A turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas

Abstract

The present invention discloses a turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas, comprising an expander housing and a rotor motor disposed within the expander housing. The rotor motor's rotating shaft is rotatably fixed to bearings disposed at both ends of the expander housing. One end of the rotating shaft extends from the expansion end of the expander housing and is fixed to a two-phase expansion impeller, while the other end extends from the brake end of the expander housing and is fixed to the brake impeller. Each impeller flow channel of the two-phase expansion impeller is provided with a through hole extending to the impeller back. The inlet of the through hole is located on the inner slope of the impeller back, and the outlet of the through hole is located on the hub surface of the impeller flow channel near the expansion impeller outlet. A movable sealing disk is provided on the impeller back of the two-phase expansion impeller. The air intake of the through hole is adjusted by adjusting the gap between the movable sealing disk and the back of the two-phase expansion impeller. The present invention can reduce flow losses, thereby improving the liquid carryover rate and operational stability of the two-phase turbine expander.

Description

Technical Field

[0001] The invention relates to the technical field of two-phase turbine expanders, in particular to a turbine expander with adjustable gas-liquid two-phase deposited droplet purge gas. Background Art

[0002] A centrifugal turbine expander is a high-speed rotary machine used for low-temperature refrigeration and energy recovery and conversion. Its operating principle is to expand a high-temperature, high-pressure gaseous medium within the impeller flow path, generating a kinetic moment that drives the impeller to rotate and perform work. The pressure and temperature of the medium decrease after expansion through the centrifugal turbine. This actual thermodynamic process is approximately an isentropic expansion process, where the thermodynamic enthalpy of the medium decreases after expansion, converting a portion of its internal energy into mechanical energy. Therefore, centrifugal turbine expanders are not only used for low-temperature refrigeration (gas liquefaction, space environment simulation), but are also widely used in various power cycles (organic Rankine cycle, Kalina cycle), recovering low-grade heat sources for reuse to achieve energy conservation and emission reduction.

[0003] For safe and stable operation, currently common industrial centrifugal turbine expanders maintain a single-phase, superheated working fluid throughout the expansion process. However, to further improve system thermal efficiency and economics, the design and application of centrifugal turbine expanders are gradually expanding from the pure single-phase region to the two-phase region. Theoretical analysis shows that the deeper the expanding gas enters the two-phase region, the greater the specific enthalpy drop during the expansion process, resulting in greater cooling capacity or output power. This indicates that, compared to single-phase turbine expanders, two-phase turbine expanders offer a higher expansion ratio and isentropic efficiency under the same inlet conditions. However, when the gas expands from the superheated region into the two-phase region, if the degree of subcooling is low, non-equilibrium condensation can occur between the two phases, forming extremely small droplets that are evenly distributed in a mist-like manner, or no condensation occurs. This situation has little impact on the stable operation of the centrifugal turbine. Currently, centrifugal turbine expanders used in air separation plants can easily achieve a liquid carryover rate of 6% to 8%. However, as the degree of subcooling increases, the rate of two-phase condensation accelerates and the droplet size increases, causing droplet deposition on the impeller surface. Under the centrifugal force of the impeller, the deposited liquid is unable to escape and collide with the impeller, forming secondary droplets. These secondary droplets have a relatively large radius, which is the main cause of blade damage and rotor instability. If the problem of non-equilibrium condensation droplet deposition in centrifugal turbines can be improved to increase the liquid carryover rate in two-phase turbines, a greater enthalpy drop can be achieved.

[0004] Currently, research on two-phase flow in turboexpanders is primarily focused on theoretical research. Researchers at Xi'an Jiaotong University in China have conducted numerical calculations of nucleation and droplet growth models for two-phase air flow in cryogenic turboexpanders, and analyzed fluid losses. However, theoretical research on two-phase turboexpanders is virtually nonexistent internationally.

