Phosphoric acid production device and maintenance method

Abstract

The invention discloses a phosphoric acid production device and a maintenance method, and belongs to the technical field of phosphorus chemical industry. Comprising M reaction tanks and N digestion tanks, each reaction tank comprises a tank body and a tank top, each tank top sequentially comprises an anti-corrosion layer, a conductive layer and a concrete layer from bottom to top, and each tank body sequentially comprises a carbon brick layer, an anti-corrosion layer, a conductive layer and a concrete layer from inside to outside; for the tank top of the K1-K2th reaction tank, a KPI acid-resistant daub layer, a PC layer and a steel plate layer are sequentially arranged between the concrete layer and the conductive layer from top to bottom, and the lower side of the concrete layer and the upper and lower sides of the steel plate layer are all subjected to sand blasting treatment; the thickness of the KPI acid-resistant daub layer is 3-10 mm, PC is brushed on the upper side of the steel plate layer to form a PC layer, the thickness of the steel plate layer is 3-6 mm, and the steel plate layer is fixed to the concrete layer through expansion bolts. And for the tank tops of the K1-K3 reaction tanks, a polytetrafluoroethylene layer is also arranged on the lower side of the anti-corrosion layer, and the thickness of the polytetrafluoroethylene layer is 0.6-1.5 mm.

Description

Technical Field

[0001] The invention belongs to the technical field of phosphorus chemical industry, and in particular relates to a phosphoric acid production device and a maintenance method. Background Art

[0002] Phosphoric acid is a commonly used acid in the chemical industry. During the wet process, phosphoric acid is prepared by decomposing phosphate rock slurry with concentrated sulfuric acid to produce a mixed slurry of phosphoric acid and calcium sulfate dihydrate crystals. During the decomposition process, reaction conditions such as sulfuric acid concentration and temperature must be controlled to obtain coarse, uniform calcium sulfate dihydrate crystals that are easy to filter and wash. The resulting mixed slurry of phosphoric acid and calcium sulfate dihydrate crystals is then vacuum filtered for liquid-solid separation to produce dilute phosphoric acid and phosphogypsum, respectively. Side reactions also occur during the decomposition process, generating gases such as carbon dioxide, hydrogen fluoride, and silicon tetrafluoride. All of these reactions occur in an extraction tank.

[0003] The extraction tank consists of a rectangular array of multiple (usually 4-12) square tanks, including multiple reaction tanks and digestion tanks. Each square tank consists of a tank body and a tank roof. The tank body is usually composed of a layer of carbon bricks, rubber sheets, and concrete, but the tank roof cannot be made of carbon bricks (due to its weight).

[0004] For example, Chinese patent publication number CN205575649U discloses a single-paddle multi-tank wet phosphoric acid extraction device, which consists of multiple reaction tanks and digestion tanks. Each reaction tank is equipped with an agitator, and the bottoms of the reaction tanks are connected in sequence by pipes. The first reaction tank is equipped with a phosphate slurry inlet, and the second and third reaction tanks are equipped with sulfuric acid inlets.

[0005] For example, the patent application number CN201620887343.9 discloses an anti-corrosion structure for the top beam of a wet-process phosphoric acid extraction tank, which includes a concrete structure of the top beam of the extraction tank. The inner wall of the top beam of the extraction tank is provided with an epoxy resin primer layer, a conductive layer, and a rubber plate structural layer in sequence on the concrete base layer, and the outer side of the rubber plate structural layer is provided with a graphite plate structural layer and a furan resin mastic surface layer in sequence.

