Liquid injection device, oil-free wet screw compressor and liquid injection method

Abstract

The application discloses a liquid injection device, an oil-free wet screw compressor and a liquid injection method. The liquid injection device comprises a liquid injection nipple, at least four gas-liquid mixing pipes, a gas pre-distribution pipe and a liquid pre-distribution pipe. The bottom of the liquid injection nipple is used for connecting an inlet pipeline of the oil-free wet screw compressor, and the liquid injection nipple is provided with a central through hole extending in the axial direction. The gas pre-distribution pipe is provided with a gas inlet, and the liquid pre-distribution pipe is provided with a liquid inlet. The at least four gas-liquid mixing pipes are uniformly arranged along the circumferential direction of the liquid injection nipple. The gas inlets of the gas-liquid mixing pipes are communicated with the gas pre-distribution pipe, the liquid inlets of the gas-liquid mixing pipes are communicated with the liquid pre-distribution pipe, the gas-liquid mixing outlets of the gas-liquid mixing pipes are connected with the outer circumferential surface of the liquid injection nipple, and the gas-liquid mixing outlets penetrate the wall of the central through hole of the liquid injection nipple. The application can generate uniform and small liquid droplets, and significantly improves the gas-liquid heat transfer efficiency.

Description

Technical Field

[0001] This invention relates to screw compressor technology, and more particularly to liquid injection technology for oil-free wet screw compressors. Background Technology

[0002] Oil-free wet screw compressors are widely used in industries such as petrochemicals, coal chemicals, steel, and chlor-alkali chemicals. They exhibit excellent adaptability for compressing and transporting process gases that are dusty, liquid-laden, easily polymerizable, flammable, or explosive, such as coke oven gas, flare gas, butadiene, styrene tail gas, and acetylene. An oil-free wet screw compressor has a pair of male and female rotors and a pair of synchronous gears. Gaps exist between the rotors and between the rotors and the inner wall of the casing. The synchronous gears drive the rotors to rotate, achieving the purpose of gas compression. During compression, the gas temperature rises rapidly. To achieve a certain outlet pressure while preventing rotor expansion and deformation due to excessively high outlet temperature, liquid is injected at the compressor inlet for cooling. The injected liquid must not react with the compressed gas. The liquid injected into the compressor cavity cools the high-temperature gas and, for easily polymerizable gases, washes away polymers adhering to the rotor. Simultaneously, the liquid forms a liquid film in the rotor gaps, providing excellent sealing and noise reduction, reducing leakage within the compressor cavity, and significantly improving the compressor's volumetric efficiency.

[0003] During the liquid injection heat absorption process, the cooling effect per unit volume of sprayed water can be divided into two stages: the first stage is the latent heat of vaporization heat absorption stage, and the second stage is the mass transfer heat absorption stage. Studies have shown that the cooling effect per unit volume of sprayed water generated by the latent heat of vaporization is significantly higher than the cooling effect of the gas-liquid mass transfer heat absorption stage. Therefore, in the first stage, the sprayed water volume should be increased as much as possible, the droplet size should be reduced, and the uniformity of the sprayed liquid should be improved to accelerate the vaporization of the sprayed liquid and remove more heat in the first stage. In the second stage, the sprayed water volume only needs to meet the exhaust temperature. Since the temperature difference between the sprayed liquid temperature and the exhaust temperature decreases in the second stage, a larger sprayed water volume is required per unit temperature decrease, resulting in a non-linear relationship. Excessive spraying will consume compression work and increase the load on the downstream gas-liquid separator, thus deteriorating the gas-liquid separation effect.

[0004] Heat exchange between gas and liquid relies on the liquid temperature and the gas-liquid contact area. When the temperature of the injected liquid is constant, reducing the droplet diameter can effectively increase the droplet's specific surface area and improve heat exchange efficiency. Studies have shown that reducing the droplet diameter from 2 mm to 0.1 mm can improve the compressor's adiabatic efficiency by more than 5%. Therefore, reducing the diameter of the inlet spray droplets in oil-free wet screw compressors and increasing the uniformity of the spray is crucial for improving compressor performance.

