Two-stage screw expander

Abstract

The utility model discloses a two-stage screw expander. The two-stage screw expander comprises a first-stage screw expander, an interstage gear assembly, a second-stage screw expander and a regulating valve assembly, the first-stage screw expander is a high-pressure-stage screw expander, and the second-stage screw expander is a low-pressure-stage screw expander; the two-stage screw expander is provided with an air inlet and an air outlet; an inter-stage gear assembly is arranged between the first-stage screw expander and the second-stage screw expander, and the adjusting valve assembly is arranged on the second-stage screw expander and can conduct corresponding adjustment according to pressure changes of the air inlet and the air outlet. According to the two-stage screw expander, the optimal expansion ratio can be automatically adjusted according to changes of external working conditions, so that the screw expander can work efficiently at any time.

Description

Technical Field

[0001] The utility model belongs to the technical field of expander equipment and relates to a screw expander, in particular to a two-stage screw expander. Background Art

[0002] At present, most of the screw expanders on the market are single-unit screw expanders. When a single-unit screw expander faces a high expansion ratio and a large pressure difference, due to the structural limitations of the screw expander (the range of the expansion ratio is small), the expansion end pressure of this type of screw expander is lower than the rated exhaust pressure when facing a large expansion ratio. The screw expander is often in an over-expansion state, which will reduce the output efficiency of the screw expander and affect the vibration and noise of the screw expander. Therefore, the maximum volume ratio that the existing single screw expander can achieve often cannot meet the optimal matching volume ratio.

[0003] When the screw expander is running, the intake pressure and exhaust pressure are often affected by external factors and change. At this time, the expansion ratio of the screw expander will change. For the orifice with a fixed volume ratio (Vi), the changed operating conditions no longer match the orifice, causing the expander to be in an over-expanded or under-expanded state, resulting in additional power consumption losses, and increased vibration and noise.

[0004] In order to meet the requirements of high expansion ratio and large pressure difference, a small number of single screw expanders are connected in series to meet the requirements, but this type of design requires a double-shaft generator and a larger installation space and a more complex control system, which greatly increases the cost. The above-mentioned screw expanders on the market cannot adapt well to the changes in expansion ratio caused by changes in inlet and exhaust pressures, causing the screw expanders to be in a more expanded or under-expanded state when the working conditions change, thereby causing additional power consumption losses, reducing the efficiency of the screw expanders, and increasing vibration and noise.

[0005] In view of this, there is an urgent need to design a new screw expander to overcome at least some of the above-mentioned defects of the existing screw expanders. Utility Model Content

[0006] The utility model provides a two-stage screw expander, which can automatically adjust the optimal expansion ratio according to the change of external working conditions, so that the screw expander can maintain efficient work at any time.

[0007] In order to solve the above technical problems, according to one aspect of the utility model, the following technical solution is adopted:

[0008] A two-stage screw expander, comprising: a first-stage screw expander, an interstage gear assembly, a second-stage screw expander and a regulating valve assembly;

[0009] The first-stage screw expander is a high-pressure screw expander, and the second-stage screw expander is a low-pressure screw expander; the two-stage screw expander is provided with an air inlet and an air outlet;

[0010] An interstage gear assembly is provided between the first-stage screw expander and the second-stage screw expander, and the regulating valve assembly is arranged on the second-stage screw expander. The regulating valve assembly can make corresponding adjustments according to the pressure changes of the air inlet and the exhaust port.

[0011] As an implementation mode of the utility model, the regulating valve assembly is a lifting valve assembly; the lifting valve assembly includes a lifting valve core, a first hydraulic cylinder, a second hydraulic cylinder, a solenoid valve and a control circuit;

[0012] The first hydraulic cylinder and the second hydraulic cylinder are both provided with oil holes, and the oil holes control the injection and discharge of high-pressure oil through the solenoid valve; the control circuit is connected to the solenoid valve and can control the operation of the solenoid valve;

[0013] The two ends of the force-bearing part of the lifting valve core are respectively arranged on the first hydraulic cylinder and the second hydraulic cylinder. The lifting valve core moves under the action of the electromagnetic valve controlling the injection and discharge of high-pressure oil, thereby adjusting the exhaust sealing line of the low-pressure stage body of the second-stage screw expander.

