Phosphoric acid regeneration process and device for activated carbon waste liquid, waste water and waste gas column waste water

Abstract

The application discloses a phosphoric acid regeneration process and device for activated carbon waste liquid, waste water and waste gas tower waste water, and belongs to the technical field of phosphoric acid regeneration. The device comprises an activated carbon waste liquid treatment branch, an activated carbon waste water treatment branch, a waste gas tower waste water treatment branch, a nanofiltration unit and a regeneration concentration unit; the activated carbon waste liquid is subjected to solid-liquid separation and membrane filtration, the activated carbon waste water is subjected to membrane filtration and membrane concentration, the waste gas tower waste water is subjected to membrane filtration and low-temperature evaporation, the phosphorus-containing material liquid obtained from each branch is combined with evaporation condensate water to enter the nanofiltration unit, calcium and magnesium impurities in the material liquid are intercepted, the nanofiltration water is concentrated by low-temperature evaporation to obtain reusable phosphoric acid; wherein, the condensate water is used as a dilution component of the combined material liquid and is recycled and consumed in the nanofiltration and evaporation loop. The application does not need to introduce chemical agents in the whole process, does not produce solid by-products, recycles the phosphoric acid which can be used for activated carbon production, and consumes high chemical oxygen demand condensate water to reduce discharge.

Description

Technical Field

[0001] This invention belongs to the field of phosphoric acid regeneration technology, specifically relating to a phosphoric acid regeneration process and apparatus for activated carbon waste liquid, wastewater and waste gas tower wastewater. Background Technology

[0002] The phosphoric acid method (also known as the phosphoric acid activation method) is one of the important processes for preparing activated carbon. Its basic process includes: sieving the carbonaceous raw material and placing it in an impregnation tank, adding phosphoric acid solution for impregnation, and then sending it to a carbonization and activation device for carbonization and activation at high temperature; the activated carbon obtained is then washed with water until it is close to neutral, dehydrated and dried to obtain the finished activated carbon product. In the aforementioned production process, phosphoric acid mainly acts as an activator in the impregnation and activation reactions, and forms various phosphorus-containing waste materials along with processes such as washing and tail gas treatment. These mainly include: First, washing wastewater generated after washing and activation of activated carbon. This type of wastewater is low-concentration phosphorus-containing wastewater and contains a large amount of calcium and magnesium ions. Second, activated carbon waste liquid formed when the phosphoric acid solution is partially discarded during impregnation and activation due to the accumulation or concentration changes of impurity ions such as calcium and magnesium. This type of waste liquid has a relatively high phosphoric acid concentration and a high content of calcium and magnesium impurities. Third, exhaust gas tower wastewater formed after the tail gas generated in carbonization, activation, and washing processes is absorbed and treated by exhaust gas towers (such as spray towers or water washing towers). This type of wastewater usually contains organic pollutants such as coal tar, phenols, and cyanides, and is characterized by high chemical oxygen demand, high biological oxygen demand, complex composition, and high toxicity.

[0003] For the three types of phosphorus-containing waste materials mentioned above, direct discharge into wastewater treatment plants for centralized treatment would require a large amount of neutralizing agents and generate a large amount of phosphorus-containing sludge, resulting in high costs for both the agents and sludge disposal. Furthermore, the phosphoric acid contained within these materials cannot be recovered, leading to a waste of phosphoric acid resources. Wastewater from exhaust gas treatment towers, in particular, has high concentrations of organic pollutants, complex compositions, and a certain degree of toxicity. Conventional physicochemical-biological combined treatment processes are lengthy and costly, and improper treatment poses a risk of secondary pollution. In addition, the presence of impurities such as calcium and magnesium in these waste liquids further increases the difficulty of their recovery and reuse.

[0004] In existing technologies, various attempts have been made to treat phosphorus-containing materials and recover phosphoric acid during activated carbon production. For example, some schemes collect, filter, soften, and concentrate low-concentration phosphoric acid wastewater, and then recover phosphoric acid through calcium salt precipitation combined with acid hydrolysis. However, this method requires the introduction of chemical agents such as calcium salts, alkalis, and sulfuric acid, and generates solid-phase byproducts, resulting in a long process flow and high operating costs. Another example is the use of nanofiltration membranes to purify wet-process phosphoric acid, retaining high-valence metal ions such as calcium and magnesium. However, this type of scheme mainly targets the product refining stage of phosphoric acid production and does not address the recovery and treatment of phosphorus-containing wastewater during activated carbon production. Yet another example is the separate treatment of different wastewaters generated during activated carbon production. For instance, some phosphorus-containing wastewater is concentrated using membrane technology and reused in production, while the remaining wastewater is treated through oxidation and other methods to meet discharge standards. However, in these schemes, the various materials are still basically treated separately, without forming a unified phosphoric acid recovery system, and the overall integration and resource recovery efficiency still need to be improved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a phosphoric acid regeneration process and apparatus for activated carbon waste liquid, wastewater, and waste gas tower wastewater, aiming to solve the problem of how to effectively recover and utilize phosphoric acid from phosphorus-containing waste materials from the above-mentioned multiple sources while reducing reagent and treatment costs.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a phosphoric acid regeneration device for activated carbon waste liquid, wastewater, and wastewater from a waste gas tower, comprising: The activated carbon waste liquid treatment branch includes a solid-liquid separation unit and a first membrane filtration unit connected in sequence, which are used to perform solid-liquid separation and membrane filtration of activated carbon waste liquid to obtain waste liquid membrane filtration permeate; The activated carbon wastewater treatment branch includes a second membrane filtration unit and a membrane concentration unit connected in sequence, which are used to perform membrane filtration and membrane concentration on activated carbon wastewater to obtain wastewater membrane concentrate. The wastewater treatment branch of the exhaust gas tower includes a third membrane filtration unit and a low-temperature evaporation unit connected in sequence. The low-temperature evaporation unit is equipped with a concentrate collection unit and a condensate collection unit, which are used to perform membrane filtration and low-temperature evaporation on the wastewater from the exhaust gas tower to obtain concentrate and condensate. The nanofiltration unit has an inlet for receiving a combined feed solution from the membrane filtration permeate outlet of the activated carbon wastewater treatment branch, the membrane concentrate outlet of the activated carbon wastewater treatment branch, and the condensate collection unit. This unit performs nanofiltration separation on the combined feed solution to remove calcium and magnesium impurities, yielding nanofiltration permeate and nanofiltration concentrate. A regeneration and concentration unit is connected to the permeate outlet of the nanofiltration unit and performs low-temperature evaporation and concentration on the nanofiltration permeate to obtain reusable phosphoric acid. The wastewater membrane filtration permeate, the wastewater membrane concentrate, and the condensate are combined before entering the nanofiltration unit, with the condensate serving as a diluent component of the combined feed solution.

