US2183604A

US2183604A - Method of stabilizing volatile

Info

Publication number: US2183604A
Authority: US
Publication date: 1939-12-19
Anticipated expiration: 1956-12-19

Description

Dec. 19, 1939. P D. BARTON Er A1.

METHOD OF STABILIZING VOLATILE LIQUIDS Filed NOV. 28, 1934 3 Sheets-Sheet l Dec. 19, 1939. P. D. BARTON x-:T AL

METHOD OF S TABILIZING' VOLATILE LIQUIDS Filed NOV. 28, 1934 3 Sheets-Sheet 2 Dec. 19, 1939. P. D. BARTON Er A1.

METHOD OF STABILIZING VOLATILE LIQUIDS Filed Nov. 28. 1934 3 Sheets-Sheet 3 Nazi Patented Dec. 19, 1939 UNITED STATES PATENT OFFCE METHOD OF STABILIZING VOLATILE LIQUIDS York Application November 28, 1934, Serial No. 755,152

12 Claims.

Our invention relates to a stabilization and gas recovery process and more particularly to an improvement in the stabilization of crude petroleum, and pressure distillates and the recovery of stabilized light gasolines from these and refinery or natural gases.

Cracked gasoline, which is usually termed pressure distillate, is generally separated, after condensation, from its attendant gases, at pressures varying from a few pounds per square inch gauge to 200 pounds per square inch or more. The condensate, which is generally termed raw pressure distillate, contains hydrocarbon constituents, ranging from methane and other normally gaseous hydrocarbons to gasoline and heavier fractions depending upon the control of the temperature at the top of the fractionating tower of the cracking unit. The amount of the lighter components, such as methane, ethane and propane, the presence of which is not desired in the linished motor fuel lproduct, is dependent on the pressure and temperature conditions of the sepa-ration. A practice sometimes resorted to in endeavoring to eliminate these components from the condensate, is to operate the separator at a relatively high temperature of approximately 130 F. and a low pressure of 2 or 3 pounds per square inch gauge. The elimination in such practice, however, is not complete and under these conditions relatively large amounts of desirable constituents such. as butane, pentane, hexane, and some heavier hydrocarbons pass off with the rejected gases and must be recovered in order to provide for an efcient operation. Under higher pressures and lower temperatures the amount of desirable constituents which must be recovered from the rejected gases is, of course, less.

In practically all cases it is economical and desirable to fractionate the raw pressure distillate to eliminate propane and lighter fractions therefrom, so that the butane content will give the desired Vapor pressure of the finished motor fuel. The raw pressure distillate, further, must be treated to remove sulphur compounds and other undesirable substances. The distribution of these compounds is usually such that concentrations are found between certain boiling ranges of the raw pressure distillate. It is, therefore, generally found expedient to fractionate the raw pressure distillate into various cuts containing these concentrations vduring the process of eliminating the propane and lighter fractions. The cuts may then be treated separately according to the sulphur compounds and the like present.

(Cl. ISG-8) For example, a simple case is the fractionation of raw pressure distillate into three boiling range fluids, namelyJ propane and lighter, with butano in excess of that desired for vapor pressure requirements; butano, pentane, hexane and some heavier fractions; heptane and the heavier oomponents, The first, or propane cut, is usually passed to fuel system. The second, or light gasoline cut, may be treated satisfactorily with a caustic wash. The third, or heavy gasoline cut, may be acid treated. It is sometimes of advantage to fiactionate the heavy gasoline into two or incre cuts depending upon the concentrations of detrimental compounds.

After treating and such other subsequent processing as may be necessary, the gasoline cuts are blended and mixed with straight-run gasoline to make the rlrished motor fuel. The separation of the light gasoline cut from the heavy gasoline eliminates excessive vaporization, treating, and rerunning losses which would otherwise prevail during the processing required by the heavy gasoline cut.

The fractionation of the raw pressure distillate is conventionally done by one of two methods. The rst is to charge the raw pressure distillate to a high pressure fraotionating tower from which the propane and lighter fractions are removed overhead. The heaviest fraction from this tower is passed to a second, lower pressure, tower, from which the light gasoline is recovered as an overhead or distillate product and the heavy gasoline as a bottom product. The heat required in this method is high because of the large quantity of redux required in the high pressure tower and the high reboiling temperature necessary. Then, too, the high pressure tower is expensive since it must be relatively large to handle the total charge of raw pressure distillate.

In order to overcome these objections a second method is used in which the raw pressure distillate is charged to a low pressure tower from which the light gasoline, propane and lighter hydrocarbons are removed overhead, as a cornbined out, and the heavy gasoline is removed from the bottom. The fractions removed overhead are condensed as completely as possible. Then the uncondensed vapors are passed to the `einery absorption plant or vapor recovery systeni for extraction of valued constituents, and the condensate is passed to a high pressure tower. The propane and lighter constituents are removed from this tower overhead and the light gasoline is withdrawn as a bottom product. The

objection to the second method is the additional processing to which the usually large volume of uncondensed vapors must be subjected.