[0014] As an implementation mode of the utility model, when the first hydraulic cylinder is filled with high-pressure oil and the second hydraulic cylinder is emptied of oil, the lifting valve is in a closed state, and the lifting valve core will delay the exhaust sealing line of the low-pressure stage body of the second-stage screw expander, which is suitable for working conditions with high expansion ratios, prolonging the expansion process of the working medium in the yin and yang rotor cavities, so that it has a larger expansion ratio;

[0015] When the second hydraulic cylinder is filled with high-pressure oil and the first hydraulic cylinder is emptied of oil, the lifting valve is in an open state. The lifting valve core will advance the exhaust sealing line of the low-pressure stage body of the second-stage screw expander, which is suitable for low expansion ratio conditions, reducing the expansion process of the working fluid in the yin and yang rotor cavities, making it have a smaller expansion ratio.

[0016] As an embodiment of the present utility model, the poppet valve assembly further includes an elastic mechanism, a guide mechanism and a sealing mechanism;

[0017] The lifting valve core is connected to the guide mechanism and can move under the guidance of the guide mechanism; the lifting valve core is connected to the elastic mechanism to ensure that the lifting valve core works smoothly under the elastic deformation of the elastic mechanism;

[0018] Sealing mechanisms are respectively provided at the connection points between the lifting valve core and the first hydraulic cylinder and the second hydraulic cylinder.

[0019] As an embodiment of the utility model, the lifting valve assembly is arranged on the first sealing tooth groove at the exhaust end of the low-pressure stage body of the second-stage screw expander, the lifting valve core is a component of the rotor working chamber of the low-pressure stage body, and the opening and closing of the lifting valve core are controlled by the hydraulic cylinder and the control circuit;

[0020] When the lifting valve core is in the closed state, the lifting valve core will delay the exhaust sealing line of the low-pressure stage body of the second-stage screw expander, prolong the expansion process of the working medium in the yin and yang rotor cavities, and make it have a larger expansion ratio;

[0021] When the lifting valve core is in the open state, the lifting valve core will advance the exhaust sealing line of the low-pressure stage body of the second-stage screw expander, reduce the expansion process of the working fluid in the yin and yang rotor cavities, and make it have a smaller expansion ratio.

[0022] As an implementation mode of the present utility model, the two-stage screw expander is arranged horizontally as a whole, and the first-stage screw expander and the second-stage screw expander are respectively located on both sides of the inter-stage gear assembly.

[0023] As an embodiment of the present utility model, the first-stage screw expander comprises a high-pressure stage low-pressure end body, a high-pressure stage body, a high-pressure stage high-pressure end body and a high-pressure stage rotor; the high-pressure stage low-pressure end body, the high-pressure stage body and the high-pressure stage high-pressure end body are sequentially connected in series, and the high-pressure stage rotor is contained therein;

[0024] The high-pressure stage body is provided with an air inlet of the screw expander, and the high-pressure stage rotor comprises a high-pressure stage male rotor and a high-pressure stage female rotor, and the high-pressure stage male rotor and the high-pressure stage female rotor are arranged up and down;

[0025] A first rotating shaft and a second rotating shaft are provided at both ends of the high-pressure stage positive rotor, a driving gear is arranged on the first rotating shaft, bearings and seals are arranged between the first rotating shaft and the high-pressure end body of the high-pressure stage, bearings and seals are arranged between the second rotating shaft of the high-pressure stage positive rotor and the high-pressure low-pressure end body of the high-pressure stage; bearings and seals are distributed on the shafts at both ends of the high-pressure stage negative rotor.

[0026] As an embodiment of the present utility model, the second-stage screw expander comprises a low-pressure end body, a low-pressure machine body, a low-pressure high-pressure end body and a low-pressure rotor; the low-pressure end body, the low-pressure machine body and the low-pressure high-pressure end body are connected in series in sequence, and the low-pressure rotor is contained therein;

[0027] The exhaust port of the two-stage screw expander is arranged on the low-pressure stage body, and the low-pressure stage rotor includes a low-pressure stage male rotor and a low-pressure stage female rotor, and the low-pressure stage male rotor and the low-pressure stage female rotor are arranged up and down;

[0028] A third rotating shaft and a fourth rotating shaft are arranged at both ends of the low-pressure stage positive rotor, the third rotating shaft is connected to the generator, and bearings and seals are arranged between the third rotating shaft and the low-pressure end body of the low-pressure stage; a driven gear is arranged on the fourth rotating shaft, and bearings and seals are arranged between the fourth rotating shaft and the high-pressure end body of the low-pressure stage.

