US2012324943A1PendingUtilityA1

Two Step Nitrogen and Methane Separation Process

Individually held — no corporate assignee on recordPriority: Jun 21, 2011Filed: Jun 21, 2011Published: Dec 27, 2012

Est. expiryJun 21, 2031(~4.9 yrs left)· nominal 20-yr term from priority

F25J 3/0209F25J 3/0238F25J 2200/04F25J 2200/08F25J 2235/60F25J 2230/32F25J 2200/74F25J 2200/70F25J 2270/02F25J 3/0214F25J 3/0257F25J 3/0233

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Claims

Abstract

A system and method for removing nitrogen and producing a high pressure methane product stream from natural gas feed streams is disclosed. A system for also producing natural gas liquids in conjunction with nitrogen removal from natural gas feed streams is also disclosed. The system and method of the invention are particularly suitable for use with feed streams in excess of 50 MMSCFD and up to 750 MMSCFD and containing up to 75 ppm carbon dioxide. Typical power requirements for compressing the methane product stream to produce a suitably high pressure stream for sale are reduced according to the system and method of the invention.

Claims

exact text as granted — not AI-modified

1 . A system for removing nitrogen and for producing a high pressure methane product stream from a feed stream comprising nitrogen, methane, and other components, the system comprising:
a first fractionating column wherein the feed stream is separated into a first overhead stream and a first bottoms stream; a second fractionating column wherein the first overhead stream is separated into a second overhead stream and a second bottoms stream; a splitter for dividing the second bottoms stream into a high pressure stream, an intermediate pressure stream, and a low pressure stream; a first heat exchanger for cooling the feed stream prior to the first fractionating column through heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream, high pressure stream, and at least a portion of the first bottoms stream; a second heat exchanger for cooling the first overhead stream prior to the second fractionating column through heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream and the high pressure stream; a series of compressors for successively compressing the low pressure stream, then a first combined stream comprising the compressed low pressure stream and the intermediate stream, and then a second combined stream comprising the first combined stream and high pressure stream; and a mixer for mixing second combined stream with at least a portion of the first bottoms stream to produce a high pressure methane product stream.

2 . The system of claim 1 wherein the feed stream is cooled to between −140° F. and −175° F., depending on inlet gas compositions, prior to entering the first fractionating column.

3 . The system of claim 2 further comprising a Joule-Thomson valve for reducing the pressure of and further cooling the feed stream after the first heat exchanger and prior to entering the first fractionating column.

4 . The system of claim 3 wherein the pressure of the feed stream is between 500 psia and 650 psia when it enters the first fractionating column.

5 . The system of claim 1 , further comprising a series of vessels between each of the series of compressors to allow for cooling of the streams being compressed.

6 . The system of claim 1 , further comprising a pump for pumping at least a portion of the first bottoms stream at a pressure substantially equal to that of the combined low pressure, intermediate pressure, and high pressure streams after passing through the series of compressors.

7 . The system of claim 6 further comprising a second splitter for dividing the first bottoms stream into a first and second portions prior to the pump, wherein the first portion of the first bottoms stream is directed to the pump.

8 . The system of claim 7 further comprising a second mixer for mixing the low pressure stream with a second portion of the first bottoms stream prior to the second heat exchanger, with the combined stream continuing through the system as the low pressure stream.

9 . The system of claim 1 , further comprising a Joule-Thomson valve for reducing the pressure of the first overhead stream prior to entering the second fractionating column.

10 . The system of claim 9 wherein the pressure of the first overhead stream is between 200 psia and 400 psia when it enters the second fractionating column.

11 . The system of claim 9 , further comprising a second Joule-Thomson valve for reducing the pressure of the low pressure stream and a third Joule-Thomson valve for reducing the pressure of the intermediate pressure stream, both prior to the second heat exchanger.

12 . The system of claim 11 , further comprising a third heat exchanger for cooling the low pressure stream prior to the second Joule-Thomson valve in heat exchange with the second overhead stream.

