A method for multi-stage integrated purification of landfill leachate separation reaction

Abstract

This invention belongs to the field of environmental protection and discloses a multi-stage integrated purification method for landfill leachate separation reaction. The method uses an evaporator to convert volatile organic compounds, ammonia nitrogen, and water in the landfill leachate into a gaseous phase. High-boiling-point organic pollutants and inorganic salts that cannot be evaporated are further concentrated in a vacuum evaporator to form a mixed slurry, which is then transported to a pyrolysis furnace for high-temperature pyrolysis in an oxygen atmosphere. The purified effluent indicators throughout the process meet the national "Pollution Control Standard for Municipal Solid Waste Landfills." Furthermore, this method comprehensively utilizes the waste heat of the purified water, the latent heat of steam, and the heat of oxygen-induced decomposition reaction, significantly reducing energy consumption in the purification process and eliminating the generation of secondary pollution.

Description

Technical Field

[0001] This invention relates to a multi-stage integrated purification method for landfill leachate separation reaction, belonging to the field of environmental protection, and applied to the treatment of leachate from high-salt municipal solid waste. Background Technology

[0002] Landfill leachate contains recalcitrant organic matter, inorganic salts, heavy metals, and other pollutants. Direct discharge of these pollutants will contaminate soil and natural water bodies, seriously threatening the ecological environment and human health. Patent CN115477390A discloses a combined process of "biochemical reaction + membrane separation," which is currently a commonly used method for landfill leachate treatment. Depending on the water quality and quantity, the process flow and specific combination of biochemical reaction and membrane separation will vary. For example, patent CN109553185A discloses a method for purifying landfill leachate using a multi-stage membrane series of "ultrafiltration-nanofiltration-reverse osmosis," and patent CN108911132A discloses a method for purifying landfill leachate using "microbial nitrification-denitrification." However, this traditional combined process has the following drawbacks: the anaerobic-aerobic biological treatment process generates a large amount of activated sludge, requiring additional treatment processes such as dewatering, drying, and incineration, or outsourcing to a third party for disposal, significantly increasing process operating costs and equipment investment. While multi-stage membrane separation technology can achieve compliant water discharge, the resulting membrane concentrate contains a large amount of recalcitrant organic matter, miscellaneous salts, and other pollutants, making it more difficult to treat than the original leachate. Patent CN110482632A discloses an evaporation method for treating membrane concentrate, but direct evaporation consumes a large amount of energy, and the latent heat of vapor in the evaporated water is directly released into the environment, resulting in energy waste. Patent CN217627972U discloses a method for treating membrane concentrate using multi-stage MVR technology. Although this method utilizes the steam energy generated during evaporation, it still produces solid waste containing recalcitrant organic matter, failing to fundamentally remove it from the membrane concentrate. The resulting solid waste needs to be sent to an incineration plant for further treatment. Patent CN112794571B discloses an advanced oxidation process for treating landfill leachate. However, advanced oxidation technology has low purification efficiency for small molecule pollutants, requiring independent purification processes in practical applications, and suffers from harsh reaction conditions and poor treatment efficiency. Summary of the Invention

[0003] This invention addresses the problems in existing landfill leachate treatment technologies, such as difficulties in disposing of membrane concentrate, high energy consumption in the evaporation process, and low efficiency in the oxidation reaction of recalcitrant organic matter. It abandons traditional biological and membrane treatment processes and provides a low-energy landfill leachate treatment method based on the integration of evaporation and reaction.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A method for multi-stage integrated purification of landfill leachate separation reaction includes the following steps: after preheating, the landfill leachate is evaporated and concentrated to obtain a concentrated liquid containing high-boiling-point organic pollutants and inorganic salts, as well as water vapor containing volatile organic compounds and light components.

[0006] The concentrated liquid containing high-boiling-point organic pollutants and inorganic salts is further concentrated by vacuum evaporation to form a mixed slurry, which then enters the pyrolysis process. In pure oxygen, high-temperature pyrolysis decomposes the high-boiling-point organic matter into pyrolysis gas containing gaseous organic matter. The obtained pyrolysis gas and water vapor containing volatile organic matter and light components are fed into an oxygen-based pyrolysis reactor, where organic pollutants and free ammonia are converted into small molecules under the action of a catalyst.

[0007] In the technical solution of this invention: the heat released by the oxygen-induced cracking reaction is carried out of the device by the reaction steam, and is used as a heat medium to evaporate the preheated landfill leachate in the evaporator. After the reaction steam heat exchange is completed, the steam condensate is formed and used as a heat medium to heat the raw material landfill leachate in the preheater.