[0007] Furthermore, the solid-liquid separation unit is a filter press; the first membrane filtration unit, the second membrane filtration unit, and the third membrane filtration unit are respectively a first membrane filtration device, a second membrane filtration device, and a third membrane filtration device; The membrane concentration unit is a two-stage membrane concentration system comprising a primary membrane concentration system and a secondary membrane concentration system connected in sequence. The nanofiltration unit is a two-stage nanofiltration system comprising a primary nanofiltration system and a secondary nanofiltration system; The low-temperature evaporation unit and the regeneration concentration unit are respectively a low-temperature evaporation device and a regeneration evaporation device; In the activated carbon waste liquid treatment branch, the filter press and the first membrane filtration device are connected in sequence, and the activated carbon waste liquid treatment branch also includes an activated carbon waste liquid collection tank, a filtrate collection tank and a waste liquid permeate collection tank. The activated carbon waste liquid collection tank is connected to the feed side of the filter press, the filtrate collection tank is connected between the filter press and the first membrane filtration device, and the waste liquid permeate collection tank is connected to the permeate side of the first membrane filtration device. The waste liquid membrane filtration permeate is collected in the waste liquid permeate collection tank. In the activated carbon wastewater treatment branch, the second membrane filtration device is sequentially connected to the two-stage membrane concentration system. The activated carbon wastewater treatment branch also includes an activated carbon wastewater collection tank, a wastewater product water collection tank, a primary concentrate collection tank, and a secondary concentrate collection tank. The activated carbon wastewater collection tank is connected to the feed side of the second membrane filtration device. The wastewater product water collection tank is connected between the second membrane filtration device and the primary membrane concentration system. The primary concentrate collection tank is connected between the primary membrane concentration system and the secondary membrane concentration system. The secondary concentrate collection tank is connected to the concentrate outlet side of the secondary membrane concentration system. The wastewater membrane concentrate is collected in the secondary concentrate collection tank. In the wastewater treatment branch of the exhaust gas tower, the third membrane filtration device and the low-temperature evaporation device are connected in sequence, and the wastewater treatment branch of the exhaust gas tower also includes a wastewater collection tank, a waste gas product water collection tank, a waste gas concentrate collection tank and a condensate collection tank. The wastewater collection tank is connected to the feed side of the third membrane filtration device, the waste gas product water collection tank is connected between the third membrane filtration device and the low-temperature evaporation device, and the waste gas concentrate collection tank and the condensate collection tank are respectively connected to the concentrate outlet and the condensate outlet of the low-temperature evaporation device. The feed inlet of the primary nanofiltration system is connected to the waste liquid permeate collection tank, the secondary concentrate collection tank is connected to the waste liquid permeate collection tank, the condensate collection tank is connected to the waste liquid permeate collection tank, the concentrate outlet of the primary nanofiltration system is connected to the feed inlet of the secondary nanofiltration system, the permeate outlet of the secondary nanofiltration system is connected to the feed inlet of the regeneration evaporation equipment, and the outlet of the regeneration evaporation equipment is connected to the acid recovery tank.

[0008] Furthermore, the first membrane filtration device, the second membrane filtration device, and the third membrane filtration device are all MCR filtration devices; The MCR filtration equipment is equipped with a sludge discharge pump, a backwash pump, and an aeration device. The backwash pump is connected to the product water collection tank of the corresponding branch. The fine filtration membrane of the MCR filtration device has a pore size of 0.1–10 μm and a porosity of 70%–90%.

[0009] Furthermore, both the primary membrane concentration system and the secondary membrane concentration system use acid-resistant membranes, with the primary concentration membrane having a pressure resistance of ≤40 kg / cm² and the secondary concentration membrane having a pressure resistance of ≤70 kg / cm². The specific gravity of the concentrate after concentration by the primary membrane concentration system is 1.06–1.10 g / mL, and the specific gravity of the concentrate after concentration by the secondary membrane concentration system is 1.10–1.20 g / mL.

[0010] Furthermore, the nanofiltration membrane used in the nanofiltration unit has a pressure resistance of ≤40 kg / cm². The phosphoric acid recovery rates of both primary and secondary nanofiltration were 50%–70%. The feed inlet of the secondary nanofiltration system is also connected to the condensate collection tank, which is used to dilute the primary nanofiltration concentrate with the condensate before it enters the secondary nanofiltration system.

[0011] Furthermore, both the regeneration evaporation equipment and the low-temperature evaporation equipment adopt a combined cooling and heating system, and the evaporation temperature is 30-40℃. Metering pumps are provided between the activated carbon waste liquid collection tank, the activated carbon wastewater collection tank, and the waste gas tower wastewater collection tank and the corresponding membrane filtration equipment. The feed side of the regeneration evaporation equipment is provided with a liquid inlet valve, and the regeneration evaporation equipment is provided with a discharge valve connected to the discharge pump.

[0012] Secondly, the present invention provides a phosphoric acid regeneration process for activated carbon waste liquid, wastewater, and wastewater from waste gas towers, comprising the following steps: (1) The wastewater from the exhaust gas tower is subjected to membrane filtration and low-temperature evaporation concentration to obtain concentrated liquid and condensate; (2) The activated carbon wastewater is subjected to membrane filtration and membrane concentration to obtain wastewater membrane concentrate; (3) Solid-liquid separation and membrane filtration are performed on activated carbon wastewater to obtain wastewater membrane filtration product water; (4) The waste liquid membrane filtration permeate, the waste water membrane concentrate and the condensate are combined and then separated by nanofiltration to remove calcium and magnesium impurities, so as to obtain nanofiltration permeate and nanofiltration concentrate; wherein, the condensate is used as a diluent for nanofiltration feed; (5) The nanofiltration permeate is concentrated by low-temperature evaporation to obtain reusable phosphoric acid.