13 . The system of claim 1 wherein no reflux stream from the first overhead stream is recycled to the first fractionating column.

14 . The system of claim 13 further comprising a condenser for recycling a reflux stream from the second overhead stream into the second fractionating column.

15 . The system of claim 1 wherein the methane product stream is comprised of at least 90% methane and wherein the second overhead stream is comprised of at least 90% nitrogen.

16 . The system of claim 15 wherein the second fractionation tower overhead stream may be is recycled for enhanced oil and gas recovery operations.

17 . The system of claim 15 wherein the feed stream is between 50 and 750 MMSCFD.

18 . The system of claim 17 wherein the feed stream comprises up to 75 ppm carbon dioxide.

19 . The system of claim 18 wherein the carbon dioxide is stripped from the feed stream in the first fractionating column and exits the first fractionating column as part of the bottoms product stream.

20 . The system of claim 1 wherein at least a first portion of the energy released from the first heat exchanger is supplied to an intermediate stage of the first fractionating column.

21 . The system of claim 20 wherein at least a second portion of the energy released from the first heat exchanger is supplied to reboil fluid at the bottom of the first fractionating column to provide a recycled vapor stream back to the first fractionating column and wherein the first bottoms stream is a liquid stream.

22 . The system of claim 1 wherein at least a first portion of the energy released from the second heat exchanger is supplied to an intermediate stage of the second fractionating column.

23 . The system of claim 22 wherein at least a second portion of the energy released from the second heat exchanger is supplied to a bottom stage of the second fractionating column.

24 . The system of claim 23 further comprising a reboiler for the second stage fractionating column, wherein a liquid stream and a vapor stream exit the reboiler;
wherein the second bottoms stream is the liquid stream; and
wherein the vapor stream is recycled back to the second fractionating column.

25 . The system of claim 24 wherein at least a third portion of the energy released from the second heat exchanger is supplied to the reboiler.

26 . A method for removing nitrogen and for producing a high pressure methane product stream, the method comprising:
providing a feed stream comprising nitrogen and methane; separating the feed stream into a first overhead stream and a first bottoms stream in a first fractionating column; separating the first overhead stream into a second overhead stream and a second bottoms stream in a second fractionating column; dividing the second bottoms stream into a high pressure stream, an intermediate pressure stream, and a low pressure stream; cooling the feed stream prior to separating through heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream, high pressure stream, and at least a portion of the first bottoms stream; cooling the first overhead stream prior to separating through heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream and the high pressure stream; successively compressing the low pressure stream, then a first combined stream comprising the compressed low pressure stream and the intermediate stream, and then a second combined stream comprising the first combined stream and high pressure stream; and mixing the second combined stream with at least a portion of the first bottoms stream to produce a high pressure methane product stream.

27 . The method of claim 26 wherein the feed stream is cooled to between −130° F. and −175° F. prior to entering the first fractionating column.

28 . The method of claim 27 further comprising expanding the feed stream after the first heat exchanger and prior to entering the first fractionating column through a first Joule-Thomson valve.

29 . The method of claim 28 wherein the pressure of the feed stream is between 500 psia and 650 psia when it enters the first fractionating column.

30 . The method of claim 26 , further comprising expanding the first overhead stream through a Joule-Thomson valve prior to entering the second fractionating column.

31 . The method of claim 30 wherein the pressure of the first overhead stream is between 200 psia and 400 psia when it enters the second fractionating column.

32 . The method of claim 30 , further comprising reducing the pressure of the low pressure stream and the intermediate pressure stream through a second and third Joule-Thomson valves, both prior to heat exchange with the first overhead stream.

33 . The method of claim 26 wherein the first overhead stream is not condensed prior to cooling and no reflux stream is recycled to the first fractionating column.

34 . The method of claim 33 further comprising recycling a reflux stream from the second overhead stream into the second fractionating column.

35 . The method of claim 26 wherein the methane product stream is comprised of at least 90% methane and wherein the second overhead stream is comprised of at least 90% nitrogen.

