Discharge temperature control method and system for two-stage dry screw compressors

Abstract

A method and system for controlling the discharge temperature of a two-stage dry screw compressor. The method includes controlling the discharge temperature of the two-stage dry screw compressor during operation, specifically as follows: when the pressure in the interstage piping of the two-stage dry screw compressor is lower than the lower limit of a preset pressure range, one or more of the following adjustment methods are used: reducing the opening of the primary reflux regulating valve, increasing the speed of the primary compressor, reducing the speed of the secondary compressor, and increasing the opening of the secondary reflux regulating valve; when the pressure in the interstage piping is higher than the upper limit of the preset pressure range, one or more of the following adjustment methods are used: reducing the opening of the secondary reflux regulating valve, increasing the speed of the secondary compressor, reducing the speed of the primary compressor, and increasing the opening of the primary reflux regulating valve. This invention can control the discharge temperature of the two-stage dry screw compressor within a reasonable range.

Description

Technical Field

[0001] This invention relates to multi-stage dry compressor operation control technology, and more particularly to two-stage dry screw compressor technology. Background Technology

[0002] Positive displacement compressors compress gases through volume changes. During this process, as gas pressure increases, so does gas temperature. Wet compressors lower gas temperature through liquid injection, while dry compressors lack effective cooling methods and typically have higher exhaust temperatures. Therefore, during operation, dry screw compressors experience significant rotor thermal expansion due to the high exhaust temperature, causing changes in the meshing clearance. For high-temperature units, if the clearance is too small, rotor rubbing is likely to occur during operation; if the clearance is too large, gas leakage is likely, affecting compressor efficiency. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method and system for controlling the exhaust temperature of a two-stage dry screw compressor, which can control the exhaust temperature of the first-stage compressor and the second-stage compressor of the two-stage dry screw compressor to be within a reasonable range.

[0004] According to a first aspect of the present invention, a method for controlling the exhaust temperature of a two-stage dry screw compressor is provided, comprising controlling the exhaust temperature during the operation of the two-stage dry screw compressor, wherein controlling the exhaust temperature during the operation of the two-stage dry screw compressor includes:

[0005] When the pressure in the interstage piping of a two-stage dry screw compressor is lower than the lower limit of a preset pressure range, one or more of the following adjustment methods are used to adjust the pressure in the interstage piping until the pressure in the interstage piping is adjusted to the preset pressure range. These adjustment methods include reducing the opening of the first-stage return regulating valve, increasing the speed of the first-stage compressor, reducing the speed of the second-stage compressor, and increasing the opening of the second-stage return valve.

[0006] When the pressure in the interstage piping of a two-stage dry screw compressor is higher than the upper limit of the preset pressure range, one or more of the following adjustment methods are used to adjust the pressure in the interstage piping until the pressure in the interstage piping is adjusted to the preset pressure range. These adjustment methods include reducing the opening of the two-way double-flow regulating valve, increasing the speed of the second-stage compressor, reducing the speed of the first-stage compressor, and increasing the opening of the single-way single-flow regulating valve.

[0007] The single-circuit regulating valve and the double-circuit regulating valve are respectively installed in the single-circuit reflux pipeline and the double-circuit reflux pipeline. The single-circuit reflux pipeline is connected between the interstage pipeline and the intake pipeline of the two-stage dry screw compressor, and the double-circuit reflux pipeline is connected between the exhaust pipeline and the interstage pipeline of the two-stage dry screw compressor.

[0008] The above-mentioned method for controlling the exhaust temperature of a two-stage dry screw compressor also includes controlling the exhaust temperature during the start-up process of the two-stage dry screw compressor. Controlling the exhaust temperature during the start-up process of the two-stage dry screw compressor includes: when the ratio of the external pressure ratio to the internal pressure ratio of each stage compressor exceeds a preset ratio range, adjusting the internal volume ratio adjustment structure of that stage compressor until the ratio of the external pressure ratio to the internal pressure ratio of each stage compressor is adjusted to the preset ratio range.

