An energy recovery optimization method for a large air separation steam-electric double-drive coaxial unit

Abstract

The present invention provides an energy recovery optimization method for a large-scale air separation steam-electric dual-drive coaxial unit. The method includes the following steps: Step 1, adopt a large-scale air separation steam-electric dual-drive unit with an independent lubricating oil and regulating oil system; Step 2, automatic start control of the regulating oil pump; Step 3, operation control of the large-scale air separation steam-electric dual-drive unit; Step 4, automatic stop control of the regulating oil pump; Step 5, interlock control of the regulating oil pump. The present invention is aimed at industries such as non-ferrous smelting, uses a steam turbine as a waste heat recovery system, jointly drives an air compressor with an electric motor, directly converts waste heat energy from heat energy into mechanical energy, has a high recovery efficiency, and does not affect the normal operation of the main process. At the same time, the unit also has a power generation function, can replace a waste heat power generation unit, the whole unit structure is more compact, more energy-efficient, and reduces the initial investment of users.

Description

Technical Field

[0001] The present invention belongs to the technical field of air separation, relates to air separation equipment, and particularly relates to an energy recovery optimization method for a large air separation steam-electric double-drive coaxial unit. Background Art

[0002] Air separation equipment is a basic industrial equipment, which is widely used in industrial fields such as metallurgy, petrochemical, and chemical industries. As the raw material gas compressor in the air separation process system, the air compressor is the core equipment of the air separation device, the equipment with the largest power and the highest energy consumption in the air separation system. Its efficiency and stability directly affect the reliability and economy of the entire air separation system, thus affecting the entire production line. In recent years, with the development and operation of domestic large air separation units for industrial use, such as air separation devices above 80,000 and 100,000 grades, the technical blockade of imported equipment against China has been broken.

[0003] In industries such as non-ferrous smelting, a large amount of waste heat steam is generated during the smelting process. In order to recover this part of waste heat, existing technical solutions all use separate waste heat steam turbines for power generation and grid connection; while the air compressors used in production use separate electric drives or steam drives.

[0004] Existing solutions require two sets of equipment, namely a separate generator set and an air compressor set, which occupy a large area and are scattered in layout. Moreover, the recovered waste heat needs to be first converted from mechanical energy into electrical energy and transmitted to the power grid; then the motor takes power from the power grid, and the electrical energy is converted back into mechanical energy to drive the air compressor. The recovered waste heat undergoes several conversions, resulting in large energy losses. Therefore, existing solutions have technical defects such as low energy recovery efficiency, high initial investment for users, and complex power generation and grid connection procedures. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an energy recovery optimization method for a large air separation steam-electric double-drive coaxial unit, so as to solve the technical problem that it is difficult for the existing energy recovery method to balance energy recovery efficiency and initial investment cost.

[0006] To solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0007] An energy recovery optimization method for a large air separation steam-electric double-drive coaxial unit, the method comprising the following steps:

[0008] Step 1, adopt a large air separation steam-electric double-drive unit with an independent lubricating oil and regulating oil system:

[0009] The large air separation steam-electric dual-drive unit with an independent lubricating oil and regulating oil system includes a main oil tank. A lubricating oil pump is connected to the main oil tank. The lubricating oil pump supplies the lubricating oil required for the operation of the large air separation steam-electric dual-drive unit through a lubricating oil pipeline, forming a lubricating oil circuit.

[0010] A regulating oil pump is connected to the main oil tank. The regulating oil pump supplies the regulating oil required for the operation of the regulating system through a regulating oil pipeline, forming a regulating oil circuit.

[0011] The lubricating oil pump and the regulating oil pump are respectively connected to the unit DCS system and independently controlled, so that the lubricating oil circuit and the regulating oil circuit are independent of each other.

[0012] The unit DCS system is connected to the steam inlet main pipe of the steam turbine, and collects the inlet pressure on the steam inlet main pipe of the steam turbine, which is used to control the automatic start and stop of the regulating oil pump.

