Low-grade waste heat utilization system for phosphoric acid process

Abstract

This invention relates to the field of waste heat recovery systems, specifically to a low-grade waste heat recovery system for phosphoric acid processes. It includes a single-effect concentration system, a pre-concentration component, a preheating component, a circulating humidified air component, and a circulating water inlet component. The circulating humidified air component is connected to both the pre-concentration component and the circulating water inlet component. The pre-concentration component is connected to the single-effect concentration system. Simultaneously, the pre-concentration component is connected to the preheating component, and the preheating component is also connected to the single-effect concentration system. This system simultaneously concentrates and heats dilute phosphoric acid and heats the third-wash water, saving steam consumption and reducing the amount of water added. It avoids the additional consumption caused by the subsequent addition of third-wash water to phosphoric acid after it becomes second-wash or first-wash water, achieving true multi-use of heat. It can solve the problems of waste heat waste, dilute phosphoric acid concentration, and third-wash water heating in one step, recovering the heat from previously wasted concentrated phosphoric acid, steam condensate, and wastewater, achieving energy saving and carbon reduction effects.

Description

Technical Field

[0001] This invention relates to the field of waste heat utilization systems, and more specifically, to a low-grade waste heat utilization system for phosphoric acid processes. Background Technology

[0002] As key suppliers of essential fertilizers for agricultural production, phosphate fertilizer companies play a vital role in ensuring food security and sustainable agricultural development. However, their production process faces numerous challenges, including the critical need for concentrated dilute phosphoric acid and the generation and treatment of large quantities of washing wastewater. Firstly, traditional technologies for concentrated dilute phosphoric acid and washing wastewater treatment suffer from high energy consumption, low concentration efficiency, and complex processes, making it difficult to achieve efficient purification of dilute phosphoric acid and resource recovery of washing wastewater. Secondly, increasingly stringent environmental policies and resource utilization standards require washing wastewater to be recycled or have near-zero emissions, standards that traditional technologies often fail to meet, placing phosphate fertilizer companies under dual pressure to optimize processes and comply with environmental regulations. Therefore, developing an integrated technology for low-energy consumption, high-efficiency, and pollution-free concentrated dilute phosphoric acid and recycling of washing wastewater has significant practical application value and market potential.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a low-grade waste heat utilization system for phosphoric acid processes. The low-grade waste heat utilization system for phosphoric acid processes provided in this invention reduces energy consumption in phosphoric acid concentration, saves steam consumption, and achieves comprehensive utilization and multiple uses of waste heat.

[0005] This invention is implemented as follows: In a first aspect, the present invention provides a low-grade waste heat utilization system for phosphoric acid process, which includes a single-effect concentration system for concentrating dilute phosphoric acid, a pre-concentration component for pre-concentrating dilute phosphoric acid, a preheating component for preheating the pre-concentrated dilute phosphoric acid, and a circulating humidified air component and a circulating water inlet component for circulating humidified air and purified water, respectively. The circulating humidified air assembly is connected to the pre-concentration assembly and the circulating water inlet assembly, respectively. The pre-concentration component is connected to the single-effect concentration system; simultaneously, the pre-concentration component is connected to the preheating component; the preheating component is connected to the single-effect concentration system. The pre-concentration component includes a heating component that uses steam condensate, concentrated phosphoric acid, and continuous wastewater to heat dilute phosphoric acid, and an absorption tower. The heating component is connected to a single-effect concentration system and the absorption tower. The absorption tower is connected to the preheating component and the circulating humidified air component. The circulating humidified air assembly includes a purification component and a regeneration tower. The absorption tower and the regeneration tower are respectively connected to the purification component, and the regeneration tower is connected to the circulating water inlet assembly. The circulating water intake assembly includes a fourth heat exchanger for heating the third wash water. The inlet of the fourth heat exchanger is connected to the outlet of the regeneration tower, and the outlet of the fourth heat exchanger is connected to the inlet of the regeneration tower.

[0006] In an optional embodiment, the heating assembly includes a second heat exchanger, a first heat exchanger, and a third heat exchanger connected in sequence. The first heat exchanger and the second heat exchanger are respectively connected to the single-effect concentration system, and the third heat exchanger is connected to the feed inlet of the absorption tower.

