An oxygen release kinetic and expansion cold energy cascade coupling recovery device and method

Abstract

The application relates to an oxygen diffusion kinetic energy and expansion cold energy cascade coupling recovery device and method, and relates to the technical field of energy recovery and utilization. The device comprises a diffusion tower pipeline side, a turbine expansion generator set, a safe diffusion system, a post-treatment and tail gas emission system and an instrument control interlocking system. The application has the effects of high-efficiency recovery of pressure energy, improvement of cold energy cascade utilization and realization of noise reduction and environmental protection.

Description

Technical Field

[0001] This application relates to the field of energy recovery and utilization technology, and in particular to a device and method for the cascade coupling and recovery of oxygen release kinetic energy and expansion cold energy. Background Technology

[0002] Cryogenic air separation is currently the mainstream technology for producing high-purity oxygen on an industrial scale. It is widely used in large-scale industrial fields such as metallurgy, petrochemicals, and coal chemicals. Its basic process is as follows: the raw air is filtered, compressed, pre-cooled, and purified (to remove impurities such as moisture and carbon dioxide) before entering the main heat exchanger to exchange heat with the reflux low-temperature gas. After being cooled to near the liquefaction temperature, it enters the distillation column (fractionation column) for low-temperature distillation separation. Utilizing the difference in boiling points between oxygen and nitrogen, gas-liquid mass and heat transfer are achieved on the column plates. Finally, high-purity liquid oxygen is obtained at the bottom of the upper column, which is then reheated by the main heat exchanger and sent to the oxygen pipeline network for user use.

[0003] In the actual operation of cryogenic air separation units, oxygen storage and transportation are usually carried out in medium-pressure mode. Oxygen from the fractionation tower is compressed to 2.5MPa by an oxygen compressor and then sent to a medium-pressure oxygen spherical tank for storage. After being depressurized to the pressure required by the user (generally 0.6-1.6MPa) by a pressure reducing valve group, it is then transported to various oxygen consumption points. In the following operating conditions, medium-pressure oxygen needs to be released through a venting pipeline: (1) Oxygen surplus caused by fluctuations in oxygen consumption: When the oxygen consumption of downstream users decreases sharply (such as steelmaking converter maintenance, blast furnace shutdown, etc.), while the oxygen consumption of downstream users decreases sharply, the oxygen consumption of downstream users decreases sharply. (1) When the pressure of the medium-pressure spherical tank rises to the upper limit of safety, the excess oxygen must be released through the vent valve to ensure the safety of the system. (2) Equipment maintenance and repair: When the oxygen compressor, spherical tank or pipeline is repaired, the residual medium-pressure oxygen in the system must be vented through the vent pipeline. (3) Start-up and shutdown of air separation unit and change of operating conditions: When the oxygen purity of the product does not meet the standard or the output does not match the demand during the start-up, shutdown or load adjustment of air separation unit, the unqualified oxygen must be released.

[0004] Regarding the above-mentioned technologies, the following technical defects exist: (1) Serious energy waste: When medium-pressure oxygen is depressurized through the throttling valve / venting valve, its pressure energy is completely converted into heat energy and sound energy and dissipated into the atmosphere without doing any useful work; (2) High noise pollution: When high-pressure oxygen passes through the venting valve and silencer at high speed, it generates strong noise. Even after being treated by the silencer, the noise is still relatively strong, which seriously affects the plant area and the surrounding environment; (3) High safety risk: During the throttling and depressurization process of high-pressure oxygen, the high-speed airflow rubs against the inner wall of the valve body to generate static electricity and local high temperature. In the oxygen-rich environment, there is a risk of combustion or even explosion. The oxygen pressure reducing valve is subjected to high-speed scouring and friction. Leakage failures caused by rubbing occur frequently; (4) Waste of cold energy: The oxygen output from the air separation unit has a low temperature (15-25℃). If the cold energy of its temperature difference can be used during the release process, it can be used for refrigeration or pre-cooling of fresh air. However, in the prior art, this part of the cold energy is also wasted; (5) Poor regulation quality: When the traditional pressure reducing valve changes significantly, the pressure fluctuation after the valve is large and it is difficult to control accurately. Especially under intermittent release conditions, frequent valve opening and closing exacerbates valve seat wear and shortens valve service life; Based on the above, this application provides an oxygen release and expansion cold energy cascade coupling recovery device and recovery method to improve the above problems. Summary of the Invention

[0005] In order to efficiently recover pressure energy, improve the cascade utilization of cold energy, and achieve noise reduction and environmental protection, this application provides a device and method for the cascade coupling and recovery of oxygen release kinetic energy and expansion cold energy.