[0013] Step two, automatic start control of the regulating oil pump:

[0014] Before the steam turbine runs, there is no steam in the steam main pipe of the steam turbine. When the waste heat system generates steam, it is sent to the steam turbine through the steam inlet main pipe of the steam turbine, and the pressure in the steam inlet main pipe of the steam turbine will gradually rise; when the pressure P of the steam inlet main pipe of the steam turbine > the set pressure P0, after a time delay, the unit DCS system judges that the steam turbine is to be started, and the unit DCS system automatically starts the regulating oil pump.

[0015] Step three, operation control of the large air separation steam-electric dual-drive unit.

[0016] Step four, automatic stop control of the regulating oil pump:

[0017] When the steam of the waste heat system is to be used for other process production, the steam volume in the steam main pipe of the steam turbine gradually decreases. When the pressure P of the steam inlet main pipe of the steam turbine ≤ the set pressure P0, after a time delay, the unit DCS system judges that the steam turbine is to be stopped, and the unit DCS system automatically stops the regulating oil pump.

[0018] Step five, interlock control of the regulating oil pump:

[0019] In order to prevent the regulating oil pump from closing when the steam turbine has a speed, an interlock condition is set in the unit DCS system: when the speed of the steam turbine ≠ 0, the regulating oil pump cannot be stopped.

[0020] The present invention also has the following technical features:

[0021] The specific process in step three is as follows:

[0022] Step 301, after the steam turbine starts, the steam drives the steam turbine to increase speed. After reaching the working speed, the clutch engages:

[0023] Step 302: After the unit DCS system receives the engagement signal of the clutch, it sends a signal to the speed control system of the steam turbine. The steam turbine switches to valve position control, and the steam valve position of the steam turbine is controlled through the speed control system to further increase. At this time, the power output by the steam turbine is continuously transmitted to the air compressor, and the air compressor is jointly driven by the steam turbine and the motor to operate.

[0024] Step 303: When the steam inlet valve is opened to about 80%, an operation is performed in the unit DCS system to switch the steam turbine to front pressure control, and the opening of the steam inlet valve of the steam turbine is adjusted according to the pressure fluctuation of the waste heat steam.

[0025] Step 304: The waste heat energy recovered by the steam turbine is directly transmitted to the air compressor through the variable speed clutch, realizing the operation of the air compressor driven by both the steam turbine and the motor, and achieving efficient recovery of waste heat energy. At the same time, when there is sufficient waste heat steam and the output power of the steam turbine is greater than the load of the compressor, the excess energy can be used for power generation by the motor.

[0026] Preferably, in step two, the delay is 1 minute.

[0027] Preferably, in step four, the delay is 5 minutes.

[0028] Preferably, in step one, there are two lubricating oil pumps, one in use and one in standby; there are two regulating oil pumps, one in use and one in standby.

[0029] Specifically, in step one, the large-scale air separation steam-electric dual-drive unit with an independent lubricating oil and regulating oil system further includes a large-scale air separation steam-electric dual-drive unit formed by a steam turbine, a variable speed clutch, an electric motor, a gearbox, and an air compressor connected in sequence on the same axis. The large-scale air separation steam-electric dual-drive unit also includes a speed control system, a waste heat system, and a unit DCS system. The speed control system is connected to the steam turbine, the waste heat system is connected to the steam turbine through the steam inlet main pipe of the steam turbine, and the unit DCS system is used to control the large-scale air separation steam-electric dual-drive unit.

[0030] Compared with the prior art, the present invention has the following technical effects:

[0031] (Ⅰ) The present invention is aimed at industries such as non-ferrous smelting. It uses a steam turbine as a waste heat recovery system and jointly drives the air compressor with an electric motor. The waste heat energy is directly converted from heat energy into mechanical energy, with high recovery efficiency. Moreover, it does not affect the normal operation of the main process. At the same time, the unit also has a power generation function, can replace the waste heat power generation unit, and the entire unit structure is more compact, more energy-efficient, and reduces the initial investment of users.

[0032] (II) For the large air compressor steam-electric dual-drive unit of the present invention, the lubricating oil pumps of the regulating oil system and the lubricating oil system are independently arranged to optimize the lubricating oil system and the regulating oil system of the unit; the start and stop of the regulating oil pump are controlled by the steam inlet pressure of the steam main pipe of the steam turbine. When the main pipe steam pressure P > P0, the regulating oil pump is automatically started; when P ≤ P0, the regulating oil pump is automatically stopped.

