A system and method for purifying and recycling waste heat and heavy metals from dilute acid liquid

Abstract

The present application relates to copper smelting acid gas purification utilization technical field, including flash tank, waste heat recycling unit and heavy metal recovery processing unit, the flash tank is used for generating flash steam to the dilute acid liquid into the flash tank, the upper side of the flash tank is equipped with flash steam outlet, the waste heat recycling unit is connected with the flash steam outlet, the waste heat recycling unit is used for recycling the heat of flash steam to heat the desalted water, the bottom of the flash tank is equipped with the slag discharge port, the slag discharge port is connected with the heavy metal recovery processing unit, the heavy metal recovery processing unit is used for separating the precipitated heavy metal from the dilute acid liquid, the present application solves how to recycle the waste heat from the purified dilute acid liquid and removes the heavy metal dissolved in the purified dilute acid liquid.

Description

Technical Field

[0001] This invention relates to the field of copper smelting acid production flue gas purification and utilization technology, specifically to a system and method for purifying dilute acid liquid, recovering waste heat, and treating heavy metals. Background Technology

[0002] In addition to SO3, the acid flue gas produced by copper smelting also contains some gaseous and solid harmful impurities. The purpose of flue gas purification is to cool down, remove dust, and remove impurities such as SO3. The washing liquid was originally process water, which becomes a dilute acid with a temperature of 70°C and an acid concentration of 3.5-5% after circulating washing. It contains heavy metals such as arsenic trioxide, sulfur trioxide, carbon monoxide, copper oxide, and zinc oxide.

[0003] To ensure the normal production of sulfuric acid, the temperature of the flue gas exiting the purification system must be below 40°C. Therefore, the only options are to increase the cooling volume of the dilute acid solution or add clean water to lower its temperature. This method of cooling consumes electricity and water. Furthermore, if the cooling is insufficient, some heavy metals may not have reached their crystallization temperature due to the high temperature of the dilute acid solution and may remain in the solution as ions, which increases the difficulty of separating heavy metals from the solution.

[0004] Therefore, the problem in the existing technology is how to recover and utilize the waste heat from the purification of dilute acid solution and remove the heavy metals dissolved in the purification of dilute acid solution. Summary of the Invention

[0005] This invention provides a system and method for recovering and utilizing waste heat from the purification of dilute acid and for recovering and treating heavy metals, aiming to solve the problem of how to achieve the recovery and utilization of waste heat from the purification of dilute acid and the recovery and treatment of heavy metals.

[0006] The technical solution used in this invention is as follows:

[0007] The first aspect of this application proposes a system for recovering and utilizing waste heat from purified dilute acid and for recovering heavy metals, including a flash tank, a waste heat recovery unit, and a heavy metal recovery unit. The flash tank is used to generate flash vapor from the dilute acid entering the flash tank. A flash vapor outlet is provided on the upper side of the flash tank, and the waste heat recovery unit is connected to the flash vapor outlet. The waste heat recovery unit is used to recover and utilize the heat of the flash vapor to heat the demineralized water. A slag discharge port is provided at the bottom of the flash tank, and the slag discharge port is connected to the heavy metal recovery unit. The heavy metal recovery unit is used to separate the precipitated heavy metals from the dilute acid.

[0008] Furthermore, the flash tank has a dilute acid inlet, an exhaust port, and a safety port on its side wall. The dilute acid inlet is connected to one end of a dilute acid delivery pipe, and the other end of the dilute acid delivery pipe is connected to the circulation tank of the primary scrubber for acid purification. A dilute acid delivery pump is installed on the dilute acid delivery pipe. A valve is installed at the input end of the dilute acid delivery pump, and a flow meter and a pressure reducing valve are installed between the output end of the dilute acid delivery pump and the flash tank. The flow meter is used to measure the flow rate of the dilute acid delivery pipe, and the pressure reducing valve is used to reduce the pressure of the dilute acid delivered by the dilute acid delivery pump. The exhaust port is connected to an exhaust pipe, and the other end of the exhaust pipe is connected to the flue gas inlet pipe of the secondary scrubber for acid purification. A vacuum pump is installed on the exhaust pipe. Valves are installed at the input and output ends of the vacuum pump. A safety valve is installed on the safety port.

[0009] Furthermore, a flash reactor is installed at the dilute acid inlet of the flash tank. The flash reactor is made of a circular pipe with openings on all four sides. An L-shaped flash tube is installed on the flash reactor, with one end extending vertically into the interior of the flash reactor and flash nozzles evenly arranged on it. The other end of the flash tube extends from the dilute acid inlet of the flash tank and connects to the pipeline on the pressure reducing valve side. Monitoring devices such as a first pressure gauge, a first thermometer, and a first sampling point are installed sequentially on the flash tube. A vapor-liquid separator and a metal wire mesh drip remover are installed sequentially at the upper part of the interior of the flash tank. A second pressure gauge, a second thermometer, and a second sampling point are installed on the upper side wall of the flash tank.

[0010] Furthermore, the heavy metal recovery and treatment unit includes a plate and frame filter press, with a plate and frame slag-water transfer pump between the filter press and the slag discharge port; the plate and frame filter press is used for dry and wet separation of the slag and liquid discharged from the flash tank; an automatic slag and water discharge valve and a valve are installed on the pipeline between the slag discharge port and the plate and frame slag-water transfer pump; a valve is installed on the pipeline between the plate and frame slag-water transfer pump and the plate and frame filter press; a heavy metal packaging device is installed on the lower side of the plate and frame filter press; the waste liquid output end of the plate and frame filter press is connected to an underground tank, and a dilute acid liquid pump is installed inside the underground tank.

[0011] Furthermore, the waste heat recovery and utilization unit includes a mixing cylinder and a plate heat exchanger; the mixing cylinder is used to mix the waste heat boiler steam and flash steam to form flash mixed steam; the plate heat exchanger is used to exchange heat with the flash mixed steam and demineralized water in a countercurrent manner to heat the demineralized water.