[0006] Firstly, the oxygen release kinetic energy and expansion cold energy cascade coupling recovery device provided in this application adopts the following technical solution: A cascade coupling recovery device for oxygen release kinetic energy and expansion cold energy includes a release tower pipeline side, a turbine expansion generator set, a safety release system, an after-treatment and exhaust gas emission system, and an instrumentation and control interlocking system.

[0007] Preferably, the venting tower pipeline includes an oxygen venting tower, an oxygen venting pipe, a first inlet shut-off valve, an inlet filter, a vortex flow meter, a temperature and pressure measuring unit, and a pre-buffered pressure stabilizing tank. The oxygen venting pipe is connected to the outlet side of the oxygen venting tower. The first inlet shut-off valve is installed on the oxygen venting pipe. The inlet filter is connected in series downstream of the first inlet shut-off valve. The filtration accuracy of the inlet filter is ≥5μm. A differential pressure transmitter is connected in series with the inlet filter. The differential pressure transmitter issues an alarm when the differential pressure exceeds a set value to prompt cleaning or replacement of the filter element. The set value is 0.05MPa. The vortex flow meter is installed downstream of the inlet filter and is communicatively connected to a DCS system. The temperature and pressure measuring unit includes a first temperature transmitter and a first pressure transmitter, which are installed downstream of the vortex flow meter. The pre-buffered pressure stabilizing tank is installed downstream of the temperature and pressure measuring unit, and the volume of the pre-buffered pressure stabilizing tank is ≥0.3m³.

[0008] Preferably, the turbine expander generator set includes an oxygen turbine expander and a generator. The oxygen turbine expander includes a primary turbine expander and a secondary turbine expander. The primary turbine expander is connected to a pre-buffered pressure stabilizing tank. An interstage heater is provided between the primary turbine expander and the secondary turbine expander. The generator is coaxially and directly connected to the primary turbine expander.

[0009] Preferably, a safety valve and a second inlet shut-off valve are sequentially provided at the rear end of the pre-buffered pressure tank, and a guide vane is provided at the rear end of the second inlet shut-off valve.

[0010] Preferably, the safety venting system includes a bypass pressure reducing line and an emergency venting line. The bypass pressure reducing line is connected in parallel with the oxygen turbine expander. A pneumatic regulating valve is installed on the bypass pressure reducing line and is communicatively connected to the DCS system. The emergency venting line is connected to the top of the oxygen venting tower. A pneumatic quick-opening valve is connected in series on the emergency venting line and is communicatively connected to the DCS system.

[0011] Preferably, the aftertreatment and exhaust gas emission system includes an outlet temperature regulating device, which includes a cold energy recovery heat exchanger. The cold energy recovery heat exchanger is connected to a second vent pipe and is connected to a bypass pressure reducing pipeline through the second vent pipe. A silencer and a flame arrester are sequentially installed on the second vent pipe. The cold energy recovery heat exchanger is connected to a circulating water tank, and a pressure regulating valve is installed on the outlet side of the cold energy recovery heat exchanger.

[0012] Preferably, the secondary turbine expander is connected to the cold energy recovery heat exchanger, and a second temperature transmitter and a second pressure transmitter are provided between the secondary turbine expander and the cold energy recovery heat exchanger.

[0013] Preferably, the generator is connected to a frequency converter, the back end of the frequency converter is connected to a transformer, the back end of the transformer is connected to a grid connection point, the grid connection point is connected to a 10kV power grid, the generator is also connected to an energy storage converter, and the back end of the energy storage converter is connected to an energy storage battery pack.

[0014] Preferably, the instrumentation and control interlocking system is controlled by the DCS system to achieve process monitoring, power regulation and safety interlocking protection.

[0015] Secondly, the method for the graded coupling recovery of oxygen release kinetic energy and expansion cold energy provided in this application adopts the following technical solution: A method for the graded coupling and recovery of oxygen release kinetic energy and expansion cold energy includes the following steps: S1: Medium-pressure oxygen is drawn out from the oxygen vent pipe, passes through the first inlet shut-off valve, inlet filter, and vortex flow meter, and enters the pre-buffer pressure stabilizing tank for pressure stabilization. After pressure stabilization, the medium-pressure oxygen enters the turbine expander generator set to expand and do work. S2: During the expansion of medium-pressure oxygen, the oxygen pressure drops from 2.5MPa to 0.1-0.15MPa, and the temperature drops from 25℃ to -20℃-10℃; S3: The expander drives the generator to generate electricity. The electrical energy is rectified and inverted by the frequency converter and then fed into the internal power grid or stored in the energy storage unit. S4: After expansion, the low-pressure and low-temperature oxygen is heated to 5-15℃ by the cold energy recovery heat exchanger and then enters the silencer for noise reduction treatment. Finally, it is discharged into the atmosphere through the oxygen venting tower. S5: When the expander malfunctions or the throughput is insufficient, oxygen is discharged into the exhaust gas system after being depressurized by the pneumatic regulating valve through the bypass pressure reducing line. When the system experiences an emergency overpressure, the safety valve or pneumatic quick-opening valve in the emergency venting line is opened directly to release pressure.

