AU2014201746A1 - Enhanced operation of lng facility equipped with refluxed heavies removal column - Google Patents

Abstract

improved methodology for starting up a INGi facility employing a refluxed heavies removal column. The improved metodology involves varying the temperature of the feed to the heavies removal colmn between start-up and normal operation. This allows a larger amount of the stream produced from the top of the heavis removal colmn during startup to be used to more rapidly start up the TANG facility.

Description

ENHANCED OPERATION OF LNG FACILITY EQUIPPED WITH REFLUXED HEAVIES REMOVAL COLUMN The present applicaton is a divisional application from Australian Patent Application No. 201320 8, the entire disclosure of which is incorporated herein by reference [his invention rates to a method and apparatus for liquefying natural gas. In another aspect. the nvention concerns an improved methodology for starting up and operanng a liquefied natural gas (LNG) ciity employing a reluxed heavies removal column. he cryogenic liquefaction of natural gas is routinely practiced as a means of convering natural gas into a more conveniernt frm fbr transportation and storage. Suh liquefaction reduces the volume of the natural gas by about 608-fold and results in a product which can be stored and transported at near atmosph eric pressure. Natural gas is frequently transported by pipeline from the supply source of supply to a distant market. It is desirable to operate the pipeline under a substantially constant and high load factor but often the deliverability or capacity of the pipeline will exceed demand while at other tines the demand may exceed the deliverability of the pipeline, In order to shave off the peaks where demand exceeds supply or the valleys when supply exceeds demand, it is desirable to store the excess gas in such a manner that it can be delivered when demand exceeds supply. Such practice allows future demand peaks to be met with material from storage. One practical means for doing this to convert the gas to a liquefied state for storage and to then vaporize the liquid as demand requires. The liquefaction of natural gas is of even greater importance when transporting gas from a supply source which is separated by great distances from the candidate market and a pipeline either is not available or is impractical. This is particularly true where transport must be made by ocean-going vessels. Ship transportation in the gaseous state is generally not practical because appreciable pressurization is required to significantly reduce the specific volume of the gas. Such pressurization requires the use of more expensive storage containers. in order to store and transport natural gas in the liquid state, the natural gas is preferably cooled -15 1C to -162TC .240N to -2601) where the liquefed natural gas (LNG) possesses a nar atmospheric vapour pressure. Numerous systems exist in the pri art for the liquefaction of natural gas in wich the gas is liuefied by sequentially passing the gas at an elevated pressure through a pNraity of coonng stages whereupon the gas is cooled to successively lower temperatures unti the liquefaction temperature is reached. Cooling is generally accomplished by indirect beat exchange with one or more refrigerants such as propane, propylene, etbane. ethylene methane, nitrogen, carbon dioxide, or combations of the preceding refrigerants(eg. mixed refrigerant systems) A liquefaction methodology which is particularly applicable to the current invention employs anopen methane cycle for the |fnal refrgeration cycle wherein a pressurized LNC.-bearing strearn is flashed| and the flash vapors (iae. the flash gas stream(|s)) are subsequently employed as cooilmg agents recompressed, cooled, combined with the processed natural gas feed stream and liquefied thereby producing the prewurized LNG-beaung stream. in most LNG faite A is necessary to reoe heavy opponents benzene, tclueneylene, and ot/cychoexane) from the proessednatural gas store m in order to prevent freezing of the heavy coymonens isn downstream heat exchangers It is known that refiuxed heavies coinna can provide significantly more effective and efficient heavies removal than non-refluxed columns. However, one drawback of using a refluxed heaviesamoval column in conventional LNG facilities has been the significart delay in starting up the LNO facilities caused by the refluxed heavies remove column The main reason for this delay in srarting up the LNG facility was that during start-up. the refux stream to the heavies removal olumn originaMed from a lower otlet of the heavies removal column During start-up, the bulkof the feed ream entering the haves removal cumn exd an upper outlet of the heavies removal col m n As a result, only a sal poron o e fe team entering the heavies removal column during start-up exited the lower outlet and was available for routing back to the column as the reflux stream. As start-tp progressed, the quantity of the feed stream available for use as refux gradually increased to its optimum desigd fow rate over a period of many hours or even days Hoeer, the refluxed heavies removal column could not effectively remov heavies from he processed naturM as stream until theefiux stream was flowing at its designed rate. Thus, conventional start-up of an L.NG facility employing a refiuxed heavies removal columnn took mnn hours of eveday A |further disadvantage of nventional LNGi olant start-up procedures was tha th processed natural gas stream exiting the upper pon ofthe reluxed heavies treoval clun was simpi flared because the elevated heavies concenuration of this stream would freeze in downstream heat exchangers. Thus. because the bulk of the ponssed natural gas stream eterig the reluxed hea es removalcolm dAing stat-p exted the upper portion of the Mlun and as subsequemty flared, conventional stat-up procedures for art LNG facility employlng a refluxed heavies removal column wasted a significant portionofthe proessed natal gnas tem it is, therefore, desirable to provide a faster start-up procedure for a LNG facility empioying arefluxed heavies removal column Again it is desirable to provide a more efficient startup procedure for a LNG facility employinag a refluxed heavies iemoval column wvnereim the start-tp procedure does not waste (en, flare) a signifiant portion of the processed natural gas stream. I should be understood that the above desires are exemplar and need not al be aceompished by the invention claimed herein Other advantages ofthe ineon will be apparent from the wratten description and draw inns.