[0029] As an implementation mode of the utility model, the interstage gear assembly is an interstage gear box, and the interstage gear box is composed of a high-pressure end body of a high-pressure stage, a high-pressure end body of a low-pressure stage, a driving gear and a driven gear;

[0030] The driving gear is located on the first rotating shaft of the high-pressure stage positive rotor, and the driven gear is located on the fourth rotating shaft of the low-pressure stage positive rotor; the output work of the first-stage screw expander is transmitted to the second-stage screw expander through the gear, and then the fourth rotating shaft of the low-pressure stage positive rotor of the second-stage screw expander outputs the work done by the first-stage screw expander and the second-stage screw expander to the setting device;

[0031] The transmission ratio of the gear is determined by the required rotational speeds of the first-stage screw expander and the second-stage screw expander, and the rotational speed is usually determined by the optimal tooth tip speed of the rotors of the two-stage screw expander, so as to maximize the efficiency of the screw expander;

[0032] As an implementation mode of the utility model, in the process of exhausting air from the first-stage screw expander of the two-stage screw expander to the air intake of the second-stage screw expander, an inter-stage closed flow channel is arranged;

[0033] The closed flow channel separates the interstage gear box from the first-stage high-pressure end bearing chamber and the second-stage high-pressure end bearing chamber, so that the low-temperature lubricating oil sprayed into the gear box and the bearing chamber does not mix with the interstage airflow, thereby minimizing the influence of the low-temperature lubricating oil on the interstage working fluid and improving the output efficiency of the expander.

[0034] The beneficial effect of the utility model is that the two-stage screw expander proposed by the utility model changes the expansion ratio of the screw expander by controlling the opening and closing of the lifting valve core when the rated pressure working conditions of the inlet and exhaust ports are changed due to external factors, thereby matching the optimal expansion ratio change caused by the change in the pressure working conditions. In this way, the screw expander maintains efficient work at all times.

[0035] The utility model connects two single-stage screw expanders in series through interstage gears, and the gas circuits and oil circuits of the two-stage expanders are connected in series using casting shells, which greatly reduces the required installation space, simplifies the system, and reduces the operation and maintenance costs.

[0036] The interstage gears adopted by the utility model can match the operating speed required by the screw expander, so that the rotor tooth top speeds of the first-stage screw expander and the second-stage screw expander are the optimal tooth top speeds, so as to obtain higher efficiency.

[0037] The utility model adopts an interstage flow channel, which is a closed flow channel setting. The closed flow channel separates the interstage gearbox and the first stage high pressure end bearing cavity and the second stage high pressure end bearing cavity, so that the low temperature lubricating oil sprayed into the gearbox and the bearing cavity does not mix with the interstage airflow, thereby minimizing the influence of the low temperature lubricating oil on the interstage working medium and improving the output efficiency of the expander. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a perspective view of a two-stage screw expander in one embodiment of the utility model.

[0039] Figure 2 This is another perspective view of the two-stage screw expander in one embodiment of the utility model.

[0040] Figure 3 This is a structural schematic diagram of a two-stage screw expander in one embodiment of the utility model.

[0041] Figure 4 It is a three-dimensional diagram of a two-stage screw expander in one embodiment of the utility model.

[0042] Figure 5 It is a structural schematic diagram of a lift valve assembly in one embodiment of the utility model.

[0043] Figure 6 It is a structural schematic diagram of a lift valve assembly in one embodiment of the utility model. DETAILED DESCRIPTION

[0044] The preferred embodiments of the present utility model are described in detail below with reference to the accompanying drawings.

[0045] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0046] The description in this section is only for several typical embodiments, and the present invention is not limited to the scope of the embodiments. The same or similar prior art means and some technical features in the embodiments are mutually replaced and are also within the scope of the present invention.

[0047] The term “connection” in the specification includes both direct connection and indirect connection.