[0006] In the prior art, the extraction tank is a reinforced concrete structure, which is a reaction vessel for sulfuric acid and phosphate rock. During the reaction process, multiple mixed acids such as phosphoric acid, sulfuric acid, and hydrogen fluoride are present, so the corrosion intensity of the tank body is relatively large; in particular, the top of the tank is about 1m away from the liquid surface of the reaction slurry, and a large amount of reaction heat, foam skin, hydrogen fluoride and other gases generated during the reaction process exist in the high space. The reaction heat will cause inconsistent expansion between the rubber sheet and the concrete, forming an external force that destroys the bonding. The foam will carry incompletely reacted concentrated sulfuric acid to contact the rubber sheet, causing aging of the rubber sheet; hydrogen fluoride gas accumulates on the surface of the rubber sheet to form silica gel. Excessive accumulation will also cause destructive force on the bonding of the rubber sheet due to gravity. Therefore, in order to reduce the corrosion effect, strict slurry level control, timely removal of reaction heat, reduction of hydrogen fluoride gas accumulation and addition of defoaming agents are adopted. However, the effect is not ideal, and it will also cause increased manpower and material resources, increased process costs, and complicated processes.

[0007] At present, the bottom of the phosphoric acid extraction tank is mainly lined with pre-vulcanized rubber as an anti-seepage and corrosion-resistant layer, and graphite impregnated carbon bricks are added as a wear-resistant and heat-insulating layer. The top uses a pre-vulcanized rubber plate as an anti-corrosion layer. Although it can improve the anti-corrosion performance to a certain extent, its temperature resistance in an environment of about 85°C is not good. The adhesive is prone to sticking, bubbling, and aging in this environment for a long time. Especially in the acid addition zone, the instantaneous exothermic temperature reaches 150°C, which is a challenge for rubber and corrodes more rapidly. In addition, after the rubber is corroded, acidic gas or medium enters the concrete, which reduces the strength of the concrete and gradually reduces the bonding strength after acid maintenance. The service life is getting shorter and shorter, which seriously affects the production start-up rate, thereby reducing output and causing economic losses. Summary of the Invention

[0008] To address the above-mentioned issues, embodiments of the present invention provide a phosphoric acid production device and maintenance method, which have the advantages of a longer service life, a longer maintenance cycle, and similar corrosion rates for each reaction tank (facilitating unified maintenance). The technical solution is as follows: On the one hand, an embodiment of the present invention provides a phosphoric acid production device, comprising M reaction tanks 1 and N digestion tanks 2, wherein the reaction tank 1 comprises a tank body and a tank top, wherein the tank top comprises an anti-corrosion layer 7, a conductive layer 6 and a concrete layer 3 from bottom to top, and the tank body comprises a carbon brick layer, an anti-corrosion layer 7, a conductive layer 6 and a concrete layer 3 from inside to outside, wherein the anti-corrosion layer 7 is a vulcanized rubber plate; for the tank tops of the K1-K2 reaction tanks 1: a KPI acid-resistant clay layer 4, a PC layer and a steel plate layer 5 are sequentially provided between the concrete layer 3 and the conductive layer 6 from top to bottom, and the lower side of the concrete layer 3 and the upper side of the steel plate layer 5 are Both sides are sandblasted; the thickness of the KPI acid-resistant putty layer 4 is 3-10 mm, and PC is applied on the upper side of the steel plate layer 5 to form a PC layer. The thickness of the steel plate layer 5 is 3-6 mm and is fixed to the concrete layer 3 by expansion bolts 8; for the tops of the K1-K3 reaction tanks 1: a polytetrafluoroethylene layer is further provided on the lower side of the anti-corrosion layer 7, and the thickness of the polytetrafluoroethylene layer is 0.6-1.5 mm; wherein, M is an integer of 3-9, N is an integer of 1-5, K1 is 2-3, M-K2=1 or 2, K3 is less than or equal to K2 and is less than 5.

[0009] Among them, the anti-corrosion layer 7 in the embodiment of the present invention is a vulcanized butyl rubber plate with a thickness of 3-8 mm; the thickness of the concrete layer 3 is greater than 200 mm and a steel skeleton is provided therein; the conductive layer 6 is KCH conductive putty with a thickness of 2-4 mm, the carbon brick layer is bonded to the anti-corrosion layer 7 by furan resin and has a thickness of 20-50 mm, and the thickness of the PC layer is 1-2 mm.

