US3354663A

US3354663A - Hydrate removal from wet natural gas

Info

Publication number: US3354663A
Application number: US116763A
Authority: US
Inventors: Lloyd T Hendrix
Original assignee: Atlantic Richfield Co
Current assignee: Atlantic Richfield Co
Priority date: 1961-06-13
Filing date: 1961-06-13
Publication date: 1967-11-28
Anticipated expiration: 1984-11-28

Description

Nov. 28, 1967 L. T. HENDRIX HYDRATE REMOVAL FROM WET NATURAL GAS 5 Sheets-Sheet l Filed June' 13, 1961 INVENTOR Lm/0 7. HEA/ZQ/X MW Nov. 28, 1967 l L. T. HENDRIX 3,354,663

HYDRATE REMQVAL FROM WET NATURAL GAS Filed June 13, 1961 3 Sheets-Sheet 2 am@ Z/L/-A/e/A/ BY Z @Tragt/5y Nov. 28, 1967V L. T. HENDRIX HYDRATE REMOVAL FROM WET NATURAL GAS 5 sheets-sheet s Filed June 13, 1961 INVENTOR .LVD Z HEIVIQ/ BY v United States Patent fll Thepresent'invention relates to a refrigeration ,process Iand more particularly relates Vto ya Arefrigeration process vfor `recovering propane and heavier vhydrocarbons `from wet natural gas. One specific embodiment of my present invention relates to a combin'edprocess for dehydrating wet n-'aturalgas and thereafter recovering Vpropane and 'heavier hydrocarbon-s fromfthe wet natural gas by `a refrigeration and fractionation process.

Naturalgas produced at pressures substantially higher 'than those required for its v'end `use may be 'refrigerated 'or chilled by 'suitable heat exchange 'and throttling apparatus to reduce the temperature from 'ambient temperature to temperatures on the order of 'zero to minus 20 Fahrenheit and thereby condense propane and heavier hydrocarbons from the wet natural gas. When it vis'desired y`to process a gas by chilling and a large pressure drop is lnot available for refrigeration, then it is necessary to provide refrigeration from an outside source, most cornmonly a vapor compression-liquid evaporation type of refrigeration unit.

Wet natural gas is normally refrigerated after it has been dehydrated and cooled by heat exchange. The cost of the dehydration unit is normally a substantial amount in addition to the refrigeration and fractionation units. The liquid hydrocarbons condensed from the wet gases are usually fractionated to produce a depropanized natural gasoline. Such fractionation units normally merely reduce the pressure on the condensed liquids to ash off the methane, ethane, and propane and some butanes to produce a stable gasoline which is pumped into the crude without further handling. In such prior a'rt processes most of the propane and some of the b'utanes are lost, that is, not recovered from the natural gas stream unless expensive deethanization equipment, such 4as a column refrigerated to -20 F. to 50 F. is utilized, and then `the spread between the equilibrium constants of propane and ethane and methane is such that ethane corresponds with propane.

One of the diiculties with any refrigeration system or any system for recovering heavier hydrocarbons is not so much condensing propane and butane, but retaining them as liquids after they have been condensed and the condensate stabilized to adjust the vapor pressure of the gasoline stripped. Normally the condensate is stabilized vby fractionation and the propane and part of the isobutane are lost. Prior attempts to recover a large percentage of propane have been found uneconomical because of such prior processes require refrigeration to sub-zero temperatures, on the order of 20 F. Even by such methods a recovery of 40% of the propane as liquid was considered good. Attempts to recover propane as a side stream are generally not economical because of the excessive amount of low temperature reflux required.

It has also been suggested in the prior art to combine a refrigeration process with a lean oil absorption 'system to improve the efficiency of the absorption process. One variation on this procedure is the production of a Yheavy 'fraction from the condensed-absorbed hydrocarbon product which is used as the lean oil. The heavy fraction produced over and above the lean oil requirements is returned to the crude oil.

It is an object of my invention to provide an improved refrigeration process.

3,354,663 Patented Nov. 28, 1967 ICC heavier hydrocarbons from a'wet natural 4gas'streani by refrigeration.

rvIt is also 'anobject of my present invention to provide -a 4method 'and 4apparatus for recovering propane yand heavier hydrocarbons from -a natural gas lstream by "a refrigeration process whereby a liquid propane stream -is recovered.

It is also an-object of my present invention to provide a process and apparatus 'for recovering propane and heavier hydrocarbons from a wet natural gas by a coinrningl'e `refrigeration process whereby a compression condensate is used `as the commingleliquid.

Itis aifurther object of my present invention to provide a method and apparatus for recovering propane vand heavier hydrocarbons from a naturalgas stream by re- -frigeration whereby the natural gas is dehydrated by heat exchange 'supplied by lthe refrigeration v`unit.

It is a furtherobject'of r'ny present invention to lprovide a method and apparatus for recovering propane an'd heavier hydrocarbons from 'La wet natural vgas stream by refrigeration whereby the A4natural gas is dehydrated by injecting va dehyd-rating agent into the natural gas stream to effect dehydration `'duri'ng'the refrigeration process.

It is also 'an object of my present invention toprovid'e *a process -of dehydratin-g in a refrigeration system by injecting a'dehydrating agent into the condensed refrigerant and subsequently recycling a 'rst portion of the dehydrating agent and regenerating a second portion of said dehydrating agent.

Itis a further object of the'presentinvention to 'provide Aa methodand apparatus 'for recovering vpropane and nat- Vperature so that it can be rejected directly to the atmosphere byan air-'cooled exchanger.

Other objects anda more complete understanding of my present invention will become apparent by reference to the appended Aclaims and the following lspeciiicatio'n taken in `conjunction with the drawings, in which:

FIGURE -1 shows a flow diagram illustrating an embodiment of my present invention utilizing a vunique reversing type'exchange dehydration and a recycled-commingled liquid separated by a pair of fractionators.

