A method for treating high-salt organic wastewater

Abstract

The present invention relates to a method for treating high-salt organic wastewater, which comprises the steps of low-temperature drying, organic matter desorption, high-temperature desalination, secondary incineration, waste heat recovery and flue gas purification. The high-salt organic wastewater is first subjected to low-temperature drying for volume reduction and then the organic matter is desorbed. The solid salt particles are separated from the flue gas by high-temperature desalination, and the adhesion of molten salt on a waste heat recovery device is avoided to ensure the normal operation of the waste heat recovery device. In addition, the energy utilization rate is improved due to the use of low-temperature drying and waste heat recovery.

Description

Technical Field

[0001] The invention belongs to the technical field of saline wastewater treatment, and in particular relates to a method for treating high-salt organic wastewater. Background Art

[0002] High-salt organic wastewater refers to wastewater containing organic matter and total dissolved solids (TDS) with a mass fraction of not less than 3.5%. High-salt wastewater containing complex organic matter is widely found in chemical, petrochemical and pesticide industries. Conventional distillation and crystallization treatment is difficult to meet environmental protection requirements. Generally, high-temperature incineration and decomposition methods are used to oxidize and decompose organic oxygen. When existing high-temperature incineration equipment treats high-content organic wastewater, the incineration temperature is greater than the melting point of the salt, which will cause a large amount of salt to evaporate and gasify. The salt-containing fly ash is easy to adhere to the surface of the equipment during the cooling process, causing blockage, and will also cause high-temperature corrosion, which will lead to unstable system operation and ultimately cause the waste heat to be unable to be recycled.

[0003] After searching, it was found that the Chinese patent application with publication number CN112499875A discloses a desalination system and desalination method for saline organic wastewater. It utilizes the principle of combining cyclic flash evaporation with alcohol precipitation, and adopts a two-step method of gas-liquid separation and solid-liquid separation to achieve complete separation of organic wastewater and salt, and effectively solve the problem of easy blockage of the system; the Chinese patent with publication number CN111517549A discloses a treatment process for saline organic wastewater. After pre-treatment by adjusting the pH value of the wastewater, the wastewater is concentrated by a nanofiltration membrane concentration system, and the concentrated liquid is concentrated into block, flake or powder solid discharge by a drying device. The process can simultaneously treat organic matter and inorganic salts in the wastewater, eliminating the evaporation and crystallization process. The organic matter is completely converted into dry material by the drying equipment, saving outsourcing costs, and the organic matter and salt in the wastewater can be selectively retained. Patent CN112499875A uses centrifuge separation, which is not a thorough separation method. The salt after separation must still contain water and organic matter. At the same time, the flash evaporation temperature is not high, and the salt and flash gas after flash evaporation will contain organic waste. That is, the salt obtained in this patent will still have residual water and organic matter, and the organic matter in the separated product (such as salt and flash gas) is not processed. Patent CN111517549A uses membrane filtration to filter organic matter and salt together. There is also the problem that the salt after filtration contains organic matter, and the treatment is not thorough and cannot be directly recycled. In addition, the membrane needs to be regenerated and replaced after long-term use, which is costly. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art of high-temperature incineration of wastewater, such as melting blockage, high-temperature corrosion and inability to recover residual heat, and to provide a method for treating high-salt organic wastewater.