[0012] Furthermore, a flash steam inlet is located on the left side of the mixing cylinder, and a mixed gas outlet is located on the right side. The flash steam inlet is connected to the flash steam outlet via a flash steam inlet pipe, which is equipped with a valve. A mixing port and a mixing safety port are sequentially located on the upper side of the mixing cylinder, with a safety valve connected to the mixing safety port. A third pressure gauge, a third thermometer, and a third sampling point are respectively installed on the upper side of the mixing cylinder. A mixing pipe is connected to the mixing port, with the other end of the mixing pipe connected to the outlet end of the water spray desuperheater. The inlet end of the water spray desuperheater is connected to the boiler steam pipe, and the other end of the boiler steam pipe is used to connect to the external smelting waste heat boiler steam. The spray end of the water spray desuperheater is connected to the demineralized water pipe, and the other end of the demineralized water pipe is used to connect to the external demineralized water. Valves are respectively installed on the boiler steam pipe and the demineralized water pipe.

[0013] Furthermore, the plate heat exchanger has four ports: a flash mixed steam inlet, a flash mixed steam outlet, a demineralized water inlet, and a demineralized water outlet. The flash mixed steam inlet is connected to the mixed gas exhaust port of the mixing cylinder via a mixed steam connecting pipe. A flow meter and valve are installed on the mixed steam connecting pipe. The flash mixed steam outlet is used to connect to an external electrolysis plant. The demineralized water inlet is connected to a demineralized water inlet pipe, the other end of which is used to connect to external demineralized water. The demineralized water outlet is connected to a demineralized water outlet pipe, and valves are installed on both the demineralized water inlet and outlet pipes.

[0014] The second aspect of this application proposes a method for recovering and utilizing waste heat from the purification of dilute acid solution and for treating heavy metals, comprising the following steps.

[0015] Step S1: The pressure inside the flash tank is evacuated to absolute pressure of 8 kPa to maintain a vacuum inside the flash tank; 70°C dilute acid solution is pumped in via a dilute acid solution transfer pump at a rate of 65 m... 3 The volumetric flow rate is 24.5 m / s, which is delivered to the flash tank and sprayed out under reduced pressure. During the spraying process, the dilute acid absorbs most of the heat from the dilute acid and generates "flash steam" with a temperature of 65°C.

[0016] In step S2, after the flash steam is generated, some water droplets are removed through the holes of the flash reactor and then enter the flash tank. The flow rate is reduced to 1.5 m / s, and large water droplets settle directly to the bottom of the flash tank. The larger water droplets are then removed by the steam-water separator and then enter the metal wire mesh drip remover to remove the remaining water droplets. The flash steam is then introduced into the combined steam cylinder through the flash steam outlet.

[0017] In step S3, 65°C flash steam enters the mixing cylinder through the flash steam inlet. At the same time, the waste heat boiler steam from the smelting boiler is de-heated and depressurized by the water spray desuperheater and then enters the mixing cylinder to mix with the flash steam to form flash mixed steam. The temperature of the flash mixed steam is 70°C. The flash mixed steam is discharged through the mixed steam exhaust port.

[0018] In step S4, the flash mixed steam enters the plate heat exchanger through the flash mixed steam inlet plate heat exchanger and exchanges heat countercurrently with the demineralized water from the smelter. After heat exchange, the flash mixed steam is converted, and its temperature drops from 70°C to 45°C, becoming a water-steam mixture. It is then discharged from the flash mixed steam outlet plate heat exchanger and sent to the electrolysis plant for electrolyte distribution. The demineralized water from the copper smelter, at 25°C, is heated to 44.6°C after heat exchange with the flash mixed steam in the plate heat exchanger. It is then discharged from the demineralized water outlet plate heat exchanger and sent to the copper smelter's waste heat boiler to produce medium-pressure saturated steam.

[0019] In step S5, the temperature of the remaining dilute acid solution after flash evaporation drops below 40°C, and it all flows to the bottom of the flash tank. As the temperature of the dilute acid solution decreases, heavy metals precipitate out. At the bottom of the flash tank, it separates into two layers: the upper layer is the dilute acid solution, and the lower layer is a heavy metal compound mainly composed of arsenic trioxide and mineral dust adsorbed in the dilute acid solution. The slag-water mixture is discharged to the plate and frame filter press via the automatic slag discharge valve at the bottom of the flash tank and sent to the plate and frame filter press for dry-wet separation. The slag is sent to the heavy metal packaging device and sealed in multiple layers of heavy metal packaging bags before being partially sold. The dilute acid water flows by gravity to the underground tank and is then pumped by the dilute acid solution pump to the wastewater treatment workshop for harmless treatment. After meeting the discharge standards, it is sent to various branch plants for use as process water.

[0020] The beneficial effects achieved by this invention are as follows:

[0021] The essence of absorbing the residual heat from the flue gas purification of dilute acid liquid and enriching arsenic trioxide and other heavy metals is to send a portion of the acid produced by the flue gas purification of dilute acid liquid to a flash evaporation tank for treatment. The dilute acid liquid, containing hot water at 65-70°C, is rapidly ejected in an absolute pressure environment of 8 kPa inside the flash evaporation tank. Some of the hot water in the dilute acid liquid absorbs heat to generate steam, which is called "flash steam". Because of its low temperature and pressure, when the "flash steam" is used to heat the demineralized water used in boilers, it is necessary to add depressurized boiler steam or other steam to improve the utilization rate of the "flash steam".

