Start-up method for a compressor

Abstract

The application discloses a starting method for a compressor (1), characterized in that the method comprises the following steps: before starting the compressor (1), closing the outlet (4) of the compressor (1) and reducing the pressure at the inlet end of the compressor (1); after the pressure at the inlet end of the compressor (1) is reduced to a first pressure, starting the compressor (1); and after the compressor (1) is stably operated, gradually increasing the pressure at the inlet end of the compressor (1) to a second pressure, and opening the outlet (4) of the compressor (1).

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of compressors, in particular to a pressure-reducing start-up method for large centrifugal ethylene compressors to protect the thrust bearing. BACKGROUND

[0002] When an ethylene compressor (especially some models such as K2010, SV4-M) is started up at a normal process inlet pressure (e.g. 2.7 MPa or 27 barg), the rotor thereof will generate a huge axial thrust (e.g. up to 26-27 kgf). However, the allowable load of the thrust bearing (or thrust disc) inside the compressor during the start-up phase (when the lubrication condition can not be sufficient) is much lower than this value (e.g. less than 18 kgf), and even under normal lubrication operating conditions, the maximum allowable load thereof can be only about 24 kgf. Therefore, directly starting up at a high inlet pressure will cause the axial thrust to far exceed the carrying capacity of the thrust bearing, thereby causing damage to the thrust bearing and affecting the stable operation and service life of the compressor and even the entire ethylene plant. There is an urgent need in the prior art for a start-up method that can effectively reduce the axial thrust during the start-up phase and protect the thrust bearing. SUMMARY

[0003] The present application aims to solve the problem that the existing ethylene compressor is damaged due to the excessive axial thrust during the initial start-up phase when the compressor is started up at a normal process inlet pressure.

[0004] The present application proposes a start-up method for a compressor, characterized in that the method comprises the following steps: before starting up the compressor, closing the outlet of the compressor and reducing the pressure at the inlet end of the compressor; after the pressure at the inlet end of the compressor is reduced to a first pressure, starting up the compressor; and after the compressor is stably operated, gradually increasing the pressure at the inlet end of the compressor to a second pressure and opening the outlet of the compressor.

[0005] According to an optional embodiment, the first pressure is between 1.0 MPa and 2.0 MPa, preferably 1.6 MPa; and the second pressure is between 2.5 MPa and 3.0 MPa, preferably 2.7 MPa.

[0006] According to an optional embodiment, the first pressure is determined based on the maximum allowable load of the thrust bearing of the compressor during the start-up phase.

[0007] According to an optional embodiment, the total time from starting up the compressor to the inlet pressure of the compressor reaching the second pressure is not more than a first time length.

[0008] According to an optional embodiment, the first time length is 10 minutes.

[0009] According to an optional implementation, the stable operation of the compressor comprises that a rotation speed of the compressor reaches 95% of a preset start-up rotation speed.

[0010] According to an optional implementation, the gradual pressure build-up at the inlet end of the compressor comprises pressure build-up at a preset pressure build-up rate or pressure build-up in stages.

[0011] According to an optional implementation, the compressor is an ethylene compressor.

[0012] According to an optional implementation, the compressor comprises: a housing having an inlet and an outlet, and internally provided with a rotor and a thrust bearing; an inlet pipeline connected to the inlet; an outlet pipeline connected to the outlet; an inlet shut-off valve provided in the inlet pipeline upstream of the inlet; an outlet shut-off valve provided in the outlet pipeline downstream of the outlet; a pressure relief valve connected at one end to a pipe section of the outlet pipeline between the outlet shut-off valve and the outlet, and at the other end to a low-pressure discharge system; a bypass pipeline connected at one end to a pipe section of the inlet pipeline between the inlet shut-off valve and the inlet, and at the other end to a pipe section of the inlet pipeline upstream of the inlet shut-off valve, wherein a pipe diameter of the bypass pipeline is smaller than a pipe diameter of the inlet pipeline; a bypass valve provided in the bypass pipeline; a return pipeline having one end connected to a pipe section of the inlet pipeline between the inlet shut-off valve and the inlet, and the other end connected to a pipe section of the outlet pipeline between the outlet shut-off valve and the outlet; a return valve provided in the return pipeline; and a control unit configured to: before starting the compressor, close the inlet shut-off valve, the bypass valve and the outlet shut-off valve to isolate the section between the inlet shut-off valve and the outlet shut-off valve as a whole, and open the return valve to connect the outlet directly back to the inlet; open the pressure relief valve to reduce the pressure in the isolated section to a first pressure; after the pressure in the isolated section reaches the first pressure, close the pressure relief valve, and then start the compressor; after the stable operation of the compressor, open the bypass valve to gradually build up the pressure in the isolated section to a second pressure; and after the pressure in the isolated section reaches the second pressure, close the bypass valve, open the outlet shut-off valve, and gradually close the return valve.

