US2982722A

US2982722A - Method of controlling dephlegmation

Info

Publication number: US2982722A
Application number: US692702A
Authority: US
Inventors: Malcolm D Gish
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1957-10-28
Filing date: 1957-10-28
Publication date: 1961-05-02
Anticipated expiration: 1978-05-02

Description

y 2, 1961 M. D. GISH 2,982,722

METHOD OF CONTROLLING DEPHLEGMATION Filed Oct. 28, 1957 I ll l2 l8 GASOLINE i vAPoRs 8 IO 1 4 .YTPFZ .9 l 2 7 I I J n I L' 1 I VAPORS FROM WATER 25 2 BOILING,

WAT ER 1 INVENTOR. M D. G IS H BY W ,4

United States Patent C METHOD OF CONTROLLING DEPHLEGMATION Malcolm D; Gish, Bartl'esville, Okla assignor to Phillips Petroleum Company, a corporation of Delaware Filed Oct. 28, 1957, Ser. No. 692,702

2 Claims. (Cl. 20834'1) Thisinvention relates to a dephlegmator control and.

method. In one of its aspects, the invention relates to a method and means for. the recovery of hydrocarbon or gasoline vapors such as natural gasoline vaporsfrom an absorber oil by dephlegmating said vapors in a tower employing a reflux stream fed to the top of saidtower responsive to the temperature at the top of said tower, measuring the vapor pressure of at least a-portionof the kettle product from said tower and resetting the com trol of the reflux stream responsive to said-vapor pres sure. In another of its aspects, the invention provides means and method substantially as described wherein kettle bottoms are removed, passed through a'temperature' adjusting Zone constantly maintained at a given liquid;

level in a vapor pressuresensing zone following which;

the vaporpressure is used to reset the tower'top tem perature I control. 1

Since this invention is particularly adapted to the recovery of natural gasoline vapors, it will'be' described in connection therewith.

It is now knownto dephlegmate gasoline containing vapors obtained from a stripping still in which the gasoline. is stripped from an absorber oil. The vapors unavoidably' containsome absorber oil. Also,'due to variation in conditions or compositions offeed, the stripper efiluent' vapors vary in composition from time'to time. This results either in removing overhead withgasoline vapors from the .dephlegmator, absorber oil which then constitutes a loss of oil from the system, or in returning. with the-dephlegmator oil bottoms to the stripper fornre' use as a lean oil which is so rich in gasoline to reduce materially the throughput ofthe stripper.

It has occurred to me that the vapor pressure: of the absorber oil willva'ry quite readily detectably with variationsin the still vapors fed .tothe dephlegmator, Further, it has occurred to me that detecting's'aid vaporpressure will permit control of the dephlegrnator' tower top temperature responsive. .tolsaid vapors which in turn will; avoid loss of absorber oil overhead with the gasoline or" return of gasoline with the absorber oil bottoms to .the

stripper. j r I It is an object of this invention to provide an improved dephlegmator control and method. It is another object of this invention to'provide an improved methoda'nd.

apparatus for recovery of hydrocarbon vapors such asnatur-al gasoline vapors from an absorber oil. Otheraspects, objects and'the several advantages of I this invention are apparent'fro'm a studyof this disclosure,

the drawing and the appended claims.

According to this invention, there are provided a meth- 2,982,722 Patented May 2, 1961 a strippingstill containing some absorber oil unavoidably 6, cooling condenser 7 and through valve control pipe 8' to spray 9 in the top of the tower a controlled amount of water. Thus, valve 10 in pipe 8 is controlled by temperature recorder controller 11,'which in turn is responsive to thetower top temperature detected at 12 and to the control of the invention.

According to the inventionthe oil phase at the foot of the dephlegmator is removed byway of pipe 13 and passes in part by way of pipe 14 into vapor pressure detecting device 15. The remainder of the oil phase is returned by way of pipe 16 to the stripper. still. Also, water is withdrawn from dephlegmator 2 by way of pipe 17 and gasolinevapors are taken overhead byfpipe 13. Returning now to vapor pressure detecting device 15, the oil. phase enters cooling coil 19 and passes into the top ofchamber 20 wherein the liquid level is maintained 7' byway of controller 21 and valve 22 in pipe 23. Still another heating coil 24 is provided for temperature adjustment. It is advantageoustoadjust the temperature of the oil in vessel 20 to theboiling point of water. To

thisend, boiling water or water. near its boiling pointis introduced into the space surroundingcoilw by way of.

pipe 25. By adjusting amounts of water and/or steam introduced, the temperature of thevapor in, space 20 can bezrnaintained constant. Temperature controllers are advantageously employed for this purpose. Temperaturerecorder-controller "-31" responsive to temperature sensing.

