Supercritical gasification and salt fractionation disposal and recovery process for high-concentration salt-containing organic wastewater

Abstract

The supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater involves first removing impurity anions from the wastewater using soluble alkaline earth metal salts, then removing divalent and higher-valent metal ions through flocculation and air flotation using water-soluble organic macromolecular alkali metal salts. The scum is dewatered and then disposed of or utilized harmlessly. Next, the wastewater is pressurized to ≥22.1 MPa using a high-pressure pump. A supercritical water gasification reaction is then performed at 360-700℃ using an electromagnetically heated tubular reactor and a supercritical delayed gasification reactor, with a residence time of 0.1-80 minutes. This generates syngas, a supercritical high-temperature purified water mixture, and a high-concentration alkali metal salt slurry. After heat exchange in the supercritical water-gas mixture, gas-liquid separation occurs. The syngas is discharged, and the high-concentration alkali metal salt slurry is switched through the bottom lock bucket of the supercritical delayed gasification reactor and diluted with dilute brine to form a high-temperature concentrated brine before being discharged. After cooling, the concentrated brine undergoes classification and crystallization to precipitate pure alkali metal salts as the product, while the dilute brine is returned to the lock bucket for recycling.

Description

Technical Field

[0001] This invention provides a supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater, which relates to the chemical and environmental protection fields. Background Technology

[0002] High-concentration saline organic wastewater has a complex composition, rich not only in inorganic salts but also in some organic matter and heavy metal ions, making it highly polluting. It contains a large number of ions and inorganic salts, with cations mainly including Ca2+. 2+ Mg 2+ Na + 、 K + These substances inhibit the growth and reproduction of microorganisms; while anions are mainly SO42-. 2- NO3 - OH - Such substances can enhance the activity of microorganisms; however, they contain organic pollutants, some of which are at high concentrations, significantly limiting the application of traditional methods for treating saline organic wastewater. Direct discharge not only wastes water resources but also causes serious environmental pollution problems. Therefore, society has paid considerable attention to the resource utilization of high-concentration saline organic wastewater, and how to maximize its resource utilization is a current hot topic of discussion.

[0003] The resource-based treatment of high-concentration saline organic wastewater typically aims to recover soluble alkali metal salts such as NaCl, Na₂SO₄, NaNO₃, KCl, K₂SO₄, KNO₃, LiCl, Li₂SO₄, or LiNO₃, employing a combined treatment process of "pretreatment + membrane treatment + evaporation crystallization." Conventional pretreatment technologies include coagulation sedimentation, advanced oxidation, multi-media filtration, and ultrafiltration. Commonly used coagulants in pretreatment are primarily aluminum-based and iron-based, supplemented by polymeric coagulants; advanced oxidation technologies mainly include ozone oxidation, electrocatalytic oxidation, and Fenton-like processes. After pretreatment such as flotation, coagulation, and filtration, the high-concentration saline organic wastewater enters a membrane concentration system. Currently, many enterprises use a dual-membrane method (ultrafiltration + reverse osmosis) for treatment. The freshwater obtained in this process can be used as makeup water for the circulating cooling water system or recycled water for enterprise production, while the concentrated brine, accounting for approximately 35% of the treated volume, enters the secondary concentration unit for concentrated brine. Depending on the needs, the wastewater may require softening treatment before secondary membrane concentration to further reduce calcium content. 2+ Mg 2+ Ba 2+Depending on the concentration of scaling ions and organic matter, lime softening and nanofiltration membrane methods are commonly used in practical engineering. After secondary concentration, a high-concentration brine is produced, accounting for approximately 5% of the saline wastewater volume, with a salinity of 5%-8% or even higher. This brine is then subjected to evaporation and crystallization, where the salt in the wastewater is precipitated out via thermal or membrane concentration. The distillate is collected in a distillation tank and then transported to a heat exchanger to exchange heat with the incoming liquid. The temperature drops to approximately 18°C, after which the brine leaves the evaporation and crystallization system and is sent to a reuse pond. The mother liquor is sent to a biological treatment system or dried. Salt sludge is discharged from the evaporation and crystallization system to a storage silo for temporary storage, and then transported by vehicles for further processing. However, due to its lengthy process, large investment and land area requirements, and high operating costs and energy consumption (the energy consumption per ton of water for the salt separation process alone is 100-240 kWh, and the operating cost is 30-60 yuan), even the most advanced fractional crystallization process still produces about 5% unusable crystalline salts after the fractional crystallization of mixed salts to produce industrial salt. These crystalline mixed salts are enriched with complex organic compounds such as benzene, lipids, quinoline, and pyridine, and even small amounts of heavy metals. They must be disposed of separately as hazardous solid waste, with current treatment costs of approximately 3,000 yuan per ton. Furthermore, these mixed salts have strong solubility, poor stability, and solidification properties. They will leach out when exposed to rain, causing secondary pollution. Pretreatment through solidification / stabilization is necessary to enhance the chemical inertness of pollutants or encapsulate and isolate them, thereby reducing the toxicity and mobility of the waste. This has become a major environmental challenge.