[0007] In an optional embodiment, the purification assembly includes a two-stage fluorine absorber and a gas scrubbing device. The inlet of the two-stage fluorine absorber is connected to the humidified air outlet of the absorption tower, the outlet of the two-stage fluorine absorber is connected to the inlet of the gas scrubbing device, the outlet of the gas scrubbing device is connected to the inlet of the regeneration tower, and the humidified air outlet of the regeneration tower is connected to the humidified air inlet of the absorption tower.

[0008] In an optional embodiment, the circulating water intake assembly includes a fresh air heater, the outlet of the regeneration tower is connected to the inlet of the fresh air heater, and the outlet of the fresh air heater is connected to the inlet of the regeneration tower.

[0009] In an optional embodiment, the single-effect concentration system includes a graphite heat exchanger, a separator, and a secondary steam treatment component connected in sequence; the graphite heat exchanger is connected to the second heat exchanger, the separator is connected to the first heat exchanger, and the secondary steam treatment component is connected to the preheating component.

[0010] In an optional embodiment, the secondary steam treatment assembly includes two stages of fluorine absorbers and a condenser connected in sequence, the two stages of fluorine absorbers being connected to the separator, and the condenser being connected to the preheating assembly.

[0011] In an optional embodiment, the preheating assembly includes a dilute phosphoric acid preheater and an electric heat pump connected in sequence. The inlet of the dilute phosphoric acid preheater is connected to the outlet of the absorption tower, the outlet of the dilute phosphoric acid preheater is connected to the graphite heat exchanger, and the electric heat pump is connected to the condenser.

[0012] In an optional embodiment, a demineralized water heater is also included, which is connected to the second heat exchanger.

[0013] In an optional embodiment, the system further includes a concentrated sulfuric acid preparation system and a phosphoric acid preparation system that uses concentrated sulfuric acid to treat phosphate rock. The concentrated sulfuric acid preparation system is connected to the phosphoric acid preparation system. The fourth heat exchanger and the second heat exchanger are respectively connected to the phosphoric acid preparation system. The demineralized water heater is connected to the concentrated sulfuric acid preparation system.

[0014] In an optional embodiment, the concentrated sulfuric acid preparation system includes a sulfur burner, a waste heat boiler, an air preheater, and a concentrated sulfuric acid generator connected in sequence. The concentrated sulfuric acid generator is connected to the phosphoric acid preparation system, and the demineralized water heater is connected to the waste heat boiler. The phosphoric acid preparation system further includes a crusher, a phosphoric acid pulper, a filter, and a three-wash tank connected in sequence. The phosphoric acid pulper is connected to the concentrated sulfuric acid generator, the three-wash tank is connected to the fourth heat exchanger, the filter is connected to the second heat exchanger through a fine adjuster, and the three-wash tank is connected to the phosphoric acid pulper.

[0015] The present invention has the following beneficial effects: (1) The present invention embodiment concentrates and heats dilute phosphoric acid, and heats the three wash water at the same time, which saves the steam consumption that would have been required to heat the three wash water, and reduces the amount of water added to the three wash water, avoiding the additional consumption caused by the subsequent addition of the three wash water to the phosphoric acid after it becomes the second wash water and the first wash water, thus achieving true multi-use of heat.

[0016] (2) The present invention solves the problems of waste heat, dilute phosphoric acid concentration and heating of the three wash water in one step.

[0017] (3) The embodiments of the present invention recover the heat of concentrated phosphoric acid, steam condensate, and continuous drainage that were originally wasted, thus achieving the effect of energy saving and carbon reduction. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the low-grade waste heat utilization system for phosphoric acid production provided by the present invention.

[0020] Icons: 100-Low-grade waste heat utilization system for phosphoric acid process; 101-Sulfur burner; 102-Waste heat boiler; 103-Air preheater; 104-Concentrated sulfuric acid preparer; 105-Crusher; 106-Phosphoric acid slurry preparer; 107-Filter; 108-First scrubbing tank; 109-Second scrubbing tank; 110-Third scrubbing tank; 111-Precision conditioner; 112-Second heat exchanger; 113-First heat exchanger; 114-Third heat exchanger; 115-Absorber tower; 116-Two-stage fluoride absorber; 117-Gas scrubbing device; 118-Regeneration tower; 119-Fourth heat exchanger; 120-Fresh air heater; 121-Dilute phosphoric acid preheater; 122-Electric heat pump; 123-Graphite heat exchanger; 124-Separator; 125-Demineralized water heater; 126-Condenser. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] like Figure 1 As shown, the phosphoric acid process low-grade waste heat utilization system 100 provided in this embodiment of the invention includes: A concentrated sulfuric acid preparation system is used to generate concentrated sulfuric acid. Specifically, it includes a sulfur burner 101, a waste heat boiler 102, an air preheater 103, and a concentrated sulfuric acid generator 104 connected in sequence. Sulfur is introduced into the sulfur burner for combustion to form sulfur trioxide. The sulfur trioxide is introduced into the waste heat boiler 102 for heat exchange, heating demineralized water to produce steam. To maintain a stable ion concentration of approximately 1%, the demineralized water is discharged as wastewater. The sulfur trioxide is then introduced into the air preheater 103 for heat exchange again. The hot gas from the air preheater 103 is then recycled back to the waste heat boiler 102. The sulfur trioxide from the air preheater 103 is mixed with water in the concentrated sulfuric acid generator 104 to form concentrated sulfuric acid.