[0013] Furthermore, in step (4): The wastewater membrane filtration permeate, the wastewater membrane concentrate, and the condensate are mixed in a certain proportion to make the specific gravity of the mixture 1.1-1.2 g / mL before being sent to a first-stage nanofiltration system. The first-stage nanofiltration system operates at a pressure of ≤40 kg / cm², and the specific gravity of the concentrate is controlled to be less than 1.3 g / mL, and the calcium and magnesium removal rate is not less than 90%. The primary nanofiltration concentrate is diluted with the condensate to a specific gravity of 1.1–1.2 g / mL and then fed into the secondary nanofiltration system. The secondary nanofiltration system operates at a pressure of ≤40 kg / cm², with the concentrate specific gravity controlled to be less than 1.3 g / mL and the calcium and magnesium removal rate controlled to be no less than 90%. The phosphoric acid recovery rate of both the primary nanofiltration and the secondary nanofiltration is 50% to 70%. When the standardized permeate flow rate decreases by 10%–15%, the salt permeate rate increases by 30%–40%, or the standardized pressure differential increases by 25%, the membrane element is chemically cleaned.

[0014] Furthermore, in step (2): The membrane concentration is a two-stage membrane concentration. The first-stage membrane concentration operates at a pressure of ≤40 kg / cm², and the specific gravity of the first-stage concentrate is 1.06~1.10 g / mL. The secondary membrane concentration operates at a pressure of ≤70 kg / cm², with a feed water specific gravity of 1.06–1.10 g / mL and a concentrate specific gravity of 1.10–1.20 g / mL. When the standardized permeate flow rate decreases by 10%–15%, the salt permeate rate increases by 30%–40%, or the standardized pressure differential increases by 25%, the membrane element is chemically cleaned.

[0015] Further, in step (1), the membrane filtration is operated as follows: it is stopped for 1 to 3 minutes every 8 to 12 minutes of operation, backwashed for 5 to 10 minutes after 8 to 12 cycles, and the slag is discharged when the vacuum degree of the equipment is greater than 40 kPa; In step (5), the low-temperature evaporation and concentration are carried out at 30-40°C, and the phosphoric acid is concentrated to a mass fraction of not less than 60% before being reused.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention addresses the characteristics of the dispersed sources and large differences in physical properties of three types of phosphorus-containing materials: activated carbon waste liquid, activated carbon wastewater, and waste gas tower wastewater. It sets up separate pretreatment branches such as solid-liquid separation and membrane filtration (activated carbon waste liquid treatment branch), membrane filtration and membrane concentration (activated carbon wastewater treatment branch), and membrane filtration and low-temperature evaporation (waste gas tower wastewater treatment branch). The phosphorus-containing liquids obtained from each branch are combined and uniformly subjected to nanofiltration for impurity removal and low-temperature evaporation for regeneration. The entire process does not require the introduction of chemical agents such as calcium salts, alkalis, and acids, and does not produce solid-phase chemical byproducts. It can significantly reduce the consumption of neutralizing agents and the amount of phosphorus-containing sludge generated. At the same time, it enables the recovery of phosphoric acid in the discharged materials in a reusable form, resulting in a high phosphoric acid resource utilization rate.

[0017] (2) The present invention sets nanofiltration for impurity removal on the main line of phosphoric acid recovery and regeneration. When the combined liquid enters the nanofiltration unit, divalent metal impurities such as calcium and magnesium are simultaneously intercepted, so that the calcium and magnesium impurity content in the recovered phosphoric acid obtained by low-temperature evaporation is low, which can meet the requirements of return activation process reuse. It avoids the scale formation of calcium and magnesium impurities during reuse and evaporation concentration, which affects the activation effect and stable operation of equipment. It overcomes the limitation of existing technology where the recovery route relies on chemical precipitation for impurity removal, while nanofiltration for impurity removal is only used for phosphoric acid product refining.

[0018] (3) The present invention uses the condensate obtained by low-temperature evaporation of wastewater from the exhaust gas tower as a dilution component of the nanofiltration feed, so that this type of high chemical oxygen demand condensate is circulated and consumed within the nanofiltration-low-temperature evaporation loop. There is no need to set up a separate advanced oxidation or biochemical treatment unit, which can shorten the overall treatment process, reduce operating costs, reduce the amount of wastewater discharged, and reduce the risk of secondary pollution. The condensate participating in the dilution can also adjust the concentration and specific gravity of the nanofiltration feed, which is beneficial to improve the operating conditions of the nanofiltration membrane and inhibit the scaling on the membrane surface. In the preferred embodiment, a high phosphoric acid recovery rate and a high calcium and magnesium rejection rate can be achieved.

[0019] (4) In this invention, the phosphoric acid concentration of activated carbon wastewater with low phosphoric acid concentration is increased by membrane concentration first, and the nanofiltration permeate of the combined liquid is concentrated by low-temperature evaporation. The preferred method is to use a low-temperature operation mode of combined cooling and heating, which can utilize low-grade heat energy for evaporation and concentration, effectively reducing the energy consumption and operating cost of the concentration process of low-concentration phosphorus-containing materials, and improving the overall economic efficiency of multi-source phosphorus-containing material treatment.

[0020] (5) Through the above-mentioned integrated design of pretreatment, nanofiltration and low-temperature evaporation regeneration, the present invention incorporates phosphorus-containing materials such as activated carbon waste liquid, activated carbon wastewater and waste gas tower wastewater into a unified phosphoric acid recovery system. The pretreatment units of each branch and the nanofiltration and evaporation units after the merger are coordinated and have good equipment commonality. The system integration is high, which can reduce equipment investment and floor space. The phosphorus-containing concentrate and recovered phosphoric acid obtained in the treatment process can be returned to the production process for recycling. Only conventional biochemical / reuse treatment is required for disposal. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure and connection of a phosphoric acid regeneration device for activated carbon waste liquid, wastewater and waste gas tower wastewater according to the present invention.