[0004] Furthermore, emerging deep thermal treatment technologies, such as incineration, while maximizing COD removal, suffer from coking and slagging issues in the furnace and flue. When co-incinerated waste contains precursors such as chlorine and benzene rings, toxic substances like dioxins easily adhere to the salt surface, hindering the resource utilization of the salt. Deep thermal treatment technologies, such as pyrolysis, can prevent the formation of highly toxic substances (like dioxins) at the source, convert organic matter in wastewater into high-calorific-value fuel gas, and thoroughly detoxify the separated salts. While reducing treatment costs and achieving the harmless and resource-based treatment of high-salt organic wastewater, they present challenges due to the presence of tar in the fuel gas, resulting in difficult-to-treat phenol-containing wastewater and secondary pollution. Deep thermal treatment technologies, such as gasification, achieve complete separation of organic components and salts, eliminating secondary pollution from dioxins and phenol-containing wastewater, while simultaneously converting organic matter in wastewater into high-calorific-value fuel gas. This is currently a hot research topic and focus. However, all of the aforementioned deep thermal treatment processes suffer from the presence of harmful heavy metals in the recovered salt, requiring recrystallization and purification, further increasing costs. Additionally, they all require the vaporization and evaporation of the predominantly water, resulting in excessively high energy consumption due to the significant latent heat of vaporization. Therefore, there is an urgent need to develop methods and equipment technologies for the treatment of high-concentration saline organic wastewater that maximize resource utilization through salt classification, organic matter conversion into syngas, and short-process, low-investment, low-energy-consumption, and low-cost methods. This would solve the environmental problems of wastewater treatment, eliminate organic matter and heavy metal ions in high-concentration saline wastewater, mitigate their negative impact on resource recovery, and then proceed with the crystallization and recovery of water and inorganic salts, laying the foundation for the comprehensive utilization of inorganic salts and water resources. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies for maximizing the resource utilization and treatment of high-concentration saline organic wastewater. This invention provides a supercritical gasification and salt-stage treatment and recovery process for high-concentration saline organic wastewater. First, the main anions and cations and impurities in the wastewater are separated according to their concentrations. Excess soluble secondary or higher metal ion salts are used for conditioning to remove impurity anions from the wastewater. Then, excess soluble macromolecular organic alkali metal salts are used for reaction flocculation and flotation to remove divalent or higher metal cations from the wastewater, ensuring complete removal of anions, cations, and impurities. Finally, the purified organic wastewater, containing a large amount of soluble macromolecular organic anions and alkali metal salts, undergoes a supercritical gasification reaction to completely convert organic matter into syngas, while alkali metal salts precipitate from the supercritical aqueous phase. The high-temperature waste heat and alkali metal salts are then staged for recovery and utilization. This process eliminates the need for pretreatment and membrane separation, offering a low-cost, short-process, low-investment, and low-energy-consumption solution to the problem of maximizing the resource utilization of high-concentration saline organic wastewater.

[0006] The technical solution of this invention is as follows: A supercritical gasification and salt-stage treatment and recovery process for high-concentration saline organic wastewater. First, the high-concentration saline organic wastewater is divided into major anions and cations and impurities based on their concentrations. Then, soluble alkaline earth metals and heavy metal salts react with the impurities to generate insoluble substances, thereby conditioning and removing the impurities from the wastewater. Next, water-soluble organic macromolecules and major alkali metal ions react with divalent and higher-valent metal ions to generate flocculants for air flotation removal. The purified organic wastewater containing alkali metal salts is pressurized to ≥22.1 MPa by a high-pressure pump and mixed with high-temperature syngas / supercritical water from supercritical gasification for staged preheating. The scum is dewatered and then disposed of or utilized. An electromagnetically heated tubular reactor is used to raise the temperature of the preheated purified organic saline wastewater to 360-700℃ for supercritical water gasification. The liquid flow rate in the electromagnetically heated tubular reactor is 1-15... With a flow rate of m / s and a liquid residence time of 1-60 seconds, the supercritical gasified liquid re-enters the supercritical delayed gasification reactor and resides for 0.1-80 minutes. The generated high-temperature syngas is mixed with supercritical water and a high-concentration alkali metal salt slurry is produced. The high-temperature syngas and supercritical water mixture undergoes a second-stage heat exchange with pressurized depurified organic saline wastewater, followed by gas-liquid separation. The syngas is discharged, and the purified water undergoes a first-stage heat exchange with the pressurized depurified organic saline wastewater for recycling. The high-concentration alkali metal salt slurry is switched through the bottom lock bucket of the supercritical delayed gasification reactor and diluted with dilute brine to form high-temperature concentrated brine before being discharged. After cooling, the concentrated brine undergoes graded crystallization to precipitate pure alkali metal salts as products, while the dilute brine is returned to the lock bucket for recycling.