, operatively connected to-vapo12spaceZ0 passes a. signal by way of pipe-27 to temperature recorder. controller 11 to reset the same to maintaina tower top temperature responsive to-the detected vapor pressure. 7

While the .vapor pressure detectingarrangement, which hasbeen shown is that which is now preferred, it will be i 4 obvious to those skilled in theart in possession of'this disclosure that. other means can beemployed to detect the vapor pressure of the oil phase'leaving column 2 andtolreset the reflux to the top of the tower, and, there- .fore, the tower top'tem'perature is responsive to said vapor 7 pressure, according tothe invention. v

, The system isioperated so that only traces of lean oil will appearinthe overhead gasoline vapors taken off in pipe 18. 'Theamount of leanoil inthevaporsin pipe .18 can be determined by a suitable means or method;

0d, and means, for recovery ofvapors from an ab'sorber g oil which comprises passing vapors containing some'of a said absorber oili into a dephlegmator or-r fract-ionation A simple; manner oi detection involved is'an Engler type distillation which-results in a residue oi lean oilwhich can be readily measuredf Sincefonly traces of leanv .oil. are

to befound in; the overhead vapors leaving'by way ofpipe 18, it is preferred tjo""operat'e' v the inventionso thatthere column, controlling a, .reflu x to the top of said column responsiveto the temperature at the top of said column, detecting the vapor pressure of absorber oil bottoms, from said column and resetting the-control ofthegtower top.

will'be only traces of lean, oil visible'in the fiask pthug avoidiiigactual measurementlof lean oilQin the flask, "Furthermore, ,20 is maintained constant, thus, when the vapo of the hydrocarbons in chamber 20 increas he po p sur n a sher tolerable amount, controller 26 will reset controller '11 to decrease cooling water entering dephlegmator 2 at 9, thus, to take overhead more gasoline vapors, in effect lowering the vapor pressure of the oil finding its way to If at any time during operachamber 20 and vice versa. tion it is found that gasoline vapors condensed from pipe 18 contain an undesirable amount of lean oil, controller 13 is readjusted to maintain an oil vapor pressure in vessel or chamber 20 and vice versa if insufficient gasoline is being recovered overhead through pipe 18.

Usually the pressure in chamber 20-will be above atmospheric, in which event, oil removed by way of valve 22 and pipe 23 to tank 23 and flows through pressure drop tank 28 being maintained at atmospheric pressure. Oil from tank 28 is removed by way of pipe 29 and controlled by valve 30. This oil can be returned for further use to absorb gasoline. If, for any reason, it is desired to operate chamber 20 below atmospheric pressure, tank 28 will be operated at a pressure lower than that of the pressure to be maintained in chamber 20.

Under ordinary conditions the vapor pressure maintained in chamber 20 can vary from as low as 10 to as high as 50 pounds per square inch absolute. The actual vapor pressure which will be maintained in chamber '20 will, of course, depend upon factors extant in the operation but is to an extent subject to control of the operator since conditions can be changed by maintaining some what different temperatures and pressures at various places in the operation. 7

Although the invention has been described with respect to the recovery of natural gasoline from absorber oil vapors with which it is admixed, it will be obvious to one skilled in the art in possession of this disclosure that the modusoperandi, which is a physical one, is applicable to other vapor recovery or fractionation systems.

Specific example The following operational data are given in connection with the operation of a low pressure dephleg'mator operated in conjunction with a combination of high and low pressure streams.

2. Dephlegmator Top 165-185 ill-45 p.s.i.g.

18. Gasoline v a p o r s overhead 288 mols water per day: 3240 mols hydrocarbons per day;

combined specific gravity 2 at 60 F.; 160-45 p.s.1.g. 7. V a p o r s to dephlegmator 7,748 mols hydrocarbons per day; 29.744 mols water per day; 380 11- -50 p.s.i.g.

16. Condensed Hydrocar- .bons 4,498 mols per day279 F.

4. Reflux water out of dephlegmator 260 F.385 g.p.m.

9. Reflux water into de- 14. 1/2 gallon minute. I

closure have been shown.v Likewise, the omission of an element vwhich oneskilled in the artmight include in an actual unit does not mean that sucks. piece of equipment is intended to be omitted simply because it does not appear in the drawing. .Sufiice to say, the drawing is for illustrative purposes as is the, description thereof.

