US2246934A

US2246934A - Fractional distillation

Info

Publication number: US2246934A
Authority: US
Inventors: Courtlandt F Denney
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1938-11-26
Filing date: 1938-11-26
Publication date: 1941-06-24
Anticipated expiration: 1958-06-24

Description

June 24, 1941. c, F DENNEY 2,246,934

FRACTIONAL DISTILLATI 0N CHARGE INVENTOR COI/ETLA/VT E/WVEY control, and means for carrying out Patented June 24, 1941 FRACTIONAL DISTILLATION Y Courtlandt F. Denney, Westfield, N.

to Foster Wheeler Corporation, N. Y., a corporation of New York I., assignor New York,

Application November '26, 193s. serial No. 242,464

12 Claims.

This invention relates to the fractional distillation of composite liquids such as hydrocarbon oils and the like, and more particularly pertains to the control of fractions obtained from such liquids.

The present invention provides va method of the method, which will function to maintain side streams or intermediate fractions as definite percentages of the charge regardless of variations in the throughput or of variations in the temperature of the charge or of variations in the steam usedv in the tower, so long as thecharge contains the components of said intermediate fractions in vapor or in vaporizable form under the operating conditions present.

This application ferred form of apparatus embodying and employing the invention, and

Fig. 2 is an enlarged view showing diagrammatically one of the ratio flow controllers and its connections.

able pockets ory depressions 24. The heaviest l is a continuation-in-part of application Serial No. 19,636, filed May 3, 1935.

The invention will be disclosed in connection with the control of side streamsA or intermeacter IIJ designates a tube still having a furnace l II, a bank of convection tubes I2 and a bank of roof tubes I3. The charging stock is introduced through line I4 and afterpassing through the tube banks I2 and I3 is Aconducted through transfer line I5 into the lower portion of a fractionating tower I6 provided with a plurality of superposed bubble trays, or the equivalent, I1. Superheated steam is introduced intov the bottom of the tower through a perforated steam coil I8. The lightest fraction is withdrawn overhead in vapor form through line I9 and part of the condensate of the overhead vapors is returned to the top of the tower through une zo vasI reux. Side streams are withdrawn from fraction or bottoms is withdrawn from the bot` tom of the tower through line 25. The specifications ofthe overhead fraction are controlled rby a temperature controller preferably of the Foxboro throttling reset type manufactured by the Foxboro Company of Foxboro, Massachusetts, the essential features of which are disclosed in Mason Re. Patent 20,092, granted September 1, 1936. This includes a thermostat 26 responsive to the temperature of the vapors leaving the top of the tower which operates a controller 21 to control the pressure of air delivered to pipe 28 through pipe 29 for operating a motor valve 30 in the reflux line 2l).- The ,operation is such that as the temperature tends to increase at the top of the tower, motor valve 30 will operate to permit a greater quantity of reflux to be sup- -pliedjto the top of the tower and as the temperature at the top of the tower tends to decrease, motor valve 30 willvbe actuated to restrict the flow of reflux into the tower. By means of this control the percentage of the charge .taken overhead is automatically controlled.

The charge is Vautomatically controlled by a rate of flow controller 3| of the Foxboro throt-. tling reset type manufactured by the Foxboro Company of Foxboro, Massachusetts. This device controls the motor valve 32 in. the 'charge line I 4 in response to the differential in pressure caused by the flow of the charge across the orice plate 33 which results -in a deflection of the mercury in differential pressure chambers 34the f a nozzle which controls the flow and pressure oi o airin air line 31 to operate the motor valve 32, the essential features of which are -disclosed in Mason Re. Patent 20,092, granted September 1, 1936. Air is supplied to pipe 31 from a suitable source of air pressure through line 38 to pipe 39 which is connected through the controller to pipo 31. *f-