3 Throughout the description and caims of this speifiation the word "comprise" and variations of that word, such as "comprises" and comprising, are not intended to exlde other additives or components orintegers The present invemion relates to a method of starting up a cascade-type liqueied Pnatural gas family employiing a refluxed heavies removal olumn between two refrigeration cycles of the faciy saidhod includinghe steps of: (a) operating the refxed heavies removal colun in an initiating mode, said initiating mode including initiating the flow of a natural gas stream through a feed inet of thge fuxed heavies removal column and into the refluxed havis con Ad refluxed heavies removal column including a refMux inlet spaced fRom the feed iNlet, said renu inlt having substantially no hydrocarbon containing fluid flowing therethrough and into the fuxed heavies removal column during operation in the initiating mode; (b) subsequent to step (a), operating the refuxed heavies removal colum in a start-up mode, said start-up mode including using the refluxed heavies removal column to separate the natural gas stream into a first heavies stream and a first lights stream, said start-up mode including discharging the first lights stream froM the refluxed heavies removal column, said start-up mode including routing at least a portion of the discharged first lights stream to the reflux inlet; and (c) subsequent to step (hi, operating the reluxed heavies removal column in a normal mode, said normal mode including using the refluxed heavies removal column to separate the natural gas stream into a second heavies stream and a second lights stream, said normal mode including discharging the second lights stream from the refluxed heavies removal column, said normal mode including routing at least a portion of the discharged second lights stream to the retlux inlet. in some embodiments, the start-up method includes any one or combination of the following wherein said natural gas stream enters the refiuxed heavies removal column at a fr inlt temperature during the start-up mode, said natural gas streamantes the rAiuxed heaves removal column at a second inet temperature during the normal mode, said second inlet temperature is at least 2MF greater than the first inlet temperature: said second inlet temperature is in the range of from about 4 to about 12"F greater than the first inlet temperature; said natural gas steam has a firt vapor/liquid hydrocarbon eparation point during the start-up moade, said natural gas stream has a second vapor/iquid hydrocarbon separation point C~~y 1 during the normal mode, 4 wherein X and y are integens representing the number of carbon ators in the hydrocarbon molecules of the respective natural gas stream. wherein X and Y are in the range of from 2 to 10 wherein X is at least 1 greater than V wherein X is in the range of from 3 to 5 and Y is in the range of from 5 to ; wherein Y is at least 2 greater than X; wherein X is 4 and Y is 6 and/or said refluxed heavies removal column includes a stopping gas inlet, said refluxed inlet is spaced from and located above the feed and stripping gas inlets, said feed inlet is spaced from and located above the stripping gas inlet; said heavies removal column includes first and second sets of intemal packing, said first set of internal packing is vertically disposed between the feed inlet and the stripping gas inlet, said second set of internal packing is verticlly deposed between the feed inlet and the tcflux inlet. In some embodiments, the start-up method of the present invention further includes any one or combination of the following: A) upstream of the refhxed heavies removal column, cooing the natural gas stream in a first refrigeration cycle employing a first compressor to compress a firstrefrigerant. (e) switching from the startup mode to the normal mode by adjsting the differenial pressure of the first refrigerant across the frst compressor (f) downstream of the refluxed heaves removal column cooling the natural gas stram in a second refrigeration cycle employing a second refrigerant including predominantly methane; (g) upstream of the first refrigeration ce cooling the natural gas stream in a third refrigeration cycle employing a third refrigerant comprising predominantly propane or propylene, said first refrigerant comprising predominantly ethane or ethyle (b) vaporizing liquefied natural gas produced by the liquefed natuma gas facility during the normal mode. In some embodiments, the stan-op method includes including any one or combination of the following wherein step (e) includes decreasing the differential pressure of the first refrigerant across the first compressor; or said first refrigerant includes predominantly propane, propylene ethane, ethylene, or carbon dioxide. The present invention can also provide computer simulation proess including the step of using a computer to simulate the method according to the first aspect of the present invention.

4a The present inventionalso relates to a liquefied natural gas product produced by the process of the present invention. A preferred embodiment of the present invention is described in detail below with reference to the attached drawing figures, wherein: FIG. 1 is a simphfied flow diagram of a cascaded-type LNG facility within which the methodology of the present invention can be employed; and FIG. 2 is a schematic sectional view ofa reflexed heaes removal column that can be controlled via dhe inventive methodology A cascaded refrigeration process uses one or more refrigerants for transferring heat energy from the natural gas stream to the refrigerant and ultimately transferring said heat energy to the environment. in essence. the overall refrigeration system functions as a heat pump by removing heat energy from the natural gas stream as the stream is progressively cooled to lower and lower temperatures. The design of a cascaded refrigeration process involves a balancing of thermodynamics efficiencies and capital costs. In heat transfer processes, thermodynamic irreversibilities are reduced as the temperature gradients between heating and cooling fluids become smaller, but obtaining such small temperature gradients generally requires signifcant increases in the amount of heat transfer area, major medications to various process equipment, and the s proper selection of fow rates through such equipment so as to ensure that both flow rates and approach and outlet temperatures are compatible with the required heating/cooling duty. As used herein, the term open-cycle cascaded refrigeration process reters to a cascaded refrigeration process comprising at least one closed refrigeration cycle and 10 one open aefrigeration cycle where the boiling point of the refigerant/cooling agent employed in the open cycle is less than the boiling point of the refrigerating agent or agents employed in the closed cycles) and a portion of the cooling duty to condense the compressed open-cycle refrigerant/cooling agent is provided by one or more of the closed cycles. In the current invention, a predominately methane stream is employed as is the refrigerant/cooling agent in the open cycle. This predominantly methane stream originates from the processed natural gas feed stream and can include the compressed open methane cycle gas streams. As used herein,t terms "predominantly", 'primarily", "principally", and "in major portion", when used to describe the presence of a particular component of a fluid stream, shall mean that the iuid stream comprises at 2o least 50 mole percent of the stated component. For example, a "predomainantly" methane stream, a "primarily' methane stream, a stream "principally" comprised of methane, or a stream comprised' 'in major portion" of methane each denote a stream comprising at least 50 mole percent methane. One of the most efficient and effective means of liquefying natural gas is 25via an optimized cascade-type operation in combination with expansion-lyre cooling. Such a liquefaction process involves the cascade-type cooling of a natural gas stream at an elevated pressure, (e.g., about 4.48 Mvea (650 psi)) by sequentially cooling the gas stream via passage through a multistage propane cycle, a multistage ethane or ethylene cycle, and an open-end methane cycle which utilizes a portion of the feed gas as a source 30 of methane and which includes therein a multistage expansion cycle to farther cool the same and reduce the pressure to near-atmospheric pressure, In the sequence of cooling cycles, the refrigerant having the highest boiling point is utilized first followed by a refrigerant having an intermediate boiling point and finally by a refrigerant having the lowest boiling point. As used herein, the tenMs "upstream" and "downstream shall be used to describe the relative positions of vaius components of a natural gas liquefaction plant along the flow path of natural gas through the plant. s Various pretreatment steps provide a means for removing undesirable components, such as acid gases, mrercaptan, mercury, and moisture from the natural gas feed stream delivered to the LNG facility The composition of this gas stream may vary significantly As used herein, a natural gas stream is any stream principally comprised of methane which originates in major portion from a natural gas feed stream, such feed C strearn for example containing at least 85 mole percent rnethane, with the balance being thane, higher hydrocarbons, nitrogen, carbon dioxide, and a minor amount of other contaminants such as mercury, hydrogen sulfide, and mercaptan, The pretreatment steps may be separate steps located either upstream of the cooling cycles or located down stream of one of the early stages of cooling in the initial cycle. The following is a non-inclusive listing of soni of the available means which are readily known to one skilled in the art Acid gases and to a lesser extent mnercaptan are routinely removed via a sorption process employing an aqueous amine-bearing solution. This treatment step is generally performed upstream of the cooling stages in the initial cycle. A major portion of the water is routinely removed as a liquid via two-phase gas-liquid separation 2 following gas compression and cooling upstream of the initial cooling cycle and also downstream of the first cooling stage in the initial cooling cycle. Mercury is routinely roved via mercury sorbent beds Residual amounts of water and acid gases are routinely removed via the use of properly selected sorbent beds such as regenerable molecular sieves The pretreated natural gas feed stream is generally delivered to the lquef-actin process at an elevated pressure or is compressed to an elevated pressure generally greater than 3.44 Ma (500 psia), preferably about 3,44 Ma to about 2067 MTa (about 520 psia to about 3000 psia), still more preferably about 3.44 MP ato about 6,894 MAa (about 500 psia to about 1000 psi still yet more preferably about 4,14 MPa to about 5.51 M a (about 600 psia to about 800 psia) The feed stream temperature is typically near ambient to slightly above ambient. A representative temperature range being 15C to 65.5*% (60 to 150").