[0033] According to the adjustment of the production working conditions, when the steam turbine does not operate, the regulating oil pump is timely closed, which can achieve the purpose of energy saving and improve the automatic control degree of the unit at the same time.

[0034] (III) For the large air separation steam-electric dual-drive air compressor unit of the present invention, in view of the fluctuating steam pressure of the waste heat recovery system, the steam turbine adopts three different control strategies: speed control, valve position control, and front pressure control to ensure that the steam turbine operates in the high-efficiency area to the greatest extent and improve the recovery efficiency of waste heat energy.

[0035] (IV) For the large air compressor steam-electric dual-drive unit of the present invention, by optimizing the configuration and control scheme of the unit, while ensuring the safe and reliable operation of the unit, the recovery efficiency of waste heat energy is effectively improved. Description of the Drawings

[0036] Figure 1 is a schematic diagram of a large air separation steam-electric dual-drive unit with an integrated lubricating and regulating oil system in the prior art.

[0037] Figure 2 is a schematic diagram of a large air separation steam-electric dual-drive unit with an independent lubricating oil and regulating oil system in the present invention.

[0038] Figure 3 is a schematic diagram of the start logic of the regulating oil pump.

[0039] Figure 4 is a schematic diagram of the stop logic of the regulating oil pump.

[0040] The following further elaborates on the specific content of the present invention in conjunction with embodiments. Detailed Embodiments

[0041] It should be noted that all the equipment and systems in the present invention, unless otherwise specified, all adopt the equipment systems known in the prior art. For example, the speed control system, waste heat system, and unit DCS (distributed control) system all adopt the systems known in the prior art.

[0042] For large air separation units in the non-ferrous smelting industry, the waste heat recovery power generation system is combined with the air separation unit. The recovered waste heat is connected to the air compressor unit through a steam turbine, and a variable speed clutch is used to connect the steam turbine and the motor. When the steam volume of the steam turbine is sufficient, the variable speed clutch engages, and the steam turbine and the motor jointly drive the air compressor to operate; when the steam volume of the steam turbine is insufficient, the variable speed clutch disengages, and the air compressor is driven solely by the motor, without affecting the normal process operation.

[0043] Meanwhile, to ensure the safe and reliable operation of the entire unit, a lubricating oil system and a governing oil system must be set up. The lubricating oil system continuously supplies lubricating oil to the bearings of the equipment, and the governing oil system provides a power source for the steam turbine servomotor. In general steam turbine-driven units, the lubricating oil system and the governing oil system are both supplied with oil uniformly by a lubricating and governing oil station, and the same oil pump is used. After being reduced in pressure by two self-operated regulating valves, the oil pressure is reduced to the lubricating oil supply pressure and the governing oil supply pressure, respectively, to supply the lubricating oil system and the governing oil system.

[0044] In the prior art, as Figure 1 shown, during the operation of a steam-electric dual-drive unit, due to the instability of the steam in the waste heat system or the use of steam for other process production, the steam turbine may experience long-term shutdowns, and the air compressor is driven solely by the motor. At this time, the unit only requires lubricating oil and does not require governing oil, while the oil pump operates at full flow, and the governing oil part flows back to the oil tank again, resulting in energy waste.

[0045] In the present invention, as Figure 2 shown, the oil circuits of the lubricating oil system and the governing oil system in the lubricating oil station are separately arranged, and a lubricating oil pump and a governing oil pump are respectively set up to supply lubricating oil and governing oil to the unit; meanwhile, an automatic control strategy is adopted. When the steam turbine shuts down or needs to start, the automatic start and stop of the governing oil pump can be realized through the DCS system. This can not only reduce energy waste and achieve the purpose of energy conservation, but also improve the automation level of the unit.

[0046] The following gives specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solutions of this application fall within the protection scope of the present invention.