It is desirable to recover a large light gasoline cut, since the treating requirements of this cut are the simplest and least expensive and for the advantages mentioned above with respect to the treating of the heavy gasoline cut. In order to accomplish this in the second method outlined, a deep cut (generally 20% or more of the raw pressure distillate) is made, leaving a heavy bottom product containing practically no hexanes and lighter constituents. The amount of condensation of the overhead cut, which also contains the normally gaseous components, is controlled by the available cooling water temperature and pressure obtainable in the condenser. The pressure is, in turn, partly dependent upon the heating medium available for reboiling the bottoms and in many instances upon temperature limitations due to the deleterious effect of high temperatures on the character of the bottoms. At the normally limited reboiling temperatures, only low pressures, relative to the pressures desired for condensation of the overhead without an unduly large portion remaining uncondensed, can be obtained because of the high boiling constituents in the bottoms. Under the relatively low condensing pressures, 20% to 60% of the overhead cut will generally remain uncondensed and pass off as wet gas. The recovery of valuable constituents from the wet gas is an added uneconomical step, particularly in view of the low pressure at which it is available.

It has been our experience that it has not been generally possible to effect substantially complete condensation of the overhead cut with the conventional system described above.

This difliculty may be overcome by removing from the raw pressure distillate prior to its introduction into the rst, or low pressure, tower most of the undesirable light hydrocarbon constituents, methane and ethane, with a good portion of the propane. The absence of these removed, lighter fractions in the subsequent, overhead cut from the low pressure tower will permit complete or substantially complete condensation of this cut under temperature and pressure conditions readily obtainable in practically all installations.

Similarly, in high pressure absorption plants and/or absorption plants operated for high butane recovery from natural or renery gases, methane, ethane and propane are absorbed along With the heavier fractions. These lighter fractions cause a difcult problem in the subsequent distillation and recovery of the gasoline components desired. Condensation of these components after distillation from the absorption medium is extremely diicult at the usual available temperatures of cooling water unless high pressures (8O to 200 pounds per square inch) are used. Naturally, high distillation pressures are disadvantageous from the standpoint of the consumption of stripping steam and general economical operation. The distillation pressures usually required are in excess of available steam pressure, condensation of distilled fractions is incomplete, vent gases are so rich as to require recompression or reabsorption, and the condensate has an excessively high vapor pressure, necessitating storage under pressure to prevent undue loss of gasoline prior to fractionation.

As we have pointed out in connection with the second method of fractionation of raw pressure distillate, these difliculties may be overcome if the absorbed methane, ethane and propane are substantially eliminated prior to distillation. The gasoline fractions may then readily be completely condensed and recycling practically eliminated.

It is also to be noted that crude oils of low specinc gravity contain relatively large percentages of low boiling gasoline and lighter fractions. Straight run gasolines from such crudes have a high vapor pressure, require stabilization and suffer undue vapor losses in their production. The process of our invention is particularly adapted to the stabilization of such crude oils and the simultaneous recovery of light gasoline from the natural gas present in the crude oil as it cornes rom the well. Thus it is to be observed that the character of the raw or inl-et charging stock is not limited to loW boiling hydrocarbons such as the pressure distillate and natural or refinery gases previously referred to.

It is an object of our invention to provide a process for recovering a stabilized gasoline from pressure distillate, natural or refinery gases, wherein the formation of wet gas requiring recycling or reprocessing is substantially eliminated.

It is a further object of our invention to provide a gasoline fractionating or recovery process in which the low boiling hydrocarbons which normally prevent complete condensation of the desired products at the temperature of the available cooling water are eliminated from the overhead products removed from the low pressure fractionating tower or still.

It is an object of our invention to provide a process for fractionating a distillate or long boiling range stock in which a high recovery of desired fractions at lower reboiling temperatures may be had.

it is another object of our invention to provide a process for recovering a stabilized gasoline and desir-ed components from natural or refinery gases in which distillation with the use of lower distillation pressures may be employed.

It is an additional object of our process to provide an economical fractionation and/or absorption recovery in which utility requirements of heating, stripping, cooling and/or power are materially decreased.

It is a further object of our invention to provide a process for the separation of stocks into fractions prior to treating wherein treating is facilitated, losses minimized and a high recovery of desired fractions is effected.

Another object of our invention is to provide a combined absorption-fractionation process wherein the usual separate distillation step of conventional absorption recovery systems is eliminated.

A further object of our invention is to provide a process for stabilizing low specific gravity crude oils containing relatively large percentages of low boiling gasoline and lighter fractions.

Another object of our invention is to provide a combination absorption fractionation process for the recovery of gasoline fractions from natural gas and the removal of undesired low boiling fractions from crude oil.

Other and further objects of our invention will appear from the following description and the appended claims.

In the accompanying drawings which form part of the instant specification and are to be read in conjunction therewith and in which like numbers refer to like parts throughout the several views;

Figure l is a schematic showing of one form of renery or natural gas absorption stabilization system capable of carrying out the process of our invention.