[0013] According to an optional implementation, one or more of the pressure relief valve, the bypass valve and the return valve is a regulating valve.

[0014] In the context of the present application, 1 MPa is used interchangeably with 10 bar and 10 kgf of gas pressure to indicate the same engineering gas pressure without considering the minor deviation of conversion. According to the start-up method of the present application, by significantly reducing the compressor inlet pressure to 16 kgf before start-up, the axial thrust at the moment of start-up is lower than the allowable load of the thrust bearing (such as 18 kgf), thereby effectively protecting the thrust bearing. After the compressor is stably running, the inlet pressure is gradually restored to the normal operating pressure. This method is particularly suitable for large centrifugal ethylene compressors, which solves the problem that the thrust bearing is easily damaged due to excessive axial thrust when directly starting at high inlet pressure, improves the reliability and service life of the compressor, and ensures the stable production of the entire ethylene plant. BRIEF DESCRIPTION OF DRAWINGS

[0015] Hereinafter, the embodiments of the present application will be described in more detail with reference to the accompanying drawings, in which:

[0016] Figure 1 is a schematic view of a compressor according to the present application.

[0017] Figure 2 is a flow chart of a start-up method for a compressor according to the present application.

[0018] It should be understood that the drawings are designed solely for purposes of illustration and are not intended to limit the scope of the present application. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be described in detail below with reference to the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0020] It should be noted that similar reference numerals and letters indicate similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0021] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0022] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise explicitly and specifically limited.

[0023] In order to solve the problem that the existing compressor (especially some models such as ethylene compressor K2010, SV4-M) is damaged due to excessive axial thrust (for example, up to 26-27 kgf) exceeding the allowable load (for example, less than 18 kgf) of the thrust bearing during the start-up phase when starting at the required inlet pressure during normal operation, the present application provides a start-up method for a compressor and a corresponding compressor.

[0024] Referring to Figure 1 which shows a schematic view of a compressor according to the present application. The compressor 1 can be a large centrifugal ethylene compressor, for example but not limited to K2010 model or SV4-M model. The compressor 1 comprises a casing 2 having an inlet 3 and an outlet 4. Inside the casing 2, a rotor 5 and a thrust bearing 6 for bearing the axial thrust of the rotor 5 are arranged. The maximum allowable load of the thrust bearing 6 during the start-up phase (when the lubrication condition can not be sufficient) is less than or equal to 18 kgf, while under normal lubrication operating conditions, its maximum allowable load is about 24 kgf.

[0025] An inlet line 7 is connected to the inlet 3 of the compressor 1 for supplying process gas (such as ethylene) to the compressor 1. An outlet line 8 is connected to the outlet 4 of the compressor 1 for discharging the gas compressed by the compressor 1.

[0026] In the inlet line 7, an inlet shut-off valve 9 is arranged upstream of the inlet 3. In the outlet line 8, an outlet shut-off valve 10 is arranged downstream of the outlet 4. The two shut-off valves are used to isolate the compressor 1 under certain operating conditions.

[0027] The pressure relief valve 11 is connected at one end to the section of the outlet line 8 between the outlet shut-off valve 10 and the outlet 4, and at the other end to the low pressure discharge system 12. The pressure relief valve 11 can be opened when necessary to reduce the pressure in the compressor 1, in particular the inlet pressure of the compressor 1. The low pressure discharge system 12 can be any system capable of safely receiving and disposing of the discharged gas, such as a flare system or a recovery system.

[0028] The bypass line 13 is used to gradually restore the inlet pressure of the compressor 1 after it is started. One end of the bypass line 13 is connected to the section of the inlet line 7 between the inlet shut-off valve 9 and the inlet 3, and the other end is connected to the section of the inlet line 7 upstream of the inlet shut-off valve 9 (i.e. using the pressure of the process system itself to boost the pressure). The diameter of the bypass line 13 is usually smaller than that of the inlet line 7 to facilitate slow pressure build-up. A bypass valve 14 is provided in the bypass line 13.

[0029] During the process of increasing the speed and pressure of the compressor 1, it is necessary to maintain full flow from the outlet 4 to the inlet 3. One end of the flow-back line is connected to the section of the inlet line 7 between the inlet shut-off valve 9 and the inlet 3, and the other end is connected to the section of the outlet line 8 between the outlet shut-off valve 10 and the outlet 4. A flow-back valve is provided in the flow-back line to control the opening and closing of the flow-back line.