The side streams are .controlled by ratio flow controllers of the-Foxboro throttling reset type alsoV manufactured by the Foxboro Company of Foxboro, Massachusetts. These controllers maintain the quantities of the respective side streams withdrawn as definite percentages of the charge irrespective of variations in the quantity or temperature of the charge or of the quantities of steam introduced intothe tower, so long as the charge contains the components of the side the operating conditions present.

stream Withdrawn through pipe 2| is controlled by a ratio flow controller 48 having two sets oi dilerential pressure chambers 4| and 42 respectively, set 4| being connected through

lines

35 and 36 to the oriiice plate 33 in the charge line I4, and the other set 42 being connected to the orifice plate 43 in side stream draw-off line 2| through

lines

44 and 45. y

The operation is as follows: Charge to the tube stills ows through line I4 and through the orice plate 33, therebyproducing a differential in pressure between the upstream point at which.

line 351s connected to line I4, and the downstream point at which line 36 is connected to line I4, the pressure in line 35 being greater than that in line 36. This pressure diierential is transmitted to mercury chamber 4| for the primary stream, in this instance the charge to the stili, and mercury chamber 42 for the secondary stream, which in this instance is sidestream 2| from the fractionating tower. This pressure differential results'in a relative differential in the levels of mercury in the two arms of thev mercury chambers 4I and 42 so that oats 51 and 58 in primary and secondary mercury chambers respectively, are caused to rise and fall as the dierential mercury level varies. As float 51 rises in response to an increase in the rate of ing to close valve 41, which results in a decrease in the iiow of liquid through sidestream line 2|.

If, for some reason, the iiow or liquid through sidestream line 2| should become less than the desired amount, the diierential set up by the iiow of the liquid through oriilce plate 43. will decrease, float 58 will drop, which will result in the movement of ilapper valve 55 to the left and toward nozzle 54 thereby diminishing the ease of escape of air through nozzle 54 and increasingthe pressure inlines 64 and 63, which will result in an increase in the 'pressure in diaphragm 68 andan expansion of the diaphragm, thereby moving stem 65 and valve 6| to the right, decreasing the opening for the passage of air into vline 46 and increasing the opening for the escape The foregoing description of the operation is based on the assumption that the tlow through charge line I4 is constant. If, however, the flow through line I4 varies, it is necessary that an adjustment be made whereby the ilow through ow of charge through line I4, airnozzle 54 ential in-pressure set up by orice plate 43 and transmitted through the connecting

lines

44 and 45 to the mercury chamber 42, causes the iloat y 58 to rise and to move bell crank lever 56 counterclockwise. Lever 56 is connected to one end of a link 1|, the other end of which is plvotally connected to a flapper 55 which is pivoted at its upper end in close proximity to nozzle 54 so that movement of the apper will aiect the iiow of airfrom the nozzle. As the iioat 58 rises, the napper will be moved to the right as seen in Fig. 2.

Assuming a condition of constant ilow oi the charge through line I4, the nozzle 54 will remain in a xed position so that if the flow through line 2| tends to increase, apper 55 will move away from the nozzle. The supply of air provided to the controller through line 38 passes through valve mechanism 66 into line 62, through a controlling valve 59 into line 64 and outward to the atmosphere through nozzle 54. This air is supplied at a constant rate, the rate being adjusted by the throttling valve 59 and 'when .allowed to. escape at a constant rate through nozzle 54 maintains a definite pressure in the closed diaphragm 68, which is connected to line 64 by line 63. However, when the position of the dapper valve is changed as indicated above, by movement ofthe apper to the right and away from the nozzle, the air escapes more readily through the nozzle opening and consequently the pressure in

lines

64 and 63 decreases,

which in turn results in a decrease in the presin the diaphragm of control valve 41 andtendsure in diaphragm 68. The`left hand end of diasidestream line 2| will be kept proportional to that through charge line I4. 'I'his is accomplished automatically by means of the connection of nozzle 54 to oat 51 whereby if, for instance, the ow through charge line I4 increases, the diierential pressure set up by orice plate 33 and transmitted to the mercury chamber 4| thereby moving valve stem and valve 6I to the right, which will allow air to escape around the valve stem 65 from the line` 46 and will result in an increase in the flow of liquid through sidestream line 2|. Ii the flow of charge through line I4 decreases, the opposite reactions will resuit and the ilow of liquid through sidestream 2| will be decreased'. The mechanisms described above are so proportioned and constructed that any change in the iiow of liquid through charge line I4 will cause a proportionate change in iiow through thesidestream line 2 I.

