Apparatus and process for the multistage wet oxidation treatment of wastewater

Abstract

This invention provides an apparatus and process for multi-stage wet oxidation treatment of wastewater. The apparatus includes a wastewater inlet, an oxygen inlet, and a first guide tube arranged sequentially from bottom to top at the lower part of a wet oxidation main reactor. The oxygen inlet is located at the bottom of the first guide tube. An air inlet is located in the middle of the wet oxidation main reactor. A second guide tube is located at the upper part of the wet oxidation main reactor, and the outlet of the wet oxidation main reactor is located at the top. The process involves wastewater first reacting with oxygen, with a portion forming a circulation and the other portion reacting upwards with air to form a circulation. This invention improves the COD removal rate by optimizing the internal components of the wet oxidation reactor, thereby increasing the wastewater residence time and gas-liquid mixing efficiency. By using some pure oxygen instead of air, the preheating temperature and compression energy consumption of the wet oxidation are reduced, thus lowering the operating cost of the wet oxidation process.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to an apparatus and process for multi-stage wet oxidation treatment of wastewater. Background Technology

[0002] Wet oxidation technology is a highly efficient and environmentally friendly wastewater treatment method suitable for treating wastewater with high COD (10-100 g / L). This technology operates under high temperature (200-325℃) and high pressure (5-15 MPa) conditions, oxidizing organic matter or reducible substances in wastewater with air to produce carbon dioxide and water. Wet oxidation does not generate secondary pollutants such as NOx, SO2, HCl, dioxins, furans, or fly ash. When treating wastewater with a COD exceeding 20,000 mg / L, the wet oxidation reaction is self-sustaining and can output excess energy, further improving economic efficiency. Due to its high efficiency and economy, wet oxidation technology is widely considered a green and environmentally friendly wastewater treatment technology, especially suitable for treating high-salt, high-concentration, and recalcitrant wastewater.

[0003] Despite the significant advantages of wet oxidation technology, it still faces several challenges in practical engineering applications. First, wet oxidation requires operation under high temperature and pressure conditions, resulting in high equipment investment and operating costs. Second, current wet oxidation reactors suffer from short wastewater retention times and poor gas-liquid mixing efficiency, leading to unsatisfactory COD removal efficiency. Finally, air is currently the primary oxidant in wet oxidation, and the energy consumption required to compress air to operating pressure typically accounts for more than 50% of the entire process. This is because air contains a large amount of nitrogen in addition to oxygen, requiring additional nitrogen compression during compression. While using pure oxygen can save this compression energy consumption, it poses a higher safety risk. Summary of the Invention

[0004] To address the problems of the prior art, this invention proposes a device and process for multi-stage wet oxidation treatment of wastewater, which can effectively improve the wastewater residence time and gas-liquid mixing efficiency in the wet oxidation reactor. At the same time, it can reduce the safety risks associated with using pure oxygen and save the pressure energy required to compress additional nitrogen, thereby significantly reducing the operating cost of wet oxidation.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A multi-stage wet oxidation device for treating wastewater includes a wet oxidation main reactor 12. The lower part of the wet oxidation main reactor is an oxygen wet oxidation section. From bottom to top, a wastewater inlet, an oxygen inlet, and a first guide tube 10 are sequentially arranged in the oxygen wet oxidation section. The oxygen inlet is located at the bottom of the first guide tube 10.

[0007] An air inlet is provided in the middle of the wet oxidation main reactor 12, and a second guide tube 15 is provided in the upper part of the wet oxidation main reactor 12.

[0008] The outlet of the wet oxidation main reactor 12 is located at the top.

[0009] Furthermore, the height of the oxygen wet oxidation section is 30-60% of the height of the wet oxidation main reactor 12.

[0010] Furthermore, the height of the first guide tube 10 is 40-80% of the height of the oxygen wet oxidation section.

[0011] Furthermore, an air vent valve is provided at the bottom of the wet oxidation main reactor 12.

