heat of the acid produced everywhere and improve the water temperature.

[0031] Specifically, in one embodiment, the flue gas purification section 1 includes a venturi scrubber 11, a packed cooling tower 12, a re-cooling tower 13, an electrostatic demister (including a first electrostatic demister 14 and a second electrostatic demister 15, for multiple demisting to ensure good demisting effect), and a booster fan 16 connected in sequence; The re-cooling tower 13 is also bypassed with a refrigeration unit 17; The flue gas inlet is the inlet of the venturi scrubber 11, and the flue gas outlet is the outlet of the booster fan 16. The impurities in the SO2 flue gas are removed by water washing, and the excessive moisture in the SO2 flue gas is removed by condensation using equipment such as the packed cooling tower 12, the re-cooling tower 13, and the refrigeration unit 17.

[0032] Specifically, in one embodiment, the preheater 22 is a gas-gas heat exchanger, which has a better heat exchange effect and is more suitable for heat exchange between gases.

[0033] Specifically, in one embodiment, the top of the combined absorption tower 21 is also connected to a tail gas treatment section 4. After the above series of reactions, most of the sulfur elements are converted into sulfuric acid. However, a small amount of SO2 is limited by the reaction equilibrium and needs to be deeply purified to meet the current environmental protection emission requirements. In the tail gas treatment section 4, the hydrogen peroxide combined tower 41 is used to first humidify and cool the flue gas to <65°C, and then 27.5wt% hydrogen peroxide is used as a solvent to oxidize and absorb the residual SO2 pollutants in the tail gas. The obtained dilute acid solution is incorporated into the concentrated sulfuric acid product without external discharge. During the process of absorbing SO2 with hydrogen peroxide, acid mist will be generated as the concentration of the absorbed acid increases. The tail gas needs to be further demisted and purified by the tail gas electrostatic demister 42 to meet the emission standards.

[0034] The present invention also provides a process for wet preparation of sulfuric acid and waste heat recovery during the preparation process. The wet sulfuric acid preparation and waste heat recovery equipment described above is used for wet sulfuric acid production and waste heat recovery, including the following steps: S1. The SO2 flue gas with a volume ratio concentration of less than 2.5% is sent into the acid production section 213 of the condenser in the combined absorption tower 21 for internal circulation after being washed, cooled, dust-removed, and demisted, and then the SO2 flue gas with a volume ratio concentration of less than 2.5% is sent into the combined reactor. S2. In the combined reactor, the SO2 flue gas with a volume ratio concentration of less than 2.5% undergoes a catalytic reaction, and the SO2 flue gas reacts with O2 to generate SO3 flue gas. S3. The SO3 flue gas is sent into the circulating acid heat transfer section 212 of the combined absorption tower 21. The SO3 flue gas includes SO3 and H2O. SO3 and H2O combine to form sulfuric acid vapor, and the heat generated by the reaction itself is absorbed by concentrated sulfuric acid with a mass ratio concentration of 99.2% - 99.8%. The sulfuric acid vapor is cooled by the SO2 flue gas with a volume ratio concentration of less than 2.5% in the acid production section 213 of the condenser, and the sulfuric acid vapor condenses into sulfuric acid liquid and is discharged. S4. The concentrated sulfuric acid with a mass ratio concentration of 99.2% - 99.8% after absorbing heat is pumped by the acid circulation pump of the acid circulation tank 215 and sent to the evaporator 34 to transfer the heat to the water in the evaporator 34.

[0035] In the process of this application, the high-temperature waste heat from the conversion of SO2 to SO3 (maintaining its own reaction and preheating the SO2 flue gas for the second time), the medium-temperature waste heat from the formation of sulfuric acid vapor by SO3 and H2O (preheating the SO2 flue gas for the first time and heating the circulating acid), and the low-temperature waste heat carried out by the circulating acid (heating the process water to generate steam C) are all effectively utilized.

