On-line switching system and method for main machine and standby machine based on coaxial refrigerating unit

Abstract

The invention relates to the technical field of compressor control, in particular to a main and standby machine online switching system and method based on a coaxial refrigerating unit, and the system comprises a coaxial main machine unit, a standby machine unit connected with the main machine unit in parallel, a gas path switching unit and a control unit; the gas path switching unit comprises an inlet main pipeline, a gas-liquid separator connected with the output end of the inlet main pipeline, a first inlet adjusting pipeline connected with the gas output end of the gas-liquid separator and the input end of the main unit, and a second inlet adjusting pipeline connected with the gas output end of the gas-liquid separator and the input end of the standby unit. And a main engine anti-surge return pipeline and a standby engine anti-surge return pipeline. The main machine unit and the standby machine unit share one section of separator behind the inlet main pipeline, the standby machine unit only stops rotating, is standby and maintains pressure under the condition that the main machine unit normally operates through the inlet stop valve and the outlet stop valve, and therefore online switching between the main machine unit and the standby machine unit is achieved based on the gas circuit switching unit.

Description

Technical Field

[0001] The present application relates to the field of compressor control technology, and in particular to a system and method for online switching of a main and standby machine based on a coaxial refrigeration unit. Background Art

[0002] An industrial refrigeration unit is a combination of equipment used in industrial production processes to transfer heat from low-temperature objects or spaces to high-temperature environments through a refrigeration cycle, thereby reducing the temperature of specific industrial equipment, process fluids or spaces.

[0003] With the development of modern industry, industrial refrigeration units have become indispensable equipment in many industries. At present, each refrigeration unit in a factory has different cooling capacity and different temperatures. Taking into account the intensiveness and energy consumption of the equipment, users of new projects usually consider concentrating all refrigeration units in one centrifugal compression refrigeration unit to reduce the floor space, improve efficiency, save energy and reduce carbon emissions; but this can easily lead to the failure of the cooling equipment of the entire factory to operate normally in the event of a failure in any of the equipment. Therefore, during the construction of the refrigeration unit, the factory will set up two sets of the same unit, one main and one standby, for standby in case of failure. However, since the compressor of the centrifugal compression refrigeration unit generally needs to be replaced with nitrogen first and then with refrigerant when starting, this will result in the standby machine starting time being too long in the event of a failure of the main equipment, and it is often unable to meet the requirements of the refrigeration unit to put the standby machine into use before the reserve refrigerant is exhausted. Summary of the invention

[0004] In response to the above problems, the present application provides an online switching system and method for main and standby unit switching based on a coaxial refrigeration unit, wherein the main unit and the standby unit share a separator after the inlet main line, and through the inlet shut-off valve and the outlet shut-off valve, the main unit operates normally while the standby unit only stops and waits for pressure to be maintained, thereby achieving online switching between the main unit and the standby unit based on the gas circuit switching unit, ensuring centralized and stable cooling throughout the plant with high efficiency and low cost.

[0005] To achieve the purpose of this application, this application provides the following technical solutions:

[0006] In a first aspect, the present application provides a master-standby online switching system based on a coaxial refrigeration unit, comprising:

[0007] The main engine unit comprises a first compressor, a steam turbine, a first gearbox and a first electric generator arranged coaxially; the first compressor comprises at least two compression sections;

[0008] A standby unit, installed in parallel with the main unit, comprises a second compressor, a second gearbox and a second electric motor; the second compressor comprises at least two compression sections;

[0009] A gas circuit switching unit, comprising an inlet main line, a gas-liquid separator connected to the output end of the inlet main line, a first inlet regulating pipeline for connecting the gas output end of the gas-liquid separator and the input end of the main machine unit, a second inlet regulating pipeline for connecting the gas output end of the gas-liquid separator and the input end of the standby machine unit, a first outlet main line of the main machine unit, a second outlet main line of the standby machine unit, a main machine second-stage pipeline connected between the inlet main line and the second compression section of the first compressor, and a standby machine second-stage pipeline connected between the inlet main line and the second compression section of the second compressor; wherein the first inlet regulating pipeline and the second inlet regulating pipeline are arranged in parallel, and the output end of the first outlet main line and the output end of the second outlet main line are simultaneously connected to the next process equipment; an inlet cut-off valve is installed on the inlet main line, and a first inlet regulating valve and a second inlet regulating valve are installed on the first inlet regulating pipeline and the second inlet regulating pipeline respectively, and the first outlet main line and The first outlet shut-off valve and the second outlet shut-off valve are respectively installed on the second outlet main pipeline; the second inlet shut-off valve of the main engine, the second separator of the main engine and the second inlet regulating valve of the main engine are sequentially installed on the second section pipeline of the main engine along the air inlet direction, and the second inlet shut-off valve of the standby engine, the second separator of the standby engine and the second inlet regulating valve of the standby engine are sequentially installed on the second section pipeline of the standby engine along the air inlet direction; the first return pipeline of the main engine is arranged between the compressor outlet pipeline and the inlet main pipeline of the main engine unit, and the outlet pipeline of the compressor of the main engine unit and the second section pipeline of the main engine are arranged between the outlet pipeline of the compressor of the main engine unit and the second section pipeline of the main engine. A main machine second return pipeline is provided between the main machine unit, a main machine first return anti-surge valve is provided on the main machine first return pipeline, and a main machine second return anti-surge valve is provided on the main machine second return pipeline; a standby machine first return pipeline is provided between the compressor outlet pipeline and the inlet main pipeline of the standby machine unit, a standby machine second return pipeline is provided between the compressor outlet pipeline of the standby machine unit and the standby machine second section pipeline, a standby machine first return anti-surge valve is provided on the standby machine first return pipeline, and a standby machine second return anti-surge valve is provided on the standby machine second return pipeline;

[0010] A control unit is used to obtain the operating parameters of the main unit and the standby unit, and to perform switching control on the gas path switching unit based on the operating parameters.

[0011] In a possible implementation, one end of the first return pipeline of the main machine is connected between the inlet cut-off valve and the gas-liquid separation unit, and one end of the second return pipeline of the main machine is connected between the second-stage inlet cut-off valve of the main machine and the second-stage separator of the main machine; one end of the first return pipeline of the standby machine is connected between the inlet cut-off valve and the gas-liquid separation unit, and one end of the second return pipeline of the standby machine is connected between the second-stage inlet cut-off valve of the standby machine and the second-stage separator of the standby machine.