[0005] In terms of practical application, there are almost no reports on the actual operation of two-phase turbine expanders in China. To avoid the potential dangers of droplet deposition during two-phase operation, companies strictly require that the expander design and operating conditions keep the gas in a superheated state throughout the entire process. In addition, to reduce erosion of the two-phase fluid, high-strength titanium alloys, 7075 aviation aluminum, and other materials are often used, or special material coatings are applied to the impeller surface to increase the life cycle of the two-phase turbine expander impeller and reduce flow losses. No other solution has yet been found to reduce flow losses and unbalanced condensation droplet deposition in two-phase turbine expanders. Summary of the Invention

[0006] In order to solve the problem of non-equilibrium condensation droplet deposition in a centripetal turbine expander, the present invention provides a turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas, which can reduce flow loss to improve the liquid entrainment rate and operating stability of the two-phase turbine expander.

[0007] A turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas comprises an expander housing and a rotor motor disposed within the expander housing; a rotating shaft of the rotor motor is rotatably fixed to bearings disposed at both ends of the expander housing;

[0008] One end of the rotating shaft extends out of the expansion end of the expander housing and is fixed to the two-phase expansion impeller, and the other end extends out of the braking end of the expander housing and is fixed to the braking impeller;

[0009] Each impeller flow channel of the two-phase expansion impeller is provided with a through hole extending to the impeller wheel back; the inlet of the through hole is located at the inner slope surface of the impeller wheel back, and the outlet of the through hole is located on the hub surface of the impeller flow channel near the expansion impeller outlet;

[0010] A movable sealing disk is provided at the back of the impeller of the two-phase expansion impeller; a gear disk meshing with a pinion is provided on the periphery of the movable sealing disk, and the pinion is connected to the output shaft of the gear adjustment motor; the pinion is driven to rotate by the gear adjustment motor, thereby adjusting the gap between the movable sealing disk and the back of the two-phase expansion impeller, and then adjusting the air intake volume of the through hole.

[0011] The turbine expander of the present invention is suitable for air and alkane working gases such as methane. Superheated gas enters from the volute inlet of the expansion end of the turbine expander, is guided by the volute and uniformly intakes along the circumference. The first expansion process is completed in the stationary blade nozzle, resulting in a decrease in temperature and pressure, conversion of gas internal energy into kinetic energy, and an increase in flow rate. The high-speed gas continues to enter the high-speed rotating two-phase expansion impeller for secondary expansion. The low-temperature gas may cross the saturation line and enter the two-phase region as the temperature drops further. When the degree of supercooling increases further, the gas will undergo non-equilibrium spontaneous condensation into small droplets in the flow channel. As the temperature decreases and the droplets grow, the condensed droplets will adhere to the blade surface or accumulate on the hub surface of the impeller flow channel. The hub surface of the impeller flow channel is connected to the impeller wheel back through a through hole. The working gas enters the back of the impeller through the gap between the dynamic and static expansion impellers, so the pressure in the back space is the same as the pressure at the impeller inlet. The pressure of the gas at the impeller flow channel outlet is low after full expansion, so there is a pressure difference between the impeller back space pressure and the impeller outlet. The gas at the back of the impeller flows rapidly to the impeller outlet through the small holes, which can blow away the deposited droplets in the two-phase impeller flow channel, avoiding the large-scale deposition of two-phase non-equilibrium condensation droplets in the flow channel.

[0012] The gap between the impeller back and the movable sealing disc can be flexibly adjusted. This gap size controls the amount of air entering the back, and thus the amount of purge air passing through the impeller through-holes. The movable sealing disc also meshes with a pinion gear and is driven by a gear motor, which adjusts the relative position of the movable sealing disc and the expansion impeller.

[0013] Alternatively, the through hole may be a through hole of constant diameter, a gradually converging through hole, a gradually expanding through hole, or a gradually converging and gradually expanding through hole. To achieve the purpose of reducing pressure and increasing speed, when the Mach number of the flow velocity of the gas at the back of the expansion impeller is less than 1, the through hole adopts a gradually converging nozzle type; when the Mach number of the flow velocity of the gas at the back of the expansion impeller is greater than 1, the through hole adopts a gradually expanding nozzle type; when it is necessary to expand gas with a flow velocity of Mach number less than 1 to a Mach number greater than 1, a gradually converging and gradually expanding nozzle type may be considered.

[0014] Optionally, the number of through holes in each impeller flow channel may be one or more, and the number and aperture size of the through holes may be arranged and designed according to actual flow requirements.

[0015] Furthermore, the impeller back as a whole adopts a groove structure design.

[0016] Optionally, the two-phase expansion impeller may be a semi-open impeller, a closed impeller, an impeller with separated blades, or an impeller without separated blades.

