CA1145706A - Apparatus for distillation column side stream withdrawal - Google Patents
Apparatus for distillation column side stream withdrawalInfo
- Publication number
- CA1145706A CA1145706A CA000336369A CA336369A CA1145706A CA 1145706 A CA1145706 A CA 1145706A CA 000336369 A CA000336369 A CA 000336369A CA 336369 A CA336369 A CA 336369A CA 1145706 A CA1145706 A CA 1145706A
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- CA
- Canada
- Prior art keywords
- liquid
- reflux
- reservoir
- flow
- side stream
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/14—Fractional distillation or use of a fractionation or rectification column
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/42—Regulation; Control
- B01D3/4211—Regulation; Control of columns
- B01D3/4261—Side stream
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
Abstract
A B S T R A C T
An apparatus for use in combination with a conventional distillation column to provide for measurement and control of reflux flow from a column intermediate fractionation stage at which a liquid side stream draw is taken. The apparatus comprises liquid reservoir, flow control, and flow metering elements of particular description, and of particular relative position.
An apparatus for use in combination with a conventional distillation column to provide for measurement and control of reflux flow from a column intermediate fractionation stage at which a liquid side stream draw is taken. The apparatus comprises liquid reservoir, flow control, and flow metering elements of particular description, and of particular relative position.
Description
APP~RAT~S FOR DISTI~LATIO~ COL~MN SIDE STREAM
WIT~DRAWAL
~ he present invention relates to an apparatus for monitoring and controlling the operation of a distillation column. More specifically, the invention relate~ to measurement and control of internal liquid reflux from a distillation column partial side ~tream draw tray.
Separation of a fluid mixture into VariGU~ component fractions according to relative boiling points or boiling point ran6es may be accomplished by fractional distillatio~
- generally carried out in a vertical column oontainin~ tray~
or bed~ of packing material which effect intimate contact between the ~apour flowing up through the column and the liquid flowing down. Such distillation columns yield an overhead product con~isting of a lower boiling fraction and a bottoms product of a higher boiling fraction. In addition, it i~ often desired to remo~e one or more inter-mediate boiling fraction~ as Eide streama from intermediate locations in the column. When a liquid side stream with-drawal i~ made, it usually comprises only a part of the l~quid flowlng down the tower at the point of withdrawal.
In thle situation of partial withdrawal, the remainder of the liquid pae~e~ to the fractionation stages of the column below the ~lde etream draw as a reflux to maintain liquid-~apour contact and effect efficient fractionation in this portion of the column.
In order to take such a partial side stream draw, it i8 nece~ary to accompli~h a di~i~ion of liquid flow, or traffic, down the column lnto a side stream and a reflux.
Since the reflux liquid remain~ within the distillation prooess and influenoe~ it~ operation, it is often advantageous to make thio di~ision in a manner which allows both measurement and control of reflux flowxate. Additional-ly, it is mo~t desirable that the mea~urement- and control funotion~ be carried out in a manner ~uch that no more of a ~, ~ .
., ~
57~6 hydraulic driving force is required than that which i8 normally available for gra~ity flow of liquid from a column side stream draw tray to the next lower fract$onation stage.
Operating within the constraint~ of gravity flow obviate~
the need for the pumping of reflux flow through metering and control devices, a common conventional practice.
At least one de~ice ha~ already been proposed for use in dividing the liquid traffic into side ~tream and reflux which also accomplishe~ metering of the reflus flow rate.
~his known device is an apparatus comprising a chamber for collecting the total liquid traffic down the column at the point of the desired partial side stream draw. Reflux and side stream flow continuously out of the chamber, each through one of two outlets. The reflux outlet consist~ of a oalibrated orifice located on the bottom of the chamber.
Since flow through the orifice is dapendent in a known manner upon liquid head above the orifice, monitoring of liquid level in the chamber provides indirect measurement of reflus flow rate.
Thl~ known concept of flow measurement can be adapted to provide some degree of reflux flow control. For instance, if a given constant flow of reflux through the chamber orifice 1~ desired, the side ~tream flowrate could, in theory, be ~aried as neces~ary to provide a given constant liquid level in the chamber and thus a constant reflux flow.