1 .Reasonable variation and modification arefp'ossible within the scope ,of the foregoing disclosure, drawing,

and the appended claims to the invention, the essence of which is. that avapor recovery or fractionation'tower overhead temperature is controlled responsive to the vapor pressure ofat least a portion of the kettle'product' substantially, as set'forth and described herein.:

I-clai rnzf v 1 1. Airiethod-for recovering a-maxlmum amounto-f by said mixture of vapors and entrained absorber oil, I

gasoline, and removing absorber oil, from a mixture of gasoline vapors and entrained absorber oil unavoidably entrained when said vapors are stripped in a stripping zone from a gasoline component-rich absorber oil obtained in the recovery of natural gasoline, which comprises feeding said mixture of gasoline vapors and entrained absorber oil to a dephlegmation zone heated only condensing in said dephlegmation zone some gasoline component and absorber oil, refluxing said dephlegma tion zone with water, removing from said dephlegmation zone at the top portion thereof gasoline vapors from which entrained absorber oil has been removed, collecting in said dephlegmation zone, at a point substantially removed from the top portion thereof at which gasoline vapors are removed, water which has been introduced into said dephlegmation zone, passing at least a portion of said water to the top portion of said dephlegmation zone as reflux therefor, controlling the temperature of the gasoline vapors removed from the top portion of said dephlegmation zone by, in a controlling zone, .con-

1 said .dephlegmation zone, at a point substantially re;

trolling the reflux introduced into the top portion of said dephlegmation zone responsive to said temperature, thus while keeping the temperature of the gasoline vapors exiting from the top portion of said dephlegmation zone at a constant level permitting the temperature of liquid collecting in the bottom portion of said dephlegmation zone to vary, removing at least a portion of said liquid collecting in the bottom portion of said dephlegmation zone, passing the removed liquid to a vapor pressure sensing zone, in said vapor pressure sensing zone adjusting the removed liquid passed thereto to a constant predetermined temperature, sensing the vapor pressure of the l1qu1d in said vapor pressure sensing zone at said con stant predetermined temperature, relaying a signal corresponding to said sensed vapor pressure to said controlling zone and resetting the controlling zone to control the temperature of the gasoline vapors removed from the top of said dephlegmation'zone so as to maintain the vapor pressure of said removed liquid, when sensed at said constant predetermined temperature, at a constant predetermined value, thereby removing from the mixture of gasoline vapors and absorber oil, a maximum amount of gasoline so that absorber oil returned to the recovery of natural gasoline will have a maximum capacity for recovering additional components of gasoline and ultimately a maximum amount of gasoline is recovered from both the gasoline recovery system and the dephlegmation zone.

2. A method for recovering a maximum amount of vapors and removing absorber medium from a mixture of vapors and enrtained absorber medium, unavoidably entrained when said vapors are-stripped in a stripping zone from a'vapor-rich absorber medium which comprises of said mixture of vapors and entrained absorber medium. 'therein, refluxing said dephlegmation zone with a portion of the liquid: therein, removing from said dephlegmation zone, at the top portion thereof vapors from which entrained absorber medium has been removed, collecting in moved from the top portion thereof at which vapors are removed, liquid which has, been introduced into said dephlegmation zone and which hasbeen obtained as stated herein, passing at least a portion of said liquid to the top portion'of said dephlegmation zone as reflux therefor, controlling the temperaturenf'the vapors removed from the top portion of said dephlegmation zone by, in a controlled zone, controlling the reflux introduced into the top portion of said dephlegmation zone responsive to said temperature, thus while keeping the temperature of the vapors exiting from the top portionio-f said dephlegmation zone at a, constant level permitting the temperature of 'the liq- 5 uid collecting in the bottom portion of said dephlegm'ation zone to vary, removing at least a portion of the liquid collecting in the bottom portion of said dephlegmation zone, passing the removed liquid to a vapor pressure sensing zone, in said vapor pressure sensing zone adjusting the removed liquid passed thereto to a constant predetermined temperature, sensing the vapor pressure of the liquid in said vapor pressure sensing zone at said constant predetermined temperature, relaying a signal corresponding to said sensed vapor pressure to said controlling zone and resetting the controlling zone to control the temperature of the vapors removed from the top of said dephlegmation Zone so as to maintain the vapor pressure of said removed liquid, when sensed at said constant predetermined temperature, at a constant predetermined value, thereby removing from the mixture of vapors and absorber medium a maximum amount of vapors so that the absorber medium removed from the dephlegmation zone Will have a maximum capacity for recovering additional absorbable vapors so that ultimately a maximum amount of vapor is recovered from both a vapor recovery system using said absorber medium and the dephlegmation zone.