36 . The method of claim 35 further comprising recycling the second overhead stream for enhanced oil and gas recovery operations.

37 . The method of claim 35 wherein the feed stream is between 50 and 750 MMSCFD.

38 . The method of claim 37 wherein the feed stream comprises up to 75 ppm carbon dioxide.

39 . The method of claim 38 wherein the first bottoms stream comprises substantially all of the carbon dioxide from the feed stream and the first overhead stream is substantially free of carbon dioxide.

40 . The method of claim 26 further comprising supplying at least a first portion of the energy released from cooling the feed stream to an intermediate stage of the first fractionating column.

41 . The method of claim 40 further comprising supplying at least a second portion of the energy released from cooling the feed stream to the bottom of the first fractioning column;
reboiling fluid at the bottom of the first fractionating column to produce a vapor stream and a liquid stream;
recycling the vapor stream back to the first fractionating column; and
wherein the first bottoms stream is the liquid stream.

42 . The method of claim 26 further comprising supplying at least a first portion of the energy released from cooling the first overhead stream to an intermediate stage of the second fractionating column.

43 . The method of claim 42 further comprising supplying at least a second portion of the energy released from cooling the first overhead stream to a bottom stage of the second fractionating column.

44 . The method of claim 43 further comprising reboiling a bottom stream from the second fractionating column to produce a vapor stream and a liquid stream, wherein the second bottoms stream is the liquid stream; and
recycling the vapor stream back to the second fractionating column.

45 . The method of claim 44 further comprising supplying at least a third portion of the energy released from cooling the first overhead stream to reboil the bottom stream from the second fractionating column.

46 . A method for removing nitrogen and for producing a high pressure methane product stream, the method comprising:
providing a feed stream comprising nitrogen and methane; separating the feed stream into a first overhead stream and a first bottoms stream in a first fractionating column; separating the first overhead stream into a second overhead stream and a second bottoms stream in a second fractionating column; dividing the second bottoms stream into a first split stream, a second split stream, and a high pressure stream; cooling the first split stream through heat exchange with the second overhead stream; reducing the pressure of the cooled first split stream by passing through a first expansion valve to form a low pressure stream; reducing the pressure of the second split stream by passing through a second expansion valve to form an intermediate pressure stream; cooling the feed stream prior to entering the first fractionating column through heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream, high pressure stream, and at least a portion of the first bottoms stream; cooling the first overhead stream prior to entering the second fractionating column through heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream and the high pressure stream; compressing the low pressure stream to a pressure substantially equal to that of the intermediate pressure stream and combining the two streams to form a first compressed stream; compressing the first compressed stream to a pressure substantially equal to that of the high pressure stream and combining the two streams to form a second compressed stream; compressing the second compressed stream to a pressure substantially equal to that of the at least a portion of the first bottoms stream to form a third compressed stream; and mixing the third compressed stream with at least a portion of the first bottoms stream to produce a high pressure methane product stream.

47 . The method of claim 46 wherein the feed stream is cooled to between −130° F. and 175° F. prior to entering the first fractionating column.

48 . The method of claim 47 wherein the pressure of the feed stream is between 500 psia and 650 psia when it enters the first fractionating column.

49 . The method of claim 48 wherein the feed stream comprises up to 75 ppm carbon dioxide.

50 . The method of claim 49 wherein the first bottoms stream comprises substantially all of the carbon dioxide from the feed stream and the first overhead stream is substantially free of carbon dioxide.

51 . The method of claim 48 wherein the first overhead stream is not condensed prior to cooling and no reflux stream is recycled to the first fractionating column.

52 . The method of claim 47 further comprising supplying at least a portion of the energy released from cooling the feed stream to the first fractionating column and supplying at least a portion of the energy released from cooling the first overhead stream to the second fractionating column.

