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EP-4621313-B1 - REFRIGERATION CIRCUIT

EP4621313B1EP 4621313 B1EP4621313 B1EP 4621313B1EP-4621313-B1

Inventors

  • ATENCIA ESCUDERO, JAVIER
  • Catalán Gil, Jesús

Dates

Publication Date
20260513
Application Date
20240320

Claims (16)

  1. A refrigeration circuit, configured to use CO2 as refrigerant, comprising: - at least one first compressor (1), - a first gas-cooler (7), connected to the at least one first compressor (1) through a common discharge line (41), - a medium temperature expansion valve (19), - a medium temperature heat exchanger (20), - a liquid receiver (17) that is connected to: - an outlet liquid line (80) that splits in a first liquid line (81) that connects with the medium temperature heat exchanger (20) and a second liquid line (82) that comprises a first expansion valve (28), - a first pressure reduction valve (14) located on a gas-cooler outlet line (50) connecting the outlet of the first gas-cooler (7) with an inlet of the liquid receiver (17), and - a first heat exchanger (18), wherein: the refrigerant flowing through the second liquid line (82) and depressurized by the first expansion valve (28) is also mixed with the refrigerant from the first liquid line (81) leaving the medium temperature heat exchanger (20) and the mixture enters the first heat exchanger (18) to exchange heat with the refrigerant in the first liquid line to be directed to the at least one first compressor (1) through a suction line (59), the refrigeration circuit being characterised in that it further comprises: - a second compressor (2) connected to the at least one first compressor (1) in parallel to the common discharge line (41), - a second heat exchanger (10) that exchanges heat between the refrigerant leaving the first gas-cooler (7) and the refrigerant flowing through a first fluid line (51) that branches from the gas-cooler outlet line (50), either at the inlet or at the outlet of the third heat exchanger (10), and depressurized by a third expansion valve (12), and - a second pipe (65) that connects the inlet of the second compressor (2) with the first fluid line (51) leaving the second heat exchanger (10).
  2. The refrigeration circuit of claim 1, further comprising: - an outlet vapor line (90), comprising a second pressure reduction valve (16), which connects the liquid receiver (17) with the suction line (59) at the outlet of the first heat exchanger (18), and - a third heat exchanger (13) that exchanges heat between the refrigerant flowing through the gas-cooler outlet line (50) upstream the first pressure reduction valve (14), and the refrigerant flowing through the suction line (59) after mixing with the outlet vapor line (90).
  3. The refrigeration circuit of claim 2, that further comprises: - a first motorised multi way valve (27) located in the suction line (59) either at the inlet or at the outlet of the third heat exchanger (13), and - a first pipe (75) connected to the first motorised multi way valve (27) and bypassing the third heat exchanger (13) so that the refrigerant flows from the first heat exchanger (18) mixed with the refrigerant from the outlet vapor line (90) to the at least one first compressor (1) either through the third heat exchanger (13), directly through the first pipe (75), or as a mixture through both elements (13, 75).
  4. The refrigeration circuit of claim 2 or 3, that comprises: - a first vapor line (62) with a first motorised valve (15), connecting the outlet vapor line (90) to the first fluid line (51) at the inlet of the second heat exchanger (10).
  5. The refrigeration circuit of claim 4, that comprises: - a cooling line (43) that connects the first liquid line (81) and the first vapor line (62) and further comprises a cooling coil (91) located within the liquid receiver (17) and a fourth expansion valve (29).
  6. The refrigeration circuit of any of the previous claims, wherein the discharge line (41) comprises a second motorised multi way valve (4) that is connected to the inlet of a fourth heat exchanger (5) through a first branch (42), the outlet of the fourth heat exchanger (5) being connected to the inlet of the first gas-cooler (7).
  7. The refrigeration circuit of any of the previous claims, wherein the discharge line (41), comprises a third motorised multi way valve (6) that is connected to the outlet gas-cooler line (50) through a second branch (66), bypassing the first gas-cooler (7).
