System and method for removing hardness and organics from reverse osmosis concentrate

Abstract

The application discloses a system for removing hardness and organic matters in reverse osmosis concentrated brine from industrial waste gas, comprising a direct filtration membrane, wherein an input end of the direct filtration membrane is connected with waste water, and an output end of the direct filtration membrane is sequentially connected with a reverse osmosis membrane, a buffer adjusting tank, a reaction device, a mixing device, an inorganic membrane and a subsequent treatment unit; the system further comprises a shift condensate stripping unit, a low-temperature methanol washing unit and a power plant dust removal unit; the shift condensate stripping unit is sequentially connected with an ammonia-containing tail gas storage tank and the buffer adjusting tank; the low-temperature methanol washing unit is sequentially connected with a CO2-containing tail gas storage tank and the reaction device; and the power plant dust removal unit is sequentially connected with a porous solid waste material storage tank and the reaction device. The application further discloses a method for removing hardness and organic matters in reverse osmosis concentrated brine by using the system. The method utilizes industrial waste gas NH3 and CO2 and industrial solid waste materials, realizes the reuse of waste, and realizes the efficient removal of hardness and organic matters in reverse osmosis concentrated brine.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial concentrated brine treatment systems and methods, and relates to a system for removing hardness and organic matter from reverse osmosis concentrated brine using industrial waste gas. This invention also relates to a method for removing hardness and organic matter from reverse osmosis concentrated brine using the above system. Background Technology

[0002] The waste gas generated by coal chemical projects mainly consists of NH3, CO, N2, CO2, H2S, COS, H2O, CH4, and HCl, with complex compositions that are unusable in the process. To ensure the normal operation and safety of chemical production units, corresponding flare gas emission networks and flares are generally installed. Materials from various emission systems are first introduced into flare gas separators for gas-liquid separation. The liquid is returned to the recovery device, while the gas is introduced into a flare gas sealing tank. The gas from the sealing tank is then introduced into the flare chimney, where it is burned, and the main gas components are CO2 and H2O. The ammonia-containing tail gas from the shift converter condensate stripping and the top condensate from the stripping tower contain large amounts of NH3 and CO2. Additionally, the industrial tail gas emitted from the low-temperature methanol washing unit has a high CO2 concentration. Large amounts of CO2 emissions contribute to the greenhouse effect, and with policy changes, CO2 emission limits will gradually decrease. Improper treatment of emitted CO2 waste gas will affect the normal production and profitability of related coal chemical projects.

[0003] The utilization of mine water resources both domestically and internationally mainly includes industrial production water, agricultural production water, ecological replenishment water, and domestic water. Given the water shortage situation in Northwest China, the utilization of treated high-salinity mine water primarily includes coal production, washing and processing, power plant replenishment water, and coal chemical projects. Mine water treatment products are designed to meet standards for coal processing projects, Yellow River water, and cooling circulating water (HG / T3923-2007), and research and construction of zero-discharge mine water projects are being conducted. Currently, the main technical process for zero-discharge mine water treatment is "pretreatment + membrane concentration + secondary concentration + evaporation pretreatment + evaporation crystallization." During mine water operation, to prevent reverse osmosis and evaporator scaling, calcium and magnesium hardness ions in the mine water need to be removed. Current methods for calcium and magnesium ion removal include scale inhibitor methods, chemical precipitation methods, and ion exchange methods. Chemical precipitation methods consume large amounts of NaOH, CaO, and Na2CO3, increasing water treatment costs and introducing salt ions throughout the treatment process.

[0004] A patent application published on March 1, 2022, with publication number CN114105376A, discloses an electrochemical method for removing hardness from coal gasification ash water with high hardness and low carbonate alkalinity. This method utilizes carbon dioxide emitted from coal chemical processes to supplement inorganic carbon into the high-hardness, low-carbonate alkalinity coal gasification ash water. It employs an electrochemical hardening method primarily based on diaphragm electrolysis, supplemented by alkali supplementation, to improve the electrochemical hardening effect, reduce energy consumption, alleviate scaling problems in coal gasification systems, and achieve water conservation and emission reduction in coal gasification systems. However, this method suffers from complex operation procedures and unsatisfactory electrochemical performance under high-salt conditions.

[0005] A patent application published on November 2, 2021, with publication number CN113582399A, discloses a method for removing hardness using waste gas CO2. This method utilizes a pressurized dissolved gas reactor to better dissolve carbon dioxide gas into the liquid, achieving effective and thorough mixing of gas and liquid, improving reaction efficiency, and reducing gas waste caused by overflow. However, in practice, this method suffers from problems such as slow CO2 dissolution rate, slow reaction between CO2 and calcium and magnesium ions, and unsatisfactory hardness removal effect. Summary of the Invention

[0006] The purpose of this invention is to provide a system for removing hardness and organic matter from reverse osmosis brine in industrial waste gas. The system has a simple structure, low cost, and achieves efficient removal of hardness and organic matter from reverse osmosis brine.

[0007] Another objective of this invention is to provide a method for removing hardness and organic matter from reverse osmosis brine using industrial waste gas, which utilizes industrial waste gas NH3 and CO2, as well as industrial solid waste materials, to achieve efficient removal of hardness and organic matter from reverse osmosis brine.

