A double-flash evaporation concentration device and method for waste sulfuric acid

Abstract

This invention discloses a double flash evaporation concentration device and method for waste sulfuric acid. The concentration method employs double flash evaporation, where 91% sulfuric acid undergoes self-flash evaporation under a certain vacuum to concentrate the sulfuric acid to approximately 92%. This effectively reduces the temperature of the intermediate concentrated sulfuric acid, avoiding the impact on the service life of the hand pump when using it. Furthermore, self-flash evaporation reduces the subsequent evaporation amount, preventing large pressure losses in the gas phase tube from affecting the target concentration obtained. The method can achieve the target concentration of 96% sulfuric acid, effectively reducing production costs.

Description

Technical Field

[0001] This invention relates to the field of sulfuric acid concentration technology, specifically to a waste sulfuric acid double flash evaporation device and concentration method. Background Technology

[0002] The high-concentration sections of the waste sulfuric acid plant are the third and fourth stages. The third stage concentrates sulfuric acid from 82% to 91%, operating at 182–189℃ and 7–9 kPa. The fourth stage concentrates sulfuric acid from 91% to 96%, operating at 180–185℃ and 1–1.5 kPa. The high-temperature 91% sulfuric acid from the third stage is pumped to the fourth stage at a pressure of approximately 0.5 MPa. Because the 91% sulfuric acid pumped in the third stage of the waste sulfuric acid vacuum concentration unit is at a high temperature (typically around 180℃), and the previously imported 91% sulfuric acid pumps typically operate for only 3–6 months, the short operating time results in high replacement costs and impacts production operations, leading to significant downtime losses.

[0003] The existing technology is as follows: the high-concentration section of the waste sulfuric acid plant uses single-stage flash evaporation, and the three-stage transfer pump is a PTFE-lined magnetic pump. The sulfuric acid temperature is approximately 180℃, and the transfer medium operates under the extreme conditions of the transfer pump. Problems exist:

[0004] (1) The third-stage 91% sulfuric acid transfer pump has too short an operating time and is frequently replaced, resulting in high pump replacement costs; it affects the operation of the production unit and causes significant losses due to shutdown.

[0005] (2) The evaporation rate of the fourth-stage flash evaporator is too high, and the pressure loss of the gas phase tube is large, which affects the operating pressure in the flash vapor and makes it difficult for the production unit to reach the design value (sulfuric acid concentration of 96%). It can generally only be maintained at 95.3-95.7%.

[0006] (3) If a high silicon iron pump is used, there is a problem of pump seal leakage under operating pressure.

[0007] Therefore, it is necessary to design a new concentration method to avoid the aforementioned defects of single-stage flash evaporation under high-temperature conveying in existing technologies. Summary of the Invention

[0008] This invention proposes a waste sulfuric acid double flash evaporation device and concentration method, which solves the defect of the existing technology where the sulfuric acid transport temperature is too high due to single-stage flash evaporation, which affects the flash evaporation effect and makes the concentrated sulfuric acid concentration fail to reach the target value.

[0009] In view of this, the solution of the present invention is as follows:

[0010] A method for concentrating waste sulfuric acid by double flash evaporation includes the following steps:

[0011] S1.82% waste sulfuric acid is pre-evaporated under vacuum to obtain sulfuric acid with a concentration of 91%, and the evaporation temperature is 182-189℃;

[0012] S2. The 91% sulfuric acid obtained in step S1 is flash-evaporated to a concentration of 92% under a vacuum of 1-1.5 kPa, and then preheated before being flash-evaporated a second time to obtain sulfuric acid of the target concentration.

[0013] Furthermore, the temperature of the 92% sulfuric acid in step S2 is 158–160°C.

[0014] Furthermore, the gas phase obtained from the two flash evaporations in step S2 is absorbed by an adsorption tower, and the resulting liquid phase enters the pre-evaporation process described in step S1.

[0015] Furthermore, the pressure of the second flash evaporation is 1–1.5 kPa, and the temperature is 180–185 °C.

