Low-energy-consumption waste acid recycling method

Abstract

The invention relates to the field of industrial production waste liquid treatment, and particularly provides a low-energy-consumption waste acid recycling method. The main process comprises the steps of pretreatment, ultrafiltration, resin adsorption and membrane distillation. Impurities such as oil in the waste acid raw material are removed in the pretreatment link; sS, foam and the like in the waste acid are removed in the ultrafiltration link; impurities such as heavy metals in the waste acid are removed in the resin adsorption link; in the membrane distillation link, a hydrophobic membrane is used as a filtering medium, the steam pressure difference on the two sides of the membrane is used as mass transfer driving force, under the heating condition, water molecules in the raw material liquid are evaporated into water vapor penetrating through the membrane, the solution cannot penetrate through the membrane, the raw material is concentrated along with continuous evaporation of the water molecules, the purpose of concentrating the material liquid is achieved, and waste acid recovery is achieved. According to the method, waste acid is recycled, waste heat of the system is recycled, and the whole technological process is simple, low in operation cost, stable in operation and high in automation degree.

Description

Technical Field

[0001] The invention relates to the field of industrial production waste liquid treatment, and specifically provides a low-energy consumption waste acid recovery and utilization method. Background Art

[0002] In industrial production, waste acid is generated in the processes of nitration, esterification, sulfonation, alkylation, catalysis and gas drying of organic matter, or in the processes of titanium dioxide production, steel pickling and gas drying. The main types of waste acid include waste sulfuric acid, waste nitric acid, waste phosphoric acid, waste hydrofluoric acid, etc., among which waste sulfuric acid accounts for the vast majority of emissions.

[0003] At present, China's annual waste acid production is about 100 million tons, of which waste sulfuric acid accounts for 95.2%, waste hydrochloric acid, waste nitric acid, waste phosphoric acid, and waste chlorofluoric acid account for 3.5%, 0.9%, 0.3%, and 0.2%, respectively. From the source of waste acid output, the main industries that produce waste acid are the titanium dioxide industry, non-ferrous metal smelting industry, and steel industry, with waste acid output accounting for 28.2%, 12.3%, and 10.8%, respectively.

[0004] There are two main methods for disposing of waste acid. One is the neutralization method, which is also the most commonly used method at present. That is, the waste acid is neutralized with lime, carbide slag and slaked lime. The pH value of the treated waste liquid can meet the requirements, but a large amount of mud will be produced after the neutralization treatment, and a large amount of heavy metal ions will remain in the waste liquid, which is easy to cause secondary pollution. The second is the recovery of waste acid. Common treatment processes include high-temperature cracking regeneration, high-temperature concentration, membrane separation, spray roasting, extraction, etc. In 2019, China's waste acid recovery volume was about 36.58 million tons, and the waste acid recovery rate was about 36%. With the continuous improvement of environmental protection policies and the improvement of waste acid recovery mechanisms, my country's waste acid recovery volume will continue to maintain a growth trend. It is predicted that my country's waste acid recovery volume will exceed 42 million tons in 2025.

[0005] Acid recovery has both economic and social benefits while producing environmental benefits. However, traditional acid recovery methods have long process flows, high energy consumption, and even produce secondary pollution. Therefore, innovation in acid recovery technology is essential.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a low-energy consumption waste acid recovery and utilization method.

[0008] In order to achieve the above object, the present invention particularly adopts the following technical solutions:

[0009] A low-energy consumption waste acid recovery and utilization method comprises the following steps:

[0010] (1) Feed: The amount of waste acid raw material entering the pretreatment system is regulated by a feed pump.

[0011] (2) Pretreatment: The pretreatment adopts flotation to remove oil impurities and a small amount of organic matter in the waste acid raw materials through the flotation device.

[0012] (3) Ultrafiltration: Ultrafiltration uses hollow fiber membranes to remove solid impurities and foam from waste acid raw materials through the interception effect of hollow fiber membranes.

[0013] (4) Resin adsorption: After the waste acid is adsorbed by the resin, the heavy metal cations remain on the adsorption column, and the column liquid enters the membrane distillation system. After the resin adsorption is saturated, the adsorption column is regenerated, and the regenerated liquid returns to the front-end pre-treatment flotation device.

