CN110044132B - Control method of propylene flooded refrigeration system - Google Patents
Control method of propylene flooded refrigeration system Download PDFInfo
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- CN110044132B CN110044132B CN201910401365.8A CN201910401365A CN110044132B CN 110044132 B CN110044132 B CN 110044132B CN 201910401365 A CN201910401365 A CN 201910401365A CN 110044132 B CN110044132 B CN 110044132B
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- refrigerant
- propylene
- control module
- compressor assembly
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- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 title claims abstract description 69
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 title claims abstract description 69
- 238000005057 refrigeration Methods 0.000 title claims abstract description 55
- 238000000034 method Methods 0.000 title claims abstract description 36
- 239000003507 refrigerant Substances 0.000 claims abstract description 113
- 239000007788 liquid Substances 0.000 claims abstract description 95
- 230000000712 assembly Effects 0.000 claims description 18
- 238000000429 assembly Methods 0.000 claims description 18
- 210000001503 joint Anatomy 0.000 claims description 11
- 238000002485 combustion reaction Methods 0.000 claims description 9
- 238000001514 detection method Methods 0.000 claims description 4
- 230000005540 biological transmission Effects 0.000 claims description 3
- 238000001704 evaporation Methods 0.000 abstract description 7
- 230000008020 evaporation Effects 0.000 abstract description 7
- 230000000694 effects Effects 0.000 abstract description 5
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 abstract description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 9
- 238000001816 cooling Methods 0.000 description 5
- 239000000047 product Substances 0.000 description 4
- 150000001336 alkenes Chemical class 0.000 description 3
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000013589 supplement Substances 0.000 description 2
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
- F25J1/008—Hydrocarbons
- F25J1/0087—Propane; Propylene
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
- F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
- F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
- F25J1/0244—Operation; Control and regulation; Instrumentation
Abstract
The invention relates to a control method of a propylene flooded refrigeration system, which designs and constructs a refrigeration system based on propylene as a refrigerant by fully utilizing the characteristics of the propylene, designs a circulating pipeline control method, and realizes refrigeration operation through the circulation change of different gaseous and liquid states of the propylene, so that the whole refrigeration system taking the propylene as the refrigerant has the following advantages: 1. the OBD value of the refrigerant is 0, and the refrigerant does not damage the ozone layer at all; 2. the unit mass flow rate is large; 3. the thermodynamic performance is better; 4. the lowest evaporation temperature of-60 ℃ can be obtained; 5. the propylene is easy to extract as an auxiliary product of the MTO device, and the cost is relatively low; 6. the system shares the refrigerant system, and the partial load efficiency is higher; the control method of the propylene flooded refrigeration system provided by the invention can fully improve the utilization rate of the refrigerant while ensuring the refrigeration effect.
Description
Technical Field
The invention relates to a control method of a propylene flooded refrigeration system, belonging to the technical field of refrigeration system control.
Background
The technology-MTO for preparing olefin from methanol is a key technology for preparing ethylene and propylene at present, is widely applied at present, and the project for preparing olefin from methanol is increasing at home. One of the key process points of the project for preparing olefin from methanol is the primary cooling liquefaction process of propylene, and as an essential key equipment refrigerating unit in the propylene cooling process, the methanol-to-olefin refrigeration process is used for cooling propylene at 50 ℃ to-38 ℃ at one time, wherein the refrigerant of a common refrigerating unit is difficult to meet the process characteristic requirements of large cooling capacity, large temperature difference and the like. Propylene is an important product in a methanol-to-olefin production device, is a novel refrigerating unit refrigerant, and has many advantages when propylene R1270A is used as a refrigerant: 1. the OBD value of the refrigerant is 0, and the refrigerant does not damage the ozone layer at all; 2. the unit mass flow rate is large; 3. the thermodynamic performance is better; 4. the lowest evaporation temperature of-60 ℃ can be obtained; 5. the propylene is easy to extract as an auxiliary product of the MTO device, and the cost is relatively low; 6. the system shares the refrigerant system, and the partial load efficiency is higher; therefore, if propylene is used as a refrigerant, equipment is designed to realize refrigeration, and the application efficiency of the refrigeration technology is greatly improved.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a control method of a propylene flooded refrigeration system, which realizes refrigeration based on propylene as a refrigerant, and can fully improve the utilization rate of the refrigerant while ensuring the refrigeration effect.