  8. The refrigeration circuit of claim 7, that further comprises: - a first check valve (9) located in the gas-cooler outlet line (50) upstream the connection to the second branch (66), - a third branch (71), comprising a third motorised valve (45) that connects the inlet to the first gas-cooler (7) with the outlet vapor line (90), and - a fourth branch (83) comprising a second expansion valve (11) and a second check valve (9'), that connects the first liquid line (81) with the gas-cooler outlet line (50) upstream the first check valve (9).
  9. The refrigeration circuit of any of the previous claims 2 to 8, further comprising: - a second fluid line (93), with a second motorised valve (22), that connects the gas-cooler outlet line (50) at the outlet of the third heat exchanger (13) with the liquid receiver (17), - a pressure increaser device (95) located at the outlet of the second compressor (2), - a fourth fluid line (94) that connects the second pipe (65) to the pressure increaser device (95), - a pressure exchanger (21) configured to exchange pressure between the refrigerant flowing through the second fluid line (93) and the refrigerant flowing through the fourth fluid line (94).
  10. The refrigeration circuit of any of the previous claims 2 to 8, further comprising: - a second fluid line (93), with a second motorised valve (22), that connects the gas-cooler outlet line (50) at the outlet of the third heat exchanger (13) with the liquid receiver (17), - a fifth fluid line (67) connecting the second pipe (65) with the first gas-cooler outlet line (50) and comprising a second gas-cooler (8) and a pump (38), and - a pressure exchanger (21) configured to exchange pressure between the refrigerant flowing through the second fluid line (93) and the fifth fluid line (67).
  11. The refrigeration circuit of any of the previous claims 2 to 8, further comprising: - a second fluid line (93), with a second motorised valve (22), that connects the gas-cooler outlet line (50) at the outlet of the third heat exchanger (13) with the liquid receiver (17), - a sixth fluid line (68) connecting the second pipe (65) with the first gas-cooler outlet line (50), - a pressure exchanger (21) configured to exchange pressure between the refrigerant flowing through the second fluid line (93) and the sixth fluid line (68), and wherein the first gas-cooler (7) comprises an additional circuit where the sixth fluid line (68) is connected downstream the pressure exchanger (21), and - a pump (38) located in the sixth fluid line (68) at the outlet of the additional circuit.
  12. The refrigeration circuit of any of claims 9 to 11, that comprises: - a third compressor (3) connected to the rest of the compressors (1, 2) in parallel to the common discharge line (41), a fourth motorised multi-way valve (31) located on the second pipe (65) feeding the second compressor (2) and connected to the suction line (59), wherein the fourth motorised multi-way valve (31) is configured to switch a refrigerant flow between a refrigerant flowing through the suction line (59) to the pressure exchanger (21) and a refrigerant flowing through the second pipe (65) to the pressure exchanger (21). _
  13. The refrigeration circuit of any of claims 1 to 12, that further comprises: a low temperature liquid line (84) connecting the first liquid line (81) with the suction line (59), the low temperature liquid line (84) comprising: - a low temperature expansion valve (25), - a low temperature heat exchanger (23), - a low temperature compressor (39), and - a desuperheater (37).
  14. The refrigeration circuit of the claim 13, wherein the low temperature liquid line (84) at the outlet of the low temperature heat exchanger (23) is connected to the first heat exchanger (18) upstream the low temperature compressor (39), the first heat exchanger (18) being configured to exchange heat between the refrigerant in the low temperature liquid line (84) and the refrigerant flowing through the first liquid line (81).
  15. The refrigeration circuit of the claim 14, that comprises: - a seventh motorised multi-way valve (88) disposed downstream the low temperature heat exchanger (23) and - a seventh fluid line (89) that connects the seventh motorised multi-way valve (88) with the inlet of the low temperature compressor (39), so that - the refrigerant may either flow to the low temperature compressor (39), bypassing the first heat exchanger (18), or to the first heat exchanger (18).
  16. The refrigeration circuit of any of claims 13 to 15, that further comprises a sixth motorised multi way valve (86) located at the outlet of the desuperheater (37), wherein - the sixth motorised multi valve (86) is configured so that the refrigerant flowing from the desuperheater (37) can be switched between the suction line (59) to flow to the at least one first compressor (1) and the sixth fluid line (68) at the inlet of the pressure exchanger (21).

