Saturated steam dry gas sealing device and system of screw machine

Abstract

The invention discloses a saturated steam dry gas sealing device and system of a screw machine. The saturated steam dry gas sealing device of the screw machine comprises a front seal, a dry gas seal, an isolation seal and a heat insulation sleeve. The heat insulation sleeve is located between the isolation seal and a bearing cavity of the screw machine, the rotor shaft is sleeved with the heat insulation sleeve, and a sealing structure is arranged between the heat insulation sleeve and the peripheral face of the rotor shaft. A balance opening is formed in the position, corresponding to the front seal, of a shell of the screw machine, an overheated steam inlet is formed in the gap position between the front seal and the dry gas seal, an exhaust port is formed in the position corresponding to the dry gas seal, and a hot nitrogen inlet is formed in the position corresponding to the isolation seal. And an emptying opening is formed in a position corresponding to the heat insulation sleeve. The sealing body is safe and stable in operation, good in sealing effect and long in service life.

Description

Technical Field

[0001] This invention relates to the field of process equipment sealing technology, and more particularly to the sealing technology of screw compressors. Background Technology

[0002] Under the dual-carbon framework of "3060," industrial energy conservation has become a key area for carbon reduction. The recovery and utilization of low-grade waste heat is one of the important measures for industrial energy conservation, involving the recovery and utilization of low-grade steam waste heat. Since low-temperature waste heat is usually difficult to utilize due to its low temperature and pressure, it can be pressurized and heated using compressors to achieve reuse. Among the aforementioned energy-saving technologies, steam compressors are the core equipment. In recent years, China has successively developed steam compressors suitable for various operating conditions, among which shaft seal performance is crucial to the safe and stable operation of the equipment. Due to the high heat exchange efficiency of saturated steam, most compressor outlet gas is in a saturated state (a state of gas-liquid coexistence), which brings certain difficulties to the selection of seals. Common shaft seals for compressors include carbon ring seals (or labyrinth seals), mechanical seals, and dry gas seals. When the exhaust gas of a screw compressor is saturated gas (e.g., saturated water vapor), mechanical seals and inert gas dry gas seals are insufficient to prevent external impurities such as lubricating oil from entering the system. The combination of carbon ring seals and a condensate extraction system can prevent external impurities from entering the system, but it suffers from problems such as large saturated gas leakage, high power consumption for extraction, and high condensate consumption. Furthermore, the carbon rings experience accelerated wear during prolonged operation, making it highly susceptible to saturated gas entering the lubrication system, causing poor bearing lubrication and media leakage. Conventional dry gas seals are non-contact seals with good sealing performance and long service life, but when low-temperature saturated gas passes through the sealing surface, it causes severe wear and failure of the sealing surface; currently, there is no effective solution available on the market. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a saturated steam dry gas sealing device and system for screw compressors, which has a safe and stable operation, good sealing effect, long service life, and will not cause pollution to the working medium in the working chamber of the screw compressor.

[0004] According to a first aspect of the present invention, a saturated steam dry gas sealing device for a screw compressor is provided, comprising a pre-seal, a dry gas seal, and an isolation seal; the pre-seal, dry gas seal, and isolation seal are respectively installed in a cavity between the rotor shaft and the housing of the screw compressor, the dry gas seal being located between the pre-seal and the isolation seal, and the pre-seal being close to the working chamber of the screw compressor; characterized in that the saturated steam dry gas sealing device further comprises a heat insulation sleeve, the heat insulation sleeve being installed in the cavity between the rotor shaft and the housing of the screw compressor, and located between the isolation seal and the bearing cavity of the screw compressor, the heat insulation sleeve being sleeved outside the rotor shaft, and the heat insulation sleeve being positioned between the outer circumferential surface of the rotor shaft and the heat insulation sleeve. The compressor housing is equipped with a sealing structure; a balance port is provided at the position corresponding to the pre-seal, an overheated steam inlet is provided at the position corresponding to the gap between the pre-seal and the dry gas seal, an exhaust port is provided at the position corresponding to the dry gas seal, a hot nitrogen inlet is provided at the position corresponding to the isolation seal, and a vent is provided at the position corresponding to the heat insulation sleeve; the side wall of the pre-seal has a balance gas outlet communicating with the balance port, the side wall of the dry gas seal has a sealing gas outlet communicating with the exhaust port, the side wall of the isolation seal has an isolation sealing gas inlet communicating with the hot nitrogen inlet, and the side wall of the heat insulation sleeve has a vent outlet communicating with the vent.