[0009] According to a second aspect of the present invention, an exhaust temperature control system for a two-stage dry screw compressor is also provided. The two-stage dry screw compressor includes a primary compressor, a secondary compressor, a first drive device, a second drive device, an intake pipe, an interstage pipe, an exhaust pipe, a single-cycle reflux pipe, and a double-cycle reflux pipe. The first drive device and the second drive device are used to drive the primary compressor and the secondary compressor respectively, and can adjust the speed of the primary compressor and the secondary compressor. The intake pipe is connected to the inlet of the primary compressor, the interstage pipe is connected between the outlet of the primary compressor and the inlet of the secondary compressor, and the exhaust pipe is connected to the outlet of the secondary compressor. A single-loop reflux pipe connects the interstage pipe and the intake pipe, while a double-loop reflux pipe connects the exhaust pipe and the interstage pipe. The exhaust temperature control system of the two-stage dry compressor includes pressure sensors PT01, PT02, PT03, and PT04, a single-loop reflux regulating valve, a double-loop reflux regulating valve, and a controller. Pressure sensor PT01 is located in the intake pipe, pressure sensors PT02 and PT03 are located in the interstage pipes, and pressure sensor PT04 is located in the exhaust pipe. Pressure sensors PT01 to PT04 are used to detect the intake pressure of the first stage. The controller measures the primary exhaust pressure, secondary intake pressure, and secondary exhaust pressure. A single-loop reflux regulating valve and a double-loop reflux regulating valve are respectively installed in the single-loop reflux pipeline and the double-loop reflux pipeline. The controller receives the pressure detection results from pressure sensors PT01 to PT04, as well as the valve status signals from the single-loop reflux regulating valve and the double-loop reflux regulating valve. During the operation of the two-stage dry screw compressor, when the detected pressure of pressure sensor PT03 or PT02 is lower than the lower limit of the preset pressure range, one or more of the following adjustment methods are used until the detected pressure of pressure sensor PT03 or PT02 is within the preset pressure range. The various adjustment methods include reducing the opening of the primary reflux regulating valve, increasing the speed of the primary compressor, reducing the speed of the secondary compressor, and increasing the opening of the secondary reflux regulating valve. When the pressure detected by pressure sensor PT03 or PT02 is higher than the upper limit of the preset pressure range during the operation of the two-stage dry screw compressor, one or more of the following adjustment methods are used until the pressure detected by pressure sensor PT03 or PT02 is within the preset pressure range. These various adjustment methods include reducing the opening of the secondary reflux regulating valve, increasing the speed of the secondary compressor, reducing the speed of the primary compressor, and increasing the opening of the primary reflux regulating valve.

[0010] The present invention has at least the following advantages:

[0011] This invention maintains the matching of internal and external pressure ratios during the startup process of a two-stage dry screw compressor, ensuring that the pressure ratio distribution between the first-stage and second-stage compressors is within the design requirements during stable operation. This, in turn, keeps the exhaust temperatures of the first-stage and second-stage compressors of the two-stage dry screw compressor unit consistently stable and within a reasonable range. Attached Figure Description

[0012] Figure 1 A schematic diagram of a two-stage dry screw compressor employing an exhaust temperature control system according to an embodiment of the present invention is shown.

[0013] Figure 2 This diagram illustrates the control logic of a specific embodiment of the present invention for controlling the exhaust temperature during the operation of a two-stage dry screw compressor. Detailed Implementation

[0014] In practical design, the static clearance of a screw compressor is fixed, thus corresponding to a reasonable temperature range for hot operation, which is usually determined by the discharge temperature. For dry screw compressors, the inlet temperature, pressure ratio, and efficiency directly determine the discharge temperature. If the discharge temperature is too low, the rotor expansion is small, increasing leakage and reducing operating efficiency. If the discharge temperature is too high, rotor rubbing can occur, leading to unit shutdown, equipment failure, and economic losses. Therefore, excessively high discharge temperatures can cause more serious consequences. In actual operation, due to fluctuations in incoming gas and unstable discharge pressure, the pressure ratio of dry screw compressors is prone to deviation, causing significant changes in discharge temperature, especially in multi-stage compressors. Taking a two-stage dry screw compressor as an example, under stable pressures at the upstream and downstream ends of the process, the mismatch in gas volume between the first and second stage compressors can lead to interstage pressure changes. If the interstage pressure is too high, the first stage compressor's pressure ratio will be too high, causing it to overheat. Conversely, if the interstage pressure is too low, the second stage compressor's pressure ratio will be too high, also causing it to overheat. Therefore, by reasonably controlling the interstage pressure and ensuring a reasonable pressure ratio distribution, the discharge temperature of the two-stage dry screw compressor can be kept within a reasonable range, thus ensuring stable operation of the unit.