[0048] The utility model discloses a two-stage screw expander. Figures 1 to 4 This is a schematic diagram of the structure of a two-stage screw expander in one embodiment of the present invention; please refer to Figures 1 to 4, the two-stage screw expander comprises: a first-stage screw expander 1, an interstage gear assembly 3, a second-stage screw expander 2 and a regulating valve assembly 4. The first-stage screw expander 1 is a high-pressure screw expander, and the second-stage screw expander 2 is a low-pressure screw expander. The exhaust end of the first-stage screw expander 1 is connected to the intake end of the second-stage screw expander 2 through the interstage channel 5. The two-stage screw expander is provided with an air inlet 6 and an exhaust port 7; wherein the air inlet 6 serves as the air inlet of the first-stage screw expander 1, and the exhaust port 7 serves as the exhaust port of the second-stage screw expander 2. An interstage gear assembly 3 is provided between the first-stage screw expander 1 and the second-stage screw expander 2, and the regulating valve assembly 4 is arranged on the second-stage screw expander 2, and the regulating valve assembly 4 can make corresponding adjustments according to the pressure changes of the air inlet 6 and the exhaust port 7.

[0049] In one embodiment of the utility model, the regulating valve assembly 4 is a lifting valve assembly; the lifting valve assembly includes a lifting valve core 41, a first hydraulic cylinder 42, a second hydraulic cylinder 43, a solenoid valve and a control circuit. The first hydraulic cylinder 42 and the second hydraulic cylinder 43 are both provided with oil holes 44 and 45, and the oil holes 44 and 45 control the injection and discharge of high-pressure oil through the solenoid valve; the control circuit is connected to the solenoid valve and can control the operation of the solenoid valve.

[0050] The two ends of the force-bearing part 49 of the lifting valve core 41 are respectively arranged on the first hydraulic cylinder 42 and the second hydraulic cylinder 43. The lifting valve core 41 moves accordingly under the action of the solenoid valve controlling the injection and discharge of high-pressure oil (including injecting hydraulic oil from the second hydraulic cylinder 43 into the first hydraulic cylinder 42, at which time the hydraulic oil is discharged from the second hydraulic cylinder 43 and injected into the first hydraulic cylinder 42; or injecting hydraulic oil from the first hydraulic cylinder 42 into the second hydraulic cylinder 43, at which time the hydraulic oil is discharged from the first hydraulic cylinder 42 and injected into the second hydraulic cylinder 43), thereby adjusting the exhaust sealing line of the low-pressure stage body of the second-stage screw expander 2.

[0051] When the first hydraulic cylinder 42 is filled with high-pressure oil and the second hydraulic cylinder 43 is emptied of oil, the lifting valve is in a closed state, and the lifting valve core 41 will delay the exhaust sealing line of the low-pressure stage body of the second-stage screw expander 2, which is suitable for working conditions with high expansion ratios, prolonging the expansion process of the working medium in the yin and yang rotor cavities, so that it has a larger expansion ratio;

[0052] When the second hydraulic cylinder 43 is filled with high-pressure oil and the first hydraulic cylinder 42 is emptied of oil, the lifting valve is in an open state. The lifting valve core 41 will advance the exhaust sealing line of the low-pressure stage body of the second-stage screw expander 2, which is suitable for low expansion ratio conditions, reducing the expansion process of the working fluid in the yin and yang rotor cavities, so that it has a smaller expansion ratio.

[0053] In addition, the lift valve assembly 4 may further include an elastic mechanism 46, a guide mechanism 47 and a sealing mechanism 48. The lift valve core 41 is connected to the guide mechanism 47 and can move under the guidance of the guide mechanism 47; the lift valve core 41 is connected to the elastic mechanism 46 to ensure that the lift valve core 41 works smoothly under the elastic deformation of the elastic mechanism 46; the sealing mechanisms 48 are respectively provided at the connection between the lift valve core 41 and the first hydraulic cylinder 42 and the second hydraulic cylinder 43.

[0054] In one embodiment of the utility model, the lifting valve assembly is arranged on the first sealing tooth groove at the exhaust end of the low-pressure stage body 27 in the second-stage screw expander 2, and the lifting valve core 41 can be used as a component of the rotor working chamber of the low-pressure stage body 27, and the opening and closing of the lifting valve core 41 are controlled by a hydraulic cylinder and a control circuit.

[0055] When the lifting valve core 41 is in the closed state, the lifting valve core 41 will delay the exhaust sealing line of the low-pressure stage body of the second-stage screw expander 2, prolong the expansion process of the working medium in the yin and yang rotor chambers, and make it have a larger expansion ratio. When the lifting valve core 41 is in the open state, the lifting valve core 41 will advance the exhaust sealing line of the low-pressure stage body of the second-stage screw expander 2, reduce the expansion process of the working medium in the yin and yang rotor chambers, and make it have a smaller expansion ratio.