[0022] Figure 2 This is a flowchart of a method for regenerating phosphoric acid from activated carbon waste liquid, wastewater, and waste gas tower wastewater according to the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention; in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0024] like Figure 1 As shown, this invention provides a phosphoric acid regeneration device for activated carbon waste liquid, wastewater, and wastewater from an exhaust gas tower. The device includes an activated carbon waste liquid treatment branch, an activated carbon wastewater treatment branch, an exhaust gas tower wastewater treatment branch, a nanofiltration unit, and a regeneration and concentration unit. The three treatment branches respectively pre-treat the activated carbon waste liquid, activated carbon wastewater, and exhaust gas tower wastewater. The phosphorus-containing liquids obtained from the pre-treatment are then combined and enter the nanofiltration unit, where calcium and magnesium impurities are removed. The nanofiltration permeate is then concentrated by low-temperature evaporation in the regeneration and concentration unit to obtain reusable phosphoric acid. The condensate obtained from the low-temperature evaporation of the exhaust gas tower wastewater branch has a high chemical oxygen demand (COD) and is difficult to discharge directly. In this embodiment, it is used as a diluent component of the combined liquids and circulated within the system for disposal, eliminating the need for a separate advanced oxidation or biochemical treatment unit for this condensate.

[0025] Specifically, such as Figure 1 As shown, in the activated carbon waste liquid treatment branch, the filter press and the first membrane filtration device are connected in sequence: the activated carbon waste liquid collection tank is connected to the feed side of the filter press, the filtrate collection tank is connected between the filter press and the first membrane filtration device to receive the filtrate obtained by the filter press, and the waste liquid permeate collection tank is connected to the permeate side of the first membrane filtration device to collect the waste liquid permeate after membrane filtration.

[0026] In the activated carbon wastewater treatment branch, the second membrane filtration device is connected to the two-stage membrane concentration system in sequence: the two-stage membrane concentration system consists of a first-stage membrane concentration system and a second-stage membrane concentration system connected in sequence. The activated carbon wastewater collection tank is connected to the feed side of the second membrane filtration device, the wastewater product water collection tank is connected between the second membrane filtration device and the first-stage membrane concentration system, the first-stage concentrate collection tank is connected between the first-stage membrane concentration system and the second-stage membrane concentration system, and the second-stage concentrate collection tank is connected to the concentrate outlet side of the second-stage membrane concentration system for collecting wastewater membrane concentrate.

[0027] In the wastewater treatment branch of the exhaust gas tower, the third membrane filtration equipment and the low-temperature evaporation equipment are connected in sequence: the wastewater collection tank of the exhaust gas tower is connected to the feed side of the third membrane filtration equipment, the wastewater collection tank of the exhaust gas is connected between the third membrane filtration equipment and the low-temperature evaporation equipment, and the concentrated liquid outlet and condensate outlet of the low-temperature evaporation equipment are respectively connected to the waste gas concentrated liquid collection tank and the condensate collection tank.

[0028] The nanofiltration unit is a two-stage nanofiltration system comprising a primary nanofiltration system and a secondary nanofiltration system. The regeneration and concentration unit includes a regeneration evaporation device and a recovery acid tank. Regarding cross-branch connections, the outlet of the wastewater / permeable collection tank is connected to the inlet of the primary nanofiltration system; the secondary concentrate collection tank and the condensate collection tank are respectively connected to the wastewater / permeable collection tank via pipelines; the concentrate outlet of the primary nanofiltration system is connected to the inlet of the secondary nanofiltration system; the permeable outlet of the secondary nanofiltration system is connected to the inlet of the regeneration evaporation device; and the outlet of the regeneration evaporation device is connected to the recovery acid tank.

[0029] Thus, the wastewater membrane filtration permeate from the activated carbon wastewater branch, the wastewater membrane concentrate from the activated carbon wastewater branch, and the condensate from the waste gas tower wastewater branch are combined in the wastewater permeate collection tank before entering the primary nanofiltration system. The condensate plays the role of diluting the components in the combined liquid.

[0030] In this embodiment, the first membrane filtration device, the second membrane filtration device, and the third membrane filtration device can all be the MCR filtration device referred to in this application, that is, a membrane filtration device equipped with an aeration device, a backwashing device, and a sludge removal device, which relies on the membrane module to trap suspended particles and maintains membrane flux through periodic aeration disturbance, backwashing, and sludge removal. The fine filtration membrane pore size of the MCR filtration device can be 0.1 to 10 μm, the membrane porosity can be 70% to 90%, and the pore density can be 10. 7 ~10 8 The MCR filtration equipment features a high filtration efficiency of [number] particles per cm², resulting in low suspended solids content in the effluent. It is equipped with a sludge discharge pump and a backwash pump, with the backwash pump connected to the corresponding branch's permeate collection tank. This allows for backwashing of the membrane modules using permeate, thus delaying membrane fouling, extending the lifespan of the membrane modules, and maintaining stable permeate water quality. The MCR filtration equipment also includes an aeration device, which further inhibits pollutant deposition on the membrane surface by agitating the membrane surface with aeration.

[0031] The two-stage membrane concentration system can use acid-resistant membranes: the pressure resistance of the concentration membrane in the first-stage system is ≤40 kg / cm², and the pressure resistance of the concentration membrane in the second-stage system is ≤70 kg / cm², to meet the operating pressure requirements of different concentration stages. Under optimal operating conditions, the specific gravity of the concentrate after concentration by the first-stage membrane concentration system is 1.06–1.10 g / mL, the specific gravity of the feed water entering the second-stage membrane concentration system is 1.06–1.10 g / mL, and the specific gravity of the concentrate after concentration by the second-stage system is 1.10–1.20 g / mL. The flow rate ratios of permeate, circulating water, and concentrate can be adjusted during operation of each membrane concentration system; for example, the permeate flow rate ratio can be 40%–70%, the circulating water flow rate ratio can be 30%–60%, and the concentrate flow rate ratio can be 10%–30%.

