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CN-121993914-A - Ultralow temperature cascade unit and control method thereof

CN121993914ACN 121993914 ACN121993914 ACN 121993914ACN-121993914-A

Abstract

The invention relates to the technical field of refrigeration, in particular to an ultralow temperature cascade unit and a control method thereof. The ultralow temperature cascade unit comprises a first heat exchange loop and a second heat exchange loop, a maintenance unit and a second heat exchanger, wherein the second heat exchange loop comprises a second compressor and a second liquid reservoir which are sequentially communicated, a third heat exchange channel and a fourth heat exchange channel are arranged in the second heat exchanger, the third heat exchange channel and the fourth heat exchange channel are mutually independent and can exchange heat mutually, the maintenance unit is communicated with the third heat exchange channel, the second liquid reservoir is communicated with the fourth heat exchange channel, the maintenance unit is always kept in an operation state, a unit condenser and a unit evaporator are communicated with the first heat exchange loop, and the unit evaporator is communicated with the second heat exchange loop. The device has the advantages that the refrigerant in the second liquid storage device in the second heat exchange loop is kept in a low-temperature state through the maintenance unit which is always operated and the second heat exchanger, so that the expansion and the pressurization of the refrigerant are prevented.

Inventors

  • ZHOU JIANI
  • FAN ZHONGYANG
  • XU DENGPAN

Assignees

  • 浙江盾安机电科技有限公司

Dates

Publication Date
20260508
Application Date
20241106

Claims (11)