[0010] Preferably, in the embodiment of the present invention, for the tank tops of the K1-K3 reaction tanks 1, the thickness of the anti-corrosion layer 7 is 5-8 mm; for the tank tops of the remaining reaction tanks 1, the thickness of the anti-corrosion layer 7 is 3-5 mm.

[0011] In the embodiment of the present invention, the reaction tank 1 and the digestion tank 2 are both rectangular tanks, and M reaction tanks 1 and N digestion tanks 2 are arranged in an array.

[0012] Specifically, in the embodiment of the present invention, M is 6, N is 3, concentrated sulfuric acid inlets are provided on the second and third reaction tanks 1 , K1 is 2, K2 is 5, and K3 is 3.

[0013] Among them, the steel plate layer 5 in the embodiment of the present invention is formed by splicing and welding multiple square plates. When the steel plate layer 5 is installed, the weld is polished; an upward convex groove is provided on the lower side of the steel plate layer 5 and located at the expansion bolt 8, and the expansion bolt 8 is used to lock and fix the steel plate layer 5 through the locking nut thereon; the locking nut is against the lower side of the steel plate layer 5, it is located in the groove, it is welded and fixed on the steel plate layer 5, and its lower side is polished to be flush with the lower side of the steel plate layer 5, and the gap between it and the steel plate layer 5 is filled by welding.

[0014] Specifically, the size of the square plate in the embodiment of the present invention is 1200-2000 mm*1200-2000 mm, and each square plate is locked and fixed by four expansion bolts 8, and the four expansion bolts 8 are distributed in a square shape.

[0015] Among them, the top of the digester 2 in the embodiment of the present invention includes a steel tank body and a conductive layer 6 and an anti-corrosion layer 7 arranged on its inner side in sequence, and its tank body includes a steel tank body and a conductive layer 6, an anti-corrosion layer 7 and a carbon brick layer arranged on its inner side in sequence.

[0016] On the other hand, an embodiment of the present invention further provides a maintenance method for a phosphoric acid production device, which includes the following steps when maintaining the tank top of the K1-K2 reaction tank 1: S101: Cleaning the structure under the concrete layer 3; S102: Cleaning the concrete layer 3 with alkali solution and clean water in sequence; S103: sandblasting the lower side of the concrete layer 3; S104: Cut and re-weld the severely corroded steel bars in the concrete layer 3; S105: Install expansion bolts 8 at predetermined positions on the concrete layer 3 and drill holes and set grooves at corresponding positions on the steel plate layer 5; S106: sandblasting the upper and lower sides of the steel plate layer 5 and applying PC on the upper side to form a PC layer; S107: Install the steel plate layer 5 treated in step S106, and fill the KPI acid-resistant mortar layer 4 between the steel plate layer 5 and the concrete layer 3. Secure the steel plate layer 5 with the locking nuts on the expansion bolts 8, and weld the locking nuts to the steel plate layer 5. S108: Grinding the lower side of the locking nut and welding and leveling the gap between the locking nut and the steel plate layer 5; S109: A conductive layer 6 and an anti-corrosion layer 7 are sequentially provided on the lower side of the steel plate layer 5, and a polytetrafluoroethylene layer may be provided or not provided as required.

[0017] The service life of the tank top of the reaction tank 1 is 4-5 years during initial use; and maintenance is required every 2.5-3.0 years thereafter.

[0018] The present invention has the following advantages: (1) It has better anti-corrosion performance. When initially used, the service life of the top of a conventional reaction tank is about 2.5-3.0 years, and it is subsequently maintained about once a year. The service life of the top of the reaction tank of this patent is 4-5 years, and it is subsequently maintained every 2.5-3.0 years. The service life and maintenance cycle are extended, and the time for each maintenance is 8-10 days (the existing technology is 6-8 days), which increases the output.

[0019] (2) Based on the long-term test results, different settings are adopted for the tops of different reaction tanks; so that the service life and maintenance cycle of each reaction tank are similar, maintenance can be unified at a unified time, further reducing maintenance time and increasing production.

