An apparatus and process for wet production of sulfuric acid with waste heat recovery during production

Abstract

The present application belongs to the technical field of wet acid preparation, and particularly relates to a device and a process for preparing sulfuric acid by wet method and recovering waste heat in the preparation process. The present application comprises: a flue gas purification section comprising a flue gas inlet and a flue gas outlet; a flue gas acid preparation section comprising a combined converter and a combined absorption tower, the combined absorption tower being provided with a condensation inlet, a condensation outlet and a conversion gas inlet, the condensation inlet being in communication with the flue gas outlet, the combined converter being provided with a process gas inlet and a conversion gas outlet, the process gas inlet being in communication with the condensation outlet, and the conversion gas outlet being in communication with the conversion gas inlet; and a waste heat recovery section comprising an evaporator, the evaporator being in communication with an acid circulating tank at the bottom of the combined absorption tower. The present application is used to solve the technical problem of low waste heat recovery rate of the existing wet sulfuric acid preparation device and process.

Description

Technical Field

[0001] This invention belongs to the field of wet sulfuric acid production technology, specifically relating to a device and process for wet sulfuric acid preparation and waste heat recovery during the preparation process. Background Technology

[0002] The wet process for sulfuric acid production generates a significant amount of heat, which originates from three sources: the combustion of sulfur-containing feedstocks, the conversion of sulfur dioxide, and the absorption (or condensation) of sulfur dioxide into acid. In the wet process, the purified flue gas is preheated in 2-3 stages to a temperature of 400-420℃ before entering the combined reactor for conversion (stage two when the SO2 volume ratio concentration is 0-2.5%, and stage three when it is >2.5%). The heat generated at this stage is called high-temperature waste heat. The heat generated when the converted flue gas cools to approximately 280±5℃ (above the flue gas dew point temperature; the dew point temperature of saturated acidic gases is generally around 252±4℃) is called medium-temperature waste heat. The heat generated during the condensation process, from 240℃ to approximately 105℃, is called low-temperature waste heat.

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

[0004] In addition, the existing heat recovery tower has an integrated straight-through structure with a liquid collection tank at the bottom, which is connected to the circulation tank by a connecting pipe. The middle section is the absorption section, which has two parts: the lower section is the high-temperature absorption section, and the upper section is the low-temperature absorption section. The high-temperature absorption section and the low-temperature absorption section are directly connected. The low-temperature, low-concentration sulfuric acid in the low-temperature absorption section is directly mixed into the high-temperature, high-concentration sulfuric acid in the high-temperature absorption section, which reduces the temperature and concentration of the high-temperature, high-concentration sulfuric acid, reduces the low-pressure steam output of the evaporator, and increases the flow rate of the high-temperature, high-concentration sulfuric acid, thereby increasing the power consumption of the equipment and the heat exchange area of ​​the heat exchanger. Summary of the Invention

[0005] This invention provides an equipment and process for wet sulfuric acid production and waste heat recovery during the production process, which solves the technical problem of low waste heat recovery and utilization rate in existing wet sulfuric acid production equipment and processes.

[0006] This invention discloses an apparatus for the wet preparation of sulfuric acid and the recovery of waste heat during the preparation process, comprising:

[0007] The flue gas purification section includes a flue gas inlet and a flue gas outlet;

[0008] The flue gas acid production section includes a combined converter and a combined absorption tower. The combined absorption tower is provided with a condensate inlet, a condensate outlet, and a converted gas inlet. The condensate inlet is connected to the flue gas outlet. The combined converter is provided with a process gas inlet and a converted gas outlet. The process gas inlet is connected to the condensate outlet, and the converted gas outlet is connected to the converted gas inlet.

[0009] The waste heat recovery section includes an evaporator, which is connected to the acid circulation tank at the bottom of the combined absorption tower.

[0010] Further: the combined converter includes a preheater and an interlayer heat exchanger, the preheater includes the process gas inlet and process gas outlet, as well as the converter gas outlet and converter gas preheating inlet;

[0011] The inlet of the interlayer heat exchanger is connected to the outlet of the process gas, and the outlet of the interlayer heat exchanger is connected to the preheating inlet of the conversion gas. The beneficial effects of this step are: SO2 flue gas enters from the preheater, then enters the interlayer heat exchanger to react and generate SO3 flue gas. The SO3 flue gas then enters the preheater again, where it preheats the SO2 flue gas, increasing its temperature. This not only promotes the conversion of SO2 flue gas into SO3 flue gas, but also utilizes the heat generated from the conversion of SO3 flue gas to lower its temperature, preventing the SO3 flue gas from raising the temperature of the circulating acid too high in the combined absorption tower, which could lead to overheating and failure of the acid circulation pump.