[0016] In summary, this application includes at least one of the following beneficial technical effects: 1. This application can efficiently recover pressure energy by replacing the traditional pressure reducing valve with a turbo expander, converting the pressure energy during the release of medium-pressure oxygen into electrical energy, thereby recovering the released kinetic energy. At the same time, the recovered kinetic energy can reduce the amount of electricity purchased by the enterprise and indirectly reduce carbon emissions. 2. This application can realize the cascade utilization of cold energy. The cold energy of the expanded oxygen is recovered through the cold energy recovery heat exchanger and used to reduce the temperature of the circulating water and reduce the load of the cooling fan of the circulating water system, thereby realizing the cascade utilization of energy. At the same time, the heat energy of the circulating water is transferred to the oxygen released between stages, effectively preventing the temperature from dropping below the liquefaction point during the oxygen expansion process, which would lead to liquid oxygen precipitation and reduce the risk of liquid hammer. 3. This application can realize multi-level safety interlocks, setting up four levels of interlock protection: emergency stop, deceleration operation, bypass switching, and anti-liquid hammer, covering all key safety risks such as vibration, overspeed, overpressure, and overtemperature, ensuring that the system can safely shut down and automatically depressurize under any abnormal operating conditions; 4. This application can achieve noise reduction and environmental protection. The expander consumes the pressure energy of oxygen during operation, and the outlet oxygen speed and pressure are greatly reduced, thus significantly improving the sound environment of the plant area. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a cascade coupling recovery device for oxygen release kinetic energy and expansion cold energy according to an embodiment of this application.

[0018] Explanation of reference numerals in the attached diagram: 1. Oxygen vent pipe; 2. First inlet shut-off valve; 3. Inlet filter; 4. Differential pressure transmitter before and after the filter; 5. Vortex flow meter; 6. First temperature transmitter; 7. First pressure transmitter; 8. Pre-buffered pressure stabilizing tank; 9. Safety valve; 10. Second inlet shut-off valve; 11. Guide vane; 12. First-stage turbine expander; 13. Interstage heater; 14. Second-stage turbine expander; 15. Generator; 16. Frequency converter; 17. Variable frequency drive. 18. Grid connection point; 19. Energy storage converter; 20. Energy storage battery pack; 21. Second temperature transmitter; 22. Second pressure transmitter; 23. Cold energy recovery heat exchanger; 24. Pressure regulating valve; 25. Flame arrester; 26. Second vent pipe; 27. DCS system; 28. Pneumatic regulating valve; 29. ​​Bypass pressure reducing line; 30. Pneumatic quick-opening valve; 31. Oxygen venting tower; 32. Silencer; 33. Emergency venting line; 34. Circulating water tank. Detailed Implementation

[0019] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.

[0020] This application discloses a cascaded coupling recovery device for oxygen release kinetic energy and expansion cold energy. (Refer to...) Figure 1 The system includes a venting tower pipeline side, 15 sets of turbine expander generators, a safety venting system, an after-treatment and exhaust gas emission system, and an instrumentation and control interlocking system.

[0021] Reference Figure 1 The venting tower pipeline includes an oxygen venting tower 31, an oxygen venting pipe 1, a first inlet shut-off valve 2, an inlet filter 3, a vortex flow meter 5, a temperature and pressure measuring unit, and a pre-buffered pressure stabilizing tank 8. The oxygen venting pipe 1 is connected to the outlet side of the oxygen venting tower 31. The first inlet shut-off valve 2 is installed on the oxygen venting pipe 1. After the vented oxygen is drawn out from the oxygen venting tower 31, it first passes through the first inlet shut-off valve 2 (a starting ball valve, a fire-resistant and safe type for oxygen, can be used). This valve quickly cuts off the gas source in case of emergency shutdown or system interlocking.