[0022] After the purified 70℃ dilute acid solution partially absorbs heat and flashes into "flash vapor," the remaining portion absorbs heat and its temperature drops below 40 degrees Celsius, which is lower than the crystallization temperature required for arsenic trioxide (As2O3) and other oxides and other heavy metals. Therefore, it crystallizes and aggregates with mineral dust, settling at the bottom of the flash tank. It is then sent to a plate and frame filter press for liquid-solid separation, and the solid heavy metal mineral dust is sealed and packaged. Sampling and analysis show that the As2O3 precipitated from the packaged mineral dust has a purity of over 45%, while the content of other heavy metals is very low. The As2O3 is sold to units that use arsenic ore as raw material for further processing or to diplomatic professional units for handling. The dilute acid solution separated by the plate and frame filter press is stored and sent to a sewage treatment plant for harmless treatment. After meeting the discharge standards, it is sent to various workshops for use.

[0023] The copper smelting flue gas is used to produce acid, with a dilute acid solution concentration of 3.5% and a temperature of 70℃. The dilute acid flow rate is 65 m³ / s. 3 / h, capable of converting approximately 25m³ of flash steam 3 The recovered heat energy is equivalent to 126 kg / h of standard coal. Heavy metals can precipitate from dilute sulfuric acid solution, thus being enriched and recovered. For many years, a good technology for recovering and utilizing the waste heat of dilute acid solution in the sulfuric acid production process of copper smelting flue gas has not been developed, which is a problem that has plagued copper smelting sulfuric acid enterprises. This technology uses flash evaporation to produce "flash steam" from the waste heat of the purified flue gas, and then uses the flash steam to heat demineralized water and send it to the smelting boiler to produce steam to drive fans or generate electricity. When flash steam is generated, some water is converted into flash steam, and some dilute acid solution and heavy metals settle at the bottom of the flash evaporator. Due to the cooling of the dilute acid solution, the precipitated heavy metals are of high purity, thus being enriched and reduced in quantity. With the increasing scarcity of energy resources, the waste heat recovery technology in dilute acid solution of flue gas purification is becoming more and more important. It has important social significance for improving the economic efficiency of enterprises, saving energy and reducing emissions, realizing a low-carbon economy, and advancing sulfuric acid production technology. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the waste heat recovery and heavy metal recovery system for the purification of dilute acid liquid of the present invention.

[0025] Figure 2 This is a schematic diagram of the flash tank structure of the present invention. Figure 1 .

[0026] Figure 3 This is a schematic diagram of the flash tank structure of the present invention. Figure 2 .

[0027] Figure 4 This is a schematic diagram of the heavy metal recycling and processing unit of the present invention.

[0028] Figure 5 This is a schematic diagram of the waste heat recovery and utilization unit structure of the present invention. Figure 1 .

[0029] Figure 6 This is a schematic diagram of the waste heat recovery and utilization unit structure of the present invention. Figure 2 .

[0030] In the diagram: 1. Flash tank; 2. Flash steam outlet; 3. Slag discharge port; 4. Dilute acid inlet; 5. Vacuum port; 6. Safety valve; 7. Dilute acid delivery pipe; 8. Dilute acid transport pump; 9. Flow meter; 10. Pressure reducing valve; 11. Vacuum pipe; 12. Vacuum pump; 14. Safety valve; 15. Flash reactor; 16. Flash tube; 17. Flash nozzle; 18. First pressure gauge; 19. First thermometer; 20. Sampling point; 21. Steam-water separator; 22. Metal wire mesh drip remover; 23. Second pressure gauge; 24. Second thermometer; 25. Second sampling point; 26. Plate and frame slag-water transport pump; 27. Plate and frame filter press; 28. Heavy metal bag. 29. Underground tank; 30. Dilute acid submersible pump; 31. Combining cylinder; 32. Plate heat exchanger; 33. Flash steam inlet; 34. Mixed gas exhaust port; 35. Flash steam inlet pipe; 37. Combining port; 38. Combining safety port; 39. Combining pipe; 40. Water spray desuperheater; 41. Boiler steam pipe; 42. Demineralized water pipe; 43. Flash steam mixed gas inlet plate changer; 44. Flash steam mixed gas outlet plate changer; 45. Demineralized water inlet plate changer; 46. Demineralized water outlet plate changer; 47. Mixed steam connecting pipe; 48. Demineralized water inlet pipe; 49. Demineralized water outlet pipe; 50. Third pressure gauge; 51. Third thermometer; 52. Third sampling point. Detailed Implementation

[0031] To facilitate understanding of the present invention by those skilled in the art, specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0032] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood through the specific circumstances.

[0033] First, we will introduce the dilute acid solution discharged from the existing copper smelting flue gas acid purification process.

[0034] Dilute acid flow rate and composition: The acid purification process of copper smelting flue gas uses dilute sulfuric acid solution for adiabatic evaporation and washing to remove impurities and heavy metals from the flue gas; after being washed in the first-stage dynamic wave scrubber, the flue gas enters the subsequent chemical process; part of the dilute acid solution is discharged, and most of the rest is recycled in the dynamic wave scrubber.

[0035] The primary power wave scrubber circulates dilute acid solution containing 92% water, approximately 5% standard acid, and approximately 3% particulate matter at a temperature of 65℃ and a pressure of 0.14MPa. The discharged dilute acid solution flow rate is 65 m³ / h. The main impurities are listed below:

[0036]

[0037] From the composition of impurities in the dilute acid solution listed in the table above, it can be concluded that the content of harmful arsenic is high; after arsenic vaporization, it dissolves in water to form arsenic trioxide; after flash evaporation, the temperature of the dilute acid is below 40 degrees Celsius, and about 28 kg of As2O3 can be precipitated in 24 hours, along with about 50 kg of mineral dust and other heavy metal oxides.

[0038] See Figure 1 This invention provides a system for recovering and utilizing waste heat from purified dilute acid solution and for treating heavy metals. The system includes a flash tank 1, a waste heat recovery unit, and a heavy metal treatment unit. The flash tank 1 is used to generate flash vapor from the dilute acid solution entering the flash tank 1. A flash vapor outlet 2 is provided on the upper side of the flash tank 1, and the waste heat recovery unit is connected to the flash vapor outlet 2. The waste heat recovery unit is used to recover and utilize the heat of the flash vapor to heat the demineralized water. A slag discharge port 3 is provided at the bottom of the flash tank 1, and the slag discharge port 3 is connected to the heavy metal treatment unit. The heavy metal treatment unit is used to separate the precipitated heavy metals from the dilute acid solution.