[0012] In a possible implementation, when the first compressor and the second compressor both include three compression stages, the gas circuit switching unit also includes: a three-section main machine pipeline connected between the inlet main pipeline and the third compression stage of the first compressor and a three-section standby machine pipeline connected between the inlet main pipeline and the third compression stage of the second compressor, the three-section main machine pipeline including a three-section main machine inlet shut-off valve, a three-section main machine separator and a three-section main machine inlet regulating valve being sequentially installed along the air intake direction, and the three-section standby machine pipeline including a three-section standby machine inlet shut-off valve, a three-section standby machine separator and a three-section standby machine inlet regulating valve being sequentially installed along the air intake direction.

[0013] In a possible implementation, a host third return pipeline is provided between the compressor outlet pipeline of the host unit and the host three-stage pipeline, and a host third return anti-surge valve is provided on the host third return pipeline; a standby third return pipeline is provided between the compressor outlet pipeline of the standby unit and the standby three-stage pipeline, and a standby third return anti-surge valve is provided on the standby third return pipeline; wherein, one end of the host third return pipeline is connected between the host three-stage inlet cut-off valve and the host three-stage separator, and one end of the standby third return pipeline is connected between the standby three-stage inlet cut-off valve and the standby three-stage separator.

[0014] In one possible implementation, the first electric generator is used in the main engine unit to generate electricity based on excess steam and store the generated electric energy so as to perform compensatory work based on the first electric generator when the steam supply of the main engine unit is insufficient for a short period of time.

[0015] In a possible implementation, both the main unit and the standby unit are provided with a dry gas seal auxiliary subsystem, and the dry gas seal auxiliary subsystems of the main unit and the standby unit are put into use at the same time;

[0016] The main engine unit and the standby engine unit share a set of lubricating oil system through a cut-off valve, so that the main engine unit and the standby engine unit can be inspected and maintained separately.

[0017] In a possible implementation, a first outlet check valve is installed on the first outlet pipeline, and the first outlet check valve is arranged between the first return point of the main machine return pipeline and the first outlet cut-off valve along the outlet direction of the first outlet pipeline; a second outlet check valve is installed on the second outlet pipeline, and the second outlet check valve is arranged between the second return point of the standby machine return pipeline and the second outlet cut-off valve along the outlet direction of the second outlet pipeline; wherein the first return point is simultaneously the return point of the first return pipeline of the main machine and the second return pipeline of the main machine, and the second return point is simultaneously the return point of the first return pipeline of the standby machine and the second return pipeline of the standby machine.

[0018] In a second aspect, the present application provides a method for online switching of a master and standby machine based on a coaxial refrigeration unit, which is applied to the above-mentioned master and standby machine online switching system based on a coaxial refrigeration unit, and the method includes:

[0019] When confirming that the backflow anti-surge valve of the host unit, the backflow anti-surge valve of the standby unit, the outlet cut-off valve provided on the compressor outlet pipeline of the standby unit and the inlet regulating valve of the standby unit meet the preset conditions, start the standby unit and increase the speed of the standby unit to the working frequency;

[0020] Switching the backflow anti-surge valve of the main engine unit to a semi-automatic control state;

[0021] Gradually reduce the opening of the backflow anti-surge valve of the standby unit until the pressure difference before and after the inlet cut-off valve of the main unit is less than 10kPa, open the inlet cut-off valve of other compression sections of the standby unit, and switch the backflow anti-surge valve corresponding to the other compression sections to the automatic adjustment state;

[0022] The inlet regulating valve of the standby unit is gradually increased, and the opening of the inlet regulating valve of the main unit is gradually reduced to 10%-15%, and then the inlet cut-off valve of the main unit is closed.

[0023] In one possible implementation, the confirmation that the backflow anti-surge valve of the main unit, the backflow anti-surge valve of the standby unit, the outlet cut-off valve arranged on the compressor outlet pipeline of the standby unit and the inlet regulating valve of the standby unit meet the preset conditions includes: when the backflow anti-surge valve of the main unit is in an automatic control state, controlling the backflow anti-surge valve of the standby unit to be fully opened, and after opening the outlet cut-off valve of the standby unit, opening the inlet regulating valve of the standby unit to 10%-15%.

[0024] In a possible implementation, the method further includes: when the main unit is started for the first time, all the backflow anti-surge valves of the main unit are fully opened; all the inlet shut-off valves and outlet shut-off valves of the main unit are fully opened; the opening of all the inlet regulating valves of the main unit is adjusted to 15%-25%; after the turbine of the main unit is warmed up, the turbine speed is increased to the minimum continuous operating speed according to a preset speed increase curve; based on the minimum continuous operating speed, the turbine speed is slowly increased, and all the inlet regulating valves are alternately opened and all the backflow anti-surge valves are closed until the exhaust pressure is established and the refrigerant to be discharged can be liquefied, indicating that the process is open; the compressor of the main unit is increased to the power generation operating speed, and the electric generator is closed, and the turbine is switched from speed control to load control to complete the start-up of the main unit.

[0025] In a possible implementation, the refrigerant is propylene.

[0026] The present application provides a main-standby online switching system and method based on a coaxial refrigeration unit. The main and standby gas circuits are switched between the coaxially arranged main unit and the standby unit through a gas circuit switching unit. The main unit and the standby unit share a separator after the inlet main circuit. By setting an inlet shut-off valve and an outlet shut-off valve, the standby unit only stops and waits for pressure maintenance when the main unit is operating normally, thereby achieving simultaneous replacement between the main unit and the standby unit based on a separator, ensuring centralized and stable cooling throughout the plant with high efficiency and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the present application and form a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation to the present application.

[0028] Figure 1 An optional structural diagram of a master-standby online switching system based on a coaxial refrigeration unit provided in an embodiment of the present application;

[0029] Figure 2 An optional flow chart of a method for online switching of a master and standby machine based on a coaxial refrigeration unit provided in an embodiment of the present application;

[0030] Figure 3 An optional flow chart of a method for online switching of a master and standby machine based on a coaxial refrigeration unit provided in an embodiment of the present application;

[0031] Figure 4 An optional structural schematic diagram of a master-standby online switching system based on a coaxial refrigeration unit provided in an embodiment of the present application;

[0032] Figure 5An optional flow chart of a method for online switching of a master and standby machine based on a coaxial refrigeration unit provided in an embodiment of the present application;

[0033] Figure 6 An optional flow chart of an online switching method of a master-slave machine based on a coaxial refrigeration unit provided in an embodiment of the present application.