[0005] According to a second aspect of the present invention, a saturated steam dry gas sealing system for a screw compressor is provided. The screw compressor includes a plurality of rotors, and the aforementioned saturated steam dry gas sealing device is mounted on the rotor shafts on both sides of each rotor. The saturated steam dry gas sealing system includes a balance pipeline, a steam inlet pipeline, an exhaust pipeline, a nitrogen pipeline, a vent pipeline, a first pressure tapping pipeline, a second pressure tapping pipeline, and a differential pressure transmitter. The number of balance pipelines is the same as the number of rotors, and both ends of each balance pipeline are connected to the balance ports of the corresponding saturated steam dry gas sealing devices on both sides of the rotor. The inlet end of the steam inlet pipeline is connected to the vent on the high-pressure side of the screw compressor, and the outlet end of the steam inlet pipeline is connected to the superheated steam inlet of each saturated steam dry gas sealing device. A steam heater, a differential pressure regulating valve, a steam temperature transmitter, and a steam pressure transmitter are provided on the steam inlet pipeline. The exhaust pipeline is connected to the exhaust port of each saturated steam dry gas sealing device. The outlet end of the nitrogen pipeline is connected to the hot nitrogen inlet of each saturated steam dry gas sealing device. A nitrogen heater, a nitrogen temperature transmitter, and a differential pressure transmitter are provided on the nitrogen pipeline. A nitrogen pressure transmitter; the vent line is connected to the vent ports of each saturated steam dry gas sealing device; the first end of the first pressure tapping line is connected to the section of the superheated steam inlet line downstream of the differential pressure regulating valve, and the second end of the first pressure tapping line is connected to the first end of the differential pressure transmitter; the first end of the second pressure tapping line is connected to the balancing line, and the second end of the second pressure tapping line is connected to the second end of the differential pressure transmitter; the controller is used to receive the temperature measurement results from the steam temperature transmitter and the nitrogen temperature transmitter, and the steam pressure transmitter and the nitrogen pressure transmitter. The pressure measurement results of the transmitter, the differential pressure measurement results of the differential pressure transmitter, and the valve status feedback from the differential pressure regulating valve are used to control the heating power of the steam heater and the nitrogen heater, so that the superheated steam output from the outlet of the steam inlet pipeline has a superheat of more than 20°C, and the temperature of the nitrogen output from the outlet of the nitrogen pipeline is more than 20°C higher than the saturation temperature of the vented steam at the venting pressure. The opening of the differential pressure regulating valve is controlled according to the differential pressure measurement results, so that the pressure difference between the first and second ends of the differential pressure transmitter is greater than 0.

[0006] By adopting the above technical solution, the present invention has at least the following advantages: 1. The saturated steam dry gas sealing device of the present invention reduces leakage by using the throttling effect of the pre-sealed gas near the medium side (working chamber side). It uses superheated steam injected into the superheated steam inlet as the first sealing gas for the dry gas seal and hot nitrogen injected into the hot nitrogen inlet as the second sealing gas for the dry gas seal. This can block the leakage of working medium gas. At the same time, the sealing gas and the leakage of working medium gas are discharged by the exhaust port set at the position corresponding to the dry gas seal, preventing the sealing gas from mixing with the working medium and entering the working chamber of the screw compressor. The vent port set at the position corresponding to the heat insulation sleeve can vent hot nitrogen gas and oil gas from the bearing side. The isolation seal and the heat insulation sleeve can prevent lubricating oil from contaminating the end face of the dry gas seal. 2. The dry gas sealing system of this embodiment of the invention uses an external heat source such as a heater to increase the temperature of the saturated gas and make it overheat, preventing it from condensing on the sealing surface on the medium side. Hot nitrogen is used to continuously heat the sealing device to ensure that the sealing surface on the leakage side (i.e., the bearing side) is maintained at a high temperature, preventing the condensation of the leaked trace amount of medium gas. A heat insulation sleeve with a sealing structure (such as comb teeth or carbon rings) is used to reduce the leakage and heating effect of hot nitrogen on the bearing side, avoiding the bearing from failing due to excessively high temperature. The above measures extend the service life of the sealing device and the bearing. Attached Figure Description

[0007] Figure 1 A cross-sectional schematic diagram of an embodiment of a saturated steam dry gas sealing device for a screw compressor according to the present invention is shown.

[0008] Figure 2 A schematic diagram of an embodiment of a saturated vapor dry gas sealing system for a screw compressor according to the present invention is shown. Detailed Implementation

[0009] The invention will now be further described with reference to the accompanying drawings.