[0005] Currently, the liquid injection method for oil-free wet screw compressors in engineering applications mostly adopts the traditional pipe wall perforation method. This method involves extending the injection pipe into the compressor inlet, sealing the end of the pipe, and uniformly perforating the pipe wall. The size and number of perforations depend on the required injection volume. In some large units, due to the large injection volume, even coarse injection through the pipe is used. The advantages of these traditional methods are simple structure and low manufacturing cost. However, the pipe wall perforation injection method results in insufficient gas-liquid contact area due to the liquid being ejected in a stream, leading to limited cooling effect. Furthermore, this method is only suitable for smaller compressor models. When the injection volume of large units exceeds a certain limit, high pressure drop in the injection pipe, a large stream, or even failure to meet the injection volume requirements occur. In this case, more coolant needs to be injected to maintain the required outlet exhaust temperature, resulting in increased compressor power consumption and overload of the downstream gas-liquid separator. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a liquid injection device for an oil-free wet screw compressor, as well as an oil-free wet screw compressor and a liquid injection method, which can generate uniform and fine liquid droplets, significantly improve the gas-liquid heat transfer efficiency, and enhance the cooling effect of compressed gas.

[0007] This invention provides a liquid injection device for an oil-free wet screw compressor, comprising a liquid injection section, at least four gas-liquid mixing pipes, a gas pre-distribution pipe, and a liquid pre-distribution pipe. The bottom of the liquid injection section is used to connect to the inlet pipe of the oil-free wet screw compressor, and the liquid injection section has a central through hole extending axially. The gas pre-distribution pipe has a gas inlet, and the liquid pre-distribution pipe has a liquid inlet. The at least four gas-liquid mixing pipes are evenly arranged along the circumferential direction of the liquid injection section. The gas inlet of each gas-liquid mixing pipe is connected to the gas pre-distribution pipe, the liquid inlet of each gas-liquid mixing pipe is connected to the liquid pre-distribution pipe, and the gas-liquid mixture outlet of each gas-liquid mixing pipe is connected to the outer peripheral surface of the liquid injection section and penetrates the wall of the central through hole of the liquid injection section.

[0008] The present invention also provides an oil-free wet screw compressor having an inlet pipe, the oil-free wet screw compressor including the aforementioned liquid injection device, the bottom of the liquid injection section of the liquid injection device being connected to the inlet pipe.

[0009] The present invention also provides a liquid injection method for a liquid injection device of an oil-free wet screw compressor, which includes the following steps:

[0010] The spray medium is introduced into the liquid pre-distribution pipe, and after pre-distribution, it enters the liquid inlet of each gas-liquid mixing jet pipe.

[0011] Gas with a pressure of 0.3 MPa to 2 MPa is introduced into the gas pre-distribution pipe and then pre-distributed into the gas inlet of each gas-liquid mixing pipe.

[0012] The kinetic energy of the gas entering the gas-liquid mixing tube is used to break up the sprayed liquid into uniformly distributed tiny droplets, which are then ejected from the gas-liquid mixture outlet of the gas-liquid mixing tube.

[0013] The present invention has at least the following advantages:

[0014] This invention injects liquid and pressurized gas simultaneously into a gas mixing tube. The kinetic energy of the pressurized gas shears the liquid, forming uniformly distributed fine droplets. This accelerates the vaporization rate and mass transfer of the droplets in the high-temperature gas, improves the heat transfer rate, reduces the amount of liquid used, lowers the power consumption of the compressor, and reduces the operating load of the back-end cooler and gas-liquid separator of the oil-free wet screw compressor system. Attached Figure Description

[0015] Figure 1 and Figure 2 Schematic diagrams of a liquid spraying device according to an embodiment of the present invention are shown from different angles.

[0016] Figure 3 A cross-sectional schematic diagram of a gas-liquid mixing tube according to an embodiment of the present invention is shown.

[0017] Figure 4 A schematic diagram of the arrangement of a gas-liquid mixing tube according to an embodiment of the present invention is shown.

[0018] Figure 5 and Figure 6 Two different outlet shapes of the gas-liquid mixing nozzle according to embodiments of the present invention are shown.

[0019] Figure 7 A schematic diagram of the installation of a liquid spraying device and an oil-free wet screw compressor according to an embodiment of the present invention is shown. Detailed Implementation

[0020] The invention will now be further described with reference to the accompanying drawings.

[0021] Please refer to Figures 1 to 3 According to an embodiment of the present invention, the liquid injection device 100 of the oil-free wet screw compressor includes a liquid injection section 1, at least four gas-liquid mixing pipes 2, a gas pre-distribution pipe 3, and a liquid pre-distribution pipe 4.

[0022] The bottom of the liquid injection short section 1 is used to connect to the inlet pipe of the oil-free wet screw compressor. The liquid injection short section 1 has a central through hole 10 extending axially. Depending on the size of the inlet pipe and the compressor inlet size, the liquid injection short section 1 can be a cylindrical short section or a reducing short section. In this embodiment, the height of the liquid injection short section 1 is 300–500 mm. The bottom and top of the liquid injection short section 1 are respectively provided with a first flange 11 and a second flange 12, which can be connected to the flange of the compressor inlet pipe and the flange of the intake pipe, respectively.