[0005] In order to solve the above technical problems, the present invention provides a method for treating high-salt organic wastewater, comprising the following steps:

[0006] S1. Low temperature drying - low temperature drying of high salt organic wastewater until the moisture content of the material is 5% to 10% to obtain solid material;

[0007] S2, desorption of organic matter: high-temperature flue gas is introduced into the solid material after the drying treatment in step S1 to heat it, and the organic matter and water in the solid material are gasified and removed from the material to form salt-containing high-temperature flue gas, and the remaining solid material is solid salt for recovery;

[0008] S3, high temperature desalination: the salt-containing high temperature flue gas generated in step S2 is transported to a high temperature desalter, and the granular salt in the flue gas is removed by filtration to obtain recyclable granular salt and flue gas;

[0009] S4, secondary incineration: the flue gas after high-temperature desalination and filtration in step S3 is mixed with the dry tail gas containing organic matter and water vapor produced by low-temperature drying in step S1, and then heated and incinerated, so that the organic matter in the mixed gas is oxidized and decomposed to obtain high-temperature flue gas;

[0010] S5, waste heat recovery - the high-temperature flue gas obtained after the secondary incineration in step S4 is transported to the air heat exchanger for heat exchange to recover the heat of the high-temperature flue gas, so that the flue gas temperature drops to 180-200°C;

[0011] S6, flue gas purification - the flue gas after the waste heat recovery in step S5 is subjected to deacidification and denitrification treatment, and the treated flue gas is discharged from the chimney.

[0012] The method of the present invention changes the previous method of direct atomization incineration and rapid cooling with a large amount of water. It adopts low-temperature drying, thermal desorption of organic matter, high-temperature desalination, secondary incineration, waste heat recovery, flue gas purification and emission and other steps. High-salt organic wastewater is first subjected to low-temperature drying and volume reduction before the organic matter is desorbed. The solid salt particles are separated from the flue gas through high-temperature desalination, and the molten salt is prevented from adhering to the waste heat recovery device to ensure the normal operation of the waste heat recovery device. In addition, due to the use of low-temperature drying and waste heat recovery, the energy utilization rate is improved.

[0013] The technical solution further optimized by the present invention is as follows:

[0014] In the step S1, the high-salt organic wastewater is dried at low temperature by a scraper drum dryer. The heat source of the scraper drum dryer comes from the flue gas generated by the combustion of fuel. When the fuel is burned, the heat recovered from the waste heat in step S5 is used for preheating and combustion. The heat transfer medium of the scraper drum dryer is heat transfer oil or low-pressure steam of 0.5 to 0.8 MPa, and the drying temperature is 100 to 200°C.

[0015] In the step S2, the organic matter is desorbed by spiral indirect heating or direct heating, and the temperature of the introduced high-temperature flue gas is 500-700°C. The high-temperature flue gas comes from fuel combustion, and the heat recovered from the waste heat in step S5 is used for preheating and combustion assistance during fuel combustion.

[0016] In step S3, a ceramic fiber filter tube resistant to acid and alkali corrosion is arranged in the high-temperature desalter, and a group of filter holes with a pore size of 1 to 10 microns are arranged on the filter tube, and the filtration efficiency is as high as 99.9% to 99.99%.

[0017] In step S4, the flue gas obtained after high-temperature desalination is mixed with the dry tail gas discharged after low-temperature drying in step S1, and the mixed flue gas is heated and burned in the combustion chamber. The heating and burning temperature is 1100-1150° C., and the residence time of the mixed flue gas in the combustion chamber is 2s.

[0018] The dry tail gas mentioned above contains organic matter, and the flue gas may also contain incompletely decomposed organic matter. Secondary combustion can ensure that the organic matter is completely decomposed. The hazardous waste incineration specification GB18484 requires that the flue gas generated by hazardous waste stay at a temperature above 1100°C for more than 2 seconds, so the mixed flue gas needs to stay in the combustion chamber for 2 seconds.

[0019] In step S5, the high-temperature flue gas exchanges heat with air in the air heat exchanger to preheat the air, and the temperature of the flue gas after the heat exchange drops to 180-200°C. The heat of the preheated air is used to support combustion of the fuel, and the high-temperature flue gas generated by the fuel combustion is used to provide heat for the low-temperature drying of S1 and the desorption of organic matter in S2.