[0010] Please refer to Figure 1 According to an embodiment of the present invention, a saturated steam dry gas sealing device 100 for a screw compressor includes a pre-seal 11, a dry gas seal 12, an isolation seal 13, a heat insulation sleeve 14, and a pressure cap assembly 15.

[0011] The pre-seal 11, dry gas seal 12, and isolation seal 13 are respectively installed in the cavity between the rotor shaft 21 and the housing 22 of the screw compressor 200. The dry gas seal 12 is located between the pre-seal 11 and the isolation seal 13, and the pre-seal 11 is close to the working cavity of the screw compressor 200. The heat insulation sleeve 14 and the gland assembly 15 are respectively installed in the cavity between the rotor shaft 21 and the housing 22 of the screw compressor 200. The heat insulation sleeve 14 is located between the isolation seal 13 and the gland assembly 15, and the gland assembly 15 is close to the bearing cavity of the screw compressor 200. The heat insulation sleeve 14 is sleeved on the outside of the rotor shaft 21, and a sealing structure is provided between the heat insulation sleeve 14 and the outer peripheral surface of the rotor shaft 21. This sealing structure includes, but is not limited to, a comb-tooth sealing structure (the inner peripheral surface of the heat insulation sleeve 14 is provided with comb teeth) or a carbon ring sealing structure.

[0012] In this embodiment, the rotor shaft 21 includes a rotor shaft body 21a and a bushing 21b. The bushing 21b is fitted over the rotor shaft body 21a and is connected to the moving ring 12a of the dry gas seal 12. The bushing 21b is integrated with the dry gas seal 12 and the isolation seal 13.

[0013] The gland assembly 15 is sleeved on the rotor shaft 21 of the screw compressor 200 and connected to the housing 22 of the screw compressor 200. The gland assembly 15 abuts against the heat insulation sleeve 14 and the bushing 21b respectively to restrict the axial movement of the bushing 21b and the heat insulation sleeve 14 towards the bearing cavity of the screw compressor 200. In this embodiment, the gland assembly 15 includes a gland body 15a and a nut 15b. The gland body 15a is connected to the housing 22 and abuts against the heat insulation sleeve 14. The nut 15b is screwed to the rotor shaft body 21a and abuts against the bushing 21b. The nut 15b extends into the axial through hole of the gland body 15a.

[0014] The casing 22 of the screw compressor 200 has a balance port A at the position corresponding to the front seal 11, an overheated steam inlet B at the gap between the front seal 11 and the dry gas seal 12, an exhaust port C at the position corresponding to the dry gas seal 12, a hot nitrogen inlet D at the position corresponding to the isolation seal 13, and a vent port E at the position corresponding to the heat insulation sleeve 14.

[0015] The sidewall of the front seal 11 is provided with a balance gas outlet communicating with the balance port A, so as to connect the gap between the inner wall of the front seal 11 and the outer peripheral wall of the rotor shaft 21 with the balance port A. In this embodiment, the balance gas outlet includes a first annular groove 111 and a plurality of first through holes 112. The first annular groove 111 is opened on the outer side of the front seal 11 and extends along the circumference of the front seal. The plurality of first through holes 112 are distributed at intervals along the circumferential direction of the front seal 11. One end of each first through hole 112 opens into the bottom surface of the first annular groove 111, and the other end of each first through hole 112 penetrates the inner wall of the front seal 11.

[0016] The sidewall of the dry gas seal 12 is provided with a sealing gas outlet communicating with the exhaust port C, so as to connect the gap between the moving ring 12a and the stationary ring 12b of the dry gas seal 12 with the exhaust port C. In this embodiment, the sealing gas outlet includes a second annular groove 121 and a plurality of second through holes 122. The second annular groove is formed on the outer side of the dry gas seal 12 and extends along the circumference of the dry gas seal. The plurality of second through holes 122 are distributed at intervals along the circumferential direction of the dry gas seal 12. One end of each second through hole 122 opens into the bottom surface of the second annular groove 121, and the other end of each second through hole 122 communicates with the interior of the dry gas seal 12 (communicating the gap between the moving ring 12a and the stationary ring 12b).