[0023] Furthermore, the system also includes a phosphoric acid preparation system for preparing phosphoric acid, which is connected to a concentrated sulfuric acid preparation system. Specifically, the phosphoric acid preparation system is connected to a concentrated sulfuric acid generator 104. Specifically, the phosphoric acid preparation system also includes a crusher 105, a phosphoric acid pulper 106, a filter 107, and a three-washing tank connected in sequence. The phosphoric acid pulper 106 is connected to the concentrated sulfuric acid generator 104, and the three-washing tank is connected to the phosphoric acid pulper 106. The three-washing tank includes a first washing tank 108, a second washing tank 109, and a third washing tank 110 connected in sequence. The inlet of the first washing tank 108 is connected to the outlet of the filter 107, and the outlet of the first washing tank 108 is connected to the inlet of the phosphoric acid pulper 106. Phosphate rock is crushed and ground in crusher 105 to form phosphate rock powder. The phosphate rock powder is then mixed with concentrated sulfuric acid and wash water from the first washing tank 108 to form a slurry. The slurry is then filtered through filter 107 to form phosphogypsum and crude dilute phosphoric acid. The phosphogypsum is washed sequentially in the first washing tank 108, the second washing tank 109, and the third washing tank 110 to obtain washed phosphogypsum. Simultaneously, the wash water from the third washing tank 110 is recycled to the second washing tank 109 for a second wash, the wash water from the second washing tank 109 is recycled to the first washing tank 108 for a first wash, and the wash water is recycled to the phosphoric acid slurry 106 for slurry preparation.

[0024] It also includes a pre-concentration component for pre-concentrating dilute phosphoric acid. The pre-concentration component includes a heating component that uses steam condensate, concentrated phosphoric acid and continuous wastewater to heat the dilute phosphoric acid, and an absorption tower 115. The heating component is connected to the absorption tower 115, and the filter 107 is connected to the fine adjuster 111. The fine adjuster 111 is connected to the heating component.

[0025] Specifically, the heating assembly includes a second heat exchanger 112, a first heat exchanger 113, and a third heat exchanger 114 connected in sequence. The second heat exchanger 112 is connected to the outlet of the fine-tuning device 111, and the third heat exchanger 114 is connected to the inlet of the absorption tower 115. The third heat exchanger 114 is also connected to the waste heat boiler 102, using continuous drainage to heat the dilute phosphoric acid. The finely regulated dilute phosphoric acid is heated sequentially through the second heat exchanger 112, the first heat exchanger 113, and the third heat exchanger 114 before entering the absorption tower 115 for concentration. Inside the absorption tower 115, it comes into direct contact with the humidified air, directly transferring heat and moisture to the humidified air.

[0026] Furthermore, it also includes a circulating humidified air assembly for circulating humidified air. The circulating humidified air assembly is connected to the pre-concentration assembly and to the absorption tower 115. Specifically, the circulating humidified air assembly includes a purification assembly and a regeneration tower 118. The humidified air outlet of the absorption tower 115 is connected to the purification assembly, the purification assembly is connected to the humidified air inlet of the regeneration tower 118, and the humidified air outlet of the regeneration tower 118 is connected to the humidified air inlet of the absorption tower 115.

[0027] Furthermore, the purification assembly includes a two-stage fluorine absorber 116 and a scrubbing device 117. The inlet of the two-stage fluorine absorber 116 is connected to the humidified air outlet of the absorption tower 115, the outlet of the two-stage fluorine absorber 116 is connected to the inlet of the scrubbing device 117, the outlet of the scrubbing device 117 is connected to the humidified air inlet of the regeneration tower 118, and the humidified air outlet of the regeneration tower 118 is connected to the humidified air inlet of the absorption tower 115.