[0020] (3) It is easier to set up an anti-corrosion layer and a conductive layer on a steel plate layer than on a concrete layer (the concrete layer is more difficult to level), which not only reduces the difficulty of maintenance, but also reduces the maintenance time. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the reaction tank and digestion tank combination provided by an embodiment of the present invention; Figure 2 It is a structural schematic diagram of part of the reaction tank; Figure 3 This is a flow chart of a maintenance method for a phosphoric acid production unit.

[0022] In the figure: 1 reaction tank, 2 digestion tank, 3 concrete layer, 4 KPI acid-resistant mortar layer, 5 steel plate layer, 6 conductive layer, 7 anti-corrosion layer, 8 expansion bolts. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0024] During long-term monitoring of the extraction tanks, the applicant discovered that, for a structure consisting of six reaction tanks and three digestion tanks, Reactor Tank 1 and Digestor Tank 2 were constructed in 2009; in 2013, to expand production capacity, an additional Reactor Tank 1 and Digestor Tank 2 were built. The dimensions of the first extraction tank group were 4.5m*4.5m*6m; the dimensions of the second extraction tank group were 5.2m*5.2m*6.5m. The roofs of the first extraction tank group had an initial service life of approximately 2.6 years, with annual maintenance lasting approximately six days. The roofs of the second extraction tank group had an initial service life of approximately 3.0 years, with annual maintenance lasting approximately seven days. During actual testing, it was found that the roofs of the first and last reaction tanks showed the least corrosion, while the roofs of the second and third reaction tanks (which house the sulfuric acid inlet) showed the most severe corrosion. This observation led to the design of this patent.

[0025] Example 1 See also Figure 1-2 Example 1 provides a phosphoric acid production apparatus comprising M reaction tanks 1 and N digestion tanks 2, where M is an integer from 3 to 9 and N is an integer from 1 to 5, and is designed based on the production process. Specifically, the reaction tanks 1 and digestion tanks 2 are rectangular tanks, and the M reaction tanks 1 and N digestion tanks 2 are arranged in an array, as in the prior art.

[0026] The reaction tank 1 comprises a tank body and a tank roof, which is equipped with an agitator. The tank roof, from bottom to top, comprises an anti-corrosion layer 7, a conductive layer 6, and a concrete layer 3. The tank body, from inside to outside, comprises a carbon brick layer, an anti-corrosion layer 7, a conductive layer 6, and a concrete layer 3. The concrete layer 3 is greater than 200 mm thick and contains a steel reinforcement. The conductive layer 6 is made of KCH conductive mortar and has a thickness of 2-4 mm. The anti-corrosion layer 7 is a vulcanized butyl rubber sheet and has a thickness of 3-8 mm. The carbon brick layer is bonded to the anti-corrosion layer 7 with furan resin and has a thickness of 20-50 mm.

[0027] The aforementioned structure is essentially the same as that of the existing extraction tank 1, with the following differences: For the roofs of reaction tanks K1-K2, a KPI acid-resistant mastic layer 4, a PC layer, and a steel plate layer 5 are sequentially arranged between the concrete layer 3 and the conductive layer 6, from top to bottom. The underside of the concrete layer 3 and the upper and lower sides of the steel plate layer 5 are sandblasted to level and improve roughness (thus ensuring adhesion of the adhesive layer). The KPI acid-resistant mastic layer 4 is 3-10 mm thick, and the PC layer is applied (1-3 times) on top of the steel plate layer 5 to form a PC layer. The PC layer is 1-2 mm thick. The steel plate layer 5 is 3-6 mm thick and is secured to the concrete layer 3 via vertical expansion bolts 8. For the roofs of reaction tanks K1-K3, a polytetrafluoroethylene layer is also provided below the anti-corrosion layer 7. The thickness of the polytetrafluoroethylene layer is 0.6-1.5 mm. Among them, K1 is 2-3, M-K2=1 or 2, K3 is less than or equal to K2 and is less than 5.