~owever, ~uch indirect control logic ha~, in practice, proven unsuccessful for providing stable control of the reflus flowrate for the reason that liquid trafflc through a distillation column i8 generally oharacterized by continual fluctuationa in flowrate. Such fluctuation~ are ~ariable, both as to amplitude and frequency, in a manner which doe~ not permit a response of side stream control which i~ adequate to prevent these fluctuation~ from being reflected ln the chamber liquid level and hence in the reflux flowrate. In essen¢e, the particular control logic .
7~6 fails in thi~ application becau~e it is unable to reproduce the variatione in liquid traffic with identical correspon-ding ~ariations in side stream flow. As a con~equence, minor up~ets and normal variatione in the distillation process above the side draw tray are communicated to the lower EectiOn~ of the column through variations in reflux flow.
An additional ~hortcoming of many conventional metering chamber devices is their inability to adapt to sub~tantial changes in the operation of the column. ~oth metering and control functions of prior art devices are accompli~hed by the same orifice, calibrated for operation under a given mode of column operation. Over the long term, ma~or changes in the di~tillation process, involving, for instance, variation in feed flowrate, feed composition, or side ~tream flowrate, will neces~itate a shutdown of column operations for replacement of the orifice in order that it will function adequately in the new mode of operation.
It 1B an ob~ect of the present invention to offer a solution to the afore-mentioned problems. ~he invention provide~ an apparatus which a¢hieves division of liquid traffic down a di~tillation oolumn into a side stream and a metered and controlled reflux flow to lower ~ections of the column in such a manner that the reflux flowrate is not influenced by routine fluctuations in column operations above the point of side stream withdrawal. ~he invention -runctions ~pon any "liquid source" within the distillation column including, but not limited to~ "liquid traffic"
flowing from a fractionation stage in the distillation column above a aide draw outlet. Furthermoro, use of the apparatus of the invention permits continued control of reflux flowrate during periods when the column i~
operatin~ in a mode significantly different than that for which it wa~ designed. ~hese advantages are realized accordin~ to th~ invention without the need for pumping of 5 7 1~ 6 reflux flow.
The invention therefore provides an apparatus, for dividing a liquid source in a multi-stage counter-current distillation column having an upper fractionation stage above a withdrawl outlet for use in withdrawing a liquid side draw from the column and a lower fractionation stage below said withdrawal outlet, said dividing taking place into a reflux portion of measured and controlled flowrate that passes by gravity flow to the lower fractionation stage, and a sidestream portion that is withdrawn from the distillation column through said with-drawal outlet, said apparatus comprising a liquid reflux reservoir adapted to collect said liquid source, said apparatus further comprising a metering chamber, a control valve and a liquid level measuring means, and said reservoir positioned at an elevation intermediate to that of the upper and the lower fractionation stages, said reflux reservoir having in association therewith means for maintaining a liquid level within the reflux reservoir, said reflux reservoir being in liquid communi-cation with said withdrawal outlet and being adapted to direct the side stream portion of the liquid source to the withdrawal outlet, and said reflux reservoir being in liquid communication, through a first liquid conduit with the said control valve means adapted to pass a cont-rolled flowrate of said reflux portion of the liquid source, via a second liquid conduit to the said metering chamber positioned at an elevation below the reflux reservoir, said chamber having at least one flow orifice through which passes the reflux portion to the lower fractionation stage, and said chamber having in association therewith the said liquid level measuring means for monitoring of liquid level in the chamber.
B
4a An advantageous embodiment of the invention provides an apparatus for dividing liquid traffic down a distillation column having a plurality of fractionation stages through which pass liquid and vapour in countercurrent flow, an :
.., ~, .
~S736 outlet for a vapour product from the top of the column, an outlet for a liquid product from the bottom of the column, and an intermediate outlet for withdrawal of a side stream liquid product, ~aid di~iding taking place into a side stream product and a reflux flow to the fractionation ~tage below the side stream product outlet and for the measure-ment and control of reflux flowrate, said apparatu~
comprising a liquid reflux reservoir con~isting of a liquid receiver being divided by a reflux weir into a first re~ervoir and a second (side stream) reservoir~ a means for ¢ollecting all liquid traffic flowing down the distillation column from the fractionation stage above the 6ide stream outlet and for routing by gravity flow said liquid traffic into the said first reservoir of the receiver; a control valve positioned external to the column at a vertical elevation below that of the top of the reflux weir, the control valve being connected with the ~aid first reserYoir through a liquid conduit1 a metering chamber positioned at a vertical elevation below the top of the reflux weir, said chamber having one or more calibrated flow orifices in liquid communication with the next fractionation stage below the side stream outlet~ the metering chamber being connected with the oontrol valve through a liquid ¢onduit;
and a mean~ for measuring llquid level in the metering chamber, said level ha~ing a proportional relation~hip to reflux flow through said calibrated flow orifi¢es.