[0014] (5) Membrane distillation: A hydrophobic membrane is used as the filter medium. Under heating, the water molecules in the waste acid raw material evaporate and become water vapor. The water vapor pressure difference on both sides of the hydrophobic membrane is used as the driving force for mass transfer. Water vapor passes through the hydrophobic membrane, but the waste acid cannot. As the water molecules continue to evaporate, the waste acid raw material becomes concentrated. The waste acid raw material is sequentially subjected to at least one membrane distillation effect. The water vapor in each effect is cooled to obtain distilled water. The water vapor generated in the previous effect is used as the heating source for the waste acid in the next effect. This effect is taken as the last effect when the temperature of the waste acid drops to 50°C.

[0015] (6) Discharging: After the waste acid is concentrated, it is introduced into a discharging box to achieve the concentration of the waste acid raw materials.

[0016] Furthermore, in step (1), the material of the feed box is PE, PP or fiberglass, and the hydraulic retention time of the feed box is 1 to 5 hours.

[0017] Furthermore, in step (2), the flotation device is a pressure dissolved air flotation device with a surface load of 2 to 3 m 3 / m 2 ·h, the dissolved gas pressure is 0.6~0.7MPa, and the diameter of the bubbles released by the releaser is 10~50μm.

[0018] Furthermore, in step (3), the membrane material of the hollow fiber membrane is PVDF, the filtration method is external pressure type, the filtration pore size is 0.02-0.04 μm, the inner and outer diameters of the membrane are 0.7 / 1.3 mm, and the average flux is ≤60 L / (m 2 ·h), the system runs for 30 minutes, backwashes for 2 minutes, and the average backwash flux is 100-120L / (m 2 h).

[0019] Furthermore, in step (4), the adsorbent model of the resin adsorption filling is CH-90Na, the working flow rate is 10BV / H, and the saturated adsorption capacity is about 50g / L.

[0020] Preferably, when the adsorption is saturated, it is first analyzed with a hydrochloric acid solution, then backwashed with pure water or soft water, and finally transformed with sodium hydroxide.

[0021] Preferably, first use 5% hydrochloric acid solution for analysis at a flow rate of 4-5BV / H for 30-45min, then use pure water or soft water for backwashing at a backwash flow rate of 5-10BV / H for 30min, and finally use 5% sodium hydroxide solution for transformation at a transformation flow rate of 4-5BV / H for 30min.

[0022] Furthermore, in step (5), each effect of the membrane distillation is composed of a membrane assembly, one side of the membrane assembly is provided with the hydrophobic membrane for separating the waste acid from water, and the other side is provided with a condenser for condensing the water vapor transmitted by the hydrophobic membrane, and the waste acid is located on the side of the hydrophobic membrane away from the condenser.

[0023] Furthermore, the membrane module is optionally vacuumed.

[0024] Furthermore, the cold side of the condensing plate of the last effect is cooling water, and the hot side is distilled water formed by cooling the water vapor passing through the hydrophobic membrane with cooling water. The maximum temperature of the cooling water in the last effect is 30°C, and the negative pressure value of the cavity in the membrane assembly of the last effect is not higher than -0.2atm, preferably -0.3 to -0.2atm.

[0025] Furthermore, the temperature difference of the waste acid between two adjacent effects is 8-12°C, the total number of membrane distillation effects is preferably 2-6, and the pressure value of the membrane component cavity of each effect is equal to the saturated vapor pressure value corresponding to the waste acid temperature in this effect.

[0026] Furthermore, the hydrophobic membrane is a polytetrafluoroethylene membrane, and the double-sided surfaces of the polytetrafluoroethylene membrane are hydrophobized to prepare a super-hydrophobic nanowire coating, maintaining a contact angle θ in the range of 70°<θ<150°, and a sliding angle less than 10°, a membrane pore size of 0.2-0.4μm, and a thickness of 0.06-0.25mm.