[0030] The compressor 1 further comprises a control unit 15, such as a part of a PLC (Programmable Logic Controller) or a DCS (Distributed Control System). The control unit 15 is electrically or signal connected to the inlet shut-off valve 9, the outlet shut-off valve 10, the pressure relief valve 11 and the pressure boosting device 13, and is configured to perform the starting method of the present application. Preferably, the entire starting process is performed by the control unit 15 to ensure the accuracy and repeatability of the operation, and to shorten the operation time.

[0031] With reference to Figure 1 , in combination Figure 2 , the specific steps of the starting method for the compressor 1 provided by the present application are as follows:

[0032] Step S101: Preparation before starting and pressure reduction.

[0033] Before starting the compressor 1, the control unit 15 first closes the inlet shut-off valve 9, the outlet shut-off valve 10 and the bypass valve 14. In this way, the section of the compressor 1 between the inlet shut-off valve 9 and the outlet shut-off valve 10 is isolated. The control unit 15 also opens the flow-back valve to connect the outlet 4 directly back to the inlet 3.

[0034] Subsequently, the control unit 15 opens the pressure relief valve 11 to discharge the gas (such as ethylene) in the isolated section to the low pressure discharge system 12, thereby gradually reducing the pressure in the isolated section (i.e. the pressure at the inlet end of the compressor 1).

[0035] Step S102: Start the compressor after reaching the first pressure.

[0036] The control unit 15 continuously monitors the pressure in the isolated section. When the pressure is reduced to the first pressure, the control unit 15 closes the pressure relief valve 11 and starts the main motor of the compressor 1, so that the compressor 1 starts to rotate.

[0037] The first pressure is intended to ensure that the axial thrust of the compressor 1 at the start is lower than the allowable load of the thrust bearing 6 in the start-up phase. Preferably, the first pressure is between 1.0 MPa and 2.0 MPa, more preferably 1.6 MPa. This pressure value is selected because, at this inlet pressure, the axial thrust generated by the rotor 5 of the compressor when it starts is not more than the maximum allowable load of the thrust bearing 6 in the start-up phase (for example, less than or equal to 18 kgf) when the lubrication conditions can not be sufficient, thereby effectively avoiding damage to the thrust bearing.

[0038] Step S103: Increase the pressure and open the outlet as needed after stable operation.

[0039] After the compressor 1 starts and reaches a stable operation state (for example, the speed is stable, the vibration and bearing temperature are within the allowable range), the control unit 15 first opens the bypass valve 14 to slowly increase the pressure. Specifically, the stable operation of the compressor 1 can be that the speed of the compressor 1 reaches 95% (or higher, for example, 100%) of the preset start-up speed, and / or the vibration value of the key parts (such as the bearing) of the compressor 1 is lower than the preset threshold, and / or the temperature of the key parts (such as the bearing) of the compressor 1 is lower than the preset threshold and remains stable for a period of time. Optionally, the control unit 15 is configured with monitoring and alarm functions. During the pressure reduction process, if the pressure fails to decrease to the first pressure within the specified time, the control unit 15 alarms and suspends the start of the compressor 1.

[0040] The control unit 15 can increase the pressure at a preset pressure increase rate (dP / dt), or gradually increase the pressure in stages. Optionally, during the pressure increase process, the control unit 15 can monitor the axial thrust of the compressor 1 (through a sensor) or key operating parameters (such as motor current and vibration, etc.), and dynamically adjust the pressure increase rate according to these parameters to ensure that the axial thrust is always within the allowable range and smoothly transitions. Optionally, during the pressure increase process, if the control unit 15 monitors abnormal parameters (such as excessive vibration, rapid rise in bearing temperature), the pressure increase is paused or a protective shutdown is performed.

[0041] After the pressure in the isolated section reaches the second pressure. The second pressure usually corresponds to the inlet pressure required for normal operation of the compressor 1. Preferably, the second pressure is between 2.5 MPa and 3.0 MPa, more preferably 2.7 MPa.

[0042] After the pressure in the isolated section (inlet pressure) reaches the second pressure, the control unit 15 closes the bypass valve 14, opens the control outlet shut-off valve 10, and gradually closes the return valve, so that the compressor 1 enters the normal process operation flow.

[0043] In the context of the present application, a regulating valve refers to a valve capable of regulating the percentage of opening degree. In some embodiments, one or more of the pressure relief valve 11, the bypass valve 14, and the return valve are regulating valves, so as to regulate one or more of the pressure relief rate, the pressurization rate, and the return ratio.

