CO2 refrigeration system with multiple receivers

A refrigeration system, comprising:

• two or more receivers configured to collect refrigerant circulated by the refrigeration system, a first one of the receivers comprising a first gas outlet through which a gas refrigerant exits the first one of the receivers to a first suction line of one or more first compressors in a first set of compressors, and a second one of the receivers comprising a second gas outlet through which the gas refrigerant exits the second one of the receivers to a second suction line of one or more second compressors in the first set of compressors, the one or more second compressors of the first set of compressors operating in parallel with the one or more first compressors of the first set of compressors;
• a liquid refrigerant feed line between a first liquid refrigerant outlet of the first one of the receivers and a liquid refrigerant inlet of the second one of the receivers having a receiver operating pressure lower than a receiver operating pressure of the first one of the receivers;
• one or more first evaporators comprising a first group of evaporators and a second group of evaporators, the second group of evaporators comprising a group of low temperature (LT) evaporators, and the first one of the receivers is configured to direct a first liquid refrigerant to the first group of evaporators, and the second one of the receivers is configured to direct a second liquid refrigerant to the second group of evaporators;
• a fluid conduit fluidly connecting a second liquid refrigerant outlet of the first one of the receivers with the first group of evaporators of the one or more first evaporators;
• one or more second evaporators configured to operate at a different pressure than the one or more first evaporators, the one or more second evaporators fluidly coupled with and configured to direct part of the gas refrigerant to the one or more second compressors operating in parallel, the one or more second compressors configured to operate in a transcritical state, the second one of the receivers comprising a secondary receiver liquid refrigerant outlet through which a part of the second liquid refrigerant exits to the one or more second evaporators;
• one or more feed control valves in the liquid refrigerant feed line;
• and
• a controller configured to operate the feed control valves to control a level of the liquid refrigerant in at least the second one of the receivers.

A method for operating a refrigeration system, the method comprising:

• collecting a refrigerant circulated by the refrigeration system within a primary receiver having a primary receiver operating pressure, the primary receiver comprising a primary receiver gas outlet through which a gas refrigerant exits the primary receiver to a first suction line of one or more first compressors in a first set of compressors, the primary receiver comprising a first liquid refrigerant outlet through which at least part of a liquid refrigerant exits the primary receiver, and a second liquid refrigerant outlet through which another part of the liquid refrigerant exits the primary receiver to one or more first evaporators;
• providing the at least part of the liquid refrigerant from the primary receiver to a secondary receiver having a secondary receiver operating pressure that is lower than the primary operating pressure;
• operating a first gas bypass valve fluidly coupled to the primary receiver gas outlet to control a flow of the gas refrigerant from the primary receiver through the first gas bypass valve and to the first suction line;
• operating a second gas bypass valve fluidly coupled to a secondary receiver gas outlet to control a flow of the gas refrigerant from the secondary receiver through the second gas bypass valve and to a second suction line of one or more second compressors in the first set of compressors;
• operating a feed control valve to control a flow of the at least part of the liquid refrigerant from the primary receiver to the secondary receiver;
• and
• operating the one or more first compressors in parallel with the one or more second compressors;
• wherein the refrigeration system further comprises one or more expansion valves and one or more second evaporators configured to operate at a different pressure than the one or more first evaporators, the one or more second evaporators fluidly coupled with the one or more expansion valves and the one or more second compressors operating in parallel, the secondary receiver comprising a secondary receiver liquid refrigerant outlet through which at least a second part of the liquid refrigerant exits to the one or more expansion valves, and the method further comprises operating the one or more expansion valves to expand the second part of the liquid refrigerant received from the secondary receiver liquid refrigerant outlet, and direct the expanded refrigerant to the one or more second evaporators, and the method further comprises providing the another part of the liquid refrigerant from the primary receiver to a first group of evaporators of the one or more first evaporators, and providing a third part of the liquid refrigerant from the secondary receiver to a second group of evaporators of the one or more first evaporators, the second group of evaporators comprising a group of low temperature (LT) evaporators.

A method for operating a refrigeration system, the method comprising:

• collecting a gas refrigerant circulated by the refrigeration system within a primary receiver having a primary operating pressure, the primary receiver comprising a primary receiver gas outlet through which a gas refrigerant exits the primary receiver to a first suction line of one or more first compressors in a first set of compressors, the primary receiver comprising a first liquid refrigerant outlet through which at least part of a liquid refrigerant exits the primary receiver, and a second liquid refrigerant outlet through which another part of the liquid refrigerant exits the primary receiver to one or more first evaporators;
• providing the at least part of the liquid refrigerant from the primary receiver to a secondary receiver having a secondary receiver operating pressure that is less than the primary receiver operating pressure, the secondary receiver comprising a secondary receiver gas outlet to which the gas refrigerant exits the secondary receiver to a second suction line of one or more second compressors in the first set of compressors;
• operating a feed control valve to control a flow of the at least part of the liquid refrigerant from the primary receiver to the secondary receiver to maintain a level of the liquid refrigerant in the secondary receiver within a particular operating range;
• and
• operating the one or more first compressors in parallel with the one or more second compressors;
• wherein the refrigeration system further comprises one or more expansion valves and one or more second evaporators configured to operate at a different pressure than the one or more first evaporators, the one or more second evaporators fluidly coupled with the one or more expansion valves and the one or more second compressors operating in parallel, the secondary receiver comprising a secondary receiver liquid refrigerant outlet through which a second part of the liquid refrigerant exits to the one or more expansion valves, the method further comprising operating the one or more expansion valves to expand the second part of the liquid refrigerant received from the secondary receiver liquid refrigerant outlet, and direct the expanded refrigerant to the one or more second evaporators, and the method further comprises providing the another part of the liquid refrigerant from the primary receiver to a first group of evaporators of the one or more first evaporators, and providing a third part of the liquid refrigerant from the secondary receiver to a second group of evaporators of the one or more first evaporators, the second group of evaporators comprising a group of low temperature (LT) evaporators.