Method and system for preparing concentrated sulfuric acid from dilute sulfuric acid

Abstract

This invention discloses a method and system for preparing concentrated sulfuric acid from dilute sulfuric acid, belonging to the field of concentrated sulfuric acid preparation technology. The method includes: dilute sulfuric acid A is flash-evaporated via flash evaporation A to obtain dilute sulfuric acid B; dilute sulfuric acid B is then flash-evaporated in flash evaporation B to obtain dilute sulfuric acid E; dilute sulfuric acid E is then flash-evaporated in flash evaporation C to obtain concentrated sulfuric acid F; wherein, the steam generated from flash evaporation A and flash evaporation B is mixed and then compressed and heated in booster compressor A; the temperature of the first saturated steam after compression is increased and then returned to flash evaporation A and flash evaporation B for heating; the saturated condensate generated during heating preheats dilute sulfuric acid A, and the preheated dilute sulfuric acid A is then returned to flash evaporation A; the steam generated from flash evaporation C is compressed and heated in booster compressor B; the temperature of the second saturated steam after compression is increased and then returned to flash evaporation C for heating. This invention can realize the recovery of low-concentration dilute sulfuric acid to prepare high-concentration sulfuric acid, significantly reducing the cost of dilute sulfuric acid concentration.

Description

Technical Field

[0001] This invention relates to the field of concentrated sulfuric acid preparation technology, and in particular to a method and system for preparing concentrated sulfuric acid from dilute sulfuric acid; especially, it can recover dilute sulfuric acid with a concentration of less than 10% and produce concentrated sulfuric acid with a concentration of 98%. Background Technology

[0002] I. Properties of Sulfuric Acid

[0003] (1) Boiling point of sulfuric acid

[0004] (2) Effect of negative pressure on boiling point

[0005] (3) Decomposition of sulfuric acid

[0006] II. Existing methods for preparing concentrated sulfuric acid from dilute sulfuric acid

[0007] (1) Using dilute sulfuric acid to absorb sulfur trioxide gas to produce concentrated sulfuric acid

[0008] In China, the current industrial production of 98% concentrated sulfuric acid generally uses the method of absorbing sulfur trioxide with dilute sulfuric acid. The basic principle of using dilute sulfuric acid to absorb sulfur trioxide gas to prepare concentrated sulfuric acid is to allow the water in the dilute sulfuric acid to react with the sulfur trioxide to produce sulfuric acid, thereby consuming the water in the dilute sulfuric acid and ultimately turning the dilute sulfuric acid into concentrated sulfuric acid.

[0009] For example, Chinese patent CN106477530B discloses a concentrated sulfuric acid preparation device based on low-temperature waste heat organic Rankine cycle recovery, including an absorption tower, a heat pipe steam generator, a generator, an expander, a condenser, a storage tank, a condenser, a circulating acid pump, and a circulating acid tank. This document improves the device to realize the recovery and utilization of waste heat in the absorption method of sulfuric acid production.

[0010] For example, Chinese patent application CN120081340A discloses a sulfuric acid concentration device and a method for producing concentrated sulfuric acid using the device. The sulfuric acid concentration device includes a waste acid regeneration unit that incinerates sulfur-containing waste acid and acidic gas to produce sulfuric acid, and a sulfuric acid concentration unit that concentrates the sulfuric acid produced by the waste acid regeneration unit. The sulfuric acid concentration unit includes a combustion chamber where liquid sulfur is burned to generate sulfur dioxide. A steam generator is installed in the combustion chamber. The combustion chamber is connected to a reactor via a process gas delivery pipe. Sulfur dioxide undergoes a catalytic reaction in the reactor to generate sulfur trioxide. The reactor is connected to an absorption tower via a process gas discharge pipe. The absorption tower is equipped with a sulfuric acid reflux pipe. Unqualified sulfuric acid from the waste acid regeneration unit and the refluxed sulfuric acid absorb sulfur trioxide in the absorption tower to generate sulfuric acid, thereby achieving sulfuric acid concentration.

[0011] Although the absorption method is simple, technically easy, and low-cost, the inventors have noticed that the absorption method for preparing concentrated sulfuric acid requires the construction of a sulfur trioxide synthesis device. This device involves chemical reactions involving toxic and harmful substances, which can cause serious damage to human health and the environment. It is a key regulated process and is difficult to implement in some areas.

[0012] (2) Concentrate dilute sulfuric acid to obtain concentrated sulfuric acid.

[0013] Currently, concentrated sulfuric acid is rarely produced using concentration methods, except when a large amount of intermediate product dilute sulfuric acid needs to be recycled. Existing multi-stage flash evaporation concentration methods typically concentrate dilute sulfuric acid to 80% for reuse. For example, in the sulfuric acid process for titanium dioxide, multi-stage flash evaporation concentrates approximately 30% dilute sulfuric acid to 80% for reuse. This process is energy-intensive, especially when concentrating extremely dilute sulfuric acid to high concentration, which consumes even more steam, making its operating costs far higher than the sulfur trioxide absorption method for sulfuric acid production. Therefore, flash evaporation not only makes it difficult to produce concentrated sulfuric acid of 95% or higher, but also consumes a lot of steam, especially when concentrating even dilute sulfuric acid to 98% concentration, which is even less economical.

