Multiple pressure mixed refrigerant cooling system

An apparatus for liquefying a hydrocarbon feed stream comprising:

• a plurality of heat exchange sections, the plurality of heat exchange sections comprising a warmest heat exchange section and a coldest heat exchange section;
• a first hydrocarbon circuit that extends through each of the plurality of heat exchange sections, the first hydrocarbon circuit being downstream from and in fluid flow communication with a supply of a hydrocarbon fluid;
• a second refrigerant circuit that extends through each of the plurality of heat exchange sections, the second refrigerant circuit containing a second refrigerant;
• a first precooling refrigerant circuit that extends through the warmest heat exchange section, the first precooling refrigerant circuit containing a first refrigerant;
• a second precooling refrigerant circuit that extends through the warmest heat exchange section and the coldest heat exchange section, the second precooling refrigerant circuit containing the first refrigerant;
• a first precooling refrigerant circuit inlet located at an upstream end of the first precooling refrigerant circuit, a first pressure letdown device located at a downstream end of the first precooling refrigerant circuit, and a first expanded refrigerant conduit downstream from and in fluid flow communication with the first pressure letdown device and upstream from and in fluid flow communication with a first cold circuit of the warmest heat exchange section;
• a second precooling refrigerant circuit inlet located at an upstream end of the second precooling refrigerant circuit, a second pressure letdown device located at a downstream end of the second precooling refrigerant circuit, and a second expanded refrigerant conduit downstream from and in fluid flow communication with the second pressure letdown device and upstream from and in fluid flow communication with a second cold circuit of the coldest heat exchange section;
• a compression system comprising:
• a low pressure first refrigerant conduit in fluid flow communication with a first compression stage and a warm end of the coldest heat exchange section;
• a medium pressure first refrigerant conduit in fluid flow communication with a second compression stage and a warm end of a first heat exchange section;
• a first aftercooler downstream from the second compression stage;
• a first vapor-liquid separation device having a first inlet in fluid flow communication with, and downstream from, the first aftercooler, a first vapor outlet located in an upper half of the first vapor-liquid separation device, a first liquid outlet located in a lower half of the first vapor-liquid separation device, the first liquid outlet being upstream from and in fluid flow communication with the first precooling refrigerant circuit inlet;
• a third compression stage downstream from the first vapor outlet;
• and
• a second aftercooler downstream from the third compression stage;
• a main heat exchanger having a second hydrocarbon circuit that is downstream from and in fluid flow communication with the first hydrocarbon circuit for receiving a precooled hydrocarbon stream from the first hydrocarbon circuit, the main heat exchanger being also downstream from and in fluid flow communication with the second refrigerant circuit of the plurality of heat exchange sections, the main heat exchanger being operationally configured to at least partially liquefy the precooled hydrocarbon stream by indirect heat exchange against the second refrigerant to produce a first liquefied hydrocarbon stream;
• a third vapor-liquid separation device downstream from and in fluid flow communication with the main heat exchanger that is operationally configured to separate the first liquefied hydrocarbon stream into a flash gas stream and a second liquefied hydrocarbon stream;
• a recycle gas circuit downstream from and in fluid flow communication with the third vapor-liquid separation device, the recycle gas circuit extending through a flash heat exchanger and having a recycle stream outlet in fluid flow communication with the first hydrocarbon circuit upstream from the warmest heat exchange section;
• and
• wherein the flash gas heat exchanger is operationally configured to warm the flash gas stream against at least one warming stream;
• wherein the warmest heat exchange section is operationally configured to partially precool the hydrocarbon fluid flowing through the first hydrocarbon circuit, the second refrigerant flowing through the second refrigerant circuit, the first refrigerant flowing through the first precooling first refrigerant circuit, and the second precooling refrigerant circuit against the first refrigerant flowing through the first cold circuit of the warmest heat exchange section;
• and
• wherein the coldest heat exchange section is operationally configured to precool the hydrocarbon fluid flowing through the first hydrocarbon circuit to produce a precooled hydrocarbon stream, to precool the second refrigerant flowing through the second refrigerant circuit to produce a precooled second refrigerant stream, and to pre-cool the first refrigerant flowing through the second precooling refrigerant circuit against the first refrigerant flowing through the first cold circuit of the coldest heat exchange section.