[0022] Reference Figure 1 The inlet filter 3 is connected in series with the first inlet shut-off valve 2. The filtration accuracy of the inlet filter 3 is ≥5μm. It is used to intercept possible solid particulate impurities (such as rust, welding slag, etc.) in the pipeline and prevent particles from entering the turbine expander and causing erosion damage under the high speed of the impeller. The inlet filter 3 is connected in series with a differential pressure transmitter 4 before and after the filter. When the differential pressure exceeds the set value, the differential pressure transmitter 4 will issue an alarm to prompt cleaning or replacement of the filter element. The set value is 0.05MPa.

[0023] Reference Figure 1 The vortex flow meter 5 is installed at the rear end of the inlet filter 3 to measure the oxygen flow rate. The vortex flow meter 5 is connected to the DCS system 27 and uploads the flow signal to the DCS system 27 as a key parameter for expander speed control and energy recovery efficiency calculation. The temperature and pressure measurement unit includes a first temperature transmitter 6 and a first pressure transmitter 7. The first temperature transmitter 6 and the first pressure transmitter 7 are installed after the vortex flow meter 5 to monitor the thermodynamic state parameters of the oxygen entering the expander in real time, and calculate the inlet enthalpy and theoretical available work in conjunction with the flow data.

[0024] Reference Figure 1 The pre-buffer pressure stabilizing tank 8 is located behind the temperature and pressure measurement unit. The volume of the pre-buffer pressure stabilizing tank 8 is ≥0.3m³. It is used to absorb pressure fluctuations caused by pressure fluctuations in the spherical tank and changes in upstream operating conditions, to ensure stable airflow pressure entering the expander, and to avoid large fluctuations in expander speed or even surge caused by pressure fluctuations. A safety valve 9 is installed on the pre-buffer pressure stabilizing tank 8, with a set pressure of 1.1 times the system design pressure, as an overpressure protection measure for the pipeline system.

[0025] Reference Figure 1 The 15 sets of turboexpander generators include an oxygen turboexpander and a generator 15. The oxygen turboexpander adopts a single-stage or multi-stage radial turboexpander. The specific number of stages is determined according to the inlet pressure and expansion ratio. When the expansion ratio (inlet absolute pressure / outlet absolute pressure) is ≤4, a single-stage expansion is adopted. When the expansion ratio is >4, a two-stage expansion plus intermediate heating scheme is adopted. The expander impeller is made of oxygen-specific flame-retardant alloy material (such as Monel alloy).

[0026] Reference Figure 1The oxygen turbine expander includes a primary turbine expander 12 and a secondary turbine expander 14. The primary turbine expander 12 is connected to the pre-buffered pressure stabilizing tank 8. The expander bearing adopts an active magnetic levitation bearing, which does not require lubrication oil, thus fundamentally eliminating the risk of combustion and explosion caused by lubricating oil in the oxygen environment. The magnetic levitation bearing has a real-time vibration monitoring function, and the bearing displacement, vibration value, current value and other signals are uploaded to the DCS system 27 in real time. When the vibration exceeds the set threshold, it automatically performs deceleration or shutdown protection. The critical speed of the expander rotor is designed to be more than 1.3 times the rated speed to ensure that the operating speed range avoids the critical speed resonance zone. The expander casing adopts a double-layer structure, with self-produced nitrogen gas introduced into the interlayer as an inert gas sealing and protection layer to prevent oxygen from leaking from the shaft seal to the atmosphere or bearing cavity.

[0027] Reference Figure 1 The generator 15 is a permanent magnet synchronous generator 15, coaxially and directly connected to the expander, without a gear speed increaser, reducing mechanical transmission losses and maintenance points. The rated speed of the generator 15 matches the design speed of the expander. The variable frequency and variable voltage AC power output by the generator 15 is rectified into DC power and then inverted into industrial frequency AC power, which is connected to the enterprise's internal power grid or directly drives the plant's load via the step-up transformer 17. The generator 15 is connected to a frequency converter 16, and the transformer 17 is connected to the back end of the frequency converter 16. The grid connection point 18 is connected to the back end of the transformer 17. The grid connection point 18 is connected to the 10kV power grid. The generator 15 is also connected to an energy storage converter 19, and the energy storage battery pack 20 is connected to the back end of the energy storage converter 19.

