Centrifugal refrigeration unit and control method thereof

Abstract

The present invention discloses a centrifugal refrigeration unit and a control method thereof. The centrifugal refrigeration unit comprises: a condenser, a throttling device, a flasher, an evaporator and a centrifugal compressor forming a refrigeration circuit. An air supply branch is provided between the flasher and the centrifugal compressor. The heating device in the centrifugal refrigeration unit is cooled by the cooling branch. An energy recovery device is connected to the refrigeration circuit. When the gaseous refrigerant in the refrigeration circuit drives the energy recovery device to work, the energy recovery device sends the gaseous refrigerant after expansion and cooling back to the flasher, and at the same time absorbs the liquid refrigerant in the refrigeration circuit, pressurizes the liquid refrigerant and sends it to the cooling branch. The present invention utilizes the energy recovery device to recover the excess pressure of the refrigeration circuit, recycles the recovered energy, reduces the cooling loss of the compressor main circuit, reduces the compressor operating power, and achieves energy saving and energy efficiency improvement.

Description

Technical Field

[0001] The present invention relates to the technical field of refrigeration units, and in particular to a centrifugal refrigeration unit and a control method thereof. Background Art

[0002] The centrifugal refrigeration unit mainly consists of: evaporator, condenser, flasher, throttling device and centrifugal compressor. The evaporator mainly absorbs heat from the refrigerant to lower the temperature of the water system to achieve refrigeration. The condenser mainly transfers the heat of the superheated gas of the refrigerant to the water system to achieve refrigerant cooling; the flasher mainly throttles the liquid in the condenser to produce low-temperature gaseous refrigerant and sends it to the middle air supply port of the centrifugal compressor to achieve secondary air supply and cooling of the compressor and reduce the power consumption of the centrifugal compressor; the throttling device mainly throttles and cools the high-temperature and high-pressure refrigerant in the condenser to achieve the pressure on the evaporator side. The pressure change in this process is dissipated through the throttling device; the centrifugal compressor mainly compresses the refrigerant and converts the low-temperature and low-pressure refrigerant into high-temperature and high-pressure refrigerant, which is achieved by consuming electrical energy in this process.

[0003] When the unit is in normal operation, the compressor absorbs low-temperature and low-pressure gaseous refrigerant from the evaporator and reaches the intermediate pressure after passing through the first-stage compressor. At this time, the compressor gas is in an overheated state and a flash evaporator is required to provide low-temperature gas for cooling and neutralization. However, the traditional technology only relies on the gaseous refrigerant produced by the pure throttling device, which is prone to the problem of gas replenishment and liquid, affecting the operating reliability of the compressor.

[0004] In addition, during the operation of the compressor, electrical components such as the motor and inverter will generate heat, and it is necessary to dissipate the heat of the heating components in time to maintain the normal operation of the refrigeration unit. Figure 1 As shown, the traditional cooling method is to use the liquid refrigerant of the condenser 2 for cooling, in which the high pressure of the condenser 2 is used to transport the liquid refrigerant to the cooling branch 9 of the motor and controller 10, and this part of the energy is generated after the compressor 1, which consumes part of the power of the compressor 1, increases the power consumption of the unit, and reduces the energy efficiency of the unit.

[0005] Therefore, how to provide a centrifugal refrigeration unit with energy recovery function is a technical problem that needs to be solved urgently in the industry. Summary of the invention

[0006] In order to solve the defects existing in the prior art, the present invention proposes a centrifugal refrigeration unit and a control method thereof. The centrifugal refrigeration unit utilizes an energy recovery device to recover excess pressure in the refrigeration circuit, recycles the recovered energy, reduces the cooling loss of the compressor main circuit, reduces the compressor operating power, and achieves energy saving and improves energy efficiency.

[0007] The technical solution adopted by the present invention is to design a centrifugal refrigeration unit, including: a condenser, a throttling device, a flash evaporator and a centrifugal compressor forming a refrigeration circuit, an air supply branch is provided between the flash evaporator and the centrifugal compressor, and an energy recovery device is connected to the refrigeration circuit. When the gaseous refrigerant in the refrigeration circuit drives the energy recovery device to work, the energy recovery device sends the gaseous refrigerant after expansion and cooling back to the flash evaporator.

[0008] Among them, the heat-generating device in the centrifugal refrigeration unit is cooled through a cooling branch, the outlet of the cooling branch is connected to the evaporator, and the energy recovery device absorbs the liquid refrigerant in the refrigeration circuit when working, and pressurizes the liquid refrigerant and sends it to the cooling branch.