[0014] For example, Chinese patent application CN1608716A discloses a method for recovering waste sulfuric acid and waste gas generated during the production of titanium dioxide. The method includes: feeding the furnace waste gas and waste sulfuric acid generated during titanium dioxide production into a "titanium dioxide furnace tail gas concentration graphite tower" for mixing, gas-liquid contact, concentration, separation of the acid from the titanium dioxide contained therein, crystallization and separation of inorganic salts in the acid solution, and further feeding the acid solution into a silicon carbide evaporator, where some water is evaporated under negative pressure to achieve an acid concentration of 80-90%. This method yields 30% sulfuric acid from the waste gas, which is then evaporated in three stages to obtain 45%, 60%, and 65-70% sulfuric acid, respectively, before finally being concentrated to obtain 80-90% concentrated acid.

[0015] For example, Chinese patent application CN101214931A discloses a method for concentrating and removing impurities from dilute sulfuric acid during the sulfuric acid process for producing titanium dioxide. This method involves directly heating the evaporator with steam or using a heat exchanger under normal pressure, so that 23.5% dilute sulfuric acid for titanium dioxide is evaporated through multiple effects to obtain 60% sulfuric acid.

[0016] For example, US Patent US6548038B: Process for the concentration of dilutesulphuric acid solutions, without disclosing pressure, describes the second-stage concentration as greater than 50%, and the final concentrated acid concentration should be less than 70%.

[0017] For example, US Patent 5228885A - Process of concentrating a dilute sulfuric acid in a three-stage forced-circulation vacuum evaporation plant, as shown in the table below, uses a three-stage negative pressure distillation method and only obtains 95% concentrated sulfuric acid.

[0018]

[0019] In summary, at present, the methods for recovering and preparing high-concentration sulfuric acid, especially 98% concentrated sulfuric acid, from dilute sulfuric acid are either through sulfur trioxide absorption or by using a high-energy-consuming multi-stage negative pressure distillation method. Summary of the Invention

[0020] Based on this, according to one embodiment of the present invention, the objective is to provide a method and system for preparing concentrated sulfuric acid from dilute sulfuric acid. The present invention achieves the recovery of low-concentration dilute sulfuric acid to prepare high-concentration sulfuric acid, which is more energy-efficient than existing multi-stage negative pressure distillation, and in particular, can recover dilute sulfuric acid with a concentration below 10% to prepare 98% concentrated sulfuric acid.

[0021] The above objective can be achieved through the following technical solutions: According to one aspect of the present invention, a method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid is provided, comprising: dilute sulfuric acid A is flashed through flash evaporation A to obtain dilute sulfuric acid B, dilute sulfuric acid B is flashed through flash evaporation B to obtain dilute sulfuric acid E, and dilute sulfuric acid E is flashed through flash evaporation C to obtain concentrated sulfuric acid F; The steam generated by flash evaporation A and flash evaporation B is mixed and then enters the booster A for compression and heating. The temperature of the first saturated steam after compression is increased and then returned to flash evaporation A and flash evaporation B for heating. The saturated condensate generated by heating preheats dilute sulfuric acid A, and the preheated dilute sulfuric acid A enters flash evaporation A. The steam generated by flash evaporator C enters the booster compressor B for compression and heating. After compression, the temperature of the second saturated steam is increased and it returns to flash evaporator C for further heating.

[0022] Preferably, the dilute sulfuric acid A is dilute sulfuric acid A with a concentration of 8%-70%.

[0023] Preferably, the pressure of flash evaporation A is no higher than 56 kPa absolute pressure.

[0024] Preferably, in flash evaporation A, dilute sulfuric acid A is heated by the first saturated steam to maintain the flash evaporation temperature at not less than 90°C.

[0025] Preferably, the saturated condensate generated by heating preheats dilute sulfuric acid A to 85°C-95°C.

[0026] Preferably, the pressure of flash evaporation B is an absolute pressure not exceeding 56 kPa.

[0027] Preferably, in flash evaporation B, dilute sulfuric acid B is heated by the first saturated steam to maintain the flash evaporation temperature at not less than 103°C.

[0028] Preferably, before dilute sulfuric acid B enters flash evaporator B, it first enters a heat exchanger and is heated by the first saturated steam.

[0029] Alternatively, preferably, before entering flash evaporator B, dilute sulfuric acid B is mixed with circulating dilute sulfuric acid C discharged from flash evaporator B and then enters the heat exchanger to be heated by the first saturated steam.

[0030] Preferably, the pressure of flash evaporation C is no higher than 5 kPa absolute pressure; Preferably, in flash evaporation C, dilute sulfuric acid E is heated by a second saturated steam to maintain the flash evaporation temperature at ≥77°C, so as to obtain concentrated sulfuric acid F with a concentration of ≥70%.

[0031] Preferably, the method further includes adjusting the flash temperature of flash C according to the desired concentration of concentrated sulfuric acid F.

