Liquid-cooled rotary compressor and cooling liquid supply method therefor

Abstract

To suppress the lowering of an injection speed of a cooling liquid even if a quantity of the cooling liquid injected into a compressor chamber is reduced.SOLUTION: A liquid cooling type rotating compressor comprises a compressor main body having a compression chamber formed of a fixed wall and a rotating wall for compressing a gas, and a liquid injection path for injecting a cooling liquid into the compression chamber, and adjusts a discharge flow rate by changing a rotational speed of the rotating wall. Also, the compressor comprises a liquid quantity adjustment part for adjusting a quantity of the cooling liquid supplied to the compressor main body from the liquid injection path according to a change of the rotational speed of the rotating wall, and a compressed gas supply path for supplying a compressed gas to a downstream side of the liquid quantity adjustment part in the liquid injection path, and supplies the compressed gas to the liquid injection path from the compressed gas supply path according to the quantity of the cooling liquid which is supplied to the compressor main body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a liquid-cooled rotary compressor and a cooling liquid supply method therefor, which is suitable for, for example, an oil-cooled screw compressor or a water-injection screw compressor. [Background technology]

[0002] A liquid-cooled rotary compressor is a machine that compresses gas, such as air, contained in an internal space (compression chamber) surrounded by a fixed wall such as a casing and a rotating wall such as a rotor using rotational force while narrowing the space, slowly cooling the heat of compression with a liquid (coolant) such as oil or water, and extracting the compressed gas. The cooling liquid for slow cooling is injected from liquid injection nozzles attached to the inner wall of the fixed wall that forms the compression chamber, where it exchanges heat with the compressed gas and the rotating wall, raising its temperature, and is discharged from the compression chamber outlet (discharge port) together with the compressed gas (compressed gas). It is then separated from the compressed gas in a gas-liquid separator such as an oil separator. The separated liquid is cooled by heat exchange in a cooler and returned to the compression chamber, completing a circulation cycle.

[0003] If the coolant is oil (lubricant) and the gas being compressed is air, the amount of heat that needs to be removed by the oil coolant is proportional to the amount of air being compressed. For this reason, if the compressor is operated at a slower speed than rated operation, it is possible to reduce the amount of circulating liquid (amount of circulating oil). If the amount (mass) of liquid supplied to the compression chamber can be reduced, the acceleration work done on the coolant by the rotational force of the compressor can be reduced, which results in reduced power consumption.

[0004] A related known example is that described in Japanese Patent Application Laid-Open No. 8-42476 (Patent Document 1), which describes increasing or decreasing the amount of lubricating oil injected into the working chamber (compression chamber) depending on the rotational speed of the compressor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-42476 Summary of the Invention [Problem to be solved by the invention]

[0006] In the device disclosed in Patent Document 1, the amount of coolant injected into the compression chamber is increased or decreased depending on the rotational speed of the compressor, but reducing the amount of coolant injected into the compression chamber also reduces the injection speed of the injected coolant. If the injection speed of the coolant decreases, the coolant does not sufficiently reach the rotating wall surfaces (e.g., the wall surfaces of the screw rotors) that form the compression chamber, which poses a problem that it becomes impossible to sufficiently lubricate or seal between the rotating wall surfaces (between the rotors) or between the rotating wall surfaces and the fixed wall surfaces, or to sufficiently cool the compressed gas.

[0007] An object of the present invention is to provide a liquid-cooled rotary compressor and a liquid coolant supply method therefor that can suppress a decrease in the injection speed of the liquid coolant even if the amount of liquid coolant injected into the compression chamber is reduced. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a compressor in which a compression chamber is formed by a fixed wall and a rotating wall. and a liquid injection passage for injecting a cooling liquid into the compression chamber, and a liquid-cooled rotary compressor for adjusting a discharge flow rate of compressed gas by supplying the liquid to the pressure vessel through the liquid injection passage; The amount of the cooling liquid supplied to the compressor body is adjusted in accordance with a change in the load factor of the compressor body. a pressure adjusting section for supplying compressed gas to the downstream side of the liquid injection path of the liquid amount adjusting section; a cooling gas supply passage, and the liquid injection passage is configured to supply the cooling liquid to the compressor body in accordance with the amount of the cooling liquid supplied to the compressor body. The compressed gas is supplied to the passage from the compressed gas supply passage. The amount of compressed gas supplied from the compressed gas supply passage to the liquid injection passage increases as the amount of cooling liquid supplied to the compressor body decreases. It is characterized by:

[0009] Another feature of the present invention is a method for supplying coolant to a liquid-cooled rotary compressor in which coolant is injected from a liquid injection passage into a compression chamber of the compressor, the method comprising controlling the amount of coolant supplied to the compressor in accordance with the load factor of the compressor, supplying a portion of the compressed gas discharged from the compressor to the liquid injection passage in accordance with the amount of coolant supplied to the compressor, and controlling the volumetric flow rate of a gas-liquid mixture fluid consisting of the coolant and the compressed gas to be approximately constant regardless of the load factor of the compressor. [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain a liquid-cooled rotary compressor and a liquid coolant supply method therefor, which can suppress a decrease in the injection speed of the liquid coolant even if the amount of liquid coolant injected into the compression chamber is reduced. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a first embodiment of a liquid-cooled rotary compressor of the present invention, and is a system diagram showing the overall configuration. [Figure 2] 2 is a cross-sectional view of a main part of the compressor body in FIG. 1, illustrating a state in which a bubble flow is injected into a compression chamber from an injection port. FIG. [Figure 3] FIG. 2 is a cross-sectional view showing an example in which cheese is used as the gas-liquid mixing section shown in FIG. [Figure 4] FIG. 2 is a cross-sectional view showing an example in which a two-fluid nozzle is used as the gas-liquid mixing section shown in FIG. [Figure 5] 2 is a cross-sectional view showing an example in which a liquid jet ejector is used as the gas-liquid mixing section shown in FIG. 1. [Figure 6] FIG. 2 is a cross-sectional view showing an example in which a perforated plate is used as the gas-liquid mixing section shown in FIG. 1. [Figure 7] FIG. 7 is a perspective view of the perforated plate shown in FIG. 6. [Figure 8] 2 is a pressure-volume curve diagram illustrating the relationship between the change in compression chamber volume and the pressure inside the compression chamber in the compressor body shown in FIG. 1. [Figure 9] This is a schematic time transition diagram of physical quantities that explains the relationship between the change in load factor and the flow rate and heat generation amount of compressed air in the liquid-cooled rotary compressor shown in Figure 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid-cooled rotary compressor according to a preferred embodiment of the present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numerals denote like or corresponding parts. [Example]

[0013] Fig. 1 is a diagram showing a first embodiment of a liquid-cooled rotary compressor of the present invention, and is a system diagram showing the overall configuration, and Fig. 2 is a cross-sectional view of a main part of the compressor body in Fig. 1, and is a diagram explaining the state in which an air bubble flow is injected from an injection port into a compression chamber. In addition, in this embodiment, the liquid-cooled rotary compressor will be described as an oil-cooled screw compressor that compresses air to produce compressed air.

[0014] As shown in FIG. 1, outside air passes through an intake filter 1 and an intake throttle valve 2 and is drawn into the compressor body (compressor) 3 through an intake port 3b provided in the casing (fixed wall) 3a of the compressor body (compressor). A screw rotor (rotor; rotating wall) is provided inside the compressor body 3. The air is drawn into a compression chamber formed by the casing and screw rotor, where it is compressed, and then discharged through a discharge port 3c provided in the casing 3a. The casing 3a is also provided with an injection port 3d for injecting lubricating oil (coolant) into the compression chamber, and cooled lubricating oil is injected into the compression chamber. The lubricating oil injected into the compression chamber is mixed with the compressed air and provides lubrication and seals gaps between the screw rotors and between the screw rotor and the casing 3a inside the compressor body 3. It also absorbs heat from the compressed air and screw rotor, which have become hot due to the heat of compression generated during the compression process, thereby cooling them.

[0015] The mixed fluid of compressed air compressed to a predetermined pressure and lubricating oil injected into the compression chamber is discharged from the discharge port 3c, and this mixed fluid flows into an oil separator (gas-liquid separator) 4 where it is separated into compressed air and lubricating oil. The compressed air from which most of the lubricating oil has been separated passes through a discharge flow path 5 such as a discharge piping and is supplied to the use (destination) of the compressed air.

[0016] The lubricating oil 6 separated by the oil separator 4 enters an oil cooler (liquid cooler) 7 via piping, where it is cooled, passes through an oil filter 8, and then passes through an oil supply piping (liquid injection path) 9 before being injected from the injection port 3d of the compressor body 3 into the compression chambers in the intermediate compression process. That is, the pressure inside the oil separator 4 is almost the same as the discharge pressure, while the pressure in the compression chambers in the intermediate compression process into which the lubricating oil is injected is lower than the discharge pressure, so the lubricating oil is injected into the compression chambers due to the pressure difference. The lubricating oil flows through this circulation path, fulfilling roles such as lubrication, sealing, and cooling of the compressed air within the compressor body 3.

[0017] Reference numeral 10 denotes an electric motor that drives the screw rotor of the compressor main body 3, and 11 denotes an inverter that converts the frequency of power from a commercial AC power source and supplies it to the electric motor 10, and the rotation speed of the compressor is controlled according to the amount of air required by the consumer who requires compressed air. That is, commercial AC power supplied from an external source is converted by the inverter 11 into a frequency and voltage that correspond to the load on the compressor and supplied to the electric motor 10. The compressor main body 3 changes its rotation speed (load factor) to adjust the discharge flow rate and control the discharge pressure to be approximately constant.

[0018] When the demand for air volume increases and the rotation speed of the screw rotor of the compressor body 3 is increased, the amount of air drawn into the compressor body 3 and compressed increases, and therefore more compression heat is generated. Conversely, when the rotation speed decreases, the generation of compression heat also decreases. Therefore, in this embodiment, a flow rate control valve (first flow rate control valve) 12 is provided as a liquid volume control section midway along the oil supply pipe (liquid injection path) 9, and a control device 13 is provided to control this flow rate control valve 12.