[0028] That is, for the tops of the first to K1 (excluding K1) reaction tanks 1, the tops, from bottom to top, include, in order: an anti-corrosion layer 7, a conductive layer 6, and a concrete layer 3. For the tops of the K1-K3 reaction tanks 1, the tops, from bottom to top, include, in order: a polytetrafluoroethylene layer, an anti-corrosion layer 7, a conductive layer 6, a steel plate layer 5, a PC layer, a KPI acid-resistant mastic layer 4, and a concrete layer 3. For the tops of the K3 (excluding K3)-K2 reaction tanks 1, the tops, from bottom to top, include, in order: an anti-corrosion layer 7, a conductive layer 6, a steel plate layer 5, a PC layer, a KPI acid-resistant mastic layer 4, and a concrete layer 3. For the tops of the reaction tanks 1 from K2 (excluding K2) to the last reaction tank 1, the tops, from bottom to top, include, in order: an anti-corrosion layer 7, a conductive layer 6, and a concrete layer 3.

[0029] The steel plate layer 5 in this embodiment of the present invention is formed by welding together multiple square plates (with a side length of less than or equal to 2000 mm). The welds are polished during installation. An upwardly projecting groove (which can be formed by stamping and punching, with a depth of 3-5 mm) is provided on the underside of the steel plate layer 5, located at the expansion bolt 8. The expansion bolt 8 is secured to the steel plate layer 5 via a locking nut mounted thereon. The locking nut rests against the underside of the steel plate layer 5, located in the groove. It is welded to the steel plate layer 5, and its underside is polished to be flush with or slightly protruding downward from the underside of the steel plate layer 5. The gap between the locking nut and the steel plate layer 5 is welded.

[0030] Specifically, the square panels in the embodiment of the present invention have dimensions of 1200-2000 mm by 1200-2000 mm, and each panel is secured by four expansion bolts 8. The four expansion bolts 8 are arranged in a square pattern, one at each of the four corners of the panel. Multiple expansion bolts 8 are evenly distributed and arranged in a square array.

[0031] Among them, the top of the digester 2 in the embodiment of the present invention includes a steel tank body and a conductive layer 6 and an anti-corrosion layer 7 arranged on its inner side in sequence, and its tank body includes a steel tank body and a conductive layer 6, an anti-corrosion layer 7 and a carbon brick layer arranged on its inner side in sequence.

[0032] Example 2 Example 2 provides a phosphoric acid production apparatus having a structure substantially identical to that of Example 1, except that: For the tops of reaction tanks K1 through K3, the thickness of the anti-corrosion layer 7 is 5 to 8 mm to enhance corrosion resistance. For the tops of the remaining reaction tanks 1, the thickness of the anti-corrosion layer 7 is 3 to 5 mm.

[0033] Example 3 Example 3 provides a phosphoric acid production device, which has a structure that is basically the same as that of Example 2, except that: in this embodiment, M is 6, N is 3, the second and third reaction tanks 1 are provided with concentrated sulfuric acid inlets, K1 is 2, K2 is 5, and K3 is 3. That is, for the top of the first reaction tank 1, the top includes, from bottom to top, an anti-corrosion layer 7, a conductive layer 6, and a concrete layer 3, and the thickness of the anti-corrosion layer 7 is 4 mm. For the tops of the second and third reaction tanks 1, the tops include, from bottom to top, a polytetrafluoroethylene layer, an anti-corrosion layer 7, a conductive layer 6, a steel plate layer 5, a PC layer, a KPI acid-resistant mastic layer 4, and a concrete layer 3, and the thickness of the anti-corrosion layer 7 is 6 mm. For the tops of the fourth and fifth reaction tanks 1, the tops include, from bottom to top, an anti-corrosion layer 7, a conductive layer 6, a steel plate layer 5, a PC layer, a KPI acid-resistant mastic layer 4, and a concrete layer 3, and the thickness of the anti-corrosion layer 7 is 4 mm. As for the top of the last reaction tank 1, the top includes an anti-corrosion layer 7, a conductive layer 6 and a concrete layer 3 from bottom to top, and the thickness of the anti-corrosion layer 7 is 4 mm.

