Method for recycling tail gas of oxygen generation system

Abstract

According to the method for recycling the tail gas of the oxygen generation system, the tail gas of the oxygen generation system serves as blow-off gas and is fed into an ozone reaction tank, nitrogen in the tail gas of the oxygen generation system can reach 85%-95%, oxygen in sewage can be accelerated to be diffused into a gas phase due to the fact that the gas pressure of a liquid phase is increased according to the gas-liquid phase gas pressure balance principle, and dissolved oxygen in the sewage is removed.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection and pollution control, and more specifically, relates to a method for recycling tail gas from an oxygen production system. Background Art

[0002] During the treatment of industrial wastewater and some municipal wastewater with higher discharge requirements, ozone oxidation-related processes are usually used to improve the biodegradability of wastewater, so that the subsequent biochemical treatment unit can better play the treatment effect. The ozone generator used in the ozone oxidation unit is often equipped with an oxygen production system to prepare the high-purity oxygen required by the ozone generator. The oxygen production system mostly adopts PSA or VPSA process, using air as raw material, and produces high-purity oxygen through molecular sieve adsorption, and at the same time produces a nitrogen-rich tail gas, which is usually discharged directly into the atmosphere.

[0003] In order to save energy consumption in sewage treatment, biochemical methods will continue to be used after the ozone oxidation unit to further reduce the pollutant content. Common processes include denitrification filter, aerated biological filter, etc. When a denitrification filter is used for denitrification treatment, the dissolved oxygen carried in the ozone oxidation effluent will greatly hinder the formation of a denitrification anoxic environment and affect the denitrification treatment effect. Therefore, people usually use the following two technical means to achieve the removal of dissolved oxygen: one is to add a carbon source to the denitrification filter; the other is to add aeration air to the ozone reaction tank 13.

[0004] Adding carbon source to the denitrification filter to remove dissolved oxygen will not only increase the dosage of reagents, but also waste part of the denitrification filter capacity in the stage of reducing dissolved oxygen, increasing civil engineering and equipment investment. The method of air stripping can only reduce the dissolved oxygen in the sewage to the saturation value, and carbon source still needs to be added to the denitrification filter later, which cannot fundamentally solve the problem. Summary of the invention

[0005] The purpose of the present invention is to provide a method for recycling tail gas from an oxygen production system, so as to solve the problem that the blast air stripping method in the prior art can only reduce the dissolved oxygen in sewage to a saturation value.

[0006] In order to achieve the above object, the present invention provides a method for recycling tail gas from an oxygen production system, comprising:

[0007] The tail gas from the oxygen production system is used as stripping gas and sent to the ozone reaction tank to remove dissolved oxygen in the sewage.

[0008] Furthermore, before the tail gas of the oxygen production system is used as the stripping gas, the method further comprises:

[0009] The exhaust temperature of the oxygen production system is adjusted to below the set temperature;

[0010] Exhaust moisture removal from oxygen production system;

[0011] The tail gas pressure of the oxygen production system is adjusted to the final set pressure;

[0012] The exhaust gas flow rate of the oxygen production system is adjusted to the designed exhaust gas air volume.

[0013] Furthermore, when the oxygen production system is a VPSA oxygen production system, before the tail gas pressure of the oxygen production system is adjusted to the final set pressure, the following steps are further included:

[0014] The exhaust gas pressure fluctuation of the oxygen production system weakens the regulation.

[0015] Further, the tail gas temperature of the oxygen production system is adjusted to below a set temperature, including:

[0016] The tail gas outputted by the Roots vacuum pump is adjusted to a set temperature by using a heat exchanger and a temperature transmitter, wherein the temperature transmitter is arranged at the outlet of the heat exchanger and is used to detect the tail gas temperature at the outlet of the heat exchanger, and the heat exchanger is adjusted according to the detection value of the temperature transmitter;

[0017] Exhaust gas moisture removal from oxygen production system, including:

[0018] The tail gas outputted by the heat exchanger is dehumidified by using a buffer liquid separation tank, wherein the inlet end of the buffer liquid separation tank is connected to the outlet end of the heat exchanger;

[0019] The oxygen production system tail gas pressure fluctuation reduction regulation includes:

[0020] A pressure expansion tank is used to adjust the pressure fluctuation of the tail gas output from the buffer liquid separation tank, and the inlet end of the pressure expansion tank is connected to the outlet end of the buffer liquid separation tank;

[0021] The oxygen production system tail gas pressure is adjusted to the final set pressure including:

[0022] The tail gas outputted from the pressure expansion tank is adjusted to a first set pressure by using a pressure transmitter and a pressure regulating valve, wherein the pressure transmitter is arranged at the outlet of the pressure expansion tank and detects the tail gas pressure at the outlet of the pressure expansion tank, and the pressure regulating valve is arranged at the inlet of the heat exchanger, and the pressure regulating valve releases or replenishes pressure according to the detection value of the pressure transmitter;

[0023] The tail gas output from the pressure expansion tank is adjusted to a final set pressure by a booster fan, the inlet end of the booster fan is connected to the outlet end of the pressure expansion tank, and the outlet end of the booster fan is connected to the ozone reaction tank.