  1. 1. An ultra-low temperature cascade unit, comprising: A first heat exchange flow path, a second heat exchange flow path and a first heat exchanger (30), wherein the first heat exchanger (30) is provided with a first heat exchange channel and a second heat exchange channel which are independent, the first heat exchange channel and the second heat exchange channel can exchange heat with each other, the first heat exchange flow path is communicated with the first heat exchange channel and defines a first heat exchange loop (10), and the second heat exchange flow path is communicated with the second heat exchange channel and defines a second heat exchange loop (20); The maintenance unit (40) and the second heat exchanger (25), the second heat exchange loop (20) comprises a second compressor (21) and a second liquid reservoir (23), the second compressor (21) is communicated with the second liquid reservoir (23), a third heat exchange channel and a fourth heat exchange channel are arranged in the second heat exchanger (25), the third heat exchange channel and the fourth heat exchange channel are mutually independent and can mutually exchange heat, the maintenance unit (40) is communicated with the third heat exchange channel, the second liquid reservoir (23) is communicated with the fourth heat exchange channel, and the maintenance unit (40) is always kept in an operating state; The unit condenser is communicated with the first heat exchange loop (10), and the unit evaporator is communicated with the second heat exchange loop (20).
  2. 2. The cryogenic cascade unit according to claim 1, characterized in that the first heat exchange circuit (10) comprises a first compressor (11), a first oil separator (12), a first liquid reservoir (13) and a first gas-liquid separator (14), the first compressor (11) is in communication with the first oil separator (12), an inlet of the unit condenser is in communication with the first oil separator (12) through a first oil separator exhaust pipe (121), an outlet of the unit condenser is in communication with the first liquid reservoir (13), the first liquid reservoir (13) is in communication with the first gas-liquid separator (14) through the first heat exchanger (30), and the first gas-liquid separator (14) is in communication with the first compressor (11) and forms a circuit.
  3. 3. The ultralow temperature cascade unit according to claim 2, characterized in that the first heat exchange circuit (10) further comprises a first balance pipe (15), one end of the first balance pipe (15) is communicated with the first liquid reservoir (13), and the other end is communicated with the first oil separator exhaust pipe (121).
  4. 4. The cryogenic cascade unit according to claim 2, characterized in that the first oil separator (12) has a first oil return port, and the first oil return port communicates with the first compressor (11); The second heat exchange circuit (20) further comprises a second oil separator (22), wherein the second oil separator (22) is provided with a second oil return port, and the second oil return port is communicated with the second compressor (21).
  5. 5. The cryogenic cascade unit according to claim 1, characterized in that the second heat exchange circuit (20) further comprises a second oil separator (22) and a third heat exchanger (26), wherein the third heat exchanger (26) is provided with a fifth heat exchange channel and a sixth heat exchange channel which are mutually independent, an inlet of the second oil separator (22) is communicated with the second compressor (21), an outlet of the second oil separator (22) is communicated with an inlet of the fifth heat exchange channel, an outlet of the fifth heat exchange channel is communicated with the second liquid reservoir (23) through the first heat exchanger (30), and the sixth heat exchange channel is communicated with the maintenance unit (40).
  6. 6. The ultralow temperature cascade unit according to claim 5, characterized in that the outlet of the fifth heat exchange channel is communicated with the inlet of the second heat exchange channel through a third heat exchanger exhaust pipe (261), and the outlet of the second heat exchange channel is communicated with the second liquid reservoir (23); The second heat exchange loop (20) further comprises a second balance pipe (27), one end of the second balance pipe (27) is communicated with the second liquid reservoir (23), and the other end of the second balance pipe is communicated with the third heat exchanger exhaust pipe (261).
  7. 7. The ultralow temperature cascade unit according to claim 5, characterized in that the second heat exchange circuit (20) further comprises a second gas-liquid separator (24), a bypass pipe (29) and a fourth switching valve (291), wherein an inlet of the second gas-liquid separator (24) is communicated with the unit evaporator through a second gas-liquid separator air inlet pipe (241), one end of the bypass pipe (29) is communicated with the second gas-liquid separator air inlet pipe (241), and the other end is communicated with an outlet of the second oil separator (22).
  8. 8. A control method for implementing an operation control of the cryogenic cascade unit according to any one of claims 1-7, the first heat exchange circuit (10) further comprising a first compressor (11), the control method comprising: Acquiring the suction pressure PH1 of the first compressor (11), comparing the suction pressure PH1 with a preset pressure, and starting the first compressor (11) when PH1 is more than or equal to the preset pressure plus the loading pressure difference and the duration reaches t 1; When PH1< preset pressure + loading pressure difference and the duration reaches t2, turning off the first compressor (11); acquiring the suction pressure PL1 of the second compressor (21), comparing the suction pressure PL1 with a preset pressure, and starting the second compressor (21) when PL1 is more than or equal to the preset pressure+loading differential pressure and the duration reaches t 3; when PL1< preset pressure + loading pressure difference and the duration reaches t4, the second compressor (21) is turned off.
  9. 9. The control method according to claim 8, characterized in that the first compressor (11) and the second compressor (21) each comprise an oil pressure difference switch; Acquiring an oil pressure difference A1 in the first compressor (11) through the oil pressure difference switch, comparing the oil pressure difference A1 with a preset oil pressure difference A2, triggering time calculation when A1 is smaller than A2, and triggering an alarm if A1 is still smaller than A2 after time delay t 5; And acquiring an oil pressure difference A3 in the second compressor (21) through the oil pressure difference switch, comparing the oil pressure difference A3 with a preset oil pressure difference A4, triggering time calculation when A3 is smaller than A4, and triggering an alarm if A3 is still smaller than A4 after time delay t 6.
  10. 10. The control method according to claim 8, characterized in that a first switching valve (16) is provided in the first heat exchange circuit (10), the second heat exchange circuit (20) comprising a second switching valve (28); acquiring the suction superheat degree of the first compressor (11), and comparing the suction superheat degree of the first compressor (11) with a target superheat degree to control the opening degree of the first switch valve (16); and acquiring the suction superheat degree of the second compressor (21), and comparing the suction superheat degree of the second compressor (21) with a target superheat degree to control the opening degree of the second switch valve (28).
  11. 11. The control method according to claim 8, characterized in that a third on-off valve (41) is provided between the maintenance unit (40) and the second heat exchanger (25); -acquiring an operating condition of the second compressor (21); when the second compressor (21) is in an operating state, the third switch valve (41) is closed; When the second compressor (21) is in a closed state, the third switching valve (41) is opened after a delay t 7.