[0015] Figure 1 A schematic diagram of a two-stage dry screw compressor employing an exhaust temperature control system according to an embodiment of the present invention is shown. Please refer to... Figure 1 The two-stage dry screw compressor includes a primary compressor 11, a secondary compressor 12, a first drive unit 21, a second drive unit 22, an intake pipe 31, an interstage pipe 32, an exhaust pipe 33, a first-cycle return pipe 34, and a second-cycle return pipe 35.

[0016] The first drive device 21 and the second drive device 22 are used to drive the primary compressor 11 and the secondary compressor 12 respectively, and can adjust the speed of the primary compressor 11 and the secondary compressor 12. In this embodiment, both the primary compressor 11 and the secondary compressor 12 are twin-screw compressors.

[0017] The intake pipe 31 is connected to the inlet of the first-stage compressor 11, the interstage pipe 32 is connected between the outlet of the first-stage compressor 11 and the inlet of the second-stage compressor 12, and the exhaust pipe 33 is connected to the outlet of the second-stage compressor 12. A single-cycle return pipe 34 is connected between the interstage pipe 32 and the intake pipe 31, and a double-cycle return pipe 35 is connected between the exhaust pipe 33 and the interstage pipe 32.

[0018] The exhaust temperature control system of the two-stage dry compressor in this embodiment includes pressure sensor PT01, pressure sensor PT02, pressure sensor PT03, pressure sensor PT04, a single-return-single-return regulating valve PV01, a double-return-double-return regulating valve PV02, and a controller (not shown in the figure).

[0019] Pressure sensor PT01 is installed in the intake pipe 31 to detect the first-stage intake pressure (i.e., the pressure in the intake pipe 31); pressure sensors PT02 and PT03 are installed in the interstage pipe 32 to detect the first-stage exhaust pressure and the second-stage intake pressure, respectively; pressure sensor PT04 is installed in the exhaust pipe 33 to detect the second-stage exhaust pressure (i.e., the pressure in the exhaust pipe 33).

[0020] The single-circuit reflux regulating valve PV01 and the double-circuit reflux regulating valve PV02 are respectively installed in the single-circuit reflux pipeline 34 and the double-circuit reflux pipeline 35 to regulate the flow rate.

[0021] The controller receives pressure detection results from pressure sensors PT01 to PT04, as well as valve status signals from the single-return regulating valve PV01 and the double-return regulating valve PV02. When the pressure detected by pressure sensor PT03 is lower than the lower limit of a preset pressure range during the operation of the two-stage dry screw compressor, it employs one or more of the following adjustment methods until the pressure detected by pressure sensor PT03 is within the preset pressure range. These adjustment methods include reducing the opening of the single-return regulating valve PV01 and increasing the speed of the first-stage compressor 11. When the pressure detected by the pressure sensor PT03 is higher than the upper limit of the preset pressure range during the operation of the two-stage dry screw compressor, one or more of the following adjustment methods are adopted until the pressure detected by the pressure sensor PT03 is within the preset pressure range: reducing the speed of the second-stage compressor 12, increasing the speed of the second-stage compressor 12, reducing the speed of the first-stage compressor 12, and increasing the opening of the first-stage reflux regulating valve PV01.

[0022] The aforementioned preset pressure range is n1*P0~n2*P0, where P0 is the design value of the pressure in the interstage pipe 32, which is related to the structural properties of the compressor and is determined when designing a two-stage dry screw compressor. n1=0.94~0.96, n2=1.04~1.06.

[0023] In this embodiment, both the first drive device 21 and the second drive device 22 include a frequency converter and a motor, with the frequency converter electrically connected to the controller and the motor, respectively. Adjusting the speed of the primary compressor 11 and the secondary compressor 12 is achieved by the controller controlling the frequency converter to increase or decrease the motor speed. Optionally, the controller may be a PLC controller, but it is not limited to this.