[0012] 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 serves as a heat compensation tool. When this application is initially working, there is no converted SO3 flue gas to preheat the SO2 flue gas, and the temperature of the SO2 flue gas can be increased by the electric furnace.

[0013] Furthermore: 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 from bottom to top;

[0014] The demisting section includes several sets of cylindrical fiber demisters;

[0015] The acid-producing section of the condenser includes a glass condenser tube, the condenser inlet and the condenser outlet correspond to the acid-producing section of the condenser, and the acid-producing section of the condenser is also provided with an acid outlet.

[0016] The circulating acid heat transfer section includes a packing area and an acid separator located above the packing area. A gas lift cap is provided between the circulating acid heat transfer section and the acid production section of the condenser. The circulating acid heat transfer section also corresponds to the conversion gas inlet.

[0017] The liquid accumulation section includes an acid circulation pump and an acid circulation tank. The acid circulation pump transports the acid in the acid circulation tank to the evaporator. The beneficial effects of this step are as follows: SO3 flue gas enters from the circulating acid heat transfer section of the combined absorption tower. SO3 and H2O in the SO3 flue gas react to generate sulfuric acid vapor. Part of the heat is transferred to the circulating acid, which then enters the evaporator to heat the water in the evaporator into water vapor, thus realizing the utilization of low-temperature waste heat. Another part of the heat enters the acid production section of the condenser with the sulfuric acid vapor, where it condenses into sulfuric acid liquid in the glass condenser tubes. It can also raise the temperature of the SO2 flue gas flowing through the acid production section of the condenser, thus realizing the utilization of medium-temperature waste heat.

[0018] Furthermore: 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 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 that as the acid production section of the condenser continuously produces acid, the liquid accumulation section will also increase slightly to form sulfuric acid liquid, and the produced acid and excess acid are transported to the acid storage tank.

[0019] Furthermore: the flue gas purification section includes a venturi cleaner, a packed cooling tower, a recooling tower, an electrostatic precipitator, and a booster fan connected in sequence;

[0020] The recooling tower is also connected to a refrigeration unit;

[0021] 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 effects of this step are: removing impurities from the SO2 flue gas by water washing, and removing excessive moisture and acid mist from the SO2 flue gas by packing cooling tower, re-cooling tower, electrostatic precipitator and refrigeration unit, so as to avoid the adverse effects of low flue gas purification on the wet catalyst.

[0022] Furthermore: the preheater is a gas-to-gas heat exchanger. The beneficial effect of this step is that the gas-to-gas heat exchanger has a better heat exchange effect and is more suitable for heat exchange between gases.

[0023] Furthermore, the top of the combined absorption tower is also connected to a tail gas treatment section. The beneficial effect of this step is that the tail gas treatment section removes excess sulfur oxides from the tail gas, enabling the tail gas to meet emission standards.

[0024] This invention also provides a process for wet sulfuric acid production and waste heat recovery during the production process. The process utilizes the aforementioned equipment for wet sulfuric acid production and waste heat recovery, and includes the following steps:

[0025] S1. SO2 flue gas with a volume concentration of less than 2.5% is washed, cooled, dusted and demisted and then sent to the acid production section of the condenser of the combined absorption tower for circulation. Then SO2 flue gas with a volume concentration of less than 2.5% is sent to the combined reactor.

[0026] S2. SO2 flue gas with a volume concentration of less than 2.5% undergoes a catalytic reaction in the combined reactor, where SO2 flue gas reacts with O2 to generate SO3 flue gas.

[0027] S3. The SO3 flue gas is fed into the circulating acid heat transfer section of 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 reaction is absorbed by concentrated sulfuric acid with a mass ratio concentration of 99.2%~99.8%. The sulfuric acid vapor is cooled by SO2 flue gas with a volume ratio concentration of less than 2.5% in the acid production section of the condenser. The sulfuric acid vapor is condensed into sulfuric acid liquid and discharged.

[0028] S4. After absorbing heat, concentrated sulfuric acid with a mass ratio of 99.2%~99.8% is transported to the evaporator through the acid circulation pump of the acid circulation tank, transferring heat to the water in the evaporator.