[0056] The two-stage screw expander is arranged horizontally as a whole, and the first-stage screw expander 1 and the second-stage screw expander 2 are respectively located on both sides of the inter-stage gear assembly 3 .

[0057] See also Figure 1 , Figure 2 In one embodiment of the utility model, the first stage screw expander 1 comprises a high-pressure stage low-pressure end body 17, a high-pressure stage body 16, a high-pressure stage high-pressure end body 18 and a high-pressure stage rotor; the high-pressure stage low-pressure end body 17, the high-pressure stage body 16 and the high-pressure stage high-pressure end body 18 are connected in series in sequence, and the high-pressure stage rotor is contained therein. The high-pressure stage body 16 is provided with an air inlet 6 of the screw expander, and the high-pressure stage rotor comprises a high-pressure stage male rotor 11 and a high-pressure stage female rotor, and the high-pressure stage male rotor 11 and the high-pressure stage female rotor are arranged up and down. The high-pressure stage male rotor 11 is provided with a first rotating shaft and a second rotating shaft at both ends, and a driving gear 31 is arranged on the first rotating shaft, and a bearing 12 and a seal 14 are arranged between the first rotating shaft and the high-pressure stage high-pressure end body 17, and a bearing 13 and a seal 15 are arranged between the second rotating shaft of the high-pressure stage male rotor and the high-pressure stage low-pressure end body 18; bearings and seals are distributed on the shafts at both ends of the high-pressure stage female rotor.

[0058] The second-stage screw expander 2 includes a low-pressure end body 28, a low-pressure body 27, a low-pressure high-pressure end body 29 and a low-pressure rotor; the low-pressure end body 28, the low-pressure body 27 and the low-pressure high-pressure end body 29 are connected in series in sequence, and the low-pressure rotor is contained therein. The exhaust port 7 of the two-stage screw expander is arranged on the low-pressure body 27, and the low-pressure rotor includes a low-pressure male rotor 21 and a low-pressure female rotor, and the low-pressure male rotor 21 and the low-pressure female rotor are arranged up and down. The third rotating shaft 26 and the fourth rotating shaft are arranged at both ends of the low-pressure male rotor 21, and the third rotating shaft 26 is connected to the generator. A bearing 22 and a seal 24 are arranged between the third rotating shaft and the low-pressure end body 28; a driven gear 32 is arranged on the fourth rotating shaft, and a bearing and a seal are arranged between the fourth rotating shaft and the low-pressure high-pressure end body 29.

[0059] In one embodiment, the interstage gear assembly 3 is an interstage gear box, and the interstage gear box comprises a high-pressure end body 17 of a high-pressure stage, a high-pressure end body 29 of a low-pressure stage, a driving gear 31 and a driven gear 32 .

[0060] The driving gear 31 is located on the first rotating shaft of the high-pressure stage positive rotor 11, and the driven gear 32 is located on the fourth rotating shaft of the low-pressure stage positive rotor 21; the output work of the first-stage screw expander 1 is transmitted to the second-stage screw expander 2 through gears, and then the fourth rotating shaft of the low-pressure stage positive rotor of the second-stage screw expander 2 outputs the work done by the first-stage screw expander 1 and the second-stage screw expander 2 to the setting device.

[0061] The transmission ratio of the gears is determined by the required rotational speeds of the first-stage screw expander 1 and the second-stage screw expander 2, and the rotational speeds are usually determined by the optimal tooth top speeds of the rotors of the two-stage screw expanders, thereby maximizing the efficiency of the screw expanders.

[0062] In one embodiment of the utility model, in the process of exhausting the first-stage screw expander of the two-stage screw expander to the intake of the second-stage screw expander, an interstage closed flow channel is used. The closed flow channel separates the interstage gearbox and the first-stage high-pressure end bearing chamber and the second-stage high-pressure end bearing chamber, so that the low-temperature lubricating oil sprayed into the gearbox and the bearing chamber does not mix with the interstage airflow, thereby minimizing the influence of the low-temperature lubricating oil on the interstage working medium and improving the output efficiency of the expander.

[0063] In summary, the two-stage screw expander proposed in the utility model changes the expansion ratio of the screw expander by controlling the opening and closing of the lifting valve core when the rated pressure conditions of the inlet and exhaust ports change due to external factors, thereby matching the optimal expansion ratio change caused by the change in pressure conditions. This allows the screw expander to maintain efficient work at all times.