In it~ simplest aspects, the apparatus aocordin~ to the invention provides for oollection Or liquid source, in particular liquid traffio down a distillation ¢olumn, at th0 fractionation stage from which side stream withdrawal i8 deslred, into a liquid reflux reservoir or receiver. The liquid reflux ressrvoir or receiver maintains an essential-ly constant level sour¢e of reflux liquid by means of suitable means for maintaining a liquid level within the reflux reservoir. A reflux weir is an advantageous means , 57~6 for this service. Reflux flow pagses fxom this receiver through a conduit external to the column.
~he conduit contain~ a control valve which i~ used to control flow of the reflux. Downstream of the control val~e, - 5 reflux flow enter~ a metering chamber containing one or more calibrated orifices, preferably on one or more of its vertical walls, which orifices permit reflux flow onto the fractionation ~tage below the point of side stream with-drawal to be indirectly measured as a function of liquid level in the ¢hamber. ~hat liquid source, in particular liquid traffic which enter~ the liquid reflux reservoir (or receiver) but which iB not taken as reflux through the control and metering elements of the apparatu~ is conti-nuously withdrawn from the distillation process as ~ide stream. ~he apparatus of the invention, provides for a more stable and preoise control of reflux than wa~ hereto-fore practised. ~he control sy~tem does not attempt to respond to the fluctuations in column liquid traffic 80 a~
to reproduce these ~ame fluctuation~ in side stream flow.
Instead, the control function provided by the invention operates in a manner essentially independent of the influ3xe of suoh fluctuations.
~ he apparatus according to the invention comprises three elements, in combination with a distillation column ¢ontaining a plurality of fractionation stages. ~he three elements must be interconnected with conduits for liquid flow and positioned in such a manner that the liquid flow passes, by action of gra~ity, sequentially to each of the elements in a precise order. ~ppermost of tbe elements of the apparatus according to the inYention is a liquid reflux reservoir into whi¢h passes all liquid source, in particular liquid traffic down the distillation column at an intermediate location in the column from which a ~ide ctxeam withdrawal is desired and at which an outlet from the column ie pro~ided for said withdrawal. The liquid .....
1~57~6 -xeflux reservoir is provided with ~uitable means for maintaining a liquid level within the reflux re~ervoir and effects separation of the liquid source or traffic into a side stream and a reflux. At a vertical elevation below that of the liquid reflux reservoir i8 104ated the seoond element of the invention, a control valve. ~ocated downstream of the control valve, the third element is a metering chamber which, in effect, translates a flowrate parameter into a more readily determinable liquid level or, equivalently, a differential pressure parameter by means of the use of one or more flow orifice~. While the liquid reflux re~ervoir and metering chamber may conceivably be, at least in part, located external to the column, it i8 preferred that they are located within the column walls. As will be illustrated below, through reference to the drawing8, these element~ may be arranged within the column in a manner which necessitQtee the use of no more internal column 6pace than i8 normally provided for conventional means of side stream wlthdrawal.
~he apparatus of the invention ie intended to be applied in combination with a distillation column of any oonventional design. As the invention generally provides a means for withdrawing a side stream from a distillation column, it is to be under~tood that the column comprises fractionation stages both above and below the relative vertical position of the side stream outlet. ~ractionation stage~ as the term is used here, is intended to broadly appl~ to any conventional means of effecting vapour-liquid contact within a distillation column, common example~ of which are valve trays, sieve trays, packed column sections, and the like.