[0029] Furthermore, it is necessary to control the volume ratio of SO2 to H2O in the SO2 flue gas with a volume concentration of less than 2.5% in step S2 to be 1:1~4, and to control the temperature of the generated SO3 flue gas to be 240~280℃. This ensures that the partial pressure of H2O in the SO3 flue gas in step S3 is lower than the partial pressure of H2O vapor in concentrated sulfuric acid with a mass concentration of 99.2%~99.8%, and that the partial pressure of SO3 in the SO3 flue gas in step S3 is lower than the partial pressure of SO3 vapor in concentrated sulfuric acid with a mass concentration of 99.2%~99.8%. This guarantees that the circulating acid does not absorb SO3 and H2O, and only acts as a heat transfer medium.

[0030] The beneficial effects of this invention are:

[0031] This application uses a preheater to raise the temperature of the SO2 flue gas exiting the acid-producing section of the condenser by using high-temperature waste heat. It also uses the medium-temperature waste heat of sulfuric acid vapor in the acid-producing section of the condenser to raise the temperature of the SO2 flue gas entering the acid-producing section of the condenser. Finally, it uses circulating acid to transfer the low-temperature waste heat generated by SO3 flue gas to water vapor through an evaporator. The water vapor is then sent to the pipeline network for reuse. This method can make full use of the waste heat generated in each stage of wet acid production, thereby achieving energy conservation. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 A schematic diagram of a process for wet sulfuric acid preparation and waste heat recovery during the preparation process provided by the present invention;

[0034] Figure 2 A schematic diagram of the flue gas sulfuric acid production section of an equipment for wet sulfuric acid preparation and waste heat recovery during the preparation process, provided by the present invention;

[0035] Figure 3 This invention provides a schematic diagram of the waste heat recovery section of an equipment for wet sulfuric acid preparation and waste heat recovery during the preparation process.

[0036] Figure label:

[0037] 1- Flue gas purification section; 2- Flue gas acid production section; 3- Waste heat recovery section; 4- Tail gas treatment section;

[0038] 11-Venturi tube cleaner; 12-Packed cooling tower; 13-Recooling tower; 14-First electrostatic precipitator; 15-Second electrostatic precipitator; 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-Sewage tank; 36-Mixed acid tank; 37-Acid storage tank; 41-Hydrogen peroxide combined tower; 42-Tail gas electrostatic precipitator;

[0039] 211-Liquid accumulation section; 212-Circulating acid heat transfer section; 213-Condenser acid generation section; 214-Demisting section; 215-Acid circulation tank;

[0040] A - SO2 flue gas with a volume concentration of less than 2.5%;

[0041] B-deionized water;

[0042] C - Water vapor;

[0043] In the diagram, thin lines represent sulfur-containing gases or sulfuric acid, thick lines represent process water (including demineralized water and steam), and dashed lines represent the scope of each section. Detailed Implementation

[0044] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0045] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0046] Example

[0047] This application addresses the problem of low utilization and recovery rates of high-temperature, medium-temperature, and low-temperature waste heat generated during the existing wet acid production equipment and process. The specific solutions are as follows:

[0048] like Figures 1-3 As shown, the apparatus for wet preparation of sulfuric acid and waste heat recovery during the preparation process provided by the present invention includes:

[0049] The flue gas purification section 1 includes a flue gas inlet and a flue gas outlet. SO2 flue gas A with a volume ratio concentration of less than 2.5% is introduced through the flue gas inlet and discharged through the flue gas outlet after passing through various purification measures.

[0050] The flue gas acid production section 2 includes a combined converter and a combined absorption tower 21. The combined absorption tower 21 is equipped with a condensate inlet, a condensate outlet, and a conversion gas inlet. The condensate inlet is connected to the flue gas outlet. The combined converter is equipped with a process gas inlet and a conversion gas outlet. The process gas inlet is connected to the condensate outlet, and the conversion gas outlet is connected to the conversion gas inlet. SO2 flue gas A with a volume concentration of less than 2.5% enters from the condensate inlet of the combined absorption tower 21, exits from the condensate outlet, and enters the process gas inlet of the combined converter. After conversion, it becomes SO3 flue gas, which then exits from the conversion gas outlet and enters the conversion gas inlet of the combined absorption tower 21. The SO3 flue gas is absorbed into sulfuric acid in the combined absorption tower 21 and discharged. 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 set at the rear end of the combined absorption tower 21.