FIGURE 2 is a flow diagram of a modification of my present linvention using a compression condensate as the commingle liquid and `a glycol dehydration technique integral with the commingle'refrigeration unit.

Briefly stated, an embodiment of my invention resides in lirst dehydrating natural gas in a series of Areversing type neat exchangers followed `by passing the dehydrated Wet gas together with a recycled liquid hydrocarbon stream recovered by the process, through one or more reversing type commingle `heat exchangers to recover the propane and heavier hydrocarbons as liquids and -thereafter separating the dry gas from the recovered liquids and fractionating the recovered liquid to separate'out a natural gasoline product and a propane lcontaining tream. In one embodiment of my invention, the heat is removed by refrigeration and rejected by exchange directly to air, to outlet gas'strea'm or to water. Propane recovery -is 'effected 4by a first low pressure yfractionation to remove heavy ends from 'the natural gasoline product and -the compression Vof the overhead gases including propane, and the subsequent separation of propane from the natural gas by fractionation at the high 'pressure Without excessive top refrigeration or reflux.

A second embodiment of my present invention relates to commingle refrigeration process wherein a compression condensate is utilized as the commingle fluid, thereby eliminating the need for a second fractionator to produce a recycle stream which Will function as the cornmingle liquid, and wherein dehydration of the natural gas is effected by injecting glycol to the commingle mixture as it enters the refrigeration units.

In a third embodiment of my invention shown in FIG. 3, a combination of the above two embodiments is ernployed. This embodiment invloves the use of a commingle refrigeration process to obtain a compression condensate utilized as commingle uid either alone or as a supplement to commingle fluid recycled from a subsequent fractionation step, along with the use of alternating commingle chillers.

With reference to FIGURE l, generally, dehydration is accomplished with the reversing heat exchangers 16 and 18 after which the dehydrated wet gas commingled With recycled hydrocarbon liquid bottoms from the fractionation unit 40, Which have been cooled by heat exchange, is charged into the reversing commingle exchangers 48 and 58. Dry gas is separated from liquid hydrocarbons recovered in the commingle exchangers, in a separator or scrubber 56 and returned to the dehydrating exchangers 16 and 18 to provide cooling therefor, after which the dry gas is transferred to the pipe line for natural gas sales or well injection. The recovered liquid drawn olf from the scrubber 56 is heated through heat exchange means and passed into a low pressure fractionator 40 to recover a natural gasoline stream, a portion of which is recycled for use as the commingle liquid, and the overhead from this fractionation column is compressed and further fractionated in the high pressure fractionation column Si) to recover a propane containing stream. In the process represented in FIGURE 2, dehydration is accomplished by injecting glycol into the commingle mixture through lines 134 and 135 and subsequently separating the glycol solution from the hydrocarbons in the scrubber 140, recycling a rst portion of the solution and regenerating a second portion of the separated glycol solution in refrigeration equipment 178.

Referring now more particularly to FIGURE l, wet natural gas Hows in through inlet line 1t) through a threeway valve 12 to dehydration equipment 11 which includes in the equipment illustrated, heat exchangers 16 and 18 and scrubber 14 with associated valves and piping. The dehydration equipment may be any type of dehydrator which functions to remove a substantial portion of the moisture from the wet natural gas; or the dehydrating function may be performed concurrently with the gasoline extraction as in the apparatus shown in FIGURE 2, as will be hereinafter described. Gas to be dehydrated in dehydrator 11 flows into heat exchanger 16 and then into the scrubber 14 where hydrates and moisture condensed by the temperature drop in the gas, effected by the heat exchange in exchanger 16, are separated off from the gas. The partially dehydrated gas then passes through another heat exchanger 18 where further cooling of the wet natural gas is effected and its moisture content further reduced due to the formation of hydrates and ice on the heat exchanger internal surfaces and as suspended solids in the condensed hydrocarbons. The dehydrated Wet natural gas is passed from the heat exchanger 18 through three-way valve 20 preparatory to entering the commingle heat exchanger area.

Installations having existing dehydrating plants or employing other dehydration systems such as that shown in FIGURE 2 using a glycol recycle in the commingle refrigeration unit may not require the reversing type exchange equipment 11. Where the Wet gas stream has previously been dehydrated, the dehydrated wet natural gas enters the present system through the pipe 44 from the existing dehydrator, which in those instances, of course,

performs the dehydrating function of the reversing type exchange equipment 11.

Refrigeration is accomplished in my above-described dehydration facilities by heat exchange with a dry gas Which has been refrigerated as hereinbelow described. The refrigerated gas flows through a three-way valve 22 and during the dehydration cycle passes through heat exchanger 18 where the cold dry gas is in heat exchange relation to the wet natural gas which has been partially dehydrated in heat exchanger 16, and absorbs heat from the wet partially dehydrated natural gas flowing through heat exchanger 18. The cooling gas after flowing through exchanger 18 then Hows through pipe 26 and through heat exchanger 16 wherein it absorbs heat from the Wet undehydrated natural gas passing therethrough. Sucient heat has then been absorbed from the wet undehydrated natural gas by the refrigerated dry gas to reduce the temperature of the wet undehydrated natural gas suciently to effect the condensation of the moisture contained in the natural gas and the formation of hydrates on the heat exchange surface. The dry gas is then passed through the three-Way valve 2S to the dry gas outlet pipe 30 where the diy gas may be transferred to natural gas sales facilities or reinjected into a well.