[0008] In the technical solution of this invention: the COD concentration of the landfill leachate is 5000-100000 mg / L, the NH3-N concentration is 800-3000 mg / L, and the salt mass fraction is 0.1-2%.

[0009] In the technical solution of this invention: the temperature of the steam condensate in the preheater is 95-100℃, and the temperature of the landfill leachate reaches 45-55℃ after preheating from room temperature.

[0010] The temperature of the water vapor containing volatile organic compounds and light components evaporated from the evaporator is 100-120°C.

[0011] In the technical solution of this invention: the temperature range of the reduced pressure evaporator is 60-95℃; the pressure in the reduced pressure evaporator is 10-30kPa.

[0012] In the technical solution of this invention, the temperature range of the pyrolysis furnace is 400–700℃.

[0013] In the technical solution of this invention: the catalyst type in the oxygen pyrolysis reactor is acidic silicon-aluminum encapsulated metal oxide, that is: metal oxide@acidic silicon-aluminum;

[0014] The metal oxide is one or two of vanadium oxide, copper oxide, cerium oxide, manganese oxide, and cobalt oxide; the acidic silica-alumina is one of Y-type, β-type molecular sieve, and amorphous silica-alumina; and the loading of the metal oxide is 10-35%.

[0015] In the technical solution of this invention: the oxygen pyrolysis reaction temperature is 250-350℃, and the space velocity is 10-500 h⁻¹. -1 The outlet steam temperature of the oxygen pyrolysis reactor is 300–450℃.

[0016] In some more specific technical solutions:

[0017] The oxygen-induced cracking catalyst metal oxide@acidic silicon aluminum is prepared based on a dual-solvent method, including the following steps:

[0018] (1) Place acidic silica-alumina in a vacuum drying apparatus and activate it for 5-10 hours at a temperature of 150-200℃ and a vacuum of 15-25Pa.

[0019] (2) The activated acidic silica-alumina is placed in a hydrophobic solvent cyclohexane or a mixed solution of n-hexane and water, stirred evenly, and then the metal oxide precursor metal chloride salt is added.

[0020] (3) After removing the hydrophobic solvent and water by a rotary evaporator and drying, the solid obtained is heat-treated at a high temperature of 400-600℃ for 4-6 hours; after heat treatment, the metal chloride salt is converted into metal oxide, and finally acidic silicon aluminum encapsulated metal oxide catalyst is obtained.

[0021] The mass ratio of the hydrophobic solvent cyclohexane or n-hexane to the acidic silica-alumina is 30:1 to 50:1;

[0022] The metal chloride salt is one or two of vanadium chloride, copper chloride dihydrate, cerium chloride heptahydrate, manganese chloride tetrahydrate, and cobalt chloride hexahydrate.

[0023] In the technical solution of this invention, the pressure is gauge pressure.

[0024] The beneficial effects of this invention are reflected in:

[0025] (1) All required indicators of the treatment results meet the national standard for pollution control of municipal solid waste landfills;

[0026] (2) This method does not generate biological sludge and membrane concentrate, and does not generate secondary pollution. No additional process treatment of secondary pollutants is required.

[0027] (3) This method makes full use of the sensible heat, latent heat of steam and heat of oxygen-induced cracking reaction of the water in the treatment process, which greatly reduces the energy consumption of the purification process.

[0028] (4) The organic matter index (TOC) of the solid salt generated in the landfill leachate treated by this method is ≤10.0 mg / kg, which can be recovered and utilized through the chlor-alkali industry. Attached Figure Description

[0029] Figure 1This is a flowchart of a multi-stage integrated purification method for landfill leachate separation reaction according to the present invention. Detailed Implementation

[0030] The invention will be further illustrated below through implementation examples.

[0031] Example 1

[0032] The leachate to be treated has a COD concentration of 5000 mg / L, an ammonia nitrogen concentration of 3000 mg / L, and a salt content of 2%. Figure 1 During the preheating process, the temperature of the condensate from the heat transfer medium is 100℃, and the refrigerant leachate is heated to 45℃ after heat exchange in the preheater before being introduced into the evaporator. The heat transfer medium in the evaporator comes from the outlet steam of the oxygen-fired pyrolysis reactor, with a steam temperature of 300℃, and evaporates into water vapor containing volatile organic compounds and light components at a temperature of 100℃.