[0019] The lubricating oil supplied to the compressor body 3 has cooling, lubricating, and sealing functions. Because the mass of lubricating oil is significantly greater than that of air, it causes agitation loss due to the rotation of the screw rotor. For this reason, it is desirable to minimize the amount of lubricating oil supplied, but it has been found that reducing the amount of lubricating oil supplied causes the following new problems.

[0020] Information on the rotational speed of the compressor is sent from the inverter 11 to the control device 13, and the control device 13 controls the flow rate adjustment valve 12 according to the rotational speed of the compressor to increase or decrease the amount of lubricating oil to the compressor body 3. However, when the amount of lubricating oil is reduced, the mass flow rate Qm kg / s and the volume flow rate Qv m 3 / s also decreases. Therefore, the injection port (injection nozzle) 3d (cross-sectional area A m 2 The injection velocity U m / s of the lubricating oil injected from the nozzle decreases to "Qv / A".

[0021] The injection port 3d is provided on the lower side of the casing 3a, which allows for greater flexibility in handling. As a result, the lubricating oil injected from the injection port 3d into the compression chamber is injected upward against gravity. If the amount of lubricating oil decreases, the injection speed of the lubricating oil injected from the injection port 3d also decreases, which prevents the lubricating oil from reaching the wall surface of the screw rotor that forms the compression chamber, resulting in the problem of not being able to supply enough lubricating oil to the entire compression chamber.

[0022] Furthermore, the injection port 3d is usually composed of multiple injection nozzles, which create a collision jet and supply it to the compression chamber as fine oil droplets. However, if the amount of lubricating oil supplied decreases, when creating a collision jet using multiple injection nozzles, the injection speed of the injected lubricating oil decreases, which creates the problem of not being able to obtain sufficient droplet characteristics, i.e., sufficiently fine droplets.

[0023] In order to solve these problems, in the present invention, compressed gas is supplied to the oil supply pipe (liquid injection path) 9 according to the amount of lubricating oil (coolant) supplied to the compressor main body 3, and the volumetric flow rate of the gas-liquid mixed fluid, which is a combination of lubricating oil and compressed gas supplied to the compressor main body 3, is controlled to be approximately constant regardless of the compressor rotation speed and is supplied to the compressor main body 3.

[0024] 1, a gas-liquid mixing section 14 is provided downstream of a flow rate control valve 12 in the oil supply pipe 9, and a compressed gas supply path (return air pipe) 15 that introduces a portion of the compressed gas separated in the oil separator 4 is connected to this gas-liquid mixing section 14. In addition, a flow rate control valve (second flow rate control valve) 16 is provided in the compressed gas supply path 15, and the flow rate control valve 16 is controlled by the control device 13 so that the amount of compressed gas supplied from the compressed gas supply path 15 to the oil supply pipe 9 increases as the amount of lubricating oil (coolant) supplied to the compressor body 3 decreases.

[0025] That is, in this embodiment, compressed gas is supplied to the oil supply pipe 9 at a volumetric flow rate approximately equal to the changing volumetric flow rate of the lubricating oil supplied to the compressor main body 3 in accordance with the amount of change in the volumetric flow rate of the lubricating oil, and is supplied to the compressor main body 3 so that the volumetric flow rate of the gas-liquid mixed flow (gas bubble flow) combining the lubricating oil and compressed gas downstream of the gas-liquid mixing section 14 is kept approximately constant.

[0026] In addition, in this embodiment, a flow rate detector (flow meter) 17 for detecting a volumetric flow rate is provided downstream of the gas-liquid mixing section 14, and the control device 13 controls the flow rate control valve 12 provided in the oil supply pipe 9 and the flow rate control valve 16 provided in the compressed gas supply path 15 based on the value of the volumetric flow rate detected by the flow rate detector 17.

[0027] That is, the control device 13 controls the flow rate adjustment valve 12 of the oil supply pipe 9 to adjust the amount of lubricating oil supplied to the compressor in accordance with changes in the rotational speed of the screw rotor of the compressor main body (compressor) 3. At this time, the control device 13 controls the flow rate adjustment valve 12 based on the value detected by the flow rate detector 17 so that a predetermined amount of lubricating oil is supplied in accordance with the rotational speed. The control device 13 also controls the flow rate adjustment valve 16 of the compressed gas supply path 15 in accordance with the amount of lubricating oil supplied to the compressor, and supplies the lubricating oil to the compressor main body 3 so that the volumetric flow rate of the gas-liquid mixed flow of lubricating oil and compressed gas downstream of the gas-liquid mixing section 14 remains approximately constant regardless of changes in the amount of lubricating oil.

[0028] Specifically, by supplying compressed gas to the oil supply pipe 9 at a volumetric flow rate approximately equal to the changing volumetric flow rate of the lubricating oil, the volumetric flow rate of the gas-liquid mixture flow supplied to the compressor is controlled so as not to change even if the rotation speed changes and the amount of lubricating oil supplied to the compressor decreases. In the above-described embodiment, the load factor is changed by changing the rotation speed of the electric motor. However, as a means for changing the load factor, for example, the electric motor may be set to a constant speed and the intake air amount may be adjusted by the intake throttle valve 2.