[0009] In one embodiment, the energy recovery device includes: a casing, a rotating shaft arranged in the casing, a bearing supporting the rotating shaft, an expansion wheel fixed at one end of the rotating shaft, and a compression wheel fixed at the other end of the rotating shaft. The casing is provided with an expansion chamber for accommodating the expansion wheel and a compression chamber for accommodating the compression wheel. Gaseous refrigerant flows through the expansion chamber to drive the expansion wheel to rotate. When the compression wheel rotates, it absorbs liquid refrigerant in the refrigeration circuit and pressurizes it.

[0010] Preferably, the expansion chamber is provided with an air inlet and an air outlet, the air inlet of the expansion chamber is connected to the top of the heat exchange tube of the condenser, and the air outlet of the expansion chamber is connected to the liquid inlet of the flasher.

[0011] Preferably, the compression chamber is provided with a liquid inlet and a liquid outlet, the liquid inlet of the compression chamber is connected to the bottom of the heat exchange tube of the evaporator, and the liquid outlet of the compression chamber is connected to the cooling branch.

[0012] Preferably, the throttling device comprises: a first throttling element connected in series between the outlet of the condenser and the liquid inlet of the flasher, and a second throttling element connected in series between the liquid outlet of the flasher and the inlet of the evaporator.

[0013] Preferably, a cooling outlet is provided at the bottom of the heat exchange tube of the condenser, and the cooling outlet is connected to the cooling branch through a control valve.

[0014] The present invention also provides a control method for the above-mentioned centrifugal refrigeration unit, comprising the following steps: detecting the high-pressure side parameters of the centrifugal refrigeration unit; judging whether the high-pressure side parameters reach the set conditions; if so, closing the control valve, if not, opening the control valve.

[0015] In one embodiment, the high-pressure side parameters include high-pressure side temperature and high-pressure side pressure, and the setting condition is that the high-pressure side temperature and the high-pressure side pressure are not lower than their respective corresponding setting values.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The supercooling pressure in the refrigeration circuit is recovered and utilized through the energy recovery device, and the expanded and cooled air is sent to the flash unit for air replenishment and cooling, thus realizing the secondary air replenishment and enthalpy increase of the centrifugal compressor, avoiding the problem of air replenishment with liquid, and improving the reliability of the unit;

[0018] 2. The recovered energy is used to pressurize the liquid refrigerant to provide flow power, and the liquid refrigerant is transported to the motor, controller and other heating devices through the cooling branch for cooling. This process converts the pressure energy into mechanical energy, reducing the power consumed by the cooling system, thereby realizing the energy-saving effect of the unit by recovering turbine energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is described in detail below with reference to the embodiments and accompanying drawings, wherein:

[0020] Figure 1 It is the system connection diagram of the refrigeration unit in the traditional technology;

[0021] Figure 2 is a system connection diagram of the refrigerant group in the present invention;

[0022] Figure 3 It is a structural schematic diagram of the energy recovery device in the present invention. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The principle of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0025] like Figure 2 As shown, the centrifugal refrigeration unit proposed by the present invention forms a refrigeration circuit in which the refrigerant circulates through a condenser 2, a throttling device, a flash evaporator 3, an evaporator 4 and a centrifugal compressor 1, and an air supply branch 5 is provided between the flash evaporator 3 and the centrifugal compressor 1. The throttling device includes: a first throttling element 6 connected in series between the outlet of the condenser 2 and the liquid inlet of the flash evaporator 3, and a second throttling element 7 connected in series between the liquid outlet of the flash evaporator 3 and the inlet of the evaporator 4. The first throttling element 6 is used to reduce the pressure of the refrigerant flowing out of the condenser 2 into a low-pressure and low-temperature refrigerant, and the second throttling element 7 is used to increase the subcooling degree of the liquid refrigerant flowing out of the flash evaporator 3. The first throttling element 6 and the second throttling element 7 can be electronic expansion valves.

[0026] An energy recovery device 8 is connected to the refrigeration circuit. When the high-temperature gaseous refrigerant in the refrigeration circuit drives the energy recovery device 8 to work, the high-temperature gaseous refrigerant does work due to expansion, and its internal energy, temperature and pressure are reduced. The energy recovery device 8 returns the medium-temperature gaseous refrigerant after expansion and cooling to the flash ignitor 3. The gaseous refrigerant in the flash ignitor 3 mainly consists of two parts, one part is the low-temperature and low-pressure gaseous refrigerant produced by the first throttling element 6, and the other part is the medium-temperature and medium-pressure gaseous refrigerant produced by the energy recovery device 8. The two parts of gas are mixed in the flash ignitor 3 to replenish gas to the centrifugal compressor 1. The medium-temperature gaseous refrigerant and the low-temperature gaseous refrigerant are mixed in the flash ignitor 3, and the liquid component in the low-temperature gaseous refrigerant absorbs heat and vaporizes, thereby avoiding the problem of gas replenishment with liquid caused by the pure throttling device in the prior art.