[0064] The utility model connects two single-stage screw expanders in series through interstage gears, and the gas circuits and oil circuits of the two-stage expanders are connected in series using casting shells, which greatly reduces the required installation space, simplifies the system, and reduces the operation and maintenance costs.

[0065] The interstage gears adopted by the utility model can match the operating speed required by the screw expander, so that the rotor tooth top speeds of the first-stage screw expander and the second-stage screw expander are the optimal tooth top speeds, so as to obtain higher efficiency.

[0066] The utility model adopts an interstage flow channel, which is a closed flow channel setting. The closed flow channel separates the interstage gearbox and the first stage high pressure end bearing cavity and the second stage high pressure end bearing cavity, so that the low temperature lubricating oil sprayed into the gearbox and the bearing cavity does not mix with the interstage airflow, thereby minimizing the influence of the low temperature lubricating oil on the interstage working medium and improving the output efficiency of the expander.

[0067] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The description and application of the utility model here are illustrative, and it is not intended to limit the scope of the utility model to the above-mentioned embodiments. The effects or advantages involved in the embodiments may not be embodied in the embodiments due to interference from various factors, and the description of the effects or advantages is not used to limit the embodiments. The deformation and changes of the embodiments disclosed here are possible, and the replacement of the embodiments and the various equivalent components are well known to those of ordinary skill in the art. It should be clear to those skilled in the art that the utility model can be implemented in other forms, structures, arrangements, proportions, and with other components, materials and parts without departing from the spirit or essential features of the utility model. Other deformations and changes can be made to the embodiments disclosed here without departing from the scope and spirit of the utility model.

Claims

1. A two-stage screw expander, characterized in that: The two-stage screw expander comprises: a first-stage screw expander, an interstage gear assembly, a second-stage screw expander and a regulating valve assembly; The first-stage screw expander is a high-pressure screw expander, and the second-stage screw expander is a low-pressure screw expander; the two-stage screw expander is provided with an air inlet and an air outlet; An interstage gear assembly is provided between the first-stage screw expander and the second-stage screw expander, and the regulating valve assembly is provided on the second-stage screw expander, and the regulating valve assembly can be adjusted accordingly according to the pressure changes of the air inlet and the exhaust port; The regulating valve assembly is a lifting valve assembly; the lifting valve assembly comprises a lifting valve core, a first hydraulic cylinder, a second hydraulic cylinder, a solenoid valve and a control circuit; The first hydraulic cylinder and the second hydraulic cylinder are both provided with oil holes, and the oil holes control the injection and discharge of high-pressure oil through the solenoid valve; the control circuit is connected to the solenoid valve and can control the operation of the solenoid valve; The two ends of the force-bearing part of the lifting valve core are respectively arranged on the first hydraulic cylinder and the second hydraulic cylinder. The lifting valve core moves under the action of the electromagnetic valve controlling the injection and discharge of high-pressure oil, thereby adjusting the exhaust sealing line of the low-pressure stage body of the second-stage screw expander.

2. The two-stage screw expander according to claim 1, characterized in that: When the first hydraulic cylinder is filled with high-pressure oil and the second hydraulic cylinder is emptied of oil, the lifting valve is in a closed state. The lifting valve core will delay the exhaust sealing line of the low-pressure stage body of the second-stage screw expander, which is suitable for working conditions with high expansion ratios, prolonging the expansion process of the working medium in the yin and yang rotor cavities, making it have a larger expansion ratio; When the second hydraulic cylinder is filled with high-pressure oil and the first hydraulic cylinder is emptied of oil, the lifting valve is in an open state. The lifting valve core will advance the exhaust sealing line of the low-pressure stage body of the second-stage screw expander, which is suitable for low expansion ratio conditions, reducing the expansion process of the working fluid in the yin and yang rotor cavities, making it have a smaller expansion ratio.

3. The two-stage screw expander according to claim 1, characterized in that: The poppet valve assembly further includes an elastic mechanism, a guide mechanism and a sealing mechanism; The lifting valve core is connected to the guide mechanism and can move under the guidance of the guide mechanism; the lifting valve core is connected to the elastic mechanism to ensure that the lifting valve core works smoothly under the elastic deformation of the elastic mechanism; the connection between the lifting valve core and the first hydraulic cylinder and the second hydraulic cylinder is respectively provided with a sealing mechanism.