[0032] Preferably, when a concentrated sulfuric acid F with a concentration of ≥80% is to be obtained, the flash temperature of flash evaporation C is adjusted to ≥115.3℃.

[0033] Preferably, when obtaining concentrated sulfuric acid F with a concentration ≥90%, the flash temperature of flash evaporation C is adjusted to ≥139.4℃.

[0034] Preferably, when obtaining concentrated sulfuric acid F with a concentration ≥93%, the flash temperature of flash evaporation C is adjusted to ≥156.6℃.

[0035] Preferably, when obtaining concentrated sulfuric acid F with a concentration ≥95%, the flash temperature of flash evaporation C is adjusted to ≥170.5℃.

[0036] Preferably, when obtaining concentrated sulfuric acid F with a concentration ≥98%, the flash temperature of flash evaporation C is adjusted to ≥193°C.

[0037] Preferably, when obtaining concentrated sulfuric acid F with a concentration ≥ 79%, before dilute sulfuric acid E enters flash evaporation C, the method further includes: preheating dilute sulfuric acid E to the flash evaporation temperature of flash evaporation C by external steam heating or electric heating.

[0038] Preferably, the booster A and booster B are centrifugal boosters, wherein the pressure of the steam increases by no less than 50 kPa after being compressed by the centrifugal booster, and the temperature of the saturated steam increases by no less than 18°C ​​after compression.

[0039] Preferably, dilute sulfuric acid A with a concentration of 8%-12% is flash-evaporated in flash evaporation A to obtain dilute sulfuric acid B with a concentration of 18-22%. Dilute sulfuric acid B is then flash-evaporated in flash evaporation B to obtain dilute sulfuric acid E with a concentration of 42-46%. Dilute sulfuric acid E is then flash-evaporated in flash evaporation C to obtain concentrated sulfuric acid F with a concentration of 70%-98%.

[0040] According to one aspect of the present invention, a system for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid is provided, comprising: flash evaporators A, B and C connected in sequence, and booster A and booster B; Among them, the steam outlets of flash A and flash B are connected to the inlet of booster A, the steam outlet of booster A is connected to the heat source inlet of flash A and flash B, the heat source outlets of flash A and flash B are connected to the heat source inlet of the heat exchange device, and the cold source outlet of the heat exchange device is connected to the acid inlet of flash A. The steam outlet of flash evaporator C is connected to the inlet of booster compressor B, and the steam outlet of booster compressor B is connected to the heat source inlet of flash evaporator C.

[0041] Preferably, it further includes: a heat exchanger, wherein the heat source inlet of the heat exchanger is connected to the booster A, the cold source inlet is connected to flash A and flash B respectively, and the cold source outlet is connected to flash B, for using the first saturated steam to heat the dilute sulfuric acid B from flash A and the circulating dilute sulfuric acid C discharged from flash B and then send them to flash B.

[0042] Preferably, it further includes: a preheating system, wherein the inlet of the preheating system is connected to the dilute sulfuric acid outlet of flash evaporation B, and the outlet of the preheating system is connected to the dilute sulfuric acid inlet of flash evaporation C, for preheating the dilute sulfuric acid E from flash evaporation B by external steam heating or electric heating when a concentrated sulfuric acid F with a concentration ≥79% is to be obtained, and sending the dilute sulfuric acid E to the flash evaporation temperature of flash evaporation C.

[0043] Preferably, it further includes: a salt filtration device, used to filter or press-filter concentrated sulfuric acid F when the raw material contains sulfate, to separate concentrated sulfuric acid G and salt.

[0044] Preferably, it further includes: a separation tank A and a vacuum pump A connected thereto, wherein the heat source outlets of flash A and flash B are connected to the heat source inlet of the heat exchange device through the separation tank A and the transfer pump; the vacuum pump A is used to discharge non-condensable gases from the saturated condensate in the separation tank A and to maintain the pressure of flash A and flash B.

[0045] Preferably, it further includes: a separation tank B and a vacuum pump B connected thereto, wherein the separation tank B is connected to the heat source outlet of the flash evaporation C, and the condensate generated after heating enters the separation tank B; the vacuum pump B is used to discharge non-condensable gases from the condensate in the separation tank B and maintain the pressure of the flash evaporation C.

[0046] According to one embodiment of the present invention, by using three-stage flash distillation (A, B, and C) and pressurizing the secondary steam, high-concentration sulfuric acid can be prepared from low-concentration dilute sulfuric acid. This method is more energy-efficient and significantly reduces operating costs compared to existing multi-stage negative pressure distillation.

[0047] Compared with the prior art, the present invention also has the following advantages and beneficial effects: (1) This invention is applicable to the concentration and reuse of dilute sulfuric acid of any concentration. The pressure and temperature of flash evaporation A, B, and C can be adjusted as needed to achieve the concentration adjustment of the flash evaporation sulfuric acid at each stage.

[0048] In a preferred embodiment, by simply adjusting the temperature of flash evaporation C (e.g., 77°C-193°C), concentrated sulfuric acid of the corresponding concentration (70%-98%) can be obtained, with a maximum concentration of 98%.