Figure 2 is a schematic showing of one form of pressure distillate stabilization system capable of carrying out the process or" our invention.

Figure 3 is a schematic showing oi one form of a combination absorption-fractionation system capable of carrying out the process of our invention.

In general, we have provided a process by which the large volume of uncondensed wet gas incident to refinery absorption and fractionation systems are greatly diminished, with resultant economies or operation due to elimination of the usual recycling or reabso-rption operations and reduction in reboiling temperatures or distillation pressures.

We have accomplished this b-y eliminating, from the feed to the usual low pressure fractionator of the fractionation system or to the combined still and rectifier of the absorption system, those very light gaseous hydrocarbons which are normally uncondensable at the temperature of the available cooling water and the relatively low pressure existing in the low pressure tower. Such hydrocarbons are predominantly methane and ethane either alone, together, or admixed with propane and minor quantities of butane and heavier hydrocarbons. As a result of the elirnination oi the greater proportion or" these light constituents, the gases and vapors taken oi overhead -from the low pressure tower may be substantially completely condensed, or, as in the stabilization of crude oil, the percentage of uncondensed overhead products may be greatly den creased to provide the raw charging material for the high pressure iractionating tower, as well as reflux for the low pressure tower and the flash tower used to remove the lightest hydrocarbons. |The light hydrocarbons removed from the inaterial being passed to the low pressure tower, are subjected to fractionation with the charge to the high pressure fractionator when maximum gasoline recovery is desired. A condensate from the gaseous overhead products from the high pressure tower is returned thereto as reflux. The heaviest fraction of reflux condensate rorn the low pressure tower of the fractionation system is stabilized pressure distillate of low vapor pressure, ready for delivery to a treating step. The heaviest fractions from the low pressure towers in the absorption systems are the lean oils from which the natural or refinery gases have been distilled, The eaviest fraction of reiiux condensate from the high pressure iractionating tower in the fractionation and absorption systems, is a stable light gasoline of desired vapor pressure specifications for use as produced, or for blending with heavier gasoline for motor fuel.

More particularly referring now to Figure l, we have disclosed an absorption system for the recovery of stabilized light gasoline from natural, refinery, or gases from any suitable source, by the process of our invention. A gaseous mixture from the selected source containing methane and ethane and heavier hydrocarbons is fed through the line l to the bottom of an absorption tower 2 in which it rises upwardly and comes into intimate Contact with a suitable absorption oil flowing down the tower. Those gases which are not absorbed by the oil pass oli overhead through the residue gas line 3. The rich oil is withdrawn by means of a line 4 having a pump 5 and passes at relatively high pressure through a plurality of heat exchangers B in heat exchange relationship with hot lean oil returning to the absorption tower. The oil is further heated by passing through a heater 'i which is supplied with heating through a line il and removed through a line 9. The hot oil is delivered through the line 4a and valve 4b to a iiash distillation tower HJ, the pressure being controlled therein by valve Ha at from to 30D pounds per square inch, for example. This pressure and the ash tower temperature is so controlled as to cause most of the methane, ethane and propane, together with smaller amounts oi butane and heavier hydrocarbons to be volatilised from the rich cil and delivered as an overhead cut, together with vaporized reiiuX troni the flash tower, through the line El. The characteristics of this out may be controlled by means oi the fractionating trays I2 and reilux which is introduced at the top of the tower by inea-ns of the line i3 controlled by the valve i3d. The iiash tower i8 is provided with a plurality of bafes l2.

rl'he liquid product which accumulates in the base or the Flash tower and which now contains but a trn of methane and ethane caused to now iro'egh the line and the valve to a selected one of number of trays l5 located in a low pressure combined still and rectiier i6. It is to be understood that any desired number trays may be provided within the tower controlling the characteristics of the products to be removed f1 i. tower par cularly for preventing the passage of absorption oil vapors into the overhead pro lusts. tower for example, .normally main ai sure relately lower than th for example, a tower pres Direct steam eased with the tower will serve to strip, from absorption oil, the rein "ung absorbed hydrocarbons which, together with vaporized redux, are taken overhead through the line the vapors being partially condensed by means or the reiiutr condenser El, and delivered therefrom through the line 22 to a gasoline reflux accumulator This gasoline condensate is pumpe thro 13h e Zit l aving a pump to a suitable point in the rectifying portion of the tower l5 use as ensure that absorption oil vapors are fr back the tower. when direct steam ih for stripping and the top temperature tower SG is such that under its operating press-ure steam will condense, this steam co; may be separated from the liquid gasoline and withdrawn from tower i^ 3y line Ela. Steam not condensed in tower l is coxdensed in reflui; conde iser 2i, separatei from the r flux in accumulator 233 and withdrawn om by line 2da. unccnd sed vapors j products) from the accumulator 23 pas through the line 28 to a final condenser 2'? whe-re substantially complete condensation of the products st from the oil is ef ed at the temperature of the available cooling and at tl e pressure existing in the combined still and rectifier it, The condensate from the vapor condenser 2? is delivered through the line 28 to an accumulator 29. Those vapors which are uncondensed, the quantity of which will be comparatively negligible in accordance with the desired objects of our invention, will pass olf through the lines 3@ and 3i' to a fuel gas system or to a gas recovery system. The pressure on combined still and rectifier lli is controlled by valve 2da or valve Sila which controls thev pressure on accumulator 29.