[0039] Flash evaporator 1 is made of SMO254 material, which can withstand the abrasion of solid suspended matter and high pressure of 1.0 MPa. It is also resistant to corrosion by 3.5–5% dilute sulfuric acid solution. Flash evaporator 1 has an airtight structure, ensuring no deformation at a vacuum level of -98 kPa. Figure 2 As shown, the flash tank 1 has a dilute acid inlet 4, an exhaust port 5, and a safety port 6 on its side wall. The dilute acid inlet 4 is connected to one end of the dilute acid delivery pipe 7, and the other end of the dilute acid delivery pipe 7 is connected to the circulation tank of the first-stage scrubber for acid purification. The dilute acid discharged from the copper smelting flue gas purification process has a temperature of 70℃ and an acid concentration of 3.5-5%, containing heavy metals such as arsenic trioxide, sulfur trioxide, carbon monoxide, copper oxide, and zinc oxide. A dilute acid delivery pump 8 is installed on the dilute acid delivery pipe 7. A valve is installed at the input end of the dilute acid delivery pump 8, and a flow meter 9 is installed between the output end of the dilute acid delivery pump 8 and the flash tank 1. Pressure reducing valve 10; flow meter 9 is used to measure the flow rate of dilute acid liquid conveying pipe 7, and pressure reducing valve 10 is used to reduce the pressure of dilute acid liquid conveyed by dilute acid liquid transport pump 8; air extraction port 5 is connected to air extraction pipe 11, and the other end of air extraction pipe 11 is used to connect to the flue gas inlet pipe of acid purification secondary scrubber; vacuum pump 12 is installed on air extraction pipe 11; valves are respectively installed at the input and output ends of vacuum pump 12; safety valve 14 is installed on safety port 6; safety valve 14 is used to control the internal pressure of flash tank 1 to not exceed the specified value, so as to protect the safe operation of the equipment; when the internal pressure of flash tank exceeds the set safety value, safety valve 14 will automatically open.

[0040] Vacuum pump 12 draws the pressure inside flash tank 1 to absolute pressure of 8 kPa. The extracted gas is sent to the flue gas inlet pipe of the secondary scrubber for acid production purification, maintaining a long-term vacuum inside flash tank 1. After purification, the copper smelting acid production flue gas produces dilute acid. The dilute acid is then transported by dilute acid transport pump 8 to a 65m³ flow rate. 3 The volumetric flow rate of / h passes through flow meter 9 and pressure reducing valve 10, and is then delivered to flash tank 1 for depressurization and spraying. During the spraying process, the dilute acid absorbs most of the heat from the dilute acid and generates flash vapor. The flash vapor is then delivered to the waste heat recovery unit through flash vapor outlet 2. After flash evaporation, part of the dilute acid becomes flash vapor, carrying away most of the heat. The remaining dilute acid cools to below 40°C and flows entirely to...

[0041] At the bottom of the flash tank, due to the decrease in temperature of the dilute acid solution, heavy metals precipitate out of the dilute acid solution. The precipitated heavy metals and dilute acid solution are transported to the heavy metal recovery and treatment unit through the slag discharge port 3.

[0042] like Figure 3 As shown, a flash reactor 15 is provided at the dilute acid inlet 4 of the flash tank 1. The flash reactor 15 is made of a circular pipe with openings on the top, bottom, left, and right sides. An L-shaped flash tube 16 is provided on the flash reactor 15. One end of the flash tube 16 extends vertically into the interior of the flash reactor 15, and five flash nozzles 17 are evenly arranged on it. The other end of the flash tube 16 extends from the dilute acid inlet 4 of the flash tank 1 out of the flash reactor 15 and connects to the pipeline on the side of the pressure reducing valve 10. Monitoring devices such as a first pressure gauge 18, a first thermometer 19, and a first sampling point 20 are arranged sequentially on the flash tube 16. A vapor-liquid separator 21 and a metal wire mesh drip remover 22 are arranged sequentially at the upper end of the interior of the flash tank 1. Monitoring devices such as a second pressure gauge 23, a second thermometer 24, and a second sampling point 25 are arranged on the upper side wall of the flash tank 1.

[0043] The working principle of the flash tank 1 in this invention is as follows: A dilute acid solution at 70°C and with an acid concentration of 3.5-5% is transported by a dilute acid solution transport pump 8, measured by a flow meter 9, and then reduced in pressure by a pressure reducing valve 10 before entering the flash tube 16. It is then sprayed out through five flash nozzles 17 at a flow rate of 24.5 m / s. During the spraying process, the dilute acid solution absorbs most of the heat generated by the dilute acid solution, producing "flash steam." After the flash steam is generated, it enters the flash tank 1 through the holes of the flash reactor 15. The flow rate of the flash steam decreases to 1.5 m / s, and then most of the water droplets are removed by a steam-water separator 21. Afterward, it enters a metal wire mesh drip remover 22 to remove the remaining water droplets, and then exits through the flash steam outlet 2. The flash steam is introduced into the waste heat recovery unit; the flash steam temperature is 65℃, thus carrying a large amount of water droplets; to recover and reuse the flash steam, the water droplets must be removed; this application removes water droplets through a three-part structure: First, small holes are drilled around the flash reactor 15, and when the flash steam passes through the small holes, some water droplets are blocked on the hole wall and flow down the wall to the bottom of the flash tank 1; Second, when the flash steam enters the tank, the flow velocity drops to 1.5m / s, and the water droplet density carried by the flash steam is greater than that of the flash steam, so large water droplets directly settle to the bottom of the flash tank; Third, a steam-water separator 21 is provided in the middle of the flash evaporator to remove slightly larger water droplets; Fourth, a metal wire mesh drip remover 22 is provided at the outlet of the flash tank 1 to remove tiny water droplets.