[0017] The sidewall of the isolation seal 13 is provided with an isolation seal gas inlet communicating with the hot nitrogen inlet D, so as to connect the gap between the inner wall of the isolation seal and the outer peripheral wall of the rotor shaft 21 with the hot nitrogen inlet D. In this embodiment, the isolation seal gas inlet includes a third annular groove 131 and a plurality of third through holes 132. The third annular groove 131 is formed on the outer surface of the isolation seal 13 and extends along the circumference of the isolation seal. The plurality of third through holes 131 are spaced apart along the circumferential direction of the isolation seal 13. One end of each third through hole 132 opens into the bottom surface of the third annular groove 131, and the other end of each third through hole 132 penetrates the inner wall of the isolation seal 13.

[0018] The side wall of the heat insulation sleeve 14 is provided with a vent outlet communicating with the vent port E, so as to connect the gap between the inner wall of the heat insulation sleeve and the outer peripheral wall of the rotor shaft 21 with the vent port E. In this embodiment, the vent outlet includes a fourth annular groove 141 and a plurality of fourth through holes 142. The fourth annular groove 141 is opened on the outer side of the heat insulation sleeve 14 and extends along the circumference of the heat insulation sleeve. The plurality of fourth through holes 142 are spaced apart along the circumferential direction of the heat insulation sleeve 14. One end of each fourth through hole 142 opens into the bottom surface of the fourth annular groove 141, and the other end of each fourth through hole 142 penetrates the inner wall of the heat insulation sleeve 14.

[0019] In this embodiment, the pre-seal 11 uses a comb-tooth seal or a carbon ring seal. The isolation seal 13 uses a comb-tooth seal, a carbon ring seal, or a dry gas seal. Depending on actual needs, the dry gas seal 12 can be a single-end dry gas seal, a double-end dry gas seal, or a series dry gas seal. The heat insulation sleeve 14 is used to isolate the high-temperature working chamber from the bearing chamber, thereby preventing the lubricating oil from emulsifying at high temperatures. The gland assembly 15 is used to fix the dynamic and static structures of the sealing device and also serves as an oil baffle ring. The static ring components of the dry gas seal 12 can be fixed to the dry gas seal housing with screws, and the dynamic ring components can be fixed to the bushing 21b with threads or screws. The bushing 21b is fixedly connected to the rotor shaft body 21a.

[0020] Preferably, the saturated vapor dry gas sealing device in this embodiment has a modular structure, which makes it easier to install.

[0021] The screw compressor in this embodiment of the invention can be a screw compressor or a screw expander. Optionally, the screw compressor is a twin-screw compressor, and the screw expander is a twin-screw expander.

[0022] Taking the operation of a screw compressor as an example: The leaking working medium gas from the working chamber, after being throttled by the pre-seal 11, has its pressure reduced from the high-pressure outlet pressure to the outlet pressure. The superheated steam injected from the superheated steam inlet B acts as a barrier against the leaking gas. Most of the injected superheated steam flows out from the balance port A and subsequently enters the inlet balance chamber of the screw compressor, thus re-entering the inlet. The remaining trace amount flows into the exhaust port C through the gap between the moving ring 12a and the stationary ring 12b of the dry gas seal 12. A portion of the hot nitrogen injected from the hot nitrogen inlet D, carrying a small amount of leaking working medium gas and superheated steam, is discharged from the exhaust port C, while the other portion is discharged through the vent port E. The heat insulation sleeve 14 has a hollow structure, which can provide heat insulation, effectively isolating the high-temperature shaft seal area from the low-temperature bearing area. The gland assembly 15 serves to fix the seal and also acts as an oil baffle to prevent lubricating oil from splashing and contaminating the seal. A small amount of oil and gas generated during bearing lubrication can be released through the gland assembly 15 and the heat insulation sleeve 14, and then released through the vent port E.

[0023] Figure 2 A schematic diagram of an embodiment of a saturated steam dry gas sealing system for a screw compressor according to the present invention is shown. The screw compressor 200 of the saturated steam dry gas sealing system according to an embodiment of the present invention includes a plurality of rotors, and the aforementioned saturated steam dry gas sealing device 100 is mounted on the rotor shafts on both sides of each rotor.

[0024] exist Figure 2 In the example, the screw compressor 200 is a twin-screw compressor, and the aforementioned saturated steam dry gas sealing device 100 is installed on both sides (i.e., the high-pressure side and the low-pressure side) of the female rotor and the male rotor of the twin-screw compressor.

[0025] The saturated vapor dry gas sealing system of this invention includes a balance pipeline 31, a vapor inlet pipeline 32, an exhaust pipeline 33, a nitrogen pipeline 34, a venting pipeline 35, a first pressure tapping pipeline 361, a second pressure tapping pipeline 362, and a differential pressure transmitter 37.