[0020] The waste heat recovery device in the above steps is an air-to-air heat exchanger. The high-temperature flue gas and normal-temperature air are respectively introduced into the air heat exchanger for heat exchange. The heat of the high-temperature flue gas is transferred to the air to preheat the air, and the preheated air is used as combustion air for fuel combustion. The high-temperature flue gas generated after fuel combustion is used as the heat source of S1 and S2.

[0021] In step S6, the flue gas is deacidified by a flue gas purification deacidification agent, the flue gas purification deacidification agent is sodium bicarbonate powder ground to 500 meshes, and the deacidification efficiency reaches 85% to 90%; the denitrification process is low-temperature SCR, and the denitrification agent is ammonia.

[0022] The invention has the advantages of being able to simultaneously treat salt and organic matter in high-salt wastewater, and the salt can be directly recycled after thorough treatment, and has a wide range of applications and can be adapted to various concentrations of salt-containing organic wastewater. It does not produce wastewater, waste gas, or secondary pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a process flow chart of the present invention.

[0024] Figure 2 It is a system flow chart of the present invention.

[0025] In the figure: 1. Water inlet pipe, 2. Drum scraper dryer, 3. Elevator, 4. Dry exhaust pipe, 5. Burner, 6. Thermal desorption device, 7. High-temperature desalter, 8. Granular salt recovery pipe, 9. Secondary combustion chamber, 10. Flue gas heat exchanger, 11. Normal temperature air pipe, 12. Flue gas purification system, 13. Chimney. DETAILED DESCRIPTION

[0026] Example 1

[0027] This embodiment provides a method for treating high-salt organic wastewater, which comes from the production line of a pesticide factory. The total salt content of the wastewater is 18%, the organic matter is 7%, and the water content is 75%.

[0028] The high-salt organic wastewater treatment method of this embodiment is as follows: Figure 1 As shown, the following steps are included:

[0029] S1. Low temperature drying

[0030] High-salt organic wastewater is pumped to the scraper drum dryer 2 through the water inlet pipe 1. High-temperature flue gas of 0.5MPa(G) (temperature 159°C) is introduced into the scraper drum dryer 2 to dry the high-salt organic wastewater at low temperature. After drying, the moisture content of the material is 8% and the material is in a solid state.

[0031] The drum scraper dryer 2 performs low-temperature drying of high-salt organic wastewater. The heat source of the drum scraper dryer 2 comes from the high-temperature flue gas generated by the combustion of fuel in the burner 5. The fuel combustion in the burner 5 uses the heat recovered from the waste heat of S5 for combustion support. The heat transfer medium of the drum scraper dryer 2 uses thermal oil, and the drying temperature is 100-200°C. The high-temperature flue gas is used as a heat source to heat the thermal oil inside the drum scraper. The thermal oil circulates inside the drum to heat the material outside the drum. The drum rotates continuously on the salt-containing wastewater to heat the material on its surface. As the material dries, it finally adheres to the surface of the drum and is scraped off by the scraper, and then the material continues to be dried. The high-temperature flue gas can also be used to heat the boiler to generate 0.5-0.8MPa steam to circulate and dry the material in the drum. The dry tail gas generated by the drum scraper dryer 2 during the low-temperature drying process is transported to the secondary combustion chamber 9 through the dry tail gas pipeline 4 for secondary combustion.

[0032] S2. Organic matter desorption

[0033] The solid material treated by S1 is conveyed to the thermal desorption device 6 by using an elevator 3 (i.e., a belt conveyor). The thermal desorption device 6 uses a screw conveyor with an outer jacket. A 650°C high-temperature flue gas is introduced into the outer jacket to heat the solid material. During the heating of the solid material, organic matter and residual water evaporate from the solid material to form a desorption gas (i.e., a salt-containing high-temperature flue gas). The remaining solid matter is a recoverable solid salt, which is recovered through a granular salt recovery pipeline 8. The high-temperature flue gas required for the thermal desorption of organic matter is generated by the combustion of the fuel in the burner 5. When the fuel in the burner 5 is burned, the preheated air after the waste heat of S5 is used for combustion support.

