Phosphoric acid production system using sulfuric acid process

Abstract

The present invention relates to a phosphoric acid production system using a sulfuric acid process. The system comprises a phosphoric acid production unit, a phosphogypsum pyrolysis unit and a wet-process sulfuric acid production unit, wherein the phosphoric acid production unit comprises a reaction device and a filtration device, the reaction device being provided with a mixed feed inlet and a reaction discharge outlet, and the filtration device being provided with a reaction feed inlet, a solid discharge outlet and a liquid discharge outlet; the phosphogypsum pyrolysis unit comprises a calcination device, the calcination device being provided with a raw material feed inlet, a clinker discharge outlet and a crude flue gas discharge outlet; and the wet-process sulfuric acid production unit comprises a flue gas reaction device and an acid cooling device, the flue gas reaction device being provided with a reaction gas feed inlet and an acid gas discharge outlet, and the acid cooling device being provided with an acid gas feed inlet, a sulfuric acid discharge outlet and a tail gas discharge outlet. The present invention realizes sulfur cycle production with minimal generation of solid waste, thereby enabling clean production, and yielding good economic benefits.

Description

A sulfuric acid process for phosphoric acid production system

[0001] This application claims priority to Chinese Patent Application No. 2024233207365, filed on December 31, 2024. The entire contents of the aforementioned Chinese patent application are incorporated herein by reference. Technical Field

[0002] This invention relates to a phosphoric acid production system using the sulfuric acid process. Background Technology

[0003] Phosphogypsum is the biggest problem in the sulfuric acid process for phosphoric acid production because the amount produced is enormous. For example, a 300,000-ton / year phosphoric acid plant (converted to 100% P2O5) produces approximately 1.4 million tons of phosphogypsum annually. This represents a massive waste disposal task. Phosphogypsum contains pollutants that are highly damaging to the environment, particularly groundwater, and its treatment is costly. Furthermore, the sulfur in phosphogypsum is not utilized, resulting in resource waste and wasted sulfur procurement costs.

[0004] The production of sulfuric acid and cement from phosphogypsum was actively researched by German scientists as early as 1847. In 1969, the osw.KRUP plant of the Linz company in Austria built a cement production capacity of 200 tons per day. The process involves drying and dehydrating phosphogypsum, mixing it with coke, clay, sand, and other ingredients in the required proportions of CaO, SiO2, Al2O3, and Fe2O3, and calcining it in a hollow rotary kiln to form cement clinker. The SO2 in the kiln gas is converted and absorbed to produce sulfuric acid.

[0005] China began research on the co-production of sulfuric acid and cement from phosphogypsum as early as the 1950s, and achieved a major industrial breakthrough in the late 1980s, during which seven phosphogypsum-based sulfuric acid and cement co-production plants were built, known as the "46 Project". Nearly 20 years of production practice has proven that the process is technically feasible. However, the proportion of sulfuric acid produced using phosphogypsum is still less than 1% of the total sulfuric acid production. The main reasons for this are: high energy consumption, easy scaling of rotary kilns, incomplete decomposition of CaSO4, and low conversion rate.

[0006] The high energy consumption is mainly due to the high consumption of fuel coal. Drying phosphogypsum requires approximately 123 kg of coal (5500 kcal / kg) to produce 1 ton of clinker; calcining raw materials to produce cement clinker requires approximately 300 kg of coal (5800 kcal / kg) to produce 1 ton of clinker. To reduce the sensible heat carried away by kiln gas, a five-stage raw material preheater is currently installed at the kiln tail of the rotary kiln. This reduces clinker heat consumption by 15%-20%, lowers the sensible heat of kiln gas as a percentage of the total heat consumption during firing to 22%, and reduces the outlet temperature from 800℃ to 450℃. The rotary kiln's thermal efficiency has increased to 45%-50%. However, the high heat consumption still results in significant fuel consumption, increasing cement costs. Furthermore, the large volume of kiln gas reduces the SO2 concentration in the gas, increasing the power consumption of the sulfuric acid production system and raising production costs.

[0007] When using kiln gas from phosphogypsum calcination to produce sulfuric acid, due to the low SO2 concentration in the kiln gas, most domestic phosphogypsum-to-sulfuric acid plants currently employ a process of primary conversion with the addition of an ammonia absorption tail gas stage. This is because the kiln gas contains CO and C. n H m and NO x This can affect both SO2 conversion and SO3 absorption, leading to decreased absorption rate, poorer product acid quality, and increased acid mist generation. It also negatively impacts SO2 emissions from the ammonia absorption process, resulting in high levels of exhaust mist and poor environmental conditions. Furthermore, SO3 can affect both the ammonia absorption process and the quality of ammonium sulfite.