[0026] The number of balancing pipes 31 is the same as the number of rotors in the screw compressor. Both ends of each balancing pipe 31 are connected to the balancing port A of the saturated steam dry gas sealing device 100 on both sides of the corresponding rotor. Each balancing pipe 31 is equipped with a balancing regulating valve 311 and a balancing pressure gauge 312.

[0027] exist Figure 2In the embodiment shown, there are two balancing pipes 31. One balancing pipe is connected at both ends to the balancing port A of the saturated steam dry gas sealing device 100 at the inlet end (i.e., the air intake side of the female rotor) and the outlet end (i.e., the exhaust side of the female rotor), respectively. The other balancing pipe is connected at both ends to the balancing port A of the saturated steam dry gas sealing device 100 at the inlet end (i.e., the air intake side of the male rotor) and the outlet end (i.e., the exhaust side of the male rotor), respectively.

[0028] The inlet end of the steam inlet pipe 32 is connected to the vent on the high-pressure side of the screw compressor, and the outlet end of the steam inlet pipe 32 is connected to the superheated steam inlet B of each saturated steam dry gas sealing device 100. The steam inlet pipe is equipped with a steam filter 321, a steam heater 322, a differential pressure regulating valve 323, a steam temperature transmitter 324, a steam pressure transmitter 325, and a steam inlet assembly 326.

[0029] Steam filter 321 filters impurities from the saturated gas from the screw compressor, with a filtration accuracy of 1-2 μm, preventing damage to the dry gas seal end face. Steam heater 322 is an electric heater used to heat the saturated gas from the screw compressor to a certain degree of superheat. Steam pressure transmitter 325 is installed after differential pressure regulating valve 323 to monitor injection pressure. Steam temperature transmitter 324 is installed after steam heater 322 to monitor injection temperature. Steam inlet assembly 326 is installed after steam temperature transmitter 324 and steam pressure transmitter 325 to monitor steam inlet status. Flow monitoring instruments, valves, or combinations thereof can be installed according to process requirements. The superheated steam output from the outlet of steam inlet pipeline 32 serves as the pre-gas for the saturated steam dry gas seal device 100.

[0030] exist Figure 2 In the illustrated embodiment, the vent on the high-pressure side of the screw compressor is the exhaust port of the twin-screw compressor. The start-up nitrogen line 38 is connected to the inlet of the superheated steam inlet line 32 and is only used for operation when there is no steam during startup.

[0031] The exhaust pipe 33 is connected to the exhaust port C of each saturated steam dry gas sealing device. The exhaust pipe 33 is used to discharge trace amounts of steam and nitrogen mixture leaking from the dry gas seal. Since the exhaust contains process steam, it can be determined whether the exhaust pipe 33 is connected to the flare or for high-level venting based on the type of steam. In this embodiment, the working medium is water vapor, so high-level venting can be performed directly.

[0032] The outlet end of the nitrogen pipeline 34 is connected to the hot nitrogen inlet D of each saturated steam dry gas sealing device. The nitrogen pipeline is equipped with a nitrogen filter 341, a nitrogen heater 342, a nitrogen temperature transmitter 343, a nitrogen pressure transmitter 344, and a nitrogen inlet assembly 345.

[0033] Nitrogen filter 341 is used for filtering nitrogen, with a filtration accuracy selectable to 10µm. Nitrogen heater 342 is an electric heater used for heating nitrogen, thereby preventing the condensation of leaked overheated vapor. Nitrogen temperature transmitter 343 is installed after nitrogen heater 342, and nitrogen pressure transmitter 344 is installed after nitrogen filter 341, used to monitor nitrogen injection temperature and pressure. Nitrogen inlet assembly 345 is installed after nitrogen temperature transmitter 343 and nitrogen pressure transmitter 344, used to control and monitor nitrogen injection flow rate and status, and can be equipped with flow monitoring instruments, orifice plates, regulating needle valves, or combinations thereof according to process requirements. The hot nitrogen output from nitrogen pipeline 34 is used as the isolation gas for the saturated steam dry gas sealing device. In this embodiment, room temperature isolation nitrogen is heated by the exhaust gas from the twin-screw compressor or the saturated gas from the balance pipeline 31 before being injected into the inlet of nitrogen pipeline 34.

[0034] Vent line 35 is connected to the vent port E of each saturated steam dry gas sealing device and is used to discharge hot nitrogen gas leaking from the isolation seal. Since the vent gas component is mainly nitrogen gas, vent line 35 is a high-level vent.