4. The two-stage screw expander according to claim 1, characterized in that: The lifting valve assembly is arranged on the first sealing tooth groove at the exhaust end of the low-pressure stage body of the second-stage screw expander, the lifting valve core is a component of the rotor working chamber of the low-pressure stage body, and the opening and closing of the lifting valve core are controlled by the hydraulic cylinder and the control circuit; When the lifting valve core is in the closed state, the lifting valve core will delay the exhaust sealing line of the low-pressure stage body of the second-stage screw expander, prolong the expansion process of the working medium in the yin and yang rotor cavities, and make it have a larger expansion ratio; When the lifting valve core is in the open state, the lifting valve core will advance the exhaust sealing line of the low-pressure stage body of the second-stage screw expander, reduce the expansion process of the working fluid in the yin and yang rotor cavities, and make it have a smaller expansion ratio.

5. The two-stage screw expander according to claim 1, characterized in that: The two-stage screw expander is arranged horizontally as a whole, and the first-stage screw expander and the second-stage screw expander are respectively located on both sides of the inter-stage gear assembly.

6. The two-stage screw expander according to claim 1, characterized in that: The first-stage screw expander comprises a high-pressure stage low-pressure end body, a high-pressure stage body, a high-pressure stage high-pressure end body and a high-pressure stage rotor; the high-pressure stage low-pressure end body, the high-pressure stage body and the high-pressure stage high-pressure end body are connected in series in sequence, and contain a high-pressure stage rotor inside; The high-pressure stage body is provided with an air inlet of the screw expander, and the high-pressure stage rotor comprises a high-pressure stage male rotor and a high-pressure stage female rotor, and the high-pressure stage male rotor and the high-pressure stage female rotor are arranged up and down; A first rotating shaft and a second rotating shaft are provided at both ends of the high-pressure stage positive rotor, a driving gear is arranged on the first rotating shaft, bearings and seals are arranged between the first rotating shaft and the high-pressure end body of the high-pressure stage, bearings and seals are arranged between the second rotating shaft of the high-pressure stage positive rotor and the high-pressure low-pressure end body of the high-pressure stage; bearings and seals are distributed on the shafts at both ends of the high-pressure stage negative rotor.

7. The two-stage screw expander according to claim 1, characterized in that: The second-stage screw expander comprises a low-pressure end body, a low-pressure machine body, a low-pressure high-pressure end body and a low-pressure rotor; the low-pressure end body, the low-pressure machine body and the low-pressure high-pressure end body are connected in series in sequence, and contain a low-pressure rotor inside; The exhaust port of the two-stage screw expander is arranged on the low-pressure stage body, and the low-pressure stage rotor includes a low-pressure stage male rotor and a low-pressure stage female rotor, and the low-pressure stage male rotor and the low-pressure stage female rotor are arranged up and down; A third rotating shaft and a fourth rotating shaft are arranged at both ends of the low-pressure stage positive rotor, the third rotating shaft is connected to the generator, and bearings and seals are arranged between the third rotating shaft and the low-pressure end body of the low-pressure stage; a driven gear is arranged on the fourth rotating shaft, and bearings and seals are arranged between the fourth rotating shaft and the high-pressure end body of the low-pressure stage.

8. The two-stage screw expander according to claim 1, characterized in that: The interstage gear assembly is an interstage gear box, which consists of a high-pressure end body of a high-pressure stage, a high-pressure end body of a low-pressure stage, a driving gear and a driven gear; The driving gear is located on the first rotating shaft of the high-pressure stage positive rotor, and the driven gear is located on the fourth rotating shaft of the low-pressure stage positive rotor; the output work of the first-stage screw expander is transmitted to the second-stage screw expander through the gears, and then the fourth rotating shaft of the low-pressure stage positive rotor of the second-stage screw expander outputs the work done by the first-stage screw expander and the second-stage screw expander to the setting device.

9. The two-stage screw expander according to claim 1, characterized in that: In the process of exhaust from the first-stage screw expander to the intake of the second-stage screw expander of the two-stage screw expander, an inter-stage closed flow channel is arranged; The closed flow channel separates the interstage gearbox from the first-stage high-pressure end bearing cavity and the second-stage high-pressure end bearing cavity, so that the low-temperature lubricating oil sprayed into the gearbox and the bearing cavity does not mix with the interstage airflow.

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