[0033] The concentrated liquid containing high-boiling-point organic pollutants and inorganic salts, remaining after evaporation in the evaporator, is passed into a vacuum evaporator at 60°C and 30 kPa. Further evaporation of water yields a mixed waste containing recalcitrant organic matter and salts, which is then transported to a pyrolysis furnace operating at 400°C. High-temperature pyrolysis in pure oxygen decomposes the high-boiling-point organic matter into pyrolysis gas containing organic matter. Under these conditions, the TOC in the organic matter of the pyrolyzed waste salt is 10.0 mg / kg. Water vapor containing volatile organic compounds, ammonia nitrogen, and other light components is introduced along with the pyrolysis gas at 250°C and a space velocity of 10 h⁻¹. -1 The reactor is an oxygen-dependent pyrolysis reactor. The catalyst is a vanadium oxide-copper oxide@Y molecular sieve catalyst with a total metal oxide loading of 10%, and vanadium oxide and copper oxide loadings of 5% and 5%, respectively. Under the action of the catalyst, the pyrolysis gas, volatile organic compounds, and free ammonia are catalytically converted into carbon dioxide, nitrogen, and water, releasing energy that is transferred to the reaction steam.

[0034] The outlet steam temperature is 300℃, which is used as the heat medium to evaporate and preheat the landfill leachate in the evaporator. Finally, the steam condensate is converted into steam condensate, which is used to preheat the landfill leachate in the preheater. After heat exchange, the energy of the steam condensate is fully utilized, ultimately forming purified water that meets discharge standards. The purified effluent has a COD of 22.145 mg / L and an NH3-N concentration of 3.527 mg / L; the total non-methane hydrocarbons in the non-condensable gases throughout the process are 4.3 mg / m³. 3 All of them meet the national emission standards.

[0035] The preparation method of the oxygen-induced vanadium oxide-copper oxide@Y molecular sieve catalyst is as follows:

[0036] (1) Place 1 kg of acidic silica-alumina Y-type molecular sieve in a vacuum drying device and activate it for 5 h at a temperature of 150℃ and a vacuum of 15 Pa.

[0037] (2) The activated Y-type molecular sieve was placed in a mixed solution of 30 kg cyclohexane and 10 kg water, stirred evenly, and then 45 g of vanadium chloride and 107 g of copper chloride dihydrate were added.

[0038] (3) After removing the hydrophobic solvent and water by rotary evaporator, the solid was dried and then heat-treated at 400℃ for 4 hours. After heat treatment, the metal chloride salt vanadium chloride and copper chloride dihydrate were finally converted into vanadium oxide and copper oxide, respectively, to obtain vanadium oxide-copper oxide@Y type catalyst.

[0039] Example 2

[0040] The landfill leachate to be treated has a COD concentration of 100,000 mg / L, an ammonia nitrogen concentration of 800 mg / L, and a salt content of 0.1%. During preheating, the heat transfer medium is the evaporative condensate at a temperature of 98°C. The landfill leachate is preheated to 48°C before entering the evaporator. The heat transfer medium vapor temperature in the evaporator is 450°C, evaporating water vapor containing volatile organic compounds, ammonia nitrogen, and other light components at a temperature of 120°C.

[0041] The concentrated liquid is pumped into a vacuum evaporator at 80℃ and 10kPa. Solid waste, such as mixed salts and high-concentration recalcitrant organic matter, from the vacuum evaporator is then transferred to a pyrolysis furnace at 700℃. Under these conditions, the TOC in the organic matter of the pyrolyzed waste salt is 3.5 mg / kg. Water vapor containing volatile organic light components and ammonia nitrogen, along with pyrolysis gas, is introduced into a cerium oxide-manganese oxide@β molecular sieve catalyst at 350℃ and a space velocity of 500 h⁻¹. -1 The reactor is an oxygen-fired pyrolysis reactor; the total loading of metal oxides in the catalyst component is 35%, and the loadings of cerium oxide and manganese oxide are 15% and 20%, respectively. Water vapor containing volatile organic light components, free ammonia, and the above-mentioned pyrolysis gas are converted into carbon dioxide, nitrogen, and water under the action of the catalyst, releasing a large amount of energy.

[0042] The oxygen pyrolysis process generates reaction steam at 450℃, which releases its latent heat of steam and the sensible heat of the purified water through an evaporator and a preheater. The cooled purified water has a COD of 13.562 mg / L and an NH3-N concentration of 4.519 mg / L. The total non-methane hydrocarbons in the non-condensable gases are 8.3 mg / m³. 3 All of them meet the national emission standards.

[0043] The preparation method of the oxygen-induced pyrolysis cerium oxide-manganese oxide@β molecular sieve catalyst is as follows:

[0044] (1) Place 1 kg of acidic silica-alumina β-type molecular sieve in a vacuum drying device and activate it for 10 h at a temperature of 180 °C and a vacuum of 15 Pa.