Gas hydrates are formed on the heat exchanger `surfaces through which the wet undehydrated natural gas passes, due to the existence of favorable hydration conditions (temperature and pressure) as the water condenses out of the wet natural gas and is intimately mixed with some of the lighter hydrocarbons, principally methane, ethane and propane. These gas hydrates are formed as a white granular solid substance and may have, for example, the following compositions: methane hydrate, CH4-7H2O; ethane hydrate, C2H6-8H2O, and propane hydrate C3H8- 18H20. The specific requirements for hydrate formation at a given pressure are (l) temperature at or below hydrate-formation temperature, (2) presence of water in the liquid state, (3) means for thorough agitation of the water and gas.

Since turbulence and intimate contacting of gas and water is inevitable in pipe line and processing equipment, hydrate formation is normally prevented prior to dehydration by heating the gas. According to rny present invention, however, dehydration is accomplished by cooling or refrigerating the wet undehydrated natural gas to intentionally form hydrates in my dehydration equipment preferably on the heat exchanger surfaces through which the wet natural gas passes. I propose to remove the hydrates formed on the heat exchanger surface by reversing the flow of the dry gas through the heat exchangers 16 and 18 so that warm dry gas is passed through the heat exchangers 16 and 155 by changing the valve settings on three-way valves 28, 22, Ztl, and 12, thereby momentarily reversing the flow of the dry gas through `pipes 24 and 26 and through heat exchanger 16 and 18 to raise the temperature sufficiently in these heat exchangers to remove the hydrates from the heat exchanger surfaces. The ow of the wet natural gas through the interior of the heat exchanger surfaces is also reversed during the above reversing cycle by changing the setting of threeway valves 12 and 20 so that during the reversing cycle wet natural gas coming through pipe 1@ into valve 12 flows through pipe 32 and through pipe 34 into heat exchanger 18 where it passes therethrough and carries with it into the scrubber 14, which will accept flow in either direction, the dropped-out hydrates.

The scrubber 14 removes the hydrates from the reversed natural gas which gas then passes through heat exchanger 16 in a direction reversed to normal processing flow, to remove hydrates from the interior of the heat exchanger surfaces in heat exchanger 16. The gas containing the hydrates then passes through pipe 36 and through three-way valve 2d which is set to return iiow through pipe 34 into the heat exchanger 18 and thence into the scrubber 14 where the hydrates are scrubbed out as previously mentioned. Thus reversing the flow through `the dehydration equipment is effected to prevent the excessive buildup of `hydrates on the interior ofthe heat exchanger surfaces in the heat exchangers 16 and 1'3. The reversing cycle may be automatically controlled to periodically remove hydrates and condensate from the dehydration equipment, by utilizing conventional temperature vor pressure actuated three-Way control valves at 12, 20, and y28, or .plug valves with actuators.

VWet dehydrated gas from the dehydration unit 11 or from any other dehydrator which may conveniently be used, ,passes through pipe 44 'with a refrigerated commingle liquid wh-ich is pumped into the line 44 through line 45 with a recycle pump 46. The combined Vgascommingle liquid stream -ows through the three-way valve 42 into a commingle exchanger 48 and thence through line 52 and three-way valve 54 into a y500 lb. 'scrubbing unit '56 Where the liquids are removed from the ,gas-'liquid mixture. The commingle liquids serve lto increase `the ratio of liquid to vapor (L over V ratio) suiciently to change the amount of the `propane and heavier hydrocarbons contained in the wet gas at a given ytemperature and pressure. The net effect is `that which would .be obtained by .performing an equilibrium a'sh calculationv on a stream whose total composition `represents the mixture of the `commingle uid with the wet gas for the temperature and pressure.

vThe use of a commingle exchange reduces the total amount of refrigeration previously used to achieve the same degree of recovery because the increased L over V ratio, permits separation at a higher temperature than previously used. My commingle exchange process will also achieve a quality of recovery not achievable at lower temperatures because at lower temperatures increased amounts o'f ethane and methane are condensed. Hence the primary 'function of the commingle liquid is not cooling but increasing the L over V ratio which improves the 'eciency and the quality o'f the recovery of the liquids recovered in the commingle exchangers.

The commingleliquids may be compression condensates or liquids which have been previously fractionated out, cooled -by exchange, `and recycled back into the stream of natural gas Vin pipe 44 as heretofore described. The -type of commingle stream required depends on the amount and Vnatu-re of the hydrocarbon recovery sought. For example, to recover a rpentane plus stream a commingle stream yhaving very little pentane should be used, otherwise the pentane losses would be excessive. To recover propane, a `commingle stream low in propane .is usual.

Without the use of commingle liquid, refrigeration to approxi-mately -50 F. is required to -achieve the propane recovery realized at 0 YF. with a commingle liquid. At such low temperatures special materials of construction are required and the horsepower required for a given amount of refrigeration is greatly increased. Propane and heavier hydrocarbons, of course, are the hydrocarbons which are sought -in therrecovery process.

Because of the buildup of ice and hydrates on the internal heat 'exchange surfaces -in the commingle exchanger 48 and the need `for reversing to remove such buildup, a second exchanger 58 is provided for alternate service while the hydrates are being removed from the surfaces of the heat exchanger 48 by reversing the flow of refrigerant through the heat exchanger 48 as will hereinafter be described. Valve 42 is set to pass the gascommingle liquid mixture through pipe 60 and thence into exchanger 58 and through valve 54 `into the scrubber 56 when it is desired to utilize the alternate commingle exchanger 58. Valve 42 may be a three-way valve -designed to automatically switch flow from exchanger 48 to exchanger 58 as either the temperature or pressure iluctuates suiiciently `to indicate a need for removal of hydrates, etc. from the heat exchange surfaces in the onstream heat exchanger.