The stripped lean oil from the bottom of the low pressure combined still and rectifier l is passed through the line 62 and heat exchangers 6 to the coolers G3 having cooling liquid inlet and outlet lines G5 and 65 respectively. The cooled lean oil is delivered through the line 6G to lean oil surge tank 6l from which it is pumped through a line 68 by pump S9 to the upper part of the absorption tower 2.

The raw unstable gasoline which is collected in the accumulator 29 is delivered through the line Si by a pump 32 to the branch lines i3 and 33. A small percentage of this raw feed is delivered, as previously' pointed out, through the line i3 to the ash tower lo for reflux purposes. The remainder of the raw feed is pumped through the line S3 and heat exchangers 3d, to a header 35 from which a plurality of valved feed lines 3%, 3l and 3s lead the raw gasoline to respective trays 3@ in the high pressure fractionator lill. At the same time, the overhead cut and vaporized reflux from the flash tower lll passes through the line ll to a header il from which one or all of valved feed lines 42, d3, and ld lead the vapors and gases to the trays 39 in the tower @53. Thus all or practically all of the absorbed constituents are delivered to the high pressure fractionator without the necessity of recycling relatively large volumes of wet gas consisting of constituents originally absorbed. At the higher fractionation pressures of from 150 to 300 pounds per square inch, for example, exis-ting within this tower, the overhead products will consist mainlyT of methane, ethane and propane with a controlled amount of butane, which pass through the line l5 to the reflux condenser llb. The resultant condensate (reflux) and uncondensed vapors are delivered through the line M to reflux accumulator llS from which reflux is returned by means of a line lil by a pump 5t to the upper portion of the fractionating tower 4l). Those gases (overhead products) uncondensed by the vapor condenser fl are delivered through the lines 5l and 3l to a fuel gas system. The pressure of fractionator Ml is controlled by valve 5ta.

The bottoms of the fractionator lll are delivered through a line 52 to a reboiler 53 to which steam or other heating medium is supplied by means of a line 5G and removed by a line 55. The vapors evolved in the reboiler 53 are returned to the fractionator through the line 56, the liquid products passing through line 5l and heat eX- changers 34 where a certain amount of the heat content is abstracted by the raw feed being delivered to the fractionator lill. The partially cooled fractionated product in line 5l is delivered to the cooler 53 which is provided with cooling liquid inlet and outlet means 5?) and Sil respectively. The relatively cool stabilized light gasoline may be delivered through the line 5l to storage.

Referring now more particularly to Figure 2, we have disclosed a system for fractionating raw pressure distillate and for recovering a stabilized light gasoline in which the pressure distillate is fed through a line la to a pressure feed tank 2a from which the residue gas leaves through the line 2b and valve 2c. The distillate is withdrawn from this tank through a line l, by pump 5 and passed through the heat exchanger S, heater l, line 4a and valve lo to the flash distillation tower IIJ equipped with a plurality of fractionating trays l2 and baies l2. This tower is operated at pressures, for example, between 150 to 300 pounds per square inch and will serve to remove from the distillate, as an overhead product comprising the major portion of the light hydrocarbon gases, methane, ethane and propane, with small amounts of butane and heavier hydrocarbons which are delivered with the vaporized reflux through the line l l and valve l la to a high pressure fractionator lil as will be more fully pointed out hereinafter, The unvaporzed products in the tower are delivered through the line lll controlled by a valve lll to a header lila from which a plurality of valved feed lines lilo, ille, and ldd lead respectively to the trays lsb, l5c, ld in a low pressure fractionating tower l. It is to be understood, of course, that any suitable number of trays necessary to accomplish the desired fractionation may be provided in the tower l, which may be provided with stripping steam inlet lla. The pressure in this tower will normally vary between 20 and 100 pounds per square inch, for example, depending upon the specifications desired in the bottom products. The overhead product from this tower will be substantially devoid of methane and ethane and, together with vaporized reflux, is removed through the line 2l] and passed to the reflux condenser 2l. Reflux condensate is delivered from the condenser 2l by means of a line 22 to a reflux accumulator 23 from which reflux is delivered by means of a line 24 by pump 25 to the upper part of the fractionator I6 for end point temperature control of the evolved vapors. The remaining uncondensed vapors, which are the overhead product, pass through the line 2S to the final condenser 2l where complete or substantially complete condensation of the vapors at the temperature of the available cooling water and the pressure existing in the fractionator l5 is effected. The raw unstable light gasoline is then delivered by means of the line 28 to an accumulator 29, the relatively negligible amount of uncondensed vapors, if any, passing off through the lines 3@ and 3l to a fuel gas system or, if desired, to a recovery system. The pressure on the fractionator l@ is controlled by valve 25a or by valve Sila which controls the pressure on the accumulator 30.

