Natural Gas Liquids Recovery Plant

Abstract

A compact transportable apparatus for flexibly recovering natural gas liquids from a natural gas stream feedstock includes a replaceable segment on one or more natural gas liquids transfer lines that is removable in the field without cutting the line for replacement with different replaceable part, for example, a J-T valve replacing a length of pipe, for flexibility in adjusting performance of the apparatus to match on site or changing conditions of the natural gas stream feedstock. Insulation surrounding the replaceable segment is discontinuous with insulation surrounding the remainder of the natural gas liquids transfer line in which the segment is interposed. This allows separation of the segment from such transfer line without disturbing the insulation of the remainder of that natural gas liquids transfer line if the replaceable segment is removed and replaced with a different replaceable segment.

1 . Transportable apparatus for flexibly recovering natural gas liquids from an inlet natural gas stream having a temperature at atmospheric ambient or higher and a pressure of at least 400 psig, comprising:
 a. a skid;   b. an inlet line for receiving the inlet natural gas stream;   c. first and second one pass tube-in-shell heat exchangers supported on said skid, said second heat exchanger being connected in series with said first heat exchanger by a first transfer line, said first heat exchanger receiving said inlet natural gas stream from said inlet line;   d. a second transfer line for receiving the inlet natural gas stream exiting said second heat exchanger;   e. an NGLs condenser connected to the second transfer line for receiving inlet natural gas stream from said second heat exchanger and operatively sufficient to condense natural gas liquids in the inlet natural gas to two-phase gas-liquid NGLs,   f. a third transfer line for receiving said two-phase gas-liquid NGLs from the NGLs condenser;   g. a gas-liquid separator supported on said skid and connected to said third transfer line, said separator having lower and upper portions for separating two-phase gas-liquid NGLs from natural gas remaining in a single-phase gaseous state as a lean natural gas;   h. a fourth transfer line connected to said separator at said lower portion, for receiving and transporting two-phase gas-liquid NGLs from said separator, said fourth transfer line connecting to the shell of said first heat exchanger proximal a rear end of the shell for shell side flow of NGLs from said rear end toward a front end of the first heat exchanger counter-currently to tube side flow of the inlet natural gas stream entering the first heat exchanger from said inlet line;   i. at least one of said third and fourth transfer lines or both, including a replaceable segment that is removable without cutting the third or fourth transfer line or both, as applicable, for optional replacement of said replaceable segment by a different replaceable segment;   j. a fifth transfer line connected to the shell of said first heat exchanger proximal the front end of the first heat exchanger for receiving a shell side flow stream of NGLs from the front end of the first heat exchanger as product;   k. a sixth transfer line connected to said separator at said upper portion for receiving and transporting a lean natural gas stream from said separator, said sixth transfer line connecting to the shell of the second heat exchanger proximal a rear end of the shell for shell side flow of the lean natural gas stream from said rear end toward a front end of the second heat exchanger counter-currently to tube side flow of inlet natural gas entering the second heat exchanger from said second transfer line; and   l. a seventh transfer line connected to said second heat exchanger proximal the front end of the shell thereof for receiving a shell side flow stream of lean natural gas as a lean gas product.   
     
     
         2 . The apparatus of  claim 1  in which said replaceable segment either comprises
 a. a length of pipe with connectors connecting the pipe with upstream and downstream potions of said third or fourth transfer lines or both that includes or include said replaceable segment, said pipe being downstream of said valving for blocking flow, or 
 b. a J-T pressure reduction valve with connectors connecting the J-T valve with upstream and downstream potions of said third or fourth transfer line or both that includes or include said replaceable segment, said J-T valve being downstream of said valving for blocking flow, 
 and 
 c. if said replaceable segment comprises said length of pipe, said different replaceable segment comprises a J-T pressure reduction valve with connectors for connecting the J-T valve with upstream and downstream potions of said third or fourth transfer line, or both, that includes said replaceable segment, or 
 d. if said J-T valve comprises said replaceable segment, said different replaceable segment comprises a said length of pipe with connectors for connecting the length of pipe with upstream and downstream potions of said third or fourth transfer line, or both, that includes said replaceable segment. 
 
     
     
         3 . The apparatus of  claim 2  in which said NGLs condenser is a J-T pressure reducing valve, wherein said third transfer line receives the inlet natural gas stream at a pressure and temperature reduced from that in the second transfer line, said reduced pressure and temperature being at least sufficient to condense natural gas liquids in the inlet natural gas to two-phase gas-liquid NGLs, and wherein said replaceable segment is in said fourth transfer line. 
     