[0034] Reference numerals:

[0035] 1, inlet main pipeline; 2, first inlet regulating pipeline; 3, second inlet regulating pipeline; 10, inlet cut-off valve; 11, gas-liquid separator; 20, first outlet main pipeline; 21, main engine second section pipeline; 211, main engine second section inlet cut-off valve; 212, main engine second section separator; 213, main engine second section inlet regulating valve; 22, main engine third section pipeline; 221, main engine third section inlet cut-off valve; 222, main engine third section separator; 223, main engine third section inlet regulating valve; 23, first inlet regulating valve; 24, first outlet cut-off valve; 25, main engine first return pipeline; 251, main engine first return anti-surge valve; 26, main engine second return pipeline; 261, main engine second return anti-surge valve; 27, main engine third return pipeline 27 1. The third anti-surge valve for the main engine; 28. The first outlet check valve; 30. The second outlet main pipeline; 31. The second section pipeline of the standby machine; 311. The second section inlet cut-off valve of the standby machine; 312. The second section separator of the standby machine; 313. The second section inlet regulating valve of the standby machine; 32. The third section pipeline of the standby machine; 321. The third section inlet cut-off valve of the standby machine; 322. The third section separator of the standby machine; 323. The third section inlet regulating valve of the standby machine; 33. The second inlet regulating valve; 34. The second outlet cut-off valve; 35. The first reflux pipeline of the standby machine; 351. The first reflux anti-surge valve of the standby machine; 36. The second reflux pipeline of the standby machine; 361. The second reflux anti-surge valve of the standby machine; 37. The third reflux pipeline of the standby machine; 371. The third reflux anti-surge valve of the standby machine; 38. The second outlet check valve. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of this application, unless otherwise specified, "plurality" means two or more.

[0038] Industrial refrigeration units are a combination of equipment used in industrial production processes to transfer heat from low-temperature objects or spaces to high-temperature environments through refrigeration cycles, thereby reducing the temperature of specific industrial equipment, process fluids or spaces. As the core part of the industrial cooling system, industrial refrigeration units are mainly composed of key components such as compressors, evaporators, condensers and throttling devices. They can provide a stable cold source to meet the cooling, condensing, freezing and other needs in industrial production.

[0039] Among them, the centrifugal compressor is the core component of the unit. Its function is to compress the refrigerant vapor through the high-speed rotating impeller and promote the refrigerant to circulate in the refrigeration system. The refrigerant vapor enters from the center of the impeller and is thrown to the edge of the impeller under the action of centrifugal force, and the speed and pressure increase. After that, the kinetic energy of the high-speed airflow is converted into pressure energy through the diffuser, so that the pressure of the refrigerant is further increased. The evaporator is the place where the refrigerant vaporizes and absorbs heat in the refrigeration system. The liquid refrigerant absorbs the heat of the cooled medium (such as water or other coolants) in the evaporator, and then vaporizes into a gaseous refrigerant. The structure of the evaporator can be in various forms such as shell and tube type and plate type. Taking the shell and tube type as an example, the refrigerant flows in the tube and the cooled medium flows in the shell, and the two exchange heat through the tube wall. The main function of the condenser is to cool and condense the high-temperature and high-pressure refrigerant vapor discharged from the compressor into a liquid state. Its working process is to allow the refrigerant vapor to exchange heat with the cooling medium (air for air cooling and water for water cooling). The throttling device (expansion valve) throttles and reduces the pressure of the liquid refrigerant from the condenser, causing the pressure and temperature of the refrigerant to drop sharply, forming a low-temperature and low-pressure liquid-vapor mixture. This process allows the refrigerant to vaporize and absorb heat again in the evaporator. During the operation of the unit, the liquid refrigerant in the evaporator absorbs heat and vaporizes into gaseous refrigerant, which is sucked into the centrifugal compressor. The compressor compresses the gaseous refrigerant to turn it into high-temperature and high-pressure refrigerant vapor, and then discharges it to the condenser. In the condenser, the refrigerant vapor exchanges heat with the cooling medium, cools and condenses into liquid. After the liquid refrigerant is reduced in pressure by the throttling device, it returns to the evaporator to start the next refrigeration cycle.

[0040] Usually, a factory will set up multiple industrial refrigeration units such as piston compressors, screw compressors and centrifugal compressors according to different cooling capacities and temperatures. Considering the intensiveness and energy saving of equipment, users of new projects usually consider concentrating all cooling units in one centrifugal compression refrigeration unit to reduce floor space, improve efficiency and save energy and reduce carbon emissions. However, with the concentration of equipment, when any of the equipment fails, especially when the steam of the turbine is insufficient and the turbine needs to be shut down, or when the turbine fails, the cooling equipment of the entire plant will also fail to operate normally. Therefore, during the construction of the refrigeration unit, two sets of the same unit will be set up, one main and one standby, for standby in case of failure. However, since the compressor of the centrifugal compression refrigeration unit generally needs to be replaced with nitrogen first and then with refrigerant when starting, this will result in too long a start-up time for the standby unit in the case of a main equipment failure, which often cannot meet the cold unit's need to put the standby unit into use before the reserve refrigerant is exhausted, resulting in the shutdown of the process equipment in the industrial production process, causing certain economic losses.

[0041] In order to solve the above technical problems, the present invention proposes the following technical solutions and corresponding embodiments.

[0042] Example 1

[0043] Combine the following Figures 1 to 6 The embodiments shown describe the technical solution of the present invention:

[0044] Figure 1 The schematic diagram of the structure of the master-slave online switching system based on the coaxial refrigeration unit according to the embodiment of the present application is shown. Figure 1 As shown, the master-standby online switching system based on the coaxial refrigeration unit of the embodiment of the present application includes:

[0045] The main engine unit comprises a first compressor, a steam turbine, a first gearbox and a first electric generator arranged coaxially; wherein the first compressor comprises at least two compression sections for compressing the sucked refrigerant vapor to generate high-temperature and high-pressure refrigerant vapor to prepare for the subsequent heat release process in the condenser of the refrigeration unit; the steam turbine is used to provide power for the first compressor in the main engine unit, is coaxially connected to the first compressor, and drives the first compressor to compress the refrigerant vapor; at the same time, the steam turbine also transmits its excess steam to the first electric generator for power generation, and then feeds the electric energy back to the power grid to prevent the steam turbine from malfunctioning or the steam supply from being insufficient. In the case of a failure of the refrigeration unit, the first motor generator is quickly switched to the motor mode to provide power for the compressor, maintain the basic operation of the refrigeration unit, and avoid interruption of the refrigeration process; the first gear box is connected to the output shaft of the steam turbine and the input end of the first compressor at the same time, and is used to adjust the speed, and at the same time buffer the torque fluctuation between the steam turbine and the first compressor to a certain extent, so as to ensure the stability of power transmission; the first gear box is coaxial with the first compressor and connected to the first motor generator; the first motor generator is used to operate as a motor to drive the first compressor and the steam turbine to rotate during the startup of the main unit; and during the normal operation of the main unit, the excess energy of the steam turbine is converted into electrical energy for storage;