As previously noted, the natural gas feed stream is cooled in a plurality of multistage cycles or steps (preferably three) by indirect heat exchange with a plurality of different refrigerants (preferably three). The overall cooling efficiency for a given cycle improves as the number of stages increases but this increase in efficiency is $ accompanied by corresponding increases in net capital cost and process complexity. The feed gas is preferably passed through en effective number of refrigeration stages, nominally two, preferably twoo four, and more preferably three stages, in the rst closed refrigeration cycle utilizing a relatively high boiling refrigerant. Such relatively high boiling point refrigerant is preferably comprised in major portion of propane o propylene, or mixtures thereof, more preferably the refrigerant comprises at least about 75 mole percent propane, even more preferably at least 90 mole percent propane, and most preferably the refrigerant consists essentially of propane. Thereafter, the processed feed gas flows through an effective number of stages, nominally two, preferably two to four, and more preferably two or three, in a second closed refrgeration cycle in heat exchange with a refrigerant having a lower boiling point. Such loIwer boiling point refrigerant is preferably comprised in major portion of ethane, ethylene, or mixtures thereof, more preferably the refrigerant comprises at least about 75 mole percent ethylene, even more preferably at least 90 mole percent ethylene, and most preferably the refrigerant consists essentially of ethylene. Each cooling stage comprises a separate 20 cooling zone. As previously noted, the processed natural gas feed stream is preferably combined with one or more recycle streams (i.e, compressed open methane cycle gas streams) at various locations in the second cycle thereby producing a liquefaction stream In the last stage of the second cooling cycle, the liquefaction stream is condensed (i., liquefied) in major portion, preferably in its entirety, thereby pro ducing 25 a pressurized LNG-bearing stream Genal, the pros pressure at this location is only slightly lower than the pressure of the pretreated feed gas to the first stage of the first cycle. Generally, the natural gas feed streak will contain such quantities of C 2 + components so as to result in the formation of a Cs+ rich liquid in one or more of the cooling stages. This liquid is removed via gas-liquid separation means; preferably one or more conventional gas-liquid separators. Generally, the sequential cooling of the natural gas in each stage is controlled so as to remove as much of the C and higher -8s molecular weight hydrocarbons as possible from the gas to produce a gas stream predominating in methane and a liquid stream containing significant amounts of ethane and heavier components. An effective number of gas/liquid separation means are located at strategic locations downstream of the cooling zones for the removal of liquids 5 streams rich in C2+ components. The exact locations andnumabcr of gas/liquid separation means, preferably conventional gas/liquid separators, will he dependent on a number of operating parameters, such as the C)+ composition of the natural gas feed stream, the desired BTU content of the LNG product, the value of the 02+ components for other applications 1 ad other factors routinely considered by those siled in the art to of LNG plant and gas plant operation The C2+ hydrocarbon stream or streams may be demethanized via a single stage flash or a fractionation cohun. In the latter case, the resulting =ethane-rich stream can be directly retuned at pressure to the liquefaction process. In. the former case, this methane-rich stream can be repressurized and recycle or can be used as fol gas, The C+ hydrocarbon streanor streams or the demethanized 15 Q+ hydromabon stream may be used as fuel ormay be father processed, such as by fractionation in one or more fractination zones to produce indiualstreams ich specinO chemical constituents (eg, 02, 0 and (i+), The pressurized LN&bearing stream is then further cooed i a third cycl or step referred to as the open methane cycle vi contact in a main methane 20 economizer with flash gases (i.e, flash gas streams) generated in this third cyce in a manner to be described later and via sequential expansion of the pressurized LNG-bearing streamto near atmospheric pressure. The fash gasses used as a refrigerant in the third refrigeration cycl are preferably compared in major portion of methane, more preferably the flash gas refrigerant compeat least7mole percent 25 mhane, stilmore preferably at east 90 mole percent methane and most preferably the refrigerant consists essentially ofmethane During expansion of the pressurized LNG-bearing stream to near atmospheric pressure, the pressurized LNG-bearing stream is cooled via at least oane preferably two to four, and more preferably thee expansions where each expansion enploys an expander as a pressure reduction means Suitable 30 expanders include, for eampl, eitherdouleThomson expansion valves or hydraulic expanders. The expansion is followed by a separation of the gas4iquid product with a separator. When a hydaulic expander is employed and properoperated, the greater efficiencies associated with the recovery of power, a greater reductions team temperature, and the production of less vapor during the flash expansion step will frequently more than off-set the higher capital and operating costs associated with the expande.n one eibodiment additional cooling ofthepssurized LN-earig 5 stream prior to ashIng is made possible by first bashing a portion of this streamia one or more hydrane expanders and then via indirect heat exchange means employing said fash gas stream toc the ren t g portion of the pressurized LN1earing stream prior to flashing. The warmed flash gas stream is thenrecycled vdreturnto an appropriate location based on temperatuxe and pressure considerations in the open methane cycle and will be recompressed, The liquefactin process described herein may use one of several types of coolingvbich include but are not limited to (a) indirect beat exchange, (b) vaporzatin, and expansionn hr pressure reduction. Indiect heat exchange, a used herein, refers to a press wi0rein the refrigerant cool the substance to be coald without actua is physicalcontact between the refrigerating agent and the substance to be coled, Specific examples of indirect hea exchange means include heat exchange undergone in a she-and-tube heat exchanger a core-in-kettle heat exchanger, and a brazed aluminum platefin heatechanger The physical state ofthe refrigerant ad substance to be cooled can vary depeding onthe demands of the system and the type of heat exchanger 20 chosen. Thus a shelad-ube heat exchanger willtypicdy be utilized where the refrgerating agent is in a liquid state andthe substance to be cooled is in a liquid or gaseous state or when one of the substances udergoes a phase change and process conditions do not favor the use of a core-in-kettle heat exchanger. As a example, aluminum and aluinum ays are preferred materials of construction forthe or but 5s such materials may not be suitable for use at the designated process conditions A plate-fin heat exchanger will typically be utilied where e h refrigerant in a gaseous state and the substance tobe cooled is in a liquid or gaseous state. Finally, the core-in-kettle heat exchanger'wi typical be utilized where the substance to be cooled is quid or gas and the reigerant undergoes a phase change from a liquid state to a S gaseous state during the heat exchange Vaporization cooling refers to the cooling of a substance by the evporation or vaporzaton of a portion ofthe substance with the system matained a constant pressure. Thus, during the vaporization, the portion of the substance which evaporates absorbs heat from the portion of the substance which remains in a liquid state and hence, cools the liquid portion Finally, expansion or pressure reduction cooling refers to cooling which occurs when the pressure of a gas, liquid or a two-phase system is decreased by passing through a pressure reduction means. In one embodiment, this expansion means is a loule-Thonison expansion valve. In another embodiment, the expansion means is either a hydraulic or gas expander, Because expanders recover work energy fronI the expansion process, tower process stream