The liquid reflux reservoir provided with means for maintaining a liquid level within the reflux reservoir employed aB an element of the apparatus of the invention may be of any convenient design, so long as it provides l~s7~6 B
for collection of the entire liquid source or traffic flowing from the fractionation ~tage above the 6ide strsam draw location, for the maintenance of an es6entially constant level liquid surge capacity from which reflux flow may ~ontinually be drawn, and for the withdrawal of exce~s liquid traffic, i.e., that not taken from the re~ervoir as reflux, from the column as side stream product. In addition the liquid reflux reservoir muæt not ~ub6tantially interfere with the ~as~age of vapour traffic from the fractionation 6tage below the draw location to that above.
In one of the possible embodiment6 of the in~ention, the liquid reflux reservoir may take the general form of a conventional chimney tray. ~he tray pan is provided with two outlets, one for reflux and one for side 6tream, each of which i6 connected to a conduit for pa~sage of the respective liquid flows external to the column. ~he liquid reflux reservoir, or draw tray pan, i8 equipped with a vertical reflux weir running transversely acrosa the pan, and between the two outlets, to divide the tray into two liguid reservoirs. The reflux weir is an advantageou6 means for maintaining liquid level within the reflux re~ervoir.
~iquid traffic entering thereceiver is directed to one side of the weir and into a fir3t part of the reflux re6ervoir which is in communication with the reflux outlet through which reflux passes to the reflux control valve. That portion Or the liquid traffic which enter~ the first part of the reflux reservoir, but which iB not taken under control through the reflux outlet, overflows the reflux weir to a ~econd part, the side strsam reservoir. In oxder to assure that an essentially constant reflux re~ervoir liquid level iB always maintained by continuous flow over the reflux weir, the liquid traffic directed to the first part of the reflux reservoir must necessarily be of greater flowrate than the reflux which is drawn from the fir3t part of the reflux reservoir. While it is pos~ible to direct 114S7~6 only a portion of the liquid traffic to the first part of the reflux reservoir~ it is generally desirable that all liquid traffic enter the first part of the reflux reservoir as there is then maximum assuranoe that flow requirements for the reflux will at all times be met. Any entering liquid traffic not directed to the fir~t part of the reflux reservoir of the re¢eiver must neceesarily pa~s directly to the side stream reservoir. Division of liquid traffic in such a manner that a portion enters the first part of the reflux re~ervoir and the remainder enters the side stream reservoir would perhaps be desirable, for instance, when multipass trays with multiple downcomers are employed as column fractionation stages and when the requirements of reflux flowrate can easily be met by that portion of the total liquia traffic collected from fewer than all of the multiple passes.
The side stream reservoir, in communication with the side stream outlet, is maintained at a liquid level below the top of the reflux weir under normal operation of the apparatus. An essentially constant level source of liquid is thus provided upstream of the weir, in the first part of the reflux reservoir. If de6ired, liquid level in the side etream reservoir may be monitored by means of conventional liquid level instrumentation, and flowrate of side stream withdrawal may be controlled to maintain a given level.
Alternatively, side stream liquid may be allowed to drain freely from the side stream re6ervoir. A conduit is general~
ly provided for communication of the side stream liquid from the side stream reservoir to the side stream outlet.
In some embodiments of the invention in which the side stream reservoir is in dire¢t contact with the outlet, the reservoir itself serves as a means to channel side stream to the outlet and no other oonduit is required. It is considered most significant that fluotu2tions in side ~5 stream reservoir level and in 6ide stream flowrate are of ll~S7~6 no conoern in the operation of the apparatus of the inven-tion as they have no influence upon the control of the reflux flow.
It may al~o be desirable that the ~ide stream reservoir of the liquid reflux re~ervoir, in an advantageou~
embodiment, i~ equipped with an outlet overflow weir and an overflow downcomer to the fractionation ~tage below. ~he overflow weir extend~ to a height above the normal liquid level in the side ~tream reservoir. ~uring periods of extreme upset in column operation or of instrument mal-function, when more liquid traffic enter~ the liquid reflux re~ervoir than i~ withdrawn a~ reflux and side stream, the excess liquid overflows the overflow weir and i6 directed to the lower fractionation stage.