[0047] Embodiment:

[0048] This embodiment provides an energy recovery optimization method for a large air separation steam-electric dual-drive coaxial unit, and this method includes the following steps:

[0049] Step 1, adopt a large air separation steam-electric dual-drive unit with an independent lubricating oil and governing oil system:

[0050] A large air separation steam-electric dual-drive unit with an independent lubricating oil and governing oil system, asFigure 2 As shown, it includes a large air separation steam-electric dual-drive unit formed by a steam turbine, a variable-speed clutch, an electric motor, a gearbox, and an air compressor connected coaxially in sequence; the large air separation steam-electric dual-drive unit also includes a speed regulation system, a waste heat system, and a unit DCS system. The speed regulation system is connected to the steam turbine, the waste heat system is connected to the steam turbine through the steam inlet main pipe of the steam turbine, and the unit DCS system is used to control the large air separation steam-electric dual-drive unit.

[0051] It also includes a main oil tank, and a lubricating oil pump is connected to the main oil tank. The lubricating oil pump supplies the lubricating oil required for operation to the large air separation steam-electric dual-drive unit through a lubricating oil pipeline, forming a lubricating oil circuit.

[0052] A regulating oil pump is connected to the main oil tank. The regulating oil pump supplies the regulating oil required for operation to the regulating system through a regulating oil pipeline, forming a regulating oil circuit.

[0053] In this embodiment, there are two lubricating oil pumps, one in use and one in reserve; there are two regulating oil pumps, one in use and one in reserve.

[0054] The lubricating oil pump and the regulating oil pump are respectively connected to the unit DCS system and independently controlled, so that the lubricating oil circuit and the regulating oil circuit are independent of each other.

[0055] The unit DCS system is connected to the steam inlet main pipe of the steam turbine, collects the inlet pressure on the steam inlet main pipe of the steam turbine, and is used to control the automatic start and stop of the regulating oil pump.

[0056] Step two, automatic start control of the regulating oil pump:

[0057] As Figure 3 shown, before the steam turbine runs, there is no steam in the steam main pipe of the steam turbine. When the waste heat system generates steam, it is sent into the steam turbine through the steam inlet main pipe of the steam turbine, and the pressure in the steam inlet main pipe of the steam turbine will gradually rise; when the pressure P of the steam inlet main pipe of the steam turbine > the set pressure P0, after a delay of 1 minute, the unit DCS system determines to start the steam turbine, and the unit DCS system automatically starts the regulating oil pump.

[0058] In this embodiment, the set pressure P0 can be taken as half of the design pressure of the steam turbine, and the specific value can be appropriately adjusted according to the actual situation.

[0059] Step three, operation control of the large air separation steam-electric dual-drive unit:

[0060] Step 301, after the steam turbine starts, the steam drives the steam turbine to increase speed. After reaching the working speed, the clutch engages:

[0061] Step 302: After the unit DCS system receives the clutch engagement signal, it sends a signal to the speed control system of the steam turbine, and the steam turbine switches to valve position control. The steam valve position of the steam turbine is controlled through the speed control system and further increased. At this time, the power output by the steam turbine is continuously transmitted to the air compressor, and together with the motor, it drives the air compressor to operate, improving the energy recovery efficiency.

[0062] Step 303: When the inlet steam valve opens to about 80%, an operation is performed in the unit DCS system to switch the steam turbine to front pressure control. According to the pressure fluctuation of the waste heat steam, the opening of the inlet steam valve of the steam turbine is adjusted to ensure that the steam turbine always operates in the high-efficiency area and improve the recovery efficiency of the unit.

[0063] Step 304: The waste heat energy recovered by the steam turbine is directly transmitted to the air compressor through the variable speed clutch, realizing the operation of the air compressor driven by both the steam turbine and the motor, and achieving high-efficiency recovery of waste heat energy. At the same time, when there is sufficient waste heat steam and the output power of the steam turbine is greater than the load of the compressor, the excess energy can be used for power generation by the motor, realizing "reverse power supply".

[0064] At this time, the entire unit needs to operate normally, and the lubricating oil pump and the regulating oil pump work simultaneously. The lubricating oil pump supplies oil to the steam turbine, variable speed clutch, motor, gearbox, and air compressor through the lubricating oil circuit to ensure the normal operation of the unit. The regulating oil pump supplies oil to the speed control system of the steam turbine through the regulating oil circuit to ensure the speed regulation of the steam turbine and the operation of the oil actuator.