References Cited in the file of this patent UNITED STATES PATENTS 1,743,568 Price Ian. 14, 1930 1,940,802 Kallam Dec. 26, 1933 1,940,803 Kallam Dec. 26, 1933 2,273,412 McCullogh Feb. 17, 1942

Claims

1. A METHOD FOR RECOVERING A MAXIMUM AMOUNT OF GASOLINE, AND REMOVING ABSORBER OIL, FROM A MIXTURE OF GASOLINE VAPORS AND ENTRAINED ABSORBER OIL UNAVOIDABLY ENTRAINED WHEN SAID VAPORS ARE STRIPPED IN A STRIPPING ZONE FROM A GASOLINE COMPONENT-RICH ABSORBER OIL OBTAINED IN THE RECOVERY OF NATURAL GASOLINE, WHICH COMPRISES FEEDING SAID MIXTURE OF GASOLINE VAPORS AND ENTRAINED ABSORBER OIL TO A DEPHLEGMATION ZONE HEATED ONLY BY SAID MIXTURE OF VAPORS AND ENTRAINED ABSORBER OIL, CONDENSING IN SAID DEPHLEGMATION ZONE SOME GASOLINE COMPONENT AND ABSORBER OIL, REFLUXING SAID DEPHLEGMATION ZONE WITH WATER, REMOVING FROM SAID DEPHLEGMATION ZONE AT THE TOP PORTION THEREOF GASOLINE VAPORS FROM WHICH ENTRAINED ABSORBER OIL HAS BEEN REMOVED, COLLECTING IN SAID DEPHOLEGMATION ZONE, AT A POINT SUBSTANTIALLY REMOVED FROM THE TOP PORTION THEREOF AT WHICH GASOLINE VAPORS ARE REMOVED, WATER WHICH HAS BEEN INTRODUCED INTO SAID DEPHLEGMATION ZONE, PASSING AT LEAST A PORTION OF SAID WATER TO THE TOP PORTION OF SAID DEPHLEGMATION ZONE AS REFLUX THEREFOR, CONTROLLING ZONE, CONTHE GASOLINE VAPORS REMOVED FROM THE TOP PORTION OF SAID DEPHLEGMATION ZONE BY, IN A CONTROLLING ZONE, CONTROLLING THE REFLUX INTRODUCED INTO THE TOP PORTION OF SAID DEPHLEGMATION ZONE RESPONSIVE TO SAID TEMPERATURE, THUS WHILE KEEPING THE TEMPERATURE OF THE GASOLINE VAPORS EXITING FROM THE TOP PORTION OF SAID DEPHLEGMATION ZONE AT A CONSTANT LEVEL PERMITTING THE TEMPERATURE OF LIQUID COLLECTING IN THE BOTTOM PORTION OF SAID DEPHLEGMATION ZONE TO VARY, REMOVING AT LEAST A PORTION OF SAID LIQUID COLLECTING IN THE BOTTOM PORTION OF SAID DEPHLEGMATION ZONE, PASSING THE REMOVED LIQUID TO A VAPOR PRESSURE SENSING ZONE, IN SAID VAPOR PRESSURE SENSING ZONE ADJUSTING THE REMOVED LIQUID PASSED THERETO TO A CONSTANT PREDETERMINED TEMPERATURE, SENSING THE VAPOR PRESSURE OF THE LIQUID IN SAID VAPOR PRESSURE SENSING ZONE AT SAID CONSTANT PREDETERMINED TEMPERATURE, RELAYING A SIGNAL CORRESPONDING TO SAID SENSED VAPOR PRESSURE TO SAID CONTROLLING ZONE AND RESETTING THE CONTROLLING ZONE TO CONTROL THE TEMPERATURE OF THE GASOLINE VAPORS REMOVED FROM THE TOP OF SAID DEPHLEGMATION ZONE SO AS TO MAINTAIN THE VAPOR PRESSURE OF SAID REMOVED LIQUID, WHEN SENSED AT SAID CONSTANT PREDETERMINED TEMPERATURE, AT A CONSTANT PREDETERMINED VALUE, THEREBY REMOVING FROM THE MIXTURE OF GASOLINE VAPORS AND ABSORBER OIL, A MAXIMUM AMOUNT OF GASOLINE SO THAT ABSORBER OIL RETURNED TO THE RECOVERY OF NATURAL GASOLINE WILL HAVE A MAXIMUM CAPACITY FOR RECOVERING ADDITIONAL COMPONENTS OF GASOLINE AND ULTIMATELT A MAXIMUM AMOUNT OF GASOLINE IS RECOVERED FROM BOTH THE GASOLINE RECOVERY SYSTEM AND THE DEPHLEGMATION ZONE.