[0034] S3, high temperature desalination

[0035] The desorbed gas after S2 treatment enters the high-temperature desalter 7 under the suction of the induced draft fan, and the flue gas is filtered to remove the granular salt and recovered. The organic matter content in the filtered salt is less than 0.3%, and the moisture content is less than 0.1%. The granular salt is recovered through the granular salt recovery pipeline 8; the adsorbed gas is filtered and desalted to form flue gas.

[0036] The high temperature desalter 7 is similar to a bag filter, and is obtained by using a high temperature ceramic tube instead of the bag of the bag filter. The high temperature desalter can withstand 1200°C and can perform desalination at high temperature, while the bag filter can withstand a temperature of only 200°C.

[0037] S4. Secondary incineration

[0038] The flue gas after high-temperature desalination in S3 is mixed with the dry exhaust gas containing organic matter and water vapor produced by low-temperature drying in S1 in the secondary combustion chamber 9. The mixed flue gas is heated to 1100°C by a natural gas burner in the secondary combustion chamber 9 for incineration, and stays in the secondary combustion chamber 9 for 2 seconds to completely oxidize and decompose the residual organic matter in the mixed flue gas into CO2 and H2O to form high-temperature flue gas.

[0039] S5. Waste heat recovery

[0040] The high-temperature flue gas treated in S4 exchanges heat with the normal-temperature air sent from the normal-temperature air duct 11 in the flue gas heat exchanger 10 to recover heat. After the heat exchange, the temperature of the flue gas drops to 200°C, and the air is heated to become preheated air. The heat recovered from the preheated air is used for preheating and combustion when the burner 5 burns the fuel, and the high-temperature flue gas generated by the fuel combustion heats the drum scraper dryer 2 in step S1 and the outer jacket of the screw conveyor in S2.

[0041] S6. Flue gas purification

[0042] The low-temperature flue gas of S5 after the cooling treatment enters the flue gas purification system 12. The dry deacidification tower of the flue gas purification system 12 neutralizes the injected ground 500-mesh sodium bicarbonate powder to remove acidic gases such as HCl and SO2 in the flue gas. The treated flue gas is then denitrated and discharged from the chimney 13.

[0043] The device used in the method of this embodiment is as follows: Figure 2 As shown, it includes a drum scraper dryer 2, an elevator 3, a thermal desorption device 6, a high-temperature ceramic desalter 7, a secondary combustion chamber 9, a flue gas heat exchanger 10 and a flue gas purification system 12. The inlet of the drum scraper dryer 2 is connected to the water inlet pipe 1, the solid material outlet of the drum scraper dryer 2 is connected to the bottom inlet of the elevator 3 through a solid material conveying pipe, and the top outlet of the elevator 3 is connected to the solid material inlet of the thermal desorption device 6 through a solid material conveying pipe. The dry tail gas outlet of the drum scraper dryer 2 is connected to the flue gas inlet of the secondary combustion chamber 9 through a dry tail gas pipe. The thermal desorption device 6 is a screw conveyor with an outer jacket, and an atomizing mechanism and a burner 5 are arranged on the thermal desorption device 6. The bottom salt-containing high-temperature flue gas outlet of the thermal desorption device 6 is connected to the salt-containing high-temperature flue gas inlet of the high-temperature ceramic desalter 7 through the salt-containing high-temperature flue gas pipeline, and the flue gas outlet of the high-temperature ceramic desalter 7 is connected to the flue gas inlet of the secondary combustion chamber 9 through the flue gas pipeline. The bottom outlets of the thermal desorption device 6 and the high-temperature ceramic desalter 7 are both connected to the granular salt recovery pipeline 8. The secondary combustion chamber 9 is connected to the flue gas heat exchanger 10 through the high-temperature flue gas pipeline, and the flue gas heat exchanger 10 is connected to the flue gas purification system 12 through the low-temperature flue gas pipeline. Among them, the flue gas heat exchanger 10 has a high-temperature flue gas inlet, a low-temperature flue gas outlet, a normal-temperature air inlet and a preheated air outlet. The high-temperature flue gas inlet is connected to the high-temperature flue gas outlet of the secondary combustion chamber 9 through a high-temperature flue gas pipeline, the low-temperature flue gas outlet is connected to the flue gas inlet of the flue gas purification system 12 through a low-temperature flue gas pipeline, the normal-temperature air inlet is connected to the normal-temperature air pipeline 11, and the preheated air outlet is connected to the inlet of the burner 5 through the preheated air pipeline. The high-temperature flue gas outlet of the burner 5 is respectively connected to the thermal desorption device 6 and the drum scraper dryer 2. The outlet of the flue gas purification system 12 is connected to the chimney 13, and the flue gas purification system 12 includes a dry deacidification tower and a desulfurization tower connected in sequence.