The raw gasoline from the accumulator 2S is delivered through the line 3l by a pump 32 to the branch lines i3 and 33. A small proportion of this raw gasoline is delivered through the branch line l 3 and valve 53a to the upper part of the ash tower l0 for reflux purposes. The remainder of the raw feed passes through branch line 33 and valve 33a and heat exchangers 3s to a header 35 having a plurality of valved feed lines 36, El, and 38, connected to trays 39 in a high pressure fractionator lll. Any suitable number of trays may, of course, be provided in this tower.

The overhead cut and vaporized reflux from the iiash tower l is delivered by means of the line Il and valve lla to a header il having a plurality of valved feed lines cl2, 43 and @lil leading to the trays 39 and the tower 4t. Thus all light gasoline constitutents are sent to the high pressure fractionator and there is no recycle. It is possible by suitable manipulation of these valves to deliver the feed to the high pressure fractionator to any selected tray of the group. The overhead product and vaporized reflux in the tower lil are removed through the line i5 and delivered to a vapor condenser dal from which the condensate formed flows through the line 4l to a reflux accumulator The liquid collected in this accumulator is returned through a line 49 by pump il to upper part of the tower 4G as reflux. The uncondensed vapors and gases (overhead product) in the accumulator 48 pass off through the lines til and 3l and valve 54a to the fuel gas system. The overhead cut from the tower il@ will normally be mainly methane, ethane, and propane with a controlled amount of butane.

The bottom product in the tower 4Q is delivered by means of the line 52 to a reboiler 53 to which steam or other suitable heating medium is supplied through line 5&3 and removed through line 55. Vapors evolved in the reboiler are returned to the tower lo through the line 5b, the final fractionated product being withdrawn through the line 5l, passed through the heat exchangers 35. and then delivered to coolers 58 having cooling water inlet and outlet means lill and 6@ respec tively. The cooled. stabilized light gasoline containing the desired amount of butano for vapor pressure specifications is then delivered to storage through the line 5 l.

The liquid bottoms in the low pressure fractionator ES are delivered by a line 520. to a reboiler B2b to which suitable heating medium is supplied through a line ll and removed through a line i9. The vapors evolved in the reboiler are returned to the tower through the line @2o. the unvaporized liquid, which is the stable pressure distillate, being delivered the line through the heat exchangers 5 and coolers 553 having cooling liquid inlet and outlet lines dll and 55 respectively. The cooled distillate leaves the coolers 53 through the line Sii and is led to a treating plant (not shown).

rlhe above illustrations of the application of our process consider butanes as the lowest boiling fraction desired in the recovered products. It is to be understood that the application is not limited in this respect. Constituents boiling lower or higher than butane may readily be recovered as the lowest boiling fraction in the finished products by suitable adjustment of. temperatures and pressures. It is also understood that the number of products and points of separation are not limited to those illustrated. The bottom products from the low and high pressure fractionators may be further separated into additional products in additional fractionating towers not shown. The overhead product from the high pressure fractionators v.av be totally or partially condensed and the condensate fractionated into additional produ-ots. These and other combinations are the scope of our process.

Referring now to Figure we have disclosed a combination absorption fraotionating system for the recovery of gasoline fractions from natural gas and removal of undesired low boiling fractions from crude oil.

Crude oil containing natural gas as it comes from the well, enters through the line la into the usual field separators 2a., one of which is shown, where the gas is separated and passed through the line 2b and valve Ec to an absorber 2 where an absorption medium, in this case stabilized crude oil introduced through line 68 and valve Edo, extracts the gasoline components from the gas.

The volatile, unstable crude oil leaves the separator 2a through the line 2d and valve 2e and is pumped by pump 2f into the line 4 where it is joined by and admixed with the rich absorption oil pumped by the pump 5 from the absorber through the line 4. The mixture passes through heat exchangers 6 where it is heated by the hot stable crude oil flowing through the line 62 and, if desired, is further heated in a preheater 'l having heating liquid inlet and outlet lines 8 and 9 respectively before passing through line lla and valve "lb to the flash distillation tower l0.

The temperature of the mixture and pressure of the ash tower I9 are so regulated that a large portion of the propane and lighter constituents, together with some butanes and heavier, contained in the mixed feed are vaporized. End point temperature control of overhead vapors is generally not cfgreat importance but may readily be regulated by use of reflux and rectifying plates I2 above the flash section.