[0046] The standby unit includes a second compressor, a second gearbox and a second electric generator, and is used to switch to the standby unit online to operate for refrigeration in the event of a failure of the main unit; wherein,

[0047] The gas circuit switching unit comprises an inlet main line 1, a gas-liquid separator 11 connected to the output end of the inlet main line, a first inlet regulating pipeline 2 for connecting the gas output end of the gas-liquid separator 11 and the input end of the main unit, a second inlet regulating pipeline 3 for connecting the gas output end of the gas-liquid separator 11 and the input end of the standby unit, a first outlet main line 20 of the main unit, a second outlet main line 30 of the standby unit, a main unit second-stage pipeline 21 connected between the second-stage upstream process and the second compression stage of the first compressor, and a standby unit second-stage pipeline 31 connected between the second-stage upstream process and the second compression stage of the second compressor, wherein the second-stage pipeline 21 of the main unit is connected to the second-stage upstream process and the second compression stage of the second compressor. The main machine second stage inlet shut-off valve 211, the main machine second stage separator 212 and the main machine second stage inlet regulating valve 213 are sequentially arranged along the air inlet direction, and the standby machine second stage inlet shut-off valve 311, the standby machine second stage separator 312 and the standby machine second stage inlet regulating valve 313 are sequentially arranged along the air inlet direction on the standby machine second stage pipeline 31; wherein, the first inlet regulating pipeline 2 and the second inlet regulating pipeline 3 are arranged in parallel, and the output end of the first outlet main pipeline 20 and the output end of the second outlet main pipeline 30 are simultaneously connected to the next process equipment; wherein, the inlet main pipeline is installed with an inlet shut-off valve 10, and the first inlet regulating valve 23 and the second inlet regulating valve 23 are respectively installed on the first inlet regulating pipeline 2 and the second inlet regulating pipeline 3. A throttle valve 33 is provided, and a first outlet shut-off valve 24 and a second outlet shut-off valve 34 are installed on the first outlet main line 20 and the second outlet main line 30 respectively; a host first return line 25 is provided between the compressor outlet line and the inlet main line 1 of the host unit, and a host second return line 26 is provided between the compressor outlet line and the host second-stage line 21 of the host unit, one end of the host first return line 25 is connected between the inlet shut-off valve 10 and the gas-liquid separation unit 11, and one end of the host second return line 26 is connected between the host second-stage inlet shut-off valve 211 and the host second-stage separator 212, and a host first return anti-surge valve 251 is provided on the host first return line 25, and the A host second reflux anti-surge valve 261 is provided on the host second reflux pipeline 26; a standby first reflux pipeline 35 is provided between the compressor outlet pipeline and the inlet main pipeline 1 of the standby unit, and a standby second reflux pipeline 36 is provided between the compressor outlet pipeline of the standby unit and the standby second-stage pipeline, one end of the standby first reflux pipeline 35 is connected between the inlet cut-off valve 10 and the gas-liquid separation unit 11, and one end of the standby second reflux pipeline 36 is connected between the standby second-stage inlet cut-off valve 311 and the standby second-stage separator 312, a standby first reflux anti-surge valve 351 is provided on the standby first reflux pipeline 35, and a standby second reflux anti-surge valve 361 is provided on the standby second reflux pipeline 36;

[0048] A control unit, the control unit is used to obtain operating parameters of the main unit and the standby unit, and to perform switching control on the gas path switching unit based on the operating parameters.

[0049] In the embodiment of the present application, a first outlet check valve 28 and a second outlet check valve 38 are installed on the first outlet main line 20 and the second outlet main line 30 respectively.

[0050] In the embodiment of the present application, when the steam turbine of the main unit is insufficient and the turbine needs to be shut down, or when the turbine fails, the gas circuit switching unit quickly switches to the standby unit for refrigeration. Figure 2 As shown, the control unit controls the gas path switching unit to sequentially perform the following steps S201 to S204:

[0051] S201, when the main engine first backflow anti-surge valve 251 and the main engine second backflow anti-surge valve 261 are in the automatic control state, the standby engine first backflow anti-surge valve 351 and the standby engine second backflow anti-surge valve 361 are fully opened, and the second outlet cut-off valve 34 is opened, and then the second inlet regulating valve 33 is opened to 10%-15%;

[0052] In an embodiment of the present application, the automatic control state may be a surge control logic built into a control unit (Programmable Logic Controller), which processes the signals obtained from the flow sensor, pressure sensor and temperature sensor of the refrigeration unit according to a preset surge curve and algorithm. The surge curve refers to the one obtained through the performance test and theoretical calculation of the compressor, which is used to describe the surge boundary of the compressor under different working conditions (such as different speeds, inlet pressures, etc.). For example, the PLC compares the actually measured flow and pressure signals with the surge curve, and when it is found that the current operating point is close to or enters the surge area, a control signal is generated to start the automatic control program to adjust the opening of the backflow anti-surge valve to increase or decrease.

[0053] S202, start the standby unit (compressor refrigerant pressure maintenance cold standby) with one button, increase its speed to the working frequency, and then switch the host first backflow anti-surge valve 251 and the host second backflow anti-surge valve 261 to the semi-automatic control state;

[0054] In the embodiment of the present application, the semi-automatic control state refers to a state in which manual intervention and automatic control are combined; specifically, the operator can manually start the automatic control program or set certain parameters of the automatic control according to the operating conditions of the unit and some monitoring parameters, and then the PLC automatically adjusts the valve opening according to preset rules and algorithms to prevent compressor surge.

[0055] S203, gradually reduce the opening of the first backflow anti-surge valve 351 and the second backflow anti-surge valve 361 of the standby unit until the pressure before the inlet cut-off valve 10 is 10 kPa or less than 10 kPa higher than the pressure after the inlet cut-off valve 10, open the second-stage inlet cut-off valve 311 of the standby unit, and automatically switch the first backflow anti-surge valve 351 and the second backflow anti-surge valve 361 of the standby unit;

[0056] S204, slowly open the second inlet regulating valve 33 from 10%-15%, and slowly reduce the first inlet regulating valve 23 to 10%-15%, and close the host second stage inlet cut-off valve 211 corresponding to the host unit to shut down the host, thereby completing the main-standby switching.