[0008] China generates 25-30 million tons of phosphogypsum waste annually (dry basis). Utilizing phosphogypsum to produce sulfuric acid not only compensates for the shortage of sulfuric acid raw materials in my country, especially in regions lacking sulfuric acid raw materials but possessing phosphogypsum, but also solves the problems of land occupation and environmental pollution caused by phosphogypsum, yielding significant benefits. With the development of wet-process phosphoric acid in my country and the increasing emphasis on environmental protection, how to rationally utilize existing waste resources will become a new driving force for research on phosphogypsum-based sulfuric acid production.

[0009] Currently, some regions have applied advanced cement production technologies to phosphogypsum treatment, particularly the use of external decomposition technology in cement production. This avoids the impact of the reducing state inside the rotary kiln on cement production, and the decomposition of phosphogypsum is more complete under the reducing state outside the kiln. However, the low SO2 content in the kiln gas remains a problem, which is detrimental to acid production. There are reports of adding sulfur vapor to the kiln or external decomposition system: this addresses the low SO2 content problem and provides a reducing agent, changing the conversion from one rotary kiln and one absorption process to two rotary kilns and two absorption processes. Other reports indicate that kiln tail gas, after washing and purification, is combined with sulfur incinerator gas from sulfur-based acid production. Each method has its advantages, but the impact of water on the catalyst during the conversion process remains a persistent issue. Summary of the Invention

[0010] The technical problem to be solved by this invention is to overcome the defect of low utilization rate of phosphogypsum, a product of the existing sulfuric acid process for producing phosphoric acid, and to provide a sulfuric acid process phosphoric acid production system that realizes sulfur recycling, generates almost no solid waste, achieves clean production, and brings good economic benefits.

[0011] The present invention solves the above-mentioned technical problems through the following technical solution:

[0012] This invention provides a sulfuric acid-based phosphoric acid production system, which includes a phosphoric acid production unit, a phosphogypsum pyrolysis unit, and a wet sulfuric acid production unit;

[0013] The phosphoric acid production unit includes a reaction device and a filtration device; the reaction device is equipped with a mixing inlet and a reaction outlet; the filtration device is equipped with a reaction inlet, a solid outlet, and a liquid outlet.

[0014] The phosphogypsum pyrolysis unit includes a calcination device; the calcination device is provided with a raw material inlet, a clinker outlet, and a coarse flue gas outlet.

[0015] The wet sulfuric acid production unit includes a flue gas reaction device and an acid cooling device; the flue gas reaction device is provided with a reaction gas inlet and an acid gas outlet; the acid cooling device is provided with an acid gas inlet, a sulfuric acid outlet and a tail gas outlet;

[0016] The mixing inlet is connected to the phosphate rock source and the water source; the reaction outlet is connected to the reaction inlet; the solid outlet is connected to the raw material inlet; the coarse flue gas outlet is connected to the reaction gas inlet; the reaction gas inlet is connected to the air source and the fuel gas source; the acid gas outlet is connected to the acid gas inlet; and the sulfuric acid outlet is connected to the mixing inlet.

[0017] In this invention, the phosphoric acid production unit further includes a raw material mixing device, which is provided with a water inlet, a phosphate rock inlet, and a mixing outlet; the mixing outlet is connected to the mixing inlet.

[0018] The raw material mixing device is further provided with an acidic water inlet; the wet sulfuric acid production unit also includes a flue gas pretreatment device, which is provided with a coarse flue gas inlet, an acidic water outlet, and a flue gas outlet; the coarse flue gas outlet is connected to the coarse flue gas inlet; the acidic water outlet is connected to the acidic water inlet; and the flue gas outlet is connected to the reaction gas inlet.

[0019] In this invention, the reaction device is further provided with a circulation outlet and a circulation inlet, the circulation outlet and the circulation inlet are connected outside the reaction device through a circulation pipe, and a cooling device is provided on the circulation pipe.

[0020] In this invention, the reaction device is further provided with a tail gas outlet, which is connected to a tail gas treatment device.

[0021] In this invention, the phosphoric acid production unit further includes a concentration device; the concentration device is provided with a liquid inlet, a jacket, a fluorosilicic acid outlet and a phosphoric acid outlet; the jacket is provided with a steam inlet and a condensate outlet.

[0022] The flue gas reaction device is further provided with a boiler water inlet and a steam outlet; the steam outlet is connected to the steam inlet.

[0023] In this invention, the phosphogypsum pyrolysis unit further includes a drying device, which is provided with a phosphogypsum inlet, a hot air inlet, and a dry material outlet; the solid material outlet is connected to the phosphogypsum inlet; and the dry material outlet is connected to the raw material inlet.