[0027] During the operation of the unit, the power consumed by the compressor is mainly used to increase the pressure. However, since heat is inevitably generated when working, low-temperature liquid refrigerant is required for cooling. The heating device in the centrifugal refrigeration unit usually uses a cooling branch 9 for cooling. The outlet of the cooling branch 9 is connected to the evaporator 4. When the energy recovery device 8 is working, it absorbs the liquid refrigerant in the refrigeration circuit and pressurizes the liquid refrigerant and sends it to the cooling branch 9. In this process, since the centrifugal compressor 1 does not work on the refrigerant in the cooling branch 9, the consumption of electric energy by the centrifugal compressor 1 is reduced, the energy efficiency level of the refrigeration unit is improved, and the energy saving of the unit is achieved.

[0028] like Figure 3 As shown, the energy recovery device 8 includes: a casing, a rotating shaft 81 arranged in the casing, a bearing 82 supporting the rotating shaft 81, and an expansion wheel 83 fixed to one end of the rotating shaft 81. The casing is provided with an expansion chamber 84 for accommodating the expansion wheel 83. The expansion chamber 84 is provided with an air inlet 841 and an air outlet 842. The air inlet 841 of the expansion chamber 84 is connected to the high-pressure side of the refrigeration circuit, and the air outlet 842 of the expansion chamber 84 is connected to the liquid inlet of the flash igniter 3. The gaseous refrigerant enters the expansion chamber 84 from the air inlet 841 to drive the expansion wheel 83 to rotate. After the gaseous refrigerant does work on the expansion wheel 83, it becomes a medium-temperature and medium-pressure gaseous refrigerant and is sent back to the flash igniter 3.

[0029] Since the inlet of the condenser 2 is connected to the exhaust port of the centrifugal compressor 1, after the unit operates normally, the temperature and pressure on the high-pressure side increase, and there is high-temperature and high-pressure gaseous refrigerant at the top of the heat exchange tube of the condenser 2. The air inlet 841 of the expansion chamber 84 is connected to the top of the heat exchange tube of the condenser 2. The advantage of this design is that the excess pressure of the condenser 2 can be recycled and reused without affecting the normal operation of the refrigeration circuit.

[0030] In some embodiments, the energy recovery device 8 is a turbine-supercharged energy recovery device, a compression wheel 85 is fixed to the other end of the rotating shaft 81, the compression wheel 85 and the expansion wheel 83 are coaxially arranged, and both the compression wheel 85 and the expansion wheel 83 are turbines, the casing is provided with a compression chamber 86 for accommodating the compression wheel 85, the expansion chamber 84 and the compression chamber 86 are separated, the compression chamber 86 is provided with a liquid inlet 861 and a liquid outlet 862, the liquid inlet 861 of the compression chamber 86 is connected to the low-pressure side of the refrigeration circuit, and the liquid outlet 862 of the compression chamber 86 is connected to the cooling branch 9. When the gaseous refrigerant drives the expansion wheel 83 to rotate and work, the expansion chamber 84 sends the gaseous refrigerant after expansion and cooling back to the flash igniter 3, and at the same time, the compression chamber 86 absorbs the liquid refrigerant in the refrigeration circuit, and the compression wheel 85 rotates to pressurize the liquid refrigerant and transport it to the cooling branch 9 to cool the controller 10 and the motor of the compressor and other heating devices.

[0031] Since the outlet of the evaporator 4 is connected to the air intake of the centrifugal compressor 1, after the unit operates normally, liquid refrigerant exists at the bottom of the heat exchange tube of the evaporator 4. The liquid inlet 861 of the compression chamber 86 is connected to the bottom of the heat exchange tube of the evaporator 4. The advantage of this design is that the liquid refrigerant of the evaporator 4 can be utilized to prevent the centrifugal compressor 1 from inhaling liquid.

[0032] It should be noted that the expansion wheel 83 is driven by the high-temperature and high-pressure gaseous refrigerant, and the expansion wheel 83 drives the rotating shaft 81 to rotate, and the pressure energy is converted into mechanical energy. There are many ways to achieve energy recovery, which are not limited to the above-mentioned ways. For example, a power generation structure can be designed to convert the mechanical energy of the rotating shaft 81 into electrical energy. The bearing 82 used in the energy recovery device 8 can be a static pressure gas bearing or a dynamic pressure gas bearing. For the present invention, since the rotating shaft 82 has a rotation speed of up to tens of thousands of revolutions, a dynamic pressure gas bearing is preferred.

[0033] In a preferred embodiment, a cooling outlet is provided at the bottom of the heat exchange tube of the condenser 2, and the cooling outlet is connected to the cooling branch 9 through a control valve. The control valve is closed when the high-pressure side parameters of the centrifugal refrigeration unit reach the set conditions.