[0008] The technical solution adopted in this invention is a system for removing hardness and organic matter from reverse osmosis concentrated brine in industrial waste gas, including a direct filter membrane, the input end of which is wastewater, and the output end is sequentially connected to a reverse osmosis membrane, a buffer equalization tank, a reaction device, a mixing device, an inorganic membrane, and a subsequent treatment unit.

[0009] The system also includes a shift condensate stripping unit, a cryogenic methanol washing unit, and a power plant dust removal unit; the shift condensate stripping unit is connected to an ammonia-containing tail gas storage tank, which is connected to a buffer regulating tank; the cryogenic methanol washing unit is connected to a CO2-containing tail gas storage tank, which is connected to a reaction device; and the power plant dust removal unit is connected to a porous solid waste material storage tank, which is connected to a reaction device.

[0010] The invention is further characterized by:

[0011] The output end of the direct filtration membrane is also connected to the input end of the mixing device; the output end of the reverse osmosis membrane is also connected to the reclaimed water tank; and the output end of the inorganic membrane is also connected to the filter press.

[0012] Another technical solution adopted in this invention is a method for removing hardness and organic matter from reverse osmosis concentrated brine in industrial waste gas. Using the above-mentioned system, the reverse osmosis concentrated brine first enters a direct filter membrane for preliminary filtration, then enters a reverse osmosis membrane to remove dissolved salts, colloids, microorganisms, and organic impurities. Next, it enters a buffer conditioning tank, where waste NH3 from the shift condensate stripping unit is used to adjust the pH of the wastewater and precipitate magnesium ions. Then, it enters a reaction device, where waste CO2 from a low-temperature methanol washing unit is used to precipitate calcium ions, and porous solid waste material generated by a power plant dust removal unit is used to adjust the pH of the wastewater, promoting the precipitation of calcium and magnesium ions. The effluent from the reaction device enters a mixing device, where it is mixed with the backwash liquid from the direct filter membrane and its pH is adjusted. Then, it enters an inorganic membrane for solid-liquid separation, and finally enters a subsequent treatment unit for further processing.

[0013] Another feature of the technical solution of this invention is that:

[0014] The method for removing hardness and organic matter from reverse osmosis concentrated brine in industrial waste gas is implemented according to the following steps:

[0015] Step 1: After the reverse osmosis concentrated brine is filtered through the direct filtration membrane, the permeate is sent to the reverse osmosis membrane unit, and the backwash solution is sent to the mixing device; after the permeate from the direct filtration membrane is separated by the reverse osmosis membrane, the permeate is sent to the reclaimed water tank for reuse, and the concentrated water enters the buffer equalization tank.

[0016] Step 2: The waste ammonia gas generated by the conversion condensate stripping unit is sent to the ammonia-containing tail gas storage tank, and then sent to the buffer conditioning tank through the ammonia-containing tail gas storage tank to adjust the pH of the reverse osmosis concentrate, precipitate the magnesium ions in the concentrate, and send the product water in the buffer conditioning tank to the reaction device.

[0017] Step 3: The CO2 generated by the low-temperature methanol washing unit is sent to a CO2-containing tail gas storage tank, and then from the CO2-containing tail gas storage tank to the reaction device, where it reacts with calcium ions in the concentrate to form calcium carbonate. The porous solid waste material generated by the power plant dust removal unit is sent to a porous solid waste material storage tank, and then from the porous solid waste material storage tank to the reaction device to adjust the pH of the reverse osmosis concentrate, continuously enhancing CO2 absorption and promoting the reaction of CO2 with calcium ions. - Reacts with magnesium ions;

[0018] Step 4: The effluent from the reaction device is sent to the mixing device, where it is mixed with the backwash liquid of the direct filter membrane and the pH is adjusted. Then it enters the inorganic membrane. After solid-liquid separation by the inorganic membrane, the permeate is sent to the subsequent treatment unit and the concentrate is sent to the filter press unit.

[0019] Step 5: The filter press filters the concentrated liquid produced by the inorganic membrane, and the resulting sludge is transported off-site for treatment. The filtrate is returned to the inlet of the upstream direct filter membrane for repeated treatment.

[0020] In step 1, the recovery rate of the direct filter membrane is 90-100%, the flux is 200-600 LMH, the material is PVDF, PTFE, Al2O3, SiO2 or organic-inorganic hybrid material, the filtration method is internal pressure or external pressure, and the operating pressure is 0-0.5 MPa.

[0021] In step 1, the recovery rate of the reverse osmosis membrane is 60-100%, the operating pressure is 0-2 MPa, and the Langerier saturation index of calcium carbonate on the concentrate side of the reverse osmosis membrane is 3.0-6.0.

[0022] In step 1, a scale inhibitor is added during the reverse osmosis membrane concentration process. The scale inhibitor is a phosphorus-free scale inhibitor or a polymer-based scale inhibitor.

[0023] In step 2, the pH in the buffer conditioning tank is 9-12, and the retention time of the concentrate is 0.5-5 hours.

[0024] In step 3, the porous solid waste material is fly ash, gasification slag, or coal gangue with a particle size of 30–100 μm and an addition amount of 0–10000 mg / L; the reaction device is a reaction kettle, reaction tower, fluidized bed, bubble tower, or spray tower; the reaction temperature is 30–80℃; the reaction pressure is 0.1–2 MPa; the pH is 9–12; and the reaction time is 0.5–5 h.