temperatures are possible upon expansion The flow schematic and apparatus set forth in FIG. 1 represents a preferred embodiment of an LNG facility in which the methodology of the present invention can be employed. FIG, 2 represents a preferred eobodiment of a refluxed heavies removal column for use with the methodology of the present invention. As used herein, the term 'heavies removal column" shall denote a vessel operable to separate a heavy components) of a hydrocarbon-containing streamfom a lighter component(s) of the hydrocarbon-containing stream As ued herein, the term "reflxed heavies removal column" shall denote a heavies removal column that employs a reflux stream to aid in separating heavy and light hydrocarbon components, Those skilled in the art will recognized that FIGS. 1 and 2 are schematics only and, therefore, many items of 20 equipment that wold be needed in a commercial olant for successil operation have been omitted for the sake of clarity, Such items night include, for example, compressor cntrols, flow and level measurements and corresponding controllers, temperature and pressure controls, pumps, motors, filters, additional heat exchangers, and valves, etc. These items would be provided in accordance with standard engineering practice To facilitate an understanding of FIGS. I and 2, the following numbering nomenclature was employed. Items numbered I through 99 are process vessels and equipment which are directly associated with the liquefaction process. Items mnubered 100 through 199 correspond to flow lines or conduits which contain predominantly methane streams. Items numbered 200 through 299 corr-espond to flow lines or conduits so which contain predominantly ethylene streams. Itens numbered 300 through 399 correspond to flow lines or conduits which contain predorminattly propane streams. Referring to FIG. 1, during normal operation of the LNG( facility, gaseous propane is compressed in a multistage (preferably three-stage) compressor 18 driven by a gas turbine driver (not illustrated). The three stages of conTression preferably exist in a single unit although each stage of compression may be a separate unit and the units mechanically coupled to be driven by a single driver. Upon compression, the compressed propane is passed through conduit 300 to a cooler 20 where it is cooled and liquefied. A represent ative pressure and temperature of the liquetied propane refrigerant prior to bashing is about 37,70MC (1OOT) and about 1,30 MDa (190 psiay The stream rom cooler 20 is passed through conduit 302 to a pressure reduction means, illustrated as expansion valve 12, wherein the pressure of the liquefied propane is reduced, thereby evaporating or flashing a portion thereof, The resulting two-phase product then flows through conduit 304 into a high-stage propane chiller 2 wherein gaseous methane refrigerant introduced via conduit 152, natural gas feed introduced via conduit 100, and gaseous ethylene refrigerant introduced via conduit 202 are respectively cooled via indirect heat exchange means 4, 6, and 8, thereby producing cooled gas streams 5 respectively produced via conduits 154, 102, and 204. The gas in conduit 154 is fed to a main methane economizer 74, which will be discussed in greater detail in a subsequent section, and wherein the stream is cooled via indirect heat exchange means 97, A portion of the stream cooled in heat exchange means 97 is removed from methane economizer 74 via conduit 155 and subsequently used, after further cooling, as a refIux 20 stream in a heavies removal column 60, as discussed in greater detail below with reference to FIG 2. The portion of the cooled stream from heat exchange means 97 that is not removed for use as a reflux stream is further cooled in indirect heat exchange means 98. The resulting cooled methane recycle stream produced via conduit 158 is then combined in conduit 120 with the heavies depleted (ine., lght-hydrocaron rich) 25 vapor stream from heavies removal colum 60 and fed to an ethylene condenser 68. The propane gas from chiller 2 is returned to compressor 18 through conduit 306. Thiis gas is fed to ~te high-stage inlet port of compressor I8. The remaining liquid propane is passed through conduit 308, the pressure further reduced by passage through a pressure reduction means, illustrated as expansion valve 14, whereupon an additional portion of the liquefied propane is flashed. The resulting two-phase stream is then fed to an intermediate stage propane chiller 22 through conduit 310, thereby providing a coolant for chiller 22. The cooled feed gas stream from chiller 2 fows via conduit 102 to a knock-out vessel10 wherein gas and liquid phases are separated. The liquid phase, which i rich in C+ components is removed via conduit 101 The gaseous phase is removedia conduit 104 and then split into two separate streams which are conveyed via conduits 106 and 108, The streamin conduit 106 is fed Sto propane chiller 22. The stream in conduit 108 is employed as a stripping gas in refluxed heavies removal column 60 to aid in theremoval of heavy hydrocarbon components from the processed natural gas stream, as discussed inamore detail below with reference to FIG 2 Bthylene refrigerate kom chiller 2 is introduced to chiller 22 via conduit 204, In chiller 22, the feed gas stream, also referred to herein as a e methane-rich stream, and the ethylene refrigerant streams are respectively cooled via indirect heattransfer means 24 and 26, thereby producing cooled methaoe-rch and ethylene refrigerant streams via conduits 110 and 206 The thus evaporated portion of the propane refrigerant is separated and passed through condui 311 to the intennediate stage inlet of compressor 18. Liqud propane refrigerant fm chiller 22is removed via is conduit 314, flashed across a pressure reductionnmeans, illustrated as expansion vale 16, and then fed to a low-tage propane chiller/condenser 28 via conduit 316. As lustrated in FIG. 1 the methane-rich stream fows from intermediate-stage propane chiller 22 to the low-stage propane chiler/condenser 28 via conduit 1to. In chiller 23, the strearnis cooled via indirect heat exchange means 30. In 20 a like manner, the ethylene refigerant stream flows fromthe intermediate-stage propane Thriller 22 to low-stage propane chiller/condenser 28 via conduit 206. In the later, the ethylene refigerant is totally condensed or condensed in nearly its entirety via indirect heat exchange means $2, The vaporized propane is removed fromlow-stage propane chiller/condenser 28 and returned to the low-stage inlet of conpressor 18 via conduit 25 320. As illustrated in FIG, 1, the methane-ich stream exiiing low-stage propane chiller 28 is introduced to high-stage ethylene chiller 42 via conduit 112. Ethylene refrigerant exits low-stage propane chiller 28 via conduit 208 and is preferably fed to a separation vessel 37 wherein light components are removed via conduit 209 and so condensed ethylene is removed via conduit 210. The ethylene refrigerant at this location in the process is generally at a temperature of about -31 C (about -24F) and a pressure of about 1.96 M~vPa (about 285 pain). The ethylene refrigerant then flows to an ethylene economizer 34 wherein it is cooled via indirect heat exchange means 38, removed via conduit 211, and passed to a pressure reduction means, illustrated as an expansion valve 40, whereupon the refrigerant is flashed to a preselected temperature and pressure and fed to high-stage ethylene chiller 42 via conduit 212. Vapor is removed from chiller 42 5 via conduit 214 and routed to ethylene economizer 34 wherein the vapor fRunctions as a coolant via indirect heat exchange means 46. The ethylene vapor is then removed from ethylene economizer 34 via conduit 216 and feed to the high-stage inlet of ethylene compressor 42 The ethylene refrigerant which is not vaporized in high-stage ethylene chiller 42 is removed via conduit 218 and returned to ethylene economizer 34 for further cooling via indirect heat exchange means 50,removed fom ethylene economizer via conduit 220, and flashed in a pressure reduction means, illustrated as expansion valve 52, whereupon the resulting two-phase product is introduced into a low-stage ethylene chiller 54 via conduit 222. After cooling in indirect heat exchange means 44, the ethanerich 1 stream isremoved Am high-stage ethylene chiller 42 via conduit 116 The stream in conduit 116 is then carried