Patent Grant
9803917
The invention relates to an integrated process and apparatus for liquefaction of natural gas and recovery of natural gas liquids. In particular, the improved process and apparatus reduces the energy consumption of a Liquefied Natural Gas (LNG) unit by using a portion of the already cooled overhead vapor from a fractionation column (e.g., a light-ends fractionation column (LEFC) or a demethanizer/de-ethanizer) from an NGL (natural gas liquefaction) unit to, depending upon composition, provide, for example, reflux for fractionation in the NGL unit and/or a cold feed for the LNG unit, or by cooling, within the NGL unit (e.g., via a standalone refrigeration system), a residue gas originating from a fractionation column of the NGL unit and using the resultant cooled residue gas to, depending upon composition, provide, for example, reflux/feed for fractionation in the NGL and/or a cold feed for the LNG unit, thereby reducing the energy consumption of the LNG unit and rendering the process more energy-efficient.
Natural gas is an important commodity throughout the world, as both an energy source and a source a raw materials. Worldwide natural gas consumption is expected to rise from 110.7 trillion cubic feet in 2008 to 123 trillion cubic feet in 2015, and 168.7 trillion cubic feet in 2035 [U.S Energy Information Administration, International Energy Outlook 2011, Sep. 19, 2011, Report Number DOE/EIA-0484 (2011)].
Natural gas obtained from oil and gas production wellheads mainly contains methane, but also may contain hydrocarbons of higher molecular weight including ethane, propane, butane, pentane, their unsaturated analogs, and heavy hydrocarbons including aromatics (e.g., benzene). Natural gas often also contains non-hydrocarbon impurities such as water, hydrogen, nitrogen, helium, argon, hydrogen sulfide, carbon dioxide, and/or mercaptans.
Before being introduced into high pressure gas pipelines for delivery to consumers, natural gas is treated to remove impurities such as carbon dioxide and sulfur compounds. In addition, the natural gas may be treated to remove a portion of the natural gas liquids (NGL). These include lighter hydrocarbons, namely ethane, propane, and butane, as well as the heavier C5+ hydrocarbons. Such treatment yields a leaner natural gas, which the consumer may require, but also provides a source of valuable materials. For example, the lighter hydrocarbons can be used as feedstock for petrochemical processes and as fuel. The C5+ hydrocarbons can be used in gasoline blending.
Often factors such as the location of the wellhead and/or the absence of requisite infrastructure may preclude the possibility of transporting natural gas via pipeline. In such cases, the natural gas can be liquefied (LNG) and transported in liquid form via a cargo carrier (truck, train, ship). However, during liquefaction of natural gas by cryogenic processes, heavier hydrocarbons within the natural gas can solidify which can then lead to damage to the cryogenic equipment and interruption of the liquefaction process. Thus, in this case also it is desirable to remove heavier hydrocarbons from the natural gas.
Numerous processes are known for the recovery of natural gas liquids. For example, Buck (U.S. Pat. No. 4,617,039) describes a process wherein a natural gas feed stream is cooled, partially condensed, and then separated in a high pressure separator. The liquid stream from the separator is warmed and fed into the bottom of a distillation (deethanizer) column. The vapor stream from the separator is expanded and introduced into a separator/absorber. Bottom liquid from separator/absorber is used as liquid feed for the deethanizer column. The overhead stream from the deethanizer column is cooled and partially condensed by heat exchange with the vapor stream removed from the top of the separator/absorber. The partially condensed overhead stream from the deethanizer column is then introduced into the upper region of the separator/absorber. The vapor stream removed from the top of the separator/absorber can be further warmed by heat exchange and compressed to provide a residue gas which, upon further compression, can be reintroduced into a natural gas pipeline.
Other C2+ and/or C3+ recovery processes are known in which the fed gas is subjected to cooling and expansion to yield a vapor stream that is introduced into the bottom region of a light ends fractionation column and a liquid stream that is introduced into a high ends fractionation column. Residue gas is removed from the top of the light ends fractionation column and product liquid is removed from the bottom of the high ends fractionation column. Liquid from the bottom of the light ends fractionation column is fed to the upper region of the heavy ends fractionation column. Overhead vapor from the heavy ends fractionation column is partially condensed and the condensate portion is used as reflux in the light ends fractionation column. The gaseous portion may be combined with the residue gas. See, for example, Buck et al. (U.S. Pat. No. 4,895,584), Key et al. (U.S. Pat. No. 6,278,035), Key et al. (U.S. Pat. No. 6,311,516), and Key et al. (U.S. Pat. No. 7,544,272).
Further, there are many known processes for liquefaction of natural gas. Typically, the natural gas is distilled in a demethanizer and the resultant methane-enriched gas is subjected to cooling and expansion to produce LNG product. The bottom liquid from the demethanizer can be sent for further processing for recovery of natural gas liquids. See, for example, Shu et al. (U.S. Pat. No. 6,125,653), Wilkinson et al. (U.S. Pat. No. 6,742,358), Wilkinson et al. (U.S. Pat. No. 7,155,931), Wilkinson et al. (U.S. Pat. No. 7,204,100), Cellular et al. (U.S. Pat. No. 7,216,507), Cellular et al. (U.S. Pat. No. 7,631,516), Wilkinson et al. (US 2004/0079107). In other systems, the natural gas is cooled and partially liquefied and then separated in a gas/liquid separator. The resultant gas and liquid streams are both used as feeds to a demethanizer. A liquid product stream is removed from the bottom of the demethanizer, and the vapor stream removed from the top of the demethanizer, after providing cooling to process streams, is removed as residue gas. See, for example, Campbell et al. (U.S. Pat. No. 4,157,904) and Campbell et al. (U.S. Pat. No. 5,881,569).
In addition, many attempts have been made to integrate a NGL recovery process with a LNG process for liquefaction of natural gas. See, for example, Houshmand et al. (U.S. Pat. No. 5,615,561), Campbell et al. (U.S. Pat. No. 6,526,777), Wilkinson et al. (U.S. Pat. No. 6,889,523), Qualls et al. (US 2007/0012072), Mak et al. (US 2007/0157663), Mak (US 2008/0271480), and Roberts et al. (US 2010/0024477).
However, while these processes provide some integration of NGL recovery and LNG production, improvements are still needed with regards to achieving such integration in a simple and efficient manner, particularly in a manner which reduces energy consumption.
Therefore, an aspect of the present invention is to provide a process and apparatus which integrate NGL recovery and LNG production in a cost effective manner, and in particular reduces the energy consumption of the LNG production.
In particular, the invention provides improvements to NGL recovery processes, such as the CRYO-PLUS™ process (see, e.g., Buck (U.S. Pat. No. 4,617,039), Key et al. (U.S. Pat. No. 6,278,035), and Key et al. (U.S. Pat. No. 7,544,272)), the Gas Subcooled (GSP) process (see, e.g., Campbell et al. (U.S. Pat. No. 4,157,904)), and the Recycle Split Vapor (RSV) process (see, e.g., Campbell et al. (U.S. Pat. No. 5,881,569), that is improvements which integrate these NGL recovery processes with an LNG production process.
The specification provides other aspects and advantages of the invention.
These aspects are achieved, according to the invention, by using a side stream of the already cooled overhead vapor from a fractionation column of an NGL recovery unit, such as a light ends fractionation column or a demethanizer/de-ethanizer, to, depending upon composition, provide reflux for fractionation in the NGL and/or a cold feed for the LNG unit, thereby reducing the energy consumption of the LNG production unit while having a minimal impact on the NGL recovery unit. Alternatively, these aspects are achieved by cooling, within the NGL unit (e.g., via a standalone refrigeration system), a residue gas originating from a fractionation column of the NGL unit and using the resultant cooled residue gas to, depending upon composition, provide reflux/feed for fractionation in the NGL and/or a cold feed for the LNG unit, thereby reducing the energy consumption of the LNG unit and rendering the process more energy-efficient.
Although the inventive processes and apparatuses are generally described herein as being suitable for the treatment of natural gas, i.e., gas resulting from oil or gas production wells, the invention is suitable for treating any feed stream which contains a predominant amount of methane along with other light hydrocarbons such as ethane, propane, butane and/or pentane.