[0024] The exhaust gas flow of the oxygen production system is adjusted to the designed exhaust gas flow rate, including:

[0025] The exhaust gas output from the pressure expansion tank is adjusted to the designed exhaust gas blowing volume by using a booster fan and a flow meter, and the flow meter is arranged at the output end of the pressure expansion tank.

[0026] Furthermore, when the oxygen production system is a PSA oxygen production system, when the stripping gas is sent to the ozone reaction tank, it also includes:

[0027] Anti-backflow treatment of exhaust gas in oxygen production system.

[0028] Further,

[0029] The exhaust gas temperature of the oxygen production system is adjusted to below the set temperature, including:

[0030] The tail gas outputted by the Roots vacuum pump is adjusted to a set temperature by using a heat exchanger and a temperature transmitter, wherein the temperature transmitter is arranged at the outlet of the heat exchanger and is used to detect the tail gas temperature at the outlet of the heat exchanger, and the heat exchanger is adjusted according to the detection value of the temperature transmitter;

[0031] Exhaust gas moisture removal from oxygen production system, including:

[0032] The tail gas outputted by the heat exchanger is dehumidified by using a buffer liquid separation tank, wherein the inlet end of the buffer liquid separation tank is connected to the outlet end of the heat exchanger;

[0033] The exhaust gas flow of the oxygen production system is adjusted to the designed exhaust gas flow rate, including:

[0034] The tail gas input into the ozone reaction tank is adjusted to the designed tail gas blow-off air volume by using a flow regulating valve and a flow meter, the inlet end of the flow regulating valve is connected to the outlet end of the buffer liquid separator tank, the flow meter is arranged at the inlet end of the ozone reaction tank and detects the flow at the inlet end of the ozone reaction tank, and the flow regulating valve is adjusted according to the flow value detected by the flow meter;

[0035] The tail gas pressure of the oxygen production system is adjusted to the final set pressure, including:

[0036] The tail gas outputted from the buffer liquid separator tank is adjusted to a first set pressure by using a pressure transmitter and a pressure regulating valve; the pressure transmitter is arranged at the outlet of the buffer liquid separator tank and detects the tail gas pressure at the outlet of the buffer liquid separator tank, and the pressure regulating valve is arranged at the inlet of the heat exchanger and releases or replenishes the pressure according to the detection value of the pressure transmitter;

[0037] The tail gas output by the flow regulating valve is adjusted to a final set pressure by using a pressure reducing valve, wherein the pressure reducing valve is arranged between the flow regulating valve and the flow meter;

[0038] Oxygen production system tail gas backflow prevention treatment, including:

[0039] The tail gas outputted from the pressure reducing valve is subjected to backflow prevention treatment by using an anti-backflow tank, the inlet end of the anti-backflow tank is connected to the outlet end of the pressure reducing valve, and the outlet end of the anti-backflow tank is connected to the ozone reaction tank.

[0040] Furthermore, the set temperature is 40°C.

[0041] Furthermore, the first set pressure is -2 kPa to 2 kPa.

[0042] Furthermore, the final set pressure is 60 kPa to 80 kPa.

[0043] Furthermore, the designed exhaust gas air volume is 1 to 1.2 times the water volume treated by the ozone reaction tank 13.

[0044] The beneficial effects of the present invention are: providing a method for recycling tail gas from an oxygen production system, using the tail gas from the oxygen production system as a blow-off gas and sending it into an ozone reaction tank, the nitrogen content of the tail gas from the oxygen production system can reach 85% to 95%, and utilizing the gas-liquid phase pressure balance principle, the oxygen in the sewage will diffuse faster into the gas phase due to the increase in the liquid phase pressure, thereby achieving the removal of dissolved oxygen in the sewage.

[0045] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0047] Figure 1 A flow chart of a method for recycling tail gas from an oxygen production system according to an embodiment of the present invention is shown.

[0048] Figure 2 A schematic process flow chart of a tail gas recovery and utilization method of an oxygen production system according to an embodiment of the present invention applied to a VPSA oxygen production system is shown.

[0049] Figure 3 A schematic process flow chart of a method for recovering tail gas from an oxygen production system according to an embodiment of the present invention applied to a PSA oxygen production system is shown.