[0016] The present invention also provides a waste sulfuric acid double flash evaporation concentration device, including a pre-evaporation unit and a flash evaporation unit connected together. The pre-evaporation unit is used to concentrate waste sulfuric acid to 91%. The flash evaporation unit includes a flash evaporator one and a flash evaporator two. The liquid phase output end of flash evaporator one is connected to the feed end of flash evaporator two via a rotary tank and a heater. The liquid phase output end of flash evaporator two is provided with a finished sulfuric acid pipeline.

[0017] Furthermore, the gas phase output ends of flash evaporator one and flash evaporator two are connected to a scrubbing tower, and the liquid phase output end of the scrubbing tower is connected to a pre-evaporation unit via a pipeline.

[0018] Furthermore, the lower part of the washing tower is provided with a first circulation pipeline connected to the input end; the lower part of the flash evaporator is provided with a second circulation pipeline connected to the input end of the heater.

[0019] Furthermore, the pre-evaporation unit and the flash evaporation unit are respectively connected to a vacuum system; the liquid phase output end of the flash evaporator is inserted to a preset depth below the liquid level in the rotary tank; a preset height is provided between the flash evaporator and the rotary tank.

[0020] Preferably, the flash evaporator is lower than the output end of the pre-evaporation unit, and a U-shaped tube of a preset length is provided between the flash evaporator and the pre-evaporation unit.

[0021] Preferably, the connecting pipeline between the rotary trough and the flash evaporator is equipped with a delivery pump, and the output end of the delivery pump is connected to the input end of the U-shaped tube via a pipeline.

[0022] Compared with the prior art, the beneficial effects of the present invention include, but are not limited to:

[0023] The concentration method described in this invention employs a double flash evaporation process, where 91% sulfuric acid undergoes self-flash evaporation under vacuum to concentrate the sulfuric acid to approximately 92%. This effectively reduces the temperature of the intermediate concentrated sulfuric acid, avoiding impact on the service life of the hand pump when using it. Furthermore, self-flash evaporation reduces subsequent evaporation, preventing significant pressure loss in the vapor phase tube from affecting the target concentration obtained from the concentration. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall waste sulfuric acid double flash evaporation concentration device described in this invention.

[0025] The attached figures are labeled as follows:

[0026] 1. Evaporator; 2. Flash evaporator I; 3. Rotary hand tank; 4. Scrubber; 5. Heater; 6. Flash evaporator II; 7. Transfer pump I; 8. Transfer pump II; 9. Pressure gauge I; 10. Pressure gauge II; 11. Waste sulfuric acid feed pipe; 12. U-tube; 13. Sulfuric acid pipe I; 14. Sulfuric acid pipe II; 15. Sulfuric acid pipe III; 16. Vapor phase pipe I; 17. Vapor phase pipe II; 18. Thermometer I; 19. Thermometer II; 20. Thermometer III; 21. Transfer pump III; 22. Reflux pipe. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0029] It should also be noted that, unless otherwise explicitly specified and limited, terms such as "installation," "connection," "joining," "fixing," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0030] In one embodiment, such as Figure 1As shown, a waste sulfuric acid double flash evaporation concentration device is provided, including an evaporator 1 and a flash unit connected together. The left end of the evaporator 1 is connected to a waste sulfuric acid feed pipe 11 for feeding waste sulfuric acid. The flash unit includes a flash evaporator 1 2 and a flash evaporator 2 6. The liquid phase output end of the flash evaporator 1 2 is provided with a sulfuric acid pipe 13 connected to a rotary trough 3. The bottom of the rotary trough 3 is provided with a conveying pump 7 connected to the feed end of a heater 5. The output end of the heater 5 is connected to the feed end of the flash evaporator 2 6. The liquid phase output end of the flash evaporator 2 6 is provided with a sulfuric acid pipe 3 15 for conveying the finished sulfuric acid.