In general, the invention provides a process and an apparatus wherein a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) is processed in a natural gas liquefaction recovery (NGL) unit that comprises a main heat exchanger, a cold separator, and a fractionation system comprising either (a) a light ends fractionation column and a heavy ends fractionation column, or (b) a demethanizer/de-ethanizer, wherein at least a part of the overhead vapor stream originating from the fractionation system of the NGL unit (e.g., a part of already overhead or residue gas that is cooled by supplemental refrigeration) is used, depending upon composition, provide reflux/feed for fractionation in the NGL and/or a cold feed for the LNG unit.
According to a general process aspect of the invention there is provided a process comprising:
cooling a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) in one or more heat exchangers, wherein the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the partially condensed feed stream into a gas/liquid cold separator to produce an overhead gaseous stream and bottoms liquid stream which are to be introduced into a fractionation system comprising (a) a light ends fractionation column and a heavy ends fractionation column, or (b) a demethanizer (or deethanizer) column;
expanding at least a portion of the overhead gaseous stream from the gas/liquid cold separator and introducing this expanded overhead gaseous stream into (a) a lower region of a light ends fractionation column or (b) an upper region of a demethanizer (or deethanizer) column;
introducing at least a portion of the bottoms liquid stream from the gas/liquid cold separator into (a) a heavy ends fractionation column at an intermediate point thereof or (b) a demethanizer (or deethanizer) column at an intermediate point thereof;
removing a liquid product stream from the bottom of (a) the heavy ends fractionation column or (b) the bottom of the demethanizer (or deethanizer) column;
removing a overhead gaseous stream from the top of (a) the light ends fractionation column or (b) the demethanizer (or deethanizer) column; and
if the fractionation system comprises a light ends fractionation column and a heavy ends fractionation column, removing a bottoms liquid stream from a lower region of the light ends fractionation column, and introducing this bottoms liquid stream from the light ends fractionation column into an upper region of the heavy ends fractionation column;
In accordance with a first process aspect of the invention, there is provided a process comprising:
introducing a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the partially condensed feed stream into a gas/liquid cold separator producing an overhead gaseous stream and bottoms liquid stream;
expanding the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded overhead gaseous stream into a lower region of a light ends fractionation column;
introducing the bottoms liquid stream from the gas/liquid cold separator into a heavy ends fractionation column at an intermediate point thereof;
removing a liquid product stream from the bottom of the heavy ends fractionation column and introducing the liquid product stream into the main heat exchanger where it undergoes indirect heat exchanger with the feed stream;
removing a bottoms liquid stream from a lower region of the light ends fractionation column, and introducing the bottoms liquid stream from the light ends fractionation column into an upper region of the heavy ends fractionation column;
removing a overhead gaseous stream from the top of the light ends fractionation column, and subjecting a first portion of this overhead gaseous stream to indirect heat exchange (e.g., in a subcooler) with an overhead gaseous stream removed from the top of the heavy ends fractionation column, whereby the overhead gaseous stream from the top of the heavy ends fractionation column is cooled and partially condensed, and discharging the first portion of the second overhead gaseous stream from the light ends fractionation column as residue gas;
removing a bottoms liquid stream from a lower region of the heavy ends fractionation column, heating the bottoms liquid stream from the heavy ends fractionation column by indirect heat exchange and returning the bottoms liquid stream from the heavy ends fractionation column to the lower region of the heavy ends fractionation column as a reboiler stream;
introducing the cooled and partially condensed overhead gaseous stream from the top of the heavy ends fractionation column into the light ends fractionation column;
removing a second portion of the overhead gaseous from the light ends fractionation column as a side stream, partially liquefying the side stream across a flow-control valve, and subjecting the partially liquefied side stream to indirect heat exchange with a refrigerant fluid for further cooling,
introducing the partially liquefied side stream into a further separation means (e.g., a further gas/liquid separator or a further distillation column), recovering liquid product (containing the majority of ethane, as well as heavier hydrocarbon components, of the partially liquefied side stream) and introducing the recovered liquid product into the light ends fractionation column as a liquid reflux stream and/or into the heavy ends fractionation column as a liquid reflux stream, and
recovering an overhead vapor stream rich in methane, from the further separation means, subjecting the overhead vapor stream to indirect heat exchange with a refrigerant fluid for additional cooling and partial condensation, feeding the resultant condensate to an LNG exchanger, where liquefaction is performed.
The LNG process may be an industry standard mixed refrigerant or nitrogen refrigeration process. Thus, in the process according to the invention, a single refrigerant stream may be used to provide the cooling necessary to liquefy the natural gas into LNG. In a typical LNG process, a refrigerant cycle compressor increases the pressure of the circulating refrigerant. This high pressure refrigerant is cooled via exchange with air, water or other cooling media. The resulting cool, high pressure refrigerant, often present in both a liquid and gas phase, passes through the LNG exchanger where the refrigerant is fully liquefied or becomes a cooled vapor at high pressure. The cold refrigerant is then reduced in pressure via a Joule-Thomson valve (isenthalpic, i.e., a process that generally proceeds without any change in enthalpy) or via a turboexpander (isentropic, i.e., a process that generally proceeds without any change in entropy) to a lower pressure resulting in the flashing of the cold, high pressure refrigerant into a two-phase vapor and liquid mixture or single phase vapor that is colder than the preceding stream and is also colder in temperature than the liquefaction point (bubble point) of the LNG feed stream. This low pressure, cold, two-phase vapor and liquid mixture or single phase vapor refrigerant stream returns to the LNG exchanger to provide sufficient liquefaction cooling for both the refrigerant as well as the natural gas feed stream that is to be liquefied. Along the course of flowing through the LNG exchanger, the refrigerant stream is fully vaporized. This vapor flows to the refrigerant cycle compressor to begin the cooling cycle again.
Thus, in accordance with the invention, when a refrigerant system is used to cool a residue gas stream or a side stream from the overhead vapors of light ends fractionation column or a demethanizer, the refrigerant system can involve the use of a single refrigerant system or mixed refrigerant cooling system or an expander based system or a combination of a mixed refrigerant system and an expander based refrigeration system.
Additionally, the refrigerant system can use a refrigerant composition: either it is a pure single refrigerant (concentration >95 vol %) or a mixture of two or more components with concentrations >5 vol % each. Suitable refrigerant components include light paraffinic or olefinic hydrocarbons like methane, ethane, ethylene, propane, propylene, butane, pentane, and inorganic components like nitrogen, argon as well as possibly carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia. Further, the refrigerant system can involve (a) a closed or open loop refrigeration cycle, (b) two or more pressure levels in the entire refrigeration cycle, (c) pressure reduction from a higher pressure to a lower pressure either via work expansion (turbo expander) and/or via isenthalpic throttling (control valve, restriction orifice), or (d) phase condition of the refrigerant either all vapor phase or changing from vapor to liquid and back to vapor. For example, this refrigeration system can utilize (a) a phase-change mixed refrigerant cycle without work expansion of a high pressure gas fraction, (b) a phase-change mixed refrigerant cycle with work expansion of a high pressure gas fraction, (c) a vapor phase mixed refrigerant cycle with work expansion of a high pressure gas fraction in one or more stages, or (d) a vapor phase pure refrigerant cycle with work expansion of a high pressure gas fraction in one or more stages.
In the description herein and in the drawings, expansions of fluids are often characterized as being performed by an expansion valve or “expansion across a valve.” One skilled in the art would recognize that these expansion can be performed using various types expansion devices such as an expander, a control valve, a restrictive orifice or other device intended to reduce the pressure of the circulating fluid. The use of these expansion devices to perform the expansions described herein is included within the scope of the invention.
By removing a side stream from the overhead gaseous stream of the light ends fractionation column, cooling and partially condensing this side stream, and then delivering at least part of the resulting condensate to an LNG exchanger, an integration of the NGL and LNG processes is achieved in a manner which does not compromise the NGL recovery process. The utilization of a portion of the cold overhead gaseous stream from the LEFC of the NGL process reduces refrigeration requirements of the LNG process, thereby reducing overall energy consumption, and improving recoveries for both processes.
According to one embodiment of the invention, the liquid product recovered from the further separation means (e.g., further distillation column) is introduced into the light ends fractionation column as a liquid reflux stream. According to another embodiment of the invention, the liquid product recovered from the further separation means (e.g., further distillation column) is introduced into the heavy ends fractionation column as a liquid reflux stream.