[0017] The outer sleeve of the two-phase expansion impeller is provided with a nozzle ring, and there is a gap between the expansion impeller inlet of the two-phase expansion impeller and the inner ring of the nozzle ring. The outer periphery of the nozzle ring is provided with an expansion end volute fixed to the expander casing, and the function of the expansion end volute is circumferential air intake and closing the expansion end.

[0018] The bearing of the expansion end is fixed on the expander housing through a radial bearing seat, and the movable sealing disk is connected to the nozzle ring and the radial bearing seat respectively through threads.

[0019] The movable sealing disc adopts a labyrinth seal plus a dry gas seal to ensure that the gas at the expansion end does not leak through the gap between the rotating shafts.

[0020] When there is no droplet deposition on the hub surface of the impeller flow channel of the two-phase expansion impeller, the back clearance between the movable sealing disk and the two-phase expansion impeller is adjusted to be reduced, so as to reduce the amount of gas passing through the back of the impeller and improve the work efficiency of the expander; when there is a large amount of droplet deposition on the hub surface of the impeller flow channel of the two-phase expansion impeller, the back clearance between the movable sealing disk and the two-phase expansion impeller is adjusted to be increased, so as to increase the air intake amount of the purge gas on the back of the impeller and improve the operating stability of the expander.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. To address the problem of two-phase non-equilibrium condensed droplet deposition in a turbine expander in a refrigeration system, the present invention has specially designed and modified the two-phase expansion impeller. By utilizing the pressure difference between the impeller back and the impeller outlet, the deposited droplets are automatically purged, further improving the liquid carryover rate of the two-phase turbine expander.

[0023] 2. The turbine expander and its impeller structure provided by the present invention can discharge the deposited droplets in the impeller in a timely manner, effectively preventing the large-scale aggregation of droplets and collision with the blades, and can improve the operating stability of the two-phase turbine rotor.

[0024] 3. The present invention drives the movable sealing disk through a gear motor to adjust the gap between the back of the expansion impeller and the movable sealing disk, and can adjust the air intake according to the operating conditions to achieve efficient purging of droplets deposited on the impeller surface.

[0025] 4. The two-phase impeller structure proposed in the present invention allows the gas to reach the hub surface through the impeller holes, forming a gas protection layer on the bottom surface of the impeller flow channel, which can also reduce the impact loss to a certain extent.

[0026] 5. The two-phase expansion impeller proposed in the present invention can be designed according to the size and shape of the specific through holes according to actual needs. The structure is simple and compact, and the punching operation is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of a turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas according to the present invention;

[0028] Figure 2 Schematic diagram of the two-phase expansion impeller structure of the present invention;

[0029] Figure 3 Schematic cross-sectional view of the phase expansion impeller corresponding to different through holes in the present invention;

[0030] Figure 4 Schematic diagrams of different types of expander impellers in the present invention;

[0031] Figure 5 Schematic diagram of the adjustment mechanism of the movable sealing disk in the present invention;

[0032] Figure 6 Schematic diagrams of two different states of the movable sealing disk in the present invention.

[0033] In the figure: 1-two-phase expansion impeller, 2-nozzle ring, 3-pinion, 4-gear adjustment motor, 5-rotating shaft, 6-rotor motor, 7-expander housing, 8-brake impeller, 9-expansion end volute, 10-movable sealing disk, 11-radial bearing seat, 12-bearing, 13-brake end guide vane ring, 14-brake end volute, 15-through hole, 16-impeller back, 17-expansion impeller inlet, 18-expansion impeller outlet, 19-impeller flow channel hub surface, 20-closed impeller cover. DETAILED DESCRIPTION

[0034] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0035] like Figure 1 As shown, a turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas includes the following components: a two-phase expansion impeller 1, a nozzle ring 2, a pinion 3, a gear adjustment motor 4, a rotating shaft 5, a rotor motor 6, an expander casing 7, a brake impeller 8, an expansion end volute 9, a movable sealing disk 10, a radial bearing seat 11, a bearing 12, a brake end guide vane ring 13 and a brake end volute 14.