The bottoms from the flash tower pass through the line i4 to a header Ma having the valved branch lines lllb, |40 and Nid connected respectively to the trays I5b, 50 and ld of the crude oil fractionating tower I6 where propane and lighter fractions, together with practically all of the butane and lesser amounts of pentane and heavier, are taken overhead. Vaporized reflux, which is a condensate approaching substantial equilibrium with the overhead cut, also passes overhead. The total vapors leave the tower I6 through the line 2Q and pass through a reflux condenser 2l and line 22 into an accumulator 23 from which reflux is pumped back to the tower through a line 24 by means of a pump 25. The uncondensed gases (overhead cut) pass through line 2B and valve 25a to a final condenser 21 and thence through line 28 to an accumulator 29. In most cases complete condensation of the overhead cut cannot be obtained at the condensing temperature and pressure available. However, the absence of light fractions eliminated in the ash tower greatly increases the amount condensed. Uncondensed vapors may be sent through line 'I4 and valve 15 to fuel gas main 'Il or, if at a pressure greater than that on the main absorber 2, returned to this absorber through line 30, valve Sla, recycle line 69' and valve 13 for extraction of gasoline constituents. If their pressure is below that of the main absorber a separate reabsorber (not shown) may be used to process these vapors.

The bottoms of the crude fractionator leave through line 62a, valve B2b, and are pumped by pump 52e through a convection heated coil 62d and radiant heated coil 62e for reboiling in a furnace heater 621 which may be fired by residue dry gas or other suitable means by means of burners lll and H8. A furnace is generally desirable in order to effect a high reboiling temperature (400-600 F.) for example, at the base of the column and in turn develop as high a pressure as practicable. The higher this pressure, of course, the more complete the condensation of the overhead cut will be as previously pointed out.

The bottom product of the crude oil fractionator leaves through the line 62 and passes in countercurrent heat exchange with the mixed feed in exchangers 6 and then passes through the coolers Gli having cooling liquid inlet and outlet means S4 and E5 respectively. The cooled oil leaves through the line 68, a portion of the cooled stable crude oil passing through valve 66d and line 66o being withdrawn for use as absorption medium. This oil is delivered to the surge tank 6l from which it leaves through line 58 and is pumped by pump 69 through valve 68a into absorption tower 2. Small amounts of pentane and heavier fractions still remaining in the stable crude oil used as absorption medium will be vaporized and pass olf with the residue gas through the line 3 and valve 3a to the residue gas main ll. The quantity of gasoline constituents lost in this manner, however, will be far less than the amount absorbed from the wet gas and the net gain makes this step advantageous. If desired, a portion of the stable crude oil may be further fractionated, in towers not shown, to obtain a more suitable absorption medium and thus eliminate the losses to the absorber residue gas. In this case the rich oil may be processed in a conventional distillation unit or as already described.

The condensate collected in the final accumulator 29 is pumped by pump 32 from the line 3l through valve 33a and line 33 to join and be mixed in line H with the overhead products and vaporized reflux leaving the flash tower through the line I l. A portion of the condensato is returned through line i3 and valve l3a to be used as reiiux for the ash tower I0. The mixed condensate and flash tower vapors pass through the line Ii to a condenser 33h having cooling liquid inlet and outlet lines 33h" and 33h' respectively and thence through line 33o to accumulator 33d which is held at a pressure somewhat below the flash tower pressure. In this manner the major portion of absorbed gasoline fractions and components fractionated from the inlet crude oil are subjected to condensation at a pressure much higher than could readily and practicably be obtained by reboiling the stable crude,

Uncondensed gases and vapors leave this accumulator through line 5l and valve 68 but will be relatively small in amount and may be sent to the residue gas main 'H through valve 'I2 or returned to the main absorber 2 through line 69 and valve 1D or processed in a high pressure reabsorber not shown.

If reabsorbers are used, rich oil therefrom may be processed similar to the rich oil from the main absorber.

If desired, the flashed vapors and crude fractionator overhead condensate may be sent directly to the high pressure fractionator It!! as is shown in Figures 1 and 2.

In Figure 3, the high pressure accumulator 33d serves as a feed tank for the high pressure fractionator 55. The condensate accumulated in the feed tank leaves through the line 33e and valve 33j and is pumped by pump 33g through line 33h and heat exchangers 36 to a header 35 from which the

valved branch lines

36, 3l and 38 lead to selected trays 39 of the high pressure fractionator 45.

Propane and lighter constituents together with some butane if desired, are cut overhead, and together with vaporized reflux, leave through the line 45, pass through the refiux condenser i5 having cooling liquid inlet and outlet lines IE6 and 55" respectively, the condensate then passing through the line il to reflux accumulator 48. Reflux is returned to the tower i0 through the line @Si by the pump 55. The uncondensed gases (overhead cut) will be permitted to escape through the line 5l and valve 54a of the reflux accumulator 48.

The bottom product of the fractionator t5 will consist mainly of butane and heavier fractions. This product passes from the fractionator to a reboiler 53 through a line 52. Steam or other heating medium is admitted to the reboiler through the line 5@ and is removed through the line 55. The vapors evolved are returned to the fractionator 45 through the line 55. The unvaporized bottoms in the reboiler leave through the line 5l', pass thrcugh the heat exchangers 34 and coolers 5S, the latter having cooling liquid inlet and outlet lines 59 and EU respectively, being iinally removed as stable light gasoline through the line i5 If desired, this light gasoline bottom product may be blended with the stable crude and the mixture sent to the refinery. The straight run gasoline produced from this crude will be stable since propane and lighter fractions are not present.