[0029] Figure 2 shows a main part of the compressor body 3, illustrating the state in which a bubble flow is injected into a compression chamber 3e from an injection port 3d formed on the inner surface of a casing (fixed wall) 3a. As shown in Figure 2, the casing 3a of the compressor body 3 is provided with an injection port 3d, and a coolant flow path 3f is formed inside the casing 3a to guide lubricating oil supplied from an oil supply pipe 9 (see Figure 1) to the injection port 3d. A bubble flow (gas-liquid mixed flow) 20 generated in a gas-liquid mixing section 14 is supplied to the coolant flow path 3f. The bubble flow 20 is composed of oil and bubbles 21, and is sprayed as oil droplets 22 from the injection port 3d provided in the casing 3a into the compression chamber 3e.

[0030] The injection ports 3d are usually provided in multiple locations (for example, multiple locations along the screw groove direction or axial direction of the screw rotor), and each injection port 3d is composed of two injection nozzles 3d1, 3d2 that communicate with the compression chamber 3e and face each other. The lubricating oil injected from two directions by these two injection nozzles 3d1, 3d2 collides, causing it to disperse into the compression chamber 3e as finer oil droplets (liquid droplets). These oil droplets 22 reach the wall surface of the screw rotor (rotating wall) 3g of the compression chamber 3e and form an oil film 23, or scatter throughout the compression chamber, removing heat from the compressed air and the screw rotor 3g, thereby cooling them.

[0031] The coolant flow path 3f and the injection port 3d are generally provided on the lower side of the casing 3a, which allows for greater flexibility in installation, and the lubricating oil supplied to the coolant flow path 3f and injected into the compression chamber 3e from the injection port 3d is injected upward against gravity. If the amount of lubricating oil supplied to the coolant flow path 3f decreases, the injection speed of the lubricating oil injected from the injection port 3d also decreases. However, in this embodiment, even if the amount of lubricating oil decreases, the lubricating oil is supplied to the compressor as a bubble flow mixed with compressed air so that the volumetric flow rate does not decrease.

[0032] Therefore, a decrease in the injection speed of the lubricating oil injected from the injection port 3d can be suppressed, and the lubricating oil can be sufficiently delivered to the wall surface of the screw rotor 3g that defines the compression chamber 3e, thereby ensuring that the lubricating oil is sufficiently supplied to the entire compression chamber 3e, ensuring reliable lubrication and sealing between the rotors and between the rotor and the casing. Furthermore, since the injection speed of the lubricating oil injected from the injection port 3d can be maintained, sufficient droplet characteristics, that is, sufficiently fine droplets can be obtained by the collision jets from the multiple injection nozzles 3d1, 3d2.

[0033] As described above, according to this embodiment, even if the oil flow rate is changed according to the required cooling capacity in accordance with the rotation speed of the compressor, the volumetric flow rate of the bubble flow 20 can be kept constant, so the injection speed of the oil injected from the injection port 3d can be maintained constant, and the oil droplets 22 can be made to have the designed particle size and can reach a sufficient distance, so that the required cooling capacity can be secured while maintaining good sealing and lubrication between the rotors and between the rotor and the casing. Furthermore, by using the bubble flow 20, the mass (amount of oil) of oil entering the compression chamber 3e can be reduced while securing the volumetric flow rate, which can reduce oil churning loss and reduce power consumption.

[0034] Note that, during startup of the compressor, the pressure in the oil separator 4 may become lower than the pressure in the compression chamber 3e, causing the pressure in the lubricating oil circulation path to become unstable. In such cases, to prevent the gas and lubricating oil in the compression chamber 3e from flowing back into the oil supply pipe 9 or the compressed gas supply path 15, in this embodiment, as shown in FIG. 1, check valves 18 and 19 are provided between the first flow control valve 12 and the gas-liquid mixing section 14, and between the second flow control valve 16 and the gas-liquid mixing section 14, respectively. By providing the check valves 19 in this manner, not only can backflow from the compression chamber 3e be prevented, but also backflow from the oil supply pipe 9 to the compressed gas supply path 15 and from the compressed gas supply path 15 to the flow control valve 12 side of the oil supply pipe 9 can be prevented.

[0035] Next, the operation of the oil-cooled compressor of this embodiment will be described. The mixed fluid of compressed air and lubricating oil discharged from the compressor body 3 flows into the oil separator 4, where it is separated into compressed air and lubricating oil (oil). The separated compressed air is supplied to the demand destination, but since the separated oil is hot due to the heat of compression, it is cooled in the oil cooler 7, passes through the oil filter 8 and is led to the flow control valve 12.

[0036] The rotation speed of the electric motor 10 is output as an electric signal from the inverter 11 to the control device 13. The relationship between the rotation speed and the appropriate amount of oil supplied to the compressor body 3 is preset in the control device 13, and the control device 13 controls the opening of the flow rate control valve 12 in accordance with this relationship.