[0036] The expander housing 7 is provided with an expansion-end volute 9 and a brake-end volute 14 at each end, respectively. A rotor motor 6 is disposed within the expander housing 7. The rotor motor 6's rotating shaft 5 is rotatably secured to bearings 12 provided at both ends of the expander housing 7. One end of the rotating shaft 5 extends beyond the expansion end of the expander housing 7 and is secured to the two-phase expansion impeller 1. The other end extends beyond the brake end of the expander housing 7 and is secured to the brake impeller 8.

[0037] Each impeller flow channel of the two-phase expansion impeller 1 is provided with a through hole 15 that passes through to the impeller back 16; the inlet of the through hole 15 is located on the inner slope surface of the impeller back 16, and the outlet of the through hole 15 is located on the hub surface 19 of the impeller flow channel near the expansion impeller outlet 18.

[0038] In one embodiment, the two-phase expansion impeller 1 is connected to the shaft diameter of the rotating shaft 5 by bolts, and a movable sealing disk 10 is provided at the impeller back 16 of the two-phase expansion impeller 1. The movable sealing disk 10 adopts a labyrinth seal plus a dry gas seal to ensure that the gas at the expansion end will not leak through the gap between the rotating shafts.

[0039] The outer periphery of the two-phase expansion impeller 1 is covered with a nozzle ring 2, and there is a certain gap between the expansion impeller inlet 17 and the inner ring of the nozzle ring 2. The outer periphery of the nozzle ring 2 is the expansion end volute 9, which functions to circumferentially intake air and close the expansion end.

[0040] In this embodiment of the present invention, both the radial and axial bearings of the rotating shaft utilize hydrostatic gas bearings. In addition to hydrostatic gas bearings, these bearings can employ various other types, including but not limited to ball bearings and magnetic bearings, and can be selected based on specific circumstances. The other end of the rotating shaft is connected to a brake impeller 8, which is sealed by a brake end volute 14 and communicates with external piping.

[0041] like Figure 2 As shown in Figures (a) and (b), the two-phase expansion impeller 1 in this embodiment is a semi-open impeller with 13 blades and 13 impeller channels. Each channel has a through hole 15 obliquely penetrated and connected to the impeller back 16. The through hole 15 is a small hole of equal diameter. High-pressure gas flowing out of the nozzle enters the impeller back 16 through the gap between the moving and stationary blades. Because the pressure on the impeller back 16 is higher than the pressure at the impeller outlet, the pressure-driven gas rapidly flows from the through hole 15 to the impeller channel hub 19 at the impeller channel outlet. When the gas undergoes two-phase non-equilibrium condensation in the impeller channel due to near-isentropic expansion and cooling, droplets are easily deposited in the channel. The through-hole airflow carries the deposited liquid away from the impeller, reducing the possibility of the formation of large liquid clumps and preventing damage to the impeller from impact between the impeller and the liquid clump. It also improves the liquid carryover rate of the two-phase expander.

[0042] In the embodiment of the present invention, the applicable gases of the expander include but are not limited to air, nitrogen, carbon dioxide, and alkane gases such as methane. The number of blades and holes of the expansion wheel is only for illustration and does not limit the invention in any way.

[0043] The adjustment mechanism of the movable sealing disk 10 is as follows Figure 5As shown, the movable sealing disk 10 located behind the two-phase expansion impeller 1 is designed to mate with the impeller back 16 on the side closest to the impeller back 16. Its two sides are connected to the nozzle ring 2 and radial bearing seat 11 via threads. The outer circumference of the movable sealing disk 10 meshes with the pinion 3 via a gear, and its rotation is controlled by the gear adjustment motor 4. Therefore, the gear adjustment motor 4 can drive the movable sealing disk 10 to achieve axial movement. This method can adjust the gap between the two-phase expansion impeller 1 and the movable sealing disk 10, thereby controlling the intake volume of the purge gas.

[0044] Two different wheel back clearance states Figure 6 As shown, when there is no droplet deposition on the hub surface of the expansion impeller, the Figure 6 The small gap adjustment method in (a) can reduce the amount of gas passing through the wheel back and improve the work efficiency of the expander. When there are many droplets deposited on the hub surface of the expansion impeller, it can be used Figure 6 The large gap adjustment method in (b) increases the intake volume of the wheel back purge gas, sacrificing some efficiency to improve the operating stability of the two-phase expander.