[0057] Among them, when the host unit is operating normally, the standby unit needs to be started first, including:

[0058] S2021, when the first backflow anti-surge valve 251 and the second backflow anti-surge valve 261 of the main engine are in the automatic control state, open the first backflow anti-surge valve 351 and the second backflow anti-surge valve 361 of the standby engine, and at the same time fully open the second outlet cut-off valve 30, fully close the second stage inlet cut-off valve 211 and the third stage inlet cut-off valve 221 of the main engine, and fully close the first outlet cut-off valve 24;

[0059] S2022, control the opening of the first inlet regulating valve 23 and the main engine second stage inlet regulating valve 213 to 10%-15%, increase the speed of the main motor to the working frequency, and complete the startup of the standby unit.

[0060] In the embodiment of the present application, after the equipment of the main unit has been repaired and debugged, the running unit is adjusted from the standby unit to the main unit for refrigeration through the gas circuit switching unit. Figure 3 As shown, the control unit controls the gas path switching unit to sequentially perform the following steps S301 to S304:

[0061] S301, when the first backflow anti-surge valve 351 and the second backflow anti-surge valve 361 of the standby machine are in the automatic control state, the first backflow anti-surge valve 251 and the second backflow anti-surge valve 261 of the main machine are fully opened, and the first outlet cut-off valve 24 is opened, and then the first inlet regulating valve 23 is opened to 10%-15%;

[0062] S302, start the main unit with one button and increase its speed to the working frequency, then switch the first backflow anti-surge valve 351 and the second backflow anti-surge valve 361 of the standby unit to the semi-automatic control state;

[0063] Among them, starting the host unit normally in advance specifically includes:

[0064] S3021, the main engine first backflow anti-surge valve 251, the main engine second backflow anti-surge valve 261 are fully opened, the inlet cut-off valve 10 is fully opened, the main engine second stage inlet cut-off valve 211 is fully closed, and the first outlet cut-off valve 24 is fully closed;

[0065] S3022, after the steam turbine is warmed up, the speed of the steam turbine is increased to the minimum continuous operation speed according to the preset speed increase curve, and the opening of the first inlet regulating valve 23 and the main engine second stage inlet regulating valve 213 are controlled at 10%-15%;

[0066] S3023, gradually close the main engine first backflow anti-surge valve 251, open the first inlet regulating valve 23, the main engine second stage inlet regulating valve 213, and increase the speed of the first compressor, and alternately perform the above three actions until the first compressor speed increases to the power generation condition speed;

[0067] S3024, continue to keep the main engine first backflow anti-surge valve 251 and the main engine second backflow anti-surge valve 261 closed, and when the pressure before the main engine second stage inlet cut-off valve 211 is higher than the pressure after the main engine second stage inlet cut-off valve 211 by less than 10 kPa, open the main engine second stage inlet cut-off valve 211, and continue to open the main engine second backflow anti-surge valve 261, until the outlet pressure of the first compressor reaches 1.4 MPaA, open the first outlet cut-off valve 24, and when the outlet pressure of the first compressor reaches the condensing pressure, push open the first outlet check valve 28, so that the first compressor is incorporated into the process system;

[0068] 25) The first compressor is increased in speed to the power generation operating speed, the first motor generator is switched on, and the steam turbine is switched from speed control to load control, thus completing the start-up of the main unit;

[0069] S303, gradually reduce the opening of the main engine first backflow anti-surge valve 251 and the main engine second backflow anti-surge valve 261 in the fully open state, until the pressure before the main engine second stage inlet cut-off valve 221 is higher than the pressure after the main engine second stage inlet cut-off valve 221 and reaches 10kPa, open the main engine second stage inlet cut-off valve 211 of the main engine unit, and cut the first backflow anti-surge valve 251 automatically;

[0070] S304, slowly open the first inlet regulating valve 23, and slowly close the second inlet regulating valve 33 to 10%-15%, and close the standby second stage inlet cut-off valve 311 corresponding to the standby unit, so that the standby unit is shut down, thereby completing the main-standby switching.

[0071] As a feasible implementation mode, when the first compressor of the host unit and the second compressor of the standby unit in the embodiment of the present application are both three-stage compressors, refer to Figure 4As shown, the gas circuit switching unit also includes a main machine three-section pipeline 22 connected between the three-section upstream process equipment and the third compression stage of the first compressor and a standby machine three-section pipeline 32 connected between the three-section upstream process equipment and the third compression stage of the second compressor, and the main machine three-section inlet shut-off valve 221, the main machine three-section separator 222 and the main machine three-section inlet regulating valve 223 are sequentially installed on the main machine three-section pipeline 22 along the air intake direction, and the standby machine three-section inlet shut-off valve 321, the standby machine three-section separator 322 and the standby machine three-section inlet regulating valve 323 are sequentially installed on the standby machine three-section pipeline 32 along the air intake direction. A host third return pipeline 27 is provided between the compressor outlet pipeline of the host unit and the host three-stage pipeline 22, one end of the host third return pipeline 27 is connected between the host three-stage inlet cut-off valve 221 and the host three-stage separator 222, and a host third return anti-surge valve 271 is provided on the host third return pipeline 27; a standby third return pipeline 37 is provided between the compressor outlet pipeline of the standby unit and the standby three-stage pipeline 32, one end of the standby third return pipeline 37 is connected between the standby three-stage inlet cut-off valve 321 and the standby three-stage separator 322, and a standby third return anti-surge valve 371 is provided on the standby third return pipeline 37; in the embodiment of the present application, when the host unit is running and needs to be switched to the standby unit, refer to Figure 4 , Figure 5 As shown, the control unit controls the gas path switching unit to perform the following contents in sequence:

[0072] S501, when the first backflow anti-surge valve 251, the second backflow anti-surge valve 261 and the third backflow anti-surge valve 271 of the main machine are in the automatic control state, the first backflow anti-surge valve 351, the second backflow anti-surge valve 361 and the third backflow anti-surge valve 371 of the standby machine are fully opened, and the second outlet cut-off valve 34 is opened, and then the second inlet regulating valve 33 is opened to 10%-15%;

[0073] S502, start the standby unit (compressor refrigerant pressure maintenance cold standby), and increase its speed to the working frequency, and then switch the host first backflow anti-surge valve 251, the host second backflow anti-surge valve 261, and the host third backflow anti-surge valve 271 to semi-automatic control state;

[0074] S503, gradually reduce the opening of the first backflow anti-surge valve 351, the second backflow anti-surge valve 361, and the third backflow anti-surge valve 371 of the standby machine, until the pressure before the inlet cut-off valve of each section is 10 kPa higher than the pressure after the inlet cut-off valve, open the second-stage inlet cut-off valve 311 and the third-stage inlet cut-off valve 321 of the standby machine, and switch the second backflow anti-surge valve to automatic;

[0075] S504, slowly open the second inlet regulating valve from 10%-15%, and slowly close the first inlet regulating valve to 10%-15%, and close the host second stage inlet cut-off valve 211 and the host third stage inlet cut-off valve 221 corresponding to the host unit, so that the host is shut down, thereby completing the main-standby switching.

