Mixed refrigerant system and method

1. A method for cooling a fluid with a mixed refrigerant including the steps of:

a. separating a high pressure mixed refrigerant stream to form a high pressure vapor stream and a high pressure liquid stream;

b. cooling the high pressure vapor in a heat exchanger, to form a mixed phase cold separator feed stream;

c. separating the mixed phase cold separator feed stream with a cold vapor separator, to form a cold separator vapor stream and a cold separator liquid stream;

d. condensing the cold separator vapor stream and flashing to form a cold temperature refrigerant stream;

e. cooling the cold separator liquid stream to form a subcooled cold separator liquid stream;

f. flashing the subcooled cold separator liquid stream using a cold separator liquid expansion device to form a first mixed phase stream;

g. cooling the high pressure liquid stream in the heat exchanger, to form a subcooled high pressure liquid stream;

h. flashing the subcooled high pressure liquid stream using a high pressure liquid expansion device to form a second mixed phase stream;

i. combining the first and second mixed phase streams to form a middle temperature refrigerant stream;

j. measuring a temperature of a fluid stream exiting the cold vapor separator;

k. comparing the temperature measured in step j. with a set point temperature;

l. Controlling a flow rate through the cold separator liquid expansion device or the high pressure liquid expansion device based on the comparison of step k;

m. determining a liquid level in the cold vapor separator and controlling the cold separator liquid expansion device based on the determined liquid level;

n. combining the middle temperature refrigerant stream and the cold temperature refrigerant stream;

o. warming the combined middle temperature refrigerant stream and cold temperature refrigerant stream in the heat exchanger to form a refrigerant return stream; and

p. thermally contacting a feed fluid in the heat exchanger, to form a cooled feed fluid product stream.

2. A method for cooling a fluid with a mixed refrigerant including the steps of:

a. separating a high pressure mixed refrigerant stream to form a high pressure vapor stream and a high pressure liquid stream;

b. cooling the high pressure vapor in a heat exchanger, to form a mixed phase cold separator feed stream;

c. separating the mixed phase cold separator feed stream with a cold vapor separator, to form a cold separator vapor stream and a cold separator liquid stream;

d. condensing the cold separator vapor stream and flashing to form a cold temperature refrigerant stream;

e. cooling the cold separator liquid stream to form a subcooled cold separator liquid stream;

f. flashing the subcooled cold separator liquid stream using a cold separator liquid expansion device to form a first mixed phase stream;

g. cooling the high pressure liquid stream in the heat exchanger, to form a subcooled high pressure liquid stream;

h. flashing the subcooled high pressure liquid stream using a high pressure liquid expansion device to form a second mixed phase stream;

i. combining the first and second mixed phase streams to form a middle temperature refrigerant stream;

j. measuring a temperature of a liquid stream entering the cold separator liquid expansion device;

k. comparing the temperature measured in step j. with a set point temperature;

l. Controlling a flow rate through the cold separator liquid expansion device based on the comparison of step k;

m. combining the middle temperature refrigerant stream and the cold temperature refrigerant stream;

n. warming the combined middle temperature refrigerant stream and cold temperature refrigerant stream in the heat exchanger to form a refrigerant return stream; and

o. thermally contacting a feed fluid in the heat exchanger, to form a cooled feed fluid product stream.

3. A method for cooling a fluid with a mixed refrigerant including the steps of:

a. separating a high pressure mixed refrigerant stream to form a high pressure vapor stream and a high pressure liquid stream;

b. cooling the high pressure vapor in a heat exchanger, to form a mixed phase cold separator feed stream;

c. separating the mixed phase cold separator feed stream with a cold vapor separator, to form a cold separator vapor stream and a cold separator liquid stream;

d. condensing the cold separator vapor stream and flashing to form a cold temperature refrigerant stream;

e. cooling the cold separator liquid stream to form a subcooled cold separator liquid stream;

f. flashing the subcooled cold separator liquid stream using a cold separator liquid expansion device to form a first mixed phase stream;

g. cooling the high pressure liquid stream in the heat exchanger, to form a subcooled high pressure liquid stream;

h. flashing the subcooled high pressure liquid stream using a high pressure liquid expansion device to form a second mixed phase stream;

i. combining the first and second mixed phase streams to form a middle temperature refrigerant stream;

j. measuring a temperature of a vapor stream exiting the cold vapor separator vapor outlet;

k. comparing the temperature measured in step j. with a set point temperature;

l. Controlling a flow rate through the high pressure liquid expansion device based on the comparison of step k;

m. combining the middle temperature refrigerant stream and the cold temperature refrigerant stream;

n. warming the combined middle temperature refrigerant stream and cold temperature refrigerant stream in the heat exchanger to form a refrigerant return stream; and

o. thermally contacting a feed fluid in the heat exchanger, to form a cooled feed fluid product stream.