[0045] (2) The activated β-type molecular sieve was placed in a mixed solution of 50 kg cyclohexane and 20 kg water, stirred evenly, and then 325 g of cerium chloride heptahydrate and 250 g of manganese chloride tetrahydrate were added.

[0046] (3) After removing the hydrophobic solvent and water by rotary evaporator, the solid was dried and then heat-treated at 600℃ for 6 hours. After heat treatment, the metal chloride salts cerium chloride heptahydrate and manganese chloride tetrahydrate were finally converted into cerium oxide and manganese oxide, respectively, to obtain cerium oxide-manganese oxide@β molecular sieve catalyst.

[0047] Example 3

[0048] The leachate to be treated has a COD concentration of 75,000 mg / L, an ammonia nitrogen concentration of 1,900 mg / L, and a salt content of 1.5%. During preheating, the heat transfer medium is 95°C steam condensate, while the refrigerant leachate is heated to 50°C via a preheater before entering the evaporator. The heat transfer medium in the evaporator is steam from an oxygen-fired pyrolysis reactor at 420°C, evaporating into water vapor containing volatile organic compounds, ammonia nitrogen, and other light components at 115°C.

[0049] The concentrated liquid in the evaporator is pumped into a vacuum evaporator at 95℃ and 10kPa; the residual solid waste from evaporation is transported to a pyrolysis furnace at 600℃; under these conditions, the TOC in the organic matter of the pyrolyzed waste salt is 4.8 mg / kg. Water vapor containing light components and desorption gas are introduced into the catalyst (cobalt oxide@amorphous silicon-aluminum) at 340℃ and a space velocity (HV) of 300 h⁻¹. -1 An oxygen-dependent pyrolysis reactor is used, wherein the total loading of metal oxides in the catalyst is 20%. Pollutants are catalytically converted into carbon dioxide, nitrogen, and water under the action of the catalyst.

[0050] The heat of reaction released after the oxidation of organic matter is transferred to the reaction steam, which has a steam formation temperature of 420℃. This steam is then passed through the evaporator and preheater to release the latent heat of the steam and the sensible heat of the water. The final discharged purified water has a COD of 21.493 mg / L and an NH3-N concentration of 8.652 mg / L. The total non-methane hydrocarbons in the non-condensable gases are 6.3 mg / m³. 3 All of them meet the national emission standards.

[0051] The preparation method of cobalt oxide@amorphous silica-alumina catalyst by oxygen pyrolysis is as follows:

[0052] (1) Place 1 kg of amorphous silicon aluminum in a vacuum drying device and activate it for 5 h at a temperature of 200℃ and a vacuum of 25 Pa.

[0053] (2) The activated amorphous silicon aluminum was placed in a mixed solution of 30 kg cyclohexane and 10 kg water, stirred evenly, and then 198 g of cobalt chloride hexahydrate was added.

[0054] (3) After removing the hydrophobic solvent and water by rotary evaporator, the solid was dried and then heat-treated at 500℃ for 6 hours. After heat treatment, the metal chloride salt cobalt chloride hexahydrate was converted into cobalt oxide, and cobalt oxide@amorphous silicon aluminum catalyst was obtained.

[0055] Example 4

[0056] The landfill leachate to be treated has a COD concentration of 50,000 mg / L, an ammonia nitrogen concentration of 1,750 mg / L, and a salt content of 1.8%. During preheating, the evaporation condensate temperature is 95℃, and the landfill leachate is heated to 55℃ in the preheater before being introduced into the evaporator. The heat transfer medium steam temperature in the evaporator is 370℃, evaporating water vapor containing volatile organic compounds, free ammonia, and other light components at a temperature of 110℃.

[0057] The residual concentrate in the evaporator is pumped into a vacuum evaporator at 85℃ and 10kPa. The residual solid waste is then transported to a pyrolysis furnace at 600℃; the TOC in the organic matter of the pyrolysis waste salt is 5.6 mg / kg. Water vapor containing light components is introduced into the pyrolysis gas at 320℃ and a space velocity of 300 h⁻¹. -1 The reactor is an oxygen-dependent pyrolysis reactor; the catalyst is cobalt oxide@amorphous silica-alumina catalyst, with a total metal oxide loading of 20%. Under the action of the catalyst, the organic light components are converted into small molecules that are harmless to the environment, while releasing a large amount of reaction heat to form reaction steam at 370°C.