[0076] Here, when the standby unit is running and the host unit needs to be started and switched to, the specific execution logic can be referred to Figure 3 and Figure 4 The content is not elaborated here.

[0077] In the embodiment of the present application, when the host unit is started for the first time (all valves of the gas circuit switching unit are closed by default), the control unit executes the following control content:

[0078] 1) Fully open the first backflow anti-surge valve 251 of the main engine, the second backflow anti-surge valve 261 of the main engine, and the third backflow anti-surge valve 271 of the main engine;

[0079] 2) Fully open the inlet cut-off valve 10, the main engine second stage inlet cut-off valve 211, the main engine third stage inlet cut-off valve 221 and the first outlet cut-off valve 24;

[0080] 3) Adjust the opening of the first inlet regulating valve 23, the second stage inlet regulating valve 213 of the main engine, and the third stage inlet regulating valve 223 of the main engine to 15%-25%;

[0081] 4) After the steam turbine of the main unit is warmed up, the steam turbine speed is increased to the minimum continuous operating speed according to the preset speed increase curve;

[0082] 5) Based on the minimum continuous operation speed, the turbine speed is slowly increased, and at the same time, the first inlet regulating valve 10, the main engine second stage inlet regulating valve 213, the main engine third stage inlet regulating valve 223 are alternately opened, and the main engine first reflux anti-surge valve 251 is closed until the exhaust pressure is established and the refrigerant to be exported can be liquefied, indicating that the process is open;

[0083] 6) The first compressor is increased in speed to the power generation operating speed, the first electric generator is switched on, and the steam turbine is switched from speed control to load control to complete the start-up of the main unit.

[0084] Illustratively, the refrigerant is propylene.

[0085] In an embodiment of the present application, a main and standby gas circuit is switched between a coaxially arranged main unit and a standby unit through a gas circuit switching unit. The main unit and the standby unit share a separator after the inlet main circuit. By setting an inlet shut-off valve and an outlet shut-off valve, when the main unit is operating normally, the standby unit only stops and waits for pressure to be maintained, thereby achieving simultaneous replacement between the main unit and the standby unit based on a separator, ensuring centralized and stable cooling throughout the plant with high efficiency and low cost.

[0086] Example 2

[0087] Based on the above embodiments, the present application also discloses a method for online switching of a master and standby machine based on a coaxial refrigeration unit, which is applied to the above-mentioned master and standby machine online switching system based on a coaxial refrigeration unit, referring to Figure 6 , including the following steps S601 to S604:

[0088] S601. After confirming that the backflow anti-surge valve of the main unit, the backflow anti-surge valve of the standby unit, the outlet cut-off valve of the compressor outlet pipeline arranged on the standby unit and the inlet regulating valve of the standby unit meet the preset conditions, start the standby unit and increase the speed of the standby unit to the working frequency.

[0089] In the embodiment of the present application, the backflow anti-surge valve of the main unit is in the automatic control state, and then the backflow anti-surge valve of the standby unit is fully controlled, and after the outlet cut-off valve of the standby unit is opened, the inlet regulating valve of the standby unit is opened to 10%-15%. In the embodiment of the present application, the automatic control state and the semi-automatic control state refer to the above embodiment.

[0090] S602, switching the backflow anti-surge valve of the host unit to a semi-automatic control state;

[0091] S603, gradually reducing the opening of the backflow anti-surge valve of the standby unit until the pressure difference before and after the inlet cut-off valve of the main unit reaches 10 kPa, opening the inlet cut-off valves of other compression sections of the standby unit, and switching the backflow anti-surge valves corresponding to the other compression sections to the automatic adjustment state;

[0092] S604, gradually increase the opening of the inlet regulating valve of the standby unit, and gradually reduce the opening of the inlet regulating valve of the main unit to 10%-15%, and then close the inlet cut-off valve of the main unit.

[0093] As a result, the host unit can be shut down.

[0094] In this way, when the host unit and the backup unit need to be switched from the host unit to the backup unit, switching between the master and the backup can be achieved.

[0095] Example 3

[0096] Based on the foregoing embodiment, the embodiment of the present application further provides a method for online switching of a master and a standby machine based on a coaxial refrigeration unit. When the first compressor of the master unit and the second compressor of the standby unit are both three-stage compressors, the switching method includes:

[0097] (I) The host is running and needs to be switched to the backup machine

[0098] 1. The main engine anti-surge valve should be in automatic control mode, the standby engine anti-surge valve should be fully opened, the standby engine outlet cut-off valve should be fully opened, and the inlet regulating valve should be opened to 10% to 15%;

[0099] 2. Start the standby machine and increase the speed to the working frequency, and the main engine anti-surge valve switches to semi-automatic (for the first time);

[0100] 3. Gradually reduce the opening of the anti-surge valves at all levels of the standby machine. When the pressure before the cut-off valve at the inlet of each section is higher than the pressure after the valve by less than 10kPa, open the cut-off valves of sections 2 and 3, and the anti-surge valves will be switched to automatic mode.

[0101] 4. Slowly open the standby machine inlet regulating valve, slowly close the main machine inlet regulating valve (inlet pressure control, automatic), until the main machine inlet regulating valve is adjusted to 10%~15%, close the main machine 2, 3 section inlet cut-off valve, and the main machine can be shut down.

[0102] (2) The standby machine is running and needs to be switched to the main machine

[0103] 1. The standby machine anti-surge valve should be in automatic control mode, the host machine anti-surge valve should be fully opened, the host machine outlet cut-off valve should be fully opened, and the inlet regulating valve should be opened to 10%~15%;

[0104] 2. Start the main engine and increase the speed to the normal working speed, and the anti-surge valve switches to semi-automatic mode (for the first time);

[0105] 3. Gradually reduce the opening of each level of anti-surge valve. When the pressure before the cut-off valve at the inlet of each section is higher than the pressure after the valve by less than 10kPa, open the cut-off valves of sections 2 and 3, and the anti-surge valve will be automatically cut off.