[0027] Furthermore, the condensing sheet is an aluminum plate with an acid-resistant coating on the surface, the thickness of the aluminum plate is 0.06 to 0.25 mm, and the acid-resistant coating is a SiO2-TiO2-PDMS hybrid acid-resistant coating, wherein the mass ratio of SiO2-TiO2 is (0.05 to 0.25): 1, and the mass fraction of PDMS is 15%.

[0028] Preferably, the hot side surface of the condenser sheet is provided with a super hydrophobic fluorinated coating.

[0029] Furthermore, the vertical distance between the hydrophobic membrane and the condensing sheet which are arranged in parallel is 0.2 to 0.4 mm.

[0030] Preferably, the sealing material of the membrane assembly is a corrosion-resistant rubber product.

[0031] Furthermore, in step (6), the material of the discharge box is PE, PP or fiberglass, and the hydraulic retention time of the discharge box is 1 to 5 hours.

[0032] Compared with the prior art, the technical effects of the present invention are:

[0033] The low-energy consumption waste acid recycling method provided by the present invention has a short process flow and is safe and reliable. The core unit of the entire treatment process is membrane distillation, which is supplemented by pretreatment, ultrafiltration and resin processes. Whether it is membrane distillation or flotation in pretreatment, or ultrafiltration and resin adsorption, they are all mature and stable processes, and have low operating temperatures, simple equipment and convenient operation, so the recycling method is simple, stable and reliable.

[0034] The membrane distillation of the present invention also provides waste heat recovery, and the steam generated in the previous effect can be used as the heat source of the next effect for further evaporation and concentration. The number of effects can usually reach 2 to 6, which can greatly save the energy consumption of waste acid recovery. The power consumption of recovering one ton of acid is 2 to 10 kWh, and the steam consumption is 0 to 0.4 t.

[0035] The membrane distillation process of the present invention does not need to heat the solution to the boiling point (100°C), as long as the appropriate temperature and pressure differences are maintained on both sides of the membrane, it can be carried out. Therefore, cheap energy such as solar energy, geothermal energy, hot springs, factory waste heat or residual heat can be used to greatly reduce the energy consumption of operation.

[0036] The process of the present invention is clean and hygienic, and does not generate secondary pollution. The backwash water of the ultrafiltration and the regeneration liquid of the resin are returned to the flotation device. The membrane distillation has good sealing performance and low operating temperature due to its special hydrophobic membrane and cooling plate alternately arranged. The generated water vapor is condensed into distilled water. The whole process does not generate secondary polluting gas, waste liquid or waste residue.

[0037] In the membrane distillation process of the present invention, since only water vapor can pass through the membrane pores, the distilled water is very pure and can be recycled as pure water or even ultrapure water, which not only saves water resource consumption but also creates economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 It is a process flow chart of the waste acid recovery and utilization method of the present invention;

[0040] Figure 2 It is a schematic diagram of the membrane distillation principle of the present invention. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The low-energy consumption waste acid recycling method provided by the present invention has a process flow as follows: Figure 1 As shown, the waste acid enters the flotation device of the pretreatment stage through the adjustment of the feed box to remove oil impurities and a small amount of organic matter. Then it enters the ultrafiltration stage to remove solid impurities and foam. Then it enters the resin adsorption stage to remove heavy metal cation impurities. Then it enters the membrane distillation stage to achieve the concentration of the waste acid raw materials. After the waste acid raw materials are concentrated by the membrane distillation stage, when the temperature reaches about 50°C, they are discharged through the discharge box for industrial purposes such as drying to achieve the recycling of acid liquid.