The invention adopts the following technical scheme for solving the technical problems: the invention designs a propylene flooded refrigeration system which realizes refrigeration based on propylene as a refrigerant and comprises a control module, a condenser, a refrigerant throttling device, an evaporator, a first liquid level sensor, a temperature sensor and at least one compressor assembly, wherein the condenser is connected with the refrigerant throttling device; the output end of each compressor assembly is respectively butted with the input end of a condenser through a gas pipeline, the output end of the condenser is butted with the input end of a refrigerant throttling device through a liquid supply pipeline, the output end of the refrigerant throttling device is butted with the input end of an evaporator through an electronic expansion valve of the evaporator through a liquid supply pipeline, a first liquid level sensor is arranged in the evaporator to realize the detection of the liquid level of the refrigerant in the evaporator, a temperature sensor is arranged at the output end of the evaporator, and the output end of the evaporator is respectively butted with the input end of each compressor assembly through the gas pipeline; the propylene refrigerant sequentially passes through the compressor assembly, the condenser, the refrigerant throttling device and the evaporator and then returns to the compressor assembly, and refrigeration is realized through circulation of the propylene refrigerant;
the control module is respectively butted with each compressor assembly to realize the collection of the suction pressure of each compressor assembly and the data transmission; the control module is respectively butted with the refrigerant throttling device, the first liquid level sensor and the electronic expansion valve of the evaporator, and realizes the control of the electronic expansion valve of the evaporator according to the refrigerant liquid level in the evaporator obtained by the first liquid level sensor so as to control the refrigerant liquid supply amount of the evaporator; the control module is in butt joint with a temperature sensor and detects and obtains the temperature of the output end of the evaporator;
the control method executes the following steps in real time, and propylene is used as a refrigerant to realize refrigeration control;
step A, the control module controls the opening of the electronic expansion valve of the evaporator and the electronic expansion valve of the flash tank, namely the work of the evaporator and the flash tank is realized, and the step B is entered;
and step B, the control module obtains the current temperature Te of the output end of the evaporator, and operates according to the preset target temperature Ts of the evaporator and the preset evaporator plus-minus load temperature difference Td as follows:
if Te is more than Ts + Td, entering step C;
if Ts is more than or equal to Te and less than or equal to Ts + Td, entering the step F;
if Te is less than Ts, entering step H;
if Te is less than Ts-Td, entering step J;
c, judging whether an un-started compressor assembly exists or not, if so, randomly selecting one of the compressor assemblies aiming at the un-started compressor assemblies, updating the compressor assembly to be used as the current compressor assembly for starting, working at preset initial working power, and then entering the step D; otherwise, no further operation is carried out, and the step D is carried out;
d, judging whether Te is in a descending trend, if yes, returning to the step B when Te is less than or equal to Ts + Td; otherwise, entering the step E;
e, the control module judges whether the current load of the current compressor assembly is in a full load state, if so, the control module returns to the step C, otherwise, the power value is increased according to a preset stage, the working power of the current compressor assembly is improved, and the control module returns to the step D;
f, the control module judges whether the current load of the compressor assembly is not higher than a preset load lower limit threshold value or not aiming at the compressor assembly which is running and has the maximum running time, if so, the control module controls the compressor assembly to stop, and returns to the step B; otherwise, entering step G;
g, the control module reduces the power value according to a preset stage, reduces the working power of the current compressor assembly, namely, carries out load shedding aiming at the compressor assembly, reduces the working power of the compressor assembly, and returns to the step B;
step H, the control module compares the thermodynamic curve of the propylene refrigerant according to Te, converts the thermodynamic curve to obtain target suction pressure, sends the target suction pressure to each running compressor assembly respectively, and then enters step I;
step I, the controllers of all the running compressor assemblies respectively receive target suction pressure, and automatically reduce the working power value by combining the current suction pressure of the compressors, namely, load shedding is carried out on the compressor assemblies, and then the step B is returned;
step J, judging whether the running compressor assemblies exist or not, if so, controlling all the running compressor assemblies to stop by the control module, and then returning to the step B; otherwise, no further operation is carried out, and the step B is returned;
when the steps are executed, the control module controls the electronic expansion valve of the evaporator according to the refrigerant liquid level in the evaporator obtained by the first liquid level sensor, so that the refrigerant liquid supply amount of the evaporator is controlled, and the requirement of the preset refrigerant liquid supply amount of the evaporator is met;
meanwhile, the control module controls the electronic expansion valve of the flash tank according to the refrigerant liquid level in the flash tank obtained by the second liquid level sensor, so that the refrigerant liquid supply amount of the flash tank is controlled, and the requirement of presetting the refrigerant liquid supply amount of the flash tank is met.