[0034] Example 4 Example 4 provides a phosphoric acid production device, whose structure is basically the same as that of Example 1, except that: the size of the square plate in this embodiment is 1600mm*1600mm, the distances between the expansion bolts 8 and the corresponding two edges are 400mm and 400mm respectively, and the distance between two adjacent expansion bolts 8 is 800mm.

[0035] Verification Example In 2016, a new set of extraction tanks was built. The reaction tank 1 includes six square tanks with dimensions of 5.2m*5.2m*6.5m, and adopts the solution of Example 3. The top of the first reaction tank includes, from bottom to top, an anti-corrosion layer 7, a conductive layer 6, and a concrete layer 3. The top of the second reaction tank 1 includes, from bottom to top, a polytetrafluoroethylene layer, an anti-corrosion layer 7, a conductive layer 6, a steel plate layer 5, a PC layer, a KPI acid-resistant mastic layer 4, and a concrete layer 3. The top of the third reaction tank includes, from bottom to top, an anti-corrosion layer 7, a conductive layer 6, and a concrete layer 3 (consistent with the prior art). The top of the fourth reaction tank 1 includes, from bottom to top, an anti-corrosion layer 7, a conductive layer 6, a steel plate layer 5, a PC layer, a KPI acid-resistant mastic layer 4, and a concrete layer 3. The top of the fifth reaction tank includes, from bottom to top, an anti-corrosion layer 7, a conductive layer 6 and a concrete layer 3 (consistent with the prior art), and the top of the sixth reaction tank includes, from bottom to top, an anti-corrosion layer 7, a conductive layer 6 and a concrete layer 3.

[0036] The reaction conditions are: reaction temperature of 80-85°C, calcium sulfate dihydrate method, and phosphoric acid concentration of 22-25%.

[0037] During the annual inspection of the equipment in 2017 and 2018, the corrosion condition of the tank top was observed.

[0038] 2017: The corrosion levels of the tops of the first, second, fourth, and sixth reaction tanks were similar and all could still be used well. The corrosion level of the top of the third reaction tank was greater than that of the fifth reaction tank, which was greater than that of the first reaction tank and approximately equal to that of the sixth reaction tank. All could still be used well.

[0039] 2018: The corrosion degree of the tops of the first, second, fourth and sixth reaction tanks were similar and all could still be used well; the corrosion degree of the top of the third reaction tank was greater than the corrosion degree of the top of the fifth reaction tank; the corrosion degree of the top of the first reaction tank was ≈ the corrosion degree of the top of the sixth reaction tank; the top of the third reaction tank was severely corroded.

[0040] The final results are as follows: the roof of the second reactor tank 1 is still in good working order after 4 years of use, requiring maintenance every three years; the roof of the third reactor tank requires maintenance after 2.5 years of use, requiring maintenance every year; the roof of the fourth reactor tank 1 is still in good working order after 4 years of use, requiring maintenance every three years; the roof of the fifth reactor tank requires maintenance after 2.7 years of use, requiring maintenance every year. The roofs of the first and sixth reactor tanks 1 are still in good working order after 4 years of use, requiring maintenance every three years.

[0041] In 2020, a new set of extraction tanks was built in the branch company, using the design method of this patent. When the tops of the first to sixth reaction tanks 1 were maintained in 2024, the degree of corrosion was similar and maintenance was carried out. During the routine inspection at the beginning of 2025, the degree of corrosion of the tops of the first to sixth reaction tanks 1 was similar, and it was judged that they could still be used for at least one more year.