[0049] (2) This invention only uses external steam during the start-up phase and only uses secondary steam during normal operation, eliminating the need for external steam. Compared with the traditional steam-heated multi-stage flash evaporation concentration method, the operating cost is greatly reduced. Only when a concentrated sulfuric acid F with a concentration ≥79% is required can an external steam heating method or an electric heating method be used. The dilute sulfuric acid E is first preheated to the flash temperature of flash evaporation C and then sent to flash evaporation C for flash evaporation. During flash evaporation, it is heated by the second saturated steam to maintain the flash temperature.

[0050] (3) The lower the concentration of dilute sulfuric acid in the raw materials of this invention, the more obvious the operating cost advantage.

[0051] (4) This invention can recover and prepare concentrated sulfuric acid from dilute sulfuric acid with a concentration of less than 10%, and can realize the reuse of a large amount of dilute sulfuric acid containing sulfate with a concentration of less than 10%, providing a reuse route for intermediate product dilute sulfuric acid. Especially for some remote areas with large transportation volumes, concentrating dilute sulfuric acid into 98% sulfuric acid is the best choice.

[0052] (5) When the raw material containing dilute sulfuric acid in this invention contains sulfates, the salts can be separated by filtering the concentrated sulfuric acid F, and the sulfates can also be recovered. Since the vapor pressure of sulfuric acid with a concentration of less than 98.3% is almost entirely water pressure, sulfates will not have a significant impact on the boiling point / final quality of sulfuric acid during the concentration process; and sulfates are almost insoluble in concentrated sulfuric acid, so they can be recovered by filtration and crystallization. Of course, the filtration location can be adjusted to remove the corresponding salts according to the type and amount of salts contained in the raw material. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the process for preparing concentrated sulfuric acid from dilute sulfuric acid in one embodiment of the present invention. Detailed Implementation

[0054] The technical solution of the present invention will be clearly and completely described below with reference to embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0055] To address the high energy consumption issues in existing industrial production of concentrated sulfuric acid, and the need for recycling large quantities of sulfate-containing dilute sulfuric acid (less than 10% concentration) generated in certain emerging industries, this invention provides a method for preparing concentrated sulfuric acid from dilute sulfuric acid. Through multi-stage flash evaporation and pressurized utilization of secondary steam, it achieves the recovery of high-concentration sulfuric acid from low-concentration dilute sulfuric acid. Compared with existing multi-stage negative pressure distillation, this method is more energy-efficient, significantly reduces operating costs, and eliminates the need for neutralization of dilute sulfuric acid into gypsum followed by water recovery. Furthermore, it establishes a new process route for the preparation of concentrated sulfuric acid, especially high-concentration concentrated sulfuric acid, and has significant economic value.

[0056] In some embodiments of the present invention, a system for preparing concentrated sulfuric acid from dilute sulfuric acid is provided, comprising: flash evaporators A, B, and C connected in sequence, and booster compressors A and B; wherein the steam outlets of flash evaporators A and B are connected to the inlet of booster compressor A, the steam outlet of booster compressor A is connected to the heat source inlet of flash evaporators A and B, the heat source outlets of flash evaporators A and B are connected to the heat source inlet of a heat exchanger, and the cold source outlet of the heat exchanger is connected to the acid inlet of flash evaporator A; the steam outlet of flash evaporator C is connected to the inlet of booster compressor B, and the steam outlet of booster compressor B is connected to the heat source inlet of flash evaporator C. Booster compressors A and B can be centrifugal boosters.

[0057] By sequentially flashing preheated dilute sulfuric acid through flash evaporators A, B, and C, and then pressurizing the secondary steam generated from flash evaporators A, B, and C using booster compressors A and B respectively, high-concentration sulfuric acid can be prepared from low-concentration dilute sulfuric acid, reducing energy consumption and significantly lowering operating costs.

[0058] To achieve more efficient flash concentration in flash evaporation B, the system further includes a heat exchanger, the heat source inlet of which is connected to the booster A, the cold source inlet of which is connected to both flash evaporation A and flash evaporation B, and the cold source outlet of which is connected to flash evaporation B. This heat exchanger is used to heat the dilute sulfuric acid B from flash evaporation A and the circulating dilute sulfuric acid C discharged from flash evaporation B using the first saturated steam before sending them into flash evaporation B.

[0059] To remove non-condensable gases from the saturated condensate and maintain the pressure of flash A and flash B, the system further includes a separation tank A and a vacuum pump A connected thereto. The heat source outlets of flash A and flash B are connected to the heat source inlet of the heat exchanger via the separation tank A and the transfer pump. The vacuum pump A removes the non-condensable gases from the saturated condensate in separation tank A and maintains the pressure of flash A and flash B.

[0060] To remove non-condensable gases from the condensate and maintain the pressure of flash evaporation C, the system further includes a separator B and a vacuum pump B connected to it. Separator B is connected to the heat source outlet of flash evaporation C, and the condensate produced after heating enters separator B. The vacuum pump B removes the non-condensable gases from the condensate in separator B and maintains the pressure of flash evaporation C.