53 . A system for removing nitrogen and for producing a natural gas liquids stream and a high pressure methane product stream from a feed stream comprising nitrogen, methane, ethane, propane and other components, the system comprising:
a first fractionating column wherein the feed stream is separated into a first overhead stream and a first bottoms stream; a second fractionating column wherein the first overhead stream is separated into a second overhead stream and a second bottoms stream; a third fractionating column wherein at least a portion of the first bottoms stream is separated into a third overhead stream and a natural gas liquids product stream; a splitter for dividing the second bottoms stream into a low pressure stream, an intermediate pressure stream, and a third split stream; a mixer for mixing the third overhead stream and the third split stream to form a high pressure stream; a first heat exchanger for cooling the feed stream prior to the entering the first fractionating column, wherein the cooling is by heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream, high pressure stream, and at least a portion of the first bottoms stream prior to entering the third fractionating column; a second heat exchanger for cooling the first overhead stream prior to entering the second fractionating column, wherein the cooling is by heat exchange with the second overhead stream, low pressure stream, and intermediate pressure stream; a series of compressors for successively compressing the low pressure stream, then a first combined stream comprising the compressed low pressure stream and the intermediate stream, and then a second combined stream comprising the first combined stream and high pressure stream to produce a high pressure methane product stream.

54 . The system of claim 53 wherein the feed stream is cooled to between −130° F. and −175° F. prior to entering the first fractionating column.

55 . The system of claim 54 further comprising a first Joule-Thomson valve for reducing the pressure of the feed stream after the first heat exchanger and prior to entering the first fractionating column.

56 . The system of claim 55 wherein the pressure of the feed stream is between 500 psia and 650 psia when it enters the first fractionating column.

57 . The system of claim 53 , further comprising a series of vessels between each of the series of compressors to allow for cooling of the streams being compressed.

58 . The system of claim 55 , further comprising a second Joule-Thomson valve for reducing the pressure of and cooling at least a portion of the first bottoms stream prior to entering the first heat exchanger.

59 . The system of claim 58 further comprising a second splitter for dividing the first bottoms stream into a first and second portions prior to the second Joule-Thomson valve, wherein the first portion of the first bottoms stream is directed to the valve.

60 . The system of claim 59 further comprising a second mixer for mixing the low pressure stream with a second portion of the first bottoms stream prior to the second heat exchanger, with the combined stream continuing through the system as the low pressure stream.

61 . The system of claim 53 , further comprising a Joule-Thomson valve for reducing the pressure of the first overhead stream prior to entering the second fractionating column.

62 . The system of claim 61 wherein the pressure of the first overhead stream is between 200 psia and 400 psia when it enters the second fractionating column.

63 . The system of claim 61 , further comprising a second Joule-Thomson valve for reducing the pressure of and cooling the low pressure stream and a third Joule-Thomson valve for reducing the pressure of and cooling the intermediate pressure stream, both prior to the second heat exchanger.

64 . The system of claim 63 , further comprising a third heat exchanger prior to the second Joule-Thomson valve for cooling the low pressure stream in heat exchange with the second overhead stream.

65 . The system of claim 53 wherein no reflux stream from the first overhead stream is recycled to the first fractionating column.

66 . The system of claim 65 further comprising a condenser for recycling a reflux stream from the second overhead stream into the second fractionating column.

65 . The system of claim 53 wherein the methane product stream is comprised of at least 90% methane, the second overhead stream is comprised of at least 90% nitrogen, and the natural gas liquid product stream is comprised of at least 30% ethane and less than 5% methane.

66 . The system of claim 65 wherein the second overhead stream is recycled for enhanced oil and gas recovery operations.

67 . The system of claim 65 wherein the feed stream is between 50 and 750 MMSCFD.

68 . The system of claim 67 wherein the feed stream comprises up to 75 ppm carbon dioxide.

69 . The system of claim 68 wherein the carbon dioxide is stripped from the feed stream in the first fractionating column and exits the first fractionating column as part of the bottoms stream.