[0037] In particular, compressors with large diameter rotors (rotating walls) consume a lot of power, so by reducing the amount of oil supplied as the compressor rotation speed decreases, it is possible to reduce the loss of lubricating oil by churning, which has a significant effect in reducing power consumption. Therefore, the control device 13 controls the flow rate adjustment valve 12 so as to reduce the amount of oil supplied as the compressor rotation speed decreases, and conversely, controls the flow rate adjustment valve 12 so as to increase the amount of oil supplied as the rotation speed increases.

[0038] In addition, in this embodiment, the flow rate control valve 16 of the compressed gas supply path 15 is also controlled in accordance with or simultaneously with the control of the flow rate control valve 12, so as to maintain a constant volumetric flow rate of the bubble flow (gas-liquid mixed flow) supplied from the gas-liquid mixing section 14 to the coolant flow path 3f.

[0039] After cooling the compressed air and other materials inside the compressor body 3, the oil and air bubble flow is again separated into air and oil in the oil separator 4. Therefore, oil from which the air bubbles have been removed flows into the flow path of the oil cooler 7, and there is no reduction in heat transfer performance due to the inclusion of air bubbles. Furthermore, the power for operating the flow rate adjusting valves 12 and 16 and the flow rate detector 17 is supplied from the inverter 11, for example.

[0040] The gas-liquid mixing section 14 is provided in the oil supply pipe 9 between the oil filter 8 and the compressor body 3, and is a three-port gas-liquid mixing section having at least two inlets and one outlet. The flow rate detector 17 is provided on the outlet side (compressor body 3 side) of the gas-liquid mixing section 14, and the flow rate adjustment valve 12 is arranged in the oil supply pipe 9 on the first inlet side (oil filter 8 side) of the gas-liquid mixing section 14. The flow rate adjustment valve 16 is provided on the second inlet side (compressed gas supply passage 15 side) of the gas-liquid mixing section 14.

[0041] When the flow control valve 16 on the compressed gas side is opened while the oil is circulating, the oil and air are mixed in the gas-liquid mixing section 14, and a bubbly flow (gas-liquid mixed flow) is formed at the outlet of the gas-liquid mixing section 14. The flow detector 17 and the two flow control valves 12, 16 are connected to the control device 13, and the output of the flow detector 17 can be monitored from the control device 13, and the opening of the two flow control valves 12, 16 can be adjusted to adjust the volumetric flow rate of the bubbly flow to any or a predetermined flow rate.

[0042] In this embodiment, check valves 18 and 19 are provided, so that even if the pressure in the gas-liquid mixing section 14 is higher than the pressure on the flow rate adjustment valves 12 and 16 side, backflow to the flow rate adjustment valves 12 and 16 side can be prevented. It is also possible to use a pressure gauge and a pressure control valve instead of the flow rate control valves 12 and 16, and to control the flow rate while controlling the differential pressure.

[0043] Specific examples of the gas-liquid mixer 14 will be described below with reference to FIGS. 3 is a cross-sectional view showing an example in which a tee 14A, a T-shaped piping component consisting of three ports, is used as gas-liquid mixing section 14. Reference numeral 24 denotes lubricating oil supplied from oil supply piping 9 to a first inlet of tee 14A, and reference numeral 25 denotes compressed air supplied from compressed gas supply path 15 to a second inlet of tee 14A. The lubricating oil and compressed air are mixed in tee 14A to form air bubble flow 20, which is supplied from the outlet of tee 14A to compressor main body 3.

[0044] Using the tee 14A allows for an inexpensive configuration, but there is a possibility that the bubble flow 20 may become non-uniform. For this reason, if a submerged injection nozzle is provided on the compressed air injection side, fine bubbles can be generated.

[0045] 4 is a cross-sectional view showing an example in which a three-port bi-fluid nozzle (gas-liquid mixer) 14B is used as the gas-liquid mixing section 14. Reference numeral 24 denotes lubricating oil supplied to a first inlet of the bi-fluid nozzle 14B from the oil supply pipe 9, and reference numeral 25 denotes compressed air supplied to a second inlet of the bi-fluid nozzle 14B from the compressed gas supply path 15. The lubricating oil and compressed air are mixed within the bi-fluid nozzle 14B to form a bubbly flow 20, which is supplied to the compressor main body 3 side from the outlet of the bi-fluid nozzle 14B. The two-fluid nozzle 14B is generally used to generate a spray of a small amount of liquid with a large amount of high-pressure gas, but by adjusting the amounts of oil and air, it is also possible to generate a bubbly flow with a large amount of liquid.

[0046] 5 is a cross-sectional view showing an example in which a three-port liquid injection ejector 14C is used as the gas-liquid mixer 14. Reference numeral 24 denotes lubricating oil supplied from the oil supply pipe 9 to a first inlet of the liquid injection ejector 14C, and reference numeral 25 denotes compressed air supplied from the compressed gas supply path 15 to a second inlet of the liquid injection ejector 14C. The lubricating oil and compressed air are mixed inside the liquid injection ejector 14C to generate a bubble flow 20, which is supplied from the outlet of the liquid injection ejector 14C to the compressor main body 3 side.