[0035] The first end of the first pressure tapping line 361 is connected to the section of the steam inlet line 32 downstream of the differential pressure regulating valve 323, and the second end of the first pressure tapping line 361 is connected to the first end of the differential pressure transmitter 325; the first end of the second pressure tapping line 362 is connected to the balancing line 31, and the second end of the second pressure tapping line 362 is connected to the second end of the differential pressure transmitter 325. The differential pressure transmitter 325 is used to monitor the difference between the superheated steam injection pressure and the pressure of the saturated steam dry gas sealing device of the screw compressor.

[0036] Preferably, check valves are installed at the inlets of the steam inlet line 32 and the nitrogen line 34 to prevent steam from backflowing into the nitrogen pipeline network in extreme cases. The steam inlet line 32 and the nitrogen line 34 are insulated to enhance pipeline protection.

[0037] The controller receives temperature measurement results from steam temperature transmitter 324 and nitrogen temperature transmitter 343, pressure measurement results from steam pressure transmitter 325 and nitrogen pressure transmitter 344, differential pressure measurement results from differential pressure transmitter 37, and valve status feedback from differential pressure regulating valve 323. It controls the heating power of steam heater 322 and nitrogen heater 342 so that the superheated steam output from the outlet of steam inlet pipe 32 has a superheat of more than 20°C, and the temperature of nitrogen output from the outlet of nitrogen pipe 34 is more than 20°C higher than the saturation temperature of the vented steam at the venting pressure of exhaust port C. Based on the differential pressure measurement results, it controls the opening of differential pressure regulating valve 323 so that the pressure difference between the first and second ends of differential pressure transmitter 37 is greater than 0.

[0038] Optionally, the controller is used to control the opening of the differential pressure regulating valve 323 based on the differential pressure measurement result, so that the pressure difference between the first and second ends of the differential pressure transmitter 37 is maintained at a set value of 0.2 MPa. The controller may include, but is not limited to, a PLC controller.

[0039] When the saturated steam dry gas sealing system of this embodiment of the invention is working, superheated steam is injected into the saturated steam dry gas sealing device 100. A portion leaks into the twin-screw compressor, while the remaining superheated steam leaks out through the gap between the moving ring 12a and the stationary ring 12b of the dry gas seal 12, resulting in a small amount of steam being discharged from the exhaust port C. After hot nitrogen is injected into the sealing device, a portion is discharged from the exhaust port C, and the remaining portion of hot nitrogen is discharged from the vent port E. The outlet gas and nitrogen of the twin-screw compressor are heated by the matching system of the sealing device, and the outlet gas reaches a superheat of more than 20°C, so that the temperature of the nitrogen output from the nitrogen pipeline outlet is more than 20°C higher than the saturation temperature of the vented steam at the exhaust port C under the venting pressure. The injection pressure of the superheated steam is controlled to be 0.2 MPa higher than the outlet pressure of the balance port A, and the hot nitrogen pressure is controlled to be 50 kPa. The exhaust port C can be used to vent to the flare system or directly to a high level, depending on the type of medium, while the vent port E is used for direct high-level venting.

[0040] Two factors significantly impact the stable operation of a saturated steam dry gas sealing system: the superheat of the superheated steam and the temperature of the hot nitrogen, and the pressure difference between the superheated steam and the equilibrium port. This embodiment of the invention controls the heating power of the heater to consistently maintain a superheat of at least 20°C in the superheated steam. For example, assuming the saturation temperature of the steam output from the steam inlet pipe outlet is 100°C, the heating power of the steam heater must ensure that the temperature of the superheated steam output from the steam inlet pipe outlet is greater than or equal to 120°C. This embodiment of the invention also controls the heating power of the nitrogen heater to heat the nitrogen to a temperature at least 20°C higher than the saturation temperature of the vented steam at the exhaust port C under the exhaust pressure. For example, assuming the saturation temperature of the vented steam at the exhaust port C is 100°C under the exhaust pressure, the nitrogen temperature must be heated to greater than or equal to 120°C. Considering that the compressor outlet pressure fluctuates due to back pressure during operation, differential pressure control is a safer and more stable method. By setting a differential pressure control valve between the superheated steam and the balance port, the pressure of the superheated steam is always higher than the pressure at the balance port, thus maintaining the differential pressure value of the differential pressure transmitter 37 at the set value of 0.2 MPa. Furthermore, this embodiment of the invention also includes a low differential pressure alarm and a low differential pressure interlock. Once the seal fails and the differential pressure decreases, it triggers the compressor unit to shut down. In addition, low superheated steam and nitrogen pressure alarms are set to monitor the sealing gas supply status.