[0044] To ensure the quick response of the entire device and reduce the impact on the downstream process (for example, after the compressor is unexpectedly shut down), the total time from the start of the main motor of the compressor 1 (i.e., the time when the compressor is started in step S102) to the time when the inlet pressure of the compressor 1 reaches the second pressure (i.e., the time when the pressurization is completed in step S103) should be as short as possible. Preferably, the total time does not exceed a preset time length. The time length can be determined according to the process requirements, the characteristics of the compressor 1, and the bearing capacity of the downstream system. Preferably, the time length does not exceed 10 minutes. Through the precise control of the control unit 15 and the optimized pressurization rate, this goal can be achieved.

[0045] The embodiments of the present application effectively protect the thrust bearing by significantly reducing the compressor inlet pressure to the first pressure before starting, so that the axial thrust at the starting moment is far below the allowable load of the thrust bearing. After the compressor is stably operated, the inlet pressure is gradually restored to the second pressure. This method is particularly suitable for large centrifugal ethylene compressors, solves the problem that the thrust bearing is easily damaged due to excessive axial thrust when directly started at high inlet pressure, improves the reliability and service life of the compressor operation, and ensures the stable production of the entire ethylene device.

[0046] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A starting method for a centrifugal compressor (1), characterized in that, The centrifugal compressor (1) comprises: a housing (2) having an inlet (3) and an outlet (4) and internally provided with a rotor (5) and a thrust bearing (6); an inlet line (7) connected to the inlet (3); an outlet line (8) connected to the outlet (4); an inlet shut-off valve (9) provided in the inlet line (7) upstream of the inlet (3); an outlet shut-off valve (10) provided in the outlet line (8) downstream of the outlet (4); a pressure relief valve (11) connected at one end to a pipe section of the outlet line (8) between the outlet shut-off valve (10) and the outlet (4) and at the other end to a low-pressure discharge system (12); a bypass line (13) connected at one end to a pipe section of the inlet line (7) between the inlet shut-off valve (9) and the inlet (3) and at the other end to a pipe section of the inlet line (7) upstream of the inlet shut-off valve (9), wherein the bypass line (13) has a smaller pipe diameter than the inlet line (7); a bypass valve (14) provided in the bypass line (13); a recirculation line having one end connected to a pipe section of the inlet line (7) between the inlet shut-off valve (9) and the inlet (3) and the other end connected to a pipe section of the outlet line (8) between the outlet shut-off valve (10) and the outlet (4); a recirculation valve provided in the recirculation line; and a control unit (15) configured to execute the start-up method; the start-up method comprises the following steps: before starting the centrifugal compressor (1), closing the inlet shut-off valve (9), the bypass valve (14) and the outlet shut-off valve (10) to isolate the section between the inlet shut-off valve (9) and the outlet shut-off valve (10) as a whole and opening the recirculation valve to connect the outlet (4) directly back to the inlet (3); opening the pressure relief valve (11) to reduce the pressure in the isolated section to a first pressure; after the pressure in the isolated section reaches the first pressure, closing the pressure relief valve (11) and then starting the centrifugal compressor (1); after the centrifugal compressor (1) is running stably, opening the bypass valve (14) to gradually increase the pressure in the isolated section to a second pressure; and after the pressure in the isolated section reaches the second pressure, closing the bypass valve (14), opening the outlet shut-off valve (10) and gradually closing the recirculation valve.

2. The method according to claim 1, wherein the first pressure is between 1.0 MPa and 2.0 MPa; and the second pressure is between 2.5 MPa and 3.0 MPa.

3. The method according to claim 1, wherein the first pressure is determined based on the maximum allowable load of the thrust bearing of the centrifugal compressor (1) in the start-up phase.

4. The method according to claim 1, wherein A total time from starting the centrifugal compressor (1) to reaching a second pressure of an inlet pressure of the centrifugal compressor (1) is no more than a first time length. 5.The method of claim 4, wherein, The first time length is 10 minutes. 6.The method of claim 1, wherein, The stable operation of the centrifugal compressor (1) comprises that a rotating speed of the centrifugal compressor (1) reaches 95% of a preset starting rotating speed. 7.The method of claim 1, wherein, The gradually increasing of the pressure at the inlet end of the centrifugal compressor (1) comprises increasing the pressure at a preset pressure increasing rate or increasing the pressure in stages. 8.The method of claim 1, wherein, The centrifugal compressor (1) is an ethylene compressor.

9. The method of claim 1, wherein, One or more of the pressure relief valve (11), the bypass valve (14) and the return valve is an adjusting valve. 10.The method of claim 2, wherein, The first pressure is 1.6 MPa; and The second pressure is 2.7 MPa.

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