[0044] The principle behind flash steam formation is as follows: Based on the physical reaction principles of water, when water is heated under atmospheric pressure, 100°C is the highest permissible temperature for liquid water at this pressure. Further heating cannot increase the water's temperature; it only causes the water to transform into a gaseous state—steam. In reality, removing or adding heat before water reaches its boiling point only leads to a change in water temperature, not a phase change. This phenomenon is called the "sensible heat" of saturated water. The heat required to convert saturated water into steam under the same atmospheric pressure is called the "latent heat." Heating water under a certain pressure will raise its boiling point above 100°C, thus requiring more sensible heat. The higher the pressure, the higher the boiling point and the higher the enthalpy. When the pressure decreases, some sensible heat is released, and this excess heat is absorbed as latent heat, causing some water to flash into steam. When water evaporates, the liquid not only absorbs heat but also cools surrounding objects. This is because evaporation absorbs heat from surrounding objects through heat transfer, thereby cooling them. Based on this principle, the pressure of the acid washing dilute acid is reduced by lowering the acid production flue gas pressure, causing the washing dilute acid to release some sensible heat. This heat is then absorbed by the dilute acid in the evaporator in the form of latent heat and "flash evaporates" to form flash steam. The "flash steam" is used to heat the demineralized water, which also lowers the temperature of the remaining dilute acid liquid.

[0045] The bottom of the heavy metal recovery and treatment unit and the flash tank 1 is equipped with a slag discharge port 3; such as Figure 4The slag discharge port 3 shown is connected to the plate and frame filter press 27 via the plate and frame slag-water transfer pump 26. The plate and frame filter press 27 is used for dry and wet separation of the slag and liquid discharged from the flash tank 1. An automatic slag discharge water valve and a valve are installed on the pipeline between the slag discharge port 3 and the plate and frame slag-water transfer pump 26. A valve is also installed on the pipeline between the plate and frame slag-water transfer pump 26 and the plate and frame filter press 27. A heavy metal packaging device 28 is installed on the lower side of the plate and frame filter press 27. The plate and frame filter press 27 separates... The solid impurities contain heavy metals, which are packaged in a leak-proof manner by the heavy metal packaging device 28 and transported to the warehouse for storage. They can be sold as raw materials for deep processing of arsenic. The waste liquid output end of the plate and frame filter press 27 is connected to the underground tank 29. The underground tank 29 is equipped with a dilute acid pump 30. The liquid waste separated by the plate and frame filter press 27 flows into the water receiving pan of the plate and frame filter press 27 and flows by gravity from the water receiving pan to the underground tank 29. It is then sent to the sewage treatment workshop for harmless treatment by the dilute acid pump 30.

[0046] The heavy metal recovery and treatment unit operates on the following principle: after flash evaporation, part of the dilute acid solution is converted into flash vapor, carrying away most of the heat. The remaining dilute acid solution cools to below 40°C and flows entirely to the bottom of flash tank 1. Due to the decrease in temperature, heavy metals precipitate out of the dilute acid solution. At the bottom of the flash tank, the solution is divided into two layers: the upper layer is the dilute acid solution, and the lower layer contains heavy metal compounds, mainly arsenic trioxide, and mineral dust adsorbed in the dilute acid solution. The slag-water mixture is discharged to the plate and frame slag-water transfer pump 26 through the automatic slag discharge valve at the bottom of the flash tank, and then sent to the plate and frame filter press 27 for dry and wet separation. The slag enters the heavy metal packaging device 28, and after being sealed in multiple layers of heavy metal packaging bags, some is sold externally or sent to professional institutions for treatment. The dilute acid water flows by gravity to the underground tank 29, and is then transported by the dilute acid solution pump 30 to the wastewater treatment workshop for harmless treatment. After meeting the discharge standards, it is sent to various branch plants for use as process water.

[0047] The waste heat recovery and utilization unit includes a combined cylinder 31 and a plate heat exchanger 32; such as Figure 5As shown, the mixing cylinder 31 has a flash steam inlet 33 on the left side and a mixed gas exhaust port 34 on the right side. The flash steam inlet 33 is connected to the flash steam outlet 2 via a flash steam inlet pipe 35, which is equipped with a valve. The upper side of the mixing cylinder 31 has a mixing port 37 and a mixing safety port 38, with a safety valve 14 connected to the mixing safety port 38. The mixing cylinder 31 is a pressure vessel, and according to safety requirements, a third pressure gauge 50, a third thermometer 51, and a third sampling point 52 are respectively installed on the upper side of the mixing cylinder for monitoring the mixing cylinder. Internal monitoring is performed on 31; a gas mixing pipe 39 is connected to the gas mixing port 37, the other end of the gas mixing pipe 39 is connected to the outlet end of the water spray desuperheater 40, the inlet end of the water spray desuperheater 40 is connected to the boiler steam pipe 41, the other end of the boiler steam pipe 41 is used to connect to the external smelting waste heat boiler steam, the spray end of the water spray desuperheater 40 is connected to the demineralized water pipe 42, the other end of the demineralized water pipe 42 is used to connect to the external demineralized water; valves are respectively provided on the boiler steam pipe 41 and the demineralized water pipe 42; the opening and closing of the boiler steam pipe 41 and the demineralized water pipe 42 are controlled by the valves.

[0048] The working principle of the mixing cylinder 31 in this invention is as follows: 65°C flash steam enters the mixing cylinder 31 through the flash steam inlet 33. At the same time, the waste heat boiler steam from the smelting boiler is de-cooled and depressurized by the water spray desuperheater 40 and then enters the mixing cylinder 31 to mix with the flash steam to form flash steam mixture. The temperature of the flash steam mixture is 70°C. The flash steam mixture is discharged through the mixed gas outlet 34. This improves the quality of the flash steam and allows the flash evaporator to play a greater role.