[0106] 4. Slowly open the main machine inlet regulating valve, and slowly close the standby machine inlet regulating valve (inlet pressure control, automatic) until the standby machine inlet regulating valve is adjusted to 10%-15%, and close the standby machine 2, 3 section inlet cut-off valves. The standby machine can be shut down.

[0107] (III) The standby machine is running and the host machine starts normally

[0108] 1. The anti-surge valve is fully open, the first stage inlet cut-off valve is fully open, the second and third stage inlet cut-off valves are fully closed, and the outlet cut-off valve is fully closed;

[0109] 2. After the turbine is warmed up, it starts to increase speed according to the speed increase curve to the minimum continuous operation speed, and the opening of the three inlet regulating valves is set to 10-15%;

[0110] 3. Gradually close the anti-surge valve, open the inlet regulating valve, and increase the compressor speed. Perform these three actions alternately until the compressor reaches the operating speed;

[0111] 4. Continue to close the anti-surge valve, wait until the pressure difference before and after the second and third stage inlet cut-off valves is less than 10kPa, open the second and third stage inlet cut-off valves, continue to open the inlet regulating valve and close the anti-surge valve, until the outlet pressure reaches close to 1.4MPaA, open the outlet cut-off valve, wait until the outlet pressure reaches the condensing pressure, the check valve opens, and the compressor is integrated into the process system;

[0112] 5. The compressor continues to increase its speed to the power generation operating speed, the generator is closed, and the turbine switches from speed control to load control.

[0113] (IV) The host machine is running and the standby machine starts normally

[0114] 1. The main engine anti-surge valve is in automatic control mode, the standby engine anti-surge valves are all open, the first stage inlet cut-off valve is fully open, the second and third stage cut-off valves are closed, and the outlet cut-off valve is closed;

[0115] 2. The opening of the three inlet regulating valves is set to 10-15%, and the main motor speed is increased to the working frequency;

[0116] 3. Complete the startup.

[0117] In the embodiment of the present application, when the host unit is started for the first time (all valves of the gas circuit switching unit are closed by default), the control unit executes the following control content:

[0118] 1) Fully open the first backflow anti-surge valve and the second backflow anti-surge valve of the main engine;

[0119] 2) Fully open the inlet cut-off valve, the second stage inlet cut-off valve of the main engine and the first outlet cut-off valve;

[0120] 3) Adjust the opening of the first inlet regulating valve and the second stage inlet regulating valve of the main engine to 15%-25%;

[0121] 4) After the steam turbine of the main unit is warmed up, the steam turbine speed is increased to the minimum continuous operating speed according to the preset speed increase curve;

[0122] 5) Based on the minimum continuous operation speed, slowly increase the turbine speed, and alternately open the first inlet regulating valve, the second stage inlet regulating valve of the main engine, and close the first reflux anti-surge valve of the main engine until the exhaust pressure is established and the refrigerant to be exported can be liquefied, indicating that the process is open;

[0123] 6) The first compressor is increased in speed to the power generation operating speed, the first electric generator is switched on, and the steam turbine is switched from speed control to load control to complete the start-up of the main unit.

[0124] Illustratively, the refrigerant is propylene.

[0125] In this way, the main and standby machines of the coaxial refrigeration unit can realize one-key startup of the main machine or the standby machine, as well as one-key switching between the main and standby machines in various operating conditions.

[0126] The above embodiments are only used to illustrate the technical solution of the present application, but not to limit it. The present application is not limited to the exact structure described above and illustrated in the accompanying drawings, and it cannot be determined that the specific implementation of the present application is limited to these descriptions. For ordinary technicians in the technical field to which the present application belongs, various changes and modifications made without departing from the concept of the present application should be deemed to belong to the protection scope of the present application.

[0127] In the several embodiments provided in the present application, it should be understood that the disclosed systems, modules and methods can be implemented in other ways. For example, the module embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, modules or units, which can be electrical, mechanical or other forms.

[0128] The above embodiments are only used to illustrate the technical solution of the present application, but not to limit it. The present application is not limited to the exact structure described above and illustrated in the accompanying drawings, and it cannot be determined that the specific implementation of the present application is limited to these descriptions. For ordinary technicians in the technical field to which the present application belongs, various changes and modifications made without departing from the concept of the present application should be deemed to belong to the protection scope of the present application.

Claims

1. A master-standby online switching system based on a coaxial refrigeration unit, characterized in that: include: The main engine unit comprises a coaxial first compressor, a steam turbine, a first gearbox and a first electric generator; the first compressor comprises at least two compression sections; A standby unit, installed in parallel with the main unit, comprises a second compressor, a second gearbox and a second electric motor; the second compressor comprises at least two compression sections; A gas circuit switching unit, comprising an inlet main line, a gas-liquid separator connected to the output end of the inlet main line, a first inlet regulating pipeline connecting the gas output end of the gas-liquid separator and the input end of the main unit, a second inlet regulating pipeline connecting the gas output end of the gas-liquid separator and the input end of the standby unit, a first outlet main line of the main unit, a second outlet main line of the standby unit, a main unit second-stage pipeline connected between the inlet main line and the second compression stage of the first compressor, and a standby unit second-stage pipeline connected between the inlet main line and the second compression stage of the second compressor; The output end of the first outlet main pipeline and the output end of the second outlet main pipeline are simultaneously connected to the next process equipment; wherein, an inlet cut-off valve is installed on the inlet main pipeline, a first inlet regulating valve and a second inlet regulating valve are installed on the first inlet regulating pipeline and the second inlet regulating pipeline respectively, and a first outlet cut-off valve and a second outlet cut-off valve are installed on the first outlet main pipeline and the second outlet main pipeline respectively; the main engine second stage inlet cut-off valve, the main engine second stage separator and the main engine second stage inlet regulating valve are installed in sequence along the air inlet direction on the main engine second stage pipeline, and the standby machine second stage inlet cut-off valve, the standby machine second stage separator and the standby machine second stage inlet regulating valve are installed in sequence along the air inlet direction on the standby machine second stage pipeline ; A host first return pipeline is provided between the compressor outlet pipeline of the host unit and the inlet main pipeline, a host second return pipeline is provided between the compressor outlet pipeline of the host unit and the second-stage pipeline of the host, and a host first return anti-surge valve and a host second return anti-surge valve are provided on the first return pipeline of the host and the second return pipeline of the host, respectively; a standby first return pipeline is provided between the compressor outlet pipeline of the standby unit and the inlet main pipeline, a standby second return pipeline is provided between the compressor outlet pipeline of the standby unit and the second-stage pipeline of the standby unit, and a standby first return anti-surge valve and a standby second return anti-surge valve are provided on the first return pipeline of the standby and the second return pipeline of the standby, respectively; A control unit is used to obtain the operating parameters of the main unit and the standby unit, and to perform switching control on the gas path switching unit based on the operating parameters.