[0034] The present invention also provides a control method for the centrifugal refrigeration unit in the above preferred embodiment, comprising the following steps: detecting the high-pressure side parameters of the centrifugal refrigeration unit; determining whether the high-pressure side parameters meet the set conditions; if so, closing the control valve, if not, opening the control valve.

[0035] For ease of understanding, the centrifugal compressor using a two-stage centrifugal compressor is used as an example for explanation. The high-pressure side parameters include the high-pressure side temperature and the high-pressure side pressure, and the setting condition is that the high-pressure side temperature and the high-pressure side pressure are not lower than the corresponding set values. When the centrifugal compressor 1 is just starting up, due to the low high-pressure side temperature and the high-pressure side pressure, the operation of the energy recovery device cannot be satisfied. The control valve remains open, and the cooling of the heating device mainly relies on the pressure difference of the system for circulation, and the liquid refrigerant is taken from the bottom of the condenser 2 for cooling. When the high-pressure side temperature and the high-pressure side pressure rise to not less than the corresponding set values, the control valve is closed, and the energy recovery device 8 provides high-pressure and low-temperature liquid refrigerant for cooling. When the refrigeration unit is in the normal operation process, the centrifugal compressor 1 absorbs the low-temperature and low-pressure gaseous refrigerant from the evaporator 4 and passes through the first-stage compressor to reach the intermediate pressure. At this time, the gas of the centrifugal compressor 1 is in an overheated state, and then the gas of the flash 3 is cooled and then compressed in the second stage to reach the set pressure. Since the power consumed by the second-stage compression is reduced through the intermediate cooling, the energy efficiency level of the refrigeration equipment is indirectly improved.

[0036] The present invention can realize pressure energy recovery of the unit, reduce power consumption of the compressor, increase the air supply volume of the flasher, avoid the problem of air supply with liquid caused by the pure throttling process, and improve the operating reliability of the unit.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Centrifugal refrigeration unit, including: A condenser, a throttling device, a flash evaporator, and a centrifugal compressor forming a refrigeration circuit, wherein an air supply branch is provided between the flash evaporator and the centrifugal compressor; characterized in that it also includes: an energy recovery device connected to the refrigeration circuit; when the gaseous refrigerant in the refrigeration circuit drives the energy recovery device to work, the energy recovery device returns the gaseous refrigerant after expansion and temperature reduction to the flash evaporator; It also includes: a cooling branch for cooling the heating device in the centrifugal refrigeration unit, the outlet of the cooling branch is connected to the evaporator; when the energy recovery device is working, it absorbs the liquid refrigerant in the refrigeration circuit and pressurizes the liquid refrigerant and sends it to the cooling branch; The energy recovery device comprises: a casing, a rotating shaft arranged in the casing, a bearing supporting the rotating shaft, and an expansion wheel fixed at one end of the rotating shaft, wherein the casing is provided with an expansion chamber for accommodating the expansion wheel, and the gaseous refrigerant flows through the expansion chamber to drive the expansion wheel to rotate; The energy recovery device further comprises: a compression wheel fixed at the other end of the rotating shaft, the casing is provided with a compression chamber for accommodating the compression wheel, and the compression wheel absorbs the liquid refrigerant in the refrigeration circuit and increases the pressure when rotating.

2. The centrifugal refrigeration unit according to claim 1, characterized in that: The expansion chamber is provided with an air inlet and an air outlet. The air inlet of the expansion chamber is connected to the top of the heat exchange tube of the condenser, and the air outlet of the expansion chamber is connected to the liquid inlet of the flasher.

3. The centrifugal refrigeration unit according to claim 1, characterized in that: The compression chamber is provided with a liquid inlet and a liquid outlet. The liquid inlet of the compression chamber is connected to the bottom of the heat exchange tube of the evaporator, and the liquid outlet of the compression chamber is connected to the cooling branch.

4. The centrifugal refrigeration unit according to claim 1, characterized in that: The throttling device comprises: a first throttling element connected in series between the outlet of the condenser and the liquid inlet of the flasher, and a second throttling element connected in series between the liquid outlet of the flasher and the inlet of the evaporator.

5. The centrifugal refrigeration unit according to claim 1, characterized in that: A cooling outlet is provided at the bottom of the heat exchange tube of the condenser, and the cooling outlet is connected to the cooling branch through a control valve.

6. A control method for a centrifugal refrigeration unit, characterized in that: The centrifugal refrigeration unit adopts the centrifugal refrigeration unit according to claim 5, and the control method comprises the following steps: Detecting the high-pressure side parameters of the centrifugal refrigeration unit; Determining whether the high-voltage side parameters meet the set conditions; If yes, closing the control valve; If not, the control valve is opened.

7. The control method according to claim 6, characterized in that: The high-pressure side parameters include high-pressure side temperature and high-pressure side pressure, and the setting condition is that both the high-pressure side temperature and the high-pressure side pressure are not lower than their respective corresponding setting values.

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