70 . The system of claim 53 wherein a first portion of the energy released from the first heat exchanger is supplied to an intermediate stage of the third fractionating column; and
a second portion of the energy released from the first heat exchanger is supplied to reboil fluid at the bottom of the third fractionating column to produce a liquid stream and a vapor stream;
the vapor stream is recycled back to the third fractionating column; and
wherein the natural gas liquids product stream is the liquid stream.

71 . The system of claim 70 wherein a third portion of the energy released from the first heat exchanger is supplied to reboil fluid at the bottom of the first fractionating column to produce a liquid stream and a vapor stream;
the vapor stream is recycled back to the first fractionating column; and
wherein the first bottoms stream is the liquid stream.

72 . The system of claim 53 wherein at least a first portion of the energy released from the second heat exchanger is supplied to an intermediate stage of the second fractionating column.

73 . The system of claim 72 wherein at least a second portion of the energy released from the second heat exchanger is supplied to a bottom stage of the second fractionating column.

74 . The system of claim 73 further comprising a reboiler for the second stage fractionating column to produce a liquid stream and a vapor stream;
wherein the second bottoms stream is the liquid stream; and
wherein the vapor stream is recycled back to the second fractionating column.

75 . The system of claim 74 wherein at least a third portion of the energy released from the second heat exchanger is supplied to the reboiler.

76 . A method for removing nitrogen and for producing a high pressure methane product stream and a natural gas liquids stream, the method comprising:
providing a feed stream comprising nitrogen, methane, ethane, and propane; separating the feed stream into a first overhead stream and a first bottoms stream in a first fractionating column; separating the first overhead stream into a second overhead stream and a second bottoms stream in a second fractionating column; separating at least a portion of the first bottoms stream into a third overhead stream and a natural gas liquids product stream in a third fractionating column; dividing the second bottoms stream into a first split stream, a second split stream, and a third split stream; cooling the first split stream through heat exchange with the second overhead stream; reducing the pressure of the cooled first split stream by passing through a first expansion valve to form a low pressure stream; reducing the pressure of the second split stream by passing through a second expansion valve to form an intermediate pressure stream; mixing the third split stream and the third overhead stream to form a high pressure stream; cooling the feed stream prior to entering the first fractionating column through heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream, high pressure stream, and at least a portion of the first bottoms stream prior to entering the third fractionating column; cooling the first overhead stream prior to entering the second fractionating column through heat exchange with the second overhead stream, low pressure stream, and intermediate pressure stream; compressing the low pressure stream to a pressure substantially equal to that of the intermediate pressure stream and combining the two streams to form a first compressed stream; compressing the first compressed stream to a pressure substantially equal to that of the high pressure stream and combining the two streams to form a second compressed stream; compressing the second compressed stream to a produce a high pressure methane product stream.

77 . The method of claim 76 wherein the feed stream is cooled to between −130° F. and −175° F. prior to entering the first fractionating column.

78 . The method of claim 77 wherein the pressure of the feed stream is between 500 psia and 650 psia when it enters the first fractionating column.

79 . The method of claim 78 wherein the feed stream comprises up to 75 ppm carbon dioxide.

80 . The method of claim 79 wherein the first bottoms stream comprises substantially all of the carbon dioxide from the feed stream and the first overhead stream is substantially free of carbon dioxide.

81 . The method of claim 78 wherein the first overhead stream is not condensed prior to cooling and no reflux stream is recycled to the first fractionating column.

82 . The method of claim 77 further comprising supplying at least a portion of the energy released from cooling the feed stream to the first fractionating column and supplying at least a portion of the energy released from cooling the first overhead stream to the second fractionating column.

83 . The method of claim 82 further comprising supplying at least a second portion of the energy released from cooling the feed stream to the third fractionating column.