[0012] Furthermore, the wastewater inlet is connected to wastewater pump 1. Even further, the wastewater pump 1 is a high-pressure pump.

[0013] Furthermore, the wastewater inlet is connected to a preheating unit 4 for preheating the wastewater.

[0014] Furthermore, the preheating unit 4 is a tube sheet heat exchanger, consisting of a shell side and a tube side. Low-temperature raw wastewater flows through the tube side, while high-temperature liquid flows through the shell side.

[0015] Furthermore, an oxygen diffuser 11 is provided at the oxygen inlet.

[0016] Furthermore, the oxygen inlet is connected to the oxygen compressor 2. Even further, an oxygen flow controller 5 is provided between the oxygen compressor 2 and the oxygen inlet.

[0017] Furthermore, a distributor 13 is provided between the air inlet and the first guide tube 10.

[0018] Furthermore, an air diffuser 14 is provided at the air inlet.

[0019] Furthermore, the air inlet is connected to the air compressor 3. Even further, an air flow controller 7 is provided between the air compressor 3 and the air inlet.

[0020] Furthermore, a first thermometer 6 is provided in the middle of the wet oxidation main reactor 12.

[0021] Furthermore, a second thermometer 8 is provided at the top of the wet oxidation main reactor 12.

[0022] Furthermore, an oxygen analyzer 17 is installed at the outlet of the wet oxidation main reactor 12.

[0023] Furthermore, the oxygen analyzer 17, the first thermometer 6, and the oxygen flow controller 5 are respectively connected to the control system. The control system adjusts the oxygen flow controller 5 based on the temperature obtained by the first thermometer 6 and the tail oxygen concentration obtained by the oxygen analyzer 17, thereby controlling the COD removal rate, temperature, and tail oxygen concentration of the oxygen wet oxidation section by reducing the oxygen flow rate.

[0024] The present invention also provides a process for multi-stage wet oxidation treatment of wastewater using the above-mentioned apparatus, comprising:

[0025] Wastewater at 100~130℃ is fed into the wet oxidation main reactor, and oxygen and air at a pressure of 5~7MPa are respectively fed into the wet oxidation main reactor. The oxygen volume fraction is controlled to be 30~80% of the total air flow, and the outlet temperature of the oxygen wet oxidation section is controlled to be 220~280℃.

[0026] After entering the wet oxidation main reactor, the wastewater first mixes with oxygen to carry out a wet oxidation reaction, generating heat and raising the temperature of the wastewater. Under the guidance of the first guide tube, a portion of the wastewater forms a circulation in the oxygen wet oxidation section and mixes with the wastewater fed into the wet oxidation main reactor. Another portion enters the air wet oxidation section and mixes with air to carry out a wet oxidation reaction. Under the guidance of the second guide tube, it forms a circulation in the air wet oxidation section. Finally, the wastewater after the reaction is discharged from the outlet at the top of the wet oxidation main reactor.

[0027] Preferably, the temperature of the air or the oxygen is 60~100°C.

[0028] The energy saved is mainly the energy required to compress additional nitrogen. The amount of energy saved can be calculated as follows: if the oxygen usage accounts for X% of the total ventilation, then X / (X+25) of energy can be saved.

[0029] This invention uses oxygen to replace part of the air, which can save 55% to 75% of compression energy compared to traditional wet oxidation systems.

[0030] This invention uses oxygen as an oxidant to initiate a free radical chain reaction at a lower temperature, avoiding the safety risks associated with excessively high temperatures. Oxygen drives the wastewater to form a primary circulation in the oxygen wet oxidation section, effectively increasing the wastewater's residence time. This allows the COD removal rate in the oxygen oxidation section to be controlled at 40-60%, with the temperature maintained at 220-280℃. At this temperature, the oxygen content in the gas phase is significantly reduced, converting to carbon dioxide, thus avoiding the formation of high-temperature, high-oxygen zones. After oxygen oxidation, the temperature of the low-temperature wastewater increases, but the oxygen content decreases. Introducing air at this point can both initiate a free radical reaction and replenish oxygen to continue the reaction. Air then drives the wastewater to form a secondary circulation in the second circulation guide tube, effectively increasing the wastewater's residence time and ensuring that the COD removal rate in the air oxidation section is controlled above 70%. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the device structure in Embodiment 1 of the present invention (the control system is not shown).