[0024] Furthermore, the primary compressor 11 and the secondary compressor 12 are each equipped with an internal volume ratio adjustment structure. The controller is used to adjust the internal volume ratio adjustment structure of the compressor in each stage when the ratio of the external pressure ratio to the internal pressure ratio of each stage exceeds a preset range during the start-up process of the two-stage dry screw compressor, until the ratio of the external pressure ratio to the internal pressure ratio of each stage is adjusted to the preset range. Specifically, the external pressure ratio of the primary compressor 11 is equal to the primary discharge pressure divided by the primary intake pressure, and the external pressure ratio of the secondary compressor 12 is equal to the secondary discharge pressure divided by the secondary intake pressure. Optionally, the internal volume ratio adjustment structure is a slide valve adjustment mechanism.

[0025] In this embodiment, the preset ratio range is n3 to n4, where n3 = 0.94 to 0.96 and n4 = 1.05 to 1.15.

[0026] Furthermore, the two-stage dry screw compressor includes a two-way recirculation reflux pipe 36, which connects the exhaust pipe 33 and the intake pipe 31. The two-way recirculation reflux pipe 36 is equipped with a two-way recirculation regulating valve PV03. The function of the two-way recirculation regulating valve PV03 includes adjusting the discharge volume of the two-stage dry screw compressor during startup, etc., which is irrelevant to the technical problem to be solved in this application and will not be described further here.

[0027] A recirculation cooler 71 is installed on the common section of the secondary recirculation reflux pipe 36 and the secondary recirculation reflux pipe 35; preferably, the recirculation cooler should be able to meet the 100% recirculation cooling requirement and have a certain design margin. An aftercooler 73 is installed on the interstage pipe 32 to reduce the intake temperature of the secondary compressor 12.

[0028] In this embodiment, the intake pipe 31 is equipped with a temperature sensor TT01 for detecting the first-stage intake temperature; the interstage pipe 32 is equipped with temperature sensors TT02 and TT03, which are used to detect the first-stage exhaust temperature and the second-stage intake temperature, respectively; the exhaust pipe 33 is equipped with a temperature sensor TT04 for detecting the second-stage exhaust temperature. The signal output terminals of temperature sensors TT01 to TT04 are respectively connected to the input terminal of the controller. Temperature sensor TT02 is positioned as close as possible to the exhaust port of the first-stage compressor 11, and temperature sensor TT04 is positioned as close as possible to the exhaust port of the second-stage compressor 12.

[0029] During operation, the inlet medium gas passes sequentially through the primary inlet filter 81 and the primary inlet silencer 82 into the primary compressor 11. After being pressurized by the primary compressor 11, it passes sequentially through the primary outlet silencer 83, the aftercooler 73, the secondary inlet filter 84, and the secondary inlet silencer 85 into the secondary compressor 12. After being compressed by the secondary compressor, it passes through the secondary outlet silencer 86 to the medium gas outlet.

[0030] According to another embodiment of the present invention, a method for controlling the exhaust temperature of a two-stage dry screw compressor includes controlling the exhaust temperature during the start-up process of the two-stage dry screw compressor and controlling the exhaust temperature during the operation process of the two-stage dry screw compressor.

[0031] When the compressor starts, the pressure at the discharge end gradually builds up, and the system external pressure ratio changes continuously. When the difference between the internal and external pressure ratios is too large, it will lead to unstable compression operation and large compressor vibration. In order to ensure that the internal and external pressure ratios are matched, the compressor runs smoothly, and the gas compression does not exceed the temperature, each stage of the compressor is equipped with an internal stage ratio adjustment mechanism to adjust the internal pressure ratio ε of the compressor.

[0032] The controller is used to adjust the internal volume ratio adjustment structure of each stage compressor when the ratio of the external pressure ratio to the internal pressure ratio of each stage compressor exceeds the preset ratio range during the startup process of a two-stage dry screw compressor, until the ratio of the external pressure ratio to the internal pressure ratio of each stage compressor is adjusted to the preset ratio range.

[0033] Specifically, when the ratio of the external pressure ratio to the internal pressure ratio of each stage of the compressor is lower than the lower limit of the preset ratio range, the internal volume ratio adjustment structure of that stage of the compressor is adjusted to reduce the internal pressure ratio of the compressor; when the ratio of the external pressure ratio to the internal pressure ratio of each stage of the compressor is higher than the upper limit of the preset ratio range, the internal volume ratio adjustment structure of that stage of the compressor is adjusted to increase the internal pressure ratio of the compressor.