In like manner the side stream withdrawn through line 22 is controlled by a similar ratio ilow controller 48 `which is connected to orice plate 43 in line 22 and4 which controls the motor valve v58 in line 22. Also in like manner, the ratio flow controller 5I which is connected to the orilce plate 52 in side stream draw-oi! line 23 controls the motor valve 53 in line 23.

Flow controller' 3| operates the same as ratio flow controller 48 exceptingthat the nozzle 54 of ratio ilow controller- 48 is manually set in any desired position so as to obtain constant ilow of liquid through line |4 with orice plate 33 being connected to the ilow controller in the same manner that orifice plate 43 is connected to ratio ilowl controller 48;

lines

35 and 36 and mercury chamber 34 function in the same manner as

lines

44 and 45 and mercury chamber 42 of the ratio ow controller, and control valve 32 functions in the same manner as control valve 41, being connected to flow controller'3l by line 31 in the same manner as valve 41 is connected amount.

to ratio flow controller 40 by line 46. Thus, if for any reason the ilow of charge liquid through line I4 tends to increase, the diierential pressure established by orifice plate 33 will increase, the

`float in mercury chamber 34 will rise and draw the apper away from the nozzle of ilow controller 3| to permit air to escape'from the dia- It will be understood that either internal or external stripping sections may be utilized to strip the several side streams withdrawn from the tower, if desired. Where external stripping sections are utilized these may be placed near the ground and the structural steel work to provide access to the tower may be eliminated since all points of control for the unit may be placed in the control room or near the ground. Also, side stream seal loops which ordinarily must be employed, may also be eliminated.

of charge through line Il until the desired rate is again attained.

With this arrangement each of the side streams is automatically maintained'at all times as a denite percentage of the charging stock,

irrespective of variations in temperature or.

quantity of the charging stock and independently of variations in the quantity of steam used in the tower, so long as the charge contains the components. of the side streams in vapor or in vaporizable form under the operating conditions present.

The following example will serve to illustrate the operation of the method and vapparatus herein disclosed. Assume that it is desired to operate a towerfor topping crude and producing gasoline as the overhead vapor product and kerosene and gas oil as side streams. Assume also that the laboratory evaluation of the crude shows that it contains 20% of 400 end point gasoline, 15% of kerosene of the desired specications and 10% of gas oil, when running to the desired specifications on the residue. From previous experience, it is known that the temperature at the top of the fractionating tower will be 280 F. when 400 end point gasoline is being produced. With this temperature determination as a basis, the tower controls can be set as follows: The temperature controller at the top of the tower will be set for 280 F., the kerosene side stream controller will be set to provide 15% of lthe charge and the gas oil side stream controller will be set to provide 10% of the charge. With these settings the tower will produce products of the specifications which accord with the laboratory evaluation. As long as the temperature of the charge to the fractionating tower is suf-- flcient for the vaporization of the desired prod- .cts, variations in temperature, quantity of steam used, and throughput will not affect the products produced. The temperature controller lat the top of the tower will control the gasoline speciiicat'ions and in so functioning it is actually controlling the percentage, of the charge taken overhead which in the present example is 20%. The ratio ilow controller on the kerosene side stream being set for 15% of the charge, will at all times produce the cut corresponding tothat fraction lying between 20% and 35% of the charge, that is to say, 15%. The ratio ilow controller on the gas oil side stream having been set for 10% of the charge will produce the fraction of the crude lying between 35% and 45%, that is to say,'1 0%. This example will illustrate theease with which laboratory evaluations may be transferred to lplant operation, while at the same time the limitations inherent in the two prior methods heretofore mentioned will be entirely overcome.