[0024] The phosphogypsum pyrolysis unit further includes a mixing device, which has an auxiliary material inlet, a dry material inlet, and a raw material outlet; the dry material outlet is connected to the dry material inlet; and the raw material outlet is connected to the raw material inlet.

[0025] The acid cooling device is further provided with a jacket, which has a cold air inlet and a hot air outlet; the hot air outlet is connected to the hot air inlet.

[0026] In this invention, the wet sulfuric acid production unit further includes a tail gas treatment device, which is provided with a tail gas inlet, a treatment agent inlet, and a dilute sulfuric acid outlet; the tail gas outlet is connected to the tail gas inlet, the treatment agent inlet is connected to a hydrogen peroxide source, and the dilute sulfuric acid outlet is connected to the mixing inlet.

[0027] The positive and progressive effects of this invention are as follows:

[0028] (1) In this invention, the sulfuric acid product from flue gas conversion can be used to dissolve phosphate rock, completing the closed loop of sulfur resource recycling and saving the consumption of purchased sulfuric acid.

[0029] (2) The present invention uses the wet sulfuric acid process, which reduces the number of flue gas drying process steps and eliminates equipment such as the first and second suction towers of the drying tower and the acid circulation pump, thus reducing investment; the wet sulfuric acid process can also make full use of the heat generated during the production process;

[0030] (3) The present invention uses air cooling. 90% of the heat of the hot air at 180-200℃ after being condensed and heated by sulfuric acid vapor can be recovered and used for drying of phosphogypsum before calcination, converting wet dihydrate phosphogypsum with a moisture content of about 20% into hemihydrate gypsum, saving a lot of extra fuel consumption.

[0031] (4) In this invention, for every ton of concentrated sulfuric acid produced, 0.3-0.8 tons of low-pressure saturated steam can be produced as a byproduct, which can be sent to the phosphoric acid concentration process to provide most of the heat and reduce the use of fuels such as coal; the steam can also be used as a public works project.

[0032] (5) In this invention, hydrogen peroxide is used for tail gas washing. The dilute sulfuric acid produced after washing can be used for decomposition and water replenishment of phosphate rock, saving fresh water replenishment and reducing the consumption of raw sulfuric acid. The acidic water produced by the flue gas pretreatment device can be used as filter cake washing water or tail gas washing water in the phosphoric acid production process, saving the amount of fresh water replenishment.

[0033] (6) In this invention, the problem of moisture in the flue gas of phosphogypsum acid production and cement co-production is solved, which affects acid production; the problem of mutual restraint between phosphogypsum acid production and cement clinker calcination due to SO2 content in the tail gas is solved; the overall heat recovery rate is high, the equipment is few, the economy is reasonable, and the return on investment is high.

[0034] (7) In this invention, phosphogypsum can be better utilized and sulfur resources can be fully utilized. With the help of the wet sulfuric acid process, a closed-loop route for the green resource utilization of phosphogypsum in the phosphoric acid production process is completed, which solves the problem of heat balance in the traditional dry sulfuric acid process with low concentration SO2. At the same time, the by-products can be beneficial to supplement the demand of the phosphoric acid and phosphogypsum sections.

[0035] (8) In this invention, phosphogypsum is calcined and then used to make cement while the flue gas is recovered to produce sulfuric acid. This not only solves the problem of phosphogypsum treatment, but also produces sulfuric acid and cement products as by-products, achieving both environmental and economic benefits. Attached Figure Description

[0036] Figure 1 is a schematic diagram of the sulfuric acid process phosphoric acid production system in Example 1;

[0037] Figure 2 is a detailed diagram of the wet sulfuric acid production unit in Example 1;

[0038] The diagram shows the following units: Phosphoric acid production unit 1, raw material mixing device 11, reaction device 12, tail gas treatment device 121, cooling device 122, filtration device 13, concentration device 14, phosphogypsum pyrolysis unit 2, drying device 21, mixing device 22, calcination device 23, wet sulfuric acid production unit 3, flue gas pretreatment device 31, flue gas reaction device 32, acid cooling device 33, tail gas treatment device 34;

[0039] Cooling fan C-601, flue gas fan C-602, air fan C-603, packed tower cooler E-601, flue gas heater E-602, first stage inter-stage heat exchanger E-603, second stage inter-stage heat exchanger E-604, first process cooler E-605, second process cooler E-606, sulfuric acid vapor condenser E-607, sulfuric acid water cooler E-608;

[0040] Hot air furnace F-601, filter press M-602, power wave circulation pump P-601, packed tower circulation pump P-603, hydrogen peroxide pump P-607, sulfuric acid circulation pump P-609, bed 1 R-602, bed 2 R-603, bed 3 R-604;

[0041] Dynamic wave scrubbing tower T-601, packed tower T-602, degassing tower T-605, tail gas scrubbing tower T-606, inclined tube settling tank V-601, steam drum V-603, sulfuric acid mixing tank V-604, hydrogen peroxide tank V-605, electrostatic precipitator X-601, second electrostatic precipitator X-603, exhaust stack X-604. Detailed Implementation

[0042] The present invention will be described more clearly and completely below with reference to a preferred embodiment and the accompanying drawings.