[0034] In this embodiment, the preset ratio range is n3 to n4, where n3 = 0.94 to 0.96 and n4 = 1.05 to 1.15. In a specific implementation, the preset ratio range is 0.95 to 1.1. When the compressor's external pressure ratio is less than 0.95*ε, it means that the ratio of the compressor's external pressure ratio to its internal pressure ratio is lower than the lower limit of the preset ratio range. When the compressor's external pressure ratio is greater than 1.1*ε, it means that the ratio of the compressor's external pressure ratio to its internal pressure ratio is higher than the upper limit of the preset ratio range. When the compressor's external pressure ratio is greater than or equal to 0.95*ε and less than or equal to 1.1*ε, it means that the internal and external pressure ratios are matched and no adjustment is required.

[0035] When the compressor is running normally, the interstage pressure ratio distribution is controlled to ensure that the interstage pressure distribution is reasonable and that the compression ratio of the two-stage compressor is within the design range, which ensures that the discharge temperature of the two-stage screw compressor does not exceed the limit.

[0036] Controlling the exhaust temperature during the operation of a two-stage dry screw compressor includes:

[0037] When the pressure Pj1 in the interstage pipeline 32 of the two-stage dry screw compressor is lower than the lower limit of the preset pressure range, one or more of the following adjustment methods are used to adjust the pressure in the interstage pipeline until the pressure Pj1 in the interstage pipeline 32 is adjusted to the preset pressure range. The multiple adjustment methods include reducing the opening of the first-return-first-recirculation regulating valve PV01, increasing the speed of the first-stage compressor 11, reducing the speed of the second-stage compressor 12, and increasing the opening of the second-return-second-circulation recirculation valve PV02.

[0038] When the pressure Pj1 in the interstage pipe 32 of the two-stage dry screw compressor is higher than the upper limit of the preset pressure range, one or more of the following adjustment methods are used to adjust the pressure Pj1 in the interstage pipe until the pressure Pj1 in the interstage pipe 32 is adjusted to the preset pressure range. The multiple adjustment methods include reducing the opening of the two-way two-way reflux regulating valve PV02, increasing the speed of the second-stage compressor 12, reducing the speed of the first-stage compressor 11, and increasing the opening of the one-way one-way reflux regulating valve PV01.

[0039] The single-circuit regulating valve PV01 and the double-circuit regulating valve PV02 are respectively installed in the single-circuit reflux pipe 34 and the double-circuit reflux pipe 35. The single-circuit reflux pipe 34 is connected between the interstage pipe 32 and the intake pipe 31 of the two-stage dry screw compressor, and the double-circuit reflux pipe 35 is connected between the exhaust pipe 33 and the interstage pipe 32 of the two-stage dry screw compressor.

[0040] In this embodiment, during the adjustment of the pressure Pj1 in the interstage pipeline 32, only one adjustment method is used at a time. The next priority adjustment method is only executed if the previous priority adjustment method fails to adjust the pressure Pj1 in the interstage pipeline to the preset pressure range within a predetermined time. After each adjustment, the system is allowed to stabilize for a period of time. Then, adjustments are made cyclically based on the pressure changes in the interstage pipeline until the requirements are met.

[0041] When the pressure Pj1 in the interstage piping of the two-stage dry screw compressor is lower than the lower limit of the preset pressure range, the priority order of various adjustment methods is as follows: reduce the opening of the primary return-to-return regulating valve PV01, increase the speed of the primary compressor 11, reduce the speed of the secondary compressor 12, and increase the opening of the secondary return-to-return regulating valve PV02. When the pressure Pj1 in the interstage piping of the two-stage dry screw compressor is higher than the upper limit of the preset pressure range, the priority order of various adjustment methods is as follows: reduce the opening of the secondary return-to-return regulating valve PV02, increase the speed of the secondary compressor 12, reduce the speed of the primary compressor 11, and increase the opening of the primary return-to-return regulating valve PV01. Using the above priority order for adjustment has the advantage of high adjustment efficiency.

