Apparatus for and method of separating a hydrocarbon gas into two fractions and a method of retrofitting an existing cryogenic apparatus
First Claim
1. An apparatus for cryogenically separating an inlet hydrocarbon gas stream comprising at least methane and ethane into a residue gas stream comprising a major portion of the methane and a heavier hydrocarbon fraction comprising principally ethane and other heavier hydrocarbons, the apparatus comprising:
- (1) a main inlet for the hydrocarbon mixture;
(2) a main stream connected to the main inlet and including a first separator for separating liquid and vapour phases, the first separator having a liquid phase outlet and a vapour phase outlet;
(3) a liquid phase stream connected to the liquid phase outlet and a vapour phase stream connected to the vapour phase outlet;
(4) a branch stream connected to the main inlet;
(5) a fractionation column including first, second and third inlets, the first inlet being connected to the liquid phase stream, the second inlet being connected to the vapour phase stream and the third inlet being connected to the branch stream, whereby the flow through the third inlet has substantially the same composition as the inlet gas, the second inlet being provided above the first inlet and the third inlet being provided above the second inlet;
(6) a first outlet means located at the bottom of the fractionation column for the heavier hydrocarbon fraction and a second outlet means at the top of the fractionation column for the residue stream;
(7) an outlet conduit connected to the second outlet means;
(8) first means for cooling the branch stream, including a first heat exchanger means provided between the outlet conduit and the branch stream for heat exchange therebetween, for cooling the incoming hydrocarbon gas branch stream and heating the residue gas stream in the outlet conduit; and
(9) second means for expanding and cooling the main stream.
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Accused Products
Abstract
Disclosed is an improved cryogenic demethanizer, for separating an inlet hydrocarbon gas having a mixture of hydrocarbon components into a residual lighter gas fraction and a heavier liquid fraction. The fractionation column in the demethanizer has a main body portion and an upper portion enlarged with respect to the main body portion. A packing which may be in the form of a plurality of contact trays, or random packing is located in the upper enlarged portion of the column. The invention may be used to retrofit existing cryogenic demethanizers, or used in new installations.
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Citations
40 Claims
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1. An apparatus for cryogenically separating an inlet hydrocarbon gas stream comprising at least methane and ethane into a residue gas stream comprising a major portion of the methane and a heavier hydrocarbon fraction comprising principally ethane and other heavier hydrocarbons, the apparatus comprising:
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(1) a main inlet for the hydrocarbon mixture;
(2) a main stream connected to the main inlet and including a first separator for separating liquid and vapour phases, the first separator having a liquid phase outlet and a vapour phase outlet;
(3) a liquid phase stream connected to the liquid phase outlet and a vapour phase stream connected to the vapour phase outlet;
(4) a branch stream connected to the main inlet;
(5) a fractionation column including first, second and third inlets, the first inlet being connected to the liquid phase stream, the second inlet being connected to the vapour phase stream and the third inlet being connected to the branch stream, whereby the flow through the third inlet has substantially the same composition as the inlet gas, the second inlet being provided above the first inlet and the third inlet being provided above the second inlet;
(6) a first outlet means located at the bottom of the fractionation column for the heavier hydrocarbon fraction and a second outlet means at the top of the fractionation column for the residue stream;
(7) an outlet conduit connected to the second outlet means;
(8) first means for cooling the branch stream, including a first heat exchanger means provided between the outlet conduit and the branch stream for heat exchange therebetween, for cooling the incoming hydrocarbon gas branch stream and heating the residue gas stream in the outlet conduit; and
(9) second means for expanding and cooling the main stream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of retrofitting an existing cryogenic apparatus for separating a compressed inlet hydrocarbon gas stream comprising at least methane and ethane into a residue fraction comprising a major portion of the methane and a heavier hydrocarbon fraction comprising principally ethane and other heavier hydrocarbons, said existing apparatus comprising:
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(a) a main inlet for the hydrocarbon gas;
(b) means for expanding and cooling the inlet gas into a mixture of liquid and vapour phases connected to the main inlet;
(c) means for separating said liquid and vapour phases comprising;
(i) a fractionation column having a body portion and an upper portion above the body portion and generally enlarged with respect to the body portion, said upper portion being substantially empty and being originally intended to provide a disengagement zone;
(ii) at least one inlet means for supplying the vapour and liquid phases to the column provided on at least the body portion and connected to the means for expanding and cooling the inlet gas;
(iii) a first outlet means located at the bottom of the bottom portion for withdrawing the heavier hydrocarbon fraction from the column;
(iv) a second outlet means located at the top of the upper portion for withdrawing the residue stream from the column; and
(v) packing means in said body portion for increasing the amount of contact between the liquid and vapour phases;
the method comprising;
(1) providing additional packing in the disengagement zone in the upper enlarged portion of the column to provide additional contact between the liquid and vapour phases;
(2) providing a branch stream between the main inlet and the upper portion; and
(3) providing a first heat exchange means in the branch stream, for cooling the branch stream so that at least a portion of the branch stream is in the liquid phase, whereby hydrocarbons discharging into the upper portion from the branch stream are at least partially liquid. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
(1) providing means for expanding and cooling said vapour phase of the inlet gas;
(2) providing a static mixer, to which the branch stream, downstream from the first heat exchange means and the vapour phase, downstream from the means for expanding and cooling, are connected, and providing a connection between an outlet of the static mixer and the upper portion of the fractionation column.