[0023] The gas pre-distribution pipe 3 is provided with a gas inlet 31 for receiving pressurized gas input from the outside; the liquid pre-distribution pipe 4 is provided with a liquid inlet 41 for receiving sprayed liquid medium input from the outside. In this embodiment, both the gas pre-distribution pipe 3 and the liquid pre-distribution pipe 4 are annular and surround the spray section 1; the gas inlet 31 of the gas pre-distribution pipe 3 is located on the side of the gas pre-distribution pipe 3, and the liquid inlet 41 of the liquid pre-distribution pipe 4 is located on the side of the liquid pre-distribution pipe 4.

[0024] At least four gas-liquid injection pipes 2 are evenly arranged along the circumferential direction of the injection section 1. The gas inlet 23 of each gas-liquid injection pipe 2 is connected to the gas pre-distribution pipe 3, the liquid inlet 21 of each gas-liquid injection pipe 2 is connected to the liquid pre-distribution pipe 4, and the gas-liquid mixture outlet 22 of each gas-liquid injection pipe 2 is connected to the outer circumferential surface of the injection section 1 and penetrates the wall of the central through hole 10 of the injection section 1. Preferably, the number of gas-liquid injection pipes 2 is 6 to 8.

[0025] The liquid inlet 21 of each gas-liquid jet pipe 2 is located at the first end of the gas-liquid jet pipe 2, and the gas-liquid mixture outlet 22 of each gas-liquid jet pipe 2 is located at the second end of the gas-liquid jet pipe 2, opposite to the first end. The gas inlet 23 of each gas-liquid jet pipe is located on the side of the gas-liquid jet pipe 2. In this embodiment, the first and second ends of each gas-liquid jet pipe 2 are welded to the outer surfaces of the liquid pre-distribution pipe 4 and the spray nozzle 1, respectively. The gas inlet 23 of the gas-liquid jet pipe 2 is connected to the gas pre-distribution pipe 3 through the connecting nozzle 5. The gas inlet 23 of the gas-liquid jet pipe is perforated.

[0026] The orifice 20 of the gas-liquid mixing tube 2 has a Venturi structure. From the first end to the second end, the orifice 20 of the gas-liquid mixing tube 2 includes an inlet section 20a, a contraction section 20b, a throat 20c, and an expansion section 20d. The contraction section 20b and the expansion section 20d are conical, while the inlet section 20a and the throat 20c are both cylindrical. The gas inlet 23 of the gas-liquid mixing tube 2 is connected to the throat 20c.

[0027] In this embodiment, the contraction angle γ of the contraction section 20b is 30–45°, the diameter d of the throat 20c is 8–12 mm, the expansion angle β of the expansion section 20d is 10–15°, the length of the contraction section 20b is 2–3.5 times the throat diameter d, the length of the throat 20c is 1.2–2 times the throat diameter d, and the length of the expansion section 20d is 5–8 times the throat diameter d. The orifice diameter of the gas inlet 23 of the gas-liquid mixing tube is 2–3 mm. Using the above scheme, the droplet size can be effectively reduced, and the uniformity of the ejected liquid can be improved.

[0028] Please refer to Figure 4 In this embodiment, the angle α between the axis of the gas-liquid mixing nozzle 2 and the bottom surface of the injection section 1 is 25°–55°, and the axis of the gas-liquid mixing nozzle 2 passes through the center of the bottom surface of the injection section 1. The cross-section of the expansion section 20d of each gas-liquid mixing nozzle 2 is circular (e.g., ...). Figure 5 (As shown) or a combination of a semi-ellipse 27d and a semi-circle 28d (as shown) Figure 6 As shown in the diagram, the semicircle is located near the bottom of the injection section, and the semi-ellipse is half of a standard ellipse. With this arrangement, when the bottom of the injection section 1 is connected to the inlet pipe of the oil-free wet screw compressor, more liquid can be sprayed onto the rotor of the oil-free wet screw compressor.

[0029] Figure 7 A schematic diagram of the installation of a liquid injection device 100 and an oil-free wet screw compressor 200 according to an embodiment of the present invention is shown. The bottom of the liquid injection section 1 of the liquid injection device is connected to the inlet pipe 201 of the oil-free wet screw compressor 200. The gas inlet 31 of the gas pre-distribution pipe 3 of the liquid injection device is connected to the exhaust port 202 of the oil-free wet screw compressor 200 or an external gas source.