As a preferred technical scheme of the invention: the control module controls an electronic expansion valve of the evaporator by adopting a fuzzy PID control method according to the refrigerant liquid level in the evaporator obtained by the first liquid level sensor, so as to control the refrigerant liquid supply amount of the evaporator and meet the preset refrigerant liquid supply amount requirement of the evaporator;
the control module adopts a fuzzy PID control method to control the electronic expansion valve of the flash tank according to the refrigerant liquid level in the flash tank obtained by the second liquid level sensor, so as to control the refrigerant liquid supply amount of the flash tank and meet the preset refrigerant liquid supply amount requirement of the flash tank.
As a preferred technical scheme of the invention: the preset lower load threshold is 10%.
As a preferred technical scheme of the invention: the output end of the condenser is in butt joint with the liquid supply input end of the flash evaporator through a liquid supply pipeline and an electronic expansion valve of the flash evaporator, the output end of the flash evaporator is in butt joint with the input end of the refrigerant throttling device, the second liquid level sensor is arranged in the flash evaporator, the control module is in butt joint with the second liquid level sensor and the electronic expansion valve of the flash evaporator respectively, and the control module realizes control over the electronic expansion valve of the flash evaporator according to the liquid level of the refrigerant in the flash evaporator obtained by the second liquid level sensor so as to control the liquid supply amount of the refrigerant of the flash evaporator; meanwhile, the exhaust end of each compressor assembly is respectively butted with the air inlet end of the flash tank through a gas pipeline.
As a preferred technical scheme of the invention: the compressor further comprises a combustion discharge device connected with the control module, and key leakage points on each compressor assembly are respectively in butt joint with the input end of the combustion discharge device through a gas pipeline.
Compared with the prior art, the control method of the propylene flooded refrigeration system has the following technical effects:
the control method of the propylene flooded refrigeration system provided by the invention designs and constructs the refrigeration system based on propylene as a refrigerant by fully utilizing the characteristics of propylene, and designs the circulating pipeline control method, so that the refrigeration operation is realized through the circulating change of different gaseous and liquid states of propylene, and the whole refrigeration system using propylene as the refrigerant has the following advantages: 1. the OBD value of the refrigerant is 0, and the refrigerant does not damage the ozone layer at all; 2. the unit mass flow rate is large; 3. the thermodynamic performance is better; 4. the lowest evaporation temperature of-60 ℃ can be obtained; 5. the propylene is easy to extract as an auxiliary product of the MTO device, and the cost is relatively low; 6. the system shares the refrigerant system, and the partial load efficiency is higher; the control method of the propylene flooded refrigeration system provided by the invention can fully improve the utilization rate of the refrigerant while ensuring the refrigeration effect.
Drawings
FIG. 1 is a schematic block diagram of the present invention for a propylene flooded refrigeration system;
fig. 2 is a schematic diagram of the control architecture for a propylene flooded refrigeration system of the present invention.
Detailed Description
The following description will explain embodiments of the present invention in further detail with reference to the accompanying drawings.