[0043] Example 1

[0044] A sulfuric acid process for phosphoric acid production system, as shown in Figure 1, includes a phosphoric acid production unit 1, a phosphogypsum pyrolysis unit 2, and a wet sulfuric acid production unit 3.

[0045] In this embodiment, the phosphoric acid production unit 1 includes a raw material mixing device 11, a reaction device 12, a filtration device 13, and a concentration device 14. The raw material mixing device 11 has a water inlet, a phosphate rock inlet, an acidic water inlet, and a mixed outlet. The reaction device 12 has a mixed inlet, a circulation outlet, a circulation inlet, a tail gas outlet, and a reaction outlet; the circulation outlet and circulation inlet are connected outside the reaction device 12 via circulation pipes, and a cooling device 122 is installed on the circulation pipes. The tail gas outlet is connected to a tail gas treatment device 121. The filtration device 13 has a reaction inlet, a solid outlet, and a liquid outlet. The concentration device 14 has a liquid inlet, a jacket, a fluorosilicic acid outlet, and a phosphoric acid outlet; the jacket has a steam inlet and a condensate outlet.

[0046] In this embodiment, the phosphogypsum pyrolysis unit 2 includes a drying device 21, a mixing device 22, and a calcining device 23. The drying device 21 is provided with a phosphogypsum inlet, a hot air inlet, and a dry material outlet. The mixing device 22 is provided with an auxiliary material inlet, a dry material inlet, and a raw material outlet. The calcining device 23 is provided with a raw material inlet, a clinker outlet, and a coarse flue gas outlet; the clinker outlet is connected to the cement finished product device.

[0047] In this embodiment, the wet sulfuric acid production unit 3 includes a flue gas pretreatment device 31, a flue gas reaction device 32, an acid cooling device 33, and a tail gas treatment device 34. The flue gas pretreatment device 31 is equipped with a crude flue gas inlet, an acidic water outlet, and a flue gas outlet. The flue gas reaction device 32 is equipped with a boiler water inlet, a reaction gas inlet, a steam outlet, and an acid gas outlet. The acid cooling device 33 is equipped with an acid gas inlet, a jacket, a sulfuric acid outlet, and a tail gas outlet; the jacket is equipped with a cold air inlet and a hot air outlet. The tail gas treatment device 34 is equipped with a tail gas inlet, a treatment agent inlet, and a dilute sulfuric acid outlet.

[0048] In this embodiment, the mixing outlet of the raw material mixing device 11 is connected to the mixing inlet of the reaction device 12, the reaction outlet of the reaction device 12 is connected to the reaction inlet of the filtration device 13, and the solid outlet of the filtration device 13 is connected to the phosphogypsum inlet of the drying device 21. The dry material outlet of the drying device 21 is connected to the dry material inlet of the mixing device 22, the raw material outlet of the mixing device 22 is connected to the raw material inlet of the calcining device 23, and the flue gas outlet of the calcining device 23 is connected to the coarse flue gas inlet of the flue gas pretreatment device 31.

[0049] In this embodiment, the phosphoric acid production unit 1 and the cement production unit 2 are both mature and existing processes. The general flow is as follows: Phosphate ore is mixed in a raw material mixing device 11 to form a phosphate slurry. The phosphate slurry reacts with sulfuric acid in a reaction device 12. The resulting slurry is then sent to a filtration device 13 for solid-liquid separation. The resulting solid is phosphogypsum, and the resulting liquid is dilute phosphoric acid. The dilute phosphoric acid is concentrated in a concentration device 14 to become concentrated phosphoric acid. During the concentration process, the silicon tetrafluoride-containing gas released is recycled and absorbed to become fluorosilicic acid. The phosphogypsum is sent to the phosphogypsum cracking unit 2, where it is dried in a drying device 21, mixed with coke, clay, kiln ash, and other auxiliary materials in a mixing device 22, and then calcined in a calcining device 23 to form flue gas and cement. The flue gas is then sent to a wet sulfuric acid production unit 3 to produce sulfuric acid.