[0028] Reference Figure 1 When a two-stage expansion scheme is adopted, an interstage heater 13 is installed between the outlet of the first-stage turbine expander 12 and the inlet of the second-stage turbine expander 14. The air separation circulating water return water (about 35°C) is used as a heat source to heat the low-temperature oxygen after the first-stage expansion, thereby increasing the inlet temperature of the second-stage expansion. This prevents the oxygen temperature from dropping below the liquefaction temperature during the expansion process, which would cause liquid oxygen to precipitate. Liquid oxygen entering the expander impeller would cause liquid hammer damage. Therefore, interstage heating is a key measure to ensure the safe operation of multi-stage expansion. The interstage heater 13 adopts a shell-and-tube structure, with oxygen flowing through the tube side and the heat source flowing through the shell side. The tube material is 316L stainless steel. In addition, the circulating water return water absorbs this part of the cold energy and returns to the water tank, reducing the water temperature in the water tank and correspondingly reducing the power consumption of the water tank cooling fan.

[0029] Reference Figure 1 The front buffer pressure tank 8 is equipped with a safety valve 9 and a second inlet shut-off valve 10 in sequence at its rear end, and a guide vane 11 is provided at the rear end of the second inlet shut-off valve 10.

[0030] Reference Figure 1The safety venting system is a key redundancy measure to ensure the safe operation of the air separation unit. In the event of a failure, insufficient maintenance or handling capacity of the turbine expander generator set 15, medium-pressure oxygen can be directly vented through the bypass pipeline to ensure that the spherical tank does not overpressure. The safety venting system includes a bypass pressure reducing pipeline 29 and an emergency venting pipeline 33.

[0031] Reference Figure 1 The bypass pressure reducing line 29 is connected in parallel with the oxygen turbine expander. A pneumatic regulating valve 28 is installed on the bypass pressure reducing line 29, and the pneumatic regulating valve 28 is communicatively connected to the DCS system 27. When the expander stops or the throughput is insufficient, the valve automatically opens, sending part or all of the oxygen to the exhaust gas system after pressure reduction through the bypass. The valve adopts an equal percentage flow characteristic and, in conjunction with the DCS feedforward control algorithm, achieves pressure-free switching during the expansion start-stop process.

[0032] Reference Figure 1 The emergency venting pipeline 33 is connected to the top of the oxygen venting tower 31. A pneumatic quick-opening valve 30 is connected in series on the emergency venting pipeline 33. The pneumatic quick-opening valve 30 is connected in communication with the DCS system 27. The emergency venting pipeline 33 is directly led from the medium-pressure spherical tank or the main oxygen pipeline to the top of the oxygen venting tower 31. A spring-loaded safety valve 9 and the pneumatic quick-opening valve 30 are connected in series on the pipeline. The safety valve 9 is set at the design pressure of the spherical tank. When the system pressure exceeds the set value of the safety valve 9, it automatically opens to release pressure. The pneumatic quick-opening valve 30 is interlocked and controlled by the DCS system 27. When the pressure of the spherical tank is detected to reach a high level, the pneumatic quick-opening valve 30 releases pressure in an emergency.

[0033] Reference Figure 1 The expanded low-pressure oxygen (close to atmospheric pressure, temperature -20℃ to 10℃) needs to be safely discharged into the atmosphere. The exhaust gas system includes an outlet temperature regulating device, which includes a cold energy recovery heat exchanger 23. The temperature of the expanded oxygen may drop below 0℃. Direct discharge would cause the pipeline to freeze. The cold energy recovery heat exchanger 23 is installed on the outlet pipeline, using the circulating water of the air-cooled tower of the air separation unit or the chilled water of the pre-cooling system as the heat exchange medium. The cold energy of the expanded oxygen is recovered to reduce the temperature of the circulating water, further reducing the load on the cooling fan of the water tank, and realizing the cascade utilization of energy. The cold energy recovery heat exchanger 23 adopts a plate heat exchanger, with oxygen on the cold side and circulating water on the hot side. The amount of cold energy recovered is controlled by the pressure regulating valve 24 to ensure that the outlet oxygen temperature is not lower than 5℃ to prevent pipeline freezing.

[0034] Reference Figure 1The cold energy recovery heat exchanger 23 is connected to a second vent pipe 26. The cold energy recovery heat exchanger 23 is connected to a bypass pressure reducing pipeline through the second vent pipe 26. A silencer 32 and a flame arrester 25 are installed sequentially on the second vent pipe 26. The cold energy recovery heat exchanger 23 is connected to a circulating water tank 34. A pressure regulating valve 24 is installed on the outlet side of the cold energy recovery heat exchanger 23. The secondary turbine expander 14 is connected to the cold energy recovery heat exchanger 23. A second temperature transmitter 21 and a second pressure transmitter 22 are installed between the secondary turbine expander 14 and the cold energy recovery heat exchanger 23.

[0035] Reference Figure 1 The instrument control interlocking system is controlled by the DCS system 27 to achieve process monitoring, power regulation and safety interlocking protection.