[0049] Because the flash steam carries sulfuric acid, it cannot be used directly; the flash steam must be pressurized. The steam pressure of the smelting waste heat boiler is high, and if it is too high, the flash steam device cannot operate; the steam of the smelting waste heat boiler is cooled by the water spray desuperheater 40.

[0050] like Figure 6 As shown, the plate heat exchanger 32 has four ports: flash mixed steam inlet 43, flash mixed steam outlet 44, demineralized water inlet 45, and demineralized water outlet 46. Flash mixed steam inlet 43 is connected to the mixed gas exhaust port 34 of the mixing cylinder 31 via a mixed steam connecting pipe 47. A flow meter 9 and a valve are installed on the mixed steam connecting pipe 47. Flash mixed steam outlet 44 is used to connect to an external electrolysis plant. Demineralized water inlet 45 is connected to a demineralized water inlet pipe 48, the other end of which is used to connect to external demineralized water at 25°C. Demineralized water outlet 46 is connected to a demineralized water outlet pipe 49, and valves are installed on both the demineralized water inlet pipe 48 and the demineralized water outlet pipe 49.

[0051] The working principle of the plate heat exchanger 32 in this invention is as follows: the flash mixed steam enters the plate heat exchanger 32 through the flash mixed steam inlet plate heat exchanger 43 and exchanges heat countercurrently with the demineralized water sent from the smelter; after heat exchange, the flash mixed steam is converted, and the temperature drops from 70°C to 45°C, converting into a water-steam mixture, which is discharged from the flash mixed steam outlet plate heat exchanger 44 and sent to the electrolysis plant for electrolyte distribution; the 25°C demineralized water sent from the copper smelter is heated to 44.6°C after exchanging heat with the flash mixed steam in the plate heat exchanger 32, and is discharged through the demineralized water outlet plate heat exchanger 46 and sent to the waste heat boiler of the copper smelter to produce medium-pressure saturated steam.

[0052] The second aspect of this application proposes a method for recovering and utilizing waste heat from the purification of dilute acid solution and for treating heavy metals, comprising the following steps.

[0053] Step S1: The pressure inside flash tank 1 is evacuated to absolute pressure of 8 kPa to maintain a vacuum inside flash tank 1; 70°C dilute acid solution is pumped through dilute acid solution transfer pump 8 at a speed of 65 m... 3 The volumetric flow rate is 24.5 m / s, which is delivered to flash tank 1 and sprayed out under reduced pressure. During the spraying process, the dilute acid absorbs most of the heat from the dilute acid and generates "flash steam" with a temperature of 65°C.

[0054] In step S2, after flash steam is generated, some water droplets are removed through the holes of flash reactor 15, and then it enters the flash tank 1. The flow rate is reduced to 1.5 m / s, and large water droplets settle directly to the bottom of flash tank 1. Then, the slightly larger water droplets are removed by steam-water separator 21, and then the remaining water droplets are removed by metal wire mesh drip remover 22. Finally, the flash steam is introduced into the combined steam cylinder 31 through flash steam outlet 2.

[0055] In step S3, 65°C flash steam enters the mixing cylinder 31 through flash steam inlet 33. At the same time, the waste heat boiler steam from the smelting boiler is de-heated and depressurized by the water spray desuperheater 40 and enters the mixing cylinder 31 to mix with the flash steam to form flash mixed steam. The temperature of the flash mixed steam is 70°C. The flash mixed steam is discharged through the mixed steam exhaust port 34.

[0056] In step S4, the flash mixed steam enters the plate heat exchanger 32 through the flash mixed steam inlet plate heat exchanger 43, where it exchanges heat countercurrently with the demineralized water from the smelter. After heat exchange, the flash mixed steam is converted, and its temperature drops from 70°C to 45°C, becoming a water-steam mixture. It is then discharged from the flash mixed steam outlet plate heat exchanger 44 and sent to the electrolysis plant for electrolyte distribution. The 25°C demineralized water from the copper smelter is heated to 44.6°C after exchanging heat with the flash mixed steam in the plate heat exchanger 32. It is then discharged through the demineralized water outlet plate heat exchanger 46 and sent to the copper smelter's waste heat boiler to produce medium-pressure saturated steam.

[0057] In step S5, the temperature of the remaining dilute acid solution after flash evaporation drops below 40°C and flows entirely to the bottom of flash tank 1. As the temperature of the dilute acid solution decreases, heavy metals precipitate out. At the bottom of the flash tank, the solution is divided into two layers: the upper layer is the dilute acid solution, and the lower layer contains heavy metal compounds, mainly arsenic trioxide, and mineral dust adsorbed in the dilute acid solution. The slag-water mixture is discharged to the plate and frame slag-water transfer pump 26 through the automatic slag discharge valve at the bottom of the flash tank and sent to the plate and frame filter press 27 for dry-wet separation. The slag is fed into the heavy metal packaging device 28 and partially sold after being sealed in multiple layers of heavy metal packaging bags. The dilute acid water flows by gravity to the underground tank 29 and is then transported by the dilute acid solution pump 30 to the wastewater treatment workshop for harmless treatment. After meeting the discharge standards, it is sent to various branch plants for use as process water.

[0058] The table below shows the parameters for acid production, purification of dilute acid solution, and demineralization in this application.

[0059]

[0060] Effects Introduction

[0061] This system brings significant economic benefits to acid production enterprises and will also bring about groundbreaking changes to the acid production industry.

[0062] The following is an example of the economic and social benefits of recovering waste heat from the purification system of an 850,000-ton-per-year flue gas acid production plant: The first-stage scrubbing tower discharges 65m³ of dilute acid liquid. 3 / h, temperature 65℃, 25m of dilute acid solution converted into flash vapor by flash evaporation 3 / h, flash steam will be at 25℃, 45m 3 Heating the demineralized water to 44.6℃ per hour is equivalent to recovering 882,000 kcal of thermal energy.