[0031] In the above embodiments, the sulfuric acid can be concentrated to an intermediate concentration by flash evaporator 2, and then concentrated to the target concentration by flash evaporator 6. The concentration of flash evaporator 2 can be achieved by setting the vacuum degree to obtain intermediate sulfuric acid at a lower temperature through self-flash evaporation, avoiding the impact on service life when using a hand pump. On the other hand, self-flash evaporation can reduce the evaporation of flash evaporator 6 and avoid the large pressure loss in the gas phase tube affecting the target concentration obtained by concentration.

[0032] In a preferred embodiment, in order to recover the gas phase, reduce emissions, and increase yield, the gas phase output ends of flash evaporator 1 2 and flash evaporator 2 6 are both connected to washing tower 4, and the liquid phase output end of washing tower 4 is provided with sulfuric acid pipe 2 14 connected to waste sulfuric acid feed pipe 11.

[0033] In a preferred embodiment, the lower part of the washing tower 4 is provided with a first circulation pipeline connected to the input end; the lower part of the flash evaporator 6 is provided with a second circulation pipeline connected to the input end of the heater 5; specifically, a third delivery pump 21 and a second delivery pump 8 are respectively provided to achieve forced circulation.

[0034] In a preferred embodiment, the evaporator 1 and the flash evaporation unit are respectively connected to a vacuum system; the liquid output end of the flash evaporator 2 is inserted into the rotating tank 3 to a certain depth, and the vertical height between the flash evaporator 2 and the rotating tank 3 is greater than a preset value in order to ensure the normal gravity flow of sulfuric acid under vacuum; preferably, the depth is greater than 1m and the height is greater than 10m.

[0035] In a preferred embodiment, the flash evaporator 2 is positioned below the output height of the evaporator 1, and a U-shaped tube 12 of a preset length, preferably 2-3 m, is provided between the flash evaporator 2 and the pre-evaporation unit for liquid sealing. This prevents the liquid-sealed material in the U-shaped tube from being absorbed by self-evaporation and disrupting the vacuum of the evaporator and flash unit in the event of an unexpected shutdown of the device.

[0036] In a more preferred embodiment, the output end of the delivery pump 7 is provided with a return pipe 22 connected to the input end of the U-tube 12 to realize the circulation of intermediate sulfuric acid.

[0037] In the above embodiments, to ensure the conditions for evaporation or flash evaporation, a vapor phase pipe 16 is provided at the top of the evaporator 1, and a vapor phase pipe 17 is provided at the top of the washing tower 4; the vapor phase pipe 16 and the vapor phase pipe 17 are independently connected to an external vacuum system. Figure 1 (Not shown in the image) is used to provide a vacuum to evaporator 1, and to provide the same vacuum to flash evaporator 2, washing tower 4, and flash evaporator 6. To monitor the operating status of the concentration unit, pressure gauges 19 and 10 are respectively installed on vapor phase pipe 16 and vapor phase pipe 17. In addition, thermometer 18 is installed on evaporator 1, thermometer 19 is installed on rotary trough 3, and thermometer 20 is installed at the output end of heater 5.

[0038] As is common knowledge in the field, the above-mentioned concentration device is also equipped with valves and other instruments for flow regulation or pipeline start-up and shutdown on each pipeline, so that those skilled in the art can complete the concept and working process described in the context of this invention, which will not be repeated here.

[0039] In another embodiment, a method for concentrating waste sulfuric acid using the above-mentioned waste sulfuric acid double flash evaporation concentrator is proposed, comprising the following steps:

[0040] S1.82% waste sulfuric acid is pre-evaporated under vacuum in evaporator 1 to obtain sulfuric acid with a concentration of 91%, and the evaporation temperature is 182-189℃;

[0041] S2. The 91% sulfuric acid obtained in step S1 is flashed to a concentration of 92% under a vacuum of 1-1.5 kPa in flash evaporator 2. The 92% sulfuric acid flows by gravity to the hand tank 3 and is then transported to the heater 4 by the transfer pump 7 for preheating. The preheated 92% sulfuric acid enters flash evaporator 6 for a second flash evaporation to obtain sulfuric acid of the target concentration.