[0042] The aforementioned preset pressure range is n1*P0 to n2*P0, where P0 is the design value of the interstage pipeline pressure, n1 = 0.94 to 0.96, and n2 = 1.04 to 1.06. In a specific embodiment, the pressure Pj1 of the interstage pipeline 32 adopts the intake pressure of the two-stage compressor 12, and P0 is set to... Ps is the design value of the intake pressure of the two-stage dry screw compressor (i.e., the design value of the intake pressure of the first-stage compressor), and Pd is the design value of the discharge pressure of the two-stage dry screw compressor (i.e., the design value of the discharge pressure of the second-stage compressor). The controller can obtain the intake pressure of the second-stage compressor 12 by reading the detection result of the pressure sensor PT03. The preset pressure range is 0.95*P0~1.05*P0. When 0.95*P0≤Pj1≤1.05*P0, it means that no adjustment is needed, and the existing operating conditions can be maintained unchanged. The aforementioned preset time is 10 minutes.

[0043] In other embodiments, the pressure Pj1 of the interstage pipeline can also be the discharge pressure of the first-stage compressor as the pressure of the interstage pipeline 32, in which case P0 is set to c = 20 kPa ~ 30 kPa.

[0044] Figure 2 This diagram illustrates the control logic of a specific embodiment of the present invention for controlling the exhaust temperature during the operation of a two-stage dry screw compressor.

[0045] When the compressor is running normally, pressure sensor PT03 monitors the pressure Pj1 in the interstage pipe 32 (i.e., the pressure Pj1 in the interstage pipe 32 is equal to the detected value of pressure sensor PT03). The design value of the pressure in the interstage pipe 32 is P0. To maintain stable pressure distribution, the controller adopts the following... Figure 2 The control logic is shown below. Based on the pressure conditions of the interstage piping, it can be divided into three operating conditions, with the execution steps as follows:

[0046] Operating condition 1: Pj1 < 0.95 * P0, adjust using the following steps:

[0047] 1-1. If the opening of the reflux control valve PV01 can be reduced, then reduce the opening of the reflux control valve PV01 by 5% and then proceed to step 1-5. If not, then proceed to step 1-2.

[0048] 1-2. If the speed of motor M1 of primary compressor 11 can be increased, then increase the speed of motor M1 of primary compressor by 3% and then proceed to step 1-5. If not, then proceed to step 1-3.

[0049] 1-3. If the speed of motor M2 of the secondary compressor 12 can be reduced, then reduce the speed of motor M2 of the secondary compressor by 3% and proceed to step 1-5. If not, proceed to step 1-4.

[0050] 1-4. Increase the opening of the double-return double-flow regulating valve PV02 by 5%;

[0051] 1-5. Wait ten minutes and adjust the pressure in the interstage pipeline according to the changes.

[0052] Operating condition 2: Pj1 > 1.05 * P0, adjust using the following steps:

[0053] 2-1. If the opening of the two-way two-circuit regulating valve PV02 can be reduced, then proceed to step 2-5 after reducing the opening of the two-way two-circuit regulating valve PV02 by 5%. If not, proceed to step 2-2.

[0054] 2-2. If the speed of motor M2 of secondary compressor 12 can be increased, increase the speed of motor M2 of secondary compressor 12 by 3% and then proceed to step 2-5. If not, proceed to step 2-3.

[0055] 2-3. If the speed of motor M1 of primary compressor 11 can be reduced, reduce the speed of motor M1 of primary compressor 11 by 3% and then proceed to step 2-5. If not, proceed to step 2-4.

[0056] 2-4. Increase the opening of the reflux control valve PV01 by 5%;

[0057] 2-5. Wait ten minutes and adjust the pressure in the interstage pipeline according to the changes.

[0058] Operating condition 3: 0.95*P01≤Pj1≤1.05*P01, maintain the existing operating conditions unchanged.

[0059] Dry screw compressors are designed with thermal expansion during operation in mind, and the design clearances meet the temperature regulation range during operation. The discharge temperature of a dry screw compressor mainly depends on the pressure ratio. After setting the design pressure ratio, feedback regulation ensures that the pressure ratio distribution between the first-stage and second-stage compressors is within a reasonable range during stable operation, maintaining the compressor pressure ratio fluctuation range to less than ±5%, thereby maintaining the stability of the discharge temperature of the first-stage and second-stage compressors in a two-stage dry screw compressor.