The invention designs a propylene flooded refrigeration system, which realizes refrigeration based on propylene as a refrigerant, and in practical application, as shown in fig. 2, the propylene flooded refrigeration system specifically comprises a control module, a condenser, a refrigerant throttling device, an evaporator, a first liquid level sensor, a temperature sensor, a flash tank, a second liquid level sensor, a combustion discharge device and at least one compressor assembly.
As shown in fig. 1, the output end of each compressor assembly is respectively butted with the input end of a condenser through a gas pipeline, the output end of the condenser is butted with the liquid supply input end of a flash evaporator through a liquid supply pipeline and an electronic expansion valve of the flash evaporator, a second liquid level sensor is arranged in the flash evaporator to realize the detection of the liquid level of a refrigerant in the flash evaporator, the output end of the flash evaporator is butted with the input end of a refrigerant throttling device, the output end of the refrigerant throttling device is butted with the input end of an evaporator through the liquid supply pipeline and the electronic expansion valve of the evaporator, a first liquid level sensor is arranged in the evaporator to realize the detection of the liquid level of the refrigerant in the evaporator, a temperature sensor is arranged at the output end of the evaporator, and the output end of the evaporator is respectively butted with the input end of each; the propylene refrigerant sequentially passes through the compressor assembly, the condenser, the refrigerant throttling device and the evaporator and then returns to the compressor assembly, and refrigeration is realized through circulation of the propylene refrigerant.
The control module is respectively butted with each compressor assembly to realize the collection of the suction pressure of each compressor assembly and the data transmission; the control module is respectively butted with the refrigerant throttling device, the first liquid level sensor, the electronic expansion valve of the evaporator, the second liquid level sensor, the electronic expansion valve of the flash evaporator and the combustion discharge device; in practical application, the control module controls the electronic expansion valve of the flash tank according to the refrigerant liquid level in the flash tank obtained by the second liquid level sensor, so as to control the refrigerant liquid supply amount of the flash tank; meanwhile, the exhaust end of each compressor component is respectively butted with the air inlet end of the flash tank through a gas pipeline; the control module controls the electronic expansion valve of the evaporator according to the refrigerant liquid level in the evaporator obtained by the first liquid level sensor, so as to control the refrigerant liquid supply amount of the evaporator; the control module is in butt joint with a temperature sensor and detects and obtains the temperature of the output end of the evaporator; moreover, in practical application, key leakage points on each compressor assembly are respectively butted with the input end of the combustion discharge device through a gas pipeline.
Based on the designed propylene flooded refrigeration system, the invention specifically designs a control method based on the system, and in practical application, as shown in fig. 1 and fig. 2, the following steps are specifically executed in real time, and propylene is used as a refrigerant to realize refrigeration control.
And step A, the control module controls the opening of the electronic expansion valve of the evaporator and the electronic expansion valve of the flash evaporator to realize the work of the evaporator and the flash evaporator, and the step B is entered.
And step B, the control module obtains the current temperature Te of the output end of the evaporator, and operates according to the preset target temperature Ts of the evaporator and the preset evaporator plus-minus load temperature difference Td as follows:
if Te is more than Ts + Td, entering step C;
if Ts is more than or equal to Te and less than or equal to Ts + Td, entering the step F;
if Te is less than Ts, entering step H;
if Te < Ts-Td, go to step J.
C, judging whether an un-started compressor assembly exists or not, if so, randomly selecting one of the compressor assemblies aiming at the un-started compressor assemblies, updating the compressor assembly to be used as the current compressor assembly for starting, working at preset initial working power, and then entering the step D; otherwise, no further operation is carried out and the step D is carried out.
D, judging whether Te is in a descending trend, if yes, returning to the step B when Te is less than or equal to Ts + Td; otherwise, entering the step E.
And E, judging whether the current load of the current compressor assembly is in a full load state or not by the control module, if so, returning to the step C, otherwise, increasing the power value according to a preset stage, improving the working power of the current compressor assembly, and returning to the step D.