[0007] Among them, the soluble alkaline earth metal and heavy metal salts are the main anionic salts of calcium, barium, magnesium and silver that form insoluble substances with impurity anions, and the amount used is 1.01-4.0 times the theoretical amount of the main anionic salt that forms insoluble substances with impurity anions.

[0008] The main alkali metal ion salts of water-soluble organic macromolecules are humic acid or alginic acid, which react with divalent or higher metal ions to form insoluble substances. The amount used is 1.1-5.0 times the theoretical amount of humic acid or alginic acid, which react with divalent or higher metal ions to form insoluble substances.

[0009] The electromagnetic heating tubular reactor generates eddy currents and self-heating in the reactor wall and internal self-mixing enhanced internal components under the action of an electromagnetic heating controller. This achieves uniform heating of high-pressure dissolved oxygen causticizing waste liquid, rapid temperature rise and gasification reaction. The self-mixing enhanced internal components are of the structured packing type, X-shaped cross plate type or spiral plate type.

[0010] The supercritical delayed gasification reactor has a funnel-shaped liquid extraction port at its center, which is connected to the upper part of the reactor. A gas-liquid mixed phase discharge port is set at the top of the reactor, and two or more salt discharge locks are set at the bottom of the reactor. The salt discharge locks are equipped with a high-concentration alkali metal ion salt slurry level detector.

[0011] Before supercritical water gasification, 0-10% (wt) of oxygen, air, or oxygen-enriched air is introduced into the preheated, decontaminated organic saline wastewater to enhance the gasification reaction of organic matter.

[0012] The features of the present invention will be described in detail through embodiments. Attached Figure Description

[0013] Appendix Figure 1 This is a schematic diagram of the process of the present invention.

[0014] Appendix Figure 1 The diagram is explained as follows:

[0015] 1. Feed pump 2. Anion exchange reactor for impurity removal 3. Flocculation and flotation reactor 4. High-pressure pump 5. Electromagnetically heated tubular reactor 6. Supercritical delayed gasification reactor 7. Gas-liquid separator 8. Electromagnetic heating controller 9. First-stage heat exchanger 10. Second-stage heat exchanger A. High-concentration saline organic wastewater inlet B. Soluble alkaline earth metal and heavy metal salt inlet C. Water-soluble organic macromolecular alkali metal salt inlet D. Air inlet E. Purified water outlet F. Syngas outlet H. Scum outlet G. Concentrated brine outlet

[0016] The process features of the present invention will be described in detail below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0017] In the example, in the supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater, the main anions and cations and impurities are first separated according to their concentrations in the high-concentration saline organic wastewater. Then, the main anions and cations and impurities are pumped to the impurity removal anion reactor (2) by the feed pump (1) and reacted with the soluble alkaline earth metals and heavy metals added from the soluble alkaline earth metals and heavy metals inlet B to form insoluble substances, thereby conditioning and removing impurity anions from the wastewater. Then, the main alkali metal ions of water-soluble organic macromolecules fed from the water-soluble organic macromolecules inlet C react with the divalent and higher metal ions in the wastewater to form flocs, which are then removed by flotation in the flocculation flotation reactor (3). The scum from the scum outlet H is dewatered and then disposed of or utilized in a harmless manner. The impurity removal organic wastewater containing alkali metal salts is pressurized to ≥22.1 by the high-pressure pump (3). MPa, and then mixed with the high-temperature synthesis gas and supercritical water after supercritical gasification in the first stage heat exchanger (9) and the second stage heat exchanger (10) for staged preheating. The temperature of the preheated wastewater is 310-650℃. The preheated organic saline wastewater is heated to 360-700℃ using an electromagnetic heating tubular reactor (5) for supercritical water gasification reaction. The liquid flow rate of the electromagnetic heating tubular reactor (5) is 1-15. m / s, liquid residence reaction time 1-60 seconds, supercritical gasification liquid enters supercritical delayed gasification reactor (6) and stays for 0.1-80 minutes to generate high-temperature syngas / supercritical water mixed phase and high-concentration alkali metal salt slurry; high-temperature syngas and supercritical water mixed phase exchange heat with pressurized de-impure organic saline wastewater in the second stage heat exchanger (10) and then gas-liquid separation is carried out through gas-liquid separator (7). Syngas is discharged from syngas outlet F, and purified water is exchanged heat with pressurized de-impure organic saline wastewater in the first stage heat exchanger (9) and then recycled through purified water outlet E. High-concentration alkali metal salt slurry is switched through the bottom lock bucket of supercritical delayed gasification reactor (6) and diluted with dilute brine to high-temperature concentrated brine before being discharged. After cooling, concentrated brine is graded and crystallized to precipitate pure alkali metal salt as product, and dilute brine is returned to lock bucket for recycling.