     
         4 . The apparatus of  claim 2  in which said NGLs condenser is a shell-and-tube refrigerant flash drum chiller for receiving the inlet natural gas stream from the second transfer line on the tube side for chilling the received inlet natural gas stream sufficiently to condense natural gas liquids in the inlet natural gas to two-phase gas-liquid NGLs. 
     
     
         5 . The apparatus of  claim 4  in which both said third and fourth transfer lines include said replaceable segment, and said replaceable segment in said third transfer line comprises a said J-T pressure reduction valve. 
     
     
         6 . The apparatus of  claim 2  in which
 a. the connectors of said length of pipe comprise first and second flanges, said first flange connected to said pipe for bolting to a flange connected to said upstream portion of said third or fourth transfer lines or both that includes or include said length of pipe, and said second flange connected to said pipe for bolting to a flange connected to said downstream portion of said third or fourth transfer lines or both that includes or include said length of pipe, and in which 
 b. the connectors of said J-T pressure reduction valve comprise first and second flanges, said first flange connected to said J-T valve for bolting to a flange connected to said upstream portion of said third or fourth transfer lines or both that includes or include said J-T valve, and said second flange connected to said J-T valve for bolting to a flange connected to said downstream portion of said third or fourth transfer line or both that includes or include said J-T valve. 
 
     
     
         7 . The apparatus of  claim 2  in which said shells of said first and second heat exchangers, said NGLs condenser, said separator and said first, second, third and fourth transfer lines, including said replaceable segment of said third or fourth transfer line or both said third or fourth transfer lines, as applicable, and said sixth transfer line, being encased in a protectively covered insulation of a kind and thickness sufficient to prevent condensation on the outer surfaces of the shells, NGLs condenser, said separator, and said first, second, third and fourth transfer lines, including said included replaceable segment or segments, and said sixth transfer line, at a temperature contained within them not below the minimum temperature for which metallurgy of the gas-liquid separator is rated, the insulation surrounding said replaceable segment or segments being discontinuous with the insulation surrounding the remainder of the third or fourth transfer lines, or both, as applicable, for separation from said third or fourth transfer lines without disturbing said remainder if said replaceable segment is removed and replaced with a different replaceable segment. 
     
     
         8 . The apparatus of  claim 7  in which said insulation surrounding said segment is internally matingly contoured to the shape of the replaceable segment and is longitudinally divided and held to said segment by holders to allow nondestructive separation of said insulation from said segment for reuse of said insulation if a said different replaceable component replaces said segment. 
     
     
         9 . The apparatus of  claim 2  in which said first heat exchanger comprises a cylindrical shell pressure vessel having front and rear end, and a pass-through tube connected to said inlet line at said front end of the shell for receiving said inlet natural gas stream for tube side flow inside said shell, said first transfer line connecting to said pass-through tube at said rear end of the first heat exchanger for receiving the inlet natural gas stream exiting said first heat exchanger, and wherein said second heat exchanger comprises a hair pin cylindrical shell pressure vessel having front and rear ends and connected on said front end to said first transfer line, a pair of tube sheets being transversely affixed to said shell inside the front and rear ends of the shell, and a plurality of tubes being longitudinally arranged within the shell transversely affixed to and at least partially supported by the tube sheets for conducting the inlet natural gas stream introduced into the front end of the shell to the rear end of the shell. 
     
     
         10 . The apparatus of  claim 9  in which the pass-through tube in said first heat exchanger has, and in which the tubes in said second heat exchanger have, an inner diameter effective at the density and dynamic viscosity of the inlet natural gas stream to produce a tube side flow velocity in a turbulent flow regime, and the pass-through tube in said first heat exchanger has, and in which the tubes in said second heat exchanger have, an outer diameter relative to the inner diameter of the shell providing an annulus effective to allow a shell side fluid flow rate sufficient, at a thermal conductivity of the pass-through tube, to increase the temperature of the shell side fluid exiting the respective heat exchangers to within a predetermine temperature range less than the temperature of the inlet natural gas entering the tube side of the respective heat exchangers. 
     
     
         11 . The apparatus of  claim 10  in which said predetermined range is within 1 to 100° F. less than the temperature of the inlet natural gas entering the tube side of the first heat exchanger and is from 1 to 20° F. less than the temperature of the inlet natural gas entering the tube side of such second heat exchanger. 
     
     
         12 . The apparatus of  claim 11  in which said pass-through tube of said first heat exchanger has an exterior diameter that is, and in which said tubes of said second heat exchanger are arranged to form a tube bundle having a cross sectional dimension that is, from two-thirds to three-fourths the inner diameter of the shell vessel. 
     