[0065] Step Four: Automatic stop control of the regulating oil pump:

[0066] As Figure 4 shown, when the steam in the waste heat system is to be used for other process production, the steam volume in the steam main pipe of the steam turbine gradually decreases. When the pressure P of the inlet steam main pipe of the steam turbine ≤ the set pressure P0, after a delay of 5 minutes, the unit DCS system determines to stop the steam turbine, and the unit DCS system automatically stops the regulating oil pump.

[0067] In this embodiment, the set pressure P0 can be taken as half of the design pressure of the steam turbine, and the specific value can be appropriately adjusted according to the actual situation.

[0068] Step Five: Interlock control of the regulating oil pump:

[0069] To prevent the regulating oil pump from closing when the steam turbine has a speed, an interlock condition is set in the unit DCS system: when the speed of the steam turbine ≠ 0, the regulating oil pump cannot be stopped.

[0070] Through the above control method of this embodiment, the following objectives are achieved:

[0071] First, the lubricating oil system and the governing oil system operate independently to ensure the safe and reliable operation of the unit, as well as the operation of the speed governing system of the steam turbine and the oil servomotor. When the steam turbine is not operating, the governing oil pump is stopped to achieve the purpose of energy conservation.

[0072] Second, the steam turbine header pressure is interlocked with the governing oil pump to realize the automatic start and stop control of the governing oil pump, improving the automation level of the unit.

[0073] Third, it can enable the steam turbine to be in the high-efficiency zone for a long time, and the energy recovery efficiency of the entire unit is also improved.

[0074] Application example:

[0075] This application example presents an energy recovery optimization method for a large-scale air separation steam-electric dual-drive coaxial unit based on the above embodiments, which is specifically as follows.

[0076] Taking a domestic 80,000 air separation project's steam-electric dual-drive air compressor unit as an example, due to subsequent process adjustments, the steam turbine is used for 36 hours per month. The economic benefits generated by the present invention can be calculated in two parts:

[0077] The first part, the economic benefits generated by using the steam-electric dual-drive unit: The power of the steam turbine is about 30,000 kW. By using the steam-electric dual-drive unit, the recovered energy is directly used to drive the air compressor, and the energy recovery efficiency is about 4% higher than that of the steam turbine generating electricity and then the motor driving the air compressor. The annual operating time of the steam-electric dual-drive is about 432 hours. Therefore, 518,400 kW·h of electricity can be saved per year; calculated at 0.5 yuan per kilowatt-hour, 259,200 yuan can be generated annually; calculated based on the 20-year design life of the unit, 5.184 million yuan of economic benefits can be generated;

[0078] The second part, the economic benefits generated by separately setting the lubricating oil pump and the governing oil pump: The lubricating oil volume of the unit is about 2,700 L / min, and the governing oil volume of the steam turbine is about 400 L / min. Selecting the oil pump according to this scheme, the oil pump motor required for the lubricating oil system is 110 kW, and the oil pump motor required for the governing oil system is 22 kW; calculated based on the unit operating continuously for 8,000 hours per year, the steam turbine is in a shutdown state for 7,568 hours per year. Correspondingly, the governing oil pump can be shut down and operated, saving about 166,496 kW·h of electricity per year. Calculated at 0.5 yuan per kilowatt-hour, 83,250 yuan can be saved; calculated based on the 20-year design life of the unit, a total of 1.665 million yuan can be saved.

[0079] In summary, the present invention can generate direct economic benefits of about 6.85 million yuan per month, which is a very substantial amount. The longer the steam turbine operates, the more economic benefits are generated. In addition, the present invention also improves the automation level of the unit, realizes the automatic start and stop control of the regulating oil pump, reduces the losses caused by human misoperation, and has indirect economic benefits.