When it is desired to reverse the ow of refrigerant through the commingle exchanger -S8, vliquid refrigeran is pumped through 'pipe 62 through valve 64 and hea exchanger 58 and thence through pipe 67 intosurge tanl 69 after which it is flashed and refrigerated liquid ther passed through pipe 71 through exchanger 48 which i: then on stream where it chills the incoming streams and is vapori'zed and'thence passes in vapor form to the com pressor (not shown) through pipe '73. When it is desired to reverse the ow through commingle exchanger 4E the setting o'f valve -64 is changed so that Warm liquid refrigerant passes through :pipes and 71 and through commingle exchanger 48 and thence through valves 68 and 65 and through pipe 67 into the surge tank '69 where it is Y'ashedand passed through pipe 75 and thence through heat exchanger 58 where it emerges as a vapor. The 'refrigerant 'vapor is then passed from commingle exchanger 58 to the compressor (not shown) through pipes 66'and 73.

Scrubber 56 separates commingle liquid and recovered hydrocarbons from the natural gas and is preferably adapted to operate at a pressure of up to approximately 5,00 p.s.i`.g. The overhead drygas from the scrubber 56 in its refrigerated state is ,passed through pipe 72 back to the dehydration equipment 11 to absorb heat from the incoming Wet natural gas. The refrigerated gas is passed into the dehydration unit through Vthree-way valve 22. In the event that dehydration is "accomplished by apparatus other than that shown in the drawing, the dry 'gas is kpassed directly into the output pipe Si() to sales or injection. The scrubber r56 is `of conventional design,

preferably utilizing a steel wool element where slugs of liquid and .pieces of solid matter can readily drop out.

The liquid hydrocarbons recovered in the scrubber 56 comprising commingle liquid and liquids recovered from the wet natural gas, are at a very low temperature and are vheated by heat exchange prior to fractionation whereby the heat exchange operation provides refrigeration for other units in the process. As shown in the drawing, heat exchangers 74, 76, and 78 are utilized to increase the temperature of the liquid recovered from the scrubyber to an appropriate fractionation feed temperature 'for transfer to the fractionation unit 40 through pipe 80. The volume of ow linto the fractionator 4) is controlled by a suitable liquid level control valve 82 which is actuated by the liquid `level in the scrubber 56. The frac- 'tionator 40 may be controlled to recover as bottoms, appropriate commingle liquid for recycling to the commingle exchangers 48 and 58 which liquid in turn controls 'the recovery in the commingle exchange operation.

The overhead from the fractionator 4tlwhich contains primarily propane, butanes, and pentanes as Well as methane and ethane, is passed through pipe 86 to a compressor 84, compressed, and the compressed gas cooled `by passing through air cooler S8 after which it is charged into a high pressure fractionator 50 midway in the column.

Air cooler S8 is of conventional design with modification Afor splitting into several streams as may be required to accomplish that overall heat balance of the process and toserve as a regulator for the various unit operation. Thus by utilizing the apparatus in the arrangement as shown, my invention facilitates the rejection of heat at a high enough temperature level to permit rejection of heat by direct rejection to the atmosphere by an aircooler exchanger 88, Normally `this cooling must be accomplished by refrigeration, or heat exchange, since the heat is rejected at lower temperatures. Regarding the heat balance achieved in my present invention, it is to be realized that there are many ways of attaining balance with the same equipment or even by substitution of other apparatus and therefore the system described above is but one specific form that 'my invention maytake.

The fractionation column 40 is provided with a small amount of low 'temperature internal reflux by supplying refrigerant through pipe 90. An internal coil 91 is utilized )eliminate an external coil, pump, and an additional essel. The bottom tray liquid from the fractionator 48 is eboiled by heat exchanger 92 and a reboiler type fired eater 94. rlhe bottoms product from the lired heater 94 oes through exchanger 92 to preheat the reboiled liquid nd precool the bottoms product. The products drawn. 'if the fractionator 4t) through the heat exchangers 9'4 and l2 are controlled by the liquid level in the column 401 hrough a liquid level control valve 96. The bottoms iroduct flows through liquid level control valve 96, ixchanger 98, air cooler 88 and exchanger 78 Where it s gradually cooled in accordance with the overall heat )alance to approximately room temperature. After this nitial cooling of the bottoms product, a portion thereof s recycled as commingle liquid and a portion thereof )assed to pipeline products through pipe 101. A suitable :ontrol valve 188 controls the passage of the bottoms to :ither pipeline or recycle through a flow recorder con- ;roller (FRC) which meters the flow as well as con- Lrolling it. The liquid recycled as commingle liquid passes :hrough a chiller-exchanger 102 which is provided with external refrigeration and from there is pumped with Jump 46 through pipe 1134 to pipe d4 and the commingle exchanger 48 -or 58 where it is commingled with Wet dehydrated gas in pipe 4d for the commingle-exchanger function heretofore discussed.

The overhead from the second fractionator (500 psig.) is drawn olf through pipe 186 and cooled through heat exchanger '7d and further refrigerated through chiller-exchanger 188 and then charged into a high pressure scrubber 118 the liquid bottoms from which are pumped into the upper tray of the fractionator 50 as cold reflux. The eiuent gases separated in the high pressure chamber scrubber 118 are an off-gas and are transferred through pipe 112 and valve 22 to join the other refrigerated dry gases used in the dehydration facilities 11 and thence to gas sales or injection.

The liquid bottoms product from the high pressure fractionator 59 are heated through the reboiler 98 and a portion thereof recharged to the bottom tray of the fractionator 50. The remainder of the bottom product from the fractionator 58 may be piped through the air cooler S8 through pipe 114 and then further cooled to a suitable product temperature through the heat exchanger 76, after which it may be depropanized. The bottoms may be fed to a depropanizer of conventional design, followed Vby a debutanizer. The bottoms from the debutanizer can be combined with the excess C6 plus from the low pressure fractionator i8 which is not needed for recirculation. The flow of liquid bottoms from fractionator 5t) to products, is controlled by a suitable liquid level control valve 116 which is actuated by the liquid level in fractionator 58.