[0018] Among them, the soluble alkaline earth metal and heavy metal salts are the main anionic salts of calcium, barium, magnesium and silver that form insoluble substances with impurity anions, and the amount used is 1.0-4.0 times the theoretical amount of the main anionic salt that forms insoluble substances with impurity anions.

[0019] The main alkali metal ion salts of water-soluble organic macromolecules are humic acid or alginic acid, which react with divalent or higher metal ions to form insoluble substances. The amount used is 1.1-5.0 times the theoretical amount of humic acid or alginic acid, which react with divalent or higher metal ions to form insoluble substances.

[0020] The electromagnetic heating tubular reactor (5) generates eddy current self-heating in the tubular reactor cylinder wall and internal self-mixing enhanced internal components when the high-frequency alternating current generates an alternating magnetic field through the coil under the action of the electromagnetic heating controller (8), thereby realizing uniform heating, rapid temperature rise and reaction of high-pressure dissolved oxygen caustic waste liquid; the self-mixing enhanced internal components are regular packing type, X cross plate type or spiral plate type.

[0021] The supercritical delayed gasification reactor (6) has a funnel-shaped liquid extraction outlet in the center, which is connected to the upper part of the reactor. The top of the reactor has a gas-liquid mixed phase discharge outlet, and the bottom has two or more salt discharge locks. The salt discharge locks are equipped with a high concentration alkali metal ion salt slurry level detector.

[0022] Before supercritical water gasification, 0-10% (wt) of oxygen, air, or oxygen-enriched air can be introduced into the preheated, decontaminated organic saline wastewater to enhance the gasification reaction of organic matter.

[0023] Taking the wastewater from pulverized coal gasification as an example, Na + Cl - The main components are cations and anions. The specific reaction conditions and experimental results are as follows: (1) Soluble alkaline earth metals and heavy metal salts were selected from CaCl and BaCl, with a dosage of twice their theoretical amount. Sodium humate was selected as the main alkali metal ion salt for water-soluble organic macromolecules, with a dosage of three times their theoretical amount. After introducing 3% (wt) oxygen, the supercritical gasification reaction was carried out at 24 MPa and 450℃ for 2 seconds of heating and 10 minutes of supercritical delayed gasification reaction. The COD removal rate was 99.5%, the H2 content in the synthesis gas was 50%, the CO content was 30%, the purity of the recovered sodium chloride was 99.6%, and no heavy metal ions were detected.

[0024] (2) For soluble alkaline earth metals and heavy metal salts, CaCl and BaCl were selected, and the amount used was 1.5 times that of the theoretical amount. For water-soluble organic macromolecules, sodium alginate was selected, and the amount used was 2.5 times that of the theoretical amount. Without oxygen, at 24 MPa and 550 °C, the micro-self-heating supercritical gasification reaction was carried out for 2 seconds and the supercritical delayed gasification reaction was carried out for 5 minutes. The COD removal rate was 99.9%, the H2 content in the synthesis gas was 65%, the CO content was 8%, the purity of the recovered sodium chloride was 99.5%, and no heavy metal ions were detected.

[0025] This method can be used not only to treat coal chemical wastewater, but also for the resource-based treatment of high-concentration, biodegradable organic wastewater such as coking wastewater, pharmaceutical wastewater, printing and dyeing wastewater, and papermaking black liquor.