[0025] In step 4, the pH inside the mixing device is 6–9, and the liquid flow rate is 0.9–1.2 m / s; the working pressure of the inorganic membrane is 0.1–5 MPa, the flux is 300–900 LMH, and the material is ceramic, silicate, Al2O3, SiO2, or organic-inorganic hybrid material; the filtration method is internal pressure or external pressure, and the circulation flow rate is 100–200 m³ / h. 3 The membrane pore size is 0.05–0.5 μm, and the water content of the concentrate is 60–99%.

[0026] The beneficial effects of this invention are:

[0027] (1) The method of the present invention uses the waste NH3 generated by the condensate stripping unit of the coal chemical enterprise for pH adjustment in the hardening process, promotes the dissolution and absorption of CO2, and precipitates magnesium ions. There is no need to add alkali or calcium oxide, which reduces the cost and allows the waste ammonia to be reused. The high concentration of CO2 generated by the low temperature methanol washing unit is used as the source of carbonate to remove hardness in the water, reducing the amount of sodium carbonate added in the hardening process of concentrated water. This achieves CO2 emission reduction and CO2 resource utilization to generate carbonate for reuse. Porous solid waste material generated by coal chemical production is added to the reaction device. It is alkaline in water and has the functions of pH adjustment, CO2 adsorption and nucleation agent. It increases the solubility, adsorption rate and concentration of CO2 in the reaction device. At the same time, it can accelerate the reaction rate of CO2 with calcium and magnesium ions in wastewater. In addition, it can adsorb COD in wastewater. The technology used in the present invention has high hardening efficiency in high salt environment and can weaken the effect of salt ion effect on hardening and COD removal.

[0028] (2) In the method of the present invention, the pH is first adjusted to alkaline in the buffer adjustment tank to remove magnesium ions, while providing an alkaline environment for improving the solubility of carbon dioxide in the subsequent process. Then, magnesium ions and calcium ions are further removed by the subsequent reaction device. Compared with the existing process, it has the advantages of high removal efficiency and high carbon dioxide utilization efficiency.

[0029] (3) The industrial wastewater in the method of the present invention can be directly entered into the reverse osmosis membrane for concentration after passing through a simple direct filtration membrane. The addition of scale inhibitor can concentrate the calcium and magnesium ions in the concentrated water by a high factor, thereby improving the efficiency of subsequent hardness removal treatment.

[0030] (4) In the entire process of hardness removal from concentrated brine, no external chemical raw materials are required. All raw materials are industrial waste ammonia, CO2 and alkaline porous solid waste materials, which realizes the recycling of waste materials. While reducing the consumption of reagents in the wastewater treatment process, it also reduces the emission of CO2 and harmful gases from enterprises, and achieves efficient removal of hardness and organic matter from concentrated brine. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the system of the present invention. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0033] This invention relates to a system for removing hardness and organic matter from reverse osmosis concentrated brine in industrial waste gas, such as... Figure 1 As shown, it includes a direct filtration membrane, a reverse osmosis membrane, a reclaimed water tank, a buffer conditioning tank, a shift condensate stripping unit, an ammonia-containing tail gas storage tank, a reaction device, a low-temperature methanol washing unit, a CO2-containing tail gas storage tank, a power plant dust removal unit, a porous solid waste material storage tank, a mixing device, an inorganic membrane, a post-treatment unit, and a filter press unit.

[0034] The direct filtration membrane is used for preliminary filtration of wastewater. Its input is wastewater, and its output is sequentially connected to a reverse osmosis membrane, a buffer equalization tank, a reaction device, a mixing device, an inorganic membrane, and subsequent treatment units. The reverse osmosis membrane removes dissolved salts, colloids, microorganisms, organic matter, and other impurities from the water. The buffer equalization tank adjusts the pH of the water and precipitates magnesium ions. The reaction device precipitates calcium and magnesium ions and further adjusts the pH during the reaction process. The mixing device mixes the permeate from the direct filtration membrane and the permeate from the reaction device and further adjusts the pH. The permeate from the mixing device enters the inorganic membrane for solid-liquid separation, and then undergoes subsequent treatment.

[0035] In addition, the output of the direct filtration membrane is connected to the input of the mixing unit to deliver the permeate from the direct filtration membrane to the mixing unit. The output of the reverse osmosis membrane is also connected to a reclaimed water tank, which is used to store the permeate from the reverse osmosis membrane for reuse.

[0036] The shift condensate stripping unit is a commonly used piece of equipment in coal chemical production. This process generates waste NH3. This unit is connected to an ammonia-containing tail gas storage tank, and then to a buffer equalization tank. The purpose is to send the waste NH3 generated by the shift condensate stripping unit into the ammonia-containing tail gas storage tank for temporary storage, and then into the buffer equalization tank, where the NH3 is used to adjust the pH value of the wastewater.

[0037] The low-temperature methanol washing unit is also one of the commonly used equipment in the coal chemical industry. CO2 is generated during the production process of this process. The unit is connected to a CO2-containing tail gas storage tank and then to a reaction device. The purpose is to send the CO2 generated by the low-temperature methanol washing unit into the CO2-containing tail gas storage tank and then into the reaction device to precipitate calcium ions in the wastewater.