Hence it may be seen from the above description that a considerable savings is realized in the present invention since it is thereby not necessary to operate at a low temperature to achieve deethanization and by operating at relatively higher temperatures, Va better separation is obtained since methane and ethane do not tend to come down the column with propane as they do at lower temperatures. My process in the above described embodiment permits economical recovery of propane and butanes as well as the natural gasoline product normally recovered from a wet natural gas stream.

When the natural gas is a very wet gas it is often possible to produce a compression condensate which can serve as the commingle liquid. In such cases propane would not be recovered and a single fractionation unit is sufficient since it is not necessary to produce a C6 plus commingle recycle stream. If, in such operations, propane is to be recovered, a second fractionator is required since an attempt to take propane off as a side stream in a single column operation requires an excessive amount of reflux refrigeration to about F. and the separation operation generally becomes more difficult due to the diminishing spread in equilibrium constants.

A process utilizing compression condensate as the commincle iiuid and employing a single fractionator 148 is illustrated in FGURE 2. In the process shown in FIG- URE 2, wet undehydrated gas from the iield enters the system through line 118 and is compressed in a compressor 128, for example, to 500 pounds per square inch and subsequently cooled to approximately its pre-compression ternperature in cooler 122. The wet natural gas with compression condensate is then separated in a scrubber 12d and the liquids therefrom drawn olf into a separator 128 where the water is drained olf and the liquid hydrocarbons pumped with pump 138 back into the gas at line 126, las commingle liquid. Glycol from a recycled stream is passed through line 134 into the commingle mixture in pipe 126 as the mixture flows into the commingle heat exchanger 132.

The temperature of the commingle mixture is substantially lowered in the commingle exchanger 132 and a second portion of the glycol stream added to the partially cooled mixture and the glycol-commingle mixture charged into a commingle chiller-exchange 138 where a further temperature reduction is effected. Glycol is charged to the commingle mixture to adsorb Water vapors which are released in the refrigeration process. This glycol solution exists with the condensed hydrocarbon liquid and the stripped dehydrated natural gas. A mixture of the glycol solution with the condensed hydrocarbons and stripped, dehydrated natural gas is passed from the chiller 138 into a scrubber 148 and the gas removed from the mixture and passed through line 141 and through cornmingle exchanger 132 Where it is heated by exchange thus providing exchange cooling for the commingle exchanger 132. The dry gas from the commingle exchanger 132 is then pumped to sales or storage facilities through line 143.

The condensed hydrocarbons separated in the scrubber i? are pumped into the fractionator column 148 through pipe 142 with a pump 144. The bottoms from the fractionator column 148 are heated in reboiler 16 and a portion thereof recharged to the bottom tray of the fractionator 148. The remainder of the bottoms product from fractionator 148 may be piped through line 155 and then cooled to a suitable temperature for storage or injection into a crude pipeline. The fractionation column 148 is of conventional design and may utilize a Water cooled exchanger 152 to remove heat from the overhead after which the overhead gases are condensed in a refrigerated condenser 154 and the condensate and uncondensed vapors separated in a surge tank 156. The uncondensed vapors are passed through pipe 158 and the commingle exchanger 132 where they remove heat from the incoming commingle mixture after which the vapors are passed to sales through pipe 143. Reflux to the fractionation tower 148 is supplied from the surge tank 156. Heat is supplied to the bottom of the fractionating tower 148 by a steam-heated reboiler 16d.

Refrigeration is supplied to the commingle chiller exchanger 138 and the reflux condenser 154 by a conventional refrigeration unit, for example an ammonia refrigeration unit designated generally as 162. In such units the scrubbed ammonia gas is compressed in a compressor 1154 and condensed in a Water cooled condenser 166. The liquid ammonia is then sent to the surge tank 168 and evaporation of liquid ammonia removes heat in the condenser 154 and the commingle chiller 138 after which the ammonia vapors are sent to the scrubber 170 to remove any entrained liquid therefrom before going back to the compressor 164 to complete the refrigerant cycle.

Glycol is pumped into the commingle mixture through pipes 134 and 135 to remove water and the Water containing glycol is separated from hydrocarbon liquid and dry gas in the scrubber 140. A major portion of the glycol separated in the scrubber is recycled by pumping the glycol solution with pump 174 through line 172 into the lines 134 and 135 through Which glycol is charged to the commingle mixture as previously mentioned. A portion of the glycol fromthe-scrubber 1'40 is pumpedt'hrough-liiie 176 to a glycol regeneration unit designated generally as 178. In this glycol vregeneration equipment the glycol solution is first heated by passing the glycol solution through the heat exchanger 180 after which the hydrocarbon vapors are flashed 'off in the ash tank 182 and the glycol dehydrated in the reboiler type dehydrating tank 184 as disclosed in my copending application Ser. No. 78,019, vfor"Absorption Process and Apparatus tiled Dec.23, '1960. The regenerated'glycol is then cooled by passing through the heat exchanger 180 where it gives up heat to the incoming glycol solution vand then returns to surge tank 185. The regenerated liquid glycol is then pumped from the surge tank 185 with pump 186 back into the glycol Vrecycle pipe 172 and into the commingle mixture through pipe 134.

By recycling a major portion of the glycol and only regenerating a Vsmall portion thereof, the dehydration of the incoming wet undehydrated natural gas is made economical in my 'present system bythe fact that Vthe large volume of glycol required to adequately cover lall surfaces is recycled at the -lowest level of cooling to which the-gas stream is cooled and therefore the major portion -of glycol is not heated for regeneration thus greatly reducing the heat load von the refrigeration system for a :given glycol rate. Thus the amount of glycol that can be Iutilized is not limited by the economics of the heat load and consequently a greater prevention of hydrate formation is realized.