[0042] In the above embodiment, the evaporation pressure inside the evaporator 1 in step S1 is 7-9 kPa.

[0043] In the above embodiments, the temperature of the 92% sulfuric acid in step S2 is 158°C to 160°C. The self-flash evaporation of the flash evaporator 2 effectively reduces the temperature of the output sulfuric acid and reduces the failure rate of the delivery pump 7.

[0044] In the above embodiment, the gas phase obtained from the two flash evaporations in step S2 is absorbed by adsorption tower 4, and the absorbed liquid phase enters the pre-evaporation process described in step S1 via sulfuric acid tube 14.

[0045] In the above embodiments, the vacuum degree of flash evaporator 1 2, washing tower 4, and flash evaporator 2 6 is the same, and the pressure is 1 to 1.5 kPa; the temperature of flash evaporator 2 6 is 180 to 185°C, and the concentration of the finished sulfuric acid discharged through sulfuric acid pipe 3 15 can reach 96% after two flash evaporations.

[0046] The following is a calculation of the temperature of 91% sulfuric acid obtained from evaporator 1 during flash evaporation in flash evaporator 2. Under certain operating conditions, the output temperature of 91% sulfuric acid from evaporator 1 is 185℃, the pressure above the liquid surface is 8.5 kPa, and the flow rate is 14844.2 kg / h. After entering flash evaporator 2, the pressure above the liquid surface decreases to 1.5 kPa. The temperature of 91% sulfuric acid after flash evaporation is calculated as follows:

[0047] 1) Physical process analysis: When 91% sulfuric acid at a temperature of 185℃ and a pressure of 8.5 kPa on the liquid surface decreases to 1.5 kPa, the waste point equilibrium of 91% sulfuric acid decreases, causing it to spontaneously boil. Water and equilibrium sulfuric acid (with a sulfuric acid concentration of approximately 20% in the gas phase) evaporate, and the sulfuric acid concentration gradually increases, with the equilibrium boiling point of sulfuric acid rising synchronously. Once the sulfuric acid concentration reaches a certain value, the equilibrium temperature no longer rises. During the self-evaporation process, the heat consumed by the sulfuric acid comes from the heat released by the decrease in sulfuric acid temperature. The heat consumed is due to the heat absorbed by the evaporation of water and sulfuric acid, as well as the heat absorbed by the dehydration of sulfuric acid (the reverse of the heat released by the dilution of sulfuric acid).

[0048] 2) Estimation method:

[0049] Referring to the design data of the four-stage vacuum concentration, under a vacuum of 1.5 kPa, the feed rate of 91% sulfuric acid is 14844.2 kg / h, the output rate of 96% sulfuric acid is 13536.8 kg / h, and the steam consumption at 17 bar is 1941 kg / h.

[0050] The calculated evaporation rate of water and sulfuric acid is 1307.4 kg / h.

[0051] The latent heat of steam at 17 bar is approximately 1921 kJ / kg;

[0052] The calculated unit evaporation rate is approximately 2852 (kJ / kg) = 1921 * 1941 / 1307.4.

[0053] The specific heat of concentrated sulfuric acid is approximately 1.47 kJ / kg.

[0054] Let the evaporation rate be A, and the temperature difference be Δt;

[0055] Therefore: 1.47 * Δt * 14844.2 = 2852 * A;

[0056] According to the phase diagram, approximately 20% of the sulfuric acid on the surface of a 91% sulfuric acid solution is in the gaseous phase. Using a trial-and-error method, we assume that the sulfuric acid concentration increases to 92%, with X water evaporating and Y sulfuric acid evaporating. We then establish equations ① and ②:

[0057]

[0058] Y / (X+Y)=0.2 ②

[0059] Solving equations ① and ② simultaneously, we get: X = 165, Y = 41.22;

[0060] Evaporation rate A = X + Y = 165 + 41.22 = 206.22 kg / h;

[0061] 1.47 * △t * 14844.2 = 2852 * 206.22;

[0062] The result is: Δt = 26.95℃, which means the temperature of 92% sulfuric acid after flash evaporation is 185 - 26.95 = 158.05℃.