[0032] The nanofiltration membranes used in the two-stage nanofiltration system have a pressure resistance of ≤40 kg / cm². During nanofiltration operation, the specific gravity of the nanofiltration feed water (i.e., the pooled feed solution) is less than 1.2 g / mL, and the specific gravity of the nanofiltration concentrate is less than 1.3 g / mL; the phosphoric acid recovery rate of both the first-stage and second-stage nanofiltration can be 50%–70%. The flow rate ratios of permeate, circulating water, and concentrate can be adjusted during operation; for example, the permeate flow rate ratio can be 60%–80%, the circulating water flow rate ratio can be 30%–50%, and the concentrate flow rate ratio can be 5%–20%. Specifically, the feed inlet of the second-stage nanofiltration system is also connected to a condensate collection tank: the concentrate obtained from the first-stage nanofiltration is first mixed with condensate and diluted to a specific gravity of 1.1–1.2 g / mL before entering the second-stage nanofiltration system. This approach provides suitable influent for the secondary nanofiltration process, further improving the total phosphoric acid recovery rate, while also allowing the condensate with high chemical oxygen demand to be absorbed within the nanofiltration loop, eliminating the need for external discharge or separate deep treatment.

[0033] Both low-temperature evaporation and regeneration evaporation equipment can employ combined cooling and heating systems, utilizing system waste heat or low-grade thermal energy as the evaporation heat source, with evaporation temperatures ranging from 30 to 40°C. To achieve stable and controllable operation, metering pumps are installed between the activated carbon waste liquid collection tank, activated carbon wastewater collection tank, and wastewater collection tank of the exhaust gas tower and the corresponding membrane filtration equipment to supply materials to each branch at set flow rates. The regeneration evaporation equipment has an inlet valve on its feed side and a discharge valve connected to a discharge pump on its discharge side to control the feeding of nanofiltration permeate and the discharge of recovered acid. The concentrated waste gas obtained from low-temperature evaporation in the wastewater branch of the exhaust gas tower has a high phosphoric acid concentration (usually not less than 60%), which can be directly returned to the phosphoric acid activation and impregnation process for reuse.

[0034] The above-mentioned device is used to regenerate phosphoric acid in the activated carbon waste liquid, activated carbon wastewater, and waste gas tower wastewater generated during the phosphoric acid activated carbon production process. Figure 2 As shown, the process includes the following steps: Step (1): Membrane filtration and low-temperature evaporation of wastewater from the exhaust gas tower. The wastewater from the exhaust gas tower wastewater collection tank is sent to the third membrane filtration equipment for membrane filtration via a metering pump to obtain waste gas membrane filtration permeate, which is collected in the waste gas permeate collection tank. The membrane filtration is operated as follows: it is stopped for 1 to 3 minutes every 8 to 12 minutes of continuous operation, and backwashed for 5 to 10 minutes every 8 to 12 cycles. When the equipment vacuum degree is greater than 40 kPa, the slag discharge pump is turned on to discharge slag to maintain membrane flux and effluent quality. Subsequently, the waste gas membrane filtration permeate is sent to the low-temperature evaporation equipment via the inlet valve for low-temperature evaporation and concentration at 30 to 40°C to obtain waste gas concentrate and condensate. The waste gas concentrate is collected in the waste gas concentrate collection tank and can be directly reused, while the condensate is collected in the condensate collection tank.

[0035] Step (2): Membrane filtration and two-stage membrane concentration of activated carbon wastewater. The activated carbon wastewater in the collection tank is pumped into the second membrane filtration unit for membrane filtration, yielding wastewater membrane filtration permeate, which is collected in the wastewater permeate collection tank. The wastewater membrane filtration permeate is then pumped into a two-stage membrane concentration system for two-stage membrane concentration: the first-stage membrane concentration operates at a pressure ≤40 kg / cm², concentrating the first-stage concentrate to a specific gravity of 1.06–1.10 g / mL; the first-stage concentrate enters the second-stage membrane concentration system, where it continues to concentrate at a pressure ≤70 kg / cm², with the second-stage concentrate influent having a specific gravity of 1.06–1.10 g / mL and the second-stage concentrate concentrated to a specific gravity of 1.10–1.20 g / mL, collected in the second-stage concentrate collection tank. The freshwater generated from both the first and second-stage membrane concentrations is collected and discharged into the wastewater treatment plant. During operation, if any of the following occurs: a 10%–15% decrease in standardized permeate flow rate compared to the initial stable flow rate; a 30%–40% increase in salt permeability; or a 25% increase in standardized differential pressure, the corresponding membrane element should be chemically cleaned. Standardized permeate flow rate / standardized differential pressure refers to the converted values ​​after correcting the measured values ​​for temperature and pressure to standard conditions.

[0036] Step (3): Solid-liquid separation and membrane filtration of activated carbon waste liquid. The activated carbon waste liquid in the collection tank is pumped into a filter press (a plate and frame filter press in this embodiment) for filtration to achieve solid-liquid separation, obtaining filter residue and filtrate. The filter residue is discharged from the system, and the filtrate is collected in the filtrate collection tank. The filtrate is then filtered by the first membrane filtration device to obtain waste liquid membrane filtration permeate (i.e., waste liquid membrane filtration permeate for subsequent nanofiltration), which is collected in the waste liquid permeate collection tank.