[0043] For the membrane distillation process, its specific principle is as follows Figure 2 As shown, membrane distillation may contain a multi-effect distillation process. For example, the waste acid raw material enters the first effect, and after being heated by a heat source, the water molecules in the waste acid raw material evaporate into water vapor. A water vapor pressure difference is generated in this space and the cavity formed by the diaphragm (i.e., hydrophobic membrane) and the condenser, so that the water vapor enters the cavity through the diaphragm, and the waste acid solution cannot pass through the membrane, thereby achieving the purpose of concentrating the waste acid. Then, the waste acid concentrated in the first effect can enter the second effect, and the water vapor in the cavity of the first effect can transfer heat to the second effect through the condenser, serving as a heat source for the waste acid water molecules in the second effect to evaporate into water vapor, thereby realizing the recycling of waste heat. At the same time, the water vapor in the cavity of the first effect releases heat and becomes distilled water for recycling. In the second effect, further concentration of the waste acid is achieved according to a process similar to the first effect. By analogy, until the temperature of the waste acid after the multi-effect is about 50°C, the membrane distillation link ends, the final concentration of the waste acid is achieved, the water vapor of each effect is recycled in the form of distilled water, and the waste heat of each effect is also utilized.

[0044] In one embodiment, when the temperature of the waste acid in any effect cannot reach the boiling point of the standard atmospheric pressure of water molecules, in order to achieve evaporation of water molecules into water vapor, the atmospheric pressure value in the membrane module can be reduced so that the water molecules in the waste acid at the temperature of the effect are converted into water vapor.

[0045] The low-energy consumption waste acid recovery and utilization method provided by the present invention specifically comprises the following steps:

[0046] (1) Feed: After the waste acid enters the system, it is first stored in the feed box, which serves the purpose of regulating water quality and quantity.

[0047] In some embodiments, the material of the feed box is one of PE, PP or fiberglass but not limited thereto, and the hydraulic retention time of the feed box is 1 to 5 hours, preferably 1 to 2 hours.

[0048] (2) Pretreatment: Pretreatment mainly involves flotation equipment, which is used to remove oil impurities and a small amount of organic matter in the waste acid raw materials.

[0049] In some embodiments, the flotation device uses pressure dissolved air flotation, and the surface load is 2 to 3 m 3 / m 2 ·h, the dissolved gas pressure is 0.6~0.7MPa, and the diameter of the bubbles released by the releaser is 10~50μm.

[0050] (3) Ultrafiltration: Ultrafiltration uses hollow fiber membranes to remove solid impurities and foam from waste acid raw materials through the interception effect of hollow fiber membranes.

[0051] In some embodiments, the membrane material of the hollow fiber ultrafiltration membrane is PVDF, the filtration method is external pressure type, the filtration pore size is 0.02-0.04 μm, the inner and outer diameters of the membrane are 0.7 / 1.3 mm, and the average flux is ≤60 L / (m 2 ·h), the system runs for 30 minutes, backwashes for 2 minutes, and the average backwash flux is 100-120L / (m 2 h).

[0052] (4) Resin device: After the waste acid is adsorbed by the resin, the heavy metal cations remain on the adsorption column, and the column liquid enters the membrane distillation system. After the resin adsorption is saturated, the adsorption column is regenerated, and the regenerated liquid returns to the front-end flotation device.

[0053] In some embodiments, the adsorbent model of the resin adsorption filling is CH-90Na, the working flow rate is 10BV / H, and the saturated adsorption capacity is about 50g / L.

[0054] Preferably, when the adsorption is saturated, it is first analyzed with a hydrochloric acid solution, then backwashed with pure water or soft water, and finally transformed with sodium hydroxide.

[0055] Preferably, first use 5% hydrochloric acid solution for analysis at a flow rate of 4-5BV / H for 30-45min, then use pure water or soft water for backwashing at a backwash flow rate of 5-10BV / H for 30min, and finally use 5% sodium hydroxide solution for transformation at a transformation flow rate of 4-5BV / H for 30min.

[0056] (5) Membrane distillation: A hydrophobic membrane is used as the filtration medium, and the steam pressure difference on both sides of the membrane is used as the driving force for mass transfer. Under heating conditions, the water molecules in the raw liquid evaporate and become water vapor that permeates the membrane, while the solution cannot pass through the membrane. As the water molecules continue to evaporate, the raw material becomes more concentrated, achieving the purpose of concentrating the liquid.