2. The main and standby machine online switching system based on the coaxial refrigeration unit according to claim 1 is characterized in that: One end of the first return pipeline of the main engine is connected between the inlet cut-off valve and the gas-liquid separation unit, and one end of the second return pipeline of the main engine is connected between the second-stage inlet cut-off valve of the main engine and the second-stage separator of the main engine; One end of the first reflux pipeline of the standby machine is connected between the inlet cut-off valve and the gas-liquid separation unit, and one end of the second reflux pipeline of the standby machine is connected between the second-stage inlet cut-off valve of the standby machine and the second-stage separator of the standby machine.

3. The main and standby machine online switching system based on the coaxial refrigeration unit according to claim 1 is characterized in that: In the case where both the first compressor and the second compressor include three compression stages, the gas circuit switching unit further includes: A three-section pipeline of the main machine connected between the inlet main line and the third compression stage of the first compressor and a three-section pipeline of the standby machine connected between the inlet main line and the third compression stage of the second compressor, a three-section inlet shut-off valve of the main machine, a three-section separator of the main machine and a three-section inlet regulating valve of the main machine are sequentially installed along the air intake direction on the three-section pipeline of the main machine, and a three-section inlet shut-off valve of the standby machine, a three-section separator of the standby machine and a three-section inlet regulating valve of the standby machine are sequentially installed along the air intake direction on the three-section pipeline of the standby machine.

4. The main and standby machine online switching system based on the coaxial refrigeration unit according to claim 3 is characterized in that: A host third return pipeline is provided between the compressor outlet pipeline of the host unit and the host third section pipeline, and a host third return anti-surge valve is provided on the host third return pipeline; A third return pipeline for the standby machine is provided between the compressor outlet pipeline of the standby machine unit and the third section pipeline of the standby machine, and a third return anti-surge valve for the standby machine is provided on the third return pipeline of the standby machine; Among them, one end of the host third return pipeline is connected between the host three-stage inlet cut-off valve and the host three-stage separator, and one end of the standby third return pipeline is connected between the standby three-stage inlet cut-off valve and the standby three-stage separator.

5. The main and standby machine online switching system based on the coaxial refrigeration unit according to claim 1 is characterized in that: The main unit and the standby unit are both provided with a dry gas sealing auxiliary subsystem, and the dry gas sealing auxiliary subsystems of the main unit and the standby unit are put into use at the same time; The main engine unit and the standby engine unit share a set of lubricating oil system through a cut-off valve, so that the main engine unit and the standby engine unit can be inspected and maintained separately.

6. The master-standby online switching system based on a coaxial refrigeration unit according to any one of claims 1 to 5, characterized in that: A first outlet check valve is installed on the first outlet pipeline, and the first outlet check valve is arranged between the first return point of the main engine return pipeline and the first outlet cut-off valve along the gas outlet direction of the first outlet pipeline; A second outlet check valve is installed on the second outlet pipeline, and the second outlet check valve is arranged between the second return point of the standby machine return pipeline and the second outlet cut-off valve along the gas outlet direction of the second outlet pipeline; The first reflux point is simultaneously the reflux point of the first reflux pipeline of the host machine and the second reflux pipeline of the host machine, and the second reflux point is simultaneously the reflux point of the first reflux pipeline of the standby machine and the second reflux pipeline of the standby machine.

7. A method for online switching of a master and standby machine based on a coaxial refrigeration unit, applied to the online switching system of a master and standby machine based on a coaxial refrigeration unit according to any one of claims 1 to 6, characterized in that: include: When confirming that the backflow anti-surge valve of the host unit, the backflow anti-surge valve of the standby unit, the outlet cut-off valve provided on the compressor outlet pipeline of the standby unit and the inlet regulating valve of the standby unit meet the preset conditions, start the standby unit and increase the speed of the standby unit to the working frequency; Switching the backflow anti-surge valve of the main engine unit to a semi-automatic control state; Gradually reduce the opening of the backflow anti-surge valve of the standby unit until the pressure difference before and after the inlet cut-off valve of the main unit is less than 10kPa, open the inlet cut-off valve of other compression sections of the standby unit, and switch the backflow anti-surge valve corresponding to the other compression sections to the automatic adjustment state; The inlet regulating valve of the standby unit is gradually increased, and the opening of the inlet regulating valve of the main unit is gradually reduced to 10%-15%, and then the inlet cut-off valve of the main unit is closed.

8. The method for online switching of the master and standby machines based on the coaxial refrigeration unit according to claim 7 is characterized in that: The step of confirming that the backflow anti-surge valve of the main unit, the backflow anti-surge valve of the standby unit, the outlet cut-off valve provided on the outlet pipeline of the compressor of the standby unit, and the inlet regulating valve of the standby unit meet the preset status includes: When the backflow anti-surge valve of the main unit is in automatic control state, the backflow anti-surge valve of the standby unit is controlled to be fully opened, and after opening the outlet cut-off valve of the standby unit, the inlet regulating valve of the standby unit is opened to 10%-15%.

9. The method for online switching of the master and standby machines based on the coaxial refrigeration unit according to claim 7 is characterized in that: The method further comprises: When the main engine unit is started for the first time, all the backflow anti-surge valves of the main engine unit are fully opened; Fully open all inlet shut-off valves and outlet shut-off valves of the main engine unit; Adjust the opening of all inlet regulating valves of the main engine unit to 15%-25%; After the steam turbine of the main unit is warmed up, the speed of the steam turbine is increased to the minimum continuous operating speed according to a preset speed increase curve; Based on the minimum continuous operation speed, the turbine speed is slowly increased, and all the inlet regulating valves are opened alternately and all the backflow anti-surge valves are closed alternately, until the exhaust pressure is established and the refrigerant to be discharged can be liquefied, indicating that the process is open; The compressor of the main engine unit is increased in speed to the power generation operating speed, and the electric generator is switched on. The steam turbine is switched from speed control to load control to complete the start-up of the main engine unit.

10. The method for online switching of the master and standby machines based on a coaxial refrigeration unit according to any one of claims 7 to 9, characterized in that: The refrigerant is propylene.

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