In accordance with a second process aspect of the invention, there is provided a further process comprising:
introducing a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the partially condensed feed stream into a gas/liquid cold separator producing an overhead gaseous stream and bottoms liquid stream;
expanding the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded overhead gaseous stream into a lower region of a light ends fractionation column;
introducing the bottoms liquid stream from the gas/liquid cold separator into a heavy ends fractionation column at an intermediate point thereof;
removing a liquid product stream from the bottom of the heavy ends fractionation column and introducing the liquid product stream from the bottom of the heavy ends fractionation column into the main heat exchanger where it undergoes indirect heat exchanger with the feed stream;
removing a bottoms liquid stream from a lower region of the light ends fractionation column, and introducing the bottoms liquid stream from the light ends fractionation column into an upper region of the heavy ends fractionation column;
removing a overhead gaseous stream from the top of the light ends fractionation column, and subjecting this overhead gaseous stream to indirect heat exchange (e.g., in a subcooler) with an overhead gaseous stream removed from the top of the heavy ends fractionation column, whereby the overhead gaseous stream from the top of the heavy ends fractionation column is cooled and partially condensed, and then discharging the overhead gaseous stream from the light ends fractionation column as residue gas;
removing a bottoms liquid stream from a lower region of the heavy ends fractionation column, heating the bottoms liquid stream from the heavy ends fractionation column by indirect heat exchange and returning the bottoms liquid stream from the heavy ends fractionation column to the lower region of the heavy ends fractionation column as a reboiler stream;
introducing the cooled and partially condensed overhead gaseous stream from the top of the heavy ends fractionation column into the light ends fractionation column;
introducing a residue gas stream into the main heat exchanger wherein the residue gas stream is cooled by indirect heat exchange, and then subjecting the cooled residue gas stream to further indirect heat exchange (e.g., in the subcooler) with an overhead gaseous stream removed from the top of the heavy ends fractionation column whereby the residue gas stream is further cooled;
expanding the further cooled residue gas stream and introducing the resultant partially liquefied residue gas stream into a further separation means (e.g., a further gas/liquid separator or a further distillation column), recovering an overhead residue gas stream from the further separation means, recovering a liquid stream from the further separation means and feeding this liquid stream to an LNG exchanger, where liquefaction is performed.
In accordance with a third process aspect of the invention, there is provided a further process comprising:
introducing a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the partially condensed feed stream into a gas/liquid cold separator producing an overhead gaseous stream and bottoms liquid stream;
expanding the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded overhead gaseous stream from the gas/liquid cold separator into a lower region of a light ends fractionation column;
introducing the bottoms liquid stream from gas/liquid cold separator into a heavy ends fractionation column at an intermediate point thereof;
removing a liquid product stream from the bottom of the heavy ends fractionation column and introducing the liquid product stream from the bottom of the heavy ends fractionation column into the main heat exchanger where it undergoes indirect heat exchanger with the feed stream;
removing a bottoms liquid stream from a lower region of the light ends fractionation column, and introducing the bottoms liquid stream from the light ends fractionation column into an upper region of the heavy ends fractionation column;
removing a overhead gaseous stream from the top of the light ends fractionation column, and subjecting this overhead gaseous stream to indirect heat exchange (e.g., in a subcooler) with an overhead gaseous stream removed from the top of the heavy ends fractionation column, whereby the overhead gaseous stream from the top of the heavy ends fractionation column is cooled and partially condensed;
removing a bottoms liquid stream from a lower region of the heavy ends fractionation column, heating the bottoms liquid stream from the heavy ends fractionation column by indirect heat exchange and returning the bottoms liquid stream from the heavy ends fractionation column to the lower region of the heavy ends fractionation column as a reboiler stream;
introducing the cooled and partially condensed overhead gaseous stream from the top of the heavy ends fractionation column into the light ends fractionation column;
introducing the overhead gaseous stream from the light ends fractionation column, after being heated by heat exchange and compressed, as a residue gas into a heat exchanger wherein the residue gas is cooled and partially liquefied by indirect heat exchange; and
introducing the resultant partially liquefied residue gas stream into a further separation means (e.g., a further gas/liquid separator or a further distillation column), recovering a liquid stream from the further separation means which is introduced into the light ends fractionation column as reflux, recovering an overhead residue gas stream from the further separation means, and feeding at least a portion of the overhead residue gas stream from the further separation means to an LNG exchanger where liquefaction is performed.
According to a further embodiment of the above described processes, the bottoms liquid stream removed from the lower region of the heavy ends fractionation column that is recycled as a reboiler stream is heated in the main heat exchanger by indirect heat exchange with the feed stream (e.g., natural gas), before being returned to the lower region of the heavy ends fractionation column.
In addition, a further liquid stream can be removed from an intermediate point of the heavy ends fractionation column and also used for cooling the natural gas feed stream in the main heat exchanger. The further liquid stream is removed from a first intermediate point of the heavy ends fractionation column, heated by indirect heat exchange with the natural gas feed stream in the main heat exchanger, and then reintroduced into the heavy ends fractionation column at another intermediate point below the first intermediate point.
According to another embodiment of the invention, additional reflux streams are provided for the light ends fractionation column. A portion of the gaseous overhead stream removed from the top of cold separator, prior to expansion, is fed to a subcooler where it undergoes indirect heat exchange with the overhead vapor from the light ends fractionation column. This portion of the gaseous overhead stream is cooled and partially liquefied in the subcooler and introduced into the top region of the light ends fractionation column to provide additional reflux.
Additionally or alternatively, a portion of bottoms liquid stream from the gas/liquid cold separator is delivered to a liquid/liquid heat exchanger where it undergoes indirect heat exchange with the bottom liquid stream removed from the light ends fractionation column. Thereafter, the stream is then fed to an intermediate region of the light ends fractionation column as a liquid reflux. Each of these two additional reflux streams improves recovery of ethane and heavier hydrocarbon components.
In accordance with a further embodiment an additional reflux for the light ends fractionation column is provided through a combination of a portion of the gaseous overhead stream removed from the top of cold separator and a portion of bottoms liquid stream from cold separator. In this embodiment, prior to expansion, a portion of the gaseous overhead stream removed from the top of cold separator is combined with a portion of the bottoms liquid stream from cold separator, and the combined stream is fed to the subcooler. In the subcooler it undergoes indirect heat exchange with the overhead vapor from the light ends fractionation column. The combined stream is cooled and partially liquefied in the subcooler and introduced into the top region of the light ends fractionation column to provide additional reflux. This additional reflux stream for the light ends fractionation column improves recovery of ethane and heavier hydrocarbon components.
In one version of the above mentioned embodiment, the side stream from the overhead gaseous stream of the light ends fractionation column is eventually introduced into the light ends fractionation column. According to a modification, the side stream from the overhead gaseous stream of the light ends fractionation column is eventually introduced into the heavy ends fractionation column, rather than the light ends fractionation column. As described previously, the side stream is partially liquefied across a flow-control valve. The partially liquefied vapor undergoes indirect heat exchange with a refrigerant fluid for further cooling and is then fed into the further distillation column. The methane-rich overhead vapor stream from the further separation means (e.g., further distillation column) undergoes indirect heat exchange with the refrigerant fluid for additional cooling, and is then fed into the LNG exchanger, where liquefaction occurs. The majority of ethane as well as heavier hydrocarbon components are recovered from the bottom of the further separation means (e.g., further distillation column) as liquid product. This liquid product is introduced into the top of the heavy ends fractionation column as a liquid reflux stream.
According to a further embodiment of the invention, the system can incorporate a refrigeration loop through the NGL process which results in a reduction in energy consumption. For example, a stream of refrigerant fluid from the refrigerant system is fed through the main heat exchanger where it undergoes indirect heat exchange with the natural gas feed stream and possibly other streams (e.g., the liquid product stream from the bottom of the heavy ends fractionation column, the further liquid stream from an intermediate point of the heavy ends fractionation column, the reboiler stream removed from the bottom region of the heavy ends fractionation column, and/or the overhead vapor product stream removed from the top of the light ends fractionation column). The refrigerant stream is cooled and partially liquefied in the main heat exchanger and is then introduced into the subcooler where it is further cooled and liquefied. The refrigerant stream is then flashed across a valve, causing the fluid to reach even colder temperatures, and is then fed back to the subcooler to provide cooling for the additional reflux streams of the light ends fractionation column. The refrigerant stream then returns to the main heat exchanger, where it functions as a coolant for the NGL process streams. Thereafter, the refrigerant stream is returned to the refrigeration system for compression.