[0037] Step (4): Combination and Two-Stage Nanofiltration. The wastewater membrane concentrate from the secondary concentrate collection tank is pumped into the wastewater permeate collection tank, and simultaneously, the condensate from the condensate collection tank is pumped into the wastewater permeate collection tank, ensuring uniform mixing of the three liquids (wastewater membrane filtration permeate, wastewater membrane concentrate, and condensate) within the wastewater permeate collection tank. The ratio of the three liquids is controlled using a flow meter or metering pump, ensuring the specific gravity of the combined liquid is 1.1–1.2 g / mL. Subsequently, the combined liquid is pumped into the primary nanofiltration system under high pressure, operating at a pressure ≤40 kg / cm², controlling the specific gravity of the nanofiltration concentrate to be less than 1.3 g / mL and the calcium and magnesium removal rate to be no less than 90%. The concentrate obtained from the primary nanofiltration is mixed and diluted with condensate to a specific gravity of 1.1–1.2 g / mL before being sent to the secondary nanofiltration system, operating at a pressure ≤40 kg / cm², again controlling the specific gravity of the concentrate to be less than 1.3 g / mL and the calcium and magnesium removal rate to be no less than 90%. Phosphoric acid recovery rates for both primary and secondary nanofiltration can range from 50% to 70%. During the operation of both nanofiltration stages, chemical cleaning of the nanofiltration membrane elements is performed when situations occur such as a 10%–15% decrease in standardized permeate flow, a 30%–40% increase in salt permeability, or a 25% increase in standardized pressure differential. The permeate from both nanofiltration stages is then combined to form the nanofiltration permeate. The nanofiltration concentrate is highly enriched with impurities such as calcium and magnesium, which can be disposed of separately or utilized as resources, depending on the actual situation.

[0038] Step (5): Regeneration and Concentration. Nanofiltration permeate is fed into the regeneration evaporation equipment through the inlet valve and concentrated at a low temperature of 30-40℃. When the phosphoric acid mass fraction in the concentrate reaches more than 60%, a recovered acid that can be directly reused in the activation process is obtained. The recovered acid is discharged into the recovered acid tank through the discharge pump and discharge valve and returned to production. The secondary condensate generated by evaporation is discharged into the wastewater treatment plant for unified treatment.

[0039] Taking the actual operation of a phosphoric acid activated carbon production enterprise as an example, the main components of the enterprise's activated carbon wastewater (activated carbon washing wastewater), activated carbon waste liquid, and waste gas tower wastewater for the current month are shown in Table 1. Among the three materials, the activated carbon wastewater is a low-concentration phosphorus-containing wastewater, while the activated carbon waste liquid and waste gas tower wastewater have high phosphorus content, high calcium and magnesium impurities, or high organic pollutant content, and their physical properties differ significantly, making separate pretreatment suitable.

[0040] Table 1 shows the main components of the three phosphorus-containing materials used.

[0041] Note: "—" indicates that the material was not tested or that this indicator was not involved.

[0042] (I) Wastewater Branch of the Exhaust Gas Tower. After the wastewater from the exhaust gas tower is filtered by MCR, the membrane filtration permeate is concentrated by low-temperature evaporation at 30-40℃. The main components of the resulting waste gas concentrate and condensate are shown in Table 2. As can be seen from Table 2, the phosphoric acid mass fraction in the waste gas concentrate reaches 66.4%, which can be directly reused; the phosphorus content in the condensate is extremely low, while the chemical oxygen demand (COD) is high (approximately 15850 mg / L), which is a high COD wastewater that is difficult to directly meet discharge standards. In this embodiment, the condensate is used as a diluent for nanofiltration feed and disposed of within the system (see (IV) below for details), without the need for a separate advanced oxidation or biochemical treatment unit.

[0043] Table 2 shows the composition of the products obtained from low-temperature evaporation of wastewater from the waste gas tower branch.

[0044] Note: "—" indicates that it was not detected or not involved.

[0045] (II) Activated carbon wastewater branch and (III) Activated carbon waste liquid branch. The activated carbon wastewater, after MCR filtration, enters a two-stage membrane concentration system: the first-stage system concentrates the raw water specific gravity from 1.01 g / mL to 1.06 g / mL at a pressure ≤40 kg / cm², and the second-stage system concentrates the influent specific gravity from 1.06 g / mL to 1.20 g / mL at a pressure ≤70 kg / cm². The desalinated water produced by membrane concentration is collected and discharged into the wastewater treatment plant. The activated carbon waste liquid, after plate and frame filter press and MCR filtration, has its waste liquid membrane filtration permeate collected in a waste liquid permeate collection tank.

[0046] (IV) Combining and Two-Stage Nanofiltration. The wastewater membrane concentrate from the secondary concentrate collection tank and the condensate from the condensate collection tank are pumped into the wastewater permeate collection tank and mixed thoroughly with the wastewater membrane filtration permeate. The combined solution has a specific gravity of 1.12 g / mL. The combined solution enters the primary nanofiltration system and operates at a pressure ≤40 kg / cm². The main components and operating results of the primary nanofiltration influent, permeate, and concentrate are shown in Table 3. The primary nanofiltration permeate has a calcium and magnesium removal rate of approximately 97% and a phosphoric acid recovery rate of approximately 65%. The primary nanofiltration concentrate is then diluted with condensate to a specific gravity of 1.12 g / mL before entering the secondary nanofiltration system, which operates at a pressure ≤40 kg / cm². The secondary nanofiltration has a calcium and magnesium removal rate of approximately 96% and a phosphoric acid recovery rate of approximately 67%. The combined permeate from the two-stage nanofiltration system has a specific gravity of 1.10 g / mL, with a Ca content of approximately 31 mg / L and a Mg content of approximately 16 mg / L, indicating that calcium and magnesium impurities have been largely removed.

[0047] Table 3 shows the main components and operational results of each feed stream in the two-stage nanofiltration process.

[0048] Note: Primary nanofiltration achieves approximately 97% calcium and magnesium removal and approximately 65% ​​phosphoric acid recovery; secondary nanofiltration achieves approximately 96% calcium and magnesium removal and approximately 67% phosphoric acid recovery; "—" indicates that it is not involved or is operated at volumetric flow rate and not separately metered.