[0038] The power plant dust removal unit is the dust removal process in the power plant. This process generates a large amount of porous solid waste material. The unit is connected to a porous solid waste material storage tank, and then to a reaction device. The purpose is to send the porous solid waste material generated by the power plant dust removal unit into the porous solid waste material storage tank, and then into the reaction device to further adjust the pH of the wastewater.

[0039] In addition, the output end of the inorganic membrane is connected to a filter press for pressing the concentrated liquid produced by the inorganic membrane. The sludge produced after pressing is transported off-site for treatment, and the filtrate is returned to the inlet end of the upstream direct filter membrane for repeated treatment.

[0040] The method for removing hardness and organic matter from reverse osmosis concentrated brine in industrial waste gas according to the present invention is based on the above system and is implemented according to the following steps:

[0041] Step 1: After industrial wastewater is filtered through a direct filtration membrane, the permeate is sent to the reverse osmosis membrane unit, and the backwash liquid is sent to the inlet of the subsequent mixing device. During the reverse osmosis membrane concentration process, a high-efficiency scale inhibitor is added. After the permeate from the direct filtration membrane is separated by the reverse osmosis membrane, the permeate is sent to the recycled water tank for reuse, and the concentrated water enters the buffer equalization tank.

[0042] The influent suspended solids are 0–5000 mg / L, TDS is 1000–10000 mg / L, hardness is 200–1000 mg / L, and COD is 0–1000 mg / L.

[0043] The recovery rate of the direct filter membrane is 90-100%, the flux is 200-600 LMH, the material is PVDF, PTFE, Al2O3, SiO2 or organic-inorganic hybrid material, the filtration method is internal pressure or external pressure, and the operating pressure is 0-0.5 MPa.

[0044] The recovery rate of the reverse osmosis membrane is 60-100%, the operating pressure is 0-2 MPa, the scale inhibitor used is a phosphorus-free scale inhibitor or a polymer scale inhibitor, and the Langerier saturation index of calcium carbonate on the concentrate side of the reverse osmosis membrane is 3.0-6.0.

[0045] Step 2: The waste ammonia gas generated by the conversion condensate stripping unit is sent to the ammonia-containing tail gas storage tank, and then sent to the buffer conditioning tank through the ammonia-containing tail gas storage tank to adjust the pH of the reverse osmosis concentrate, directly precipitating magnesium ions in the concentrate. The permeate in the buffer conditioning tank is sent to the reaction device.

[0046] In this unit, the pressure of the ammonia-containing waste gas from the condensate stripping process is 0.1–0.5 MPa, and the temperature is 90–150℃; the pH in the buffer equalization tank is 9–12; and the concentrate retention time is 0.5–5 h. As the concentrate enters the buffer equalization tank, the scale inhibitor becomes ineffective, releasing calcium and magnesium ions. The following reaction then occurs within the buffer equalization tank: NH3 + H2O → NH4+ + +OH - OH - +Mg 2+ —Mg(OH)2↓.

[0047] Step 3: The CO2 generated by the low-temperature methanol washing unit is sent to a CO2-containing tail gas storage tank, and then from the CO2-containing tail gas storage tank to the reaction device, where it reacts with calcium ions in the concentrate to produce calcium carbonate. The alkaline solid waste generated by the power plant dust removal unit is sent to a porous solid waste material storage tank, and then from the porous solid waste material storage tank to the reaction device. This process adjusts the pH of the reverse osmosis concentrate, continuously enhancing CO2 absorption, while simultaneously enhancing the precipitation of calcium carbonate and magnesium hydroxide crystals, promoting the reaction between CO2 and calcium ions, and increasing OH-. - Reacts with magnesium ions;

[0048] The low-temperature methanol washing unit generates CO2 at a pressure of 0.1–0.5 MPa and a temperature of 20–100°C. The porous solid waste material is fly ash, gasification slag, or coal gangue with a particle size of 30–100 μm and a dosage of 0–10000 mg / L. The reaction device can be a reactor, reaction tower, fluidized bed, bubble tower, or spray tower. The reaction temperature is 30–80°C, the reaction pressure is 0.1–2 MPa, the pH is 9–12, and the reaction time is 0.5–5 h.

[0049] The reaction principle of waste gas and concentrated water in the reaction device is as follows:

[0050] The pH of the reverse osmosis concentrate is adjusted to alkaline using ammonia-containing waste gas, which then enters the reaction device. The CO2 in the waste gas reacts with calcium ions in the concentrate to form calcium carbonate and OH-. - It reacts with magnesium ions to form magnesium hydroxide; as CO2 dissolves and OH-... - The pH inside the reaction device decreases due to the consumption of carbon dioxide. Then, alkaline porous solid waste material is added to restore the pH inside the reaction device to alkalinity, promoting the dissolution of carbon dioxide and thus promoting the production of calcium carbonate and magnesium hydroxide. The produced calcium carbonate and magnesium hydroxide crystals are adsorbed on the surface of the alkaline porous solid waste material, which can also adsorb COD in the concentrated water.

[0051] NH3 + H2O → NH4 + +OH -

[0052] OH - +Mg 2+ →Mg(OH)2↓

[0053] CO2 + H2O → H2CO3

[0054] H2CO3→HCO3 - +H +

[0055] HCO3 - →H + +CO3 2-

[0056] Ca(OH)2→Ca 2+ +2OH -

[0057] Ca 2+ +CO3 2- →CaCO3↓

[0058] Step 4: The effluent from the reaction device is sent to the mixing device, where it is mixed with the backwash liquid from the direct filter membrane and the pH is adjusted. Then it enters the inorganic membrane. After solid-liquid separation by the inorganic membrane, the permeate is sent to the subsequent treatment unit, and the concentrate is sent to the filter press unit.