[0041] The embodiments of the present invention effectively solve the problems of difficult shaft seal selection and complex supporting systems of existing steam compressors, and have the following advantages: A. This type of saturated steam dry gas sealing system can be used in any saturated steam compressor, without being limited by the medium, compressor model, speed, or other process and operating conditions. The pre-gas uses the compressor outlet gas, and most of the gas returns to the process system, with only a small amount of leakage and discharge. This avoids the increased post-processing work and process gas loss caused by the introduction of non-condensable steam into the process system. B. The sealing body adopts a relatively mature sealing structure, which can be promoted and applied quickly. C. The sealing control system is simple, safe, reasonable, and easy to operate, which can reduce the initial investment in the sealing system.

Claims

1. A saturated steam dry gas sealing device for a screw compressor, wherein the saturated steam dry gas sealing device comprises a pre-seal, a dry gas seal, and an isolation seal; the pre-seal, the dry gas seal, and the isolation seal are respectively installed in a cavity between the rotor shaft of the screw compressor and the housing of the screw compressor, the dry gas seal is located between the pre-seal and the isolation seal, and the pre-seal is close to the working cavity of the screw compressor; characterized in that, The saturated steam dry gas sealing device further includes a heat insulation sleeve, which is installed in the cavity between the rotor shaft and the housing of the screw compressor and is located between the isolation seal and the bearing cavity of the screw compressor. The heat insulation sleeve is sleeved on the outside of the rotor shaft, and a sealing structure is provided between the heat insulation sleeve and the outer circumferential surface of the rotor shaft. The screw compressor housing has a balance port at the position corresponding to the pre-seal, an overheated steam inlet at the position corresponding to the gap between the pre-seal and the dry gas seal, an exhaust port at the position corresponding to the dry gas seal, a hot nitrogen inlet at the position corresponding to the isolation seal, and a vent port at the position corresponding to the heat insulation sleeve. The side wall of the pre-seal is provided with a balance gas outlet connected to the balance port, the side wall of the dry gas seal is provided with a sealing gas outlet connected to the exhaust port, the side wall of the isolation seal is provided with an isolation sealing gas inlet connected to the hot nitrogen inlet, and the side wall of the heat insulation sleeve is provided with a vent outlet connected to the vent port.

2. The saturated steam dry gas sealing device for a screw compressor as described in claim 1, characterized in that, The balancing gas outlet includes a first annular groove and a plurality of first through holes. The first annular groove is formed on the outer side of the front seal and extends circumferentially along the front seal. The plurality of first through holes are spaced apart along the circumferential direction of the front seal. One end of each first through hole opens into the bottom surface of the first annular groove, and the other end of each first through hole penetrates the inner wall of the front seal.

3. The saturated steam dry gas sealing device for a screw compressor as described in claim 1, characterized in that, The sealing gas outlet includes a second annular groove and a plurality of second through holes. The second annular groove is formed on the outer side of the dry gas seal and extends circumferentially along the dry gas seal. The plurality of second through holes are spaced apart along the circumferential direction of the dry gas seal. One end of each second through hole opens into the bottom surface of the second annular groove, and the other end of each second through hole communicates with the interior of the dry gas seal.

4. The saturated steam dry gas sealing device for a screw compressor as described in claim 1, characterized in that, The isolation and sealing air inlet includes a third annular groove and a plurality of third through holes. The third annular groove is formed on the outer surface of the isolation seal and extends along the circumference of the isolation seal. The plurality of third through holes are spaced apart along the circumferential direction of the isolation seal. One end of each third through hole opens into the bottom surface of the third annular groove, and the other end of each third through hole penetrates the inner wall of the isolation seal.

5. The saturated steam dry gas sealing device for a screw compressor as described in claim 1, characterized in that, The vent outlet includes a fourth annular groove and a plurality of fourth through holes. The fourth annular groove is formed on the outer side of the heat insulation sleeve and extends along the circumference of the heat insulation sleeve. The plurality of fourth through holes are spaced apart along the circumferential direction of the heat insulation sleeve. One end of each fourth through hole opens into the bottom surface of the fourth annular groove, and the other end of each fourth through hole penetrates the inner wall of the heat insulation sleeve.