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27. A method as claimed in claim 26, which additionally includes:
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(1) providing second separation means, connected to the outlet of the static mixer and including a second vapour phase outlet and a second vapour phase inlet;
(2) providing a connection between the second liquid phase outlet and the upper portion of the fractionation column; and
(3) providing an outlet conduit for residue gas, and connecting the outlet conduit to both the second outlet means and the second vapour phase outlet.
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28. A method of separating a hydrocarbon feed gas stream comprising at least methane and ethane into a residue gas fraction comprising a major portion of the methane and a heavier hydrocarbon fraction comprising principally ethane and other heavier hydrocarbons, the method comprising:
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(1) passing the hydrocarbon gas stream through a first heat exchange means to cool the gas stream;
(2) separating the gas stream into first, second and third streams, with the second stream comprising a major portion of the gas flow;
(3) expanding the gas, after it has been cooled, to lower the temperature of the first, second and third streams, wherein the third stream, after cooling and expansion, is substantially in the liquid phase;
(4) providing a fractionation column including packing;
(5) supplying the third stream to the top of the fractionation column, the second stream to the fractionation column below the third stream and the first stream to the fractionation column below the second stream;
(6) collecting the residue gas fraction from the top of the fractionation column and the heavier hydrocarbon fraction from the bottom of the fractionation column, and passing the residue gas fraction through the first heat exchange means to transfer heat to the residue gas. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
step (5) comprises supplying the third stream to the top of the upper portion, the second stream to the top of one of the transition section and one of the upper and lower portions adjacent the transition section and the first stream to the lower portion below the second stream; and
whereinstep (6) comprises collecting the residue gas fraction from the top of the upper portion and the heavier hydrocarbon fraction from the bottom of the lower portion, wherein the residue gas fraction passes through the first heat exchange means to reheat the residue gas fraction and cool the incoming gas.
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30. A method as claimed in claim 29, which comprises:
splitting the inlet hydrocarbon gas stream into a main stream and a branch stream, the branch stream comprising the third stream and the main stream being subsequently split into the first and second streams.
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31. A method as claimed in claim 30, which includes splitting a portion of the hydrocarbon feed gas stream off into a further branch stream, and passing the further branch stream through reboiling means and then recombining the further branch stream with the main stream, the reboiler means, reboiling lighter hydrocarbon fractions from the fractionation column.
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32. A method as claimed in claim 31, which includes passing the main gas stream through a second heat exchange means and the main and branch streams together through a third heat exchange means, to cool the main and branch streams, and passing the residue gas stream through the second and third heat exchangers to extract heat from the main and branch streams.
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33. A method as claimed in claim 32, which further comprises:
passing the main gas stream, after cooling, to a first separator and separating the main gas stream into liquid and vapour phases, with the liquid phase forming the first stream and the vapour phase forming the second stream.
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34. A method as claimed in claim 33, which includes passing the first stream through a throttle valve to expand the first stream and passing the second stream through an expander, to expand the second stream.
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35. A method as claimed in claim 34, which includes passing the residue stream, after leaving the third heat exchange means, through compressor and driving the compressor by the expander.
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36. A method as claimed in claim 34, which includes combining the vapour stream and the branch stream in a static mixer, and then supplying the combined branch and vapour stream as a single stream to the top of the upper portion of the fractionation column.
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37. A method as claimed in claim 36, which comprises mixing together the branch stream and the vapour stream sufficiently to effect contacting approximately equivalent to one theoretical stage of contacting.
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38. A method as claimed in claim 36, which includes:
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(1) separating the combined vapour stream and branch stream in a separator into a second vapour phase and a second liquid phase;
(2) supplying the second liquid phase to the upper portion of the fractionation column, and combining the second vapour stream with gas flow from the top of the upper portion of the fractionation column, to form the residue gas fraction.
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39. A method as claimed in claim 28, which includes:
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(1) splitting the inlet hydrocarbon gas stream into a main stream and a branch stream, the branch stream comprising the third stream;
(2) passing the main gas stream, after cooling, to a first separator and separating the main gas stream into a first liquid phase and a first vapour phase, with the first liquid phase forming the first stream and the first vapour phase forming the second stream;
(3) passing the second stream through an expander to expand the second stream;
(4) combining the second stream and the branch stream together in a static mixer, to form a combined stream;
(5) separating the combined stream in a separator into a second vapour phase and a second liquid phase;
(6) supplying the second liquid phase to the top of the fractionation column and combining the second vapour phase with gas from the top of the fractionation column, to form the residue gas fraction.
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40. A method as claimed in claim 28, wherein the inlet gas is supplied at a rate up to 600-1000 MMSCFD.
Specification