[0050] Description of reference numerals:

[0051] 1. Heat exchanger; 2. Temperature transmitter; 3. Buffer separator tank; 4. Pressure expansion tank; 5. Pressure transmitter; 6. Pressure regulating valve; 7. Booster fan; 8. Flow meter; 9. Flow regulating valve; 10. Pressure reducing valve; 11. Anti-backflow tank; 12. Roots vacuum pump; 13. Ozone reaction tank; 14. Cooling water valve; 15. Safety valve; 16. Liquid level meter; 17. Drain valve; 18. Blow-off and air distribution system. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0053] Embodiment 1

[0054] This embodiment provides a method for recycling tail gas from an oxygen production system. Figure 1 As shown, including:

[0055] The tail gas of the oxygen production system is used as the stripping gas and sent to the ozone reaction tank 13 to remove the dissolved oxygen in the sewage.

[0056] Specifically, the main components of the gases discharged from the tail gas of the oxygen production system are nitrogen, a small amount of carbon dioxide and water. Among them, nitrogen accounts for the majority, generally reaching 85% to 95%. Based on the principle of gas-liquid phase pressure balance, the tail gas of the oxygen production system (gas without oxygen) is used to blow off the sewage in the ozone oxidation tank digestion tank. The oxygen in the sewage will diffuse into the gas phase faster due to the increase in liquid phase pressure, thereby removing the dissolved oxygen in the sewage.

[0057] In this embodiment, before the tail gas of the oxygen production system is used as the stripping gas, the following steps are also included:

[0058] The exhaust temperature of the oxygen production system is adjusted to below the set temperature;

[0059] Exhaust moisture removal from oxygen production system;

[0060] The tail gas pressure of the oxygen production system is adjusted to the final set pressure;

[0061] The exhaust gas flow rate of the oxygen production system is adjusted to the designed exhaust gas air volume.

[0062] Specifically, temperature regulation, water removal, and pressure regulation can make the process system run stably, and flow regulation can control the exhaust gas flow rate within the range required by the process and better remove dissolved oxygen in the wastewater.

[0063] Optionally, when the oxygen production system is a VPSA oxygen production system, before the tail gas pressure of the oxygen production system is adjusted to the final set pressure, the following steps are further included:

[0064] The exhaust gas pressure fluctuation of the oxygen production system weakens the regulation.

[0065] Specifically, the VPSA oxygen production system uses lithium molecular sieve for low-pressure adsorption and vacuum pressure swing desorption. The adsorption pressure is provided by the booster blower 7, which is usually 0.05MPa. It is equipped with a Roots vacuum pump 12 for desorption. The exhaust pressure of the Roots vacuum pump 12 is not enough to overcome the water pressure in the ozone tank, so it is necessary to pressurize the exhaust gas in the process path. The combined effect of the pressurization treatment and the Roots vacuum pump 12 will produce exhaust pressure fluctuations, affecting the system stability, so it is necessary to perform exhaust pressure fluctuation weakening adjustment to weaken the exhaust pressure fluctuations.

[0066] Optionally, the exhaust temperature of the oxygen production system is adjusted to below a set temperature, including:

[0067] The tail gas outputted by the Roots vacuum pump 12 is adjusted to a set temperature by using the heat exchanger 1 and the temperature transmitter 2. The temperature transmitter 2 is arranged at the outlet of the heat exchanger 1 and is used to detect the tail gas temperature at the outlet of the heat exchanger 1. The heat exchanger 1 is adjusted according to the detection value of the temperature transmitter 2.

[0068] Exhaust gas moisture removal from oxygen production system, including:

[0069] The tail gas outputted from the heat exchanger 1 is dehumidified by using the buffer liquid separation tank 3, wherein the inlet end of the buffer liquid separation tank 3 is connected to the outlet end of the heat exchanger 1;

[0070] The oxygen production system tail gas pressure fluctuation reduction regulation includes:

[0071] The pressure expansion tank 4 is used to adjust the pressure fluctuation of the tail gas output from the buffer liquid separation tank 3, and the inlet end of the pressure expansion tank 4 is connected to the outlet end of the buffer liquid separation tank 3;

[0072] The oxygen production system tail gas pressure is adjusted to the final set pressure including:

[0073] The tail gas outputted from the pressure expansion tank 4 is adjusted to a first set pressure by using a pressure transmitter 5 and a pressure regulating valve 6. The pressure transmitter 5 is arranged at the outlet of the pressure expansion tank 4 and detects the tail gas pressure at the outlet of the pressure expansion tank 4. The pressure regulating valve 6 is arranged at the inlet of the heat exchanger 1. The pressure regulating valve 6 releases or replenishes pressure according to the detection value of the pressure transmitter 5.