The .principle of using a large recirculation rate of dilute glycol solution to improve the prevention of hydrate formation while at the same time not increasing the heat load by regenerating all of the glycol recirculated to the refrigeration system, can be .used with any refrigeration system and is not limited tothe type of refrigferation system utilized in the present invention. In the use of a recirculated glycol stream injected into a refrigerated gas stream lto prevent the formation of hydrates and at the same time to-dehydrate the gas stream, the separation of glycol is thus effected at the minimum temperature, thus facilitating the circulation of large quantities of glycol without increasing the refrigeration load and Without increasing the quantityoit` glycol Which -has to be regenerated. The amount of glycol regenerated regulates the size of Vthe regenerating ysystem required in the heat exchange, the reboiler, and the contacting column. For example, when diethylene glycol is used as the dehydrating agent and a F. temperature maintained 'inthe commingle chiller .138, it is possible `:to maintain approximately 80 percent of the glycol in circulation. The lglycol regeneration equipment, which is conventional equipment, vdoes `not have to `completely dehydrate the glycol but rather a 90-95% glycol is satisfactory for re- `entry into the system. Of course the more water removed Afrom Athe glycol Vbeing regenerated the less the 'amount of the glycol stream that has to be removed `from the system 'for regeneration.

Thus it can be seen'that in the system represented ir FIGURE 2, glycol is injected into the commingle chiller unit 4138 to prevent hydrate formation and `also to `dehydrate the wet natural gas. While a large :amount ol dilute glycol is normally 'sprayed into the `header to prevent hydrate formation in the chiller, this practice imposes a large 'heat loadon the regeneration unit. According to the present invention, large quantities of glycol are economically recirculated .to furnish sucient contact `with the wet vgas to ,prevent hydrates from forming Ybut this does not add to the heat and refrigeration load. The Arefrigeration load is not increased since the recirculated glycol is at the lowest temperature to which the wet gas is taken. A constant bleed of the glycol separated from the chilled commingle mixture in -the 4scrubber 140 is bled off and regenerated in order to prevent the water 4concentration of the glycol solution from increasing 'su'iciently to freeze in the chiller or Ibecome viscous and interfere with ow and heat transfer.

Referring to FIG. 3 wherein like numerals `refer to .like components of FIGS. 1 and 2, a process using a compression condensate as commingle Huid, as shown in FIG. 2, .and alternating commingle chillers, as shown in FIG. l, is illustrated. In this process Wet undehydrated gas enters through line -118 and passes to compressor .120 where it is compressed to i.e., 500' -p.s.i. and then 'cooled to about the pre-compression temperature in cooler 122. The wet natural'gas and resulting compres- -sion condensate are separated -in scrubber 12'4 with the compression condensate comprising water and liquid hydrocarbons being drawn olf into separator 128'. The water is then decanted from the condensate, and the remaining liquid hydrocarbons are pumped -with pump 130" back into the gas line 126 as commingle'liquid to forma cornmingle mixture. Additional commingle V`liquid obtained Vfrom a subsequent fractionation step may also 'be `pumped into the stream rat this .point by pump 46 via line 45. The commingle mixture flows into either commingle exchanger 48 or 58', depending upon the setting of threevWay Valve 42'., and .the commingle -mixture is then processed as earlier explained in the discussion of FIG. ll.

Example 1 As an example of my present invention, one million cubic feet of wet natural gas from the 'Wheeler Ridge field (California) having the composition shown in the attached Table I, when processed in the apparatus shown ,in FIGURE lyields a 50% lpropane recovery, 90% butane recovery, and complete recovery of pent'anes plus with a propane containing stream composition as shown in Table I. The temperature of the streams at various .points inthe process is shown vin FIGURE "l. As may be seen from the temperatures shown on the drawings, the processed streams arie never refrigerated 'below '0 F. Of the 280.62 pound moles of VC6 plus bottoms stream recovered .from the 200,p.'s.i. 'ract'ionator 40, 260 pound moles are recycled as commingle liquid into -the commingle heat exchangers 48 and 58.

TABLE I.-COMPOSITION IN POUND-MOLES A 200 psi. Fractioritor 4'0 5' L'. '8

(1 m1111011 5.0i.) A g y scrubber (11o) Feed Overhead Bottoms Overhead 'Reboiler (98) Overhead Bottoms Nitrogen -156 1587 `1.87 1 87 Methane.. 2,117 108.6 .108.6 Ethane 219 541.8 54. 8 Propane. 94 55.3 55.3 ri-Butane 18. 7 15.7 15. 7 i-Butaiie- 12 9. 45 9. 45 n-Pentane 2. 9 v2578 2. 78 i-Pentane 4. 2 3. 94 Hexane (CH-) 11.2 10.0 0.5 Heptane `131.12 Octaneplus The heat supplied by the tired heater 94 is approximately 2% million B.t.u .s per million s.c.f. intake ofwel; gas to the plant. The refrigeration load is 2.1 million B.t.ii.s per million s.c.i. intake wet gas to the plant,

or based 1 million s.c.f. wet intake gas processed per-day Withammonia as the refrigerant. 18 brake horse power is re'qui'i'edoi the 'refrigerant compressor for the air-cooled embodiment shown.

l l Example 2 Two million cubic feet of Wet natural gas from Rin- :on (California) having a composition shown in the rst :olumn of Table II Was processed in the plant shown in FIGURE 2 with the commingle Chiller 138 operating at 440 p.s.i.g. at 8 F., using a glycol recycle stream for dehydration. The results shown in Table II indicate superior recovery of butanes and pentanes as compared with prior art refrigeration units. Propane, of course, is not recovered in the process of Example 2 as it is in the process of Example 1.

