Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Patent
1998-01-28
1998-11-10
Kilner, Christopher B.
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
62612, F25J 300
Patent
active
058327452
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to cooling a fluid stream in indirect contact with an evaporating refrigerant. The fluid stream to be cooled is for example natural gas which is to be liquefied, and the refrigerant is for example a multi-component refrigerant comprising nitrogen, methane, ethane, propane, butanes, and heavier hydrocarbons.
Cooling takes place in a heat exchanger comprising a hot side and a cold side, wherein the hot side and the cold side are in contact with each other so as to allow transfer of heat from the hot side to the cold side of the heat exchanger. The fluid to be cooled passes through the hot side of a heat exchanger and the refrigerant passes through the cold side of the heat exchanger. The heat exchanger can be of any type which is used in cooling and liquefaction of gas, for example a shell and tube type heat exchanger, an extended surface type heat exchanger, a plate-fin type heat exchanger, or a spiral wound type heat exchanger. The fluids can flow counter-currently or cross-currently, and the refrigerant can flow downwards or upwards.
The present invention relates in particular to cooling a fluid stream which passes through a hot side of a main heat exchanger. Such a method of cooling a fluid stream is disclosed in U.S. Pat. No. 4,251,247.
The known method of cooling a fluid stream which passes through a hot side of a main heat exchanger comprises the steps of: pressure via at least one intermediate pressure to a high pressure to obtain refrigerant at high pressure; first two-phase fluid, and separating the first two-phase fluid into a first condensed fraction and a first gaseous fraction; auxiliary heat exchanger to obtain a cooled first condensed fraction; intermediate pressure (P1) in the cold side of the auxiliary heat exchanger to obtain refrigerant at the intermediate pressure (P1) which is subsequently supplied to the inlet of an intermediate stage of the multi-stage compressor unit; the auxiliary heat exchanger to obtain a second two-phase fluid; fraction and a penultimate gaseous fraction; heat exchanger to obtain a cooled penultimate condensed fraction; pressure in the cold side of the main heat exchanger to obtain refrigerant at low pressure which is subsequently supplied to the inlet of the first stage of the multi-stage compressor unit; main heat exchanger to obtain a cooled last condensed fraction; and pressure in the cold side of the main heat exchanger to obtain refrigerant at low pressure which is subsequently supplied to the inlet of the first stage of the multi-stage compressor unit.
In the known method a two-stage compressor unit is used, and the refrigerant at the intermediate pressure (P1) obtained in step (e) is supplied to the inlet of the second stage of a two-stage compressor unit.
The present invention concerns in particular the fluids in the cold side of the main heat exchanger, therefore, before introducing the invention, the compositions and the behaviour of the fluids in the cold side of the main heat exchanger are discussed.
In the known method, heat exchangers of the tube and shell type are used. In this type of heat exchanger the tubes forming the hot sides are arranged in the shell of the heat exchanger, which shell forms the cold side. This type is used in both the main heat exchanger and the auxiliary heat exchanger.
The main heat exchanger consists of two parts. The cold sides of the two parts are connected to form one interconnected cold side, so that the refrigerant at low pressure obtained from evaporating the last condensed fraction in step (j) passes through that part of the cold side of the main heat exchanger in which the cooled penultimate condensed fraction is allowed to evaporate in step (h). The hot side of the main heat exchanger through which the fluid to be cooled is passed comprises two interconnected tubes, each tube being arranged in a cold side of the two-part main heat exchanger.
In the interconnected cold side of the main heat exchanger both the penultimate and the last condensed fractions obtained in step (f) are allow
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patent: 4970867 (1990-11-01), Herron et al.
patent: 5613373 (1997-03-01), Grenier
Klein Nagelvoort Robert
Mercer Hilary Ann
Vink Kornelis Jan
Kilner Christopher B.
Shell Oil Company
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