[0074] The exhaust gas output from the pressure expansion tank 4 is adjusted to a final set pressure by using a booster fan 7 , the inlet end of the booster fan 7 is connected to the outlet end of the pressure expansion tank 4 , and the outlet end of the booster fan 7 is connected to the ozone reaction tank 13 .

[0075] The exhaust gas flow of the oxygen production system is adjusted to the designed exhaust gas flow rate, including:

[0076] The exhaust gas output from the pressure expansion tank 4 is adjusted to the designed exhaust gas blowing volume by using the booster fan 7 and the flow meter 8 , and the flow meter 8 is arranged at the output end of the pressure expansion tank 4 .

[0077] In this embodiment, Figure 2As shown, when the oxygen production system is a VPSA process, its tail gas comes from the pressure swing desorption link, that is, the nitrogen on the molecular sieve in the adsorption tower is desorbed by the roots vacuum pump 12, and discharged from the outlet of the roots vacuum pump 12). The tail gas from the roots vacuum pump 12 of the VPSA oxygen production system first enters the heat exchanger 1, and is cooled by cooling water to adjust the tail gas temperature to below 40°C. The heat exchanger 1 is preferably in the form of fins and tubes. A temperature transmitter 2 is provided at the outlet of the heat exchanger 1, and the opening of the cooling water valve 14 is adjusted in linkage to achieve temperature control. The gas at the outlet of the heat exchanger 1 enters the buffer liquid separation tank 3 to eliminate the air flow pulsation in the pipeline, ensure the stable supply of air flow, preliminarily cool the gas, condense part of the water vapor into liquid water, and the separated water is discharged from the bottom of the tank. The residence time of the buffer liquid separation tank 3 is set based on the designed stripping tail gas air volume, preferably 1min to 1.5min. The buffer liquid separation tank 3 is provided with a safety valve 15 to realize the overpressure protection function. The starting pressure of the safety valve 15 is preferably 3kPa to 5kPa. The outlet of the buffer liquid separation tank 3 is provided with a pressure transmitter 5, which is linked to a pressure regulating valve 6 to realize pressure control. When the detection value of the pressure transmitter 5 is higher than the upper limit of the set value (preferably 2kPa), the pressure regulating valve 6 is opened to release the pressure; when the detection value of the pressure transmitter 5 is lower than the lower limit of the set value (preferably -2kPa), the pressure regulating valve 6 is opened to supplement the pressure. A pressure expansion tank 4 is provided at the outlet end of the buffer liquid separator tank 3. The pressure expansion tank 4 can be of airbag type or diaphragm type. The pressure-regulating gas (preferably nitrogen) and the exhaust gas are separated into two parts by an airbag (or diaphragm) in the pressure expansion tank 4 to form a closed container. When the exhaust gas enters the pressure expansion tank 4, the pressure-regulating gas is compressed until the pressure reaches the same level as the exhaust gas and the intake is stopped; when the exhaust pressure decreases, the pressure-regulating gas expands, squeezing the exhaust gas out of the pressure expansion tank 4 and replenishing it into the system until the exhaust is stopped when the pressure reaches the same level as the exhaust pressure, thereby regulating the exhaust pressure fluctuation. The pressure setting range of the pressure expansion tank 4 is preferably -1kPa to 1kPa, and the volume is preferably 10 to 30 times the designed exhaust air volume. After the gas has been dehydrated and the flow rate has been adjusted by the buffer separator 3 and the pressure has been adjusted by the pressure expansion tank 4, the pressure is increased by the booster fan 7, preferably 60-80 kPa, which is determined according to the process conditions of the ozone digestion tank. The tail gas after the pressure is increased is sent to the stripping air distribution system 18 at the bottom of the ozone reaction tank 13. The air pressure balance principle of nitrogen stripping is used to reduce the dissolved oxygen of the sewage in the ozone reaction tank 13. The booster fan 7 is preferably a Roots booster fan 7, which is frequency-controlled. The booster fan 7 is linked to the flow meter 8 at the outlet. By adjusting the frequency of the booster fan 7, the air volume of the stripping tail gas is controlled within the process requirement range. The air volume of the stripping tail gas is preferably designed to be 1 to 1.2 times the amount of water treated in the ozone reaction tank 13.

[0078] Optionally, when the oxygen production system is a PSA oxygen production system, when the stripping gas is sent to the ozone reaction tank 13, it also includes:

[0079] Anti-backflow treatment of exhaust gas in oxygen production system.