[0044] High-salt organic water enters the drum dryer 2 through the water inlet pipe 1, and is dried to a moisture content of 5-10%. The solid material containing organic matter and salt is transported to the thermal desorption device 6 through the elevator 3. The high-temperature flue gas generated by the burner 5 in the thermal desorption device 6 is heated to 500-700°C. After high-temperature thermal desorption, the water and organic matter in the solid material are completely vaporized into a gaseous state. The remaining small part of the solid salt particles settles in the thermal desorption device 6 and is discharged and recovered from the particle salt recovery pipeline 8. The remaining water, organic matter, and particle salt enter the high-temperature desalter 7 with the flue gas. The particle salt obtained by filtering the ceramic fiber tube of the high-temperature desalter 7 enters the particle salt recovery pipeline 8 for discharge and recovery. The flue gas filtered by the high-temperature desalter 7 enters the secondary combustion chamber 9 and is heated to 1100°C, and stays for more than 2 seconds to completely burn the organic matter and prevent the formation of dioxins. The flue gas discharged from the secondary combustion chamber 9 enters the flue gas heat exchanger 10 to exchange heat with the air for cooling. After the air is heated by heat exchange, it is used as the combustion air of the burner 5 to save fuel. The flue gas after cooling enters the flue gas purification system 12 and is discharged after being purified by deacidification and denitrification.