As previously mentioned, one or more of the side streams may be controlled, as herein disclosed, with respect to either the overhead fraction or the bottoms fraction so that the side streams would beA automatically maintained in quantity as a definite percentage of the overhead fraction or the bottoms, regardless of variations in the quantity or temperature of the charging stock or the quantity of steam used inv the tower,v so long as the charge contains the components of the side streams in vapor or in vaporizable form under the operating conditions present.

Although one type of flow controller and ratio flow controller has been disclosed herein, it will be obvious that other controllers of the same or similar character may be employed for the purpose if desired. Such controllers may be actuated by any suitable means which are operated by or in response to mechanically, electrically, hydraulically or pneumatically operated mechanisms or ldevices.

It will also be understood that variations may be eiected in the several steps of the process and in the various parts of the apparatus disclosed without departing from the principles of the invention.- Accordingly, the invention is not to be limited except by the scope of the appended claims.

1. Apparatus for fractionally distilling hydro-A carbon oils and the like comprising a fractionating tower having an inlet through which vaporized oil is introduced into the tower, means in the tower for passing vapors of the oil in contact with reux, a conduit through which a side stream is withdrawn, a valve for controlling the quantity of the side stream withdrawn from the tower through said conduit, a flow controller for regulating the setting o-f said valve and operating in response to the rate of ilow of uid through a iiow meter in the conduit through which said side stream is withdrawn, another fluid oil conduit connected to the tower, a flow control valve in the other conduit, a flow meter in the other conduit, another flow controller connected to the valve 'and the ilow meter in the otherconduit, and connectionsbetween the ow controllers, the operation of the first mentioned ilow controller being modified in-response to the rate of ow of fluid through the other ilow meter in the other conduit connected to said tower, whichother ilowl meter also operates to maintain a. substantially uniform rate of flow of the stream passing through said other conduit, the combined action' of both ow meters resulting in the maintenance of a substantially constant ratio of flow of the two streams irrespective of variations in quantity or temperature of the oil introduced into the tower so long as such oil contains the lcomponents of said streams ln vapor or in vaporizable form under the operating conditions.v

present.

carbon oils and the like comprising a fractionating tower having an inlet through which vaporized oil is introduced' into the tower, means in the tower for passing vapors of the oil in contact with redux, a conduit through which a stream is withdrawn from the tower, a valve for controlling the quantity of the stream withdrawn from the tower through said conduit, a flow controller for regulating the setting of said valve and operating in response to the rate of f iow of fluid through a flow meter in the conduit through which said stream is withdrawn, another fluid passing through said other conduit, the comf' bined action of both flow meters resulting in the maintenance of a substantially constantl ratio of flow of the two streams irrespective of variations in quantity or temperature of the oil introduced into the towerA so long as such oil contains the components of said streams in'vapor or in vaporizable form under the operating conditions present.

3. Apparatus for fractionally distilling hydrocarbon oils and the like comprising a fractionating tower having an inlet through which vaporized oil is introduced into the tower, means in the tower for passing vapors of the oil in contact with reflux, a conduit through which a side stream is withdrawn from the tower, a valve for controlling the quantity of the side stream with- .drawn from the tower through said conduit, a

flow controller for regulating the setting or said valve and operating in response to the rate of flow of fiuid through a flow meter in the conduit through which said side stream is withdrawn, another :duid conduit connected to the tower through which oil is introduced into the tower,

a flow control valve in the other conduit, a flow meter in the other conduit, vanother fio-w controller connected to the valve and the flow meter in the other conduit, and connections between the flow controllers, the operation of the first mentioned'flow controller being modified in re- ,sponse to the rate of ow of fluid through'the other flow meter in the conduit through which oil is introduced into the tower, which other flow meter also operates vto maintain a substantially uniform rate of fiow of the oil into the tower,