     
         13 . The apparatus of  claim 2  further comprising a level controller pilot in fluid communication with the lower portion of the gas-liquid separator, for actuating either a valve connected to said fifth transfer line between the shell of said first heat exchanger and a location of transfer of the NGLs as product, or, if said replaceable segment of said fourth transfer line is a said J-T valve or is a length of pipe replaced by a said J-T valve, instead actuating said J-T valve in said fourth transfer line, for regulating discharge of NGLs from said gas-liquid separator into said fourth transfer line. 
     
     
         14 . The apparatus of  claim 2  further comprising an eighth transfer line connected either to said first transfer line or said second transfer line and valved by a temperature controlled valve controlled by a temperature controller monitoring the temperature of the gas-liquid separator, said temperature controlled valve when actuated open by said temperature controller passing inlet natural gas from said transfer line it valves to said third transfer line to warm the temperature of the inlet natural gas stream in the third transfer line passing to the gas-liquid separator to an extent preventing the temperature in the gas-liquid separator from dropping below the minimum temperature for which metallurgy of the gas-liquid separator is rated. 
     
     
         15 . A process for flexibly recovering NGLs from an inlet natural gas stream having a temperature at atmospheric ambient or higher and a pressure of at least 400 psig, comprising:
 a. passing the inlet natural gas stream as a tube side flow though a one-pass shell-and-tube first heat exchanger;   b. passing inlet natural gas effluent from the tube side of the first heat exchanger as a tube side flow stream though a shell-and-tube second heat exchanger having a plurality of one-pass tubes;   c. passing the inlet natural gas effluent from the tube side of the second heat exchanger through a NGLs condenser to reduce the temperature and pressure of the inlet natural gas at least sufficiently to condense NGLs in the inlet natural gas to two-phase gas-liquid NGLs;   d. separating the two-phase gas-liquid NGLs in a gas-liquids separator from remaining single phase natural gas as a lean natural gas;   e. passing the separated two-phase gas-liquid NGLs through a replaceable segment of a transfer line to the shell side of the first heat exchanger, said replaceable segment comprising either a length of pipe if no additional cooling of the two-phase gas-liquid NGLs is desired, or a J-T valve if additional cooling of the two-phase gas-liquid NGLs is desired;   f. passing the two-phase gas-liquid NGLs from step (e) for counter-current flow to inlet natural gas in the tube side of the first heat exchanger at a shell side flow rate effective to increase the temperature of the shell side NGLs exiting the first heat exchanger to within a predetermine temperature range less than the temperature of the inlet natural gas entering the tube side of the first heat exchanger;   g. regulating removal of NGLs from the shell side of the first heat exchanger to maintain a flow of NGLs passing to the shell side of the first heat exchanger;   h. passing the separated lean natural gas to the shell side of the second heat exchanger;   i. passing the separated lean natural gas from step (h) for counter-current flow to inlet natural gas in the tube side of the second heat exchanger at a shell side flow rate effective to increase the temperature of the shell side lean natural gas exiting the second heat exchanger to within a predetermine temperature range less than the temperature of the inlet natural gas entering the tube side of the second heat exchanger; and   j. receiving separately NGLs removed from the shell side of the first heat exchanger and lean natural gas removed from the shell side of the second heat exchanger;   k. while insulating the exterior of the shells of the first and second heat exchangers, the exterior of the separator, and passages within which the steps (c), (e), (f), and (h) are performed, to an extent sufficient to prevent condensation on the outer surfaces of the heat exchangers, the separator, and said passages at a temperature, in steps (a) and (b) in a range between the temperature of the fluid entering the shell side of the heat exchangers and the minimum temperature for which metallurgy of the separator is rated, in step (d), in a range between the temperature of the fluids entering the separator and the minimum temperature for which metallurgy of the separator is rated, and in steps (c), (e), (f), and (h), in a range between the temperature of the fluids in the passages and the minimum temperature for which metallurgy of the separator is rated.   
     
     
         16 . The process of  claim 15  in which said NGLs condenser is a J-T pressure reducing valve. 
     
     
         17 . The process of  claim 16  further comprising passing a portion of the inlet natural gas effluent from the first heat exchanger or from the second heat exchanger to the inlet natural gas stream after it is passed through the J-T valve and before passing into said gas-liquids separator to an extent warming the temperature of the stream effective to prevent the temperature of the fluids in the gas-liquid separator from dropping below a predetermined minimum temperature for which metallurgy of the gas-liquid separator is rated. 
     
     
         18 . The process of  claim 16  in which the lean natural gas shell side flow rate in the second heat exchanger is effective to increase the temperature of the shell side lean natural gas exiting the second heat exchanger to within 5 to 20° F. less than the temperature of the inlet natural gas entering the tube side of the second heat exchanger. 
     
     
         19 . The process of  claim 15  in which said NGLs condenser is a shell-and-tube refrigerant flash drum chiller.