to a feed inlt Af heavies removal column 60 wherein heavy hydrocarbon components are removed fom the methane-rich stream, as described n further detail beow with reference to F. A heavies-rich liuidtream containg a significant concentration of C44 hydrocarbons, such as benzene, toluene, xylene, cylohexarne, other aromatics, and/or heavier hydrocabon components, is removed toM the bottom of heavies removal column 60via condui14. The heaviesrh stream in conduit 14 is subsequently separated into liquid and vapor portions or preferably is flashed or faconatedin vessel 67. In either casea second heaviesrich liquid streams produced via conduit 123 and a second methane-rich vapor stream is produced via 25 conduit 121 In the preferred ebodientwhichis illustrated in FIG. the streaming conduit 121 is subsequently combined with a second stream delivered via conduit 128 -and the combined stream fed to the high-stage inlet port of the methane compressor 83. High-stage ethylene chillr 42 lso icdes an indirect heat exhanger means 43 which receives and cools the stream withdrawn fommethane economizer74 via conduit 155 3 as discussed above. The resulting cooled stream from indirect beat exchange means is conducted via conduit 157 to lowstage ethylene chiler 5 In low-stage ethylne chiler 54 the stream &om conduit 157 is cooled via indirect heat exchange means 5C 14 after cooling in indirect heat exchange means 56, the stream exits low-stage ethylene chillr 54 and is carried via conduit 159 to a reflux itet of heavies removal column 60 where it is emplyd as aeflurstream As previously noted, the gas in conduit 154 is fed to main methane L economizer 74 wherein he stream is cooled via indiret heat exchange means 97 A portion of the cooled stream fo heat exchange means 97 is then further cold in indirect heat exchange means 98. The resulting cooed streams removed fon methane economizer 74 via conduit 158 and is thereafter combinedwith the heavies-depleted vapor stream exiting the top of heaiesemoval cohunn 60, delivered via conduit 5119 10 and 120, and fed to a lowstage ethylene condenser 6S In low-stage ehylenecndens 68, this stream s cooed and condensed via indirect heat exchange moans 70 with the iWuid effluent rAmlow-stage ethylene chiler 54 wichli routed to low-stage ethylene condenser 68 via conduit 226 The condensed methane-ich product from lowstage condenser 68 is produced via conduit 1221 The vapor from low-stage ethylene chillr 15 54, withdrawn yA conduit 224, and low-stage ethylne condenser 68, withdrawn via conduit d28, are combined and routedia conduit 230, to ethyene economizer 34 wherein the vapors function as a coolantmva indirect heat exchange means P. The stream is then routed via conduit 232 ram ethyene economizer 34 to the tow-stage inlet of ethylene compressor 438 20 As noted in FIG 1, the compressor effuent from vapor introduced via the low-stage side of ethylene compressor 48 is removed via conduit 23. cooled via inter-stage cooler 71, and returned to compressor 48 via onduit 236 for injectionl with the high-stage stream present in conduit 216 Preferably, the two-stages are a single module although they may each be a separate module and the modules mechanically 25 couped to a common drive. The compressed ethylene product frm compressor 48 is rooted to a downstream cooler 72 via conduit 200. The product from cooler 72 flows via conduit 202 and is introduced, as previcuxly discussed, to high-stage propane chilir The pressurized LN&bearing stream, preferably a liquid streamin its Ro entirety, in conduit 122 is preferably at a temperature in the range of from about -28C to about -45"C (about -200 to about -50*), more preferably in the range of from about -1154C to about ~73,3*C (about -175 to about -100*F), most preferably in the range of S15 f m0iO to -82C(150 to 25 0 ). The pressure ofthe streamin conduit 122 s preferably in the range of from about 3.44 MPa to about 482 Ma (about 500 to about 700 psin), most preferably in the range of from 79 M~ a to 499 M a (550 to 725 pai). The stream in conduit 122 is directed to main methane economizer 4 wherein the stream is further coled by indirect heat exchange means/heat exchanger pass 76 as hereinafter explained. It ipreferrd for main methane economizer 74 to include a plurality ofheaexchanger passes which provide for the indirect exchange of heat between various predominantly methane streams in the economizer 74 Pefably methane economizer 74 comprises one or more platen heat exchangers The cooled o stream rmheat exchanger pass 7 exits methane economizer 74 via conduit 124. It is preferred frthe tempetue of the streamlin conduit 124 to beat least aboutl1T less than the temperature of the stream in conduit 122, more preferably at least about 25F lass than the temperature ofthe streamin conduit 122. Most preferaby, the temperature of the streaming conduit 24 is in the range of from about -1294 to about 07C (about 15 .200 to about 160*F) The pressure of the stamp in conduit 124 a then reduced by a pressure reduction means illustrated as expansion valve 78 which evaporates or lashes a portion of the gas steam thereby generating a two-phase stream The tw-phase stream from expansion valve72 is then passed to high-stage methane fash duiri80 where it is separated into a fash gatream discharged through conduit 126 and a liquid 20 phase stream(i e., pressurized LNG-earing stream) discharged through conduit 130, The fash gas stream then transferred to main methane economizer 74 via caduit 126 wherein the stream functions as a coolant in heat exchanger pass 82. The predominantly methane stream is wanted in eat exchanger pass 2, at leastin part, by indiect het exchange with the predominantly methane stream in heat exchanger pass 76. The M warmed stream exits heat exchanger pass 22 and methane economizer 74 via conduit 128. The liquidphase stream exiting high-stage flash drum 80 via conduit 130 is passed through a second methane economizer 27 wherein the iquid is further cold by downstreamfash vapors via indirectheat exchange means 82 The cooled liqud 30 exits second etane economizer 87 va conduit 132 and is expanded or washed via pressure reduction means, illutrated as expansion valve 9 , to further reduce the pressure and, at the same time, vaporize a second portion thereof This two-phase stream is then passed to an intermediate-stage methane flash drum 92 where the stream is separated into a gas phase passing through conduit 136 and a liquid phase passing through conduit 134. The gas phase lows through conduit 136 to second methane economizer 87 wherein the vapor cools the lignd introduced to economizer 87 via s conduit 130 via indirect heat exchanger means 89. Conduit 138 serves as a fow conduit between indirect heat exchange means 39 in second methane economizer 87 and heat exchanger pass 95 in main methane economizer 74. The warmed vapor stream from heat exchanger pass 95 exits main methane economizer '74 via conduit 140, is combined with the first nitrogen-reduced stream in conduit 406, and the combined streamis to conducted to the intermediate-stage inlet of methane compressor 83. The liquid phase exiting intermediate-stage flash dratn 92 via conduit 134 is further reduced in pressure by passage through a pressure reduction means, illustrated as a expansion valve 93 Again, a third portion of the liquefied gas is evaporated or flashed. The two-phase stream fronm expansion valve 93 are passed to a s final or low-stage flash drun 94 In flash dumn 94, a vapor phase is separated and passed through conduit 144 to second methane economizer 87 wherein the vapor functions as a coolant via indirect heat exchange means 9)0, exits second methane economizer 87 via conduit 146, which is connected to the rst methane economizer 74 wherein the vapor functions as a coolant via heat exchanger pass 96, The warmed vapor 20 stream from heat exchanger pass 96 exits main methane economizer 74 via conduit 148, is combined with the second nitrogen-reduced stream in conduit 403, and the combined stream is conducted to the low-stage inlet of compressor 83. The liquefed natural gas product from tow-stage fash drum 94, which is at approximately atmospheric pressure, is passed through conduit 142 to a LNG storage 25 tank 99. In accordance with conventional practice, the liquefed natural gas in storage tank 99 can be transported to a desired location (typically via an ocean-going LNG tanker). The