Description

Ultralow temperature cascade unit and control method thereof Technical Field The invention relates to the technical field of refrigeration, in particular to an ultralow temperature cascade unit and a control method thereof. Background Ultra-low temperature refrigeration systems typically use a single dual stage compression refrigeration unit or an ultra-low temperature cascade unit. The limit evaporation temperature of the single-machine double-stage compression refrigerating unit is only minus 60 ℃, and the energy consumption is higher when the single-machine double-stage compression refrigerating unit runs under the limit working condition. The ultralow temperature cascade unit adopts cascade refrigeration cycle formed by two single-machine systems, the two single-machine systems form two heat exchange loops, and the evaporator of one heat exchange loop is used as the condenser of the other loop, so that the temperature of refrigerant in the other loop is reduced, and ultralow temperature refrigeration is realized. Therefore, the load distribution among the compressors in the ultralow temperature cascade unit is balanced, so that the fault rate is reduced, the refrigeration efficiency is improved, and the energy consumption is lower than that of a single-stage refrigeration unit under the same refrigeration capacity. However, due to the ultralow temperature refrigeration requirement of the ultralow temperature cascade unit, the temperature of the refrigerant filled in the heat exchange loop is low, so that when the ultralow temperature cascade unit is stopped, the low temperature refrigerant in the liquid reservoir is easy to expand due to temperature difference conduction, and the pressure in the liquid reservoir and the heat exchange loop is increased after the refrigerant expands to cause the opening of the pressure release valve, so that the daily operation of the ultralow temperature cascade unit is influenced. Disclosure of Invention Aiming at the technical problems, the invention provides an ultralow temperature cascade unit. An ultralow-temperature cascade unit comprises a first heat exchange flow path, a second heat exchange flow path and a first heat exchanger, wherein the first heat exchanger is provided with a first heat exchange channel and a second heat exchange channel which are independent from each other, the first heat exchange channel and the second heat exchange channel can exchange heat mutually, the first heat exchange flow path is communicated with the first heat exchange channel and defines a first heat exchange loop, the second heat exchange flow path is communicated with the second heat exchange channel and defines a second heat exchange loop, a maintenance unit and a second heat exchanger, the second heat exchange loop comprises a second compressor and a second liquid storage device, the second compressor is communicated with the second liquid storage device, the second heat exchanger is internally provided with a third heat exchange channel and a fourth heat exchange channel, the third heat exchange channel and the fourth heat exchange channel are mutually independent and can exchange heat mutually, the maintenance unit is communicated with the third heat exchange channel, the second heat exchange channel and the fourth heat exchange channel are communicated, the liquid storage unit is always kept in an operating state, and the condenser unit and the evaporator unit are communicated with the second heat exchange loop. By the arrangement, the first heat exchange channel and the second heat exchange channel in the first heat exchanger are mutually independent and are in complementary communication, so that only a heat exchange phenomenon exists between the first heat exchange channel and the second heat exchange channel, and the problem of refrigerant mixing does not exist. The first heat exchange channel is located in the first heat exchange loop, and for the first heat exchange loop, the first heat exchange channel serves as an evaporator, and liquid refrigerant absorbs heat and evaporates in the evaporator, so that the second heat exchange channel is cooled. And the second heat exchange channel is used as a condenser for the second heat exchange loop, and the refrigerant flows through the second heat exchange loop to exchange heat with the first heat exchange channel so as to cool, and after the refrigerant is cooled in the second heat exchange channel, the cooling capacity provided by the refrigerant flowing to the unit evaporator becomes larger, and the temperature of the refrigerant is lower, so that the ultralow-temperature refrigeration effect is realized. And because the temperature of the refrigerant in the second heat exchange loop is very low, when the ultralow temperature cascade unit is stopped, the low-temperature refrigerant is easy to expand due to temperature difference conduction, and the pressure in the heat exchange loop is increased after the refrigerant exp