[0049] (V) Regeneration Concentration and Overall Effect. The combined permeate from the two-stage nanofiltration process is concentrated by evaporation at 30-40℃ using a regeneration evaporation device. The main components of the recovered acid are shown in Table 4: the recovered acid contains 63.8% phosphoric acid, approximately 98 mg / L of Ca, and approximately 51 mg / L of Mg, meeting the requirements for reuse in the activation process; the secondary condensate generated during evaporation is discharged into the wastewater treatment plant. As can be seen from this embodiment, without introducing any chemical reagents throughout the process, phosphoric acid from three sources of phosphorus-containing materials can be enriched into a directly reusable recovered acid through "separate pretreatment—combined nanofiltration for impurity removal—low-temperature evaporation and regeneration". At the same time, the condensate from the evaporation of the wastewater from the exhaust tower with a chemical oxygen demand of approximately 15850 mg / L is reused as nanofiltration diluent and disposed of within the system, realizing the recovery of phosphoric acid resources and the in-situ treatment of high chemical oxygen demand wastewater.

[0050] Table 4 shows the main components of the recovered acid obtained from regeneration evaporation.

[0051] It is understood that the above embodiments and parameters are merely illustrative examples and not intended to limit the invention. For example, other membrane filtration devices with equivalent retention and self-cleaning functions can also be used for MCR filtration; filter presses are not limited to plate and frame types; the number of stages, operating pressure, and specific gravity control points of two-stage membrane concentration and two-stage nanofiltration, as well as the ratio of the three feed liquids—waste liquid membrane filtration permeate, wastewater membrane concentrate, and condensate—can all be adjusted according to the actual properties of the feed liquid and reuse requirements; the heat source for low-temperature evaporation can be steam or a heat pump, in addition to combined cooling and heating systems. Any modifications, equivalent substitutions, and improvements made within the scope of the technical concept of this invention should fall within the protection scope of this invention.

Claims

1. A phosphoric acid regeneration device for activated carbon waste liquid, wastewater, and waste gas tower wastewater, characterized in that, include: The activated carbon waste liquid treatment branch includes a solid-liquid separation unit and a first membrane filtration unit connected in sequence, which are used to perform solid-liquid separation and membrane filtration of activated carbon waste liquid to obtain waste liquid membrane filtration permeate; The activated carbon wastewater treatment branch includes a second membrane filtration unit and a membrane concentration unit connected in sequence, which are used to perform membrane filtration and membrane concentration on activated carbon wastewater to obtain wastewater membrane concentrate. The wastewater treatment branch of the exhaust gas tower includes a third membrane filtration unit and a low-temperature evaporation unit connected in sequence. The low-temperature evaporation unit is equipped with a concentrate collection unit and a condensate collection unit, which are used to perform membrane filtration and low-temperature evaporation on the wastewater from the exhaust gas tower to obtain concentrate and condensate. The nanofiltration unit has an inlet for receiving the combined liquid, which comes from the membrane filtration permeate outlet of the activated carbon wastewater treatment branch, the membrane concentrate outlet of the activated carbon wastewater treatment branch, and the condensate collection unit. It is used to perform nanofiltration separation on the combined liquid to remove calcium and magnesium impurities in the liquid and obtain nanofiltration permeate and nanofiltration concentrate. And a regeneration and concentration unit, connected to the product water outlet of the nanofiltration unit, for low-temperature evaporation and concentration of the nanofiltration product water to obtain reusable phosphoric acid; The wastewater membrane filtration permeate, the wastewater membrane concentrate, and the condensate are combined before entering the nanofiltration unit, with the condensate serving as a diluent component of the combined feed solution.

2. The phosphoric acid regeneration device for activated carbon waste liquid, wastewater, and waste gas tower wastewater according to claim 1, characterized in that, The solid-liquid separation unit is a filter press; the first membrane filtration unit, the second membrane filtration unit, and the third membrane filtration unit are respectively a first membrane filtration device, a second membrane filtration device, and a third membrane filtration device; the membrane concentration unit is a two-stage membrane concentration system comprising a primary membrane concentration system and a secondary membrane concentration system connected in sequence; the low-temperature evaporation unit and the regeneration concentration unit are respectively a low-temperature evaporation device and a regeneration evaporation device; the nanofiltration unit is a two-stage nanofiltration system comprising a primary nanofiltration system and a secondary nanofiltration system; In the activated carbon waste liquid treatment branch, the filter press and the first membrane filtration device are connected in sequence, and the activated carbon waste liquid treatment branch also includes an activated carbon waste liquid collection tank, a filtrate collection tank and a waste liquid permeate collection tank. The activated carbon waste liquid collection tank is connected to the feed side of the filter press, the filtrate collection tank is connected between the filter press and the first membrane filtration device, and the waste liquid permeate collection tank is connected to the permeate side of the first membrane filtration device. The waste liquid membrane filtration permeate is collected in the waste liquid permeate collection tank. In the activated carbon wastewater treatment branch, the second membrane filtration device is sequentially connected to the two-stage membrane concentration system. The activated carbon wastewater treatment branch also includes an activated carbon wastewater collection tank, a wastewater product water collection tank, a primary concentrate collection tank, and a secondary concentrate collection tank. The activated carbon wastewater collection tank is connected to the feed side of the second membrane filtration device. The wastewater product water collection tank is connected between the second membrane filtration device and the primary membrane concentration system. The primary concentrate collection tank is connected between the primary membrane concentration system and the secondary membrane concentration system. The secondary concentrate collection tank is connected to the concentrate outlet side of the secondary membrane concentration system. The wastewater membrane concentrate is collected in the secondary concentrate collection tank. In the wastewater treatment branch of the exhaust gas tower, the third membrane filtration device and the low-temperature evaporation device are connected in sequence, and the wastewater treatment branch of the exhaust gas tower also includes a wastewater collection tank, a waste gas product water collection tank, a waste gas concentrate collection tank and a condensate collection tank. The wastewater collection tank is connected to the feed side of the third membrane filtration device, the waste gas product water collection tank is connected between the third membrane filtration device and the low-temperature evaporation device, and the waste gas concentrate collection tank and the condensate collection tank are respectively connected to the concentrate outlet and the condensate outlet of the low-temperature evaporation device. The feed inlet of the primary nanofiltration system is connected to the waste liquid permeate collection tank, the secondary concentrate collection tank is connected to the waste liquid permeate collection tank, the condensate collection tank is connected to the waste liquid permeate collection tank, the concentrate outlet of the primary nanofiltration system is connected to the feed inlet of the secondary nanofiltration system, the permeate outlet of the secondary nanofiltration system is connected to the feed inlet of the regeneration evaporation equipment, and the outlet of the regeneration evaporation equipment is connected to the acid recovery tank.