[0036] On the basis of the above technical solution, it is necessary to control the volume ratio of SO2 to H2O in the SO2 flue gas A with a volume ratio concentration less than 2.5% in step S2 to be 1:1 to 4, and control the temperature of the generated SO3 flue gas to be 240 to 280 °C, so that the partial pressure of H2O in the SO3 flue gas in step S3 is less than the vapor partial pressure of H2O in concentrated sulfuric acid with a mass ratio concentration of 99.2% to 99.8%, and the partial pressure of SO3 in the SO3 flue gas in step S3 is less than the vapor partial pressure of SO3 in concentrated sulfuric acid with a mass ratio concentration of 99.2% to 99.8%, so as to ensure that the circulating acid does not absorb SO3 and H2O and only serves as a heat transfer medium.

[0037] Finally, the chemical principle of this process is briefly described as follows: According to the "Sulfuric Acid Process Design Manual", on page 29, when the sulfuric acid concentration > 98.3% and the temperature is above 200 °C, the vapor partial pressure of H2SO4 on the sulfuric acid liquid surface is large, and the vapor partial pressure of H2O is almost zero, so it will not absorb water and will not cause the concentration of sulfuric acid to decrease. Moreover, when the acid concentration > 99.2%, there is almost no corrosion to the acid circulation pipe (material: 310S); according to the "Sulfuric Acid Process Design Manual" on page 32, when the sulfuric acid concentration is 100% at 180 °C / 200 °C, the partial pressure data of each component of its vapor are as follows: PH20: 9.33 / 27.33 (Pa); PSO3: 1853 / 4493 (Pa); The vapor partial pressure data of about 100% sulfuric acid concentration at 220 °C are deduced as follows: PH2O: 80.08 (Pa); When the dew point temperature of the converted flue gas is 260 °C, PH20 (59.26 (Pa)) < PH20 (80.08 (Pa)) (about 100% sulfuric acid concentration at 220 °C), Therefore, it meets the process requirements to use sulfuric acid with an acid concentration > 99.2% and a temperature controlled at about 250 °C as the heat transfer medium. Also, based on years of sulfuric acid operation experience, when the temperature difference between the circulating acid temperature and the temperature of the absorbed flue gas < 20 °C, a large amount of acid mist will not be generated, and there will be no situation of a large amount of acid mist when it condenses into sulfuric acid (there will be a small amount at this time).

[0038] Since the process gas contains a large amount of moisture, SO3 first combines with water vapor to form sulfuric acid vapor, and then through the method of condensation, the generated sulfuric acid vapor is separated from the gas. The sulfuric acid vapor condenses into a liquid, about 96.1% concentrated sulfuric acid. The reaction rate and equilibrium conversion rate of SO3 hydration to form sulfuric acid vapor are affected by temperature and the concentration of non-condensable gas in the gas phase. The condensation of sulfuric acid vapor generally starts at 240 - 260 °C and basically ends at 160 - 170 °C. To avoid the generation of acid mist, it is necessary to control the operating conditions of the condenser, control the cooling rate of the gas, and increase the turbulence degree of the gas, so as to reduce the generation quantity of acid mist and increase the particle size of acid mist, making it easier for the acid mist to be separated from the gas.

[0039] A small amount of acid mist generated from the condenser is captured and removed by a fiber demister (removal rate 99.5%). At this time, the flue gas temperature also needs to be controlled > 105 °C. A small amount of acid mist and SO2 are treated with 27.5 wt% hydrogen peroxide as a solvent for the tail gas later.

[0040] The following lists data at two different temperature points to prove the above view.

[0041] (1) If the purification control is SO2:H2O (volume ratio, the same below) = 1:(4 ± 0.5), about 0.243 T of saturated steam is produced: 1 T of sulfuric acid (saturated steam 3.0 MPag); The dew point temperature of the high-temperature SO3 flue gas after conversion: 257 °C + 20 °C (flue duct wall temperature) = above 277 °C is safe (no corrosion to the flue duct). At this time, the partial pressure of the gas components: PaSO3 = 14.852 (Pa), PaH2O = 59.26 (Pa); the flue gas outlet temperature is 240 °C.