[0057] In some embodiments, membrane distillation includes a feed liquid channel, a membrane assembly and a vacuum pump. The feed liquid channel inlet is connected to the water production tank of the resin device, and the treated waste acid is transported to the membrane assembly through the water production tank lift pump. A hydrophobic membrane (diaphragm) is provided on one surface of the membrane assembly to separate acid and water from the waste acid, and a condensing plate (cooling plate) is provided on the other surface to condense the water vapor escaping from the hydrophobic membrane pores to form distilled water, and the waste acid is located on the side of the hydrophobic membrane away from the condensing plate. The vacuum pump is used to evacuate the membrane assembly.

[0058] In some embodiments, the hydrophobic membrane is selected from polytetrafluoroethylene membrane but is not limited to this material, and the double-sided surface of the polytetrafluoroethylene membrane is hydrophobized to prepare a super-hydrophobic nanowire coating, and the contact angle θ is kept in the range of 70°<θ<150°, and the sliding angle is less than 10°, the membrane pore size is 0.2~0.4μm, and the thickness is 0.06~0.25mm. The cooling plate is an aluminum plate with an acid-resistant coating on the surface, the thickness of the aluminum plate is 0.06~0.25mm, and the acid-resistant coating is a SiO2-TiO2-PDMS (polydimethylsiloxane) organic-inorganic hybrid acid-resistant coating, wherein the mass ratio of SiO2-TiO2 is (0.05~0.25): 1, the mass ratio of PDMS is 15%, and the surface of the aluminum plate close to the steam side is hydrophobized to prepare a super-hydrophobic fluorinated coating. The vertical distance between the outer walls of the hydrophobic membrane and the cooling plate relative to each other is 0.2-0.4 mm, and the sealing material of the membrane assembly is a corrosion-resistant rubber product.

[0059] In some embodiments, the vacuum pump is equipped with some conventional accessories, such as a vacuum valve, a vacuum gauge, etc., but not limited thereto.

[0060] Membrane distillation waste heat recovery: The steam generated by the previous effect is used to heat the feed liquid. Under heating conditions, the water molecules in the concentrated liquid evaporate and become water vapor to pass through the membrane, while the concentrated liquid cannot pass through the membrane, further concentrating the feed liquid. This process is repeated until the temperature of the concentrated liquid reaches 50°C, and this effect is taken as the final effect. The cold side of the final effect cooling plate is cooling water, and the hot side is distilled water formed after the steam passing through the hydrophobic membrane is cooled by the cooling water. A certain negative pressure is drawn on the hot side of the final effect cooling plate to ensure that the water vapor can better pass through the hydrophobic membrane.

[0061] In some embodiments, the maximum temperature of the cooling water is 30°C, the negative pressure value on the hot side of the last effect cooling plate is not higher than -0.2atm, preferably -0.3atm to -0.2atm, the temperature difference of the concentrated liquid between two effects is about 10°C, and the total number of effects is usually 2 to 6 effects, and the specific number of effects depends on the temperature of the heat source. The pressure value of each effect is approximately equal to the saturated vapor pressure value corresponding to the temperature of this effect.

[0062] The waste heat recovery provided by the present invention can utilize the steam generated in the previous effect as the heat source of the next effect for further evaporation and concentration. The number of effects can usually reach 2 to 6, which can greatly save the energy consumption of acid recovery.

[0063] (6) Discharge: After the liquid is concentrated by the final membrane, it enters the discharge box by the suction of the suction pump. The distilled water formed by the cooling of the water vapor flows into the distilled water tank by gravity.

[0064] In some embodiments, the suction pump is used to drive the flow circulation of the feed liquid, the flow surface of the suction pump is made of all-plastic material, and the suction distance is more than 3m.

[0065] The method of the present invention is applicable to one or more of waste sulfuric acid, waste hydrochloric acid or waste phosphoric acid, but is not limited to these waste acids.

[0066] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0067] Example 1

[0068] The alkylation sulfuric acid cracking unit of a petrochemical enterprise produces 7% of waste sulfuric acid (24 tons) every day. The waste sulfuric acid needs to be recovered and used in the dry absorption section. The technical parameters of the main process sections are as follows.

[0069] (1) Feeding: The feed box has a volume of 2m 3 PE barrel, two feed barrels are set, each feed barrel is equipped with a flow rate of 1.5m 3 / h acid pump, the two pumps can serve as backup for each other.