3. The phosphoric acid regeneration device for activated carbon waste liquid, wastewater, and waste gas tower wastewater according to claim 2, characterized in that, The first membrane filtration device, the second membrane filtration device, and the third membrane filtration device are all MCR filtration devices; The MCR filtration equipment is equipped with a sludge discharge pump, a backwash pump, and an aeration device. The backwash pump is connected to the product water collection tank of the corresponding branch. The fine filtration membrane of the MCR filtration device has a pore size of 0.1–10 μm and a porosity of 70%–90%.

4. The phosphoric acid regeneration device for activated carbon waste liquid, wastewater, and waste gas tower wastewater according to claim 2, characterized in that, Both the primary membrane concentration system and the secondary membrane concentration system use acid-resistant membranes. The pressure resistance of the primary concentration membrane is ≤40kg / cm², and the pressure resistance of the secondary concentration membrane is ≤70kg / cm². The specific gravity of the concentrate after concentration by the primary membrane concentration system is 1.06–1.10 g / mL, and the specific gravity of the concentrate after concentration by the secondary membrane concentration system is 1.10–1.20 g / mL.

5. The phosphoric acid regeneration device for activated carbon waste liquid, wastewater, and waste gas tower wastewater according to claim 2, characterized in that, The nanofiltration unit uses a nanofiltration membrane with a pressure resistance of ≤40kg / cm². The phosphoric acid recovery rates of both primary and secondary nanofiltration were 50%–70%. The feed inlet of the secondary nanofiltration system is also connected to the condensate collection tank, which is used to dilute the primary nanofiltration concentrate with the condensate before it enters the secondary nanofiltration system.

6. The phosphoric acid regeneration device for activated carbon waste liquid, wastewater, and waste gas tower wastewater according to claim 2, characterized in that, Both the regeneration evaporation equipment and the low-temperature evaporation equipment adopt a combined cooling and heating system, and the evaporation temperature is 30-40℃. Metering pumps are provided between the activated carbon waste liquid collection tank, the activated carbon wastewater collection tank, and the waste gas tower wastewater collection tank and the corresponding membrane filtration equipment. The feed side of the regeneration evaporation equipment is provided with a liquid inlet valve, and the regeneration evaporation equipment is provided with a discharge valve connected to the discharge pump.

7. A phosphoric acid regeneration process for activated carbon waste liquid, wastewater, and waste gas tower wastewater, characterized in that, Includes the following steps: (1) The wastewater from the exhaust gas tower is subjected to membrane filtration and low-temperature evaporation concentration to obtain concentrated liquid and condensate; (2) The activated carbon wastewater is subjected to membrane filtration and membrane concentration to obtain wastewater membrane concentrate; (3) Solid-liquid separation and membrane filtration are performed on activated carbon wastewater to obtain wastewater membrane filtration product water; (4) The waste liquid membrane filtration permeate, the waste water membrane concentrate and the condensate are combined and then separated by nanofiltration to remove calcium and magnesium impurities, so as to obtain nanofiltration permeate and nanofiltration concentrate; wherein, the condensate is used as a diluent for nanofiltration feed; (5) The nanofiltration permeate is concentrated by low-temperature evaporation to obtain reusable phosphoric acid.

8. The phosphoric acid regeneration process for activated carbon waste liquid, wastewater, and waste gas tower wastewater according to claim 7, characterized in that, In step (4): The wastewater membrane filtration permeate, the wastewater membrane concentrate, and the condensate are mixed in a certain proportion to make the specific gravity of the mixture 1.1-1.2 g / mL before being sent to a first-stage nanofiltration system. The first-stage nanofiltration system operates at a pressure of ≤40 kg / cm², and the specific gravity of the concentrate is controlled to be less than 1.3 g / mL, and the calcium and magnesium removal rate is not less than 90%. The primary nanofiltration concentrate is diluted with the condensate to a specific gravity of 1.1–1.2 g / mL and then fed into the secondary nanofiltration system. The secondary nanofiltration system operates at a pressure of ≤40 kg / cm², with the concentrate specific gravity controlled to be less than 1.3 g / mL and the calcium and magnesium removal rate controlled to be no less than 90%. The phosphoric acid recovery rate of both the primary nanofiltration and the secondary nanofiltration is 50% to 70%. When the standardized permeate flow rate decreases by 10%–15%, the salt permeate rate increases by 30%–40%, or the standardized pressure differential increases by 25%, the membrane element is chemically cleaned.

9. The phosphoric acid regeneration process for activated carbon waste liquid, wastewater, and waste gas tower wastewater according to claim 7, characterized in that, In step (2): The membrane concentration is a two-stage membrane concentration. The first-stage membrane concentration operates at a pressure of ≤40 kg / cm², and the specific gravity of the first-stage concentrate is 1.06~1.10 g / mL. The secondary membrane concentration operates at a pressure of ≤70 kg / cm², with a feed water specific gravity of 1.06–1.10 g / mL and a concentrate specific gravity of 1.10–1.20 g / mL. When the standardized permeate flow rate decreases by 10%–15%, the salt permeate rate increases by 30%–40%, or the standardized pressure differential increases by 25%, the membrane element is chemically cleaned.

10. The phosphoric acid regeneration process for activated carbon waste liquid, wastewater, and waste gas tower wastewater according to claim 7, characterized in that, In step (1), the membrane filtration is operated as follows: the machine is stopped for 1 to 3 minutes every 8 to 12 minutes of operation, and backwashed for 5 to 10 minutes after 8 to 12 cycles. The slag is discharged when the vacuum degree of the equipment is greater than 40 kPa. In step (5), the low-temperature evaporation and concentration are carried out at 30-40°C, and the phosphoric acid is concentrated to a mass fraction of not less than 60% before being reused.

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