[0042] The data of the vapor partial pressure of the circulating sulfuric acid with a concentration of 99.2 - 99.5% at 240 °C is P L H2O > 80.08 (Pa); So, when at 257 °C, PaH20 (59.26 (Pa)) < P L H2O (80.08 (Pa)) at 240 °C; PaSO3 (14.852 (Pa)) < P L SO3 (4493 (Pa)) when the circulating sulfuric acid does not absorb SO3 or water, no acid mist will be generated, and the circulating sulfuric acid with a concentration of 99.2 - 99.5% only transfers heat simply.

[0043] (2) If the purification control is SO2:H2O = 1:(1.66 ± 0.5), about 0.39 T of saturated steam is produced: 1 T of acid (saturated steam 1.6 MPag); The dew point temperature of the converted high-temperature SO3 flue gas: 248°C + 20°C (flue wall temperature) = above 268°C is safe (no corrosion to the flue). At this time, the partial pressure of the gas components: PaSO3 = 14.5 (Pa), PaH2O = 24.2 (Pa); the flue gas outlet temperature is 220°C.

[0044] The vapor pressure data of the circulating sulfuric acid with a concentration of 99.2 - 99.5% at 200°C is P L H2O: 27.33 (Pa); Therefore, when At 248°C, PaH20 (24.2 (Pa)) < P of 200°C L H2O (27.33 (Pa)); PaSO3 (14.852 (Pa)) < P of 200°C L SO3 (4493 (Pa)), it does not absorb SO3 or water, and no acid mist will be generated. The circulating sulfuric acid with a concentration of 99.2 - 99.5% only transfers heat.

[0045] In addition, the dew point temperature of the converted sulfuric acid vapor needs to be strictly controlled (that is, control the water content in the flue gas. If the water content in the flue gas is high, the dew point temperature will be high). If the sulfuric acid vapor temperature is too high, it will cause the temperature of the circulating acid to be high, exceeding the maximum operating temperature of the acid circulation pump. Overheating will have a great adverse impact on the delivery performance and efficiency of the circulation pump, resulting in the inability to recover waste heat and having a certain impact on the recovery of low-temperature waste heat.

[0046] In the description of the present invention, a large number of specific details are set forth. However, it is understood that the embodiments of the present invention may be practiced without these specific details. In some instances, well-known methods, structures, and technologies have not been shown in detail so as not to obscure the understanding of this description. In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and the description of the present invention.

Claims

1. A device for preparing sulfuric acid by wet process and recovering waste heat during the preparation process, characterized in that: include: The flue gas purification section includes a flue gas inlet and a flue gas outlet; The flue gas acid-making section comprises a combined converter and a combined absorption tower, wherein the combined absorption tower is provided with a condensation air inlet, a condensation air outlet and a conversion gas air inlet, wherein the condensation air inlet is connected to the flue gas outlet, and the combined converter is provided with a process gas air inlet and a conversion gas air outlet, wherein the process gas air inlet is connected to the condensation air outlet, and the conversion gas air outlet is connected to the conversion gas air inlet; The waste heat recovery section includes an evaporator, and the evaporator is connected to the acid circulation tank at the bottom of the combined absorption tower.

2. The equipment for preparing sulfuric acid by wet process and recovering waste heat during the preparation process according to claim 1, characterized in that: The combined converter comprises a preheater and an interlayer heat exchanger, wherein the preheater comprises the process gas inlet and process gas outlet, and the conversion gas outlet and conversion gas preheating inlet; The air inlet of the interlayer heat exchanger is connected to the process gas outlet, and the air outlet of the interlayer heat exchanger is connected to the conversion gas preheating inlet.

3. The equipment for preparing sulfuric acid by wet process and recovering waste heat during the preparation process according to claim 2, characterized in that: An electric furnace is also provided between the preheater and the interlayer heat exchanger.