The apparatus of the invention comprises a ~onduit to route reflux from the liquid reflux reservoir to the control valve9 located external to the column at a vertioal elevation below the top of the reflux weir. ~he control valve may be operated manually or automatically in response to signal~ from appropriate instruments provided for main-tenance of a desired distillation proce3a parameter, for example, temperature on the fractionation stage below the metering chamber, flowrate of reflux through the metering chamber, etc. It is necessary that the control valve be specified so as to operate under the relatively low differential pressure provid0d by the gravity flow of the reflux from the receiver to the metering chamber. Normal tray spacing in a trayed distillation column, i.e., about two feet, will generally provide sufficient driving force for operation of a control valve. A~ a practical matter it is advisable thatthe control valve be physically located at a relative vertical elevation no higher than that of the metering chamber liquid level, in order to prevent flashing of reflux liquid to a vapour/liquid mixture downstream of the valve. An advantageou~ embodiment of the invention ~Si7~6 involves the arrangement of the control function 80 that the valve automatically provide~ conetant reflux flowrate in respon~e to signals generated by the flow metering chamber element.
A conduit i8 provided for communicating reflux liquid from the control valve into the metering chamber. The metering chamber element of the invention generally compri-8e8 a box of any convenient shape. ~he chamber i8 equipped with an inlet opening for interconnection with the conduit from the control valve and with one or more outlet - openings, in the form of calibrated flow orifices, for the flow of reflux onto the fractionation stage below the receiver. Since the flow into the chamber ie controlled and the flow out of the chamber i~ metered, and further since it is desired to meter and control the eame flow, it is - critical that the chamber have ess2ntially no other openings through which liquid may be communicated into or out of the chamber during normal operation of the apparatu~.
~his, how~ver, does not preclude a chamber open at the top, and located inside the column 80 long as the column and the apparatus of the invention are of ~ch a de~ign that liquid doe~ not normally pass into the chamber through eaid opening. It i~ generally desirable that the chamber have ~ome opening at or near the top to permit vapour to freely enter and exit the chamber vapour spaoe as the liquid level in the chamber rises and falls.
~ he one or more calibrated outlet flow oririces may be provided in one or more of the metering chamber walle, in particular the side walls. While the apparatus will be operable if some or all of the orificea are located on or near the bottom of the chamber, a wider range of effective flow mea~urement may generally be obtained if the orifice or orifices extend substantially across the full vertical dimenbion of one or more chamber ~ide walls. ~hrough appropriate sizing and vertical poeitioning of the orifices, ~57:~6 it is possible to obtain es6entially any desired functional relationship between liquid level in the chamber and flow-rate of reflux liquid out of the chamber through the orifices. Liquid level in the chamber is suitably monitored by means of any one of the many types of conventional devices known for such service, for instance, liqu~d float, sight glass, or differential pre~sure instrumentation.
The present invention will now be described by way of example in more detail with reference to the drawings, in which: -Figure 1 i~ a side view of an advantageous embodimentof the apparatus according to the invention in partial cross ~ection.
~ igure 2 ie a top sectional view of the liquid reflux reservoir and metering chamber from line 2-2 of ~iguxe 1.
Figure 3 is a side sectional view of the metering chamber from line 3-3 of Figure 2.
Figure 4 is a side sectional view of the metering ¢hamber from line 4-4 of Figure 2.
Referring now to figures 1-4, wherein the sQme referen-ce numbers indicate the eame components, the cylindrical wall of a distillation col~mn ie designated as 1. In figuree 1-4, only a portion of the vertically extending column, above and below the liquid reflux reservoir or receiver, in this example a conventional draw tray designated 31, ie pictured. One single-pas~ fractionation tray, 32, above tha draw tray, iB shown equipped with a weir 2 to maintain liquid levsl on the tray and a down¢omer 3 to direct liquid overflowing the weir to the draw tray.