[0058] The steam energy grade is improved and returned to the evaporator and preheater to heat and evaporate the leachate. The entire system fully utilizes the latent heat and sensible heat of steam, as well as the heat of reaction from the oxidation of organic matter. Finally, the cooled purified water discharged from the system has a COD of 9.726 mg / L and an NH3-N concentration of 6.875 mg / L. The total non-methane hydrocarbons in the non-condensable gases are 4.3 mg / m³. 3 All of them meet the national emission standards.

[0059] The preparation method of the oxygen-induced cracking cobalt oxide@amorphous silica-alumina catalyst is the same as in Implementation Case 3.

Claims

1. A method for multi-stage integrated purification of landfill leachate through separation and reaction, characterized in that, The process includes the following steps: after preheating, the landfill leachate is concentrated by an evaporator to obtain a concentrated liquid containing high-boiling-point organic pollutants and inorganic salts, as well as water vapor containing volatile organic compounds and light components. The concentrated liquid containing high-boiling-point organic pollutants and inorganic salts is further concentrated by a vacuum evaporator to form a mixed slurry, which then enters the pyrolysis process. In pure oxygen, the high-boiling-point organic matter is cracked into pyrolysis gas containing gaseous organic matter through high-temperature pyrolysis. The obtained pyrolysis gas and water vapor containing volatile organic matter and light components are fed into an oxygen-based cracking reactor, where organic pollutants and free ammonia are converted into small molecules under the action of a catalyst. The heat released by the oxygen pyrolysis reaction is carried out of the device by the reaction steam and used as a heat medium to evaporate the preheated landfill leachate in the evaporator. After the reaction steam heats up, the steam condensate is formed and used as a heat medium to heat the raw material landfill leachate in the preheater. The catalyst in the oxygen pyrolysis reactor is an acidic silicon-aluminum encapsulated metal oxide, i.e., metal oxide@acidic silicon-aluminum; the metal oxide is one or two of vanadium oxide, copper oxide, cerium oxide, manganese oxide, and cobalt oxide; the acidic silicon-aluminum is Y-type. β The metal oxide is selected from one of molecular sieve and amorphous silica-alumina; the loading of the metal oxide is 10-35%. Furthermore, the oxygen-induced cracking catalyst metal oxide@acidic silicon aluminum is prepared based on a dual-solvent method, including the following steps: (1) Place the acidic silica-alumina in a vacuum drying apparatus and activate it for 5-10 h at a temperature of 150-200 °C and a vacuum of 15-25 Pa. (2) The activated acidic silica-alumina is placed in a hydrophobic solvent cyclohexane or a mixed solution of n-hexane and water, stirred evenly, and then the metal oxide precursor metal chloride salt is added. (3) After removing the hydrophobic solvent and water by rotary evaporator and drying, the solid obtained is heat-treated at a high temperature of 400-600 °C for 4-6 h; after heat treatment, the metal chloride salt is converted into metal oxide, and finally acidic silicon aluminum encapsulated metal oxide catalyst is obtained. The mass ratio of the hydrophobic solvent cyclohexane or n-hexane to the acidic silica-alumina is 30:1 to 50:1; The metal chloride salt is one or two of vanadium chloride, copper chloride dihydrate, cerium chloride heptahydrate, manganese chloride tetrahydrate, and cobalt chloride hexahydrate.

2. The method for multi-stage integrated purification of landfill leachate separation reaction according to claim 1, characterized in that: The landfill leachate has a COD concentration of 5000–100000 mg / L, an NH3-N concentration of 800–3000 mg / L, and a salt mass fraction of 0.1–2%.

3. The method for multi-stage integrated purification of landfill leachate separation reaction according to claim 1, characterized in that: The temperature of the steam condensate in the preheater is 95-100 ℃, and the temperature of the landfill leachate reaches 45-55 ℃ after preheating from room temperature. The temperature of the water vapor containing volatile organic compounds and light components evaporated from the evaporator is 100–120 °C.

4. The method for multi-stage integrated purification of landfill leachate separation reaction according to claim 1, characterized in that: The temperature range of the vacuum evaporator is 60–95 °C; the pressure in the vacuum evaporator is 10–30 kPa.

5. The method for multi-stage integrated purification of landfill leachate separation reaction according to claim 1, characterized in that: The temperature range of the pyrolysis furnace is 400–700 °C.

6. The method for multi-stage integrated purification of landfill leachate separation reaction according to claim 1, characterized in that: The oxygen pyrolysis reaction temperature is 250–350 °C, and the space velocity is 10–500 h⁻¹. -1 The outlet steam temperature of the oxygen pyrolysis reactor is 300–450 °C.

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