[0070] (2) Pretreatment: pressure dissolved air flotation is used, and the surface load is 2.5m 3 / m 2 ·h, the dissolved gas pressure is 0.65MPa, and the diameter of the bubbles released by the releaser is 10~50μm.

[0071] (3) Ultrafiltration: The membrane material of the hollow fiber ultrafiltration membrane is PVDF, the filtration method is external pressure type, the filtration pore size is 0.02μm, the inner and outer diameters of the membrane are 0.7 / 1.3mm, and the average flux is 60L / (m 2 h), the system runs for 30 min and backwashes for 2 min.

[0072] (4) Resin device: The adsorbent model is CH-90Na, the working flow rate is 10BV / H, and the saturated adsorption capacity is 50g / L.

[0073] (5) Membrane distillation: Using 145°C low-pressure exhaust steam as the heat source, the steam consumption per ton of waste acid treated is 0.25t, the power consumption is 5.8KWh, and the installed capacity is 9KW. The membrane distillation unit has 6 effects, and the temperatures and pressures corresponding to the first to sixth effects are shown in Table 1. The cooling water temperature is 28°C, and the cooling water flow rate is 25t / h. The negative pressure value of the hot side of the final cooling plate is -0.2atm.

[0074] Table 1 Temperature and pressure values ​​of each effect parameter First effect Second effect The third effect Fourth Effect Fifth Effect Sixth Effect Temperature ℃ 100 90 80 70 60 50 Pressure KPa 101.3 70.1 47.4 31.2 19.9 -20

[0075] (6) Discharge: After the waste acid is concentrated by membrane distillation, 4 t / d of concentrated sulfuric acid with a concentration of 42% is produced, which is used in the dry absorption section. In addition, 20 t / d of distilled water is produced, which is recycled as clean water.

[0076] Example 2

[0077] There are hundreds of commonly used dye intermediates, large and small, and almost all of them produce waste sulfuric acid. A dye and intermediate enterprise in Cangzhou, Hebei Province produces 200 tons of 18% waste sulfuric acid every day. The project is constructed in two phases, with a processing capacity of 80t / d in the first phase and 120t / d in the second phase. This example is the first phase project situation.

[0078] (1) Feeding: The feed box has a capacity of 5m 3 PE barrel, two feed barrels are set, each feed barrel is equipped with a flow rate of 4m 3 / h acid pump, the two pumps can serve as backup for each other.

[0079] (2) Pretreatment: pressure dissolved air flotation is used, and the surface load is 2.5m 3 / m 2 ·h, the dissolved gas pressure is 0.65MPa, and the diameter of the bubbles released by the releaser is 10~50μm.

[0080] (3) Ultrafiltration: The membrane material of the hollow fiber ultrafiltration membrane is PVDF, the filtration method is external pressure type, the filtration pore size is 0.02μm, the inner and outer diameters of the membrane are 0.7 / 1.3mm, and the average flux is 60L / (m 2 h), the system runs for 30 min and backwashes for 2 min.

[0081] (4) Resin device: The adsorbent model is CH-90Na, the working flow rate is 10BV / H, and the saturated adsorption capacity is 50g / L.

[0082] (5) Membrane distillation: low-pressure steam is used as the heat source. The steam consumption per ton of waste acid treated is 0.4t, the power consumption is 5.8KWh, and the installed capacity is 30KW. The membrane distillation unit has 4 effects. The temperatures and pressures corresponding to the first to fourth effects are shown in Table 2. The cooling water temperature is 28°C and the cooling water flow rate is 80t / h. The negative pressure value of the hot side of the final cooling plate is -0.2atm.

[0083] Table 2 Temperature and pressure values ​​for each effect parameter First effect Second effect The third effect Fourth Effect Temperature ℃ 80 70 60 50 Pressure KPa 47.4 31.2 19.9 -20

[0084] (6) Discharge: After the waste acid is concentrated by membrane distillation, 36t / d of concentrated sulfuric acid with a concentration of 40% is produced, which is recycled. In addition, 44t / d of distilled water is produced, which is recycled as clean water.