84 . A method for removing nitrogen and for producing a high pressure methane product stream and a natural gas liquids product stream, the method comprising:
providing a feed stream comprising nitrogen, methane, ethane, and propane; separating the feed stream into a first overhead stream and a first bottoms stream in a first fractionating column; separating the first overhead stream into a second overhead stream and a second bottoms stream in a second fractionating column; separating the first bottoms stream into a third overhead stream and a natural gas liquids product stream in a third fractionating column; dividing the second bottoms stream into a high pressure stream, an intermediate pressure stream, and a low pressure stream; mixing the high pressure stream and the third overhead stream to form a mixed high pressure stream; cooling the feed stream prior to separation through heat exchange with the second overhead stream, low pressure stream, intermediate pressure stream, mixed high pressure stream, and at least a portion of the first bottoms stream; cooling the first overhead stream prior to separation through heat exchange with the second overhead stream, low pressure stream, and intermediate pressure stream; successively compressing the low pressure stream, then a first combined stream comprising the compressed low pressure stream and the intermediate stream, and then a second combined stream comprising the first combined stream and mixed high pressure stream to produce a high pressure methane product stream.

85 . The method of claim 84 wherein the feed stream is cooled to between −130° F. and −175° F. prior to entering the first fractionating column.

86 . The method of claim 85 further comprising reducing the pressure of the feed stream after the first heat exchanger and prior to entering the first fractionating column through a first Joule-Thomson valve.

87 . The method of claim 86 wherein the pressure of the feed stream is between 500 psia and 650 psia when it enters the first fractionating column.

88 . The method of claim 84 , further comprising reducing the pressure of the first overhead stream through a Joule-Thomson valve prior to entering the second fractionating column.

89 . The method of claim 88 wherein the pressure of the first overhead stream is between 200 psia and 400 psia when it enters the second fractionating column.

90 . The method of claim 88 , further comprising reducing the pressure of the low pressure stream and the intermediate pressure stream through a second and third Joule-Thomson valve, both prior to heat exchange with the first overhead stream.

91 . The method of claim 84 wherein the first overhead stream is not condensed prior to cooling and no reflux stream is recycled to the first fractionating column.

92 . The method of claim 91 further comprising recycling a reflux stream from the second overhead stream into the second fractionating column.

93 . The method of claim 84 wherein the methane product stream is comprised of at least 90% methane, the second overhead stream is comprised of at least 90% nitrogen, and the natural gas liquid product stream is comprised of at least 30% ethane and less than 5% methane.

94 . The method of claim 93 further comprising recycling the second overhead stream for enhanced oil and gas recovery operations.

95 . The method of claim 93 wherein the feed stream is between 50 and 750 MMSCFD.

96 . The method of claim 95 wherein the feed stream comprises up to 75 ppm carbon dioxide.

97 . The method of claim 96 wherein the first bottoms stream comprises substantially all of the carbon dioxide from the feed stream and the first overhead stream is substantially free of carbon dioxide.

98 . The method of claim 84 further comprising supplying at least a first portion of the energy released from cooling the feed stream to the bottom of the first fractioning column;
reboiling fluid at the bottom of the first fractionating column to produce a liquid stream and a vapor stream;
recycling thevapor stream back to the first fractionating column; and
wherein the first bottoms stream is the liquid stream.

99 . The method of claim 84 further comprising supplying at least a first portion of the energy released from cooling the first overhead stream to an intermediate stage of the second fractionating column.

100 . The method of claim 99 further comprising supplying at least a second portion of the energy released from cooling the first overhead stream to a bottom stage of the second fractionating column.

101 . The method of claim 100 further comprising supplying at least a third portion of the energy released from cooling the first overhead stream to reboil a bottom stream from the second fractionating column;
reboiling the bottom stream from the second fractionating column to produce a first vapor stream and a first liquid stream, wherein the second bottoms stream is the first liquid stream; and
recycling the first vapor stream back to the second fractionating column.

102 . The method of claim 101 further comprising supplying a second portion of the energy released from cooling the feed stream to an intermediate stage of the third fractionating column;
supplying a third portion of the energy released from cooling the feed stream to reboil a bottom stream from the third fractionating column;
reboiling the bottom stream from the third fractionating column to produce a second vapor stream and a second liquid stream, wherein the natural gas liquids product stream is the second liquid stream; and
recycling the second vapor stream back to the third fractionating column.

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