F, the control module judges whether the current load of the compressor assembly is not higher than a preset load lower limit threshold value or not aiming at the compressor assembly which is running and has the maximum running time, if so, the control module controls the compressor assembly to stop, and returns to the step B; otherwise, go to step G. In practical application, the preset lower load threshold is specifically selected to be 10%.
And G, reducing the power value by the control module according to a preset stage, reducing the working power of the current compressor assembly, namely carrying out load shedding aiming at the compressor assembly, reducing the working power of the compressor assembly, and returning to the step B.
And step H, comparing the thermodynamic curve of the propylene refrigerant by the control module according to Te, converting to obtain target suction pressure, respectively sending the target suction pressure to each running compressor assembly, and then entering the step I.
And step I, the controllers of the running compressor assemblies respectively receive the target suction pressure, and automatically reduce the working power value by combining the current suction pressure of the compressors, namely, load shedding is carried out on the compressor assemblies, and then the step B is returned.
Step J, judging whether the running compressor assemblies exist or not, if so, controlling all the running compressor assemblies to stop by the control module, and then returning to the step B; otherwise, no further operation is carried out, and the step B is returned.
When the steps are executed, the control module controls an electronic expansion valve of the evaporator by adopting a fuzzy PID control method according to the refrigerant liquid level in the evaporator obtained by the first liquid level sensor, so that the refrigerant liquid supply amount of the evaporator is controlled, and the preset refrigerant liquid supply amount requirement of the evaporator is met; meanwhile, the control module controls an electronic expansion valve of the flash tank by adopting a fuzzy PID control method according to the refrigerant liquid level in the flash tank obtained by the second liquid level sensor, so that the refrigerant liquid supply amount of the flash tank is controlled, and the preset refrigerant liquid supply amount requirement of the flash tank is met.
The control method of the designed propylene flooded refrigeration system is applied to practice, and 3 compressor components are selected, wherein the 1# compressor component is a propylene compressor with 200Kw refrigerating capacity; the 2# compressor assembly and the 3# compressor assembly are both 800Kw refrigerating capacity propylene refrigeration compressors; in actual working operation, when the heating heat source of the system is small, the 1# compressor assembly is started; when the load is gradually increased, the 2# compressor assembly and the 3# compressor assembly are restarted; this has the following advantages.
1. The method can adapt to different heat load requirements by starting and stopping the compressor assembly and controlling the capacity of the compressor assembly, achieves accurate control of process points, reduces the running time of the compressor assembly in a low-load interval, and prolongs the running life of a compressor unit; and the energy efficiency ratio of the compressor unit is improved.
2. The designed refrigeration system adopts the shared evaporator, and has larger heat exchange area of the usable evaporator and higher evaporation temperature of the compressor compared with an independent evaporator under partial conformity, and the compressor unit with the same specification can generate larger refrigerating capacity.
3. In the designed refrigerating system, the condenser adopts a common refrigerant system, so that lower condensing pressure can be obtained under partial load, the energy consumption of the compressor can be reduced, and the comprehensive energy efficiency ratio COP of the system can be improved.
4. In the designed refrigerating system, the flash tank enters the compressor unit for intermediate air supplement after being throttled by flash tank, so that the exhaust volume of the compressor under low-temperature working conditions can be improved, lower evaporation pressure can be provided, and higher efficiency can be provided by intermediate air supplement.
5. In the designed refrigerating system, a flash tank liquid level sensor adopts fuzzy PID for self-tuning control.
6. In the designed refrigeration system, the liquid level of the evaporator is subjected to fuzzy PID self-tuning regulation according to the measured value of the liquid level sensor of the evaporator.
7. In the designed refrigerating system, the combustion device collects propylene gas discharged from key leakage points of the system and then intensively discharges the propylene gas to a torch for combustion, thereby avoiding safety accidents such as explosion and the like.