[0059] The pH inside the mixing device is 6–9, and the liquid flow rate inside the mixing device is 0.9–1.2 m / s.

[0060] The inorganic membrane operates at a pressure of 0.1–5 MPa, with a flux of 300–900 LMH. It is made of ceramic, silicate, Al₂O₃, SiO₂, or a hybrid organic-inorganic material. The filtration method is either internal or external pressure, and the circulation flow rate is 100–200 m³ / h. 3 The membrane pore size is 0.05–0.5 μm, and the water content of the concentrate is 60–99%.

[0061] Step 5: The filter press filters the concentrated liquid produced by the inorganic membrane, and the resulting sludge is transported off-site for treatment. The filtrate is returned to the inlet of the upstream direct filter membrane for repeated treatment.

[0062] The sludge produced by the filter press has a water content of 50-80% and a pH of 6.5-8.5.

[0063] Example 1

[0064] This embodiment specifically includes the following steps:

[0065] Step 1: Mine water discharged from a coal mine in Ordos was selected as the water source to be treated. The suspended solids were 35 mg / L, the influent TDS was 1269 mg / L, the hardness was 236 mg / L, and the COD was 32 mg / L. After the mine water was filtered through a direct filtration membrane, the permeate was sent to the reverse osmosis membrane unit, and the backwash solution was sent to the inlet of the subsequent mixing device. After the permeate was separated by the reverse osmosis membrane, it was sent to the reuse water tank for reuse, and the concentrate entered the subsequent buffer conditioning tank. A high-efficiency phosphorus-free scale inhibitor was added during the reverse osmosis membrane concentration process. The recovery rate of the direct filtration membrane was 90%, the flux was 230 LMH, the material was PVDF sintered material, the filtration method was external pressure, and the operating pressure was 0.2 MPa. The recovery rate of the reverse osmosis membrane was 75%, the operating pressure was 0.95 MPa, and the Langerile saturation index of calcium carbonate on the concentrate side of the reverse osmosis membrane was 3.5.

[0066] Step 2: The waste ammonia gas with a pressure of 0.15 MPa and a temperature of 95°C generated by the condensate stripping unit is sent to the ammonia-containing tail gas storage tank, and then sent to the buffer conditioning tank through the ammonia-containing tail gas storage tank to adjust the pH of the reverse osmosis concentrate to 9.5, precipitate the magnesium ions in the concentrate, and send the permeate in the buffer conditioning tank into the reaction device.

[0067] Step 3: CO2 generated by the low-temperature methanol washing unit at a pressure of 0.15 MPa and a temperature of 25°C is pressurized and fed into a CO2-containing tail gas storage tank. Then, it is fed into the reaction tower. During the reaction, the reaction pressure is monitored, and CO2-containing tail gas is continuously added to maintain the pressure in the reaction tower at 0.5 MPa, allowing it to react with calcium ions in the concentrate to form calcium carbonate. Fly ash with a particle size of 35 μm generated by the power plant's dust removal unit is added to a porous solid waste material storage tank, and then added to the reaction tower at a concentration of 100 mg / L. This maintains the pH of the reverse osmosis concentrate in the reaction tower above 9, continuously enhancing CO2 absorption and simultaneously enhancing the precipitation of calcium carbonate and magnesium hydroxide crystals, promoting the reaction between CO2 and calcium ions, and OH... - It reacts with magnesium ions and simultaneously adsorbs COD. The temperature inside the reaction tower is 40℃, the pH is 9.6, and the reaction time is 1.5h.

[0068] Step 4: The effluent from the reaction tower is fed into a mixing device to mix with the backwash liquid from the direct filtration membrane. The pH is adjusted to 7.5, and the liquid flow rate within the mixing device is 0.95 m / s. The mixture is then fed into a subsequent inorganic membrane. After solid-liquid separation by the inorganic membrane, the permeate is sent to the subsequent treatment unit, and the concentrate is sent to the filter press unit. The inorganic membrane operates at a pressure of 0.5 MPa, has a flux of 360 LMH, is made of ceramic material, uses an internal pressure filtration method, and has a circulation flow rate of 120 m³ / s. 3 / h, membrane pore size 0.05μm, concentrate water content 75%;

[0069] Step 5: The filter press filters the concentrated liquid produced by the inorganic membrane. The resulting sludge is transported off-site for treatment. The filtrate is returned to the inlet of the front-end direct filter membrane for repeated treatment. The sludge produced by the filter press has a water content of 55% and a pH of 7.2.

[0070] The test results showed that the hardness of the reverse osmosis concentrate was 912 mg / L and the COD was 119 mg / L. After hardness removal in the buffer conditioning tank and the reaction device, the hardness was reduced to 126 mg / L and the COD was reduced to 59 mg / L. The hardness removal rate reached 86.2% and the COD removal rate reached 50.4%.