Claims

1. An energy recovery optimization method for a large-scale air separation steam-electric dual-drive coaxial unit, the method comprises the following steps: Step 1, adopt a large-scale air separation steam-electric dual-drive unit with an independent lubricating oil and regulating oil system: The large-scale air separation steam-electric dual-drive unit with an independent lubricating oil and regulating oil system includes a main oil tank, a lubricating oil pump is connected to the main oil tank, and the lubricating oil pump supplies the lubricating oil required for operation to the large-scale air separation steam-electric dual-drive unit through a lubricating oil pipeline, forming a lubricating oil circuit; It is characterized in that: A regulating oil pump is connected to the main oil tank, and the regulating oil pump supplies the regulating oil required for operation to the regulating system through a regulating oil pipeline, forming a regulating oil circuit; The lubricating oil pump and the regulating oil pump are respectively connected to the unit DCS system and independently controlled, so that the lubricating oil circuit and the regulating oil circuit are independent of each other; The unit DCS system is connected to the steam inlet main pipe of the steam turbine, and collects the inlet pressure on the steam inlet main pipe of the steam turbine, which is used to control the automatic start and stop of the regulating oil pump; Step 2, automatic start control of the regulating oil pump: Before the steam turbine runs, there is no steam in the steam main pipe of the steam turbine. After the waste heat system generates steam, it is sent into the steam turbine through the steam inlet main pipe of the steam turbine, and the pressure in the steam inlet main pipe of the steam turbine will gradually rise; when the pressure P of the steam inlet main pipe of the steam turbine > the set pressure P0, after a time delay, the unit DCS system judges that the steam turbine needs to be started, and the unit DCS system automatically starts the regulating oil pump; Step 3, operation control of the large-scale air separation steam-electric dual-drive unit; Step 4, automatic stop control of the regulating oil pump: When the steam of the waste heat system is to be used for other process production, the steam volume in the steam main pipe of the steam turbine gradually decreases. When the pressure P of the steam inlet main pipe of the steam turbine ≤ the set pressure P0, after a time delay, the unit DCS system judges that the steam turbine needs to be stopped, and the unit DCS system automatically stops the regulating oil pump; Step 5, interlock control of the regulating oil pump: In order to prevent the regulating oil pump from closing when the steam turbine has a speed, an interlock condition is set in the unit DCS system: when the speed of the steam turbine ≠ 0, the regulating oil pump cannot be stopped.

2. The energy recovery optimization method for a large-scale air separation steam-electric dual-drive coaxial unit according to claim 1, it is characterized in that, The specific process in step 3 is: Step 301, after the steam turbine starts, the steam drives the steam turbine to increase speed. After reaching the working speed, the clutch engages: Step 302, when the unit DCS system receives the engagement signal of the clutch, it sends a signal to the speed regulating system of the steam turbine, and the steam turbine changes to valve position control. The steam valve position of the steam turbine is controlled through the speed regulating system and further increased. At this time, the power output by the steam turbine is continuously transmitted to the air compressor, and the air compressor is driven to operate together with the motor; Step 303, when the inlet steam valve is opened to about 80%, an operation is performed in the unit DCS system to switch the steam turbine to front pressure control, and the opening of the steam inlet valve of the steam turbine is adjusted according to the pressure fluctuation of the waste heat steam. Step 304: The waste heat energy recovered by the steam turbine is directly transmitted to the air compressor through the variable speed clutch, enabling the steam turbine and the motor to drive the air compressor simultaneously and achieving efficient recovery of waste heat energy. Meanwhile, when there is sufficient waste heat steam and the output power of the steam turbine is greater than the load of the compressor, the excess energy can be used for power generation by the motor.

3. The energy recovery optimization method of the large air separation steam-electric dual-drive coaxial unit according to claim 1, characterized in that, in step two, the delay is 1 minute.

4. The energy recovery optimization method of the large air separation steam-electric dual-drive coaxial unit according to claim 1, characterized in that, in step four, the delay is 5 minutes.

5. The energy recovery optimization method of the large air separation steam-electric dual-drive coaxial unit according to claim 1, characterized in that, in step one, there are two lubricating oil pumps, one in use and one in reserve; and there are two regulating oil pumps, one in use and one in reserve.

6. The energy recovery optimization method of the large air separation steam-electric dual-drive coaxial unit according to claim 1, characterized in that, in step one, the large air separation steam-electric dual-drive unit with an independent lubricating oil and regulating oil system further includes a large air separation steam-electric dual-drive unit formed by a steam turbine, a variable speed clutch, a motor, a gearbox, and an air compressor connected in sequence coaxially; the large air separation steam-electric dual-drive unit also includes a speed regulation system, a waste heat system, and a unit DCS system. The speed regulation system is connected to the steam turbine, the waste heat system is connected to the steam turbine through the steam turbine inlet header pipe, and the unit DCS system is used to control the large air separation steam-electric dual-drive unit.

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