` the combined action of both ow meters resulttact with reflux, a conduit through which av stream is withdrawn from the tower, a valve for controlling the quantity of the stream withdrawn from the tower through said conduit, a

now controller for regulating the setting et said valve and operating in response to the rate of flow of fluid through a iiow meter in the conduit through which said stream is withdrawn, another fiuid conduit connected to .the tower through which oil is introduced into the tower, a flow control valve in the other conduit, a flow meter in the other conduit, another flow controller connected to the valve and the flow meter in the other conduit, and connections between the flow controllers, the operation of the first mentioned ow controller being modified in response to the rate of flow of fluid through the other flow meter in the conduit through which oil is introduced into the tower, which other flow meter also operates to maintain a substantially uniform rate of flow of the oil into the tower, the combined action of both fiow meters resulting in the maintenance ofthe quantity of the said stream as a definite percentage of the charge oil irrespective of variations in quantity or temperature thereof so long as the charge oil contains the components of said stream in vapor or in vaporizable form under the operating conditions present.

5. Apparatus for fractionally distilling hydrocarbon oils and the like comprising a fractionating tower having an inlet through which vaporized oil is introduced into the tower, means in the tower for passing vapors of the oil in contact with reflux, a plurality of conduits connected to the tower through each of which a side stream is withdrawn from the tower, a valve for controlling the quantity of side stream withdrawn through each conduit, a fiow controller for regulating the setting of each valve and operating in response to the rate of flow of fluid through a flow meter' in the conduit through which the side stream is withdrawn, another fluid oil conduit connected to the tower, a flow control valve in the other conduit, a flow meter in the other conduit, another flow controller connected to the valve and the flow meter in the other conduit, and

lconnections between the flow controllers, the

operation of each of the first mentioned flow controllers being modified in response tothe rate .of flow of fluid through the other fiow meter in the other conduit connected to the tower which other flow meter also operates to maintain a substantially uniform rate of flow of the stream passing through said other conduit, the combined action of said flow meters resulting in the maintenance of a substantially constant ratio of flow of each side stream with respect to the flow of the stream in said other conduit irrespective of variations in quantity or temperature of the oil introduced into the tower so long as such oil contains the components of vsaid streamin vapor or in vaporizable form under the operating conditions present.

6. Apparatus for fractionally distilling hydrocarbon oils and the like comprising a fractionating tower having an inlet through which vapor` ized oil is introduced into the tower, means in the tower for passing vapors of the oil in contact with reflux, a plurality of conduits connected to thetower through each of which a-side stream is withdrawn from the tower, a valve for controlling the quantity of side stream withdrawn through each conduit, a flow controller for regulating the setting of each valve and operating in response to the rate of flow of fluid through a flow meter in the conduit through which the side stream is withdrawn, another fluid conduit connected to the tower through other ow meter in the conduit through which oil is introduced into the tower, which other flow meter also operates to maintain a substantially uniform rate of ow of the oil into the tower, the combined` action of said flow meters resulting inthe maintenance ofthe quantity of each side stream as a definite percentage of the charge oil irrespective of variations in quantity or temperature thereof so long as the charge oil contains the components of the side streams in vapor or in vaporizable formunder the operating conditions present.

7. The method oi fractionally distilling hydrocarbon oils and the like which comprises introducing vaporized oil'into a fractionating zone, passing vapors of the oil countercurrent to reflux in said zone, withdrawing abside stream from said zone, controlling the quantity of side stream so withdrawn in response to the rate of ow of the side stream from said zone, modifying said controlling action in response to the rate of ilow of a fluid stream in another flow path connected with said zone, and controlling the other flow path to maintain a substantially uniform rate of flow of the stream therethrough, the resultant of said controlling actions being operative to main'- tain a substantially constant ratio of flow oi said streams irrespective of variations in quantity or temperature ofthe oil introduced into said zone so long as. such oil contains the components of said side. stream in vapor or in vaporizable form under the operating conditions present.