[0028] After the humidified air absorbs heat and moisture in the absorption tower 115, its temperature and moisture content increase. Then it enters the two-stage fluorine absorber 116 and the gas scrubbing device 117. After purification, it enters the regeneration tower 118 to exchange heat and moisture. After that, it returns to the absorption tower 115 to continue the heat and mass transfer with dilute phosphoric acid, and the cycle repeats.

[0029] Furthermore, it also includes a circulating water inlet assembly for circulating purified water; the circulating water inlet assembly is connected to the circulating humidified air assembly, specifically, the circulating water inlet assembly is connected to the regeneration tower 118.

[0030] Furthermore, the circulating water intake assembly includes a fourth heat exchanger 119 for heating the third wash water. The inlet of the fourth heat exchanger 119 is connected to the outlet of the regeneration tower 118, and the outlet of the fourth heat exchanger 119 is connected to the inlet of the regeneration tower 118. The outlet of the fourth heat exchanger 119 is connected to the third washing tank 110, and the inlet of the fourth heat exchanger 119 is connected to the third washing tank 110. The circulating purified water absorbs heat and moisture from the humidified air in the regeneration tower 118, and transfers this heat to the third wash water through the fourth heat exchanger 119. The third wash water then circulates back to the third washing tank 110. Simultaneously, the circulating purified water absorbing heat and moisture from the humidified air in the regeneration tower 118 can also be added to the concentrated sulfuric acid preparation workshop, i.e., replenished into the concentrated sulfuric acid preparer 104.

[0031] The circulating water intake assembly includes a fresh air heater 120, the outlet of the regeneration tower 118 is connected to the inlet of the fresh air heater 120, the outlet of the fresh air heater 120 is connected to the inlet of the regeneration tower 118, and the outlet of the fresh air heater 120 is connected to the air preheater 103.

[0032] Furthermore, it also includes a preheating component for preheating the pre-concentrated dilute phosphoric acid, the pre-concentration component being connected to the preheating component; the absorption tower 115 is connected to the preheating component. Specifically, the preheating component includes a dilute phosphoric acid preheater 121 and an electric heat pump 122 connected in sequence, the inlet of the dilute phosphoric acid preheater 121 being connected to the outlet of the absorption tower 115.

[0033] Furthermore, it also includes a single-effect concentration system for concentrating dilute phosphoric acid, with a preheating component connected to the single-effect concentration system and a heating component connected to the single-effect concentration system. Specifically, the first heat exchanger 113 and the second heat exchanger 112 are respectively connected to the single-effect concentration system.

[0034] Specifically, the single-effect concentration system includes a graphite heat exchanger 123, a separator 124, and a secondary steam treatment component connected in sequence. The graphite heat exchanger 123 is connected to the second heat exchanger 112, the outlet of the dilute phosphoric acid preheater 121 is connected to the graphite heat exchanger 123, the separator 124 is connected to the first heat exchanger 113, and the secondary steam treatment component is connected to the preheating component. Steam (originating from the waste heat boiler 102) enters the graphite heat exchanger 123 to heat and concentrate the incoming dilute phosphoric acid. The resulting condensate is then fed into the second heat exchanger 112 to further heat the dilute phosphoric acid. The concentrated phosphoric acid formed in the separator 124 is fed into the first heat exchanger 113 to further heat the dilute phosphoric acid.

[0035] The secondary steam treatment assembly includes a two-stage fluorine absorber 116 and a condenser 126 connected in sequence. The two-stage fluorine absorber 116 is connected to the separator 124, and the condenser 126 is connected to the preheating assembly. An electric heat pump 122 is connected to the condenser 126.

[0036] Furthermore, it also includes a demineralized water heater 125, the inlet of which is connected to the second heat exchanger 112, and the outlet of which is connected to the waste heat boiler 102.

[0037] The specific process flow of the low-grade waste heat utilization system 100 for the phosphoric acid process is as follows: (1) Steam condensate process: The steam condensate formed by the graphite heat exchanger 123 passes through the second heat exchanger 112, transferring heat to the dilute phosphoric acid. After that, the demineralized water is heated by a demineralized water heater 125.