LNG can then be vaporized at an onshore LNG terminal for transport in the gaseous state via conventional natural gas pipelines. As shown in FIG. 1, the high, intermediate, and low stages of compressor C 83 are preferably combined as single unit. However, each stage may exist a separate unit where the units are mechanically coupled together to be driven by a single driver The compressed gas from the low-stage section passes through an inter-stage cooler 85 17 and is combined with the intermediate pressure gas in conduit 140 prior to the s econd-*stage of compression. The compressed gas from the intermediate stage of compressor 83 is passed through an inter-stage cooler 84 and is combined with the high pressure gas provided via conduits 121 and 128 prior to the third-stage of compression s The compressed gas (i.e, compressed openmethane cycle gas stream) is discharged frn high stage methane compressor through conduit 150, is cooled in cooler 86, and is routed to the high pressure propane chiller 2 via conduit 152 as previously discussed, The stream is cooled in chiller 2 via indirect heat exchange means 4 and flows to main methane economizer 74 via. conduit 1f4. The compressed open methane cycle gas 1.o stream from chiller 2 which enters the main methane economizer 74 undergoes cooling in its entirety via flow through indirect heat exchange means 98. This cooled stream is then removed via conduit 158 and combined with the processed natural gas feed stream upstream of the first stage of ethylene cooling. Referring now to FI. 2, refluxed heavies column 60 generally includes is an nopper zone 61, a middle zone 62, and a lower zone 65, Upper zone 61 receives the reflux stream in conduit 159 via a reflux inlet 66, Middle zone 62 receives the processed natural gas stream in conduit 118 via a feed inlet 69. Lower zone 65 receives the stripping gas stream in conduit 108 via a stripping gas inlet 73. Upper zone 61 and middle zone 62 are separated by upper internal packing 75, while middle zone 62 and Slower zone 65 are separated by lower internal packing 77. Internal packing 75;/7 canbe any conventional structure known in the art for enhancing contact between two countercurrent streams in a vessel. Refluxed heavies removal column 60 also includes an upper outlet 79 and a lower cutlet 81. In accordance with the present invention, heavies removal column 60 can 25 be operated in three distinct modes: an initiating mode, a start-up mode; and a normal mode. The initiating mode involves initiating the flow of a hydrocarbon-containing stream into heavies removal column 60 via feed inlet 69. Immediately prior to the initiating mode, substantially no hydrocarbon-containing streams flow into or through heavies removal column 60. During the initiating mode, substantially no hydrocarbon 30 containing streams arc introduced into heavies removal column 60 through reflux inlet 66 and stripping gas inlet 73. The start-up mode of operation involves continuing the flow of the ac b, r. - C. f~.-'S is hydrocarboncontaiing stream (e~g., processed natural gas stream) into heavies removal column 60 via feed inlet 69. During the start-up mode, the stream entering column 60 via feed inlet 69 is separated into a light vapor stream, which exits column 60 via upper outlet 79, and a heavy liquid stream, which exits column 60 via lower outlet 8i. During the start-up mode, at least a portion of the light vapor stream exiting upper outlet 79 via conduit 119 is routed back to heavies removal column 60 and introduced into upper zone 61 of heavies removal column 60 via reflux inlet 66. Referring now to FIG 2, during start-up, the routing of the light vapor stream in. conduit 119 back to reflux inlet 66 of heavies removal column 60 takes place by initially routing the stream to the open to methane refrigeration cycle via conduit 120, heat exchange means 70, and conduit 122. The stream exits the open-methane cycle and is fed to methane compressor 83, Prom uethane compressor 83 the stream is then routed back to heavies removal column 60 via the following conduits and components: conduit 150, cooler 86, conduit 152, heat exchange means 4, conduit 154, heat exchange means 97, conduit 155, heat exchange is means 43, conduit 157, heat exchange means 56, and conduit 159, Referring to PIGS, 1 and 2, during the start-up mode, at least a portion of the heavy liquid stream exiting lower outlet 81 of heavies removal column 60 via conduit 114 is routed back to reflux inlet 66 of heavies removal column via the following conduits and components: vessel 67, conduit 121, conduit 128, methane compressor 83, conduit 150, cooler 86, conduit 2 1, exchange means 4, conduit 154, heat exchange means 97, conduit 155, heat exchange means 43, conduit 157, heat exchange means 56, and conduit 159. Referring again to FIG 2, during the normal mode of operation, the feed stream enters middle zone 62 of heavies removal column 60 via feed inlet 69, the reflux stream enters upper zone 61 of heavies remaval column 60 via reflux inlet 66, and the is stripping gas stream enters lower zone 65 of heavies removal column 60 via stripping gas inlet 73. During the normal mode, the downwardly flowing liquid reflux stream is contacted in upper intemal packing 75 vith the upwardly flowing vapor portion of the teed stream, while the downwardly flowing liquid portion of the feed stream is ,contacted in lower internal packing 77 with the upward flowing stripping gas, In this 2 manner, heavies removal column 60 is operable to produce a heavies-depleted (i.e, lights-rich) stream via upper outlet 79 and a heavies-rich stream via lower outlet 81 during the normal mode. Daring the normal mode, the feed introduced into heavies removalcolumn 60 via feed inlet 69 typically has a 0j concentration of at least 01 mole percent, a Q concentration of at least 2 mole percent, a benzene concentration of at least 4 ppw (parts per million by weight a cyclohexane concentration of at east 4 ppne, and/or a combined concentration ofxylene and toluene oflat least 10 ppmw s When operating during the normal mode, the heavie-depleted stream exiting heavies removal column 60 via upper outlet 79 preferably has a lower concentration of ,4+ hydrocarben components than the feed entering inlt 69, more preferably the heAes depleted stream exiting upper outlet 79 has a 0C± concentration of less than 0.1 mole percent, a C4 concentration of less than m 2mo percent, a benzene concentration ofless to than 4 ppmw, a cyclohexane concentration of less than 4 ppmw, and a onmined concentration of xylene and talene of less thaa10 ppn When operating during the normal mode, the heavics-rich stream exiting heavies removal column60 via lower cutet 31 preferably has a higheroncentratn of0+ hydocarbons than the feed aerig feed inet S9, Durtingte oqaoe i is prfe'e f o tipn a entering heavies removal column 60via shipping gas inlet 66 to comprise a higher proportion lighthydocarbons than the feed to feed inlt 69 of heavies removal column 60. More prrably theefiatreamenterng Wx n 66 of eaves removal column 60 during the normal mode compriseat least about9mole percent methane, stil more preferably at least about 95mole percent methane, and most 20 preferably at least 97 mol percent methane. Wheoperating during the nomnalmode, it Preferred for the stripping gas entering heavies emaval column 60 via stripping gas Ilet 73 to have substantially the same composition as the feed stream entering heavies removal column 60 via feed inlet 69. Referring to IGS. 1 and 2, when the LNG facility illustrated in FIG I is 2 started up, the flow of the natural gas stream iiti d ia in conduit 100. The nature gas streamis then sequentially cooled via indirect heat transfer in heat exchange means 6,243 and 4 In accordance with one embodiment of the present inention the propane and ethylene refrigeration cyclks are controlled during startip in a manerso that the cooled natural gas stream exiting heat exchange means 44 of highistage ethylene so chiller 42 and entering feed inlet 69 of heavies removal column 60 is a two-phase stream Preferably the two-phase stream entering feed inet 69 of havies removal column 60 during startup includes a vapor phase that contains predominantly light hydrocarbon components and a liquid phase that contains predominantly heavy hydrocarbon components, As used herein, the term vapor/liquid hydrocarbon separation point" or simply "hydrocarbon separation point" shall be used to identify a point of separation between the vapor and liquid phases of a hydrocarbon-containing streambased on the number of carbon atoms in the hydrocarbon molecules of the phases. When the hydrocarbon separation point is represented by the formula Capu, then a predominant molar portion of Cr hydrocarbon molecules are present in the vapor phase while a predominant molar portion of Cj)+ hydrocarbon molecules are present in the liEquid phase. For example, if the hydrocarbon separation point of a certain two-phase hydrocarbon-containing stream is C, then a predominant portion (i.e., more than 50 mole percent) of the C--hydrocarbons are present in the liquid phase while a predominant molar portion of the Cr- hydrocarbons are present in the vapor phase In other words, if the hydrocarbon separation point is Ce the vapor phase would contain more than 50 mAle percent of the CA hydrocarbons present in the two-phase stream, more than 50 mole percent of the C hydrocarbons present in the two-phase stream, more than 50 mole percent of the C2 'tons present in the two-phase stream, and more titan 50 mole percent of the C hydrocarbons present in the two-phase stream, while the liquid phase would contain more than 50 mole percent of the C, C6, C, C, etc. hydrocarbons present in the two-phase stream The stream entering feed inlet 69 of heavies removal column 60 during the start-up mode preferably has a hydrocarbon separation point which can be represented as follows: Cxx, wherein Xis an integer in the range of rom2 to t0, More preferably, X is in the range of from 2 to 6, still more preferably in the range of 2$ frn 3 to 5, and most preferably X is 4. When the feed to inlet 69 of heavies remove! column 60 has the above-described hydrocarbon separation point, it is ensured that a significant portion of the light hydrocarbon-containing vapor phase exits upper outlet 79 and a significant portion of the heavy hydrocarbon-containing liquid phase exits lower outlet 81 during start-up The hydrocarbon separation point of the two-phase stream entering feed inlet 69 of heavies removal column 60 is controlled by controlling its temperature. As the temperature of the feed stream increases, the value ofX increases. Conversely, as the temperature of the feed stream decreases, the value of X decreases, Preferably, the temperature of the stream entering feed inlet 69 of heavy removal column 60 during start-up is in the range of from about -73 3*C to about -62C (about -100 to about -80F), more preferably in the range of from about -7 3.3C to about -68"C (about -100 to ~90"F), mostpreferably in the range of from-71 9 0 C to -69,1 0 C (-97, to During the normal mode of operation, the stream entering eed inlt 69 of heavies removal column 60 preferably hasaydrocarbon separation point which can be represented as follows: Co 1 whereinY is an integer i athe range offm2 to 10. More preferably, is in the range offom4 to 3, still more preferably in the range of from 5 to 7, and most prferably Y i Preferably Y is at least 1 greater than , Most preferably, Y is 2 greater than Whe the feed to inlet 69 of heavies removed column 60 has the above-describedhydocarbon separation point, optimal heavies removal can be achieved during the normal mode In order toswitchfromthe startup operational mo de to the nomid operational me, he hyrocarbonseparation point of the feed to heavies removal column 60 is increased, As mentioned above. the hydrocarbon separation pointof the stream entering feedinlet 69 of heavies removal colmn 60 is controled by controlling its temperature Thus in order to switch from the startup mode to thenorma mode, the temperature of the feed entering heavies removal column 60 via feed inlt 69 is 20 increased A preferred way of cntrolling the tempeature of the feed entering heavies removalcolumn o via feed inlt 69 is to control the speed of ethylene compares 48, Ethylene compressor 48 is preferably a multi-stage ail or centrifugal compressor, wherein the pressure d'flerentral between the inlet and outlet of the compressor can be increased by increasing the speedof theompressor and decreased by decreasing the 2S speed ofthe compressor It preferred for the speed (and pressure differential) of ethylene compressor 48 to be greater during the stat-up modetan durng the normal mode. This provides formore chilling of the processed natural gas streaming indirect heat exchange means 44 of high-tage ethylene chilled 42 during start-up than during normaloperation. Thus, the temperature ofthe feed entering heavies removal column 30 60 via conduit 116 is Iower during start-up than during nomal operation In order to shif from the start-p mode to the normal mode, it is preferred for the speed of ethylne compressor 48 to be reduced, thereby changing the temperature and hydocarbon separation point of the feed to heavies removal column 60 as described herein. Preferably, the temperature of the feed entering heavies removal column 60 via feed inlet 69 during the normal mode is at least about -2 warmer than the feed entering heavies removal column 60 via feed inlet 69 during the start-up mode, more preferably a at least 4F warmer, and most preferably in the range of from 4 to 1 2" warmer. Preferably, the temperature of the stream entering feed inlet 69 of heavies removal column 60 during the normal mode is in the range of &om about -73.3 0 C to about -594C (about -100 to about -754), more preferably in the range of from about -70*C to about 62,2 0 C (about -95 to about -80F), most preferably in the range of from -69,2 to ~65*C (-92.5 to -85F). During the normal operational mode, it is preferred for the temperature of the reflux stream entering heavies removal column 60 via reflux inlet 66 to be cooler than the temperature of the feed stream entering heavies removal column 60 via feed inlet 69, more preferably at least about 5T* cooler, still more preferably at least about 1 cooler, and most preferably at least 35F cooler. Preferably, the temperature of the reflux stream entering reflux inlet 66 of heavies removal column 60 during the normal mode is in the range of fron about -107 to about -73.3CC (about -160 to about-lOOF) more preferably in the range of from about -98.3 C to about ~84.4CC (about -145 to about 120"F), most preferably inthe range of from -94,4CC to ~87.2CC (~1Z3 to ~125"), 2o During the normal operational mode, it is preferred for the temperature of the stripping gas stream entering heavies removal column 60 via stripping gas inlet 73 to be wanner than the temperature of the feed stream entering heavies removal colmn GO via feed inlet 69, more preferably at least about S* warmer, still more preferably at least about 20F wanner, and most preferably ar least 40" -warmer, Preferably, the temperature of 25 the stripping gas stream ent erng stripping gas inlet 66 of heavies removal column 60 during the normal mode is in the range of frot about -59*C to about -18*C (about -75 to about -"FP), more preferably in the range of from about -51*C to about -26*C (about -60 to about -15"), most preferably in the range of from -40 to -16,6C (-40 to -30), The above-described methodology allows a LN 1G facility employing a o refluxed heavies removal column to be started up faster than conventional methods because during start-up, a significantly greater amount of the separate natural gas stream exiting the heavies removal can be used to help start-up downstream equipment (e~g, the open methane cooling cycle)> In addition, the present invention also allows the LNG facility to be started up more rapidly because an adequate reflux steam to the heavies removal column is established much more rapidly than. under conventional methods. I'n one embodiment of the present inventionhe LNG production systems illustrated in FIGS. I and 2 are simulated on a computer using conventional process simulation software. Examples of suitable simulation software include YSYSm from Hyprotech, Aspen Plus@ from Aspen Technology, Inc, and PRO/II@ from simulationn Sciences Inc, The preferred forrs of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Obvious modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention. is The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of the present invention as pertains to any appartus not materially departing from but outside the literal scope of the invention as set forth in the following claims.