According to a further embodiment, a modified refrigeration loop is used. A stream of refrigerant fluid from the refrigerant system is fed through the main heat exchanger where it undergoes indirect heat exchange with the natural gas feed stream and possibly other streams (e.g., the liquid product stream from the bottom of the heavy ends fractionation column, the further liquid stream from an intermediate point of the heavy ends fractionation column, the reboiler stream removed from the bottom region of the heavy ends fractionation column, and/or the overhead vapor product stream removed from the top of the light ends fractionation column). In the main heat exchanger, the refrigerant stream is cooled and partially liquefied and is then introduced into the subcooler where it is further cooled and liquefied. This stream is then introduced into the heat exchanger used for cooling the side stream of the overhead vapor product stream from the light ends fractionation column. The refrigerant stream exits the heat exchanger and is flashed across a valve, causing the fluid to reach even colder temperatures. The resultant stream is then fed back to the same heat exchanger to provide further cooling. Thereafter, the refrigerant passes through the subcooler and then into the main heat exchanger, where it serves as a coolant to the NGL process streams. The refrigerant stream then flows back to the refrigeration system for compression.
According to a further embodiment, a residue gas stream is recovered from the partially condensed overhead vapor stream obtained from the further separation means, and this residue gas stream is used to cool, by indirect heat exchange, the overhead vapor stream from the further separation means and/or the side stream of the overhead vapor product stream from the light ends fractionation column. Thereafter, the residue gas stream can be compressed to the desired pressure. According to a further modification, the residue gas stream can be compressed and then optionally used for indirect heat exchange with the overhead vapor stream from the further separation means and/or the side stream of the overhead vapor product stream from the light ends fractionation column.
In accordance with a fourth process aspect of the invention, there is provided a further process comprising:
splitting a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into at least a first partial stream and a second partial stream;
introducing the first partial stream of the feed stream into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the first partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the second partial stream of the feed stream into a heat exchanger wherein the second partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
recombining the first and second partial streams of the feed stream, and optionally subjecting the resultant recombined feed stream to heat exchange with a refrigerant (e.g., a propane refrigerant);
introducing the cooled recombined feed stream into a gas/liquid cold separator to produce an overhead gaseous stream and bottoms liquid stream;
expanding a portion of the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded portion of the overhead gaseous stream into an upper region of a demethanizer column;
expanding a portion of the bottoms liquid stream from the gas/liquid cold separator and introducing this expanded portion of the bottoms liquid stream into an intermediate region of the demethanizer;
combining another portion of the bottoms liquid stream from the gas/liquid cold separator with another portion of the overhead gaseous stream from the gas/liquid cold separator, cooling the resultant combined cold separator stream by indirect heat exchange (e.g., in a subcooler) with overhead vapor from the demethanizer, expanding the cooled resultant combined cold separator stream, and then introducing the expanded cooled combined cold separator stream into the top of the demethanizer;
removing a liquid product stream from the bottom of the demethanizer and introducing the liquid product stream into the main heat exchanger where it undergoes indirect heat exchanger with the first partial stream of the feed stream;
removing a overhead gaseous stream from the top of the demethanizer, and subjecting this overhead gaseous stream to indirect heat exchange (e.g., in a subcooler) with the combined cold separator streams, whereby the combined cold separator streams is cooled and partially condensed and the overhead gaseous stream from the top of the demethanizer is heated, further heating the overhead gaseous stream from the top of the demethanizer by indirect heat exchange with the second partial feed stream, and then compressing and removing at least a portion of the overhead gaseous stream from the demethanizer as residue gas (another optional portion can be removed as fuel gas);
introducing at least a portion of the residue gas stream from the overhead gaseous stream of the demethanizer into the main heat exchanger wherein the residue gas stream is cooled by indirect heat exchange, and then subjecting the cooled residue gas stream to further indirect heat exchange (e.g., in the subcooler) with the overhead gaseous stream from the top of the demethanizer whereby the residue gas stream is further cooled;
expanding a first portion of the further cooled residue gas stream and introducing the resultant partially liquefied first portion of the residue gas stream into an upper region of the demethanizer; and
introducing a second portion of the further cooled residue gas stream into a further separation means (e.g., a further gas/liquid separator (LNGL separator, i.e., a separator that integrates and combines the NGL and LNG units)) or a further distillation column), recovering an overhead residue gas stream from said further separation means, recovering a liquid stream from the further separation means, and feeding this liquid stream from the further separation means to an LNG exchanger, where liquefaction is performed.
In accordance with a fifth process aspect of the invention, there is provided a further process comprising:
splitting a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into at least a first partial stream and a second partial stream;
introducing the first partial stream of the feed stream into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the first partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the second partial stream of the feed stream into a heat exchanger wherein the second partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
recombining the first and second partial streams of the feed stream, and optionally subjecting the resultant recombined feed stream to heat exchange with a refrigerant (e.g., a propane refrigerant);
introducing the cooled recombined feed stream into a gas/liquid cold separator to produce an overhead gaseous stream and bottoms liquid stream;
expanding a portion of the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded portion of the overhead gaseous stream into an upper region of a demethanizer column;
expanding a portion of the bottoms liquid stream from the gas/liquid cold separator and introducing this expanded portion of the bottoms liquid stream into an intermediate region of the demethanizer;
combining another portion of the bottoms liquid stream from the gas/liquid cold separator with another portion of the overhead gaseous stream from the gas/liquid cold separator, cooling the resultant combined cold separator stream by indirect heat exchange (e.g., in a subcooler) with overhead vapor from the demethanizer, expanding the cooled resultant combined cold separator stream, and then introducing the expanded cooled combined cold separator stream into the top of the demethanizer;
removing a liquid product stream from the bottom of the demethanizer and introducing the liquid product stream into the main heat exchanger where it undergoes indirect heat exchanger with the first partial stream of the feed stream;
removing a first portion of an overhead gaseous stream from the top of the demethanizer, and subjecting this first portion of the overhead gaseous stream to indirect heat exchange (e.g., in a subcooler) with the combined cold separator stream, whereby the combined cold separator stream is cooled and partially condensed and the overhead gaseous stream from the top of the demethanizer is heated, further heating the overhead gaseous stream from the top of the demethanizer by indirect heat exchange with the second partial feed stream, and then compressing and removing at least a portion of the overhead gaseous stream from the demethanizer as residue gas (another optional portion can be removed as fuel gas);
removing a second portion of the overhead gaseous from the demethanizer as a side stream, and subjecting the side stream to indirect heat exchange with a refrigerant fluid whereby the side stream is further cooled and partially liquefied:
introducing the partially liquefied side stream into a further separation means (e.g., a further gas/liquid separator or a further distillation column), recovering a liquid stream (containing ethane and heavier hydrocarbon components, of the partially liquefied side stream) and introducing the recovered liquid stream into the demethanizer as a liquid reflux stream, and
recovering an overhead vapor stream rich in methane, from the further separation means, subjecting the overhead vapor stream to indirect heat exchange with a refrigerant fluid for additional cooling and partial condensation, and feeding the resultant condensate to an LNG exchanger, where liquefaction is performed.
In accordance with a sixth process aspect of the invention, there is provided a further process comprising:
splitting a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into at least a first partial stream and a second partial stream;
introducing the first partial stream of the feed stream into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the first partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the second partial stream of the feed stream into a heat exchanger wherein the second partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
recombining the first and second partial streams of the feed stream, and optionally subjecting the resultant recombined feed stream to heat exchange with a refrigerant (e.g., a propane refrigerant);
introducing the cooled recombined feed stream into a gas/liquid cold separator to produce an overhead gaseous stream and bottoms liquid stream;
expanding a portion of the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded portion of the overhead gaseous stream into an upper region of a demethanizer column;
expanding a portion of the bottoms liquid stream from the gas/liquid cold separator and introducing this expanded portion of the bottoms liquid stream into an intermediate region of the demethanizer;
combining another portion of the bottoms liquid stream from the gas/liquid cold separator with another portion of the overhead gaseous stream from the gas/liquid cold separator, cooling the resultant combined cold separator stream by indirect heat exchange (e.g., in a subcooler) with overhead vapor from the demethanizer, expanding the cooled resultant combined cold separator stream, and then introducing the expanded cooled combined cold separator stream into the top of the demethanizer;
removing a liquid product stream from the bottom of the demethanizer and introducing the liquid product stream into the main heat exchanger where it undergoes indirect heat exchanger with the first partial stream of the feed stream;
removing a overhead gaseous stream from the top of the demethanizer, and subjecting this overhead gaseous stream to indirect heat exchange (e.g., in a subcooler) with the combined cold separator stream, whereby the combined cold separator stream is cooled and partially condensed and the overhead gaseous stream from the top of the demethanizer is heated, further heating the overhead gaseous stream from the top of the demethanizer by indirect heat exchange with the second partial feed stream;
recycling at least a portion of overhead gaseous stream from the top of the demethanizer, after indirect heat exchange with the second partial feed stream, as a residue gas stream to a heat exchanger wherein the residue gas stream is cooled and partially condensed by indirect heat exchange (e.g., with a refrigerant), and then introducing the cooled and partially condensed residue gas stream into a further separation means (e.g., a further gas/liquid separator or a further distillation column), recovering a residue liquid stream from the further separation means and introducing the residue liquid stream into the top region of the demethanizer as reflux; and
recovering an overhead gas stream from the further separation means, cooling the overhead gas stream by indirect heat exchange (e.g., with a refrigerant), expanding the further cooled overhead gas stream and introducing this expanded further cooled overhead gas stream into a second further separation means (e.g., a further gas/liquid separator (LNGL separator) or a further distillation column), recovering an overhead stream from the second further separation means as a further residue gas (boil off gas), recovering a liquid stream from the second further separation means, and feeding this liquid stream from the second further separation means to an LNG exchanger, where liquefaction is performed.