[0050] In this embodiment, as shown in Figure 2, the acidic water outlet of the flue gas pretreatment device 31 is connected to the acidic water inlet of the raw material mixing device 11. The flue gas outlet of the flue gas pretreatment device 31 is connected to the reaction gas inlet of the flue gas reaction device 32. The reaction gas inlet of the flue gas reaction device 32 is also connected to an air source and a fuel gas source. The steam outlet of the flue gas reaction device 32 is connected to the steam inlet of the concentration device 14. The acidic gas outlet of the flue gas reaction device 32 is connected to the acid cooling device 33. The hot air outlet of the acid cooling device 33 is connected to the hot air inlet of the drying device 21. The sulfuric acid outlet of the acid cooling device 33 is connected to the mixing inlet of the reaction device 12. The tail gas outlet of the acid cooling device 33 is connected to the tail gas inlet of the tail gas treatment device 34. The treatment agent inlet of the tail gas treatment device 34 is connected to a water source and a hydrogen peroxide source. The concentration of hydrogen peroxide is 27.5 wt%. The dilute sulfuric acid outlet of the tail gas treatment device 34 is connected to the mixing inlet of the reaction device 12.

[0051] In this embodiment, the flue gas pretreatment device 31 specifically includes a flue gas heater E-602, a dynamic wave scrubbing tower T-601, a packed tower T-602, a degassing tower T-605, and an inclined tube settling tank V-601. The flue gas heater E-602 has a tube-side hot flue gas inlet, a tube-side hot flue gas outlet, a shell-side hot flue gas inlet, and a shell-side hot flue gas outlet. The tube-side hot flue gas inlet serves as the coarse flue gas feed port of the flue gas pretreatment device 31, and the shell-side hot flue gas outlet serves as the flue gas discharge port of the flue gas pretreatment device 31. The dynamic wave scrubbing tower T-601 contains scrubbing liquid and has a first flue gas inlet, a first flue gas outlet, a circulating scrubbing liquid outlet, a circulating scrubbing liquid inlet, and a supplementary scrubbing liquid inlet. The circulating scrubbing liquid outlet and the circulating scrubbing liquid inlet are connected to the outside of the dynamic wave scrubbing tower T-601 via a circulating pipe. A dynamic wave circulating pump P-601 is installed on the circulating pipe, and a settling liquid opening is provided on the circulating pipe. The packed tower T-602 contains absorbent liquid and has a second flue gas inlet, a second flue gas outlet, a circulating absorbent liquid outlet, and a circulating absorbent liquid inlet. The circulating absorbent liquid outlet and inlet are connected to the outside of the packed tower T-602 via a second circulation pipe. The second circulation pipe is equipped with a packed tower circulation pump P-603 and a packed tower cooler E-601, and has a makeup liquid outlet. The inclined tube settling tank V-601 has a settling liquid inlet, a clear liquid outlet, and an acid sludge outlet. The acid sludge outlet is connected to the filter press M-602. The degassing tower T-605 has a clear liquid inlet, an air inlet, a flue gas outlet, a circulating acidic water outlet, and a circulating acidic water inlet. The circulating acidic water outlet and inlet are connected to the outside of the degassing tower T-605 via a third circulation pipe. The third circulation pipe has an acidic water outlet, which serves as the acidic water outlet for the flue gas pretreatment device 31.

[0052] In this embodiment, the tube-side hot flue gas outlet of the flue gas heater E-602 is connected to the first flue gas inlet of the dynamic wave scrubber T-601. The first flue gas outlet of the dynamic wave scrubber T-601 is connected to the second flue gas inlet of the packed tower T-602 via a first flue gas pipe. The second flue gas outlet of the packed tower T-602 is connected to the shell-side hot flue gas inlet of the flue gas heater E-602 via a second flue gas pipe. An electrostatic precipitator X-601 is installed on the second flue gas pipe. The replenishment liquid outlet on the second circulation pipe outside the packed tower T-602 is connected to the replenishment washing liquid inlet of the dynamic wave scrubber T-601. The settling liquid opening on the circulation pipe outside the dynamic wave scrubber T-601 is connected to the settling liquid inlet of the inclined tube settling tank V-601. The clear liquid outlet of the inclined tube settling tank V-601 is connected to the clear liquid inlet of the degassing tower T-605. The flue gas outlet of the degassing tower T-605 is connected to the first flue gas pipe. The flue gas at 320°C from phosphogypsum cracking unit 2 is cooled by flue gas heater E-602, and then passes through dynamic wave scrubbing tower T-601 and packed tower T-602 in sequence to remove impurities. It then re-enters flue gas heater E-602 for heat exchange, and the purified acidic water is sent to phosphoric acid production unit 1.