[0051] Waste heat recovery section 3 includes an evaporator 34, which is connected to the acid circulation tank 215 at the bottom of the combined absorption tower 21. Through heat exchange between water and sulfuric acid, the heat in the sulfuric acid is transferred to the water for reuse.

[0052] The chemical reactions involved in the above-mentioned sections include the following four processes:

[0053] The heat of reaction for SO2 + ½O2 → SO3+ is 96.1 kJ / mol; (1)

[0054] SO3(g) + H2O(g) = H2SO4(g) + heat of reaction (124.8 kJ / mol); (2)

[0055] H2SO4 (gas) = ​​H2SO4 (liquid) + heat of reaction (50.1 kJ / mol); (3)

[0056] H2O2 + SO2 = H2SO4 + heat of reaction (neglected); (4)

[0057] In the above reaction process, the SO2 flue gas A with a volume concentration of less than 2.5% is at a temperature of about 40°C before entering the combined absorption tower 21, and at a temperature of about 215°C when exiting the combined absorption tower 21. When entering the combined converter for conversion, the temperature needs to be further increased to about 400~420°C to generate SO3 flue gas. SO3 and H2O are generated in the combined absorption tower 21 to produce sulfuric acid vapor, and then the heat is transferred to the water for reuse through circulating sulfuric acid.

[0058] 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 converter gas outlet and the converter gas preheating inlet.

[0059] The inlet of the interlayer heat exchanger 23 is connected to the process gas outlet, and the outlet of the interlayer heat exchanger 23 is connected to the preheating inlet of the conversion gas. 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 to react and generate SO3 flue gas. The SO3 flue gas then enters the preheater 22 again. The preheater 22 preheats the SO2 flue gas, increasing its temperature. This not only promotes the conversion of SO2 flue gas into SO3 flue gas, but also utilizes the heat generated from the conversion of SO3 flue gas to lower its temperature. This prevents the SO3 flue gas from raising the temperature of the circulating acid too high in the combined absorption tower, which could lead to overheating and failure of the acid circulation pump.

[0060] In addition, SO2 flue gas conversion uses oxygen in the air as an oxidant to produce SO3 through a catalytic reaction.

[0061] This reaction is exothermic and is affected by reaction equilibrium. Higher reaction temperatures result in faster reaction rates and higher efficiency, but lower equilibrium conversion rates. If the temperature exceeds the catalyst's required reaction temperature while still achieving self-heating equilibrium, controlling the reaction temperature as low as possible is beneficial for improving the equilibrium conversion rate and overall conversion rate. Therefore, this reaction employs a multi-stage inter-stage heat exchange reaction.

[0062] The wet sulfuric acid unit uses a proprietary water-resistant catalyst specifically designed for wet sulfuric acid production. It uses V2O5 as the active ingredient, K2O and NaO salt as auxiliary agents, and TiO2 or diatomaceous earth as the carrier. The low-temperature activity is improved by doping elements such as Ce and W. In addition, because the wet process may contain impurities such as dust and arsenic, a special preparation process of MoO3 is required to improve the catalyst's resistance to poisoning. It is suitable for wet operation conditions. Ordinary sulfuric acid catalysts cannot be used in wet sulfuric acid units in process gases with high water concentrations, as their activity decays rapidly.

[0063] 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, the chemical reaction is an exothermic reaction, and the heat of reaction has already raised its internal temperature to over 420°C. This not only raises the temperature of the SO2 flue gas to the conversion temperature, but also requires the use of SO2 flue gas to maintain the temperature, keeping the internal temperature of the interlayer heat exchanger 23 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 it is necessary to raise the temperature of the SO2 flue gas through other means 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 serves as a heating device for the SO2 flue gas in the initial reaction. In addition, the electric furnace 24 can also serve 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.

[0064] Specifically, in one embodiment, the combined absorption tower 21 is provided from bottom to top as follows: a liquid accumulation section 211, a circulating acid heat transfer section 212, a condenser acid production section 213, and a demisting section 214;

[0065] The demisting section 214 includes several sets of cylindrical fiber demisters, which are generally filled with glass fiber or PTFE filaments to capture uncondensed acid mist in the flue gas.

[0066] The acid-producing section 213 of the condenser includes a glass condenser tube. The condenser inlet and the condenser outlet correspond to the acid-producing section 213 of the condenser. The acid-producing section 213 of the condenser is also provided with an acid outlet. 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 before entering the combined converter of wet acid production. The glass condenser tube is equipped with a baffle plate in the middle to increase the turbulence of the gas, so that the gas is heated evenly and the residence time is extended.