[0080] Specifically, the PSA oxygen production system uses sodium molecular sieve, and the adsorption pressure is usually between 0.6 and 0.8 MPa. An air compressor is usually used for gas supply. Desorption is to release the pressure to achieve pressure change. The exhaust pressure during the desorption process is sufficient to overcome the water pressure in the ozone tank. Therefore, no secondary pressurization is required in the process path, and no pressure fluctuation adjustment is required. Considering that the pressure of the PSA oxygen production system changes during the desorption process, it may cause the sewage in the ozone reaction tank 13 to backflow, so it is necessary to carry out tail gas backflow prevention treatment.

[0081] Optionally, the exhaust temperature of the oxygen production system is adjusted to below a set temperature, including:

[0082] The tail gas outputted by the Roots vacuum pump 12 is adjusted to a set temperature by using the heat exchanger 1 and the temperature transmitter 2. The temperature transmitter 2 is arranged at the outlet of the heat exchanger 1 and is used to detect the tail gas temperature at the outlet of the heat exchanger 1. The heat exchanger 1 is adjusted according to the detection value of the temperature transmitter 2.

[0083] Exhaust gas moisture removal from oxygen production system, including:

[0084] The tail gas outputted from the heat exchanger 1 is dehumidified by using the buffer liquid separation tank 3, wherein the inlet end of the buffer liquid separation tank 3 is connected to the outlet end of the heat exchanger 1;

[0085] The exhaust gas flow of the oxygen production system is adjusted to the designed exhaust gas flow rate, including:

[0086] The tail gas input into the ozone reaction tank 13 is adjusted to the designed tail gas blowing volume by using a flow regulating valve 9 and a flow meter 8. The inlet end of the flow regulating valve 9 is connected to the outlet end of the buffer liquid separation tank 3. The flow meter 8 is arranged at the inlet end of the ozone reaction tank 13 and detects the flow at the inlet end of the ozone reaction tank 13. The flow regulating valve 9 is adjusted according to the flow value detected by the flow meter 8.

[0087] The tail gas pressure of the oxygen production system is adjusted to the final set pressure, including:

[0088] The tail gas output from the buffer liquid separation tank 3 is adjusted to a first set pressure by using a pressure transmitter 5 and a pressure regulating valve 6; the pressure transmitter 5 is arranged at the outlet of the buffer liquid separation tank 3 and detects the tail gas pressure at the outlet of the buffer liquid separation tank 3, and the pressure regulating valve 6 is arranged at the inlet of the heat exchanger 1 and releases or replenishes the pressure according to the detection value of the pressure transmitter 5;

[0089] The tail gas outputted by the flow control valve 9 is adjusted to a final set pressure by using a pressure reducing valve 10, and the pressure reducing valve 10 is arranged between the flow control valve 9 and the flow meter 8;

[0090] Oxygen production system tail gas backflow prevention treatment, including:

[0091] The tail gas output from the pressure reducing valve 10 is prevented from backflow by using an anti-backflow tank 11 , the inlet end of the anti-backflow tank 11 is connected to the outlet end of the pressure reducing valve 10 , and the outlet end of the anti-backflow tank 11 is connected to the ozone reaction tank 13 .

[0092] Specifically, if Figure 3 As shown, when the oxygen production system is a PSA process, the adsorption pressure is high (generally ≥ 0.5MPa), and the desorption link does not need to use the Roots vacuum pump 12 to evacuate and change the pressure. The tail gas of the PSA oxygen production system directly enters the heat exchanger 1 with pressure, and the tail gas from the Roots vacuum pump 12 of the VPSA oxygen production system first enters the heat exchanger 1, and is cooled by cooling water to adjust the tail gas temperature to below 40°C. The heat exchanger 1 is preferably in the form of fins and tubes. A temperature transmitter 2 is provided at the outlet of the heat exchanger 1, and the opening of the cooling water valve 14 is adjusted in linkage to achieve temperature control. The outlet gas of the heat exchanger 1 enters the buffer liquid separation tank 3, which plays a role in regulating the gas flow and removing moisture. The separated water is discharged from the bottom of the tank. The residence time of the buffer liquid separation tank 3 is set based on the designed stripping tail gas air volume, preferably 1min to 1.5min. The buffer liquid separation tank 3 is provided with a safety valve 15 to realize the overpressure protection function, and the starting pressure of the safety valve 15 is preferably 3kPa to 5kPa. A pressure transmitter 5 is provided at the outlet of the buffer liquid separator 3, and a pressure regulating valve 6 is linked to realize pressure control. When the detection value of the pressure transmitter 5 is higher than the upper limit of the set value (preferably 2kPa), the pressure regulating valve 6 is opened to release the pressure; when the detection value of the pressure transmitter 5 is lower than the lower limit of the set value (preferably -2kPa), the pressure regulating valve 6 is opened to replenish the pressure. The exhaust gas of the buffer liquid separator 3 is exhausted through the flow regulating valve 9 to control the flow rate. The flow meter 8 is linked with the flow regulating valve 9 to adjust the flow rate to the process requirement range. Preferably, the air volume of the stripping tail gas is 1 to 1.2 times the amount of water treated by the ozone reaction tank 13. The tail gas after the flow is adjusted is pressure regulated by the pressure reducing valve 10, preferably 60kPa to 80kPa, which is determined according to the process conditions of the ozone digestion tank. The pressure reducing valve 10 is preferably a self-operated pressure regulating valve. A backflow prevention tank 11 is provided downstream of the pressure reducing valve 10. The backflow prevention tank 11 is provided with a level gauge 16 and a drain valve 17. When the pressure fluctuation in the system causes the sewage in the ozone reaction tank 13 to flow back, the level gauge 16 alarms and links to open the drain valve 17. The volume of the backflow prevention tank 11 is preferably 10 to 30 times the designed air volume of the tail gas. The gas at the outlet of the backflow prevention tank 11 is sent to the air stripping distribution system 18 at the bottom of the digestion tank of the ozone reaction tank 13 through a pipeline, and the dissolved oxygen in the sewage is reduced by using the air pressure balance principle of nitrogen stripping.