[0038] (2) Dilute phosphoric acid process: The resulting dilute phosphoric acid is passed sequentially through a second heat exchanger 112, a first heat exchanger 113, and a third heat exchanger 114, where it absorbs heat from steam condensate, concentrated phosphoric acid, and wastewater. Simultaneously, it comes into direct contact with humidified air within the absorption tower 115, directly transferring heat and moisture to the air. The dilute phosphoric acid exiting the absorption tower 115 goes to a dilute phosphoric acid preheater 121, where an electric heat pump 122 recovers heat from the cooling water of the single-effect concentration system. After heating, the dilute phosphoric acid enters a graphite heat exchanger 123 where it is further concentrated by steam heating within the single-effect concentration system.

[0039] (3) Circulating air process: After absorbing heat and moisture in the absorption tower 115, the temperature and moisture content of the humidified air increase. It then enters the two-stage fluorine absorber 116 and the gas scrubbing device 117, where it is purified before entering the regeneration tower 118. There, it comes into direct contact with the circulating purified water sprayed within the regeneration tower 118, transferring heat and moisture to the circulating purified water. Afterward, it returns to the absorption tower 115 to continue heat and mass transfer with dilute phosphoric acid, in a continuous cycle.

[0040] (4) Circulating water purification process: The circulating purified water absorbs heat and moisture from the humidified air in the regeneration tower 118, and transfers the heat to the fresh air of the diammonium phosphate hot air furnace or the fresh air of the two sets of compound fertilizer hot air furnaces through the fresh air heater 120; and transfers the heat to the three wash water through the fourth heat exchanger 119.

[0041] (5) Steam process: Steam enters the graphite heat exchanger 123 to heat and concentrate the incoming dilute phosphoric acid. The resulting secondary steam passes through the separator 124 and the two-stage fluorine absorber 116 before entering the condenser 126 to be cooled by cooling water.

[0042] (6) Cooling water / intermediate circulating water process: Cooling water enters the condenser 126 to absorb the heat of the secondary steam and then enters the electric heat pump 122. The heat is carried away by the intermediate circulating water, and the condensate is discharged. The intermediate circulating water enters the dilute phosphoric acid preheater 121, transfers the heat to the dilute phosphoric acid, and then returns to the electric heat pump 122, and so on.

[0043] Example Using 99.5% dilute phosphoric acid (containing 260 g / L of phosphoric acid solute, the remainder being water, initial temperature 60℃); fluoride impurities: 0.5% (containing corrosive components such as fluorosilicic acid, requiring corrosion protection); total liquid phase feed rate: 190 m³. 3 / h, target concentration to 48g / L, 80m 3 / h provides an explanation.

[0044] Sulfur is introduced into sulfur burner 101 at a rate of 150 t / h and burned. It combines with oxygen to produce approximately 350 t / h of sulfur trioxide. Then, the sulfur trioxide at 950°C is introduced into waste heat boiler 102 at a rate of 350 t / h. The temperature of the sulfur trioxide drops to 350°C. After passing through air preheater 103, the temperature drops to 150°C. Finally, it is mixed with water in concentrated sulfuric acid preparer 104 to form concentrated sulfuric acid.

[0045] Phosphate ore is crushed and ground in crusher 105 to form phosphate ore powder, which is then mixed with the concentrated sulfuric acid to form a slurry. The slurry is passed through filter 107 at a rate of 600 t / h for sedimentation filtration, and then passes through fine conditioner 111 to form dilute phosphoric acid containing 26 g / L of phosphoric acid solute at 60°C. The dilute phosphoric acid is then discharged at 190 m... 3 Feed rate: / h.

[0046] The dilute phosphoric acid is heated to 76°C via the second heat exchanger 112. The condensate steam entering the second heat exchanger 112 is at 100°C, with a flow rate of 110 t / h, and the condensate steam exiting the second heat exchanger 112 is at 78°C. The demineralized water is then heated from 38°C to 58°C via the demineralized water heater 125, ultimately reducing the condensate steam temperature to 43°C. This process avoids heat waste and achieves a waste heat recovery of 4.6 MW.

[0047] The dilute phosphoric acid then undergoes further heat exchange in the first heat exchanger 113, raising its temperature to 79°C. Meanwhile, the concentrated phosphoric acid introduced into the first heat exchanger 113 is at 100°C and has a temperature of 80m. 3 / h (480g / h), the temperature of concentrated phosphoric acid discharged from the first heat exchanger 113 is 80℃.