[0042] Example 5 See also Figure 3 Example 5 provides a maintenance method for a phosphoric acid production device, which includes the following steps when maintaining the top of the K1-K2 reaction tank 1: S101: Clean the structure under the concrete layer 3 (including the polytetrafluoroethylene layer, the anti-corrosion layer 7, the conductive layer 6, the steel plate layer 5, the PC layer and the KPI acid-resistant mastic layer 4).

[0043] S102: The concrete layer 3 is cleaned with an alkaline solution (specifically, a sodium carbonate solution or a sodium hydroxide solution) and clean water in sequence.

[0044] S103: The lower side of the concrete layer 3 is subjected to sandblasting.

[0045] S104: Cut and re-weld the severely corroded steel bars in the concrete layer 3.

[0046] S105 : Expansion bolts 8 are set at predetermined positions of the concrete layer 3 , and holes (specifically circular holes matching the expansion bolts 8 ) and grooves (specifically upwardly convex grooves) are opened at corresponding positions of the steel plate layer 5 .

[0047] S106: sandblasting is performed on the upper and lower sides of the steel plate layer 5 and PC is applied on the upper side (applied 1-3 times) to form a PC layer.

[0048] S107: Install the steel plate layer 5 processed in step S106, and fill the KPI acid-resistant putty layer 4 between the steel plate layer 5 and the concrete layer 3, lock and fix the steel plate layer 5 with the locking nut on the expansion bolt 8, and weld the locking nut to the steel plate layer 5.

[0049] S108: Grind the lower side of the locking nut (including the lower end of the expansion bolt 8) (flush with the steel plate layer 5 or slightly protrude downward, and must not affect the installation of the conductive layer 6 and the anti-corrosion layer 7) and weld and level the gap between the locking nut and the steel plate layer 5.

[0050] S109: A conductive layer 6 and an anti-corrosion layer 7 are then sequentially applied to the underside of the steel plate layer 5, consistent with prior art. A polytetrafluoroethylene layer may or may not be applied as needed. Specifically, the tops of the reaction tanks K1-K3 are provided with a polytetrafluoroethylene layer, while the tops of the reaction tanks K3-K2 are not provided with a polytetrafluoroethylene layer.

[0051] The maintenance method of the tank tops of the first to K1 (exclusive) reaction tanks 1 and the tank tops of the K2 (exclusive) to the last reaction tank 1 is consistent with the existing technology.

[0052] The service life of the tank top of the reaction tank 1 is 4-5 years during initial use; and maintenance is required every 2.5-3.0 years thereafter.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A phosphoric acid production device, comprising M reaction tanks (1) and N digestion tanks (2), wherein the reaction tank (1) comprises a tank body and a tank top, wherein the tank top comprises an anti-corrosion layer (7), a conductive layer (6) and a concrete layer (3) in order from bottom to top, and the tank body comprises a carbon brick layer, an anti-corrosion layer (7), a conductive layer (6) and a concrete layer (3) in order from inside to outside, wherein the anti-corrosion layer (7) is a vulcanized rubber sheet; characterized in that: For the top of the K1-K2 reaction tanks (1): a KPI acid-resistant clay layer (4), a PC layer and a steel plate layer (5) are sequentially provided between the concrete layer (3) and the conductive layer (6) from top to bottom, and the lower side of the concrete layer (3) and the upper and lower sides of the steel plate layer (5) are sandblasted; the thickness of the KPI acid-resistant clay layer (4) is 3-10 mm, and the PC layer is formed by brushing on the upper side of the steel plate layer (5); the thickness of the steel plate layer (5) is 3-6 mm and is fixed to the concrete layer (3) by expansion bolts (8); For the tank tops of the K1-K3 reaction tanks (1): a polytetrafluoroethylene layer is further provided on the lower side of the anti-corrosion layer (7), and the thickness of the polytetrafluoroethylene layer is 0.6-1.5 mm; Wherein, M is an integer of 3-9, N is an integer of 1-5, K1 is 2-3, M-K2=1 or 2, K3 is less than or equal to K2 and is less than 5.