[0063] According to the concentrated sulfuric acid waste point and temperature equilibrium diagram, under a vacuum of approximately 2 kPa, the boiling point of 92% sulfuric acid is approximately 158°C.

[0064] Conclusion: By reducing the pressure of 91% sulfuric acid at approximately 185℃ (8.5KPa) to below 2kPa, concentrated sulfuric acid with a concentration of approximately 92% can be obtained. At the same time, the temperature of the 92% concentrated sulfuric acid drops to approximately 158℃, which is far from the extreme temperature point of the equipment operation.

[0065] The concentration device and concentration method provided in the above embodiments effectively solve the operational problems of existing technical equipment; from a process perspective, they solve the problem that the final sulfuric acid concentration cannot reach the design requirements, saving an average of more than 700,000 yuan per year.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A double flash concentration apparatus for spent sulfuric acid, characterized by, The system includes a pre-evaporation unit and a flash evaporation unit connected together. The pre-evaporation unit is used to concentrate waste sulfuric acid to 91%. The flash evaporation unit includes flash evaporator one (2) and flash evaporator two (6). The liquid phase output end of flash evaporator one (2) is connected to the feed end of flash evaporator two (6) via a rotary tank (3) and a heater (5). The liquid phase output end of flash evaporator two (6) is equipped with a finished sulfuric acid pipeline. Flash evaporator one (2) is used to concentrate the concentrated 91% waste sulfuric acid to 92% at 1-1.5 kPa. The pre-evaporation unit and the flash evaporation unit are respectively connected to a vacuum system; the liquid output end of the flash evaporator (2) is inserted to a preset depth below the liquid level in the rotary tank (3); a preset height is provided between the flash evaporator (2) and the rotary tank (3); The flash evaporator (2) is lower than the output end of the pre-evaporation unit, and a U-shaped tube (12) of a preset length is provided between the flash evaporator (2) and the pre-evaporation unit. The connecting pipeline between the rotary groove (3) and the flash evaporator (6) is equipped with a delivery pump, and the output end of the delivery pump is connected to the input end of the U-shaped pipe (12) via a pipeline.

2. The spent sulfuric acid double-flash concentration apparatus according to claim 1, characterized by, The gas phase output ends of flash evaporator 1 (2) and flash evaporator 2 (6) are connected to the scrubbing tower (4), and the liquid phase output end of the scrubbing tower (4) is connected to the pre-evaporation unit via a pipeline.

3. The spent sulfuric acid double flash evaporation concentration apparatus according to claim 2, characterized by, The lower part of the washing tower (4) is provided with a first circulation pipeline connected to the input end; the lower part of the flash evaporator (6) is provided with a second circulation pipeline connected to the input end of the heater (5).

4. A method for double flash concentration of spent sulfuric acid using the double flash concentration apparatus for spent sulfuric acid according to any one of claims 1 to 3, characterized by, Includes the following steps: S1. The 82% waste sulfuric acid output from the waste sulfuric acid unit is pre-evaporated under vacuum to obtain sulfuric acid with a concentration of 91%, and the evaporation temperature is 182-189℃; S2. The 91% sulfuric acid obtained in step S1 is subjected to self-flash evaporation at 1-1.5 kPa to obtain sulfuric acid with a concentration of 92% at a temperature of 158-160℃; Sulfuric acid with a concentration of 3.92% is pumped and preheated before undergoing a second flash evaporation to obtain sulfuric acid of the target concentration.

5. The concentration method according to claim 4, characterized in that, The gas phase obtained from the self-flash evaporation in step S2 and the second flash evaporation in step S3 is absorbed by an adsorption tower. The liquid phase obtained from the absorption is recovered and combined with the 82% waste sulfuric acid in step S1 for pre-evaporation.

6. The concentration method of claim 4, wherein, The pressure of the second flash evaporation is 1-1.5 kPa, and the temperature is 180-185 °C.

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