[0053] In this embodiment, as shown in Figure 2, the flue gas reaction device 32 specifically includes a hot blast stove F-601, a reactor, a second process cooler E-606, and a steam drum V-603. The hot blast stove F-601 is provided with a flue gas inlet, a fuel mixture inlet, and a reaction gas outlet. The flue gas inlet of the hot blast stove F-601 is connected to the shell-side hot flue gas outlet of the flue gas heater E-602 via a third flue gas duct, on which a flue gas fan C-602 is installed. The fuel mixture inlet is connected to a fuel gas source; in this embodiment, the fuel gas is natural gas. In other embodiments, other combustible gases with a calorific value higher than 1000 kcal can be selected. The fuel mixture inlet is connected to an air source via an air pipeline, on which an air fan C-603 is installed. The reactor, from top to bottom, comprises a single-bed R-602, a first-stage inter-stage heat exchanger E-603, a second-bed R-603, a second-stage inter-stage heat exchanger E-604, a third-bed R-604, and a first-stage process cooler E-605. The first-stage process cooler E-605, the second-stage inter-stage heat exchanger E-604, and the first-stage inter-stage heat exchanger E-603 are respectively equipped with a tube-side cold gas inlet and a tube-side hot gas outlet. The reactor has a reaction gas inlet, serving as the reaction gas inlet for the flue gas reactor 32, and also an acid gas outlet, serving as the acid gas outlet for the flue gas reactor 32. The second-stage process cooler E-606 has a shell-side acid gas inlet, a shell-side acid gas outlet, a tube-side cold water inlet, and a tube-side hot water outlet. The steam drum V-603 has a boiler water inlet, serving as the boiler water inlet for the flue gas reactor 32, a steam outlet, serving as the steam outlet for the flue gas reactor 32, and also a circulating water outlet, a circulating water inlet, and a blowdown outlet. The reaction gas outlet of the hot blast furnace F-601 is connected to the tube-side cold gas inlet of the first process cooler E-605, and the acid gas outlet of the reactor is connected to the shell-side acid gas inlet of the second process cooler E-606.

[0054] In this embodiment, the flue gas purified and heated by the flue gas pretreatment device 31 does not need to be dried and directly enters the flue gas blower C-602 for pressurization. The pressurized flue gas is mixed in the hot blast furnace F-601. The reaction gas flowing out of the reaction gas outlet of the hot blast furnace F-601 is preheated to 400°C by passing sequentially through the first process cooler E-605 and the first interstage heat exchanger E-603, or sequentially through the second interstage heat exchanger E-604 and the first interstage heat exchanger E-603. Then, the reaction gas enters the reactor from the reaction gas inlet and passes sequentially through a bed R-602 and the first interstage heat exchanger. The reaction and heat exchange of heat exchangers E-603, R-603 (second bed), E-604 (second interstage heat exchanger), R-604 (third bed), and E-605 (first process cooler) catalytically oxidize SO2 into SO3. The resulting acid gas flows out from the acid gas outlet and exchanges heat with boiler feedwater in the second process cooler E-606 before being sent to the acid cooling unit 33. After heat exchange in the process gas cooler E-606, the boiler feedwater generates saturated steam at 5.5 MPa and 289.16 °C. After steam-water separation in the steam drum V-603, the steam is sent to the phosphoric acid production unit 1.

[0055] In this embodiment, as shown in Figure 2, the acid cooling device 33 specifically includes a sulfuric acid vapor condenser E-607 and a sulfuric acid mixing tank V-604. The sulfuric acid vapor condenser E-607 is provided with an acid gas inlet, serving as the acid gas inlet for the acid cooling device 33; a tail gas outlet, serving as the tail gas outlet for the acid cooling device 33; and a hot sulfuric acid outlet. A jacket is provided with a cold air inlet and a hot air outlet, serving as the cold air inlet and hot air outlet for the acid cooling device 33, respectively. The cold air inlet is connected to an air source via an air pipeline, on which a cooling fan C-601 is installed. The sulfuric acid mixing tank V-604 is provided with a hot sulfuric acid inlet and a circulating sulfuric acid outlet, connected via a circulating sulfuric acid pipeline. The circulating sulfuric acid pipeline is equipped with a sulfuric acid circulating pump P-609 and a sulfuric acid water cooler E-608. A sulfuric acid outlet is also provided on the circulating sulfuric acid pipeline, serving as the sulfuric acid outlet for the acid cooling device 33.