[0067] The circulating acid heat transfer section 212 includes a packing area and an acid separator located above the packing area. The acid separator is generally a spray pipe, through which the circulating acid is sprayed out and comes into contact with SO3 flue gas and sulfuric acid vapor generated by the reaction of SO3 flue gas, transferring the heat generated by the reaction of SO3 and H2O to the circulating acid. The packing area is designed to increase the contact area and contact time between SO3, H2O and sulfuric acid vapor and the circulating acid, thereby increasing the amount of heat transferred. A gas lift 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, high-concentration circulating sulfuric acid in the circulating acid heat transfer section 212 (because the wet process gas has a high water content, it is necessary to control the temperature and concentration of the high-temperature, high-concentration acid to avoid lowering it). The circulating acid heat transfer section 212 also corresponds to the conversion gas inlet and forms a liquid receiving tank on the gas lift cap. The condensed product acid flows by gravity to the mixing tank 36.

[0068] The liquid accumulation section 211 includes an acid circulation pump and an acid circulation tank 215. The acid circulation pump transports the acid in the acid circulation tank 215 to the evaporator 34. 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, which then enters the evaporator 34 to heat the water in the evaporator 34 into water vapor, thus realizing the utilization of low-temperature waste heat. Another part of the heat enters the acid production section 213 of the condenser along with the sulfuric acid vapor, where it is condensed into sulfuric acid liquid in the glass condenser tubes. This also heats the SO2 flue gas flowing through the acid production section of the condenser, thus realizing the utilization of medium-temperature waste heat.

[0069] Note: The shell of the combined absorption tower 21 is made of materials such as Q345 and 316L (Q345 with acid-resistant bricks lining the liquid accumulation section 211 and the circulating acid heat transfer section 212, condenser acid production section 213 is made of 304 with PTFE lining, and demister section 214 is made of 316L). The circulating acid pipeline and spray device are made of 310S or high silicon stainless steel.

[0070] 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 37. The acid outlet is connected to the acid storage 37. The acid circulation tank 215 is also connected to the acid storage 37. As the acid production section 213 of the condenser continuously produces acid, the liquid accumulation section 211 will also increase slightly to form sulfuric acid liquid. The produced acid and the excess acid are all transported into the acid storage 37.

[0071] In addition, for better heat exchange and extended equipment lifespan, the water used for heat transfer is preferably demineralized water B. Demineralized water B passes sequentially through the first heat exchanger 31 and the second heat exchanger 32, then through the deaerator 33, and enters the evaporator 34. In the evaporator 34, it is heated to form steam C at a pressure of approximately 3 MPa, which is then reused in the pipeline network. The second branch of the circulating acid from the evaporator 34 can enter the second heat exchanger 32 before entering the first heat exchanger 31, and finally the acid storage tank 37. The acid circulation tank 215 will retain excess circulating acid after long-term use (the circulating acid will still absorb a small amount of SO₂). 3， (Due to the influence of reaction equilibrium) it will enter the mixed acid tank 36 together with the acid produced in the acid-producing section 213 of the condenser, and then exit from the mixed acid tank 6. Together with the circulating acid from the first heat exchanger 31, it will enter the second heat exchanger 32, 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 in quantity and multiple heat exchanges are required, so as to make full use of the heat generated by acid at various points and increase the water temperature.

[0072] Specifically, in one embodiment, the flue gas purification section 1 includes a Venturi scrubber 11, a packed cooling tower 12, a recooling tower 13, an electrostatic precipitator (including a first electrostatic precipitator 14 and a second electrostatic precipitator 15, which perform multiple demisting processes to ensure good demisting effect) and a booster fan 16 connected in sequence.

[0073] The recooling tower 13 is also connected to a refrigeration unit 17;

[0074] The flue gas inlet is the inlet of the Venturi scrubber 11, and the flue gas outlet is the outlet of the booster fan. Impurities in the SO2 flue gas are removed by water washing, and excess moisture in the SO2 flue gas is removed by condensation through equipment such as the packed cooling tower 12, the recooling tower 13, and the refrigeration unit 17.

[0075] Specifically, in one embodiment, the preheater 22 is a gas-to-gas heat exchanger, which has a better heat exchange effect and is more suitable for heat exchange between gases.