4. The equipment for preparing sulfuric acid by wet process and recovering waste heat during the preparation process according to claim 1, 2 or 3, characterized in that: The combined absorption tower is provided with a liquid accumulation section, a circulating acid heat transfer section, a condenser acid production section and a demisting section in sequence from bottom to top; The demisting section includes a plurality of groups of cylindrical fiber demisters; The acid-generating section of the condenser includes a glass condenser tube, the condensation air inlet and the condensation air outlet correspond to the acid-generating section of the condenser, and the acid-generating section of the condenser is also provided with an acid outlet; The circulating acid heat transfer section includes a packing area and an acid distributor located above the packing area, and a gas lift cap is provided between the circulating acid heat transfer section and the acid production section of the condenser, and the circulating acid heat transfer section also corresponds to the conversion gas inlet; The liquid accumulation section includes an acid circulation pump and the acid circulation tank, and the acid circulation pump transports the acid in the acid circulation tank to the evaporator.

5. The equipment for preparing sulfuric acid by wet process and recovering waste heat during the preparation process according to claim 4, characterized in that: The circulating acid outlet of the evaporator is provided with two branches, the first branch returns to the combined absorption tower, and the second branch enters the acid reservoir; the acid outlet is connected to the acid reservoir; the acid circulation tank is also connected to the acid reservoir.

6. The equipment for preparing sulfuric acid by wet process and recovering waste heat during the preparation process according to claim 5, characterized in that: The flue gas purification section includes a venturi cleaner, a packing cooling tower, a recooling tower, an electric demister and a booster fan which are connected in sequence; The recooling tower is also connected to a refrigeration unit; The smoke inlet is the inlet of the venturi cleaner, and the smoke outlet is the outlet of the booster fan.

7. The equipment for preparing sulfuric acid by wet process and recovering waste heat during the preparation process according to claim 2, characterized in that: The preheater is an air-to-air heat exchanger.

8. The equipment for preparing sulfuric acid by wet process and recovering waste heat during the preparation process according to claim 7, characterized in that: The top of the combined absorption tower is also connected to a tail gas treatment section.

9. A process for preparing sulfuric acid by a wet process and recovering waste heat during the preparation process, characterized in that: The wet process of preparing sulfuric acid and recovering waste heat during the preparation process using the equipment as claimed in claim 1 comprises the following steps: S1. The SO2 flue gas with a volume concentration of less than 2.5% is sent to the combined absorption tower for circulation after being treated in the flue gas purification section; S2, sending the SO2 flue gas with a volume concentration of less than 2.5% from the combined absorption tower into a combined reactor, and after catalytic reaction, the SO2 flue gas and O2 generate SO3 flue gas; S3, sending the SO3 flue gas into the combined absorption tower, the SO3 flue gas includes SO3 and H2O, SO3 and H2O combine to form sulfuric acid vapor, and the heat generated by the self-reaction is absorbed by the concentrated sulfuric acid with a mass ratio concentration of 99.2% to 99.8%, the sulfuric acid vapor is cooled by the SO2 flue gas with a volume ratio concentration of less than 2.5% in the combined absorption tower, and the sulfuric acid vapor is condensed into sulfuric acid liquid and discharged; S4, after absorbing heat, the concentrated sulfuric acid with a mass ratio of 99.2% to 99.8% is transported to the evaporator through the acid circulation pump of the acid circulation tank, and the heat is transferred to the water in the evaporator.

10. The process for preparing sulfuric acid by wet method and recovering waste heat during the preparation process according to claim 9, characterized in that: It is necessary to control the volume ratio of SO2 and H2O in the SO2 flue gas with a volume ratio concentration of less than 2.5% in step S2 to be 1:1~4, and control the temperature of the generated SO3 flue gas to be 240~280°C, so that the gas partial pressure of H2O in the SO3 flue gas in step S3 is less than the vapor partial pressure of H2O in concentrated sulfuric acid with a mass ratio concentration of 99.2%~99.8%, and the gas partial pressure of SO3 in the SO3 flue gas in step S3 is less than the vapor partial pressure of SO3 in concentrated sulfuric acid with a mass ratio concentration of 99.2%~99.8%.

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