[0071] Example 2

[0072] This embodiment specifically includes the following steps:

[0073] Step 1: Wastewater from a coal chemical project in Ordos was selected as the treatment source. The suspended solids were 58 mg / L, the influent TDS was 2158 mg / L, the hardness was 532 mg / L, and the COD was 36 mg / L. After filtration through a direct filtration membrane, the permeate was sent to the reverse osmosis membrane unit, and the backwash solution was sent to the inlet of the subsequent mixing unit. After separation by the reverse osmosis membrane, the permeate was sent to a reuse tank for recycling, and the concentrate entered a subsequent buffer equalization tank. A high-efficiency polymer membrane antiscalant was added during the reverse osmosis membrane concentration process. The direct filtration membrane had a recovery rate of 95%, a flux of 430 LMH, was made of α-Al₂O₃ sintered material, used external pressure filtration, and operated at a pressure of 0.32 MPa. The reverse osmosis membrane had a recovery rate of 80%, an operating pressure of 1.25 MPa, and a calcium carbonate Langerier saturation index of 4.6 on the concentrate side.

[0074] Step 2: The waste ammonia gas with a pressure of 0.23 MPa and a temperature of 105°C generated by the conversion condensate stripping unit is sent to the ammonia-containing tail gas storage tank, and then sent to the buffer conditioning tank through the ammonia-containing tail gas storage tank to adjust the pH of the reverse osmosis concentrate to 10.3, precipitate the magnesium ions in the concentrate, and send the permeate in the buffer conditioning tank into the reaction device.

[0075] Step 3: CO2 generated by the low-temperature methanol washing unit at a pressure of 0.27 MPa and a temperature of 52°C is pressurized and fed into a CO2-containing tail gas storage tank. Then, it is fed into the reactor. During the reaction, the reaction pressure is monitored, and CO2-containing tail gas is continuously added to maintain the pressure inside the reactor at 1.2 MPa, allowing it to react with calcium ions in the concentrate to form calcium carbonate. Fly ash with a particle size of 50 μm generated by the power plant's dust removal unit is added to a porous solid waste material storage tank, and then added to the reactor at a concentration of 320 mg / L. This maintains the pH of the reverse osmosis concentrate in the reactor above 10, continuously enhancing CO2 absorption and simultaneously enhancing the precipitation of calcium carbonate and magnesium hydroxide crystals, promoting the reaction between CO2 and calcium ions, and OH... - It reacts with magnesium ions and simultaneously adsorbs COD. The temperature inside the reactor is 55℃, the pH is 10.5, and the reaction time is 3.5h.

[0076] Step 4: The effluent from the reactor is fed into a mixing device to mix with the backwash solution from the direct filtration membrane. The pH is adjusted to 8.2, and the liquid flow rate within the mixing device is 1.1 m / s. The mixture is then fed into a subsequent inorganic membrane. After solid-liquid separation by the inorganic membrane, the permeate is sent to the subsequent treatment unit, and the concentrate is sent to the filter press unit. The inorganic membrane operates at a pressure of 1.3 MPa, has a flux of 460 LMH, is made of silicate material, uses external pressure filtration, and has a circulation flow rate of 150 m³ / s. 3 / h, membrane pore size is 0.1μm, and the water content of the concentrate is 72%;

[0077] Step 5: The filter press filters the concentrated liquid produced by the inorganic membrane. The resulting sludge is transported off-site for treatment. The filtrate is returned to the inlet of the front-end direct filter membrane for repeated treatment. The sludge produced by the filter press has a water content of 62% and a pH of 7.5.

[0078] The test results showed that the hardness of the reverse osmosis concentrate was 2560 mg / L and the COD was 168 mg / L. After hardness removal in the buffer conditioning tank and the reaction device, the hardness was reduced to 521 mg / L and the COD was reduced to 96 mg / L. The hardness removal rate reached 79.6% and the COD removal rate reached 42.9%.

[0079] Example 3

[0080] This embodiment specifically includes the following steps:

[0081] Step 1: Mine water discharged from a coal mine in Ordos was selected as the treatment water source. The suspended solids were 126 mg / L, the influent TDS was 3259 mg / L, the hardness was 369 mg / L, and the COD was 40 mg / L. After the mine water was filtered through a direct filtration membrane, the permeate was sent to the reverse osmosis membrane unit, and the backwash solution was sent to the inlet of the subsequent mixing device. After the permeate was separated by the reverse osmosis membrane, it was sent to the reuse water tank for reuse, and the concentrate entered the subsequent buffer conditioning tank. A high-efficiency phosphorus-free scale inhibitor was added during the reverse osmosis membrane concentration process. The recovery rate of the direct filtration membrane was 98%, the flux was 520 LMH, the material was Al2O3-SiO2 sintered composite material, the filtration method was internal pressure, and the operating pressure was 0.38 MPa. The recovery rate of the reverse osmosis membrane was 70%, the operating pressure was 1.26 MPa, and the calcium carbonate Langerier saturation index on the concentrate side of the reverse osmosis membrane was 5.2.

[0082] Step 2: The waste ammonia gas with a pressure of 0.32 MPa and a temperature of 110°C generated by the conversion condensate stripping unit is sent to the ammonia-containing tail gas storage tank, and then sent to the buffer conditioning tank through the ammonia-containing tail gas storage tank to adjust the pH of the reverse osmosis concentrate to 10.5, precipitate the magnesium ions in the concentrate, and send the permeate in the buffer conditioning tank into the reaction device.