In the processing of a low specific gravity crude in the apparatus arrangement of Figure 3, the oil may issue from the well at a rock pressure of, say for example, 75 pounds per square inch. In such a case, the absorber 2 would be operated at a pressure of from 65-70 pounds per square inch, the Flash distillation tower it at a pressure of 200 pounds per square inch, and at a temperature of about 500 F., the primary low pressure fractionator at a pressure of about 80 pounds per square inch with the reboiling temperature of the bottoms about 550 F. and with the primary final condenser Zl' and accumulator 29 at a pressure of about 75 pounds per square inch to permit the return of the uncondensed gases to the absorber if it is so desired. The high pressure fractionator 48 operates at a pressure of about 265 pounds per square inch with the reboiling temperature of the bottoms around 345 F. The vapor condenser 33h and accumulator feed tank 33d interposed between the ash tower I5 and high pressure fractionator ill operate at a pressure of about 185 pounds per square inch.

The recital of pressures and temperatures is not to be considered as limitative and should be construed as by Way of example only, since it will be obvious to one skilled in the art that the operating pressures and temperatures will be determined by the character of the material being processed and the specifications desired in the products resulting therefrom.

It will be seen from the above description that our process may be used to stabilize crude oils and at the same time extract natural gasoline from natural gas. The extraction step, however, is not necessary in the accomplishment of the crude stabilization step.

It will be observed that we have accomplished the objects of our invention and provided a process by which large volumes of uncondensed wet gas usually incident to refinery absorption and fractionation systems are greatly diminished or eliminated with resultant economies of operation due to elimination of the usual recycling or reabe sorption operations.

It is also evident that our process has a wide range of application and it is understood that we are not limited to those described. Additional steps may be added to the process without departing from the spirit of the invention as defined by the appended claims. Cold vents, additional ashes, absorptions, fractionations, and/or distillations may be incorporated in various combinations and sub-combinations.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of our claims Without departing from the spirit oi our invention. It is,

thereiofe, to be understood that our invention is not to be limited to the speciic details shown and described.

Having claim is:

l. il process for recovering a stable light gasoline from a raw p'essure distillate comprising hashing the distillate o remove substantially all hydrocarbons having less than three carbon atoms per molecule, iractionating the balance of the distillate at a lower pressure, removing from the fractionation zone a liquid fraction composed mainly of hydrocarbons having more than iive carbon atoms per molecule, separately removing from the fractionation Zone vapors composed mainly of hydrocarbons having more than two and less than seven carbon atoms per molecule, substantially completely condensing the vapors, iractionating the condensate and the vapors i 'om the sh zone in second fractional-ing zone or" higher pressure, removing from the second fractionating zone hydrocarbon vapors having mainly less than for carbon atoms per molecule and separately removing *rom the second fractionation cone a stable light gasoline composed of hydrocai-bons having mainly more than three carbon atoms per molecule.

2. A process for stabilizing crude hydrocarbon oils containing relatively large percentages of low bo' g gasoline and lighter gas fractions, coming separating the crude oil into a iirst dislate traction and a crude oil residue, subjecting the crude oil residue to a iractionating at a lower pressure and removing as products thereof a second distillate vapor traction and a stabilized crude oil, said second distillate vapor Fraction by reason ci said separating operation. substantially7 completely condensable at ure no higher than that at which said fracng operation is conducted and at normal atmosph ic ter erature, condensing the second distillate vapor fraction, fractionating the vapor condensate with the iirst distillate vapor fraction at a higher pressure than that at which said first iractionating operation is conducted and removing a stable light fuel as a product of the last mentioned fractionating operation.

3. An absorptionfractionation process for stabilizing crude hydrocarbon oil and simultaneously recovering a stabilized motor fuel from natural gas in the oil comprising separating Wet gas lrom the crude oil, subjecting the Wet gas to an absorption operation with a lean absorption oil, subjecting the rich oil resulting -troni the absorption operation together with the crude oil from which the wet gas Was separated to vapcrizing conditions oi temperature and pressure suilicient to vaporize relatively low boiling hydrocarbons of the combined oils, separating oil vapors formed from the resulting liquid residue, subjecting the liquid residue resulting fr he vaporizing operation to a iracticnating operation, recovering as products of the iractiona g operation a stabilize-L crude oil distillate vapors, said distillate vapors being by reason oi said initial separating operation substantially completelycondensable under a pressure no higher than that at which fractionating operation is conducted and at normal atmospheric te ature, cooling the distillate vapors to substantially completely condense said vapors and thereby form a vapor condensate, admixing said condensate with the first mentioned oil Va- .ls described our invention, what We than tha the first fractionating operation and recoverin as a product of said last mentioned iracticna ^on operation a stabilized motor fuel.

4. The A recess or claim 3 in which a portion of the stabil ed crude oil from the rst fractionating operation is passed in an elongated confined stream e. heating zone and returned to the fractionating operation.