[0085] Example 3

[0086] An aluminum-magnesium alloy enterprise in Kunshan, Jiangsu, produces 86 tons of waste phosphoric acid every day during the production process. The concentration of phosphoric acid is 0.5%. In order to improve the factory environment, achieve sustainable development of resources and environment, save resources and reduce environmental pollution, and extend the life cycle of the enterprise, the enterprise adopts membrane distillation technology to recycle the waste phosphoric acid. The technical parameters of the main process sections are as follows.

[0087] (1) Feeding: The feed box has a capacity of 5m 3 PE barrel, two feed barrels are set, each feed barrel is equipped with a flow rate of 5m 3 / h acid pump, the two pumps can serve as backup for each other.

[0088] (2) Pretreatment: pressure dissolved air flotation is used, and the surface load is 2.5m 3 / m 2 ·h, the dissolved gas pressure is 0.65MPa, and the diameter of the bubbles released by the releaser is 10~50μm.

[0089] (3) Ultrafiltration: The membrane material of the hollow fiber ultrafiltration membrane is PVDF, the filtration method is external pressure type, the filtration pore size is 0.02μm, the inner and outer diameters of the membrane are 0.7 / 1.3mm, and the average flux is 60L / (m 2 h), the system runs for 30 min and backwashes for 2 min.

[0090] (4) Resin device: The adsorbent model is CH-90Na, the working flow rate is 10BV / H, and the saturated adsorption capacity is 50g / L.

[0091] (5) Membrane distillation: Using 86°C waste hot water as the heat source, the consumption of hot water for treating one ton of waste acid is 16.8t, the power consumption is 2.8KWh, and the installed capacity is 19KW. The membrane distillation unit has three effects, and the corresponding temperatures and pressures of the first to third effects are shown in Table 3. The cooling water temperature is 30°C, and the cooling water flow rate is 90t / h. The negative pressure value of the hot side of the final cooling plate is -0.2atm.

[0092] Table 3 Temperature and pressure values ​​for each effect parameter First effect Second effect The third effect Temperature ℃ 70 60 50 Pressure KPa 31.2 19.9 -20

[0093] (6) Discharge: After the waste acid is concentrated by membrane distillation, 1.1 t / d of concentrated phosphoric acid with a concentration of 40% is produced, which is recycled. In addition, 84.9 t / d of distilled water is produced, which is recycled as clean water.

[0094] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may also include more other equivalent embodiments without departing from the technical concept of the present invention, all of which belong to the protection scope of the present invention.

Claims

1. A low-energy consumption waste acid recovery and utilization method, characterized in that: The steps include: (1) Feeding: The amount of waste acid raw materials entering the pretreatment system is adjusted by a feed pump; (2) Pretreatment: Pretreatment uses air flotation to remove oil impurities and a small amount of organic matter in the waste acid raw materials through an air flotation device; (3) Ultrafiltration: Ultrafiltration uses hollow fiber membranes to remove solid impurities and foam in the waste acid raw materials through the interception effect of the hollow fiber membranes; (4) Resin adsorption: After the waste acid is adsorbed by the resin, the heavy metal cations remain on the adsorption column, and the column liquid enters the membrane distillation system; after the resin adsorption is saturated, the adsorption column is regenerated, and the regenerated liquid returns to the front-end pretreatment flotation device; (5) Membrane distillation: A hydrophobic membrane is used as a filter medium. When heated, water molecules in the waste acid raw material evaporate and become water vapor. The water vapor pressure difference on both sides of the hydrophobic membrane is used as the driving force for mass transfer. Water vapor passes through the hydrophobic membrane, while waste acid cannot. As water molecules continue to evaporate, the waste acid raw material becomes concentrated. The waste acid raw material is sequentially subjected to at least one membrane distillation effect. The water vapor in each effect is cooled to obtain distilled water. The water vapor generated in the previous effect is used as a heating source for the waste acid in the next effect. This effect is regarded as the last effect when the temperature of the waste acid drops to 50°C. (6) Discharging: After the waste acid is concentrated, it is introduced into a discharging box to achieve the concentration of the waste acid raw materials.