In accordance with a seventh process aspect of the invention, there is provided a further process comprising:
splitting a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into at least a first partial stream and a second partial stream;
introducing the first partial stream of the feed stream into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the first partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the second partial stream of the feed stream into a heat exchanger wherein the second partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
recombining the first and second partial streams of the feed stream, and optionally subjecting the resultant recombined feed stream to heat exchange with a refrigerant (e.g., a propane refrigerant);
introducing the cooled recombined feed stream into a gas/liquid cold separator to produce an overhead gaseous stream and bottoms liquid stream;
expanding a portion of the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded portion of the overhead gaseous stream into an upper region of a demethanizer column;
expanding a portion of the bottoms liquid stream from the gas/liquid cold separator and introducing this expanded portion of the bottoms liquid stream into an intermediate region of the demethanizer;
combining another portion of the bottoms liquid stream from the gas/liquid cold separator with another portion of the overhead gaseous stream from the gas/liquid cold separator, cooling the resultant combined cold separator stream by indirect heat exchange in a heat exchanger (e.g. a subcooler) with overhead vapor from the demethanizer, expanding the cooled resultant combined cold separator stream, and then introducing the expanded cooled combined cold separator stream into the top of the demethanizer;
removing a liquid product stream from the bottom of the demethanizer and introducing the liquid product stream into the main heat exchanger where it undergoes indirect heat exchanger with the first partial stream of the feed stream;
removing a overhead gaseous stream from the top of the demethanizer, and subjecting this overhead gaseous stream to indirect heat exchange in with the combined cold separator stream (e.g., in the subcooler), whereby the combined cold separator stream is cooled and partially condensed and the overhead gaseous stream from the top of the demethanizer is heated, further heating the overhead gaseous stream from the top of the demethanizer by indirect heat exchange with the second partial feed stream, and then compressing and removing at least a portion of the overhead gaseous stream from the demethanizer as residue gas (another optional portion can be removed as fuel gas);
subjecting at least a portion of the residue gas stream from the overhead gaseous stream of the demethanizer to heat exchange (e.g., in the subcooler) wherein the residue gas stream is cooled by indirect heat exchange with the overhead gaseous stream from the top of the demethanizer;
expanding a portion of the cooled residue gas stream and introducing the resultant expanded portion of the cooled residue gas stream into an upper region of the demethanizer, expanding another portion of the residue gas stream and introducing the resultant expanded another portion into a further separation means (e.g., a further gas/liquid separator (LNGL separator) or a further distillation column), recovering an overhead residue gas stream from the further separation means as a further residue gas (boil off gas), recovering a liquid stream from the further separation means, and feeding this liquid stream from the further separation means to an LNG exchanger where liquefaction is performed.
In accordance with a eighth process aspect of the invention, there is provided a further process comprising:
splitting a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into at least a first partial stream and a second partial stream;
introducing the first partial stream of the feed stream into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the first partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the second partial stream of the feed stream into a heat exchanger wherein the second partial stream of the feed stream is cooled and possibly partially condensed (depending upon the composition of the feed gas stream) by indirect heat exchange;
recombining the first and second partial streams of the feed stream, and optionally subjecting the resultant recombined feed stream to heat exchange with a refrigerant (e.g., a propane refrigerant);
introducing the cooled recombined feed stream into a gas/liquid cold separator to produce an overhead gaseous stream and bottoms liquid stream;
expanding a portion of the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded portion of the overhead gaseous stream into an upper region of a demethanizer column;
expanding a portion of the bottoms liquid stream from the gas/liquid cold separator and introducing this expanded portion of the bottoms liquid stream into an intermediate region of the demethanizer;
combining another portion of the bottoms liquid stream from the gas/liquid cold separator with another portion of the overhead gaseous stream from the gas/liquid cold separator, cooling the resultant combined cold separator stream by indirect heat exchange in a heat exchanger (e.g., a subcooler) with overhead vapor from the demethanizer, expanding the cooled resultant combined cold separator stream, and then introducing the expanded cooled combined cold separator stream into the top of the demethanizer;
removing a liquid product stream from the bottom of the demethanizer and introducing the liquid product stream into the main heat exchanger where it undergoes indirect heat exchanger with the first partial stream of the feed stream;
removing a overhead gaseous stream from the top of the demethanizer, and subjecting this overhead gaseous stream to indirect heat exchange with the combined cold separator stream expanding the cooled resultant combined cold separator stream, whereby the combined cold separator stream is cooled and partially condensed (depending upon the composition of the stream) and the overhead gaseous stream from the top of the demethanizer is heated, further heating the overhead gaseous stream from the top of the demethanizer by indirect heat exchange with the second partial feed stream, and then compressing and removing at least a portion of the overhead gaseous stream from the demethanizer as residue gas (another optional portion can be removed as fuel gas);
subjecting at least a portion of the residue gas stream from the overhead gaseous stream of the demethanizer to heat exchange (e.g., in the subcooler) wherein the residue gas stream is cooled by indirect heat exchange with the overhead gaseous stream from the top of the demethanizer;
separating the cooled residue gas stream into a first portion and a second portion, expanding the first portion of the cooled residue gas stream and introducing the resultant expanded first portion of the cooled residue gas stream into an upper region of the demethanizer,
further cooling and partially condensing the second portion of the cooled residue gas stream by indirect heat exchange in a heat exchanger (e.g., against a refrigerant), and then introducing the cooled and partially condensed second portion of the residue gas stream into a further separation means (e.g., a further gas/liquid separator or a further distillation column), recovering a residue liquid stream from the further separation means and introducing the residue liquid stream into the top region of the demethanizer as reflux; and
recovering an overhead gas stream from the further separation means, cooling the overhead gas stream by indirect heat exchange (e.g., with a refrigerant), expanding the further cooled overhead residue gas stream and introducing this expanded further cooled overhead residue gas stream into a second further separation means (e.g., a further gas/liquid separator (LNGL separator) or a further distillation column), recovering an overhead stream from the second further separation means as a further residue gas (boil off gas), recovering a liquid stream from the second further separation means, and feeding this liquid stream from the second further separation means to an LNG exchanger, where liquefaction is performed.