[0083] Step 3: CO2 generated at 0.32 MPa and 65°C from the low-temperature methanol washing unit is pressurized and fed into a CO2-containing tail gas storage tank. The CO2-containing tail gas is then fed into the fluidized bed. The reaction pressure is monitored during the reaction process, and CO2-containing tail gas is continuously added to maintain the pressure in the fluidized bed at 1.8 MPa, allowing it to react with calcium ions in the concentrate to form calcium carbonate. Gasification slag with a particle size of 80 μm from the coal gasification unit is added to a porous solid waste material storage tank, and then added to the fluidized bed at a concentration of 510 mg / L. This maintains the pH of the reverse osmosis concentrate in the fluidized bed above 10.5, continuously enhancing CO2 absorption and simultaneously enhancing the precipitation of calcium carbonate and magnesium hydroxide crystals, promoting the reaction of CO2 with calcium ions, and increasing OH...- It reacts with magnesium ions and simultaneously adsorbs COD. The temperature in the fluidized bed is 80℃, the pH is 10.2, and the reaction time is 5.0h.

[0084] Step 4: The fluidized bed effluent is fed into a mixing device and mixed with the backwash liquid from the direct filtration membrane. The pH is adjusted to 8.5, and the liquid flow rate within the mixing device is 1.2 m / s. The mixture is then fed into a subsequent inorganic membrane. After solid-liquid separation by the inorganic membrane, the permeate is sent to a subsequent treatment unit, and the concentrate is sent to a filter press unit. The inorganic membrane operates at a pressure of 2.3 MPa, has a flux of 630 LMH, is made of alumina material, uses an internal pressure filtration method, and has a circulation flow rate of 180 m³ / s. 3 / h, membrane pore size 0.5μm, concentrate water content 80%;

[0085] Step 5: The filter press filters the concentrated liquid produced by the inorganic membrane. The resulting sludge is transported off-site for treatment. The filtrate is returned to the inlet of the front-end direct filter membrane for repeated treatment. The sludge produced by the filter press has a water content of 65% and a pH of 8.0.

[0086] The test results showed that the hardness of the reverse osmosis concentrate was 1126 mg / L and the COD was 125 mg / L. After hardness removal in the buffer conditioning tank and the reaction device, the hardness was reduced to 136 mg / L and the COD was reduced to 62 mg / L. The hardness removal rate reached 87.9% and the COD removal rate reached 50.8%.

[0087] Example 4

[0088] This embodiment of the system for removing hardness and organic matter from reverse osmosis concentrated brine in industrial waste gas includes a direct filter membrane, with wastewater as its input and a reverse osmosis membrane, a buffer conditioning tank, a reaction device, a mixing device, an inorganic membrane, and a subsequent treatment unit connected in sequence to its output.

[0089] The system also includes a shift condensate stripping unit, a cryogenic methanol washing unit, and a power plant dust removal unit; the shift condensate stripping unit is connected to an ammonia-containing tail gas storage tank, which is connected to a buffer regulating tank; the cryogenic methanol washing unit is connected to a CO2-containing tail gas storage tank, which is connected to a reaction device; and the power plant dust removal unit is connected to a porous solid waste material storage tank, which is connected to a reaction device.

[0090] Example 5

[0091] Based on Example 4, the output end of the direct filtration membrane is also connected to the input end of the mixing device; the output end of the reverse osmosis membrane is also connected to the reclaimed water tank; and the output end of the inorganic membrane is also connected to the filter press.

[0092] Example 6

[0093] Using the system of Example 5, the method for removing hardness and organic matter from reverse osmosis brine in industrial waste gas is as follows: The reverse osmosis brine first enters a direct filter membrane for preliminary filtration, then enters a reverse osmosis membrane to remove dissolved salts, colloids, microorganisms, and organic impurities; then it enters a buffer conditioning tank, where waste NH3 from the shift condensate stripping unit is used to adjust the pH of the wastewater and precipitate magnesium ions; then it enters a reaction unit, where waste CO2 from the low-temperature methanol washing unit is used to precipitate calcium ions, and porous solid waste material generated by the power plant dust removal unit is used to adjust the pH of the wastewater to promote the precipitation of calcium and magnesium ions; the effluent from the reaction unit enters a mixing unit, where it is mixed with the backwash liquid from the direct filter membrane and the pH is adjusted, then it enters an inorganic membrane for solid-liquid separation, and finally enters a subsequent treatment unit for further treatment.

[0094] Therefore, the method of this invention for removing hardness and organic matter from concentrated brine is simple in process. It utilizes waste ammonia gas from coal chemical projects for pH adjustment in the hardening process, uses CO2 for hardness removal in wastewater, and simultaneously adds alkaline porous solid waste materials to enhance the removal of calcium and magnesium ions and COD in the wastewater. This pioneering new technology route for hardening removal in industrial wastewater achieves zero consumption of purchased reagents in the hardening process, reduces the operating costs of wastewater treatment plants, and simultaneously achieves emission reduction of waste gas and carbon from coal chemical enterprises. It has significant economic, technical, and ecological implications.