[0061] When the raw material containing dilute sulfuric acid contains salt, the system is also equipped with a salt filtration device to remove the salt from the acid. Specifically, the salt filtration device can be installed at an appropriate location in the system depending on the type and amount of salt contained in the raw material. For example, when the raw material contains sulfate, a filtration / pressure filtration device can be installed and connected to the concentrated sulfuric acid outlet of flash evaporation C via a pump. By pressure filtration / filtration of concentrated sulfuric acid F, concentrated sulfuric acid G and sulfate can be obtained. The sulfate contained in the raw material containing dilute sulfuric acid only affects the boiling point of sulfuric acid during the concentration process and does not affect the quality of the final concentrated sulfuric acid. Furthermore, sulfate is almost insoluble in concentrated sulfuric acid and can be removed and recovered through filtration and crystallization.

[0062] In some embodiments of the present invention, a method for preparing concentrated sulfuric acid from dilute sulfuric acid is provided, comprising: dilute sulfuric acid A is flash-distilled through flash evaporation A to obtain dilute sulfuric acid B; dilute sulfuric acid B is further flash-distilled in flash evaporation B to obtain dilute sulfuric acid E; dilute sulfuric acid E is flash-distilled through flash evaporation C to obtain concentrated sulfuric acid F. The steam generated from flash evaporation A and flash evaporation B is mixed and then enters booster compressor A. After compression, the temperature of the first saturated steam is increased, and it is returned to flash evaporation A and flash evaporation B for heating. The saturated condensate generated during heating preheats the dilute sulfuric acid A and is then discharged from the system. The steam generated from flash evaporation C enters booster compressor B. After compression, the temperature of the second saturated steam is increased, and it is returned to flash evaporation C for heating. The condensate generated during heating is then discharged from the system.

[0063] This method is applicable to the concentration and recovery of dilute sulfuric acid of any concentration. The sulfuric acid concentration in dilute sulfuric acid A, dilute sulfuric acid B, dilute sulfuric acid E, and dilute sulfuric acid F increases sequentially. This invention can achieve the reuse of low-concentration (8%-70%) dilute sulfuric acid, while also enabling the preparation of concentrated sulfuric acid. This invention can produce concentrated sulfuric acid with a maximum purity of 98%. The lower the concentration of dilute sulfuric acid in the raw materials, the more significant the operating cost advantage. In particular, this invention can produce 98% concentrated sulfuric acid from dilute sulfuric acid with a purity of less than 10%.

[0064] The booster A and booster B are preferably centrifugal boosters. The booster A and booster B compress steam and increase the pressure by no less than 50 kPa, and the temperature of the saturated steam after compression increases by no less than 18°C, thereby better realizing the utilization of secondary steam.

[0065] In some embodiments, the pressure of flash evaporation A is not higher than 56 kPa absolute pressure and the flash evaporation temperature is not lower than 90°C. Flash evaporation A can be more efficient in concentrating dilute sulfuric acid, which can increase the concentration of dilute sulfuric acid by about 10%. For example, dilute sulfuric acid A with a concentration of 8%-10% can be flashed under the above conditions to obtain dilute sulfuric acid B with a concentration of 18-22%.

[0066] In some embodiments, the pressure of flash evaporation B is not higher than 56 kPa absolute pressure and the flash evaporation temperature is not lower than 103°C. Flash evaporation B can concentrate sulfuric acid more efficiently, increasing the concentration of dilute sulfuric acid by approximately 25%. For example, dilute sulfuric acid B with a concentration of 18-22% can be flashed under the above conditions to obtain dilute sulfuric acid E with a concentration of 42-46%.

[0067] In some embodiments, the pressure of flash evaporation C is no higher than 5 kPa absolute pressure, and the flash evaporation temperature is ≥77°C. Flash evaporation C can concentrate sulfuric acid more efficiently, increasing the concentration of dilute sulfuric acid by approximately 55%. For example, dilute sulfuric acid E with a concentration of 42-46% can be flashed in flash evaporation C under the above conditions to obtain concentrated sulfuric acid F with a concentration of ≥70%.

[0068] This invention enables the reuse of low-concentration dilute sulfuric acid while simultaneously producing concentrated sulfuric acid, with a maximum concentration of 98%. In particular, this invention can produce 98% concentrated sulfuric acid from dilute sulfuric acid of less than 10%.

[0069] This invention enables the preparation of sulfuric acid from low concentrations of 8%-70% to concentrated concentrations of 70%-98%. Specifically, the concentration of sulfuric acid at each stage can be controlled by adjusting the pressure in one or more flash tanks (Flash A, Flash B, Flash C) and / or adjusting the temperature in one or more flash tanks (Flash A, Flash B, Flash C), thereby achieving the final concentration of concentrated sulfuric acid.

[0070] In some preferred embodiments, the final sulfuric acid concentration can be controlled simply by adjusting the flash temperature of flash C.

[0071] For example, such as: By adjusting the flash temperature of flash evaporation C to ≥77℃, concentrated sulfuric acid F with a concentration ≥70% can be obtained.