[0026] The present invention provides a method for supercritical gasification and salt classification treatment and recovery of high-concentration saline organic wastewater. This method utilizes excess soluble secondary or higher-grade metal ion salts for conditioning and removal of impurity anions from the wastewater. Then, excess soluble macromolecular organic alkali metal salts are used for reaction flocculation and flotation to remove divalent or higher-grade metal cations from the wastewater, ensuring complete removal of anions and impurities. The purified organic wastewater, containing a large amount of soluble macromolecular organic anions and alkali metal salts, is rapidly and uniformly heated through a self-mixing enhanced internal component. This heating process, combined with vortex self-heating, enhances mixing and inhibits salt precipitation, scaling, and corrosion. The supercritical delayed gasification reaction further improves... While improving gasification efficiency, the system utilizes the characteristics of supercritical water to achieve water-gas mixing and brine separation. Through supercritical gasification reaction, organic matter is completely converted into syngas, while alkali metal salts are precipitated from the supercritical aqueous phase. High-temperature waste heat and alkali metal salts are recovered and utilized in stages. The effective utilization rate of electricity is greater than 95%. Organic matter in wastewater is completely gasified to produce syngas containing more than 60% H2, COD removal rate is greater than 99%, and alkali metal salts with a purity of ≥99% are recovered and utilized. The resource-based treatment cost and investment are reduced by more than 70% compared with traditional treatment methods, providing technical support for low-cost, low-energy consumption, low-investment, and short-process treatment of high-concentration saline organic wastewater.

Claims

1. A supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater, characterized in that: First, based on the concentration of cations and anions in the high-concentration saline organic wastewater, it is divided into major cations and anions and impurities. Then, soluble alkaline earth metals and heavy metal salts are used to react with the impurity anions to form insoluble substances, thereby conditioning and removing the impurity anions from the wastewater. Next, the major alkali metal ions of water-soluble organic macromolecules react with divalent and higher-valent metal ions to form flocs for air flotation removal. The decontaminated organic wastewater containing alkali metal salts is pressurized to ≥22.1 MPa by a high-pressure pump and mixed with high-temperature syngas and supercritical water after supercritical gasification for staged preheating. The scum is dewatered and then disposed of or utilized. Finally, an electromagnetically heated tubular reactor is used to raise the temperature of the preheated decontaminated organic saline wastewater to 360-700℃ for supercritical water gasification. The liquid flow rate in the electromagnetically heated tubular reactor is 1-15. With a flow rate of m / s and a liquid residence time of 1-60 seconds, the supercritical gasified liquid re-enters the supercritical delayed gasification reactor and resides for 0.1-80 minutes. The generated high-temperature syngas mixes with supercritical water and forms a high-concentration alkali metal salt slurry. After a second-stage heat exchange with pressurized, depurified organic-containing wastewater, the high-temperature syngas and supercritical water undergo gas-liquid separation. The syngas is discharged, and the purified water undergoes a first-stage heat exchange with the pressurized, depurified organic-containing wastewater for recycling. The high-concentration alkali metal salt slurry is switched through the bottom lock hopper of the supercritical delayed gasification reactor and diluted with dilute brine to form high-temperature concentrated brine before being discharged. After cooling, the concentrated brine undergoes fractional crystallization to precipitate pure alkali metal salts as the product, while the dilute brine is returned to the lock hopper for recycling.

2. The supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater according to claim 1, characterized in that... Soluble alkaline earth metals and heavy metal salts are the main anionic salts of calcium, barium, magnesium, and silver that form insoluble compounds with impurity anions. The amount used is 1.01-4.0 times the theoretical amount of the main anionic salt that forms insoluble compounds with impurity anions.

3. The supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater according to claim 1, characterized in that... The main alkali metal ion salts of water-soluble organic macromolecules are humic acid or alginic acid, which react with divalent or higher metal ions to form insoluble substances. The amount used is 1.1-5.0 times the theoretical amount of humic acid or alginic acid, which react with divalent or higher metal ions to form insoluble substances.

4. The supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater according to claim 1, characterized in that... The electromagnetic heating tubular reactor generates eddy currents and self-heating in the reactor wall and internal self-mixing enhanced internal components under the action of an electromagnetic heating controller. This achieves uniform heating of high-pressure dissolved oxygen causticizing waste liquid, rapid temperature rise and gasification reaction. The self-mixing enhanced internal components are of the structured packing type, X-shaped cross plate type or spiral plate type.

5. The supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater according to claim 1, characterized in that... The supercritical delayed gasification reactor has a funnel-shaped liquid extraction port at its center, which is connected to the upper part of the reactor. A gas-liquid mixed phase discharge port is set at the top of the reactor, and two or more salt discharge locks are set at the bottom of the reactor. The salt discharge locks are equipped with a high-concentration alkali metal ion salt slurry level detector.

6. The supercritical gasification and salt classification treatment and recovery process for high-concentration saline organic wastewater according to claim 1, characterized in that... Before supercritical water gasification, the preheated, decontaminated organic saline wastewater is introduced with 0-10% (wt) of oxygen, air, or oxygen-enriched air.

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