An apparatus for liquefying a hydrocarbon feed stream comprising:

• a plurality of heat exchange sections, the plurality of heat exchange sections comprising a warmest heat exchange section and a coldest heat exchange section;
• a first hydrocarbon circuit that extends through each of the plurality of heat exchange sections, the first hydrocarbon circuit being downstream from and in fluid flow communication with a supply of a hydrocarbon fluid;
• a second refrigerant circuit that extends through each of the plurality of heat exchange sections, the second refrigerant circuit containing a second refrigerant;
• a precooling refrigerant circuit that extends through the plurality of heat exchange sections, the precooling refrigerant circuit containing a first refrigerant, the precooling refrigeration circuit being operationally configured to direct a first portion of the first refrigerant through an expansion device and into a shell side of the warmest heat exchange section and a second portion of the first refrigerant through the coldest heat exchange section, through an expansion device and into a shell side of the coldest heat exchange section;
• a compression system comprising:
• a low pressure first refrigerant conduit in fluid flow communication with a first compression stage and a warm end of the coldest heat exchange section;
• a medium pressure first refrigerant conduit in fluid flow communication with a second compression stage and a warm end of the warmest heat exchange section;
• a first aftercooler downstream from the second compression stage;
• a first vapor-liquid separation device having a first inlet in fluid flow communication with, and downstream from, the first aftercooler, a first vapor outlet located in an upper half of the first vapor-liquid separation device, a first liquid outlet located in a lower half of the first vapor-liquid separation device;
• a third compression stage downstream from the first vapor outlet;
• and
• a second aftercooler downstream from the third compression stage;
• a pump located downstream from and in fluid flow communication with the first liquid outlet, the pump being located upstream from and in fluid flow communication with the precooling refrigerant circuit;
• a main heat exchanger having a second hydrocarbon circuit that is downstream from and in fluid flow communication with the first hydrocarbon circuit for receiving a precooled hydrocarbon stream from the first hydrocarbon circuit, the main heat exchanger being also downstream from and in fluid flow communication with the second refrigerant circuit, the main heat exchanger being operationally configured to at least partially liquefy the precooled hydrocarbon stream by indirect heat exchange against the second refrigerant to product a first liquefied hydrocarbon stream;
• a third vapor-liquid separation device downstream from and in fluid flow communication with the main heat exchanger that is operationally configured to separate the first liquefied hydrocarbon stream into a flash gas stream and a second liquefied hydrocarbon stream;
• and
• a recycle gas circuit downstream from and in fluid flow communication with the third vapor-liquid separation device, the recycle gas circuit extending through a flash heat exchanger and having a recycle stream outlet in fluid flow communication with the first hydrocarbon circuit upstream from the warmest heat exchange section;
• wherein the flash gas heat exchanger is operationally configured to warm the flash gas stream against at least one warming stream;
• wherein the warmest heat exchange section is operationally configured to partially precool the hydrocarbon fluid flowing through the first hydrocarbon circuit, the second refrigerant flowing through the second refrigerant circuit, and the first refrigerant flowing through the precooling first refrigerant circuit against the first refrigerant flowing through the shell side of the warmest heat exchange section;
• and
• wherein the coldest heat exchange section is operationally configured to precool the hydrocarbon fluid flowing through the first hydrocarbon circuit to produce a precooled hydrocarbon stream, to precool the second refrigerant flowing through the second refrigerant circuit to produce a precooled second refrigerant stream, and to pre-cool the first refrigerant flowing through the first precooling refrigerant circuit against the first refrigerant flowing through the shell side of the coldest heat exchange section.