[0072] By adjusting the flash temperature of flash C to ≥115.3℃, concentrated sulfuric acid F with a concentration ≥80% can be obtained.

[0073] By adjusting the flash temperature of flash C to ≥139.4℃, concentrated sulfuric acid F with a concentration ≥90% can be obtained.

[0074] By adjusting the flash temperature of flash C to ≥156.6℃, concentrated sulfuric acid F with a concentration ≥93% can be obtained.

[0075] By adjusting the flash temperature of flash C to ≥170.5℃, concentrated sulfuric acid F with a concentration ≥95% can be obtained.

[0076] By adjusting the flash temperature of flash evaporation C to ≥193℃, concentrated sulfuric acid F with a concentration ≥98% can be obtained.

[0077] Furthermore, when it is necessary to obtain concentrated sulfuric acid F with a concentration of ≥79%, before dilute sulfuric acid E enters flash evaporation C, dilute sulfuric acid E is preheated to the flash evaporation temperature of flash evaporation C by external steam heating or electric heating, so as to efficiently obtain concentrated sulfuric acid of the required concentration.

[0078] Example 1

[0079] Figure 1 The schematic diagram illustrates the process flow for preparing concentrated sulfuric acid from dilute sulfuric acid in this embodiment.

[0080] This embodiment uses dilute sulfuric acid containing sulfate as raw material, specifically, it uses 10% dilute sulfuric acid containing lithium sulfate as raw material to concentrate and prepare 98% concentrated sulfuric acid.

[0081] like Figure 1 As shown, it includes: (1) The raw material containing dilute sulfuric acid A (10% sulfuric acid, 1.8% lithium sulfate) is pumped to flash evaporator A at a flow rate of 85 t / h. Before entering flash evaporator A, the raw material is preheated from 25°C to 86°C by saturated steam condensate A in a heat exchanger. After preheating, the condensate A is cooled to 26°C and discharged from the system.

[0082] (2) The pressure of flash A is absolute pressure not higher than 56 kPa, and it is heated by secondary steam A to keep the flash temperature not lower than 90°C. Flash A produces about 42.7 t of steam A (which enters the booster A for pressurization and heating), and the remaining 42.3 t of about 20% dilute sulfuric acid B is pumped to flash B.

[0083] (3) Dilute sulfuric acid B pumped from flash evaporator A is mixed with circulating dilute sulfuric acid C from flash evaporator B. The mixed dilute sulfuric acid D enters the heat exchanger and is heated by secondary steam B. After heating, it enters flash evaporator B. The pressure of flash evaporator B is absolute pressure not exceeding 56 kPa, and it is heated by secondary steam C to maintain the flash evaporation temperature not lower than 103℃. Flash evaporator B generates approximately 22.3 t of steam B (which enters the booster compressor A for pressurization and heating). The circulating dilute sulfuric acid C discharged from flash evaporator B is 200 t / h, and the approximately 42% dilute sulfuric acid E discharged from flash evaporator B is 20 t / h.

[0084] Dilute sulfuric acid E is preheated to 193°C using external steam, consuming approximately 2.6 t / h of steam. The preheated dilute sulfuric acid E is then pumped into flash evaporator C.

[0085] (4) The pressure of flash evaporation C is not higher than 5 kPa. It is heated by secondary steam D to keep the flash evaporation temperature not lower than 193°C. The steam generated by flash evaporation C enters the booster B. The concentrated sulfuric acid discharged from flash evaporation C is pumped to the pressure filter / filtration to obtain 98% concentrated sulfuric acid. After filtration, about 1.8 tons of lithium sulfate can be obtained.

[0086] Among them, booster A and booster B use centrifugal boosters. After the steam is boosted, the pressure increases by no less than 50 kPa. The saturated temperature of the secondary steam after boosting is no less than 18°C ​​higher than the temperature of the steam entering the booster.

[0087] (5) The saturated condensate of secondary saturated steam A / B / C enters the separator A. The separator A uses vacuum pump A to discharge non-condensable gas and maintains the absolute pressure of flash A and flash B not higher than 56 kPa. The saturated steam condensate A is sent to the heat exchange device by the transfer pump to preheat dilute sulfuric acid A. After preheating, the room temperature steam condensate A is discharged from the system.

[0088] (6) The saturated condensate of the secondary saturated steam D enters the separator B. The separator B uses vacuum pump B to discharge non-condensable gases and maintains the absolute pressure of flash steam C not higher than 5 kPa. The condensate B is pumped out of the system.

[0089] In this embodiment, secondary steam A, secondary steam B, and secondary steam C are all secondary saturated steam after being pressurized by booster A, and secondary steam D is secondary saturated steam after being pressurized by booster B. The labels ABCD are used to better distinguish the destination of the pressurized secondary saturated steam.

[0090] This invention uses external steam only during the start-up phase (and the preheating phase of medium-concentration dilute sulfuric acid E). During normal operation, only secondary steam is used and external steam is no longer required. Therefore, the operating cost of this invention is greatly reduced compared to the traditional steam-heated multi-stage flash evaporation concentration method.