[0045] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for treating high-salt organic wastewater, characterized in that: The device used in the method includes a drum scraper dryer, an elevator, a thermal desorption device, a high-temperature ceramic desalter, a secondary combustion chamber, a flue gas heat exchanger and a flue gas purification system. The inlet of the drum scraper dryer is connected to a water inlet pipe, the solid material outlet of the drum scraper dryer is connected to the bottom inlet of the elevator through a solid material conveying pipe, and the top outlet of the elevator is connected to the solid material inlet of the thermal desorption device through a solid material conveying pipe; the dry tail gas outlet of the drum scraper dryer is connected to the flue gas inlet of the secondary combustion chamber through a dry tail gas pipe; the thermal desorption device is a screw conveyor with an external jacket, and an atomizing mechanism and a burner are arranged on the thermal desorption device; the salt-containing high-temperature flue gas outlet at the bottom of the thermal desorption device is connected to the salt-containing high-temperature flue gas inlet of the high-temperature ceramic desalter through a salt-containing high-temperature flue gas pipe, and the flue gas outlet of the high-temperature ceramic desalter is connected to the secondary combustion chamber through a flue pipe. The flue gas inlet is connected to the bottom outlets of the thermal desorption device and the high-temperature ceramic desalter are connected to the granular salt recovery pipeline; the secondary combustion chamber is connected to the flue gas heat exchanger through a high-temperature flue gas pipeline, and the flue gas heat exchanger is connected to the flue gas purification system through a low-temperature flue gas pipeline; the flue gas heat exchanger is provided with a high-temperature flue gas inlet, a low-temperature flue gas outlet, a normal-temperature air inlet and a preheated air outlet, the high-temperature flue gas inlet is connected to the high-temperature flue gas outlet of the secondary combustion chamber through a high-temperature flue gas pipeline, the low-temperature flue gas outlet is connected to the flue gas inlet of the flue gas purification system through a low-temperature flue gas pipeline, the normal-temperature air inlet is connected to the normal-temperature air pipeline, the preheated air outlet is connected to the inlet of the burner through the preheated air pipeline, and the high-temperature flue gas outlet of the burner is respectively connected to the thermal desorption device and the drum scraper dryer; the outlet of the flue gas purification system is connected to the chimney, and the flue gas purification system includes a dry deacidification tower and a desulfurization tower connected in sequence; The method comprises the following steps: S1, low temperature drying - low temperature drying of high salt organic wastewater until the moisture content of the material is 5% to 10%; low temperature drying of high salt organic wastewater by a drum scraper dryer, the heat source of the drum scraper dryer comes from the flue gas generated by fuel combustion, and the heat recovered from the waste heat in step S5 is used for preheating and combustion during fuel combustion. The heat transfer medium of the drum scraper dryer is heat transfer oil or low-pressure steam of 0.5 to 0.8 MPa, and the drying temperature is 100 to 200°C; S2, organic matter desorption - high-temperature flue gas is introduced into the solid material after the drying treatment in step S1 for heating, and the organic matter and water in the solid material are gasified and removed from the material to form salt-containing high-temperature flue gas, and the remaining solid material is solid salt for recovery; the organic matter desorption adopts spiral indirect heating or direct heating, and the temperature of the introduced high-temperature flue gas is 500-700°C, and the high-temperature flue gas comes from fuel combustion, and the heat recovered from the waste heat in step S5 is used for preheating and combustion during fuel combustion; S3, high temperature desalination - the salt-containing high temperature flue gas generated in step S2 is transported to a high temperature desalter, and the granular salt in the flue gas is removed by filtration to obtain recyclable granular salt; the high temperature desalter is provided with a ceramic fiber filter tube resistant to acid and alkali corrosion, and a group of filter holes with a pore size of 1 to 10 microns are provided on the filter tube; S4, secondary incineration: the flue gas after high-temperature desalination and filtration in step S3 is mixed with the dry tail gas containing organic matter and water vapor produced by low-temperature drying in step S1, and then heated and incinerated, so that the organic matter in the mixed gas is oxidized and decomposed to obtain high-temperature flue gas; S5, waste heat recovery - the high-temperature flue gas obtained after the secondary incineration in step S4 is transported to the air heat exchanger for heat exchange to recover the heat of the high-temperature flue gas; S6, flue gas purification - the flue gas after the waste heat recovery in step S5 is subjected to deacidification and denitrification treatment, and the treated flue gas is discharged from the chimney.

2. A method for treating high-salt organic wastewater according to claim 1, characterized in that: In step S4, the flue gas obtained after high-temperature desalination is mixed with the dry tail gas discharged after low-temperature drying in step S1, and the mixed flue gas is heated and incinerated in the combustion chamber. The heating and incineration temperature is 1100-1150° C., and the flue gas stays in the combustion chamber for 2 seconds.

3. A method for treating high-salt organic wastewater according to claim 2, characterized in that: In step S5, the high-temperature flue gas exchanges heat with air in the air heat exchanger to preheat the air, and the temperature of the flue gas after the heat exchange drops to 180-200° C. The heat of the preheated air is used to assist combustion of the fuel.

4. A method for treating high-salt organic wastewater according to claim 3, characterized in that: In the step S6, the flue gas is deacidified by using a flue gas purification deacidification agent, and the flue gas purification deacidification agent is sodium bicarbonate powder ground to 500 meshes.

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