[0093] Preferably, the set temperature is 40°C.

[0094] Preferably, the first set pressure is -2 kPa to 2 kPa.

[0095] Preferably, the final set pressure is 60 kPa to 80 kPa.

[0096] Preferably, the designed air volume of the exhaust gas is 1 to 1.2 times the amount of water treated by the ozone reaction tank 13 .

[0097] Embodiment 2

[0098] Ozone reaction tank 13 of a sewage plant can process 1000m3 of water 3 / h, ozone generator supporting VPSA oxygen system Roots vacuum pump 12 exhaust volume 3500m 3 / h, designed exhaust air volume 1000m 3 / h.

[0099] The tail gas of the Roots vacuum pump 12 enters the heat exchanger 1, and the tail gas temperature is reduced to below 40°C by cooling water. The heat exchanger 1 is of fin type. The outlet gas of the heat exchanger 1 enters the buffer liquid separator 3 to remove moisture and adjust the flow rate. The tail gas stays in the buffer liquid separator 3 for 1 minute. The volume of the buffer liquid separator 3 is 16.8m 3 , the tripping pressure of the safety valve 15 is set to 3kPa. The upper limit pressure of the pressure transmitter 5 at the outlet of the buffer liquid separation tank 3 is set to 2kPa, and the lower limit pressure of the pressure compensation is set to -2kPa. The pressure of the pressure expansion tank 4 is set to 0kPa, and the volume is 10 times the designed exhaust air volume, that is, 2.8m 3 .

[0100] After the gas has been dehydrated and the flow rate has been adjusted by the buffer separator 3 and the pressure has been adjusted by the pressure expansion tank 4, it is pressurized to 68kPa by the booster fan 7 and sent to the stripping air distribution system 18 at the bottom of the ozone reaction tank 13 digestion tank. The stripping air distribution system 18 can achieve uniform distribution of tail gas in the tank, and use the air pressure balance principle of nitrogen stripping to reduce the dissolved oxygen in the sewage in the ozone reaction tank 13 digestion tank. A temperature transmitter 2 is provided at the outlet of the heat exchanger 1, and the opening of the cooling water valve 14 is adjusted in conjunction to achieve temperature control. The pressure transmitter 5 is linked to the pressure regulating valve 6 to achieve pressure control. When the detection value of the pressure transmitter 5 is higher than 2kPa, the pressure regulating valve 6 is opened to release the pressure; when the detection value of the pressure transmitter 5 is lower than -2kPa, the pressure regulating valve 6 is opened to supplement the pressure. The booster fan 7 is linked to the flow meter 8 at the outlet, and the frequency of the booster fan 7 is adjusted to control the air volume of the stripping tail gas at 1000m 3 / h.

[0101] After the above process, the tail gas of the VPSA oxygen production system is recycled and used as the stripping gas of the ozone reaction tank 13, and the dissolved oxygen in the effluent water is reduced to 0.5 mg / L. The comparison between the dissolved oxygen in the effluent water without stripping and with compressed air stripping is shown in Table 1.

[0102] project unit No blow-off Compressed air blow off VPSA oxygen production system tail gas stripping Dissolved oxygen mg / L 10.5 8.1 0.5

[0103] Table 1

[0104] Embodiment 3

[0105] Ozone reaction tank 13 of a sewage plant can process 500m3 of water 3 / h, ozone generator supporting PSA oxygen production system exhaust volume 2400m 3 / h, designed exhaust air volume 600m 3 / h.