Claims

1. A system for removing hardness and organic matter from reverse osmosis concentrated brine in industrial waste gas, characterized in that, It includes a direct filtration membrane, with wastewater as its input and a reverse osmosis membrane, a buffer equalization tank, a reaction device, a mixing device, an inorganic membrane, and a subsequent treatment unit connected in sequence to its output. The system also includes a shift condensate stripping unit, a low-temperature methanol washing unit, and a power plant dust removal unit; the shift condensate stripping unit is connected to an ammonia-containing tail gas storage tank, which is connected to a buffer regulating tank; the low-temperature methanol washing unit is connected to a CO2-containing tail gas storage tank, which is connected to a reaction device; and the power plant dust removal unit is connected to a porous solid waste material storage tank, which is connected to a reaction device. The output end of the direct filtration membrane is also connected to the input end of the mixing device; the reverse osmosis membrane has two output ends, one for permeate and one for concentrate, with the concentrate end connected to the buffer equalization tank and the permeate end connected to the reclaimed water tank; the output end of the inorganic membrane is also connected to the filter press. The porous solid waste material storage tank contains solid waste material generated by the power plant's dust removal unit, and this material is alkaline.

2. A method for removing hardness and organic matter from reverse osmosis concentrated brine in industrial waste gas, characterized in that, The system as described in claim 1 is implemented specifically according to the following steps: Step 1: After the reverse osmosis concentrated brine is filtered through the direct filtration membrane, the permeate is sent to the reverse osmosis membrane unit, and the backwash solution is sent to the mixing device; after the permeate from the direct filtration membrane is separated by the reverse osmosis membrane, the permeate is sent to the reclaimed water tank for reuse, and the concentrated water enters the buffer equalization tank. Step 2: The waste ammonia gas generated by the conversion condensate stripping unit is sent to the ammonia-containing tail gas storage tank, and then sent to the buffer conditioning tank through the ammonia-containing tail gas storage tank to adjust the pH of the reverse osmosis concentrate, precipitate the magnesium ions in the concentrate, and send the product water in the buffer conditioning tank to the reaction device. Step 3: The CO2 generated by the low-temperature methanol washing unit is sent to a CO2-containing tail gas storage tank, and then from the CO2-containing tail gas storage tank to the reaction device, where it reacts with calcium ions in the concentrate to form calcium carbonate. The porous solid waste material generated by the power plant dust removal unit is sent to a porous solid waste material storage tank, and then from the porous solid waste material storage tank to the reaction device to adjust the pH of the reverse osmosis concentrate, continuously enhancing CO2 absorption and promoting the reaction of CO2 with calcium ions. - Reacts with magnesium ions; Step 4: The effluent from the reaction device is sent to the mixing device, where it is mixed with the backwash liquid of the direct filter membrane and the pH is adjusted. Then it enters the inorganic membrane. After solid-liquid separation by the inorganic membrane, the permeate is sent to the subsequent treatment unit and the concentrate is sent to the filter press unit. Step 5: The filter press filters the concentrated liquid produced by the inorganic membrane, and the resulting sludge is transported off-site for treatment. The filtrate is returned to the inlet of the upstream direct filter membrane for repeated treatment.

3. The method for removing hardness and organic matter from reverse osmosis concentrated brine from industrial waste gas according to claim 2, characterized in that, In step 1, the recovery rate of the direct filter membrane is 90-100%, the flux is 200-600 LMH, the material is PVDF, PTFE, Al2O3, SiO2 or organic-inorganic hybrid material, the filtration method is internal pressure or external pressure, and the operating pressure is 0-0.5 MPa.

4. The method for removing hardness and organic matter from reverse osmosis concentrated brine from industrial waste gas according to claim 2, characterized in that, In step 1, the recovery rate of the reverse osmosis membrane is 60-100%, the operating pressure is 0-2 MPa, and the Langerier saturation index of calcium carbonate on the concentrate side of the reverse osmosis membrane is 3.0-6.

0.

5. The method for removing hardness and organic matter from reverse osmosis concentrated brine from industrial waste gas according to claim 2, characterized in that, In step 1, a scale inhibitor is added during the reverse osmosis membrane concentration process. The scale inhibitor is a phosphorus-free scale inhibitor or a polymer-based scale inhibitor.

6. The method for removing hardness and organic matter from reverse osmosis concentrated brine from industrial waste gas according to claim 2, characterized in that, In step 2, the pH in the buffer conditioning tank is 9-12, and the retention time of the concentrate is 0.5-5 hours.

7. The method for removing hardness and organic matter from reverse osmosis concentrated brine from industrial waste gas according to claim 2, characterized in that, In step 3, the porous solid waste material is fly ash, gasification slag, or coal gangue with a particle size of 30–100 μm and an addition amount of 0–10000 mg / L; the reaction device is a reaction kettle, reaction tower, fluidized bed, bubble tower, or spray tower, the reaction temperature is 30–80℃, the reaction pressure is 0.1–2 MPa, the pH is 9–12, and the reaction time is 0.5–5 h.

8. The method for removing hardness and organic matter from reverse osmosis concentrated brine from industrial waste gas according to claim 2, characterized in that, In step 4, the pH inside the mixing device is 6–9, and the liquid flow rate is 0.9–1.2 m / s; the working pressure of the inorganic membrane is 0.1–5 MPa, the flux is 300–900 LMH, and the material is ceramic, silicate, Al2O3, SiO2, or organic-inorganic hybrid material; the filtration method is internal pressure or external pressure, and the circulation flow rate is 100–200 m³ / h. 3 The membrane pore size is 0.05–0.5 μm, and the water content of the concentrate is 60–99%.

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