5. A process for recovering a desired liquid hydrocarbon product from refinery or natural gas ssure distilling the remaining constituents from the oil, fractilled constituents to recover vaabscrption oil, condensing the vapors, v resultant condensate at a higher pre the constituents flashed from the abs rp n-n cil recoverinfy the desired hydroca'bon liquid product as a product of the last named fractionating operation.

6. The process of claim 3 in which a portion of densate condensed from distillate cts of the first fractionating operation as reflux in the vaporizing operation fractionating operation for end ature control of oil vapors produced i tion-ating operation.

7. The pre se ci claim 3 including the step of er l ying sta Zed crude oil recovered as a product of the first mentioned iractionating operation s oil the absorption operation.

8. In a process wherein a hydrocarbon mixture including gasoline-like hydrocarbons is fractionin a .first iractionating zone to separate the heavier from the lighter hydrocarbons of the mixture, and wherein certain oi said lighter hydrocarbons are then fractionated in a higher pressure fractionating zone to recover a stabilized light motor fuel; the improvements comprising removing such a portion of the lighter hydrocarbons from the mixture before the iirst fractionating step is performed that hydrocarbons uncondensed by the first iractionating operation are substantially completely condensable under a pressure no h er than exists in said rst iractionating zone and at normal atmospheric temperature, then performing said rst fractionating operation on the balance only of said mixture, and, subjecting the initially removed portion of lighter hydrocarbons to fractionation in the higher pressure fractionating zone with the lighter hydrocarbons from the irst iracticnating zone.

9. A process for obtaining a stabilized light liquid product of desired vapor pressure from a liquid having higher vapor pressure comprising heating the liquid at a pressure substantially above atm @sph-eric, causing the heated liquid to be ias red into a rst vapor fraction and a rst liquid traction each having a vapor pressure higher than that of the desired product, iractionating only the rst liquid fraction and recover'lig as products of the fraotionating operation a second vapor fraction of higher vapor pressure than that or the desired product and a second liquid fr ction of lotver vap i' pressure than that of the desired product, said second vapor fraction being by reason ci said dashing operation substantially completely condensable at a normal temperature under substantially the pressure at which said fractionating operation is carried out, continuously removing the second liquid fraction from the process, substantially completely condensing the second vapor fraction without increasing the pressure thereon, subjecting condensate resulting to fractionation at a higherpressure, subjecting the rst vapor fraction to the higher pressurek fractionation with condensate obtained from the seoond vapor fraction, and recovering as a product of the last named fractionating operation the stabilized light liquid product of desired vapor pressure.

10. A process for recovering a narrow boiling range hydrocarbon fraction from a hydrocarbon fraction of relatively wider boiling range comprising introducing the hydrocarbon fraction of relatively wider boiling range as a liquid under pressure into a flash zone wherein it is ashed under reduced pressure to thereby create under the temperature and pressure conditions therein a iirst liquid residue and a first vapor fraction, separately removing the fractions from said flash zone, subjecting only the residue liquid of the flashing operation to fractionation in a fractionation zone Y of lower pressure than the flash zone to secure a second liquid residue and a second vapor fraction, said second vapor fraction being by reason of said flashing operation substantially completely condensable at the pressure existing in the fractionating zone and at normal atmospheric temperature, substantially completely condensing the second vapor fraction, returning a portion of the condensate from the second vapor fraction to the flash zone as reflux, subjecting a major portion of .the condensate to fractionation in the second fractionating zone of relatively higher pressure than that in the first fractionating zone, introducing the rst vapor fraction into the second fractionating zone, separately removing the uncondensed vapors and the desired narrow boiling range hydrocarbon fraction from the second fracl1. In a process wherein a hydrocarbon liquid comprising normally liquid and normally gaseous hydrocarbons is operated on under a relatively low pressure in a primary stabilizing zone to obtain a stabilized heavy liquid fraction and a relatively light fraction comprising the more volatile hydrocarbons and wherein said light fraction is thereafter cooled and resultant condensate operated on under a relatively high pressure in a secondary' stabilizing zone to obtain a stabilized light liquid fraction; the improvement comprising the steps of ashing said liquid prior to said primary stabilizing operation under conditions of temperature and pressure effective to free said liquid of such a portion of its excessively volatile constituents that the light fraction when obtained as aforesaid will be substantially completely condensable when cooled under a pressure no higher than that pressure under which said primary stabilizing operation is conducted, with cooling liquid at a normal temperature, carrying out said ashing operation under a pressure higher than that pressure under which said secondary stabilizing operation is carried out and operating on the portion freed from said liquid by said flashing operation in said secondary stabilizing zone to recover therefrom desired constituents thereof as a part of said stabilized light liquid fraction.

l2. The process of claim wherein the distillation operation is carried out at a temperature and pressure such as will permit substantially complete condensation of the distilled vapors at the temperature of the available cooling water.

PAUL D. BARTON. KARL FINSTERBUSCH. NATHANIEL M. FLOYD.