2. The method according to claim 1, characterized in that In step (5), each effect of the membrane distillation is composed of a membrane assembly, one side of the membrane assembly is provided with the hydrophobic membrane for separating the waste acid and water, and the other side is provided with a condenser for condensing the water vapor transmitted by the hydrophobic membrane. The waste acid is located on the side of the hydrophobic membrane away from the condenser.

3. The method according to claim 2, characterized in that The membrane module is optionally vacuumed.

4. The method according to claim 2, characterized in that: The cold side of the condenser of the last effect is cooling water, and the hot side is distilled water formed by cooling the water vapor passing through the hydrophobic membrane with cooling water. The maximum temperature of the cooling water in the last effect is 30°C, and the negative pressure value in the membrane assembly of the last effect is not higher than -0.2atm, preferably -0.3 to -0.2atm.

5. The method according to claim 2, characterized in that: The temperature difference of the waste acid between two adjacent effects is 8-12°C, the total number of membrane distillation effects is preferably 2-6, and the pressure value of the membrane component of each effect is equal to the saturated vapor pressure value corresponding to the waste acid temperature in this effect.

6. The method according to claim 2, characterized in that The hydrophobic membrane is a polytetrafluoroethylene membrane, and the surfaces on both sides of the polytetrafluoroethylene membrane are hydrophobized to prepare a super-hydrophobic nanowire coating, maintaining a contact angle θ in the range of 70°<θ<150°, and a sliding angle less than 10°, a membrane pore size of 0.2-0.4 μm, and a thickness of 0.06-0.25 mm; Preferably, the condensing sheet is an aluminum plate coated with an acid-resistant coating on the surface, the thickness of the aluminum plate is 0.06-0.25 mm, and the acid-resistant coating is a SiO2-TiO2-PDMS hybrid acid-resistant coating, wherein the mass ratio of SiO2-TiO2 is (0.05-0.25): 1, and the mass fraction of PDMS is 15%; Preferably, the hot side surface of the condenser sheet is provided with a super-hydrophobic fluorinated coating; Preferably, the vertical distance between the hydrophobic membrane and the condensing sheet arranged in parallel is 0.2 to 0.4 mm; Preferably, the sealing material of the membrane assembly is a corrosion-resistant rubber product.

7. The method according to any one of claims 1 to 6, characterized in that: In step (2), the flotation device is a pressure dissolved air flotation device with a surface load of 2 to 3 m 3 / m 2 ·h, the dissolved gas pressure is 0.6~0.7MPa, and the diameter of the bubbles released by the releaser is 10~50μm.

8. The method according to any one of claims 1 to 6, characterized in that: In step (3), the membrane material of the hollow fiber membrane is PVDF, the filtration method is external pressure type, the filtration pore size is 0.02-0.04 μm, the inner and outer diameters of the membrane are 0.7 / 1.3 mm, and the average flux is ≤60 L / (m 2 ·h), the system runs for 30 minutes, backwashes for 2 minutes, and the average backwash flux is 100-120L / (m 2 h).

9. The method according to any one of claims 1 to 6, characterized in that: In step (4), the adsorbent model of the resin adsorption filling is CH-90Na, the working flow rate is 10BV / H, and the saturated adsorption capacity is about 50g / L; Preferably, when the adsorption is saturated, it is first analyzed with a hydrochloric acid solution, then backwashed with pure water or soft water, and finally transformed with sodium hydroxide; Preferably, first use 5% hydrochloric acid solution for analysis at a flow rate of 4-5BV / H for 30-45min, then use pure water or soft water for backwashing at a backwash flow rate of 5-10BV / H for 30min, and finally use 5% sodium hydroxide solution for transformation at a transformation flow rate of 4-5BV / H for 30min.

10. The method according to any one of claims 1 to 6, characterized in that: In step (1), the material of the feed box is PE, PP or fiberglass, and the hydraulic retention time of the feed box is 1 to 5 hours; and / or, In step (6), the material of the discharge box is PE, PP or fiberglass, and the hydraulic retention time of the discharge box is 1 to 5 hours.

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