[0106] The exhaust gas enters the heat exchanger 1, and the exhaust gas temperature is reduced to below 40°C by cooling water. The heat exchanger 1 is a shell-and-tube type. The exhaust gas at the outlet of the heat exchanger 1 enters the buffer liquid separator tank 3 to remove moisture and adjust the flow rate. The exhaust gas stays in the buffer liquid separator tank 3 for 1.5 minutes. The volume of the buffer liquid separator tank 3 is 15m 3 The tripping pressure of the safety valve 15 is set to 5 kPa, the upper limit pressure of the pressure transmitter 5 at the outlet of the buffer liquid separation tank 3 is set to 2 kPa, and the lower limit pressure of the pressure compensation is set to -2 kPa.

[0107] The exhaust gas from the buffer liquid separation tank 3 is controlled at 600m through the flow regulating valve 9. 3 / h, and then the pressure is adjusted to 65kPa by the pressure reducing valve 10. The pressure reducing valve 10 is a self-operated pressure reducing valve 10. The volume of the anti-backflow tank 11 after the flow regulating valve 9 is 30 times the designed exhaust gas volume, that is, 5m 3 The gas at the outlet of the anti-backflow tank 11 is sent to the stripping and air distribution system 18 at the bottom of the ozone reaction tank 13 digestion tank through a pipeline. The stripping and air distribution system 18 can achieve uniform distribution of tail gas in the tank and reduce the dissolved oxygen of the sewage in the ozone reaction tank 13 digestion tank by using the air pressure balance principle of nitrogen stripping.

[0108] The outlet of heat exchanger 1 is equipped with temperature transmitter 2, which is linked to adjust the opening of cooling water valve 14 to achieve temperature control. Pressure transmitter 5 is linked to pressure regulating valve 6 to achieve pressure control. When the detection value of pressure transmitter 5 is higher than 2kPa, pressure regulating valve 6 is opened to release pressure; when the detection value of pressure transmitter 5 is lower than -2kPa, pressure regulating valve 6 is opened to supplement pressure. Flow meter 8 is linked to flow regulating valve 9 to control the air volume of exhaust gas at 600m 3 When the detection value of the liquid level gauge 16 on the backflow prevention tank 11 exceeds 0.5m, an alarm is triggered and the drain valve 17 is opened in linkage.

[0109] After the above process, the tail gas of the PSA oxygen production system is recycled and used as the ozone oxidation tank digestion tank stripping gas, and the dissolved oxygen in the effluent is reduced to 0.3 mg / L. The comparison between the dissolved oxygen in the effluent without stripping and with compressed air stripping is shown in Table 2.

[0110] project unit No blow-off Compressed air blow-off PSA oxygen production system tail gas stripping Dissolved oxygen mg / L 10.2 8.2mg / L 0.3

[0111] Table 2

[0112] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for recycling tail gas from an oxygen production system, characterized in that: include: The tail gas of the oxygen production system is used as the stripping gas and sent to the ozone reaction tank (13) to remove the dissolved oxygen in the sewage.

2. The method for recycling tail gas from an oxygen production system according to claim 1, characterized in that: Before using the tail gas of the oxygen production system as the stripping gas, it also includes: The exhaust temperature of the oxygen production system is adjusted to below the set temperature; Exhaust moisture removal from oxygen production system; The tail gas pressure of the oxygen production system is adjusted to the final set pressure; The exhaust gas flow rate of the oxygen production system is adjusted to the designed exhaust gas air volume.

3. The method for recycling tail gas from an oxygen production system according to claim 2, characterized in that: When the oxygen production system is a VPSA oxygen production system, before the tail gas pressure of the oxygen production system is adjusted to the final set pressure, the following steps are further included: The exhaust pressure fluctuation of the oxygen production system weakens the regulation.