In practical application, the 1# compressor assembly, the 2# compressor assembly and the 3# compressor assembly are parallel and mutually independent systems, and can be independently started, stopped and closed without mutual influence; and the condenser, the evaporator, the flash tank and the refrigerant throttling device are system shared devices, and any compressor assembly is started, and the devices are required to be put into use. The system principle is as follows: the 1# compressor assembly, the 2# compressor assembly and the 3# compressor assembly compress propylene refrigerant gas and then enter a condenser, the condenser is cooled and then enters a flash evaporator to be subjected to secondary deep cooling, the refrigerant enters a refrigerant throttling device after being cooled, the refrigerant enters an evaporator after being throttled to be subjected to heat exchange evaporation, and the evaporated propylene refrigerant gas enters a refrigeration compressor.
According to the control method of the propylene flooded refrigeration system designed by the technical scheme, the refrigeration system based on propylene as the refrigerant is designed and constructed by fully utilizing the characteristics of propylene, and the circulating pipeline control method is designed, so that the refrigeration operation is realized through the circulating change of propylene in different gaseous and liquid states, and the whole refrigeration system using propylene as the refrigerant has the following advantages: 1. the OBD value of the refrigerant is 0, and the refrigerant does not damage the ozone layer at all; 2. the unit mass flow rate is large; 3. the thermodynamic performance is better; 4. the lowest evaporation temperature of-60 ℃ can be obtained; 5. the propylene is easy to extract as an auxiliary product of the MTO device, and the cost is relatively low; 6. the system shares the refrigerant system, and the partial load efficiency is higher; the control method of the propylene flooded refrigeration system provided by the invention can fully improve the utilization rate of the refrigerant while ensuring the refrigeration effect.
The embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
Claims (5)
1. A control method of a propylene flooded refrigeration system is characterized in that: the propylene flooded refrigeration system realizes refrigeration based on propylene as a refrigerant and comprises a control module, a condenser, a refrigerant throttling device, an evaporator, a first liquid level sensor, a temperature sensor and at least one compressor assembly; the output end of each compressor assembly is respectively butted with the input end of a condenser through a gas pipeline, the output end of the condenser is butted with the input end of a refrigerant throttling device through a liquid supply pipeline, the output end of the refrigerant throttling device is butted with the input end of an evaporator through an electronic expansion valve of the evaporator through a liquid supply pipeline, a first liquid level sensor is arranged in the evaporator to realize the detection of the liquid level of the refrigerant in the evaporator, a temperature sensor is arranged at the output end of the evaporator, and the output end of the evaporator is respectively butted with the input end of each compressor assembly through the gas pipeline; the propylene refrigerant sequentially passes through the compressor assembly, the condenser, the refrigerant throttling device and the evaporator and then returns to the compressor assembly, and refrigeration is realized through circulation of the propylene refrigerant;
the control module is respectively butted with each compressor assembly to realize the collection of the suction pressure of each compressor assembly and the data transmission; the control module is respectively butted with the refrigerant throttling device, the first liquid level sensor and the electronic expansion valve of the evaporator, and realizes the control of the electronic expansion valve of the evaporator according to the refrigerant liquid level in the evaporator obtained by the first liquid level sensor so as to control the refrigerant liquid supply amount of the evaporator; the control module is in butt joint with a temperature sensor and detects and obtains the temperature of the output end of the evaporator;
the control method executes the following steps in real time, and propylene is used as a refrigerant to realize refrigeration control;
step A, the control module controls the opening of the electronic expansion valve of the evaporator and the electronic expansion valve of the flash tank, namely the work of the evaporator and the flash tank is realized, and the step B is entered;
and step B, the control module obtains the current temperature Te of the output end of the evaporator, and operates according to the preset target temperature Ts of the evaporator and the preset evaporator plus-minus load temperature difference Td as follows:
if Te is more than Ts + Td, entering step C;
if Ts is more than or equal to Te and less than or equal to Ts + Td, entering the step F;
if Te is less than Ts, entering step H;
if Te is less than Ts-Td, entering step J;