~ere, the tray 32 fun¢tione to aid in collecting the liquid traffic down the distillation column and in directing the ~low onto the receiver. ~he draw tray 31 iB supplied with one or more chimneys 4 to bypase vapour flow upward through the draw tray 31 without fractionation contact with liquid thereon. In addition, the draw tray 31 i~ equipped with a ' ll~S7 ~6 reflux weir 5 which divides the tray pan 80 a~ to provide two distinct liquid reservoirs. ~he first part of the liquid reflux reservoir upstream of the reflux weir 5, i.e.
on the side of the weir in direot communication with liquid from the downcomer 3, is generally de~ignated 6, while the second part, the side 6tream reservoir, on the other ~ide of the weir i8 generally designated 7. In operation, liquid flowing from the tray 32, through the downoomer 3, is directed into the first part 6 of the reflux reservoir to provide a constant-level ~ource of liquid from which reflux may be drawn. ~hat portion of the liquid traffic entering the draw tray 31 from the tray 32 which is not taken as reflu~ overflows the weir into the reservoir 7 from which it iB removed as side ~tream via a conduit 17 to a side stream outlet 18. ~he draw tray is further provided with an overflow weir B and an overflow downcomer 9, in order that under ma~or upseta in column operation large quantities of liquid traffio may overflow the receiver without the constraint of reflux or side stream control.
A conduit 10, in liquid communioation with the re~ervoir 6, runs external to the oolumn to a oontrol valve 11. A conduit 12 extends from the control valve 11 to an inlet into a metering ohamber having an internal spaoe generally designated 13. ~he metering ohamber floor may be ~5 coinoident with the deck of a tray 30, the fraotionation stage below the reoeiver. ~his is shown in figures 1-4. The chamber i8 further defined by at least three vertioal wall~, two of whioh are~ in figures 1-4, the oolumn wall 1 and the reoeiver overflow downoomer 9. One or more of the other vertioal wall~, 14, oontain a flow orifioe in the form of a rectangular vertioal ~lit (~lotted weir) 15 extending across ~ubstantially the full vertioal dimension of the wall 14. A liquid level monitoring and control means 16 is affixed to the metering chamber and provides a signal which direot~ the operation of the oontrol valve 11 to provide -:
.
~57~6 a metered reflux of a controlled, and here constant~ flow-rate.
~ he conduit 17 extends from the side stream reservoir 7 through the side ~tream outlet 18 to the destination of the side stream draw external to the distillation column. Mean~
for optional control of 6ide stream flo~ through the conduit ~~ 17 and measurement of liquid level in the reeervoir 7 are not shown.
Figure~ 2 and 3 particularly illustrate the disposition of the metering chamber 13 within the ~pace d~fined by the column wall 1 and the overflow downoomer 9. In the embodi-ment of the invention depicted, a third vertical wall, 14, defining the metering chamber ic shown a~ viewed from the top and from the center of the column in ~igures 2 and 3, respectively. Figure 4 indicates an orifice ~lit 15 in the wall 14 (~lotted weir).
~ he drawing depicts an application of the invention to a oonventional distillation ¢olumn containing single-pass fraotionating trays. Appropriate arrangements for manifol-ding of conduits and placement of metering chamber and¢hamber orifices wlll be apparent to those skilled in the art and may for example permit application of the invention to multipa~s trays.
Various modifications of the invention will become apparent to thoee skilled in the art fxom the foregoing description and accompanying drawing~.
Such modifications are intended to fall withln the scope of the appended claims.
WIT~DRAWAL
~ he present invention relates to an apparatus for monitoring and controlling the operation of a distillation column. More specifically, the invention relate~ to measurement and control of internal liquid reflux from a distillation column partial side ~tream draw tray.
Separation of a fluid mixture into VariGU~ component fractions according to relative boiling points or boiling point ran6es may be accomplished by fractional distillatio~
- generally carried out in a vertical column oontainin~ tray~
or bed~ of packing material which effect intimate contact between the ~apour flowing up through the column and the liquid flowing down. Such distillation columns yield an overhead product con~isting of a lower boiling fraction and a bottoms product of a higher boiling fraction. In addition, it i~ often desired to remo~e one or more inter-mediate boiling fraction~ as Eide streama from intermediate locations in the column. When a liquid side stream with-drawal i~ made, it usually comprises only a part of the l~quid flowlng down the tower at the point of withdrawal.
In thle situation of partial withdrawal, the remainder of the liquid pae~e~ to the fractionation stages of the column below the ~lde etream draw as a reflux to maintain liquid-~apour contact and effect efficient fractionation in this portion of the column.
In order to take such a partial side stream draw, it i8 nece~ary to accompli~h a di~i~ion of liquid flow, or traffic, down the column lnto a side stream and a reflux.