[0076] Specifically, in one embodiment, the top of the combined absorption tower 21 is also connected to the tail gas treatment section 4. After the above series of reactions, the sulfur element is basically 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 emission requirements. The tail gas treatment section 4 uses a hydrogen peroxide combined tower 41 to first humidify and cool the flue gas to <65°C, and then uses 27.5wt% hydrogen peroxide as a solvent to oxidize and absorb the residual SO2 pollutants in the tail gas. The resulting dilute acid solution is then 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 deeply demisted and purified by the tail gas electrostatic precipitator 42 before it can meet the emission standards.

[0077] This invention also provides a process for wet sulfuric acid production and waste heat recovery during the production process. The process utilizes the aforementioned equipment for wet sulfuric acid production and waste heat recovery, and includes the following steps:

[0078] S1. SO2 flue gas with a volume concentration of less than 2.5% is washed, cooled, dusted and demisted and then sent into the acid production section 213 of the condenser of the combined absorption tower 21 for circulation. Then SO2 flue gas with a volume concentration of less than 2.5% is sent into the combined reactor.

[0079] S2. SO2 flue gas with a volume concentration of less than 2.5% undergoes a catalytic reaction in the combined reactor, where SO2 flue gas reacts with O2 to generate SO3 flue gas.

[0080] S3. The SO3 flue gas is fed 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 is absorbed by concentrated sulfuric acid with a mass ratio concentration of 99.2%~99.8%. The sulfuric acid vapor is cooled by SO2 flue gas with a volume ratio concentration of less than 2.5% in the acid production section 213 of the condenser. The sulfuric acid vapor is condensed into sulfuric acid liquid and discharged.

[0081] S4. After absorbing heat, concentrated sulfuric acid with a mass ratio of 99.2%~99.8% is transported to evaporator 34 through the acid circulation pump of acid circulation tank 215, transferring heat to the water in evaporator 34.

[0082] In the process of this application, the high-temperature waste heat from the conversion of SO2 into SO3 (to maintain its own reaction and to preheat the SO2 flue gas a second time), the medium-temperature waste heat from the formation of sulfuric acid vapor from SO3 and H2O (to preheat the SO2 flue gas a first time and to heat the circulating acid), and the low-temperature waste heat carried out by the circulating acid (to heat the process water to generate water vapor C) are all effectively utilized.

[0083] Based on the above technical solution, it is necessary to control the volume ratio of SO2 and H2O in the SO2 flue gas A with a volume ratio concentration of less than 2.5% in step S2 to be 1:1~4, and to control the temperature of the generated SO3 flue gas to be 240~280℃. This ensures that the partial pressure of H2O in the SO3 flue gas in step S3 is lower than the partial pressure of H2O vapor in concentrated sulfuric acid with a mass ratio concentration of 99.2%~99.8%, and that the partial pressure of SO3 in the SO3 flue gas in step S3 is lower than the partial pressure of SO3 vapor in concentrated sulfuric acid with a mass ratio concentration of 99.2%~99.8%. This guarantees that the circulating acid does not absorb SO3 and H2O, and only acts as a heat transfer medium.

[0084] Finally, the chemical principles of this process are briefly explained below:

[0085] According to page 29 of the "Sulfuric Acid Process Design Manual," when the sulfuric acid concentration is >98.3% and the temperature is above 200℃, the partial pressure of H2SO4 vapor on the sulfuric acid surface is high, while the partial pressure of H2O vapor is almost non-existent. Therefore, it will not absorb water and will not cause a decrease in the sulfuric acid concentration. Furthermore, when the acid concentration is >99.2%, there is almost no corrosion to the acid circulation pipe (material: 310S). Furthermore, according to page 32 of the "Sulfuric Acid Process Design Manual," the partial pressure data of each component of the vapor at 100% sulfuric acid concentration and 180℃ / 200℃ are as follows:

[0086] PH20: 9.33 / 27.33 (Pa);

[0087] PSO3: 1853 / 4493 (Pa);

[0088] The vapor partial pressure data for approximately 100% sulfuric acid concentration at 220℃ are derived as follows:

[0089] PH2O: 80.08 (Pa);

[0090] When the dew point temperature of the converted flue gas is 260℃,

[0091] pH20 (59.26 (Pa)) < pH20 (80.08 (Pa)) (approximately at 220°C for 100% sulfuric acid concentration).