[0047] The liquid jet ejector 14C is widely used as a gas-liquid disperser in a bubble column used in chemical reactions, has good bubble dispersibility, and the relationship between gas holdup in the liquid and the gas-liquid flow rate has been clarified, so it can fully demonstrate the function of the gas-liquid mixer 14. However, there is a possibility that the pressure loss will increase.

[0048] An example in which the gas-liquid mixing section 14 is configured using a perforated plate (perforated wall) will be described with reference to Figures 6 and 7. Figure 6 is a cross-sectional view of the gas-liquid mixing section 14, and Figure 7 is a perspective view of the perforated plate 26 shown in Figure 6. In this example, a perforated plate 26 having a large number of holes 26a is provided between the gas and liquid, i.e., between the lubricating oil 24 flowing in the oil supply pipe 9 and the compressed air 25 flowing in the compressed gas supply path 15 connected to the gas-liquid mixing section 14 provided in the oil supply pipe 9, and the lubricating oil and compressed air are mixed through this perforated plate 26 to generate the bubbly flow 20. A sealing material 27 such as an O-ring is provided on the outer periphery of the perforated plate 26 provided at the connection between the lubricating oil and the compressed air to seal so that the compressed gas and lubricating oil do not leak to the outside.

[0049] In this example, the gas is turned into bubbles by the perforated plate 26 and mixed into the lubricating oil, making it easy to generate the bubbly flow 20, but if the diameter of the holes 26a formed in the perforated plate 26 is small, there is a possibility that pressure loss will increase. The perforated plate 26 may be made of a punched metal as shown in FIG. 7, or a sintered metal or a porous metal.

[0050] Figure 8 is a pressure-volume curve diagram that explains the relationship between the change in compression chamber volume and the pressure inside the compression chamber in the compressor body 3 shown in Figure 1, with the horizontal axis representing the compression chamber volume and the vertical axis representing the compression chamber pressure. Here, an example will be explained in which the liquid-cooled rotary compressor is an oil-cooled screw compressor.

[0051] Rotary compressors, such as screw compressors, operate in the order of A, B, C, and D shown in the diagram. Air that passes through the suction throttle valve 2 in Figure 1 begins to be sucked into the compressor body 3 when the compression chamber inlet opens (A). The pressure at this time is suction pressure Ps. As the screw rotor (rotor) rotates, its volume expands. When it reaches its maximum volume, the compression chamber inlet closes, completing suction and starting compression (B). As the rotor continues to rotate, the volume of the compression chamber decreases, and compression progresses. As the pressure increases, heat is generated. To cool the compressed air, lubricating oil is injected into the compression chamber through nozzle 3d, absorbing the compression heat. When the compression chamber opens to the discharge port, compression is complete and discharge begins (C). The pressure at this time is discharge pressure Pd. The compressed air, compressed to pressure Pd, is discharged from the discharge port along with the lubricating oil as the rotor rotates, completing discharge at position D. Steps A through D are then repeated as the rotor continues to rotate. A to B is the suction process, B to C is the compression process, and C to D is the discharge process.

[0052] To cool the compressed air that has been pressurized and heated during the compression process, lubricating oil is injected into the compression chamber from injection port 3d. In the example shown in FIG. 8, section E is the lubricating oil injection section. The pressure in this injection section is P1-P2, which is lower than the discharge pressure Pd. Since the pressure inside oil separator 4 is Pd, this pressure difference allows lubricating oil to be injected into the compression chamber. Note that a pressure higher than compression chamber pressure P2 is required to inject the lubricating oil, and the flow control valves 12 and 16 are controlled by control device 13 in FIG. 1 to control the amount of oil injected. It is more preferable to further install a pressure gauge downstream of flow detector 17 shown in FIG. 1, and configure the control device to read the pressure value and perform feedback control.

[0053] Fig. 9 is a schematic time transition diagram of physical quantities that explains the relationship between the change in load factor (rotation speed) and the flow rate and heat generation amount of compressed air in the liquid-cooled rotary compressor shown in Fig. 1. In this embodiment, a portion of the compressed air after oil separation in the oil separator 4 is supplied to the gas-liquid mixing section 14 of the oil supply pipe 9, and this air is called return air.

[0054] The horizontal axis of each graph (time progression diagram) (a) to (j) represents elapsed time, and the vertical axis represents each physical quantity. Graph (a) shows the situation in which the compressor is driven and the rotor begins to rotate, and after the rotation speed reaches the rated speed, it gradually decreases, then increases and returns to the rated speed. The amount of compressed air and heat generation in graph (b) are proportional to the increase or decrease in the rotation speed in (a). The same is true for the required flow rate of lubricating oil (coolant) in graph (c).

[0055] Here, the flow rate of the lubricating oil also increases or decreases in proportion to the increase or decrease in the rotation speed, but as shown in graph (d), if return air is supplied to the lubricating oil at a volumetric flow rate roughly equal to the decrease in the lubricating oil, the total volumetric flow rate of the generated air bubble flow can be kept constant, as shown in graph (e). This allows the injection speed of the oil droplets (liquid droplets) to be kept constant regardless of the increase or decrease in the rotation speed, as shown in graph (f).