TAB LE II.-GLYCOLREFRIGERATION UNIT Accumula- Ifeed to Gas from Qompres- Comprestor Over- Retrig Rerig. Gas from Theoretical sion Consion Con- Fraetiona- Fractiona- Liquid head vapors Aceum. Component Unit Unit Refrig. (gal. densate 1u densate in tor Bottoms tor Bottoms Recovery (uncon- Overhead (Mol (wol Unn (gaL/ day) Feed (vol. Feed (gaL/ (vol. per- (gal/day) (percent) densed (gar/day) percent) percent) day) percent) day) cent) fract over. head mol percent) Oxygen 0. 1 0. 10 Co2 4.11 4.o ,1 40 Nitrogen. O. 0. 4 h Methane so. 49 85. 99 32- 93 Ethane. 4. 4. 23 14. 27 Propane. 6. 01 4. 15 45 41 1-Butane 0. 83 0. 36 1 20 11-Bl1l3alle. 2. 15 0. 65 1 58 i-Pentane 0. 49 o. 059 37 3a 76. Se 1, 201 44. 95 1, 56s 0- 06 n-Pentane. 0. 49 0. 048 28 334 0 O5 Hexane 0.39 0. 013 9 318 Heptane plus 0. 54 0.002 2 571 Total 1 1,677 2, 526 6, 708 1, 564 3l 492 l M. s.c.f./day.

Although I have described my invention in considerable detail and with a degree of particularity, in order to fully set forth the best known modes of carrying out my invention, it is to be understood that my invention should not be so limited, but should be afforded the full scope of the appended claims.

I claim:

1. In a method for recovering propane and heavier hydrocarbons from Wet natural gas, the steps comprising:

(a) compressing said wet natural -gas to recover a compression condensate comprising Water and liquid hydrocarbons,

(b) separating said natural ygas from said condensate,

(c) removing said Water from said liquid hydrocarbons in said condensate,

(d) commingling said hydrocarbon condensate with said natural gas to form a liquid hydrocarbon-gas mixture,

(e) alternately passing said mixture through one of at least a pair of alternating commingle chillers to effect condensation of entrained liquid hydrocarbons,

(f) simultaneously removing solid condensates formed in the other of said commingle Chillers,

(g) separating said mixture of gas and condensed hydrocarbons, and

(h) `fractionating said separated hydrocarbons.

2. In a method for recovering propane and heavier hydrocarbons from Wet natural gas, the steps comprising:

(a) alternately passing Wet gas together with liquid hydrocarbons through one of at least a pair of alternating commingle Chillers to effect condensation of entrained liquid hydrocarbons,

('b) simultaneously removing solid condensates from the other of said commingle Chillers,

(c) separating the liquid hydrocarbons and gas,

(d) fractionating said liquid hydrocarbons to recover a gasoline product as bottoms from said fractionation,

(e) subsequently fractionating the overhead from said first fractionation to recover a propane stream as a liquid therefrom, and

said Water and hydrates are removed from said gas stream and said scrubber,

(c) passing said dehydrated gas together with a recycled natural gasoline stream through one of a pair of alternating commingle Chillers to effect cooling of said dehydrated gas and natural gasoline to about 0 F. and condensation of prop-ane plus hydrocarbons from said dehydrated gas at substantially constant pressure,

(d) periodically alternating the flow of said dehydrated gas and recycled natural gasoline from said one chiller through the other of said pair of commingle chillers when hydrate formation in said one chiller has reached a predetermined point,

(e) fractionating said separated condensed hydrocarbons to recover a gasoline as bottoms,

(f) recovering the overhead from said fractionating process,

(g) fractionating said overhead in a second fractionator to recover as bottoms therefrom a liquid propane stream, and

(h) recycling a portion of said gasoline stream to commingle with additional dehydrated Wet natural gas in said commingle Chillers.

4. In a method for dehydrating Wet natural gas and recovering propane and heavier hydrocarbons therefrom, the steps comprising:

(a) compressing said wet gas to obtain a compression condensate comprising Water and liquid hydrocarbons,

(b) separating said wet gas from said compression condensate,

(c) separating said Water from said liquid hydrocarbons,

(d) pumping said liquid hydrocarbons into said Wet gas as commingled liquid to form a mixture of said liquid hydrocarbons and said gas,

(e) injecting glycol into said commingle mixture,

(f) passing said mixture into a commingle exchanger,

(g) passing said mixture subsequently into a commingle chiller after injecting a second portion of glycol into said mixture,

(h) separating said mixture passed from said commingle chiller in a scrubber into a glycol solution, a hydrocarbon liquid, and a dry gas,

(i) passing said dry gas into heat exchange relationship with said first commingle exchanger to thereby cool the incoming mixture of wet gas and liquid hydrocarbons,

(j) recycling a portion of said separated glycol solution into said mixture passing into said commingle exchanger,

(k) regenerating a second portion of said separated glycol,

(l) recycling said regenerated glycol into said incoming mixture, and

(m) fractionating said condensed liquid hydrocarbons separated into said scrubber to stabilize said hydrocarbon product.