[0092] Therefore, using sulfuric acid with an acid concentration >99.2% and a temperature controlled at around 250℃ as the heat transfer medium meets the process requirements. Furthermore, based on years of experience in sulfuric acid operation, a large amount of acid mist will not be generated when the temperature difference between the circulating acid temperature and the flue gas temperature after absorption is <20℃, and a large amount of acid mist will not occur when condensing into sulfuric acid (at this time, there will be a small amount).

[0093] Because the process gas contains a large amount of moisture, SO3 first combines with water vapor to form sulfuric acid vapor. Then, through condensation, the generated sulfuric acid vapor is separated from the gas, condensing into a liquid of approximately 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 gases in the gas phase. Sulfuric acid vapor condensation generally begins at 240–260°C and essentially ends at 160–170°C. To avoid acid mist generation, it is necessary to control the condenser operating conditions, control the gas cooling rate, and increase the gas turbulence to reduce the amount of acid mist generated and increase the particle size of the acid mist, making it easier for the acid mist to separate from the gas.

[0094] The 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 must be controlled to be >105℃. The small amount of acid mist and SO2 are treated by using 27.5wt% hydrogen peroxide as a solvent in the tail gas.

[0095] The following data from two different temperature points are provided to support the above viewpoint.

[0096] (1) If the purification control SO2:H2O (volume ratio, the same below) = 1: (4 ± 0.5), approximately 0.243T saturated steam: 1T sulfuric acid (saturated steam 3.0MPag) will be produced.

[0097] The dew point temperature of the converted high-temperature SO3 flue gas is 257℃ + 20℃ (flue wall temperature) = 277℃ or higher to be safe (it will not corrode the flue). At this time, the partial pressure of the gas composition is: PaSO3 = 14.852 (Pa), PaH2O = 59.26 (Pa); the flue gas outlet temperature is 240℃.

[0098] The vapor partial pressure data for circulating sulfuric acid with a concentration of 99.2%–99.5% at 240℃ is P. L H2O > 80.08 (Pa);

[0099] Therefore, when

[0100] At 257℃, PaH2O (59.26 (Pa)) < P at 240℃ L H2O (80.08 (Pa));

[0101] PaSO3 (14.852 (Pa)) < P at 240℃ L When SO3 is present (4493 Pa), the circulating sulfuric acid does not absorb SO3 or water, so no acid mist is generated. The circulating sulfuric acid with a concentration of 99.2-99.5% simply transfers heat.

[0102] (2) If the purification control SO2:H2O = 1: (1.66 ± 0.5), approximately 0.39T of saturated steam will be produced: 1T of acid (1.6MPag of saturated steam);

[0103] The dew point temperature of the converted high-temperature SO3 flue gas is 248℃ + 20℃ (flue wall temperature) = 268℃ or higher to be safe (it will not corrode the flue). At this time, the partial pressure of the gas composition is: PaSO3 = 14.5 (Pa), PaH2O = 24.2 (Pa); the flue gas outlet temperature is 220℃.

[0104] The vapor partial pressure data for circulating sulfuric acid with a concentration of 99.2%–99.5% at 200℃ is P. L H2O: 27.33 (Pa);

[0105] Therefore, when

[0106] At 248℃, PaH2O (24.2 (Pa)) < P at 200℃ L H2O (27.33 Pa);

[0107] PaSO3 (14.852 (Pa)) < P at 200℃ L When SO3 (4493 Pa) is present, neither SO3 nor water is absorbed, so no acid mist is generated. The circulating sulfuric acid with a concentration of 99.2-99.5% is simply a heat transfer process.

[0108] In addition, the dew point temperature of the converted sulfuric acid vapor needs to be strictly controlled (i.e., the water content of the flue gas should be controlled; the higher the water content in the flue gas, the higher the dew point temperature). If the sulfuric acid vapor temperature is too high, the circulating acid temperature will be too high, exceeding the maximum operating temperature of the acid circulating pump. Overheating will have a significant adverse effect on the conveying performance and efficiency of the circulating pump, resulting in the inability to recover and utilize waste heat, and causing a certain degree of impact on low-temperature waste heat recovery.

[0109] Numerous specific details are set forth in this specification. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification. In the description of this specification, references to terms such as “one embodiment,” “some embodiments,” “example,” “specific example,” or “some examples,” etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions 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 suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of the different embodiments or examples without contradiction.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 specification of the present invention.