[0030] The liquid injection method of the liquid injection device of the oil-free wet screw compressor according to an embodiment of the present invention includes the following steps:

[0031] The sprayed medium is introduced into the liquid pre-distribution pipe 4, and after pre-distribution, it enters the liquid inlet 21 of each gas-liquid mixing injection pipe 2.

[0032] Gas with a pressure of 0.3 MPa to 2 MPa is introduced into the gas pre-distribution pipe 3, and after pre-distribution, it enters the gas inlet 23 of each gas-liquid mixing pipe 2.

[0033] The kinetic energy of the gas entering the gas-liquid mixing tube 2 is used to break up the sprayed liquid into uniformly distributed tiny droplets, which are then ejected from the gas-liquid mixture outlet 22 of the gas-liquid mixing tube.

[0034] Optionally, the liquid injection medium is introduced into the liquid pre-distribution pipe 4 through the compressor liquid injection circulation system, and the exhaust gas of the oil-free wet screw compressor 200 is introduced into the gas pre-distribution pipe 3 through the priming pipe. The amount of gas entering the gas pre-distribution pipe is adjusted by adjusting the priming pipe valve.

[0035] In this embodiment, the volume ratio of gas entering the gas pre-distribution pipe 3 to liquid entering the liquid pre-distribution pipe 4 is 2:1 to 5:1. The liquid velocity at the throat of the gas-liquid mixing pipe 2 is 4 to 9 m / s, and the gas velocity at the throat of the gas-liquid mixing pipe 2 is 10 to 20 m / s.

[0036] The liquid spraying device and method of this invention can significantly reduce the droplet diameter of the liquid spraying medium, increase the uniformity of the liquid spraying medium distribution, effectively enhance the cooling effect of compressed gas, reduce power consumption, and improve the performance of oil-free liquid spraying screw compressors.

[0037] The following is a comparison of the effects of using the liquid injection device of the oil-free wet screw compressor of the present invention in a petrochemical plant and using direct liquid injection through ordinary pipelines.

[0038] The process parameters of the oil-free wet screw compressor are shown in the table below:

[0039] compressor inlet actual volume flow rate <![CDATA[75m 3 / min(5500Nm 3 / h)]]> Inlet pressure 0.02 MPaG Intake temperature 40℃ Exhaust temperature 85℃ Temperature after exhaust cooling 40℃ Exhaust cooling pressure 0.6 MPaG

[0040] The specific structural parameters of the liquid injection device of the oil-free wet screw compressor are as follows:

[0041]

[0042] Other structural design parameters: The length of the contraction section of the gas-liquid mixing tube is twice the throat diameter, the length of the throat is twice the throat diameter d, and the length of the expansion section is five times the throat diameter d.

[0043] The unit operation results are compared as follows:

[0044]

[0045] The above comparison shows that, under the same operating conditions, compared with the ordinary direct injection method through the pipeline, the liquid injection device of this invention significantly reduces the amount of liquid injected into the compressor inlet, reducing the amount of liquid injected by 2500 kg / h, and improving the compressor's thermal insulation efficiency by about 6%.

[0046] In this embodiment of the invention, the gas inlets and liquid inlets of at least four gas-liquid mixing nozzles converge at gas pre-distribution and liquid pre-distribution pipes, respectively. The gas-liquid mixture outlets of the gas-liquid mixing nozzles are uniformly distributed on the injection short sections and are interconnected. Through the momentum shearing of the injected liquid by high-pressure gas, fine droplets of 50–200 μm are generated and uniformly distributed at the gas inlet of the compressor. A portion of the fine droplets rapidly vaporizes and exchanges heat with the gas, while another portion recondenses into larger droplets and exchanges mass heat with the gas. The heat exchange efficiency in both stages is significantly improved, removing most of the heat from the gas and achieving the required exhaust temperature. This injection device reduces the amount of injection liquid, lowering compressor power consumption; it also reduces the amount of liquid entering the gas-liquid separator, thereby enhancing the gas-liquid separation effect, improving the overall performance of the compressor, and ensuring the efficient operation of the process gas injection screw compressor.