[0033] In the diagram: 1 is a wastewater pump; 2 is an oxygen compressor; 3 is an air compressor; 4 is a preheating unit; 5 is an oxygen flow controller; 6 is a first thermometer; 7 is an air flow controller; 8 is a second thermometer; 9 is an vent valve; 10 is a first guide tube; 11 is an oxygen disperser; 12 is a wet oxidation main reactor; 13 is a distributor; 14 is an air disperser; 15 is a second guide tube; 16 is a valve; and 17 is an oxygen analyzer. Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0035] The present invention will now be further described with reference to the accompanying drawings.

[0036] like Figure 1 The apparatus shown is a multi-stage wet oxidation wastewater treatment device, including a wet oxidation main reactor 12. The lower part of the wet oxidation main reactor is an oxygen wet oxidation section. From bottom to top, the oxygen wet oxidation section is provided with a wastewater inlet, an oxygen inlet, and a first guide tube 10. The oxygen inlet is located at the bottom of the first guide tube 10. An air inlet is provided in the middle of the wet oxidation main reactor 12. A second guide tube 15 is provided in the upper part of the wet oxidation main reactor 12. The outlet of the wet oxidation main reactor 12 is located at the top.

[0037] The height of the oxygen wet oxidation section is 30-60% of the height of the wet oxidation main reactor 12.

[0038] The height of the first guide tube 10 is 40-80% of the height of the oxygen wet oxidation section.

[0039] An air vent valve is installed at the bottom of the wet oxidation main reactor 12.

[0040] The wastewater inlet is connected to wastewater pump 1. Furthermore, the wastewater pump 1 is a high-pressure pump.

[0041] The wastewater inlet is connected to preheating unit 4 for preheating the wastewater.

[0042] The preheating unit 4 is a tube sheet heat exchanger. It includes a shell side and a tube side. Low-temperature raw wastewater flows through the tube side, and high-temperature liquid flows through the shell side.

[0043] An oxygen diffuser 11 is provided at the oxygen inlet.

[0044] The oxygen inlet is connected to the oxygen compressor 2. Furthermore, an oxygen flow controller 5 is provided between the oxygen compressor 2 and the oxygen inlet.

[0045] A distributor 13 is provided between the air inlet and the first guide tube 10.

[0046] An air diffuser 14 is provided at the air inlet.

[0047] The air inlet is connected to the air compressor 3. Furthermore, an air flow controller 7 is provided between the air compressor 3 and the air inlet.

[0048] A first thermometer 6 is installed in the middle of the wet oxidation main reactor 12.

[0049] A second thermometer 8 is installed at the top of the wet oxidation main reactor 12.

[0050] An oxygen analyzer 17 is installed at the outlet of the wet oxidation main reactor 12.

[0051] The oxygen analyzer 17, the first thermometer 6, and the oxygen flow controller 5 are respectively connected to the control system.