Claims

1. A device for wet-process preparation of sulfuric acid and waste heat recovery 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 production section includes a combined converter and a combined absorption tower. The combined absorption tower is provided with a condensate inlet, a condensate outlet, and a converted gas inlet. The condensate inlet is connected to the flue gas outlet. The combined converter is provided with a process gas inlet and a converted gas outlet. The process gas inlet is connected to the condensate outlet, and the converted gas outlet is connected to the converted gas inlet. The waste heat recovery section includes an evaporator, which is connected to the acid circulation tank at the bottom of the combined absorption tower; The combined converter includes a preheater and an interlayer heat exchanger. The preheater includes the process gas inlet and the process gas outlet, as well as the converter gas outlet and the converter gas preheating inlet. The inlet of the interlayer heat exchanger is connected to the outlet of the process gas, and the outlet of the interlayer heat exchanger is connected to the preheating inlet of the conversion gas. An electric furnace is also provided between the preheater and the interlayer heat exchanger; The combined absorption tower is provided from bottom to top with a liquid accumulation section, a circulating acid heat transfer section, a condenser acid production section, and a demisting section; The demisting section includes several sets of cylindrical fiber demisters; The acid-producing section of the condenser includes a glass condenser tube, the condenser inlet and the condenser outlet correspond to the acid-producing section of the condenser, and the acid-producing section of the condenser is also provided with an acid outlet. The circulating acid heat transfer section includes a packing area and an acid separator located above the packing area. A gas lift cap is provided between the circulating acid heat transfer section and the acid production section of the condenser. The circulating acid heat transfer section also corresponds to the conversion gas inlet. The liquid accumulation section includes an acid circulation pump and an acid circulation tank, and the acid circulation pump delivers the acid in the acid circulation tank to the evaporator.

2. The equipment for wet preparation of sulfuric acid and waste heat recovery during the preparation process according to claim 1, characterized in that, The circulating acid outlet of the evaporator has two branches: 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.

3. The equipment for wet preparation of sulfuric acid and waste heat recovery during the preparation process according to claim 1, characterized in that, The flue gas purification section includes a venturi cleaner, a packed cooling tower, a recooling tower, an electrostatic precipitator, and a booster fan connected in sequence. The recooling tower is also connected to a refrigeration unit; The flue gas inlet is the inlet of the Venturi scrubber, and the flue gas outlet is the outlet of the booster fan.

4. The equipment for wet preparation of sulfuric acid and waste heat recovery during the preparation process according to claim 1, characterized in that, The preheater is a gas-to-gas heat exchanger.

5. The equipment for wet preparation of sulfuric acid and waste heat recovery during the preparation process according to claim 4, characterized in that, The top of the combined absorption tower is also connected to a tail gas treatment section.

6. A process for wet preparation of sulfuric acid with waste heat recovery during the preparation process, characterized in that, The wet sulfuric acid production and waste heat recovery process using the equipment described in claim 1 includes the following steps: S1. SO2 flue gas with a volume concentration of less than 2.5% is treated in the flue gas purification section and then sent into the combined absorption tower for circulation. S2. The SO2 flue gas with a volume ratio concentration of less than 2.5% from the combined absorption tower is then fed into the combined reactor. After catalytic reaction, the SO2 flue gas reacts with O2 to generate SO3 flue gas. S3. The SO3 flue gas is fed 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 reaction is absorbed by concentrated sulfuric acid with a mass ratio concentration of 99.2% to 99.8%. The sulfuric acid vapor is cooled by SO2 flue gas with a volume ratio concentration of less than 2.5% in the combined absorption tower. The sulfuric acid vapor is condensed into sulfuric acid liquid and discharged. S4. After absorbing heat, concentrated sulfuric acid with a mass ratio of 99.2%~99.8% is transported to the evaporator through the acid circulation pump of the acid circulation tank, transferring heat to the water in the evaporator.

7. The process for wet preparation of sulfuric acid and waste heat recovery during the preparation process according to claim 6, characterized in that, In step S2, the volume ratio of SO2 to H2O in the SO2 flue gas with a volume concentration of less than 2.5% needs to be controlled to be 1:1 to 4, and the temperature of the generated SO3 flue gas needs to be controlled to be 240 to 280°C. In step S3, the partial pressure of H2O in the SO3 flue gas needs to be lower than the partial pressure of H2O in concentrated sulfuric acid with a mass concentration of 99.2% to 99.8%, and the partial pressure of SO3 in the SO3 flue gas needs to be lower than the partial pressure of SO3 in concentrated sulfuric acid with a mass concentration of 99.2% to 99.8%.

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