COMBINED CASCADE AND MULTICOMPONENT REFRIGERATION SYSTEM AND METHOD

• US 3,763,658 A
• Filed: 01/12/1970
• Issued: 10/09/1973
• Est. Priority Date: 01/12/1970
• Status: Expired due to Term

• Current Assignee: Charles L. Newton, Lee S. Gaumer Jr
• Original Assignee: Charles L. Newton, Lee S. Gaumer Jr
• Inventors: Gaumer, Lee S. Jr., Newton, Charles L.
• Primary Examiner(s): Yudkoff, Norman
• Assistant Examiner(s): Purcell, Arthur F.
• Application Number:
  US05/002,447
• Time in Patent Office: 1,366 Days
• Field of Search: 62/9,11,23,24,27,28,36,40
• US Class Current: 62/612
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0055 originating from an incorporated cascade
• CPC Class Codes: F25J 1/0087 Propane; Propylene
• CPC Class Codes: F25J 1/0216 using a C3 pre-cooling cycle
• CPC Class Codes: F25J 1/0249 Controlling refrigerant inventory, i.e. composition or quantity charging or discharging refrigerants in cooling systems F25B45/00
• CPC Class Codes: F25J 1/025 Details related to the refrigerant production or treatment, e.g. make-up supply from feed gas itself
• CPC Class Codes: F25J 1/0292 Refrigerant compression by cold or cryogenic suction of the refrigerant gas
• CPC Class Codes: F25J 2205/60 using adsorption on solid adsorbents, e.g. by temperature-swing adsorption [TSA] at the hot or cold end
• CPC Class Codes: F25J 2220/60 Separating impurities from natural gas, e.g. mercury, cyclic hydrocarbons
• CPC Class Codes: F25J 2220/64 Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• CPC Class Codes: F25J 2220/68 Separating water or hydrates

Abstract

A refrigeration system and method are disclosed for liquefying a feed stream by first subjecting the feed stream to heat exchange with a single component refrigerant in a closed, cascade cycle and, thereafter, subjecting the feed stream to heat exchange with a multicomponent refrigerant in a multiple zone heat exchanger forming a portion of a second, closed refrigerant cycle.

Claims

2. The method as claimed in claim 1 further including the step of maintaining the composition of said multicomponent refrigerant so as to have an average molecular weight within the range of 24-28.

3. The method as claimed in claim 2 further including the step of maintaining a multicomponent refrigerant composition comprising 2-12 mole percent of nitrogen, 35-45 mole percent of methane, 32-42 mole percent of ethane, and 9-19 mole percent of propane.

4. The method as claimed in claim 1 wherein said precooled methane-rich feed stream is cooled in step (j) to a subcooled temperature which is sufficiently below its liquefaction temperature to maintain substantially all of said feed stream in liquid phase upon expansion thereof according to step (1).

5. The method as claimed in claim 1 wherein said multicomponent refrigerant consists of only four components, three of said components comprising C1 to C3 hydrocarbons and the fourth component being a non-hydrocarbon component having a normal boiling point substantially below that of methane.

6. The method as claimed in claim 2 wherein said average molecular weight is maintained in the order of 26.

7. The method as claimed in claim 1 wherein said multicomponent refrigerant is compressed to a pressure within the range of 725-1,200 psia.

8. A method of liquefying at least the major portion of a gaseous, methane-rich feed stream comprising the steps of:

a. supplying said methane-rich feed stream at a superatmospheric pressure, b. precooling said gaseous, superatmospheric feed stream to a temperature within the range of 0*F to -50*F in progressive heat exchange steps with a single component hydrocarbon refrigerant undergoing vaporization at a plurality of progressively lower temperatures and pressures, c. providing a separate and distinct multicomponent refrigerant including three components comprising C1-C3 hydrocarbons and one non-hydrocarbon component having a boiling point substantially below that of methane, d. maintaining the composition of said multicomponent refrigerant by maintaining 35-45 mole percent of the C1 hydrocarbon component, maintaining 32-43 mole percent of the C2 hydrocarbon component, maintaining 9-19 mole percent of the C3 hydrocarbon component, and maintaining 2-12 mole percent of the non-hydrocarbon component, e. further maintaining thE composition of said multicomponent refrigerant so as to maintain the average molecular weight of said multicomponent refrigerant within the range of 24-28, f. compressing said multicomponent refrigerant to a pressure within the range of 600-1,200 psia, g. first precooling said compressed multicomponent refrigerant by passage through a compressor after-cooler in heat exchange with a first cooling fluid, h. partially condensing 30 to 70 percent of said precooled multicomponent refrigerant by further precooling said multicomponent refrigerant to a temperature within the range of 0*F to -50*F in heat exchange steps with a single component hydrocarbon refrigerant undergoing vaporization at a plurality of progressively lower pressures and temperatures, i. phase separating all of said precooled and partially condensed multicomponent refrigerant to form a single vapor fraction and a single liquid fraction, j. subcooling said liquid fraction in heat exchange with itself after expansion to form a first subcooled liquid fraction, k. liquefying and subcooling all of said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion, to form a second subcooled liquid fraction, l. liquefying at least the major portion of said methane-rich feed stream by further cooling said precooled methane-rich feed stream to a temperature substantially below minus 200*F solely by progressive heat exchange with said first and second subcooled liquid fractions undergoing vaporization, m. returning both of said vaporized liquid fractions for recompression according to step (c), and n. expanding said liquefied methane-rich feed stream to a reduced pressure for storage.