[0045] In the specific application process, the shape of the through hole 15 on the two-phase expansion impeller 1 can be in various forms, refer to Figure 3 In (a), (b), (c), and (d), in addition to through-holes of equal diameter, other through-hole types, such as tapered, gradually diverging, or tapered-diverging-gradient, can be selected based on actual needs. The inlet of through-hole 15 is located at the edge of the impeller back, and the outlet is located on the impeller flow channel hub 19 near the expansion impeller outlet 18. The impeller back 16 is generally wedge-shaped. The number of through-holes within a single flow channel of the expansion impeller includes, but is not limited to, one.

[0046] The two-phase expansion impeller 1 can be a semi-open impeller, a closed impeller, an impeller with separation blades or an impeller without separation blades, etc. Figure 4 As shown in (a) and (b).

[0047] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas, characterized in that: The invention comprises an expander housing (7) and a rotor motor (6) arranged in the expander housing (7); a rotating shaft (5) of the rotor motor (6) and bearings (12) arranged at both ends of the expander housing (7) are rotatably fixed; One end of the rotating shaft (5) extends out of the expansion end of the expander housing (7) and is fixed to the two-phase expansion impeller (1), and the other end extends out of the braking end of the expander housing (7) and is fixed to the braking impeller (8); Each impeller flow channel of the two-phase expansion impeller (1) is provided with a through hole (15) extending to the impeller back; the inlet of the through hole (15) is located at the inner slope surface of the impeller back, and the outlet of the through hole (15) is located on the impeller flow channel hub surface near the expansion impeller outlet (18); The two-phase expansion impeller (1) is provided with a movable sealing disk (10) at the impeller back; the outer periphery of the movable sealing disk (10) is provided with a gear disk meshing with a pinion (3); the pinion (3) is connected to the output shaft of a gear adjustment motor (4); the gear adjustment motor (4) drives the pinion (3) to rotate, thereby adjusting the gap between the movable sealing disk (10) and the back of the two-phase expansion impeller (1), and further adjusting the air intake of the through hole (15).

2. The turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas according to claim 1, characterized in that: The through holes (15) are selected to be equal-diameter through holes, gradually shrinking through holes, gradually expanding through holes or gradually shrinking and expanding through holes according to different working conditions. The number of through holes in each impeller flow channel is one or more.

3. The turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas according to claim 1, characterized in that: The impeller wheel back as a whole adopts a groove structure design.

4. The turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas according to claim 1, characterized in that: The two-phase expansion impeller (1) is selected from a semi-open impeller, a closed impeller, an impeller with separation blades, or an impeller without separation blades.

5. The turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas according to claim 1, characterized in that: The outer periphery of the two-phase expansion impeller (1) is provided with a nozzle ring (2), and a gap exists between the expansion impeller inlet (17) of the two-phase expansion impeller (1) and the inner ring of the nozzle ring (2). The outer periphery of the nozzle ring (2) is provided with an expansion end volute (9) fixed to the expander housing (7), and the function of the expansion end volute (9) is to circumferentially intake air and close the expansion end.

6. The turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas according to claim 5, characterized in that: The bearing (12) of the expansion end is fixed to the expander housing (7) through the radial bearing seat (11), and the movable sealing disk (10) is connected to the nozzle ring (2) and the radial bearing seat (11) respectively through threads.

7. The turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas according to claim 1, characterized in that: The movable sealing disc (10) adopts a labyrinth seal and a dry gas seal to ensure that the gas at the expansion end does not leak through the gap between the rotating shafts (5).

8. The turbine expander with adjustable gas-liquid two-phase deposition droplet purge gas according to claim 1, characterized in that: When there is no droplet deposition on the hub surface of the impeller flow channel of the two-phase expansion impeller (1), the back clearance between the movable sealing disk (10) and the two-phase expansion impeller (1) is adjusted to be reduced, so that the amount of gas passing through the impeller back is reduced, thereby improving the work efficiency of the expander; when there is a large amount of droplet deposition on the hub surface of the impeller flow channel of the two-phase expansion impeller (1), the back clearance between the movable sealing disk (10) and the two-phase expansion impeller (1) is adjusted to be increased, thereby increasing the intake amount of the impeller back purge gas and improving the operating stability of the expander.

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