[0063] Based on the above data, the calculation is as follows:

[0064] 1. A 3.5% dilute acid solution flash evaporates to 25m 3 The dilute acid solution is converted into flash steam for recycling. This part of the dilute acid solution is no longer neutralized with carbide slag. The annual reduction in carbide slag consumption is 0.047 * 25 * 24 * 330 = 9306 t. The unit price of carbide slag is 100 yuan / t, so the total cost is 9306 * 100 / 10000 = 930,000 yuan.

[0065] 2. This results in 198,000 tons less 3.5% dilute acid solution being processed annually, and 26,000 tons less hazardous waste neutralization residue being produced. The cost of removing 50% water content is 26,000 * 0.5 * 500 (treatment cost) = 6.5 million yuan.

[0066] 3. Flash steam will reach 45m 3The demineralized water is heated from 25℃ to 44.6℃ per hour. The required standard coal equivalent per year (330 days) is 45 * 1000 * 1 * 19.6 / 7000 * 24 * 330 / 1000 = 997.92 tons. The breakdown price is 449,000 yuan.

[0067] The total of the above three transactions is 44.9 + 650 + 93 = 787.9 million yuan per year.

[0068] 4. Reduce carbon emissions by 997.92 tons of standard coal per year, reduce and enrich heavy metals, reduce storage, and sell high-purity arsenic trioxide as a raw material for production using arsenic as a raw material.

[0069] The following points need to be explained:

[0070] (1) The accompanying drawings of the embodiments of the present invention only involve the structures involved in the embodiments of the present invention. Other structures can refer to the general design.

[0071] (2) For clarity, the thickness of layers or regions is enlarged or reduced in the drawings used to describe embodiments of the invention; that is, these drawings are not drawn to scale. It is understood that when an element such as a layer, film, region, or substrate is referred to as being “above” or “below” another element, the element may be “directly” located “above” or “below” the other element, or there may be intermediate elements.

[0072] (3) Where there is no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to obtain new embodiments.

[0073] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A system for recovering and utilizing waste heat from the purification of dilute acid solution and for the recovery and treatment of heavy metals, characterized in that, The system includes a flash tank (1), a waste heat recovery unit, and a heavy metal recovery and treatment unit. The flash tank (1) is used to generate flash vapor from the dilute acid solution entering the flash tank (1). A flash vapor outlet (2) is provided on the upper side of the flash tank (1), and the waste heat recovery and treatment unit is connected to the flash vapor outlet (2). The waste heat recovery and treatment unit is used to recover and utilize the heat of the flash vapor to heat the demineralized water. A slag discharge port (3) is provided at the bottom of the flash tank (1), and the slag discharge port (3) is connected to the heavy metal recovery and treatment unit. The heavy metal recovery and treatment unit is used to separate the precipitated heavy metals from the dilute acid solution. The flash tank (1) is equipped with a flash reactor (15) at the dilute acid inlet (4). The upper part of the flash tank (1) is equipped with a steam-water separator (21) and a metal wire mesh drip remover (22) in sequence. The waste heat recovery unit includes a mixing cylinder (31) and a plate heat exchanger (32). The mixing cylinder (31) is used to mix the waste heat boiler steam and flash steam to form a flash mixed steam. The plate heat exchanger (32) is used to exchange heat with the flash mixed steam and demineralized water in a countercurrent manner to heat the demineralized water. The mixing cylinder (31) is equipped with a flash steam inlet on the left side. 33), the right side of the mixing cylinder (31) is provided with a mixed gas exhaust port (34); the flash steam inlet (33) is connected to the flash steam outlet (2) through the flash steam inlet pipe (35), and a valve is provided on the flash steam inlet pipe (35); the upper side of the mixing cylinder (31) is provided with a mixing port (37) and a mixing safety port (38), and a safety valve (14) is connected to the mixing safety port (38); the upper side of the mixing cylinder (31) is provided with a third pressure gauge (50), a third thermometer (51), and a third sampling point (52); the bottom of the mixing cylinder (31) It has a drain outlet; a gas pipe (39) is connected to the gas inlet (37), the other end of the gas pipe (39) is connected to the outlet end of the water spray desuperheater (40), the inlet end of the water spray desuperheater (40) is connected to the boiler steam pipe (41), the other end of the boiler steam pipe (41) is used to connect with the external smelting waste heat boiler steam, the spray end of the water spray desuperheater (40) is connected to the demineralized water pipe (42), the other end of the demineralized water pipe (42) is used to connect with the external demineralized water; valves are respectively provided on the boiler steam pipe (41) and the demineralized water pipe (42).

2. The system for purifying dilute acid liquid and recovering waste heat and heavy metals according to claim 1, characterized in that, The flash tank (1) has a dilute acid inlet (4), an exhaust port (5), and a safety port (6) on its side wall. The dilute acid inlet (4) is connected to one end of the dilute acid delivery pipe (7), and the other end of the dilute acid delivery pipe (7) is used to connect to the circulation tank of the first-stage acid purification scrubber. A dilute acid transport pump (8) is installed on the dilute acid delivery pipe (7). A valve is installed at the input end of the dilute acid transport pump (8), and a flow meter (9) is installed between the output end of the dilute acid transport pump (8) and the flash tank (1). Pressure reducing valve (10); flow meter (9) is used to measure the flow rate of dilute acid liquid delivery pipe (7), and pressure reducing valve (10) is used to reduce the pressure of dilute acid liquid delivered by dilute acid liquid delivery pump (8); air extraction port (5) is connected to air extraction pipe (11), and the other end of air extraction pipe (11) is used to connect to the flue gas inlet pipe of acid purification secondary scrubber; vacuum pump (12) is provided on air extraction pipe (11); valves are provided at the input end and the output end of vacuum pump (12); safety valve (14) is provided on safety port (6).