[0060] 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 method for controlling the exhaust temperature of a two-stage dry screw compressor, characterized in that, This includes controlling the exhaust temperature during the operation of a two-stage dry screw compressor. Controlling the exhaust temperature during the operation of a two-stage dry screw compressor includes: When the pressure in the interstage piping of a two-stage dry screw compressor is lower than the lower limit of a preset pressure range, one or more of the following adjustment methods are used to adjust the pressure in the interstage piping until the pressure in the interstage piping is adjusted to the preset pressure range. These adjustment methods include reducing the opening of the first-stage return regulating valve, increasing the speed of the first-stage compressor, reducing the speed of the second-stage compressor, and increasing the opening of the second-stage return valve. When the pressure in the interstage piping of a two-stage dry screw compressor is higher than the upper limit of the preset pressure range, one or more of the following adjustment methods are used to adjust the pressure in the interstage piping until the pressure in the interstage piping is adjusted to the preset pressure range. These adjustment methods include reducing the opening of the two-way double-flow regulating valve, increasing the speed of the second-stage compressor, reducing the speed of the first-stage compressor, and increasing the opening of the single-way single-flow regulating valve. The single-loop reflux regulating valve and the double-loop reflux regulating valve are respectively installed in the single-loop reflux pipeline and the double-loop reflux pipeline. The single-loop reflux pipeline is connected between the interstage pipeline and the intake pipeline of the two-stage dry screw compressor, and the double-loop reflux pipeline is connected between the exhaust pipeline and the interstage pipeline of the two-stage dry screw compressor. During the adjustment of the interstage pipeline pressure, only one adjustment method is used at a time. Only when the previous priority adjustment method fails to adjust the interstage pipeline pressure to the preset pressure range within a predetermined time is the next priority method executed. The adjustment methods for each stage are as follows: When the pressure in the interstage pipeline of the two-stage dry screw compressor is lower than the lower limit of the preset pressure range, the priority order of the various adjustment methods is: reducing the opening of the first-stage reflux regulating valve, increasing the speed of the first-stage compressor, reducing the speed of the second-stage compressor, and increasing the opening of the second-stage reflux regulating valve; When the pressure in the interstage pipeline of the two-stage dry screw compressor is higher than the upper limit of the preset pressure range, the priority order of the various adjustment methods is: reducing the opening of the second-stage reflux regulating valve, increasing the speed of the second-stage compressor, reducing the speed of the first-stage compressor, and increasing the opening of the first-stage reflux regulating valve.

2. The exhaust temperature control method for a two-stage dry screw compressor as described in claim 1, characterized in that, The preset pressure range is n1*P0 to n2*P0, where P0 is the design value of the pressure in the interstage pipeline, n1 = 0.94 to 0.96, and n2 = 1.04 to 1.

06.

3. The exhaust temperature control method for a two-stage dry screw compressor as described in claim 2, characterized in that, When the intake pressure of the two-stage compressor is used as the pressure in the interstage piping... ; When the discharge pressure of the first-stage compressor is used as the pressure of the interstage piping... ; Where Ps is the design value of the intake pressure of the two-stage dry screw compressor, Pd is the design value of the discharge pressure of the two-stage dry screw compressor, and c = 20 kPa to 30 kPa.

4. The exhaust temperature control method for a two-stage dry screw compressor as described in claim 1, characterized in that, It also includes controlling the exhaust temperature during the start-up process of a two-stage dry screw compressor. Controlling the exhaust temperature during the start-up process of a two-stage dry screw compressor includes: When the ratio of the external pressure ratio to the internal pressure ratio of each stage of the compressor exceeds the preset ratio range, the internal volume ratio adjustment structure of that stage of the compressor is adjusted until the ratio of the external pressure ratio to the internal pressure ratio of each stage of the compressor is adjusted to the preset ratio range.

5. The exhaust temperature control method for a two-stage dry screw compressor as described in claim 4, characterized in that, The preset ratio range is n3 to n4, where n3 = 0.94 to 0.96 and n4 = 1.05 to 1.

15.

6. The exhaust temperature control method for a two-stage dry screw compressor as described in claim 4, characterized in that, The volume ratio adjustment structure is a slide valve adjustment mechanism.