5. In a method for dehydrating wet natural gas and recovering propane and heavier hydrocarbons therefrom, the steps comprising:

(a) passing said wet gas through a reversing heat exchanger having a scrubber associated therewith to remove condensed moisture and hydrates from said sas,

(b) periodically reversing the ow of said gas through said reversing heat exchanger to remove the Water and hydrates from the surfaces of said heat exchanger, whereby said water and hydrates are removed from said reversed flow gas in said scrubber,

(c) passing said gas alternately through one of a pair of alternating commingle chillers together with previously separated liquid hydrocarbons in heat exchange with a refrigerant heat pump cycle the direction of flow of which is reversed serially through the respective chiller, whereby said gas is passed through one of said pair of commingle chillers while hydrates are simultaneously removed from the other of said chillers,

(d) separating the mixture of gas and liquid hydrocarbons,

(e) fractionating said separated liquid hydrocarbons in a first fractionation column,

(f) recovering as bottoms from said fractionation column, a natural gasoline stream,

(g) recycling at least a portion of said gasoline bottoms stream as commingled liquid into the wet gas passing into said commingle Chillers,

(h) recovering the overhead gases from said column,

(i) fractionating said overhead gases in a second fractionation column to recover a liquid propane stream as bottoms thereof,

(j) recovering 'the overhead gas from the second column, and

(k) passing said recovered gas into heat exchange relationship with the incoming wet gas in said dehydration unit.

6. The method of claim including the steps of compressing the overhead gases from said first fractionator, and air cooling the compressed hydrocarbons prior to feeding said hydrocarbons into said second fractionator.

7. Apparatus for dehydrating wet natural gas and recovering propane and heavier hydrocarbons therefrom, comprising in combination:

(a) means for compressing said gas to form a liquid condensate comprising water and natural gasoline, (b) means for separating said gas from said condensate, (c) decanting means for separating said water from said natural gasoline,

(d) means for combining said gas with said natural gasoline,

(e) means for chilling and simultaneously commingling a mixture of said gas and said gasoline to effect recovery of propane and heavier hydrocarbons as liquids from said natural gas,

(f) means for injecting a dehydrating agent into said commingle means,

(g) means for separating said gas from said recovered liquid hydrocarbons and said dehydrating agent,

(h) fractionation means for first depentanizing said condensed hydrocarbons, and

(i) fractionation means for subsequently recovering a propane stream as liquid from said depentanized hydrocarbons.

8. Apparatus for recovering propane and heavier hydrocarbons from wet natural gas, comprising in combination:

(a) a plurality of means for chilling and simultaneously commingling a mixture of said gas and a natural gasoline stream to effect the recovery of propane and heavier hydrocarbons as liquids from said wet natural gas,

(b) means for altering the flow of said mixture from one of said chilling means to another of said chilling means,

(c) means for altering the ow of refrigerant vapors from one of said chilling means to another of said chilling means whereby warm refrigerant vapors can be passed through one of said chilling means while cold vapors are simultaneously passed through said other chilling means,

(d) means for separating said gas from said recovered natural gasoline,

(e) fractionation means for depentanizing said condensed hydrocarbons,

(f) means for compressing the overhead gases from said fractionation means,

(g) means for air cooling said compressed hydrocarbons, and

(h) fractionation means for recovering a propane stream as liquid from the overhead from said pentanizing fractionating means.

9. Apparatus for dehydrating and recovering propane and heavier hydrocarbons from Wet natural gas, comprising in combination: a reversing heat exchanger, means for effecting cooling in said reversing heat exchanger whereby wet natural gas passed through said reversing heat eX- changer is cooled to condense moisture and form hydrates on the surfaces of said heat exchanger which condensate and hydrates can be removed from said surfaces by reversing the flow through said reversing heat exchanger, means for removing said condensate and said hydrates produced during reversal of said flow, means for chilling and simultaneously commingling said dehydrated gas with a natural gasoline stream to thereby eiect the recovery of propane and heavier hydrocarbons as liquids, means for separating said gas from said dry recovered hydrocarbon liquids, fractionation means for depentanizing said recovered hydrocarbons, and fractionation means for recovering a propane stream as liquid from said depentanized hydrocarbons.

References Cited UNITED STATES PATENTS 2,151,248 3/1939 Vaughan 62-20 2,500,353 3/1950 Gantt 62-28 2,573,341 10/1951- Kniel 62-28 2,596,785 5/1952 Nelly et al. 62-28 2,601,599 6/ 1952 Deming.

2,627,318 2/ 1953 Swerdloff 62-23 2,645,104 7/ 1953 Kniel 62-28 2,690,814 10/ 1954 Reid 62--20 2,756,568 7/ 1956 Jordan 62-474 2,952,983 9/1960 Gilmore 62-24 2,973,834 3/1961 Cicalese 62-20 3,003,007 10/1961 Newsome 62-12 3,028,332 4/1962 Forbes 62-23 NORMAN YUDKOFF, Primary Examiner.

J. MICHEL, Examiner.

M. L. MOORE, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION -Patent No. 3,354,663 November 2,8, 1967 Lloyd T. Hendrix It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 14, line 49, cancel "dry"; same line 49, before "gas" insert dry Signed and sealed this 30th day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR-

Attesting Officer Commissioner of Patents

Claims

1. IN A METHOD FOR RECOVERING PROPANE AND HEAVIER HYDEROCARBONS FROM WET NATURAL GAS, THE STEPS COMPRISING: (A) COMPRESSING SAID WET NATURAL GAS TO RECOVER A COMPRESSION CONDENSATE COMPRISING WATER AND LIQUID HYDROCARBONS, (B) SEPARATING SAID NATURAL GAS FROM SAID CONDENSATE, (C) REMOVING SAID WATER FROM SAID LIQUID HYDROCARBONSW IN SAID CONDENSATE, (D) COMMINGLING SAID HYDROCARBON CONDENSATE WITH SAID NATURAL GAS TO FORM A LIQUID HYDROCARBON-GAS MIXTURE, (E) ALTERNATELY PASSING SAID MIXTURE THROUGH ONE OF AT LEAST A PAIR OF ALTERNATING COMMINGLE CHILLERS TO EFFECT CONDENSATION OF ENTRAINED LIQUID HYDROCARBONS, (F) SIMULTANEOUSLY REMOVING SOLID CONDENSATES FORMED IN THE OTHER OF SAID COMMINGLE CHILLERS,