3. The system for waste heat recovery and heavy metal recovery of purified dilute acid liquid according to claim 2, characterized in that, The flash reactor (15) is made of a circular pipe with openings on the top, bottom, left and right sides. An L-shaped flash tube (16) is provided on the flash reactor (15). One end of the flash tube (16) extends vertically into the interior of the flash reactor (15), and flash nozzles (17) are evenly arranged on it. The other end of the flash tube (16) extends from the dilute acid inlet (4) of the flash tank (1) and connects to the pipeline on the side of the flash reactor (15) and the pressure reducing valve (10). A first pressure gauge (18), a first thermometer (19), and a first sampling point (20) are arranged on the flash tube (16) in sequence. A second pressure gauge (23), a second thermometer (24), and a second sampling point (25) are arranged on the upper side wall of the flash tank (1).

4. The system for purifying dilute acid liquid and recovering waste heat and heavy metals according to claim 1, characterized in that, The heavy metal recycling unit includes a plate and frame filter press (27), and a plate and frame slag water conveying pump (26) is provided between the plate and frame filter press (27) and the slag discharge port (3); the plate and frame filter press (27) is used to perform dry and wet separation of the slag liquid discharged from the flash tank (1); an automatic slag water discharge valve and a valve are provided on the pipeline between the slag discharge port (3) and the plate and frame slag water conveying pump (26); a valve is provided on the pipeline between the plate and frame slag water conveying pump (26) and the plate and frame filter press (27); a heavy metal packaging device (28) is provided on the lower side of the plate and frame filter press (27); the waste liquid output end of the plate and frame filter press (27) is connected to the underground tank (29), and a dilute acid liquid pump (30) is provided inside the underground tank (29).

5. The system for purifying dilute acid liquid and recovering waste heat and heavy metals according to claim 1, characterized in that, The plate heat exchanger (32) has four ports: flash mixed steam inlet (43), flash mixed steam outlet (44), demineralized water inlet (45), and demineralized water outlet (46). The flash mixed steam inlet (43) is connected to the mixed gas exhaust port (34) of the mixing cylinder (31) via a mixed steam connecting pipe (47). A flow meter (9) and a valve are provided on the mixed steam connecting pipe (47). The flash mixed steam outlet (44) is used to connect to an external electrolysis plant. The demineralized water inlet (45) is connected to the demineralized water inlet pipe (48), and the other end of the demineralized water inlet pipe (48) is used to connect to external demineralized water. The demineralized water outlet (46) is connected to the demineralized water outlet pipe (49), and valves are provided on the demineralized water inlet pipe (48) and the demineralized water outlet pipe (49), respectively.

6. A method for recovering and utilizing waste heat from the purification of dilute acid solution and for recovering heavy metals, characterized in that, Includes the following steps, Step S1: The pressure inside the flash tank (1) is evacuated to absolute pressure of 8 kPa to maintain a vacuum inside the flash tank (1); 70°C dilute acid solution is pumped through the dilute acid solution transfer pump (8) at a speed of 65 m... 3 The volumetric flow rate of / h is delivered to the flash tank (1) and sprayed out under reduced pressure at a flow rate of 24.5m / s. During the spraying process, the dilute acid absorbs most of the heat brought by the dilute acid and generates "flash steam" with a temperature of 65℃. In step S2, after the flash steam is generated, some water droplets are removed through the holes of the flash reactor (15) and then enter the flash tank (1). The flow rate drops to 1.5 m / s, and large water droplets settle directly to the bottom of the flash tank (1). The larger water droplets are then removed by the steam-water separator (21) and then enter the metal wire mesh drip remover (22) to remove the remaining water droplets. The remaining water droplets are then introduced into the combined steam cylinder (31) through the flash steam outlet (2). In step S3, 65°C flash steam enters the combined steam cylinder (31) through the flash steam inlet (33). At the same time, the waste heat boiler steam from the smelting boiler enters the combined steam cylinder (31) after being de-cooled and depressurized by the water spray desuperheater (40) and mixes with the flash steam to form flash mixed steam. The temperature of the flash mixed steam is 70°C. The flash mixed steam is discharged through the mixed steam exhaust port (34). In step S4, the flash mixed steam enters the plate heat exchanger (32) through the flash mixed steam inlet plate heat exchanger (43) and exchanges heat countercurrently with the demineralized water sent from the smelter. After heat exchange, the flash mixed steam is converted and its temperature drops from 70°C to 45°C, becoming a water-steam mixture. It is discharged from the flash mixed steam outlet plate heat exchanger (44) and sent to the electrolysis plant for electrolyte distribution. The 25°C demineralized water sent from the copper smelter is heated to 44.6°C after exchanging heat with the flash mixed steam in the plate heat exchanger (32). It is discharged through the demineralized water outlet plate heat exchanger (46) and sent to the waste heat boiler of the copper smelter to produce medium-pressure saturated steam. Step S5: The temperature of the remaining dilute acid solution after flash evaporation drops below 40°C and flows to the bottom of the flash tank (1). As the temperature of the dilute acid solution decreases, heavy metals precipitate out. The solution is divided into two layers at the bottom of the flash tank: the upper layer is the dilute acid solution, and the lower layer is a heavy metal compound mainly composed of arsenic trioxide and mineral dust adsorbed in the dilute acid solution. The slag-water mixture is discharged to the plate and frame slag-water transfer pump (26) through the automatic slag discharge valve at the bottom of the flash tank and sent to the plate and frame filter press (27) for dry and wet separation. The slag is sent to the heavy metal packaging device (28) and partially sold after being sealed in multiple layers of heavy metal packaging bags. The dilute acid water flows by gravity to the underground tank (29) and is transported by the dilute acid solution pump (30) to the sewage treatment workshop for harmless treatment. After reaching the discharge standard, it is sent to each branch plant for use as process water.

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