7. A discharge temperature control system for a two-stage dry screw compressor, wherein the two-stage dry screw compressor comprises a primary compressor, a secondary compressor, a first drive unit, a second drive unit, an intake pipe, an interstage pipe, an exhaust pipe, a single-cycle reflux pipe, and a double-cycle reflux pipe; the first drive unit and the second drive unit are used to drive the primary compressor and the secondary compressor respectively, and are capable of adjusting the speed of the primary compressor and the secondary compressor; the intake pipe is connected to the inlet of the primary compressor, the interstage pipe is connected between the outlet of the primary compressor and the inlet of the secondary compressor, and the exhaust pipe is connected to the outlet of the secondary compressor; the single-cycle reflux pipe is connected between the interstage pipe and the intake pipe, and the double-cycle reflux pipe is connected between the exhaust pipe and the interstage pipe; characterized in that, The exhaust temperature control system of the two-stage dry screw compressor includes pressure sensor PT01, pressure sensor PT02, pressure sensor PT03, pressure sensor PT04, a single-return-single-return regulating valve, a double-return-double-return regulating valve, and a controller. Pressure sensor PT01 is installed in the intake pipe, pressure sensor PT02 and pressure sensor PT03 are respectively installed in the interstage pipe, and pressure sensor PT04 is installed in the exhaust pipe. Pressure sensors PT01 to PT04 are used to detect the first-stage intake pressure, the first-stage exhaust pressure, the second-stage intake pressure and the second-stage exhaust pressure respectively. A single-circuit regulating valve and a double-circuit regulating valve are respectively installed in the single-circuit reflux pipeline and the double-circuit reflux pipeline; The controller receives pressure detection results from pressure sensors PT01 to PT04, as well as valve status signals from the primary and secondary reflux control valves. When the pressure detected by pressure sensor PT03 or PT02 is lower than the lower limit of a preset pressure range during the operation of the two-stage dry screw compressor, one or more of the following adjustment methods are used until the detected pressure of pressure sensor PT03 or PT02 is within the preset pressure range. These adjustment methods include reducing the opening of the primary reflux control valve, increasing the speed of the primary compressor, reducing the speed of the secondary compressor, and increasing the opening of the secondary reflux valve. Conversely, when the pressure detected by pressure sensor PT03 or PT02 is higher than the upper limit of the preset pressure range during the operation of the two-stage dry screw compressor, one or more of the following adjustment methods are used until the detected pressure of pressure sensor PT03 or PT02 is within the preset pressure range. These adjustment methods include reducing the opening of the secondary reflux control valve, increasing the speed of the secondary compressor, and increasing the opening of the secondary reflux valve. The adjustment methods include: reducing the speed of the compressor, decreasing the speed of the primary compressor, and increasing the opening of the reflux regulating valve. Specifically, during the process of bringing the pressure detected by pressure sensors PT03 or PT02 within the preset pressure range, only one adjustment method is used at a time. The next priority adjustment method is only executed if the previous priority adjustment method fails to bring the pressure detected by pressure sensors PT03 or PT02 within the preset pressure range within a predetermined time. When the pressure detected by pressure sensors PT03 or PT02 is lower than the lower limit of the preset pressure range, the priority order of the various adjustment methods is: decreasing the opening of the reflux regulating valve, increasing the speed of the primary compressor, decreasing the speed of the secondary compressor, and increasing the opening of the reflux regulating valve. When the pressure detected by pressure sensors PT03 or PT02 is higher than the upper limit of the preset pressure range, the priority order of the various adjustment methods is: decreasing the opening of the reflux regulating valve, increasing the speed of the secondary compressor, decreasing the speed of the primary compressor, and increasing the opening of the reflux regulating valve.

8. The exhaust temperature control system for a two-stage dry screw compressor as described in claim 7, characterized in that, The primary compressor and the secondary compressor are each equipped with an internal volume ratio adjustment structure; The controller is used to adjust the internal volume ratio adjustment structure of the compressor stage when the ratio of the external pressure ratio to the internal pressure ratio of each stage of the two-stage dry screw compressor exceeds the preset ratio range during the start-up process, until the ratio of the external pressure ratio to the internal pressure ratio of each stage of the compressor is adjusted to the preset ratio range.

9. The exhaust temperature control system for the two-stage dry screw compressor as described in claim 7, characterized in that, Both the first drive device and the second drive device include a frequency converter and a motor, and the frequency converter is electrically connected to the controller and the motor respectively.

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