[0048] The dilute phosphoric acid then passes through the third heat exchanger 114, where its temperature rises to 80°C. The wastewater entering the third heat exchanger 114 is at 150°C, with a flow rate of 2 t / h. The wastewater exiting the third heat exchanger 114 is at 100°C.

[0049] Dilute phosphoric acid at 80℃ is pre-concentrated in absorption tower 115, yielding pre-concentrated phosphoric acid at 60℃ and 266 g / L. This pre-concentrated phosphoric acid is then applied at a concentration of 186 m³ / L. 3 The phosphoric acid is introduced into the preheater 121 at a temperature of 70°C and then enters the graphite heat exchanger 123 for further concentration, achieving a waste heat recovery of 2.4MW. The total waste heat recovery here is 7MW, equivalent to a steam saving of 10t / h.

[0050] The dilute phosphoric acid in absorption tower 115 comes into direct contact with the humidified air, absorbing heat and moisture to become saturated wet air. This saturated air is then treated by a two-stage fluorine absorber 116 for fluorosilicic acid recovery, and further purified by a gas scrubbing device 117 before entering regeneration tower 118. The humidified air entering regeneration tower 118 is at 75°C and has a humidity of 28,000 Nm³. 3 / h; the humidified air discharged from regeneration tower 118 is 60℃ and 20,000 Nm³. 3 The above process can achieve a reduction of 5t / h in dilute phosphoric acid concentration. Based on the calculation of "1.2t steam to 1t condensate" for a single-effect concentration system, this saves 6t / h of steam.

[0051] Inside regeneration tower 118, purified water, after heat exchange, heats 200 m³ / h of third-wash water from 45℃ to 52.5℃ in one path and 200,000 m³ / h of fresh air from 25℃ to 50℃ in another, recovering a total of 3.7 MW of waste heat and saving 5 t / h of steam. The cooled circulating purified water returns to regeneration tower 118 for recirculation, and the enriched purified water can be used as process water within the plant. Furthermore, compared to the original method of directly heating the third-wash water with steam, which would introduce moisture, this heating method eliminates the need for subsequent concentration, thus saving an additional 3 t / h of steam required for subsequent third-wash water concentration. Therefore, a total of 8 t / h of steam is saved here.

[0052] Steam at 170℃, 400kPa, and 110t / h is introduced into a graphite heat exchanger 123 to exchange heat with dilute phosphoric acid at 70℃ generated by a dilute phosphoric acid preheater 121. The resulting 100℃ steam condensate is then introduced into a second heat exchanger 112. The dilute phosphoric acid then passes through a separator 124 to form 100℃ concentrated phosphoric acid, which is then introduced into a first heat exchanger 113. Simultaneously, the generated secondary steam passes through a secondary fluorine absorber and a condenser 126.

[0053] The operating pressure of the single-effect concentration system is designed to be 105 kPa.a (slight positive pressure), with an operating range of 100-110 kPa.a.

[0054] The cooling water flowing into condenser 126 is 80 t / h (total), with an initial temperature of 32℃ and a temperature rise of less than 8℃. After absorbing heat from the secondary steam through condenser 126, the cooling water enters electric heat pump 122. The heat is carried away by the intermediate circulating water, and then transferred to dilute phosphoric acid before returning to electric heat pump 122, achieving a waste heat recovery of 2.3MW, equivalent to a steam saving of 3 t / h.

[0055] The heat saved in this embodiment is equivalent to 6 + 8 + 10 + 3 = 27 t / h of steam. The circulating heat in this embodiment is 137 t / h of steam heat, which is reduced to 110 t / h of steam consumption through this design. Therefore, the system provided by this embodiment improves energy utilization efficiency by 27 / 137 = 20%.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-grade waste heat utilization system for phosphoric acid production, characterized in that, It includes a single-effect concentration system for concentrating dilute phosphoric acid, a pre-concentration component for pre-concentrating dilute phosphoric acid, a preheating component for preheating the pre-concentrated dilute phosphoric acid, and a circulating humidified air component and a circulating water inlet component for circulating humidified air and purified water, respectively. The circulating humidified air assembly is connected to the pre-concentration assembly and the circulating water inlet assembly, respectively. The pre-concentration component is connected to the single-effect concentration system; simultaneously, the pre-concentration component is connected to the preheating component; the preheating component is connected to the single-effect concentration system. The pre-concentration component includes a heating component that uses steam condensate, concentrated phosphoric acid, and continuous wastewater to heat dilute phosphoric acid, and an absorption tower. The heating component is connected to a single-effect concentration system and the absorption tower. The absorption tower is connected to the preheating component and the circulating humidified air component. The circulating humidified air assembly includes a purification component and a regeneration tower. The absorption tower and the regeneration tower are respectively connected to the purification component, and the regeneration tower is connected to the circulating water inlet assembly. The circulating water intake assembly includes a fourth heat exchanger for heating the third wash water. The inlet of the fourth heat exchanger is connected to the outlet of the regeneration tower, and the outlet of the fourth heat exchanger is connected to the inlet of the regeneration tower.