In accordance with a ninth process aspect of the invention, there is provided a further process comprising:
splitting a feed stream containing light hydrocarbons (e.g., a natural gas feed stream) into at least a first partial stream and a second partial stream;
introducing the first partial stream of the feed stream into a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) wherein the first partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
introducing the second partial stream of the feed stream into a heat exchanger wherein the second partial stream of the feed stream is cooled and partially condensed by indirect heat exchange;
recombining the first and second partial streams of the feed stream, and optionally subjecting the resultant recombined feed stream to heat exchange with a refrigerant (e.g., a propane refrigerant);
introducing the cooled recombined feed stream into a gas/liquid cold separator to produce an overhead gaseous stream and bottoms liquid stream;
expanding a portion of the overhead gaseous stream from the gas/liquid cold separator and then introducing the expanded portion of the overhead gaseous stream into an upper region of a demethanizer column;
expanding a portion of the bottoms liquid stream from the gas/liquid cold separator and introducing this expanded portion of the bottoms liquid stream into an intermediate region of the demethanizer;
combining another portion of the bottoms liquid stream from the gas/liquid cold separator with another portion of the overhead gaseous stream from the gas/liquid cold separator, cooling the resultant combined cold separator stream by indirect heat exchange in a heat exchanger (e.g., a subcooler) with overhead vapor from the demethanizer, expanding the cooled resultant combined cold separator stream, and then introducing the expanded cooled combined cold separator stream into the top of the demethanizer;
removing a liquid product stream from the bottom of the demethanizer and introducing the liquid product stream into the main heat exchanger where it undergoes indirect heat exchanger with the first partial stream of the feed stream;
removing a overhead gaseous stream from the top of the demethanizer, and subjecting this overhead gaseous stream to indirect heat exchange with the combined cold separator stream, (e.g., in the subcooler) whereby the combined cold separator stream is cooled and partially condensed (depending upon the composition of the stream) and the overhead gaseous stream from the top of the demethanizer is heated, further heating the overhead gaseous stream from the top of the demethanizer by indirect heat exchange with the second partial feed stream, and then compressing and removing at least a portion of the overhead gaseous stream from the demethanizer as a residue gas stream (another optional portion can be removed as fuel gas);
cooling a portion of the residue gas stream by indirect heat exchange in a heat exchanger (e.g., against a refrigerant), and then introducing the cooled portion of the residue gas stream into a further separation means (e.g., a further gas/liquid separator or a further distillation column), recovering a residue liquid stream from the further separation means and introducing the residue liquid stream into the top region of the demethanizer as reflux; and
recovering an overhead gas stream from the further separation means, cooling the overhead gas stream by indirect heat exchange (e.g., with a refrigerant), expanding the further cooled overhead residue gas stream and introducing this expanded further cooled overhead gas stream into a second further separation means (e.g., a further gas/liquid separator (LNGL separator) or a further distillation column), recovering an overhead stream from the second further separation means as a further residue gas (boil off gas), recovering a liquid stream from the second further separation means, and feeding this liquid stream from the second further separation means to an LNG exchanger, where liquefaction is performed.
According to a general apparatus aspect of the invention there is provided an apparatus comprising:
one or more heat exchangers for cooling and partially condensing by indirect heat exchange a feed stream containing light hydrocarbons (e.g., a natural gas feed stream);
gas/liquid cold separator and means (e.g., piping conduits) for introducing a partially condensed feed stream from the one or more heat exchangers into the gas/liquid cold separator, the gas/liquid cold separator having upper outlet means (e.g., piping conduits) for removing an overhead gaseous stream and lower outlet means (e.g., piping conduits) for removing a bottoms liquid stream;
means for introducing overhead gaseous stream and bottoms liquid stream from the gas/liquid cold separator into a fractionation system comprising (a) a light ends fractionation column and a heavy ends fractionation column, or (b) a demethanizer (or deethanizer) column, the means comprising an expansion device for expanding at least a portion of overhead gaseous stream from the gas/liquid cold separator and means (e.g., piping conduits) for introducing expanded overhead gaseous stream into (a) a lower region of a light ends fractionation column or (b) an upper region of a demethanizer (or deethanizer) column, and means (e.g., piping conduits) for introducing at least a portion of bottoms liquid stream from the gas/liquid cold separator into (a) a heavy ends fractionation column at an intermediate point thereof or (b) a demethanizer (or deethanizer) column at an intermediate point thereof;
means (e.g., piping conduits) for removing a liquid product stream from the bottom of (a) the heavy ends fractionation column or (b) the demethanizer (or deethanizer) column;
means (e.g., piping conduits) for removing a overhead gaseous stream from the top of (a) the light ends fractionation column or (b) the demethanizer (or deethanizer) column, and
if the fractionation system comprises a light ends fractionation column and a heavy ends fractionation column, the apparatus further comprises means (e.g., piping conduits) for removing a bottoms liquid stream from a lower region of the light ends fractionation column, and introducing this bottoms liquid stream from the light ends fractionation column into the upper region of the heavy ends fractionation column;
said apparatus further comprising:
In accordance with a first apparatus aspect of the invention, there is provided an apparatus for performing the first aspect of the inventive process. The apparatus comprises:
a light ends fractionation column and a heavy ends fractionation column;
a main heat exchanger (e.g., a plate-fin heat exchanger or shell and tube heat exchanger) for cooling and partially condensing a natural gas feed stream by indirect heat exchange;
a gas/liquid cold separator for separating a partially condensed feed stream into an overhead gaseous stream and bottoms liquid stream;
an expansion device (e.g., expansion valve, turbo-expander) for expanding overhead gaseous stream from the gas/liquid cold separator and means for introducing (e.g., pipes, conduits) expanded overhead gaseous stream into a lower region of the light ends fractionation column;
means for introducing (e.g., pipes, conduits) bottoms liquid stream from the gas/liquid cold separator into the heavy ends fractionation column at an intermediate point thereof;
means for removing (e.g., pipes, conduits) a liquid product stream from the bottom of the heavy ends fractionation column and means for introducing (e.g., pipes, conduits) liquid product stream from the bottom of the heavy ends fractionation column into the main heat exchanger for indirect heat exchange with natural gas feed stream;
means for removing (e.g., pipes, conduits, pump) bottoms liquid stream from a lower region of the light ends fractionation column and introducing it into the upper region of the heavy ends fractionation column;
means for removing (e.g., pipes, conduits) overhead gaseous stream from the top of the light ends fractionation column and introducing overhead gaseous stream from the top of the light ends fractionation column into a subcooler for indirect heat exchange with overhead gaseous stream removed from the top of the heavy ends fractionation column;
means for removing (e.g., pipes, conduits) bottoms liquid stream from a lower region of the heavy ends fractionation column, a heat exchanger for heating bottoms liquid stream from a lower region of the heavy ends fractionation column by indirect heat exchange, and means for returning (e.g., pipes, conduits) bottoms liquid stream to the lower region of the heavy ends fractionation column as a reboiler stream;
means for removing (e.g., pipes, conduits) overhead gaseous stream from the top of the heavy ends fractionation column and introducing it into the subcooler for indirect heat exchange with overhead gaseous stream from the top of the light ends fractionation column;
means for removing (e.g., pipes, conduits) cooled and partially condensed overhead gaseous stream from the subcooler and introducing it into the light ends fractionation column;
means for removing (e.g., pipes, conduits) a portion of the overhead gaseous from the light ends fractionation column as a side stream, a flow-control valve for partially liquefying the side stream, and a refrigerant heat exchanger for subjecting partially liquefied side stream to indirect heat exchange with a refrigerant fluid for further cooling;
means for introducing (e.g., pipes, conduits) partially liquefied side stream into a further separation means (e.g., a further gas/liquid separator or a further distillation column),
means for recovering (e.g., pipes, conduits) liquid product from the further separation means and introducing it into the light ends fractionation column as a liquid reflux stream and/or the heavy ends fractionation column as a liquid reflux stream, and
means for recovering (e.g., pipes, conduits) an overhead vapor stream from the further separation means,
a heat exchanger for subjecting overhead vapor stream from the further separation means to indirect heat exchange with a refrigerant fluid for additional cooling and partial condensation, and
means for feeding (e.g., pipes, conduits) resultant condensate to an LNG exchanger, where liquefaction is performed.
Second through ninth apparatus aspects of the invention are apparatus systems capable of performing the processes corresponding to each of the second to ninth process aspects described above, examples of which are illustrated in the Figures.
The invention as well as further advantages, features and examples of the present invention are explained in more detail by the following descriptions of embodiments based on the Figures, wherein:
The embodiments of
In
A liquid stream (10) is removed from the bottom of the LEFC (7) and delivered, via pump (11), to the top of the HEFC (9). An overhead vapor product (12), also called a residue gas, is removed from the top of the LEFC (7), undergoes indirect heat exchange in a subcooler (13) with a gas stream (14) discharged from the top of the HEFC (9), before being heated in the main heat exchanger (2) and then discharged from the system. A portion of this overhead vapor product can be used as fuel gas. Another portion of the overhead vapor product can be further compressed before being sent to a gas pipeline.
In a typical system, the warm overhead product from the LEFC can be sent to a gas pipeline for delivery to the consumer, or it can be 100% liquefied in an LNG unit, or a portion can flow to the gas pipeline while the remainder can be liquefied by the LNG unit. Liquefying the overhead gas product after warming the gas requires energy. However, as described further below, the inventive process uses overhead gas product from the top of the LEFC as the LNG unit feed, thereby preserving cooling of the overhead gas product and reducing energy consumption.