[0056] As shown in graphs (g) and (h), the mass flow rate of the lubricating oil injected into the compression chamber increases or decreases in proportion to the rotational speed, while the mass flow rate of the injected return air (compressed air) increases or decreases in inverse proportion. However, because the density of air is approximately 1 / 100 of that of oil, the effect of the increase in the mass flow rate of air is small, and the mass flow rate of the air bubble flow can be considered approximately the same as the mass flow rate of oil, as shown in graph (i). Therefore, in this embodiment, while maintaining the injection speed of the oil droplets (liquid droplets), it is possible to make the churning loss of the oil proportional to the increase or decrease in the rotational speed, as shown in graph (j). In the example of Figure 9, the rotation speed is changed in a stepwise manner, but similar control is possible if it is changed in a curved manner. However, it is necessary to take into consideration the time lag between the rotation speed and the flow rate when controlling.

[0057] As explained above, according to this embodiment, when the compressor rotation speed decreases, the opening of flow control valve 12 is reduced to reduce the volumetric flow rate of lubricating oil (coolant), and the opening of flow control valve 16 is increased to add compressed air to the lubricating oil at a volumetric flow rate approximately equal to the reduced volumetric flow rate of lubricating oil, making it possible to maintain a constant volumetric flow rate of the gas-liquid mixed flow (air bubble flow) supplied to the compressor. Therefore, the injection speed of the oil droplets injected from the injection port into the compression chamber can be maintained at a required value, allowing for sufficient lubrication and sealing between the rotors and between the rotor and casing.

[0058] On the other hand, since the gas-liquid mixture contains low-density compressed air, the mass flow rate can be reduced while maintaining the volume flow rate. This reduces the lubricating oil churning loss, thereby reducing power consumption. Furthermore, since the mass flow rate of the lubricating oil can be reduced, the cooling capacity of the oil cooler that cools the lubricating oil can also be reduced, and power consumption can be reduced by, for example, slowing down the cooling fan speed.

[0059] Furthermore, when the coolant is a lubricating oil containing carbon, by mixing it with compressed gas and injecting the resulting gas-liquid mixed flow into the compression chamber even during rated operation, the injection speed can be maintained even when the amount of lubricating oil is reduced, making it possible to minimize the amount of lubricating oil used, which contributes to decarbonization and environmental conservation.

[0060] The present invention is particularly suitable for an oil-cooled screw compressor in which the compressor body 3 includes a casing 3a and a pair of male and female screw rotors (screw-shaped rotors) 3g rotatably arranged within the casing 3a, the space surrounded by the screw rotor 3g and the casing 3a forms a compression chamber 3e, and the volume of the compression chamber 3e decreases as the screw rotor 3g rotates, thereby compressing air.

[0061] However, the present invention is not limited to the above-described embodiment and includes various modifications. For example, the present invention can be similarly applied to a water-injection screw compressor that injects water instead of oil. Furthermore, the compressor body is not limited to a screw compressor; the compressor body 3 can also be a scroll compressor, and the present invention can be similarly applied to any rotary compressor that injects liquid into the compression chamber. Furthermore, the above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the configurations described. [Explanation of symbols]

[0062] 1: intake filter, 2: intake throttle valve, 3: compressor body, 3a: casing (fixed wall), 3b: Suction port, 3c: Discharge port, 3d: Injection port, 3d1,3d2: Injection nozzle, 3e: compression chamber, 3f: coolant flow path, 3g: screw rotor (rotor; rotating wall), 4: Oil separator (gas-liquid separator), 5: Discharge flow path, 6: Lubricating oil, 7: Oil cooler (liquid cooler), 8: Oil filter, 9: Oil supply pipe (liquid injection path), 10: motor, 11: inverter, 12, 16: flow rate adjusting valve (12: first flow rate adjusting valve, 16: second flow rate adjusting valve), 13: control device, 14: gas-liquid mixing unit, 14A: Cheese, 14B: Two-fluid nozzle, 14C: Liquid injection ejector, 15: Compressed gas supply line (return air piping), 17: Flow detector (flow meter), 18, 19: check valves (18: first check valve, 19: second check valve), 20: bubbly flow (gas-liquid mixed flow), 21: bubbles, 22: oil droplets (liquid droplets), 23: oil film, 24: Lubricating oil (coolant), 25: Compressed air, 26: Perforated plate, 26a: Hole.

Claims

1. A liquid-cooled rotary compressor comprising: a compressor body that forms a compression chamber by a fixed wall and a rotating wall; and a liquid injection path that injects a cooling liquid into the compression chamber; and the discharge flow rate is adjusted by changing the load factor of the compressor body, a liquid amount adjusting unit that adjusts the amount of the cooling liquid supplied from the liquid injection passage to the compressor body in accordance with a change in a load factor of the compressor body; a compressed gas supply passage for supplying compressed gas to a downstream side of the liquid amount adjusting section in the liquid injection passage; supplying compressed gas from the compressed gas supply passage to the liquid injection passage in accordance with the amount of the cooling liquid supplied to the compressor body; A liquid-cooled rotary compressor, characterized in that the amount of compressed gas supplied from the compressed gas supply passage to the liquid injection passage increases as the amount of cooling liquid supplied to the compressor body decreases.