[0036] (1) Process monitoring: The DCS system collects the following parameters in real time: inlet oxygen pressure P1, temperature T1, flow rate F1, expander speed N, expander outlet pressure P2, temperature T2, generator output power Pe, current I, voltage U, inverter operating parameters, magnetic levitation bearing vibration value Vib, displacement value Disp, temperature before and after the heaters in each stage, bypass valve opening, emergency vent valve status, oxygen concentration in the environment, etc. All parameters are displayed on the DCS system operation station screen in real time and stored in the historical database at 1-second intervals.

[0037] (2) Power regulation: The DCS system calculates the required expander flow rate based on the deviation between the inlet oxygen pressure P1 and the set pressure Pset using a PID algorithm, outputs the guide vane opening command, and adjusts the guide vane angle to change the expander flow rate, thereby maintaining a stable inlet pressure. At the same time, the DCS system calculates the theoretical available power based on the inlet temperature T1, pressure P1, and flow rate F1, optimizes the guide vane opening and generator excitation current, so that the expander operates near the optimal efficiency operating point. When the discharge is lower than the minimum stable flow rate of the expander (about 10% of the rated flow rate), the expander automatically slows down to standby mode, and oxygen is discharged through the bypass valve with reduced pressure.

[0038] (3) Safety interlock protection: Multi-level interlock protection is set up, in order of priority from high to low as follows: ① Emergency Stop Interlock (Highest Priority, SIL3): Triggering conditions include—expander vibration exceeding the upper limit (Vib≥80μm), magnetic levitation bearing displacement exceeding the limit (Disp≥±100μm), expander overspeed (N≥1.1 times rated speed), inlet pressure exceeding the upper limit (P1≥design pressure×1.05), generator winding temperature exceeding the upper limit (≥155°C), and ambient oxygen concentration exceeding the upper limit (≥23%). Action: Expander emergency shutdown (guide vanes fully closed, inlet shut-off valve fully closed), while the bypass valve fully opens, and the emergency venting valve is automatically controlled according to the tank pressure to ensure safe depressurization of the system.

[0039] ② Deceleration Interlock (SIL2 Level): Triggering conditions include—expander vibration high limit (Vib≥50μm), expander outlet temperature low limit (T2≤-30°C), interstage heater malfunction resulting in substandard outlet temperature, inverter over-temperature warning, and abnormal generator power fluctuation (fluctuation rate>±20% / min). Action: The expander automatically decelerates to 50% of its rated speed, while the bypass valve partially opens to compensate for the flow, maintaining stable inlet pressure, and issuing an alarm signal to prompt the operator to check and handle the situation.

[0040] ③ Switch to bypass interlock (SIL2 level): Triggering conditions include—expander efficiency below 60%, expander continuous operation time reaching the maintenance cycle, and DCS and local controller communication interruption exceeding 3 seconds. Action: Expander shuts down normally, and the bypass valve automatically takes over the pressure regulation function, achieving a smooth switching.

[0041] ④ Liquid hammer protection interlock (SIL2 level): When the outlet temperature of any stage of the expander is lower than the liquefaction temperature of oxygen at that pressure +10°C (safety margin), a risk of liquid oxygen evolution is determined. Action: Increase the power of the interstage heater and simultaneously reduce the expansion ratio of that stage (adjusted via guide vanes). If the temperature continues to drop, the deceleration operation interlock is activated.

[0042] The implementation principle of the oxygen release kinetic energy and expansion cold energy cascade coupling recovery device in this application embodiment is as follows: During normal operation (power generation mode): medium-pressure oxygen is drawn out from the oxygen release pipe, enters the inlet filter through the first inlet shut-off valve, and the differential pressure transmitter before and after the filter monitors the filter element blockage in real time. After the filtered oxygen is measured by the vortex flow meter, the thermal parameters are collected by the first inlet temperature transmitter and the first inlet pressure transmitter, and the pressure is stabilized in the pre-buffered pressure stabilizing tank. The stabilized oxygen enters the first stage turbine expander through the first inlet shut-off valve of the expander.

[0043] Oxygen is accelerated by adjustable guide vanes (guide vane installation angle adjustable range 15°~75°) and then enters the first-stage turboexpander to expand and do work. After the first-stage expansion, the oxygen pressure drops to about 0.7MPa and the temperature drops to about -15°C. The oxygen after the first-stage expansion enters the interstage heater (shell-and-tube heat exchanger, the heat source is the high-temperature air from the air compressor outlet, the temperature is about 90°C), and is heated to about 40°C before entering the second-stage turboexpander for further expansion to an outlet pressure of 0.12MPa and an outlet temperature of about -10°C. The expander rotor (including the first-stage and second-stage impellers) is supported by magnetic levitation bearings and drives a permanent magnet synchronous generator to generate electricity.