6. The saturated steam dry gas sealing device for a screw compressor as described in any one of claims 1 to 5, characterized in that, The rotor shaft includes a rotor shaft body and a bushing. The bushing is fitted outside the rotor shaft body and is connected to the moving ring of the dry gas seal.

7. The saturated steam dry gas sealing device for a screw compressor as described in claim 6, characterized in that, The bushing is integrated with the dry gas seal and the isolation seal.

8. The saturated steam dry gas sealing device for a screw compressor as described in claim 6, characterized in that, The saturated vapor dry gas sealing device includes a gland assembly, which is sleeved on the outside of the rotor shaft of the screw compressor and connected to the housing; The gland assembly abuts against the heat insulation sleeve and the bushing respectively to restrict the bushing and the heat insulation sleeve from axially moving towards the bearing cavity of the screw compressor.

9. The saturated steam dry gas sealing device for a screw compressor as described in claim 1, characterized in that, The sealing structure between the heat insulation sleeve and the outer circumferential surface of the rotor shaft is a comb-tooth seal structure or a carbon ring seal structure.

10. The saturated steam dry gas sealing device for a screw compressor as described in claim 1, characterized in that, The pre-seal is a comb-tooth seal or a carbon ring seal; the isolation seal is a comb-tooth seal, a carbon ring seal, or a dry gas seal.

11. The saturated steam dry gas sealing device for a screw compressor as described in claim 1, characterized in that, The screw compressor is either a screw compressor or a screw expander.

12. A saturated steam dry gas sealing system for a screw compressor, the screw compressor comprising a plurality of rotors, characterized in that, The rotor shafts on both sides of each rotor are equipped with a saturated steam dry gas sealing device as described in any one of claims 1 to 10; The saturated vapor dry gas sealing system includes a balance pipeline, a vapor inlet pipeline, an exhaust pipeline, a nitrogen pipeline, a venting pipeline, a first pressure tapping pipeline, a second pressure tapping pipeline, and a differential pressure transmitter. The number of balancing pipes is the same as the number of rotors, and the two ends of each balancing pipe are connected to the balancing port of the saturated steam dry gas sealing device on both sides of the corresponding rotor. The inlet end of the steam inlet pipeline is connected to the vent on the high-pressure side of the screw compressor, and the outlet end of the steam inlet pipeline is connected to the superheated steam inlet of each saturated steam dry gas sealing device. The steam inlet pipeline is equipped with a steam heater, a differential pressure regulating valve, a steam temperature transmitter, and a steam pressure transmitter. The exhaust pipe is connected to the exhaust port of each saturated steam dry gas sealing device. The outlet end of the nitrogen pipeline is connected to the hot nitrogen inlet of each saturated vapor dry gas sealing device. The nitrogen pipeline is equipped with a nitrogen heater, a nitrogen temperature transmitter and a nitrogen pressure transmitter. The venting pipeline is connected to the venting port of each saturated steam dry gas sealing device. The first end of the first pressure tapping line is connected to the section of the steam inlet line downstream of the differential pressure regulating valve, and the second end of the first pressure tapping line is connected to the first end of the differential pressure transmitter; the first end of the second pressure tapping line is connected to the balancing line, and the second end of the second pressure tapping line is connected to the second end of the differential pressure transmitter. The controller receives temperature measurement results from the steam temperature transmitter and nitrogen temperature transmitter, pressure measurement results from the steam pressure transmitter and nitrogen pressure transmitter, differential pressure measurement results from the differential pressure transmitter, and valve status feedback from the differential pressure regulating valve. It controls the heating power of the steam heater and nitrogen heater so that the superheated steam output from the outlet of the steam inlet pipe has a superheat of more than 20°C, and the temperature of the nitrogen output from the outlet of the nitrogen pipe is more than 20°C higher than the saturation temperature of the vented steam at the venting pressure. Based on the differential pressure measurement results, it controls the opening of the differential pressure regulating valve so that the pressure difference between the first and second ends of the differential pressure transmitter is greater than 0.

13. The saturated steam dry gas sealing system for a screw compressor as described in claim 12, characterized in that, The controller is used to control the opening of the differential pressure regulating valve according to the differential pressure measurement result, so that the pressure difference between the first end and the second end of the differential pressure transmitter is maintained at 0.2 MPa.

14. The saturated steam dry gas sealing system for a screw compressor as described in claim 12, characterized in that, The screw compressor is a twin-screw compressor. The air inlet on the low-pressure side of the screw compressor is the air inlet of the twin-screw compressor, and the air inlet on the high-pressure side of the screw compressor is the exhaust port of the twin-screw compressor.

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