A liquid product stream (15) is removed from the bottom of the HEFC (9) and passed through the main heat exchanger (2) where it undergoes indirect heat exchanger with the gas feed stream (1). In addition, a further liquid stream (16) is removed from a first intermediate point of the HEFC (9). This further liquid stream (16) is heated by indirect heat exchange with the gas feed stream (1) (e.g., in main heat exchanger (2)), and then reintroduced (17) into the HEFC (9) at a second intermediate point below the first intermediate point. An additional liquid stream (18) is removed from the lower region of the HEFC (9), heated in an indirect heat exchanger (e.g., in main heat exchanger (2) acting as a reboiler for the HEFC (9), and returned (19) to the lower region of the HEFC (9). Further, as noted above, a gas stream (14) is removed from the top of the HEFC (9).
Additional structural elements shown in
In accordance with the invention, a side stream (23) is taken from the overhead vapor product of the LEFC and partially liquefied, via Joule-Thomson effect cooling, across a flow-control valve (24). The partially liquefied vapor stream is then delivered to a refrigerant system wherein it undergoes indirect heat exchange with a refrigerant fluid for further cooling. The resultant stream (25) is then fed into a further separation means (26), such as a further gas/liquid separator or a further distillation column, where the majority of ethane as well as heavier hydrocarbon components are recovered as liquid product (27) and returned to the LEFC as a liquid reflux stream. If a further distillation column is desired as the separation means, it can be integrated into the LNG unit. If the further distillation column requires a reboiler, the reboiler can be integrated into the LNG exchanger.
The overhead vapor stream (28) from the further separation means, rich in methane, undergoes indirect heat exchange with the refrigerant fluid of the refrigerant system for additional cooling. The resultant cooled stream (29) is then fed into the LNG exchanger where it is subjected to liquefaction to form the LNG product. This cooled stream (29) can then be sent to a gas/liquid separator for separating light components, such as nitrogen, before being introduced into the LNG unit.
At an intermediate point in the LNG exchanger, a vapor-liquid stream can be removed and introduced into an intermediate separator to separate heavier hydrocarbons (C2+) and return a lighter (essentially nitrogen, methane and ethane) stream to the LNG exchanger for final liquefaction, to allow the LNG product to meet desired specifications. The resulting liquids are increased in pressure via a pump and can be introduced into the LEFC as an additional reflux stream to further improve the C2+ recovery. The vapor stream from the intermediate separator reenters the LNG exchanger and proceeds, via additional cooling, to liquefy.
This integration of the NGL and LNG processes allows for a significant reduction of energy consumption in the LNG unit without compromising the NGL recovery process. The utilization of a portion of the cold overhead vapor from the LEFC of the NGL process reduces refrigeration requirements, allowing the processes to take place in a more efficient manner that not only reduces overall energy consumption, but also provides improved recoveries for both processes.
In
In addition, a portion (32) of bottoms liquid stream (8) from cold separator (3) is delivered to a liquid/liquid heat exchanger (33), where it undergoes indirect heat exchange with bottom liquid (10) removed from the bottom of the LEFC (7). The resultant stream (34) is then fed to an intermediate region of the LEFC (7) as a liquid reflux. These two additional reflux streams for the LEFC (7) improve recovery of the ethane and heavier hydrocarbon components.
A further embodiment is illustrated in
As in
The combined stream (35) is fed to the subcooler (13) where it undergoes indirect heat exchange with the overhead vapor from LEFC (7). Stream (35) is cooled and partially liquefied in the subcooler (13) and introduced into the top region of the LEFC (7) to provide additional reflux. This additional reflux stream for the LEFC (7) improves recovery of the ethane and heavier hydrocarbon components.
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Further, as in
Thus, in
A portion of the cooled high pressure reside gas stream (44) is then flashed expanded (e.g., via an expansion valve) to the operating pressure of the LEFC (7) and combined with the overhead vapor product (14) removed from the top of the HEFC, after the latter is subcooled in subcooler (13). The combined stream serves as reflux to the LEFC and is considered the top feed to the column. The remaining portion of the cooled high pressure residue gas stream (45) is flashed (e.g., via an expansion valve to a lower pressure then the other portion and is fed to the further separation means (26) (e.g., a LNGL separator). The liquid (27) removed from the bottom of the further separation means is a methane-rich liquid which is sent to an LNG storage vessel (46) before being sent to the LNG production unit. The vapor stream removed from the top of the further separation means (26) is compressed in a boil-off gas (BOG) compressor (47) and removed as a residue gas stream. The BOG compressor, compresses the potentially nitrogen rich stream from the low pressure of the liquefaction temperature to the final discharge pressure of the residue gas compressor. This boil off gas is combined with other residue gas at a point downstream of the removal of any portion of residue gas that is to be used in the system. The potentially high nitrogen concentration in the boil off gas renders it less suitable for use in the system for cooling purposes.
As shown in
The methane-rich vapors (28) from the top of the reflux separator (26) are further cooled by heat exchange in LNGL heat exchanger (48) against refrigerant and boil off gas from the LNG production unit. The resultant partially liquefied methane-rich stream (29) is then flashed (e.g., by expansion in an expansion valve) to a lower pressure and the resultant stream (49) is fed into a further separator (50), i.e., a LNGL separator. The methane-rich liquid removed the bottom of the further separator (50) is optionally sent to an LNG storage vessel (46) before being sent to further processing, if desired. The vapor 51 (i.e., boil off gas) removed from the top of the further separator (50) is subjected to heat exchange in the LNGL exchanger (48) to provide additional cooling for the portion of the LEFC overhead vapor (23), and is then compressed in a BOG compressor (47) and combined with residue gas from NGL recovery unit.
The overhead vapor stream (28) from the further separation means (26), rich in methane, undergoes indirect heat exchange in an LNGL heat exchanger with the refrigerant fluid of the refrigerant system for additional cooling. This methane rich stream leaves the LNGL exchanger as a cooled partially liquefied stream (29) and is then flashed (e.g., by expansion in an expansion valve) to a lower pressure. The resultant stream (41) is fed into a further separator (50), i.e., a LNGL separator. The methane-rich liquid removed the bottom of the further separator (50) is optionally sent to an LNG storage vessel (46) before being sent to the LNG production unit. The vapor removed from the top of the further separator (50) is compressed in BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.
Thus, as in
In addition, a portion (32) of bottoms liquid stream (8) from cold separator (3) is delivered to a liquid/liquid heat exchanger (33), where it undergoes indirect heat exchange with bottom liquid (10) removed from the bottom of the LEFC (7). The resultant stream (34) is then expanded and fed into an intermediate region of the LEFC (7) as a liquid reflux.
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As noted above,
The gaseous overhead stream (4) removed from the top of the cold separator (3) is split into two potions (30, 30A). Similarly, the bottoms liquid stream (8) from the cold separator (3) is also split into two potions (32, 32A).
A first portion of the gaseous overhead stream (30A) is expanded, for example, in a turboexpander (5), which can be optionally coupled to a compressor (63), and then introduced as stream (6) into an intermediate region of a demethanizer column (62) at a first intermediate point. A first portion of the bottoms liquid stream (32A) from the cold separator (3) is also introduced and expanded into an intermediate region of the demethanizer column (62) at a second intermediate point which is below the first intermediate point, i.e., the point of introduction of the first portion of the gaseous overhead stream (6). The second portion of the gaseous overhead stream (30) is combined with the second portion of the bottoms liquid stream (32) to form a combined cold separator stream (35), which is then cooled in a subcooler (13) by indirect heat exchange with an overhead vapor stream (12) from the top of the demethanizer (62). Stream (35) is then introduced and expanded into the upper region of the demethanizer. The demethanizer column (62) typically operates at a temperature of −70 to −115° C. and a pressure of 100 to 500 psig.