2. 2. The liquid-cooled rotary compressor according to claim 1, a liquid-cooled rotary compressor, characterized in that compressed gas is supplied to the liquid injection path at a volumetric flow rate substantially equal to the volumetric flow rate of the cooling liquid that changes in accordance with a change in the volumetric flow rate of the cooling liquid supplied to the compressor body, and a gas-liquid mixed fluid, which is a combination of the cooling liquid and the compressed gas, is supplied to the compressor body at a substantially constant volumetric flow rate.

3. 2. The liquid-cooled rotary compressor according to claim 1, the fixed wall is a casing of a rotary compressor, and the rotating wall is a rotor of the rotary compressor; The casing is provided with an intake port for sucking in gas, an outlet port for discharging compressed gas, and an injection port for injecting liquid into the compression chamber, The liquid injection path is connected to the injection port, the liquid injection path is provided with a first flow rate adjustment valve as the liquid amount adjustment unit, and a gas-liquid mixing unit provided downstream of the flow rate adjustment valve; the compressed gas supply path is connected to the gas-liquid mixing section, A liquid-cooled rotary compressor, characterized in that a second flow rate adjustment valve is provided in the compressed gas supply passage.

4. The liquid-cooled rotary compressor according to claim 3, a gas-liquid separator that separates gas and liquid from the mixed fluid of compressed gas and cooling liquid discharged from the discharge port, and a liquid cooler that cools the liquid separated by the gas-liquid separator, the liquid injection path constitutes a coolant circulation path that supplies the coolant cooled by the liquid cooler to the injection port, a compressed gas supply passage for supplying a part of the compressed gas separated in the gas-liquid separator to the gas-liquid mixing section;

5. 5. The liquid-cooled rotary compressor according to claim 4, a control device that controls a first flow rate adjustment valve provided in the liquid injection path and a second flow rate adjustment valve provided in the compressed gas supply path; the control device controls a first flow control valve in the liquid injection path to adjust the amount of liquid supplied to the compressor body in accordance with a change in the rotational speed of the rotor, and controls a second flow control valve in the compressed gas supply path in accordance with the amount of liquid supplied to the compressor body.

6. The liquid-cooled rotary compressor according to claim 5, a flow rate detector for detecting a volumetric flow rate is provided downstream of the gas-liquid mixing section in the liquid injection path; the control device controls the first flow control valve provided in the liquid injection path and the second flow control valve provided in the compressed gas supply path based on the volumetric flow rate detected by the flow detector.

7. The liquid-cooled rotary compressor according to claim 3, The liquid-cooled rotary compressor is characterized in that the gas-liquid mixing section mixes liquid from the liquid injection passage and gas from the compressed gas supply passage to generate a bubbly flow.

8. The liquid-cooled rotary compressor according to claim 7, A liquid-cooled rotary compressor, characterized in that the gas-liquid mixing section is configured using any one of a cheese, a two-fluid nozzle, a liquid injection ejector, or a perforated plate.

9. 5. The liquid-cooled rotary compressor according to claim 4, The liquid-cooled rotary compressor is an oil-cooled screw compressor, wherein the rotor is a screw rotor, the gas compressed in the compression chamber is air, and the liquid injected into the compression chamber is lubricating oil.

10. 5. The liquid-cooled rotary compressor according to claim 4, a first check valve is provided in the liquid injection path between the gas-liquid mixing section and the first flow rate adjustment valve to prevent backflow from the gas-liquid mixing section toward the first flow rate adjustment valve; a second check valve that prevents backflow from the gas-liquid mixing section toward the second flow control valve is provided in the compressed gas supply path between the gas-liquid mixing section and the second flow control valve.

11. A method for supplying coolant to a liquid-cooled rotary compressor, in which coolant is injected from a liquid injection passage into a compression chamber of the compressor, comprising: controlling the amount of the cooling liquid supplied to the compressor in accordance with a load factor of the compressor; supplying compressed gas to the liquid injection passage in accordance with the amount of the cooling liquid supplied to the compressor; a volumetric flow rate of a gas-liquid mixture fluid obtained by combining the cooling liquid and the compressed gas to be controlled to be approximately constant regardless of a load factor of the compressor, and the volumetric flow rate of the gas-liquid mixture fluid is supplied to the compressor.

12. 12. A method for supplying a cooling liquid to a liquid-cooled rotary compressor according to claim 11, comprising: A method for supplying a cooling liquid to a liquid-cooled rotary compressor, characterized in that the compressed gas supplied to the liquid injection passage is a portion of the compressed gas discharged from the compressor.

13. 13. A method for supplying a cooling liquid to a liquid-cooled rotary compressor according to claim 12, comprising: a liquid-cooled rotary compressor, characterized in that compressed gas is supplied to the liquid injection path at a volumetric flow rate substantially equal to the volumetric flow rate of the cooling liquid that changes depending on the amount of change in the volumetric flow rate of the cooling liquid supplied to the compressor, and the volumetric flow rate of a gas-liquid mixed fluid consisting of the cooling liquid and the compressed gas is kept substantially constant and supplied to the compressor.

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