4. The method for recycling tail gas from an oxygen production system according to claim 3, characterized in that: The exhaust gas temperature of the oxygen production system is adjusted to below the set temperature, including: The tail gas outputted by the Roots vacuum pump (12) is adjusted to a set temperature by using a heat exchanger (1) and a temperature transmitter (2), wherein the temperature transmitter (2) is arranged at the outlet of the heat exchanger (1) and is used to detect the tail gas temperature at the outlet of the heat exchanger (1), and the heat exchanger (1) is adjusted according to the detection value of the temperature transmitter (2); Exhaust gas moisture removal from oxygen production system, including: The tail gas outputted from the heat exchanger (1) is dehumidified by using a buffer liquid separation tank (3), wherein the inlet end of the buffer liquid separation tank (3) is connected to the outlet end of the heat exchanger (1); The oxygen production system tail gas pressure fluctuation reduction regulation includes: A pressure expansion tank (4) is used to adjust the pressure fluctuation of the tail gas output from the buffer liquid separation tank (3), wherein the inlet end of the pressure expansion tank (4) is connected to the outlet end of the buffer liquid separation tank (3); The oxygen production system tail gas pressure is adjusted to the final set pressure including: The tail gas outputted from the pressure expansion tank (4) is regulated to a first set pressure by using a pressure transmitter (5) and a pressure regulating valve (6); the pressure transmitter (5) is arranged at the outlet of the pressure expansion tank (4) and detects the tail gas pressure at the outlet of the pressure expansion tank (4); the pressure regulating valve (6) is arranged at the inlet of the heat exchanger (1); and the pressure regulating valve (6) releases or replenishes pressure according to the detection value of the pressure transmitter (5); The exhaust gas outputted from the pressure expansion tank (4) is adjusted to a final set pressure by using a booster fan (7), the inlet end of the booster fan (7) is connected to the outlet end of the pressure expansion tank (4), and the outlet end of the booster fan (7) is connected to an ozone reaction tank (13). The exhaust gas flow of the oxygen production system is adjusted to the designed exhaust gas flow rate, including: The exhaust gas output from the pressure expansion tank (4) is adjusted to a designed exhaust gas blow-off air volume using a booster fan (7) and a flow meter (8), and the flow meter (8) is arranged at the output end of the pressure expansion tank (4).

5. The method for recycling tail gas from an oxygen production system according to claim 2, characterized in that: When the oxygen production system is a PSA oxygen production system, when the stripping gas is sent to the ozone reaction tank (13), it also includes: Anti-backflow treatment of exhaust gas in oxygen production system.

6. The method for recycling tail gas from an oxygen production system according to claim 5, characterized in that: include: The exhaust gas temperature of the oxygen production system is adjusted to below the set temperature, including: The tail gas outputted by the Roots vacuum pump (12) is adjusted to a set temperature by using a heat exchanger (1) and a temperature transmitter (2), wherein the temperature transmitter (2) is arranged at the outlet of the heat exchanger (1) and is used to detect the tail gas temperature at the outlet of the heat exchanger (1), and the heat exchanger (1) is adjusted according to the detection value of the temperature transmitter (2); Exhaust gas moisture removal from oxygen production system, including: The tail gas outputted from the heat exchanger (1) is dehumidified by using a buffer liquid separation tank (3), wherein the inlet end of the buffer liquid separation tank (3) is connected to the outlet end of the heat exchanger (1); The exhaust gas flow of the oxygen production system is adjusted to the designed exhaust gas flow rate, including: The tail gas input into the ozone reaction pool (13) is adjusted to the designed tail gas blow-off air volume by using a flow regulating valve (9) and a flow meter (8); the inlet end of the flow regulating valve (9) is connected to the outlet end of the buffer liquid separation tank (3); the flow meter (8) is arranged at the inlet end of the ozone reaction pool (13) and detects the flow rate at the inlet end of the ozone reaction pool (13); the flow regulating valve (9) is adjusted according to the flow value detected by the flow meter (8); The tail gas pressure of the oxygen production system is adjusted to the final set pressure, including: The tail gas output from the buffer liquid separation tank (3) is regulated to a first set pressure by using a pressure transmitter (5) and a pressure regulating valve (6); the pressure transmitter (5) is arranged at the outlet of the buffer liquid separation tank (3) and detects the tail gas pressure at the outlet of the buffer liquid separation tank (3); the pressure regulating valve (6) is arranged at the inlet of the heat exchanger (1) and releases or replenishes pressure according to the detection value of the pressure transmitter (5); The tail gas outputted by the flow regulating valve (9) is regulated to a final set pressure by using a pressure reducing valve (10), wherein the pressure reducing valve (10) is arranged between the flow regulating valve (9) and the flow meter (8); Oxygen production system tail gas backflow prevention treatment, including: The backflow prevention tank (11) is used to prevent backflow of the tail gas output by the pressure reducing valve (10), the inlet end of the backflow prevention tank (11) is connected to the outlet end of the pressure reducing valve (10), and the outlet end of the backflow prevention tank (11) is connected to the ozone reaction tank (13).

7. A method for recycling tail gas from an oxygen production system according to any one of claims 2 to 6, characterized in that: The set temperature is 40°C.

8. A method for recycling tail gas from an oxygen production system according to any one of claims 2 to 6, characterized in that: The first set pressure is -2 kPa to 2 kPa.

9. A method for recycling tail gas from an oxygen production system according to any one of claims 2 to 6, characterized in that: The final set pressure is 60 kPa to 80 kPa.

10. A method for recycling tail gas from an oxygen production system according to any one of claims 2 to 6, characterized in that: The designed stripping tail gas air volume is 1 to 1.2 times the water volume treated by the ozone reaction tank 13 .

Images