[0047] The above description is merely a preferred embodiment of the invention and is not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A liquid injection device for an oil-free wet screw compressor, characterized in that, It includes a liquid injection section, at least four gas-liquid mixing nozzles, a gas pre-distribution nozzle, and a liquid pre-distribution nozzle; The bottom of the injection section is used to connect to the inlet pipe of the oil-free wet screw compressor, and the injection section is provided with a central through hole extending along the axial direction; Both the gas pre-distribution pipe and the liquid pre-distribution pipe are annular and surround the liquid spraying section; the gas pre-distribution pipe is provided with a gas inlet located on the side of the gas pre-distribution pipe, and the liquid pre-distribution pipe is provided with a liquid inlet located on the side of the liquid pre-distribution pipe. The at least four gas-liquid jetting tubes are evenly arranged along the circumferential direction of the spraying section. The gas inlet of each gas-liquid jetting tube is connected to the gas pre-distribution tube, the liquid inlet of each gas-liquid jetting tube is connected to the liquid pre-distribution tube, and the gas-liquid mixture outlet of each gas-liquid jetting tube is connected to the outer peripheral surface of the spraying section and penetrates the wall of the central through hole of the spraying section. The liquid inlet of each gas-liquid jetting tube is located at the first end of the gas-liquid jetting tube, and the gas-liquid mixture outlet of each gas-liquid jetting tube is located at the second end of the gas-liquid jetting tube, with the second end opposite to the first end. The gas inlet of each gas-liquid jetting tube is located on the side of the gas-liquid jetting tube.

2. The liquid injection device of the oil-free wet screw compressor as described in claim 1, characterized in that, Each of the gas-liquid mixing tubes has a venturi structure in its orifice, and from the first end to the second end, it includes a constriction section, a throat, and an expansion section in sequence; the constriction section and the expansion section are conical, and the throat is cylindrical; The gas inlet is connected to the throat.

3. The liquid injection device of the oil-free wet screw compressor as described in claim 2, characterized in that, The contraction angle γ of the contraction segment is 30~45°, the diameter d of the throat is 8~12mm, the expansion angle β of the expansion segment is 10~15°, the length of the contraction segment is 2~3.5 times the diameter d of the throat, the length of the throat is 1.2~2 times the diameter d of the throat, and the length of the expansion segment is 5~8 times the diameter d of the throat.

4. The liquid injection device of the oil-free wet screw compressor as described in claim 3, characterized in that, The orifice diameter of the gas inlet of each of the gas-liquid mixing tubes is 2~3mm.

5. The liquid injection device of the oil-free wet screw compressor as described in claim 2, characterized in that, The cross-section of the expansion section of each of the gas-liquid mixing nozzles is circular or a combination of a semi-ellipse and a semi-circle, wherein the semi-circle is close to the bottom of the liquid injection section.

6. The liquid injection device of the oil-free wet screw compressor as described in claim 1 or 5, characterized in that, The angle α between the centerline of each gas-liquid mixing nozzle and the bottom surface of the liquid spraying section is 25~55°, and the centerline of each gas-liquid mixing nozzle passes through the center of the bottom surface of the liquid spraying section.

7. The liquid injection device of the oil-free wet screw compressor as described in claim 1, characterized in that, The number of gas-liquid mixing tubes is 6 to 8.

8. An oil-free wet screw compressor, wherein the oil-free wet screw compressor has an inlet pipe, characterized in that, The oil-free wet screw compressor includes the liquid injection device as described in any one of claims 1 to 7; The bottom of the spray section of the spray device is connected to the inlet pipe.

9. The oil-free wet screw compressor as described in claim 8, characterized in that, The gas inlet of the gas pre-distribution pipe of the liquid injection device is connected to the exhaust port of the oil-free wet screw compressor or an external gas source.

10. The liquid injection method of the liquid injection device of the oil-free wet screw compressor as described in any one of claims 1 to 7, characterized in that, Includes the following steps: The spray medium is introduced into the liquid pre-distribution pipe, and after pre-distribution, it enters the liquid inlet of each gas-liquid mixing jet pipe. Gas with a pressure of 0.3 MPa to 2 MPa is introduced into the gas pre-distribution pipe and then pre-distributed into the gas inlet of each gas-liquid mixing pipe. The kinetic energy of the gas entering the gas-liquid mixing tube is used to break up the sprayed liquid into uniformly distributed tiny droplets, which are then ejected from the gas-liquid mixture outlet of the gas-liquid mixing tube.

11. The liquid injection method of the liquid injection device of the oil-free wet screw compressor as described in claim 10, characterized in that, The ratio of the volume of gas entering the gas pre-distribution tube to the volume of liquid entering the liquid pre-distribution tube is 2:1 to 5:

1.

12. The liquid injection method of the liquid injection device of the oil-free wet screw compressor as described in claim 10, characterized in that, The liquid velocity at the throat of the gas-liquid mixing tube is 4~9 m / s, and the gas velocity at the throat of the gas-liquid mixing tube is 10~20 m / s.

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