A liquid product stream is removed from the bottom of the demethanizer (62) and sent to a product surge vessel (20). Liquid from the product surge vessel (20) can be recycled to the bottom region of the demethanizer (62). The liquid product stream (15) from the product surge vessel (20) is heated by heat exchange, for example, by passage through the main heat exchanger (2) where it can undergo indirect heat exchange with the first partial feed stream (1A). In addition, a further liquid stream (16) is removed from a third intermediate point of the demethanizer, i.e., below the second intermediate point. This further liquid stream (16) is heated by indirect heat exchange, e.g., in the main heat exchanger (2) against first partial feed stream (1A), and then reintroduced (17) into the demethanizer at a fourth intermediate point i.e., below the third intermediate point. An additional liquid stream (18) is removed from the lower region of the demethanizer, i.e., below the fourth intermediate point. This additional liquid stream (18) is heated by indirect heat exchange, e.g., in the main heat exchanger (2), acting here as a reboiler, against first partial feed stream (1A), and then reintroduced (19) into the lower region of the demethanizer. Further, as noted above, an overhead vapor stream (12) is removed from the top of the demethanizer (62).
A high pressure (e.g., 300 to 1500 psig) residue gas stream (64) is introduced into the system and cooled by indirect heat exchange in heat exchanger (60) against a process stream (12), e.g., an overhead stream from the demethanizer, further cooled in the subcooler (13), and optionally further cooled in a further heat exchanger (e.g., an LNGL exchanger). A portion (65) of this cooled high pressure reside gas stream is expanded (e.g., via an expansion valve) to the operating pressure of the demethanizer (62), combined with the combined cold separator stream (35) and then introduced into the upper region of the demethanizer (62) as the top feed thereof. The remaining portion of the cooled high pressure residue gas stream is expanded (e.g., via an expansion valve) to a pressure below the operating pressure of the demethanizer and fed to a further separation means, e.g., an LNGL separator (50). A methane rich liquid stream is removed from the further separation means (50), optionally stored in an LNG storage vessel (46), before being sent to the LNG production unit. The overhead vapor (boil off gas) (51) from the further separation means is compressed in a BOG compressor (47) and sent to residue gas, e.g., combined with other residue gas from NGL recovery unit.
The embodiment of
Before being cooled in the subcooler (13), a side stream (23) is separated from the overhead vapor stream (12) of the demethanizer and is partially liquefied by heat exchange in an LNGL heat exchanger (48) against a refrigerant. The resulting stream is fed to a further separation means such as a reflux separator (26). In the reflux separator the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger, is flashed-expanded via an expansion valve to a lower pressure and fed into a further separation means (50) (e.g., an LNGL separator). A methane-rich liquid is recovered from the bottom of the further separation means (50) and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (51) (boil off gas) is removed from the top of the further separation means (50) and used in the LNGL heat exchanger (48) to provide additional cooling for the side stream (23) from the demethanizer overhead vapor stream (12) and the methane-rich vapor stream (28) removed from the top of the reflux separator (26). The vapor stream (51) from the top of the further separation means is then compressed in a BOG compressor (47) and combined with other residue gas from the GSP unit.
The embodiment of
Thus, in
A residue gas (67) is introduced into the LNGL exchanger (48), where it is cooled and liquefied. The residue gas exits the LNGL exchanger and is flashed across a valve, causing the fluid to reach even colder temperatures. The resultant stream (68) is then fed back to the LNGL exchanger (48) to provide additional cooling for the side stream (23) from the demethanizer overhead vapor stream (12) and the methane-rich vapor stream (28) removed from the top of the reflux separator (26).
Like
As shown in
In the reflux separator (26) the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer (62) as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger, is flashed-expanded via an expansion valve to a lower pressure and fed (41) into a further separation means (50) (e.g., an LNGL separator). A methane-rich rich liquid is recovered from the bottom of the further separation means (50) and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (boil off gas) (51) is removed from the top of the further separation means (50), compressed in a BOG compressor (47), and combined with other residue gas from the GSP unit.
As noted above,
The gaseous overhead stream (4) removed from the top of the cold separator (3) is split into two potions (30, 30A). Similarly, the liquid bottom stream (8) removed from the cold separator (3) is also split into two potions (32, 32A).
A first portion of the gaseous overhead stream (30A) is expanded, for example, in a turboexpander (5), which can be optionally coupled to a compressor (63) and then introduced as stream (6) into an intermediate region of a demethanizer column (62) at a first intermediate point. A first portion of the bottoms liquid stream (32A) from the cold separator (3) is also expanded and introduced into an intermediate region of the demethanizer column (62) at a second intermediate point which is below the first intermediate point, i.e., the point of introduction of the first portion of the gaseous overhead stream (6). The second portion of the gaseous overhead stream (30) is combined with the second portion of the bottoms liquid stream (32) to form a combined cold separator stream (35), which is then cooled in a subcooler (13) by indirect heat exchange with an overhead vapor stream (12) from the top of the demethanizer (62), and expanded and introduced into the upper region of the demethanizer as a top feed thereof. The demethanizer column (62) typically operates at a temperature of −70 to −115° C. and a pressure of 100 to 500 psig.
A liquid product stream is removed from the bottom of the demethanizer (62) and sent to a product surge vessel (20). Liquid from the product surge vessel can be recycled to the bottom region of the demethanizer (62). The liquid product stream (15) from the product surge vessel (2) is heated by heat exchange, for example, by passage through the main heat exchanger (2) where it can undergo indirect heat exchange with the first partial feed stream (1A). In addition, a further liquid stream (16) is removed from a third intermediate point of the demethanizer, i.e., below the second intermediate point. This further liquid stream (16) is heated by indirect heat exchange, e.g., in the main heat exchanger (2) against first partial feed stream (1A), and then reintroduced (17) into the demethanizer at a fourth intermediate point i.e., below the third intermediate point. An additional liquid stream (18) is removed from the lower region of the demethanizer, i.e., below the fourth intermediate point. This additional liquid stream (18) is heated by indirect heat exchange, e.g., in the main heat exchanger (2) (in this case acting as a reboiler) against first partial feed stream (1A), and then reintroduced (19) into the lower region of the demethanizer. Further, as noted above, an overhead vapor stream (12) is removed from the top of the demethanizer (62).
A high pressure (e.g., 300 to 1500 psig) residue gas stream (69) is introduced into the system and cooled by indirect heat exchange in the subcooler (13). At least a portion of this residue gas stream (69) is then expanded (e.g., via an expansion valve) to the operating pressure of the demethanizer and introduced (70) into the upper region of the demethanizer as another top feed thereof.
Another portion (23) of the residue gas stream (69) is expanded (e.g., via an expansion valve) to a pressure below the operating pressure of the demethanizer and fed to a further separation means (50), e.g., an LNGL separator. A methane rich liquid stream is removed from the further separation means (50) and optionally stored in an LNG storage vessel (46), before being sent to the LNG production unit. The overhead vapor stream (boil off gas) (51) removed from the further separation means (50) is compressed in a BOG compressor (47) and combined with other residue gas from the RSV unit.
The embodiment of
The embodiment of
In the reflux separator, the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger, is flashed-expanded via an expansion valve to a lower pressure and fed (41) into a further separation means (50) (e.g., an LNGL separator). A methane-rich liquid is recovered from the bottom of the further separation means and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (boil off gas) (51) is removed from the top of the further separation means, compressed in a BOG compressor (47) and combined with other residue gas from the RSV unit.
A residue gas (67) is introduced into the LNGL exchanger (48), where it is cooled and liquefied. The residue gas exits the LNGL exchanger (48) and is flashed across a valve, causing the fluid to reach even colder temperatures. The resultant stream (68) is then fed back to the LNGL exchanger to provide additional cooling for the second portion of the residue gas stream (23) and the methane-rich vapor stream (28) removed from the top of the reflux separator (26).
The embodiment of
As shown in
As shown in
In the reflux separator (26) the majority of ethane and higher hydrocarbon components are removed as a bottom liquid stream (27) and returned to the demethanizer as reflux. A methane-rich vapor stream (28) is removed from the top of the reflux separator (26), cooled by heat exchange against the refrigerant in the LNGL heat exchanger (48) and at least partially liquefied therein. The at least partially liquefied stream (29) exits the LNGL exchanger (48), is flashed-expanded via an expansion valve to a lower pressure and fed (41) into a further separation means (50) (e.g., an LNGL separator). A methane-rich liquid is recovered from the bottom of the further separation means and optionally stored in the LNG storage vessel (46) before being sent as feed to the LNG production unit. A vapor stream (boil off gas) (51) is removed from the top of the further separation means from the top of the further separation means, compressed in a BOG compressor (47) and combined with other residue gas from the RSV unit.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.
The entire disclosure[s] of all applications, patents and publications, cited herein and of priority U.S. provisional Application No. 61/746,727, filed Dec. 28, 2012 are incorporated by reference herein.
From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.
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