2. The phosphoric acid production device according to claim 1, characterized in that The anti-corrosion layer (7) is a vulcanized butyl rubber sheet with a thickness of 3-8 mm; the thickness of the concrete layer (3) is greater than 200 mm and a steel skeleton is provided therein; the conductive layer (6) is KCH conductive mortar with a thickness of 2-4 mm; the carbon brick layer is bonded to the anti-corrosion layer (7) by furan resin and has a thickness of 20-50 mm; and the thickness of the PC layer is 1-2 mm.

3. The phosphoric acid production device according to claim 2, characterized in that For the tops of the K1-K3 reaction tanks (1), the thickness of the anti-corrosion layer (7) is 5-8 mm; for the tops of the remaining reaction tanks (1), the thickness of the anti-corrosion layer (7) is 3-5 mm.

4. The phosphoric acid production device according to claim 2, characterized in that The reaction tank (1) and digestion tank (2) are both rectangular tanks, and M reaction tanks (1) and N digestion tanks (2) are arranged in an array.

5. The phosphoric acid production device according to claim 2, characterized in that: The M is 6, the N is 3, the second and third reaction tanks (1) are provided with concentrated sulfuric acid inlets, the K1 is 2, the K2 is 5, and the K3 is 3.

6. The phosphoric acid production device according to claim 2, characterized in that: The steel plate layer (5) is formed by splicing and welding a plurality of square plates, and the weld is polished when the steel plate layer (5) is installed; an upward convex groove is provided on the lower side of the steel plate layer (5) and located at the expansion bolt (8), and the expansion bolt (8) is used to lock and fix the steel plate layer (5) through the locking nut thereon; the locking nut is pressed against the lower side of the steel plate layer (5), is located in the groove, is welded and fixed on the steel plate layer (5), and its lower side is polished until it is flush with the lower side of the steel plate layer (5), and the gap between it and the steel plate layer (5) is filled by welding.

7. The phosphoric acid production device according to claim 6, characterized in that The size of the square plate is 1200-2000mm*1200-2000mm, and each square plate is locked and fixed by four expansion bolts (8), and the four expansion bolts (8) are distributed in a square shape.

8. The phosphoric acid production device according to claim 3, characterized in that: The top of the digester (2) comprises a steel tank body and a conductive layer (6) and an anti-corrosion layer (7) sequentially arranged on its inner side, and the tank body comprises a steel tank body and a conductive layer (6), an anti-corrosion layer (7) and a carbon brick layer sequentially arranged on its inner side.

9. The method for maintaining a phosphoric acid production device according to any one of claims 1 to 8, characterized in that: When the tank top of the K1-K2 reaction tank (1) is maintained, the following steps are included: S101: Cleaning the structure under the concrete layer (3); S102: Cleaning the concrete layer (3) with alkali solution and clean water in sequence; S103: sandblasting the lower side of the concrete layer (3); S104: cutting and re-welding the severely corroded steel bars in the concrete layer (3); S105: installing expansion bolts (8) at predetermined positions of the concrete layer (3) and drilling holes and providing grooves at corresponding positions of the steel plate layer (5); S106: sandblasting the upper and lower sides of the steel plate layer (5) and applying PC on the upper side thereof to form a PC layer; S107: Install the steel plate layer (5) processed in step S106, and fill the KPI acid-resistant mortar layer (4) between the steel plate layer (5) and the concrete layer (3), tighten and fix the steel plate layer (5) with the locking nut on the expansion bolt (8), and weld and fix the locking nut to the steel plate layer (5); S108: grinding the lower side of the locking nut and welding and leveling the gap between the locking nut and the steel plate layer (5); S109: A conductive layer (6) and an anti-corrosion layer (7) are sequentially provided on the lower side of the steel plate layer (5), and a polytetrafluoroethylene layer may or may not be provided as required.

10. The maintenance method according to claim 9, characterized in that: During initial use, the service life of the tank top of the reaction tank (1) is 4-5 years; and it is subsequently maintained every 2.5-3.0 years.

Images