[0044] The high-frequency AC power output from the generator is rectified into DC power by a frequency converter, then inverted into 50Hz / 380V industrial frequency AC power. After being stepped up to 10kV by a step-up transformer, it is connected to the enterprise's internal 10kV distribution network at the grid connection point. When the generator output power exceeds the grid connection point's absorption capacity, the excess electricity is stored in the energy storage battery pack via an energy storage converter. When the discharge suddenly increases or the generator power surges beyond the grid connection point's capacity limit, the battery pack discharges to assist in absorption, preventing the grid connection point from tripping due to overload.

[0045] The expanded, low-pressure, low-temperature oxygen is discharged from the outlet of the secondary expander. After being monitored by the expander outlet temperature and pressure transmitters, it enters the cold energy recovery heat exchanger (plate heat exchanger, with oxygen on the cold side and circulating water from the water tank on the hot side). The flow rate of the circulating water entering the cold energy recovery heat exchanger is controlled by a regulating valve. After recovering the cold energy of the oxygen, it flows back into the circulating water tank to lower the circulating water temperature and simultaneously regulate the oxygen temperature to 5-15°C. The temperature-regulated oxygen then enters the flame arrester and, after noise reduction treatment by a silencer, is finally discharged into the atmosphere through the oxygen vent pipe.

[0046] In bypass mode operation: When the expander generator set malfunctions, is under maintenance, or the venting flow is lower than the expander's minimum stable flow rate, the DCS system automatically opens the bypass pressure reducing regulating valve, allowing oxygen to be directly discharged into the venting pipe after pressure reduction via the bypass pipeline. During the switching process between the expander and the bypass valve, the DCS system employs a feedforward control algorithm to predict the switching time based on the rate of change of the expander guide vane opening, opening the bypass valve in advance to compensate for the flow and achieve a disturbance-free switching of the inlet pressure.

[0047] In case of emergency venting: When the pressure in the spherical tank reaches the high-high limit or the expander and bypass valve fail to release pressure, the emergency venting pneumatic quick-opening valve will automatically open fully, and oxygen will be discharged directly into the venting tower through the emergency venting pipeline.

[0048] This application also provides a method for the cascade coupling and recovery of oxygen release kinetic energy and expansion cold energy, including the following steps: S1: After medium-pressure oxygen is drawn out from the oxygen vent pipe, it enters the pre-buffered pressure stabilizing tank through the first inlet shut-off valve, inlet filter, and vortex flow meter for pressure stabilization. The stabilized medium-pressure oxygen then enters the turbine expander generator set to expand and perform work.

[0049] S2: During the medium-pressure oxygen expansion process, the oxygen pressure drops from 2.5MPa to 0.1-0.15MPa, and the temperature drops from 25℃ to -20℃-10℃ or lower (in multi-stage expansion, the oxygen is heated by the interstage heater before entering the next stage).

[0050] S3: The expander drives the generator to generate electricity. The electrical energy is rectified and inverted by the frequency converter and then fed into the internal power grid or stored in the energy storage unit.

[0051] S4: After expansion, the low-pressure, low-temperature oxygen is heated to 5-15°C by a cold energy recovery heat exchanger, then enters a silencer for noise reduction, and finally is discharged into the atmosphere through an oxygen venting tower.

[0052] S5: When the expander malfunctions or the throughput is insufficient, oxygen is discharged into the exhaust gas system after being depressurized by the pneumatic regulating valve through the bypass pressure reducing line. When the system experiences an emergency overpressure, the safety valve or pneumatic quick-opening valve in the emergency venting line is opened directly to release pressure.

[0053] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A device for the cascade coupling and recovery of oxygen release and expansion cold energy, characterized in that: It includes the venting tower pipeline side, turbine expander generator set, safety venting system, after-treatment and exhaust gas emission system, and instrumentation and control interlocking system.