[0091] Cost calculation: In this embodiment, concentrating 85t / h of 10% dilute sulfuric acid to 98% concentrated sulfuric acid requires approximately 75 tons of steam pressurization. The centrifuge for pressurization at 50kPa consumes approximately 40kWh / t of water, with an electricity price of 0.5 yuan / kWh, resulting in a total operating cost of 1500 yuan (the power of the pumps and vacuum pumps is relatively small and can be ignored). Preheating the medium-concentration sulfuric acid E requires approximately 2.7 tons of steam, with a steam price of 180 yuan / ton, resulting in an operating cost of 486 yuan. The total cost for electricity and steam is 1986 yuan.

[0092] If the multi-stage flash evaporation process with steam heating as described in US Patent US5228885A is used, 50 tons of water need to be evaporated first to concentrate the 10% dilute sulfuric acid to 24.4%. If a three-effect evaporation process with steam heating is used, this process requires 17.5 tons of steam. Then, to concentrate the 24.4% concentrated sulfuric acid to 98% concentrated sulfuric acid, another 16.5 t / h of steam is needed, for a total of 34 tons of steam. The unit price of steam is 180 yuan / ton, and the operating cost is 6120 yuan.

[0093] The comparison shows that the present invention can greatly reduce the operating cost of concentrating dilute sulfuric acid, with a cost reduction of up to 67.5%.

[0094] The above Example 1 uses 10% dilute sulfuric acid to concentrate and prepare 98% concentrated sulfuric acid. Of course, it is not limited to this. The present invention can use dilute sulfuric acid of any concentration in the range of 8%-70% as raw material to prepare concentrated sulfuric acid of any concentration in the range of 70%-98%. The specific needs can be adjusted by adjusting the pressure and / or temperature of each flash evaporation stage.

[0095] In Examples 2-6, while keeping other conditions constant, the preparation of concentrated sulfuric acid of different concentrations was achieved simply by adjusting the flash temperature of flash evaporation C (preheating temperature before flash evaporation and temperature maintained by secondary steam D).

[0096] Example 2

[0097] Preheat and maintain the flash temperature of flash C at 170.5℃ to obtain concentrated sulfuric acid with a concentration of 95%.

[0098] Example 3

[0099] Preheat and maintain the flash temperature of flash C at 156.6℃ to obtain concentrated sulfuric acid with a concentration of 93%.

[0100] Example 4

[0101] Preheat and maintain the flash temperature of flash C at 139.4℃ to obtain concentrated sulfuric acid with a concentration of 90%.

[0102] Example 5

[0103] Preheat and maintain the flash temperature of flash C at 115.3℃ to obtain concentrated sulfuric acid with a concentration of 80%.

[0104] Example 6

[0105] Without the need for external steam to preheat dilute sulfuric acid E, the flash temperature of flash evaporation C is maintained at 77°C by direct heating with secondary steam D, resulting in concentrated sulfuric acid with a concentration of 70%.

[0106] In summary, this invention enables the recovery and preparation of concentrated sulfuric acid from low-concentration dilute sulfuric acid, allowing for the reuse of large quantities of dilute sulfuric acid with a concentration of less than 10%. This provides a new approach for the reuse of intermediate product dilute sulfuric acid and also offers a low-cost production method for concentrated sulfuric acid, especially high-concentration concentrated sulfuric acid, thus possessing significant economic value.

[0107] The description of this invention is given for illustrative and descriptive purposes only and is not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid, characterized in that, This includes: dilute sulfuric acid A is flashed through flash evaporation A to obtain dilute sulfuric acid B, dilute sulfuric acid B enters flash evaporation B and is flashed to obtain dilute sulfuric acid E, dilute sulfuric acid E enters flash evaporation C and is flashed to obtain concentrated sulfuric acid F; The steam generated by flash evaporation A and flash evaporation B is mixed and then enters the booster A for compression and heating. The temperature of the first saturated steam after compression is increased and then returned to flash evaporation A and flash evaporation B for heating. The saturated condensate generated by heating preheats dilute sulfuric acid A, and the preheated dilute sulfuric acid A enters flash evaporation A. The steam generated by flash evaporator C enters the booster compressor B for compression and heating. After compression, the temperature of the second saturated steam is increased and it returns to flash evaporator C for further heating.

2. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 1, characterized in that, The dilute sulfuric acid A is dilute sulfuric acid A with a concentration of 8%-70%.

3. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 1, characterized in that, The pressure of flash evaporation A is no higher than 56 kPa absolute pressure; In flash evaporation A, dilute sulfuric acid A is heated by the first saturated steam to maintain the flash evaporation temperature at no less than 90°C; The saturated condensate generated by heating preheats dilute sulfuric acid A to 85℃-95℃.

4. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 1, characterized in that, The pressure of flash evaporation B is no higher than 56 kPa absolute pressure; In flash evaporation B, dilute sulfuric acid B is heated by the first saturated steam to maintain the flash evaporation temperature at no less than 103°C.

5. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 4, characterized in that, Before dilute sulfuric acid B enters flash evaporator B... First, it enters the heat exchanger and is heated by the first saturated steam; or, it is first mixed with the circulating dilute sulfuric acid C discharged from flash B and then enters the heat exchanger and is heated by the first saturated steam.

6. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 1, characterized in that, The pressure of flash evaporation C is no higher than 5 kPa absolute pressure; In flash evaporation C, dilute sulfuric acid E is heated by the second saturated steam to maintain the flash evaporation temperature at ≥77℃, yielding concentrated sulfuric acid F with a concentration at ≥70%.

7. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 6, characterized in that, Also includes: Adjust the flash temperature of flash C according to the desired concentration of concentrated sulfuric acid F.

8. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 7, characterized in that, The step of adjusting the flash temperature of dilute sulfuric acid E in flash evaporation C according to the desired concentration of concentrated sulfuric acid F includes: To obtain concentrated sulfuric acid F with a concentration ≥80%, the flash temperature of flash evaporation C should be adjusted to ≥115.3℃. To obtain concentrated sulfuric acid F with a concentration ≥90%, the flash temperature of flash evaporation C should be adjusted to ≥139.4℃. To obtain concentrated sulfuric acid F with a concentration ≥93%, the flash temperature of flash evaporation C should be adjusted to ≥156.6℃. To obtain concentrated sulfuric acid F with a concentration ≥95%, the flash temperature of flash evaporation C should be adjusted to ≥170.5℃. To obtain concentrated sulfuric acid F with a concentration ≥98%, adjust the flash temperature of flash evaporation C to ≥193℃.

9. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 7, characterized in that, To obtain concentrated sulfuric acid F with a concentration ≥ 79%, before dilute sulfuric acid E enters flash evaporation C, the process also includes: preheating dilute sulfuric acid E to the flash evaporation temperature of flash evaporation C using external steam heating or electric heating.

10. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 1, characterized in that, The booster A and booster B are centrifugal boosters, wherein the pressure of the steam increases by no less than 50 kPa after being compressed by the centrifugal booster, and the temperature of the saturated steam after compression increases by no less than 18°C.

11. The method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 1, characterized in that, Dilute sulfuric acid A with a concentration of 8%-12% is flashed through flash evaporation A to obtain dilute sulfuric acid B with a concentration of 18-22%. Dilute sulfuric acid B is then flashed and concentrated in flash evaporation B to obtain dilute sulfuric acid E with a concentration of 42-46%. Dilute sulfuric acid E is then flashed through flash evaporation C to obtain concentrated sulfuric acid F with a concentration of 70%-98%.

12. A system for concentrating dilute sulfuric acid to prepare concentrated sulfuric acid, characterized in that, The steps in the method for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to any one of claims 1-11; The system includes: flash evaporator A, flash evaporator B and flash evaporator C connected in sequence, and booster A and booster B; Among them, the steam outlets of flash A and flash B are connected to the inlet of booster A, the steam outlet of booster A is connected to the heat source inlet of flash A and flash B, the heat source outlets of flash A and flash B are connected to the heat source inlet of the heat exchange device, and the cold source outlet of the heat exchange device is connected to the acid inlet of flash A. The steam outlet of flash evaporator C is connected to the inlet of booster compressor B, and the steam outlet of booster compressor B is connected to the heat source inlet of flash evaporator C.

13. The system for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 12, characterized in that, It also includes: a heat exchanger, wherein the heat source inlet of the heat exchanger is connected to the booster A, the cold source inlet is connected to flash A and flash B respectively, and the cold source outlet is connected to flash B, and is used to heat the dilute sulfuric acid B from flash A and the circulating dilute sulfuric acid C discharged from flash B with the first saturated steam and then send them into flash B; And / or, it also includes: a preheating system, the inlet of which is connected to the dilute sulfuric acid outlet of flash B, and the outlet of which is connected to the dilute sulfuric acid inlet of flash C, for preheating the dilute sulfuric acid E from flash B by external steam heating or electric heating when a concentrated sulfuric acid F with a concentration ≥79% is to be obtained, and sending the dilute sulfuric acid E to the flash temperature of flash C after preheating it to flash C.

14. The system for preparing concentrated sulfuric acid by concentrating dilute sulfuric acid according to claim 12, characterized in that, It also includes: a salt filtration device, used to filter or press-filter concentrated sulfuric acid F when the raw material contains sulfate, to separate concentrated sulfuric acid G and sulfate; And / or, it further includes: a separation tank A and a vacuum pump A connected thereto, and a separation tank B and a vacuum pump B connected thereto; wherein the heat source outlets of flash evaporation A and flash evaporation B are connected to the heat source inlet of the heat exchange device through the separation tank A and the transfer pump; the vacuum pump A is used to discharge non-condensable gases from the saturated condensate in the separation tank A and maintain the pressure of flash evaporation A and flash evaporation B; the separation tank B is connected to the heat source outlet of flash evaporation C, and the condensate generated after heating enters the separation tank B; the vacuum pump B is used to discharge non-condensable gases from the condensate in the separation tank B and maintain the pressure of flash evaporation C.

Images