[0056] In this embodiment, the acid gas inlet of the sulfuric acid vapor condenser E-607 is connected to the shell-side acid gas outlet of the second process cooler E-606, and the hot sulfuric acid outlet of the sulfuric acid vapor condenser E-607 is connected to the hot sulfuric acid inlet of the sulfuric acid mixing tank V-604. In this embodiment, the cold air sent to the sulfuric acid vapor condenser E-607 is heated to 200°C after heat exchange in the sulfuric acid vapor condenser E-607 and then sent to the phosphogypsum cracking unit 2. The acid gas exchanges heat with the air in the sulfuric acid vapor condenser E-607 to lower its temperature. The resulting hot sulfuric acid is then cooled by circulating mixing with cold sulfuric acid in the sulfuric acid mixing tank V-604 to obtain concentrated sulfuric acid at 40.0°C, which is then sent to the phosphoric acid production unit 1.

[0057] In this embodiment, as shown in Figure 2, the exhaust gas treatment device 34 specifically includes an exhaust gas scrubbing tower T-606, which is equipped with a second electrostatic precipitator X-603, an exhaust gas inlet (serving as the exhaust gas inlet of the exhaust gas treatment device 34), a treatment agent outlet (serving as the treatment agent inlet of the exhaust gas treatment device 34), and a residual gas outlet (serving as the exhaust gas inlet of the exhaust gas treatment device 34). The treatment agent inlet and the treatment agent outlet are connected through a treatment agent circulation pipe, which is equipped with a dilute sulfuric acid outlet (serving as the dilute sulfuric acid outlet of the exhaust gas treatment device 34). The treatment agent circulation pipe is also equipped with a hydrogen peroxide replenishment port, which is connected to a hydrogen peroxide tank V-605 through a hydrogen peroxide pipe. A hydrogen peroxide pump P-607 is installed on the hydrogen peroxide pipe, and the residual gas outlet is connected to an exhaust stack X-604.

[0058] In this embodiment, the tail gas outlet of the sulfuric acid vapor condenser E-607 is connected to the tail gas inlet of the tail gas scrubbing tower T-606 via a tail gas pipeline, which is equipped with a demineralized water inlet. The tail gas from the sulfuric acid vapor condenser E-607 is desulfurized in the tail gas scrubbing tower T-606 under the action of 27.5 wt% hydrogen peroxide. After scrubbing, it enters the second electrostatic precipitator X-603 for demisting and purification, and is discharged through the exhaust stack X-604 after meeting the standards. The dilute sulfuric acid obtained after scrubbing is sent to the phosphoric acid production unit 1.

[0059] In this embodiment, the flue gas from phosphogypsum pyrolysis unit 2 has the following composition:

[0060] Before entering the reactor, the flue gas is supplemented with air to obtain reaction gas, which has the characteristics of low SO2 concentration and high water content.

[0061] Taking a 300,000-ton / year phosphogypsum pyrolysis flue gas treatment to sulfuric acid production scale as an example, the output and input of dry process sulfuric acid and wet process sulfuric acid are compared:

[0062] It is evident that in the co-production of acid and cement from phosphogypsum, the wet process of acid production has significant advantages over the dry process. The economic benefits of the wet process are calculated as follows:

[0063] On the one hand, 337833.3 Nm of air at 200℃ is generated in 1 hour. 3 (by 1Nm) 3 Air releases 219.4 kJ of heat when it cools from 200℃ to 25℃ (assuming a utilization rate of 50%), which is equivalent to 1260.5 kg of standard coal. Based on a price of 1474.8 yuan per ton of standard coal and an annual operating time of 7200 hours, this would result in a saving of 13,384,684.88 yuan.

[0064] On the other hand, the system produces 14.83 tons of saturated steam per hour at a pressure of 5.5 MPaG and a temperature of 389.16℃. The inlet water temperature is 104℃ and the pressure is 6.0 MPaG. Assuming that 1 kg of water at 5.5 MPa and 104℃ needs to absorb 2000 kJ of heat to become saturated steam at 5.5 MPa and 289.16℃, then 14.83 tons of water at 5.5 MPa and 104℃ needs to absorb 29,660,000 kJ of heat to become saturated steam at 5.5 MPa and 289.16℃, equivalent to 1008 kg of standard coal. Assuming a heat utilization rate of 70%, a standard coal price of 1474.8 yuan, and 7200 hours of operation per year, this translates to an annual saving of 7,492,544.9 yuan.

[0065] In summary, the present invention employs multiple methods to recover heat. For example, the flue gas at 320°C from the phosphogypsum pyrolysis unit exchanges heat with the flue gas at 60°C purified by the flue gas pretreatment device in the flue gas heater. Another example is that a heat exchanger is installed after the third bed of the reactor. These methods enable deep utilization of the heat from the flue gas, allowing self-heating balance to be achieved when the SO2 concentration in the flue gas is 3%.