2. The low-grade waste heat utilization system for phosphoric acid production according to claim 1, characterized in that, The heating assembly includes a second heat exchanger, a first heat exchanger, and a third heat exchanger connected in sequence. The first heat exchanger and the second heat exchanger are respectively connected to the single-effect concentration system, and the third heat exchanger is connected to the feed inlet of the absorption tower.

3. The low-grade waste heat utilization system for phosphoric acid production according to claim 1, characterized in that, The purification assembly includes a two-stage fluorine absorber and a gas scrubbing device. The inlet of the two-stage fluorine absorber is connected to the humidified air outlet of the absorption tower, the outlet of the two-stage fluorine absorber is connected to the inlet of the gas scrubbing device, the outlet of the gas scrubbing device is connected to the humidified air inlet of the regeneration tower, and the humidified air outlet of the regeneration tower is connected to the humidified air inlet of the absorption tower.

4. The low-grade waste heat utilization system for phosphoric acid production according to claim 1, characterized in that, The circulating water intake assembly includes a fresh air heater, the outlet of the regeneration tower is connected to the inlet of the fresh air heater, and the outlet of the fresh air heater is connected to the inlet of the regeneration tower.

5. The low-grade waste heat utilization system for phosphoric acid production according to claim 2, characterized in that, The single-effect concentration system includes a graphite heat exchanger, a separator, and a secondary steam treatment component connected in sequence; the graphite heat exchanger is connected to the second heat exchanger, the separator is connected to the first heat exchanger, and the secondary steam treatment component is connected to the preheating component.

6. The low-grade waste heat utilization system for phosphoric acid production according to claim 5, characterized in that, The secondary steam treatment assembly includes two stages of fluorine absorbers and a condenser connected in sequence. The two stages of fluorine absorbers are connected to the separator, and the condenser is connected to the preheating assembly.

7. The low-grade waste heat utilization system for phosphoric acid production according to claim 6, characterized in that, The preheating assembly includes a dilute phosphoric acid preheater and an electric heat pump connected in sequence. The inlet of the dilute phosphoric acid preheater is connected to the outlet of the absorption tower, the outlet of the dilute phosphoric acid preheater is connected to the graphite heat exchanger, and the electric heat pump is connected to the condenser.

8. The low-grade waste heat utilization system for phosphoric acid production according to claim 2, characterized in that, It also includes a demineralized water heater, which is connected to the second heat exchanger.

9. The low-grade waste heat utilization system for phosphoric acid production according to claim 8, characterized in that, It also includes a concentrated sulfuric acid preparation system and a phosphoric acid preparation system that uses concentrated sulfuric acid to treat phosphate rock. The concentrated sulfuric acid preparation system is connected to the phosphoric acid preparation system. The fourth heat exchanger and the second heat exchanger are respectively connected to the phosphoric acid preparation system. The demineralized water heater is connected to the concentrated sulfuric acid preparation system.

10. The low-grade waste heat utilization system for phosphoric acid production according to claim 9, characterized in that, The concentrated sulfuric acid preparation system includes a sulfur burner, a waste heat boiler, an air preheater, and a concentrated sulfuric acid generator connected in sequence. The concentrated sulfuric acid generator is connected to the phosphoric acid preparation system, and the demineralized water heater is connected to the waste heat boiler. The phosphoric acid preparation system further includes a crusher, a phosphoric acid pulper, a filter, and a three-wash tank connected in sequence. The phosphoric acid pulper is connected to the concentrated sulfuric acid generator, the three-wash tank is connected to the fourth heat exchanger, the filter is connected to the second heat exchanger through a fine adjuster, and the three-wash tank is connected to the phosphoric acid pulper.

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