Description

OBJECT OF THE INVENTION The present invention is related to the field of refrigeration circuits, more particularly, to refrigeration circuits using CO2 as refrigerant (R-744). An object of the present invention is to provide a R-744 refrigerant circuit able to reduce the power consumption by increasing the energy efficiency. BACKGROUND OF THE INVENTION At present, there are different improvements introduced to the circuits with R-744 to increase their efficiency, which are mainly aimed to increase the efficiency of the facility in climates with high ambient temperatures. The main problem in refrigeration circuits using R-744 is the high reduction in efficiency at medium-high ambient temperatures. This efficiency reduction is mainly despite to high power consumption of the medium-temperature compression rack (MTC). A solution proposed consists of introducing in a circuit several ejectors (Multi-Ejector racks, MEJ). This circuit compresses part of the refrigerant of medium-temperature services to intermediate pressure (liquid receiver pressure). To do that, the multi-ejector uses R-744 with high pressure as motive flow, which reduces its pressure through a nozzle below the medium-temperature services pressure and, consequently, increases its velocity. Thus, the motive flow suctions part of the refrigerant of the medium-temperature services and is compressed to intermediate pressure. This circuit is used with different types of ejectors, the most used is the high-pressure multi-ejector. The use of high-pressure multi-ejector reduces the refrigerant in the medium-temperature compression rack and consequently its power consumption. Additionally, the medium-temperature compression rack compresses part of the medium-temperature services refrigerant without a mechanical compressor taking the potential energy of the motive flow. Nevertheless, this circuit needs an additional compression denoted as parallel compression rack to compress the refrigerant in vapor state generated by the multi-ejector. The vapor quality in the liquid receiver is higher and the capacity requirements in parallel compression rack is greater than the circuits without ejectors, having a similar cooling load. The temperature at suction port of the medium-temperature compression rack is higher than the circuits without ejectors and, in consequence, the discharge temperature too, producing temperatures greater than 140°C for ambient temperatures above 35°C. The main problem of the high-pressure multi-ejector racks is that they do not operate efficiently for ambient temperatures below 30°C in R-744 circuits. Also, the cost of using high-pressure multi-ejector racks is high. In addition, it has problems with the high oil transfer rate at the parallel compression rack due to the reduced superheat in suction port. Also, the suction pressure of the parallel compression rack is fixed by a liquid receiver, storing the refrigerant, and this compressor rack does not work at its optimal operating point (maximum compressor efficiency). A lot of solutions have been proposed to improve the efficiency of a refrigeration circuit using R-744 at medium-high ambient temperatures. Nevertheless, few improvements are used at the present time. The most used improvements to R-744 circuits are the parallel compression, mechanical subcooling and ejectors, but these circuits have several limitations. Therefore, a circuit with lower limitations using R-744 for increasing the efficiency of the refrigeration process at medium-high ambient temperatures is needed. As an example, document EP3872418 refers to a refrigerant circuit for increasing energy efficiency comprising a tank, storing liquid and vapor R-744; a first R-744 liquid line, connecting the tank to a medium-temperature line, and comprising a medium-temperature expansion valve connected to a medium-temperature evaporator connected to a suction line, which connects with a medium-temperature compressor; a low-temperature line, connected to the first R-744 liquid line, and comprising a low-temperature expansion valve connected to a low-temperature evaporator connected to a low-temperature compressor connected to the suction line; an adiabatic gas-cooler, connected to the medium-temperature compressor; a first back-pressure valve, connected to the tank and to a first heat exchanger, connected to the adiabatic gas-cooler; and a R-744 vapor line, connecting the tank with the first heat exchanger and with the suction line. Document US2010180612A1 represents the closest prior art and discloses a refrigeration device that includes a compression mechanism, a radiator, a first expansion mechanism, a second expansion mechanism, an evaporator, a first internal heat exchanger, a branch pipe, a third expansion mechanism, and a second internal heat exchanger. The first internal heat exchanger causes heat to be exchanged between refrigerant that flows from the radiator to the inflow side of the first expansion mechanism, and refrige