9. A refrigeration system for totally liquefying a gaseous methane-rich feed stream at superatmospheric pressure comprising the combination of:

a. first multi-stage heat exchanger means connected to a source of a single component refrigerant and to said feed stream for precooling said feed stream in heat exchange with said single component refrigerant undergoing vaporization at a plurality of progressively lower temperatures, b. means for supplying a separate and distinct multiple component refrigerant comprising at least three hydrocarbon components having different boiling points and at least one non-hydrocarbon component having a boiling point substantially below that of methane, c. a compressor for compressing said multicomponent refrigerant to a superatmospheric pressure, d. a compressor after-cooler connected to said compressor for cooling said compressed multicomponent refrigerant to a first lower temperature, e. second multi-stage heat exchanger means connected to said after-cooler and to a source of a single component refrigerant for further cooling said cooled multicomponent refrigerant to a sufficiently lower temperature to partially condense 30 percent to 70 percent thereof in heat exchange with said single component refrigerant undergoing vaporization at a plurality of progressively lower temperatures, f. a single phase separator connected to said second multi-stage heat exchanger means for separating said partially condensed multicomponent refrigerant into a vapor fraction and a condensed liquid fraction, g. third heat exchanger means connected to said phase separator and including expansion means for subcooling said condensed liquid fraction in heat exchange with itself, after expansion in said expansion means, to form a first subcooled liquid fraction, h. fourth heat exchanger means connected to said phase separator means and including expansion means for liquefying and subcooling said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion in said expansion means, to form a second subcooled liquid fraction, i. fifth heat exchanger means consisting of no more than two staGes for further cooling said precooled feed stream to at least its liquefaction temperature, at the superatmospheric pressure thereof, and totally liquefying said precooled feed stream by passing said feed stream in heat exchange with said first subcooled liquid fraction undergoing vaporization in the first stage thereof, followed by passing said feed stream in heat exchange with said second subcooled liquid fraction undergoing vaporization in the second stage thereof, j. conduit means connected to said fifth heat exchanger means and to said compressor for returning said vaporized first and second fractions to said compressor as said multicomponent refrigerant, k. conduit means connected to said fifth heat exchanger means for withdrawing said totally liquefied feed stream from said second stage of said fifth heat exchanger means, and l. expansion means in said conduit means for expanding said totally liquefied feed stream to a substantially reduced pressure.

10. A refrigeration system for liquefying at least the major portion of a gaseous methane-rich feed stream at a superatmospheric pressure comprising the combination of:

a. first multiple stage heat exchanger means for precooling said feed stream to a temperature within the range of 0*F to -50*F in progressive heat exchange with a single component hydrocarbon refrigerant at a plurality of progressively lower pressures and temperatures, b. means for supplying a separate multicomponent refrigerant including three hydrocarbon components having different boiling points and one additional component having a boiling point substantially below that of methane, c. means for maintaining the composition of said multicomponent refrigerant with an average molecular weight within the range of 24-28, d. a compressor for compressing said separate multicomponent refrigerant to a pressure within the range of 600 to 1,200 psia, e. a compressor after-cooler connected to said compressor for first precooling said compressed multicomponent refrigerant, f. second multiple stage heat exchanger means connected to said after-cooler for further precooling and partially condensing a substantial portion of said multicomponent refrigerant in heat exchange with a single component hydrocarbon refrigerant at a plurality of progressively lower temperatures and pressures, g. a single phase separator connected to said second heat exchanger means for separating said partially condensed multicomponent refrigerant into a single vapor fraction and a single condensed fraction, h. third heat exchanger means connected to said separator and including expansion means for subcooling said condensed liquid fraction in heat exchange with itself, after expansion in said expansion means, to form a first subcooled liquid fraction, i. fourth heat exchanger means connected to said separator and including expansion means for liquefying and subcooling said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion in said expansion means, to form a second subcooled liquid fraction, j. fifth heat exchanger means connected to said first heat exchanger means including first and second stages for further cooling said feed stream to at least minus 200*F solely by heat exchange with said first and second subcooled liquid fractions undergoing vaporization in said first and second stages. k. passage means connected to the first stage of said fifth heat exchanger means for returning said first and second vaporized fractions to said compressor, and l. expansion means connected to said fifth heat exchanger means for reducing the pressure of said further cooled feed stream to a reduced pressure.

11. A refrigeration system for liquefying at least the major portion of a methane-rich feed stream comprising the combination of:

a. first and second heat exchanger means for progressively precooling and partially condensing said feed stream in heat exchange relationship with a single component hydrocarbon refrigerant undergoing vaporization at two progressively lower temperatures, b. a phase separator separating said partially condensed feed stream into a vapor fraction and a liquid condensate, c. a scrub column intermediate said first and second heat exchangers, means injecting said precooled feed stream from said first heat exchanger into said scrub column, and means injecting said liquid condensate into said scrub column as reflux whereby benzene and other heavy hydrocarbons are removed from said feed stream, d. means supplying a separate multicomponent refrigerant comprising at least three components having different boiling points including one component having a boiling point substantially below that of methane, e. third heat exchanger means for precooling and partially condensing a substantial portion of said multicomponent refrigerant in heat exchange with a single component hydrocarbon refrigerant undergoing vaporization, f. a phase separator connected to said third heat exchanger means for separating said partially condensed multicomponent refrigerant into a vapor fraction and a condensed liquid fraction, g. fourth heat exchanger means connected to said separator for subcooling said condensed liquid fraction in heat exchange with itself after expansion to form a first subcooled liquid fraction, h. fifth heat exchanger means connected to said separator for liquefying and subcooling said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion, to form a second subcooled liquid fraction, and i. sixth heat exchanger means for liquefying at least the major portion of said precooled feed stream in heat exchange with said first and second subcooled liquid fractions undergoing vaporization.

12. The refrigeration system as claimed in claim 11 further including reboiler means operatively connected to said scrub column for heating a portion of said removed benzene and heavy hydrocarbons and re-injecting the same into the bottom portion of said column as reboil fluid.