[0052] A pesticide wastewater was selected and treated using the aforementioned device through a staged pure oxygen air wet oxidation process to achieve compliant discharge. The production process generates 600 tons of pesticide wastewater daily, with an average influent COD of 31340 mg / L (classified as high COD wastewater) and a pH of 10. The design requires a 108000 Nm³ / h flow rate. 3The wastewater is oxidized using pure air per day; in this embodiment, 30% oxygen is used instead of air. The wastewater is preheated to 180°C and enters the oxygen wet oxidation section from the bottom of the wet oxidation reactor. Simultaneously, pure oxygen is dispersed into the first guide tube in the oxygen wet oxidation section through a gas distributor, mixing with the raw water to initiate the oxygen wet oxidation reaction at a low temperature. The heat generated during the reaction continuously raises the wastewater temperature. Part of the heated wastewater recirculates back into the bottom of the reactor to mix with the raw water and continue the reaction, while the other part passes through a distributor into the air wet oxidation section. Air is dispersed into the second guide tube in the air wet oxidation section through a gas distributor, mixing with the heated wastewater to initiate the air wet oxidation reaction, forming high-temperature treated wastewater. Part of the high-temperature treated wastewater recirculates into the middle of the reactor to mix with the heated wastewater, while the other part forms a gas-liquid mixture and is discharged to enter the subsequent separation stage. An oxygen analyzer is installed at the outlet to monitor the tail oxygen concentration.

[0053] This invention improves the COD removal rate by optimizing the internal components of the wet oxidation reactor, thereby increasing the wastewater retention time and gas-liquid mixing efficiency.

[0054] In comparison, the same wastewater was treated using the company's existing wet oxidation process (air oxidation), employing the same reactor size. A 108000m³ reactor was used. 3 The device uses pure air for oxidation per day, with an influent water temperature of 220℃, which is 39.1℃ higher than the influent water temperature of the device of this invention. Test results show that the COD removal rate of the effluent from the device of this invention is 72.5%, while that of the original device is only 55.7%.

[0055] The device of this invention reduces the preheating temperature and compression energy consumption of wet oxidation by using some pure oxygen instead of air, thereby reducing the operating cost of wet oxidation. Compared with conventional wet oxidation systems, the total energy consumption is reduced by about 56.2%.

Claims

1. An apparatus for the multi-stage wet oxidation treatment of wastewater, characterized by, The wet oxidation main reactor (12) comprises a lower part of an oxygen wet oxidation section, a wastewater inlet, an oxygen inlet and a first draft tube (10) arranged in the oxygen inlet from bottom to top, An air inlet is arranged in the middle part of the wet oxidation main reactor (12), and a second draft tube (15) is arranged in the upper part of the wet oxidation main reactor (12), The outlet of the wet oxidation main reactor (12) is arranged at the top; A flow distributor (13) is arranged between the air inlet and the first draft tube (10); A first thermometer (6) is arranged in the middle part of the wet oxidation main reactor (12), a second thermometer (8) is arranged in the top part of the wet oxidation main reactor (12), and an oxygen analyzer (17) is arranged at the outlet of the wet oxidation main reactor (12); The oxygen inlet is connected to an oxygen compressor (2), and the air inlet is connected to an air compressor (3); an oxygen flow controller (5) is arranged between the oxygen compressor (2) and the oxygen inlet; and an air flow controller (7) is arranged between the air compressor (3) and the air inlet.

2. The apparatus of claim 1, wherein, The height of the oxygen wet oxidation section is 30-60% of the height of the wet oxidation main reactor (12).

3. The apparatus of claim 1, wherein, The height of the first draft tube (10) is 40-80% of the height of the oxygen wet oxidation section.

4. The apparatus of claim 1, wherein, The wastewater inlet is connected to a preheating unit (4).

5. The apparatus of claim 1, wherein, An air disperser (14) is arranged at the air inlet.

6. A process for the multi-stage wet oxidation treatment of wastewater using the apparatus of any one of claims 1 to 5, characterized in that The wet oxidation main reactor (12) comprises a lower part of an oxygen wet oxidation section, a wastewater inlet, an oxygen inlet and a first draft tube (10) arranged in the oxygen inlet from bottom to top, The wet oxidation main reactor (12) comprises a lower part of an oxygen wet oxidation section, a wastewater inlet, an oxygen inlet and a first draft tube (10) arranged in the oxygen inlet from bottom to top, The temperature of the air or the oxygen is 60-100℃.

7. The process of claim 6, wherein, ​

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