Claims (7)

1. A method of starting up a cascade-type liquefied natural gas facility employing a refluxed heavies removal column between two refrigeration cycles of the facility, said method including the steps of: (a) operating the refluxed heavies removal column in an initiating mode, said initiating mode including initiating the flow of a natural gas stream through a feed inlet of the refluxed heavies removal column and into the refluxed heavies column, said refluxed heavies removal column including a reflux inlet spaced from the food inlet, said reflux inlet having substantially no hydrocarbon-containing fluids flowing therethrough and into the refluxed heavies removal column during operation in the initiating mode; (b) subsequent to step (a), operating the refluxed heavies removal column in a start-up mode, said start-up mode including using the refluxed heavies removal column to separate the natural gas stream into a first heavies stream and a first lights stream, said start-up mode including discharging the first lights stream from the refluxed heavies removal column, said start-up mode including routing at least a portion of the discharged first lights stream to the reflux inlet; and (c) subsequent to step (b), operating the refluxed heavies removal column in a normal mode said normal mode including using the refluxed heavies removal column to separate the natural gas stream into a second heavies stream and a second lights stream, said normal mode including discharging the second lights stream from the refluxed heavies removal column, said normal mode including routing at least a portion of the discharged second lights stream to the reflux inlet.

2. The start-up method of claim 1, including any one or combination of the following wherein said natural gas stream enters the refluxed heavies removal column at a first inlet temperature during the start-up mode, said natural gas stream enters the refluxed heavies removal column at a second inlet temperature during the normal mode, said second inlet temperature is at least 2 0 F greater than the first inlet temperature; said second inlet temperature is in the range of from about 4 to about 12'F greater than the first inlet temperature; said natural gas stream has a first vapor/liquid hydrocarbon separation point Cd®-I) during the start-up mode, said natural gas stream has a second vapor/liquid hydrocarbon separation point Cy(y-i) during the normal mode, wherein X and Y are integers representing the number of carbon atoms in the hydrocarbon molecules of the respective natural gas stream, 25 wherein X and Y are in the range of from 2 to 10, wherein X is at least 1 greater than Y; wherein X is in the range of from 3 to 5 and Y is in the range of from 5 to 7; wherein Y is at least 2 greater than X; wherein X is 4 and Y is 6; and/or said refluxed heavies removal column includes a stripping gas inlet, said refluxed inlet is spaced from and located above the feed and stripping gas inlets, said feed inlet is spaced from and located above the stripping gas inlet; said heavies removal column includes first and second sets of internal packing, said first set of internal packing is vertically disposed between the feed inlet and the stripping gas inlet, said second set of internal packing is vertically disposed between the feed inlet and the reflux inlet,

3. The start-up method of any one of claims I or 2, further including any one or combination of the following: (d) upstream of the refluxed heavies removal column, cooling the natural gas stream in a first refrigeration cycle employing a first compressor to compress a first refrigerant; (e) switching from the start-up mode to the normal mode by adjusting the differential pressure of the first refrigerant across the first compressor; (f) downstream of the refluxed heavies removal column, cooling the natural gas stream in a second refrigeration cycle employing a second refrigerant including predominantly methane; (g) upstream of the first refrigeration cycle, cooling the natural gas stream in a third refrigeration cycle employing a third refrigerant comprising predominantly propane or propylene, said first refrigerant comprising predominantly ethane or ethylene; (h) vaporizing liquefied natural gas produced by the liquefied natural gas facility during the normal mode.

4. The start-up method of claim 3, wherein step (e) includes decreasing the differential pressure of the first refrigerant across the first compressor.

5. The start-Lip method of claim 3 or 4, wherein said first refrigerant Includes predominantly propane, propylene, ethane, ethylene, or carbon dioxide. 26

6. A computer simulation process including the step of using a computer to simulate the method of any one of claims 1 to 5.

7. A liquefied natural gas product produced by the process of any one of claims 1 to 5.