[0066] At the same time, the low volume content of SO2 produced by calcination of phosphogypsum will not affect the operation of wet acid production, making the operating conditions for further cement clinker production more relaxed; it can handle flue gas with low SO2 content and can accept SO2 content fluctuations within a certain range in the front-end process, and can still achieve a sulfur recovery rate of over 99% in the flue gas.

[0067] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is defined by the appended claims.

Claims

1. A phosphoric acid production system using the sulfuric acid process, characterized in that, It includes a phosphoric acid production unit, a phosphogypsum pyrolysis unit, and a wet sulfuric acid production unit; The phosphoric acid production unit includes a reaction device and a filtration device; the reaction device is equipped with a mixing inlet and a reaction outlet; the filtration device is equipped with a reaction inlet, a solid outlet, and a liquid outlet. The phosphogypsum pyrolysis unit includes a calcination device; the calcination device is provided with a raw material inlet, a clinker outlet, and a coarse flue gas outlet. The wet sulfuric acid production unit includes a flue gas reaction device and an acid cooling device; the flue gas reaction device is provided with a reaction gas inlet and an acid gas outlet; the acid cooling device is provided with an acid gas inlet, a sulfuric acid outlet and a tail gas outlet; The mixing inlet is connected to the phosphate rock source and the water source; the reaction outlet is connected to the reaction inlet; the solid outlet is connected to the raw material inlet; the coarse flue gas outlet is connected to the reaction gas inlet; the reaction gas inlet is connected to the air source and the fuel gas source; the acid gas outlet is connected to the acid gas inlet; and the sulfuric acid outlet is connected to the mixing inlet.

2. The sulfuric acid process for phosphoric acid production system as described in claim 1, characterized in that, The phosphoric acid production unit also includes a raw material mixing device, which has a water inlet, a phosphate rock inlet, and a mixing outlet; the mixing outlet is connected to the mixing inlet.

3. The sulfuric acid process for phosphoric acid production system as described in claim 2, characterized in that, The raw material mixing device is also provided with an acidic water inlet; the wet sulfuric acid production unit also includes a flue gas pretreatment device, which is provided with a coarse flue gas inlet, an acidic water outlet, and a flue gas outlet; the coarse flue gas outlet is connected to the coarse flue gas inlet; the acidic water outlet is connected to the acidic water inlet; and the flue gas outlet is connected to the reaction gas inlet.

4. The sulfuric acid process for phosphoric acid production system as described in at least one of claims 1-3, characterized in that, The reaction apparatus is also provided with a circulation outlet and a circulation inlet. The circulation outlet and the circulation inlet are connected outside the reaction apparatus through a circulation pipe, and a cooling device is provided on the circulation pipe.

5. The sulfuric acid process for phosphoric acid production system as described in at least one of claims 1-4, characterized in that, The reaction device is also provided with an exhaust gas outlet, which is connected to an exhaust gas treatment device.

6. The sulfuric acid process for phosphoric acid production system as described in at least one of claims 1-5, characterized in that, The phosphoric acid production unit also includes a concentration device; the concentration device is provided with a liquid inlet, a jacket, a fluorosilicic acid outlet and a phosphoric acid outlet; the jacket is provided with a steam inlet and a condensate outlet.

7. The sulfuric acid process for phosphoric acid production system as described in claim 6, characterized in that, The flue gas reaction device is also provided with a boiler water inlet and a steam outlet; the steam outlet is connected to the steam inlet.

8. The sulfuric acid process for phosphoric acid production system according to at least one of claims 1-7, characterized in that, The phosphogypsum pyrolysis unit further includes a drying device, which has a phosphogypsum inlet, a hot air inlet, and a dry material outlet; the solid material outlet is connected to the phosphogypsum inlet; and the dry material outlet is connected to the raw material inlet.

9. The sulfuric acid process for phosphoric acid production system as described in claim 8, characterized in that, The phosphogypsum pyrolysis unit further includes a mixing device, which is provided with an auxiliary material inlet, a dry material inlet, and a raw material outlet; the dry material outlet is connected to the dry material inlet; and the raw material outlet is connected to the raw material inlet. The acid cooling device is also equipped with a jacket, which has a cold air inlet and a hot air outlet; the hot air outlet is connected to the hot air inlet.

10. The sulfuric acid process for phosphoric acid production system according to at least one of claims 1-9, characterized in that, The wet sulfuric acid production unit also includes a tail gas treatment device, which has a tail gas inlet, a treatment agent inlet, and a dilute sulfuric acid outlet. The tail gas outlet is connected to the tail gas inlet, the treatment agent inlet is connected to a hydrogen peroxide source, and the dilute sulfuric acid outlet is connected to the mixing inlet.

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