2. The oxygen release and expansion cold energy cascade coupling recovery device according to claim 1, characterized in that: The venting tower pipeline includes an oxygen venting tower, an oxygen venting pipe, a first inlet shut-off valve, an inlet filter, a vortex flow meter, a temperature and pressure measuring unit, and a pre-buffered pressure stabilizing tank. The oxygen venting pipe is connected to the outlet side of the oxygen venting tower. The first inlet shut-off valve is installed on the oxygen venting pipe. The inlet filter is connected in series downstream of the first inlet shut-off valve. The filtration accuracy of the inlet filter is ≥5μm. A differential pressure transmitter is connected in series with the filter. The differential pressure transmitter issues an alarm when the differential pressure exceeds a set value to prompt cleaning or replacement of the filter element. The set value is 0.05MPa. The vortex flow meter is installed downstream of the inlet filter and is communicatively connected to a DCS system. The temperature and pressure measuring unit includes a first temperature transmitter and a first pressure transmitter, which are installed downstream of the vortex flow meter. The pre-buffered pressure stabilizing tank is installed downstream of the temperature and pressure measuring unit and has a volume ≥0.3m³.

3. The oxygen release and expansion cold energy cascade coupling recovery device according to claim 2, characterized in that: The turbine expander generator set includes an oxygen turbine expander and a generator. The oxygen turbine expander includes a primary turbine expander and a secondary turbine expander. The primary turbine expander is connected to a pre-buffered pressure stabilizing tank. An interstage heater is provided between the primary turbine expander and the secondary turbine expander. The generator is coaxially and directly connected to the primary turbine expander.

4. The oxygen release and expansion cold energy cascade coupling recovery device according to claim 3, characterized in that: The front buffer pressure stabilizing tank is equipped with a safety valve and a second inlet shut-off valve in sequence at its rear end, and a guide vane is provided at the rear end of the second inlet shut-off valve.

5. The oxygen release and expansion cold energy cascade coupling recovery device according to claim 3, characterized in that: The safety venting system includes a bypass pressure reducing line and an emergency venting line. The bypass pressure reducing line is connected in parallel with the oxygen turbine expander. A pneumatic regulating valve is installed on the bypass pressure reducing line and is communicatively connected to the DCS system. The emergency venting line is connected to the top of the oxygen venting tower. A pneumatic quick-opening valve is connected in series on the emergency venting line and is communicatively connected to the DCS system.

6. The oxygen release and expansion cold energy cascade coupling recovery device according to claim 5, characterized in that: The aftertreatment and exhaust gas emission system includes an outlet temperature regulating device, which includes a cold energy recovery heat exchanger. The cold energy recovery heat exchanger is connected to a second vent pipe and is connected to a bypass pressure reducing pipeline through the second vent pipe. A silencer and a flame arrester are sequentially installed on the second vent pipe. The cold energy recovery heat exchanger is connected to a circulating water tank, and a pressure regulating valve is installed on the outlet side of the cold energy recovery heat exchanger.

7. The oxygen release and expansion cold energy cascade coupling recovery device according to claim 6, characterized in that: The secondary turbine expander is connected to the cold energy recovery heat exchanger, and a second temperature transmitter and a second pressure transmitter are installed between the secondary turbine expander and the cold energy recovery heat exchanger.

8. The oxygen release and expansion cold energy cascade coupling recovery device according to claim 6, characterized in that: The generator is connected to a frequency converter, the back end of which is connected to a transformer. The back end of the transformer is connected to a grid connection point, which is connected to a 10kV power grid. The generator is also connected to an energy storage converter, the back end of which is connected to an energy storage battery pack.

9. The oxygen release and expansion cold energy cascade coupling recovery device according to claim 6, characterized in that: The instrumentation and control interlocking system is controlled by the DCS system to achieve process monitoring, power regulation and safety interlocking protection.

10. A recycling method applied to the apparatus of any one of claims 1-9, characterized in that, Includes the following steps: S1: Medium-pressure oxygen is drawn out from the oxygen vent pipe, passes through the first inlet shut-off valve, inlet filter, and vortex flow meter, and enters the pre-buffer pressure stabilizing tank for pressure stabilization. After pressure stabilization, the medium-pressure oxygen enters the turbine expander generator set to expand and do work. S2: During the expansion of medium-pressure oxygen, the oxygen pressure drops from 2.5MPa to 0.1-0.15MPa, and the temperature drops from 25℃ to -20℃-10℃; S3: The expander drives the generator to generate electricity. The electrical energy is rectified and inverted by the frequency converter and then fed into the internal power grid or stored in the energy storage unit. S4: After expansion, the low-pressure and low-temperature oxygen is heated to 5-15℃ by the cold energy recovery heat exchanger and then enters the silencer for noise reduction treatment. Finally, it is discharged into the atmosphere through the oxygen venting tower. S5: When the expander malfunctions or the throughput is insufficient, oxygen is discharged into the exhaust gas system after being depressurized by the pneumatic regulating valve through the bypass pressure reducing line. When the system experiences an emergency overpressure, the safety valve or pneumatic quick-opening valve in the emergency venting line is opened directly to release pressure.

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