8. The method of fractionally distllling hydrocarbon oils and the like which comprises intro-L- ducing vaporized oil into a fractionatlng zone, passing vapors of the oil countercurrent to reux in said zone, withdrawing a stream from said zone, controlling the quantity of stream so withcontrolling actions being operative to maintain a substantially constant ratio of flow of said side stream and the oil to said zone irrespective of variations in quantity or temperature of the oil introduced into said zone so long as such oil contains the components of said side stream in vapor or in vaporizable form under the operating conditions present.

10. The method of fractionally distilling hydrocarbon oils and the like which comprises in.

troducing vaporized oil into a fractionatlng zone,

ln said zone, withdrawing a stream from said zone, controlling the quantity of stream so with- 1 drawn in response to the rate of ow of the l stream from said'zone, modifying said controlling action in response to the rate of iiow of oilv to said zone, and controlling the ow of oil to said zone to maintain a substantially uniform rate of iiow of oil thereto, the resultant of said controlling actions being operative to maintain a substantially constant ratio of flow of said stream and the oil to said zone irrespective of variations in quantity or temperature of the oil introduced into said zone so long as such oil contains the components of said streams-*in vapor or in vaporizable form under the operating conditions present.

11. 'I'he method of fractionally distllling hydrocarbon oils and the like which comprises introducing vaporized oil into a iractionating zone, .passing vapors of the oil countercurrent to reflux in said zone, withdrawing a\plurality of sidef streams from said zone, controlling the quantity of each side stream so withdrawn in response to the rate of ow of the side stream from said zone, modifying said controlling 'action of each stream in response to the rate of flow of another drawn in response to the rate of flow of the stream from said zone, modifying said controlling action in`responseto the rate of vow of ay uid stream in another flow path connected with said zone, and controlling the other. ilow path to maintain a substantially uniform rate of flow of the stream therethrough, the resultant of said controlling actions being operative to maintain a substantially constant ratio of ow of said streams irrespective of variations in quantity or temperature of the oil introduced into said zone so long as such oil contains the components of said stream in vapor or in vaporizable formunder the operating conditionspresent. 9. 'I'he methodof fractionally distllling hydrocarbon oils and the like which comprises'introducing vaporized oil into' a fractienotingzone,v passing vapors of the oil oountercurrent to retlx` in said zone. withdrawing a side stream from said mue, controlling the quantity of side stream so withdrawn in response to the rate ofow. of thel side stream from said zone, modifying said controlling action in response to the rateo! flow of oil to said zone, and controlling the-'now of oilY to said zone to maintain a substantially' uniform rate of ilow of oil thereto, the resultant of laid.

s contains the components of fluid stream in another iiow path connected with said zone, and controlling the rate of -iiow in said other ow path to maintain a substantially uniform rate oi flow of the stream therethrough, the resultant of said controlling actions beingV operative to maintain a substantially constant ratio of` owoi' each side stream with respect to said other stream4 irrespective of variations in quantity or temperature of the oil introduced into said zone so long as such oil ,contains the components of the side streams in vapor or in vaporizable form under the 'operating conditions present.

12, The method of 'fractionally distilling hydrocarbon oils and the like which comprises introducing vaporized oil into a fractionating zone. passing vapors of the oil counterourrent to reux in said zone, withdrawing a plurality of side streams from said zone, controlling the quantity of each side stream so withdrawn in response to .the rate of now oi the side stream ,from said zone, modifying said controlling action of eaohlstream in response to the rate of flow-of oilto said sone, and controlling the rate of flow of oil to said 'zonetomaintainauniformratoof."

flow of oil thereto, the resultant of said controlling'vactions being operative to maintain a substantiaily constant ratio of ow 'of said sidostroams and the oil tossici sono'inespeotivoof. variationsin quantity. vor. temperature of tho oil introduced intoislid so long flush oil'.

' wr or m under