c, judging whether an un-started compressor assembly exists or not, if so, randomly selecting one of the compressor assemblies aiming at the un-started compressor assemblies, updating the compressor assembly to be used as the current compressor assembly for starting, working at preset initial working power, and then entering the step D; otherwise, no further operation is carried out, and the step D is carried out;
d, judging whether Te is in a descending trend, if yes, returning to the step B when Te is less than or equal to Ts + Td; otherwise, entering the step E;
e, the control module judges whether the current load of the current compressor assembly is in a full load state, if so, the control module returns to the step C, otherwise, the power value is increased according to a preset stage, the working power of the current compressor assembly is improved, and the control module returns to the step D;
f, the control module judges whether the current load of the compressor assembly is not higher than a preset load lower limit threshold value or not aiming at the compressor assembly which is running and has the maximum running time, if so, the control module controls the compressor assembly to stop, and returns to the step B; otherwise, entering step G;
g, the control module reduces the power value according to a preset stage, reduces the working power of the current compressor assembly, namely, carries out load shedding aiming at the compressor assembly, reduces the working power of the compressor assembly, and returns to the step B;
step H, the control module compares the thermodynamic curve of the propylene refrigerant according to Te, converts the thermodynamic curve to obtain target suction pressure, sends the target suction pressure to each running compressor assembly respectively, and then enters step I;
step I, the controllers of all the running compressor assemblies respectively receive target suction pressure, and automatically reduce the working power value by combining the current suction pressure of the compressors, namely, load shedding is carried out on the compressor assemblies, and then the step B is returned;
step J, judging whether the running compressor assemblies exist or not, if so, controlling all the running compressor assemblies to stop by the control module, and then returning to the step B; otherwise, no further operation is carried out, and the step B is returned;
when the steps are executed, the control module controls the electronic expansion valve of the evaporator according to the refrigerant liquid level in the evaporator obtained by the first liquid level sensor, so that the refrigerant liquid supply amount of the evaporator is controlled, and the requirement of the preset refrigerant liquid supply amount of the evaporator is met; meanwhile, the control module controls the electronic expansion valve of the flash tank according to the refrigerant liquid level in the flash tank obtained by the second liquid level sensor, so that the refrigerant liquid supply amount of the flash tank is controlled, and the requirement of presetting the refrigerant liquid supply amount of the flash tank is met.
2. The control method of the propylene flooded refrigeration system as recited in claim 1, wherein: the control module controls an electronic expansion valve of the evaporator by adopting a fuzzy PID control method according to the refrigerant liquid level in the evaporator obtained by the first liquid level sensor, so as to control the refrigerant liquid supply amount of the evaporator and meet the preset refrigerant liquid supply amount requirement of the evaporator;
the control module adopts a fuzzy PID control method to control the electronic expansion valve of the flash tank according to the refrigerant liquid level in the flash tank obtained by the second liquid level sensor, so as to control the refrigerant liquid supply amount of the flash tank and meet the preset refrigerant liquid supply amount requirement of the flash tank.
3. The control method of the propylene flooded refrigeration system as recited in claim 1, wherein: the preset lower load threshold is 10%.
4. The control method of the propylene flooded refrigeration system as recited in claim 1, wherein: the output end of the condenser is in butt joint with the liquid supply input end of the flash evaporator through a liquid supply pipeline and an electronic expansion valve of the flash evaporator, the output end of the flash evaporator is in butt joint with the input end of the refrigerant throttling device, the second liquid level sensor is arranged in the flash evaporator, the control module is in butt joint with the second liquid level sensor and the electronic expansion valve of the flash evaporator respectively, and the control module realizes control over the electronic expansion valve of the flash evaporator according to the liquid level of the refrigerant in the flash evaporator obtained by the second liquid level sensor so as to control the liquid supply amount of the refrigerant of the flash evaporator; meanwhile, the exhaust end of each compressor assembly is respectively butted with the air inlet end of the flash tank through a gas pipeline.
5. A control method for a propylene flooded refrigeration system as claimed in claim 1 or 4, wherein: the compressor further comprises a combustion discharge device connected with the control module, and key leakage points on each compressor assembly are respectively in butt joint with the input end of the combustion discharge device through a gas pipeline.
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