Since the reflux liquid remain~ within the distillation prooess and influenoe~ it~ operation, it is often advantageous to make thio di~ision in a manner which allows both measurement and control of reflux flowxate. Additional-ly, it is mo~t desirable that the mea~urement- and control funotion~ be carried out in a manner ~uch that no more of a ~, ~ .
., ~
57~6 hydraulic driving force is required than that which i8 normally available for gra~ity flow of liquid from a column side stream draw tray to the next lower fract$onation stage.
Operating within the constraint~ of gravity flow obviate~
the need for the pumping of reflux flow through metering and control devices, a common conventional practice.
At least one de~ice ha~ already been proposed for use in dividing the liquid traffic into side ~tream and reflux which also accomplishe~ metering of the reflus flow rate.
~his known device is an apparatus comprising a chamber for collecting the total liquid traffic down the column at the point of the desired partial side stream draw. Reflux and side stream flow continuously out of the chamber, each through one of two outlets. The reflux outlet consist~ of a oalibrated orifice located on the bottom of the chamber.
Since flow through the orifice is dapendent in a known manner upon liquid head above the orifice, monitoring of liquid level in the chamber provides indirect measurement of reflus flow rate.
Thl~ known concept of flow measurement can be adapted to provide some degree of reflux flow control. For instance, if a given constant flow of reflux through the chamber orifice 1~ desired, the side ~tream flowrate could, in theory, be ~aried as neces~ary to provide a given constant liquid level in the chamber and thus a constant reflux flow.
~owever, ~uch indirect control logic ha~, in practice, proven unsuccessful for providing stable control of the reflus flowrate for the reason that liquid trafflc through a distillation column i8 generally oharacterized by continual fluctuationa in flowrate. Such fluctuation~ are ~ariable, both as to amplitude and frequency, in a manner which doe~ not permit a response of side stream control which i~ adequate to prevent these fluctuation~ from being reflected ln the chamber liquid level and hence in the reflux flowrate. In essen¢e, the particular control logic .
7~6 fails in thi~ application becau~e it is unable to reproduce the variatione in liquid traffic with identical correspon-ding ~ariations in side stream flow. As a con~equence, minor up~ets and normal variatione in the distillation process above the side draw tray are communicated to the lower EectiOn~ of the column through variations in reflux flow.
An additional ~hortcoming of many conventional metering chamber devices is their inability to adapt to sub~tantial changes in the operation of the column. ~oth metering and control functions of prior art devices are accompli~hed by the same orifice, calibrated for operation under a given mode of column operation. Over the long term, ma~or changes in the di~tillation process, involving, for instance, variation in feed flowrate, feed composition, or side ~tream flowrate, will neces~itate a shutdown of column operations for replacement of the orifice in order that it will function adequately in the new mode of operation.
It 1B an ob~ect of the present invention to offer a solution to the afore-mentioned problems. ~he invention provide~ an apparatus which a¢hieves division of liquid traffic down a di~tillation oolumn into a side stream and a metered and controlled reflux flow to lower ~ections of the column in such a manner that the reflux flowrate is not influenced by routine fluctuations in column operations above the point of side stream withdrawal. ~he invention -runctions ~pon any "liquid source" within the distillation column including, but not limited to~ "liquid traffic"
flowing from a fractionation stage in the distillation column above a aide draw outlet. Furthermoro, use of the apparatus of the invention permits continued control of reflux flowrate during periods when the column i~
operatin~ in a mode significantly different than that for which it wa~ designed. ~hese advantages are realized accordin~ to th~ invention without the need for pumping of 5 7 1~ 6 reflux flow.
The invention therefore provides an apparatus, for dividing a liquid source in a multi-stage counter-current distillation column having an upper fractionation stage above a withdrawl outlet for use in withdrawing a liquid side draw from the column and a lower fractionation stage below said withdrawal outlet, said dividing taking place into a reflux portion of measured and controlled flowrate that passes by gravity flow to the lower fractionation stage, and a sidestream portion that is withdrawn from the distillation column through said with-drawal outlet, said apparatus comprising a liquid reflux reservoir adapted to collect said liquid source, said apparatus further comprising a metering chamber, a control valve and a liquid level measuring means, and said reservoir positioned at an elevation intermediate to that of the upper and the lower fractionation stages, said reflux reservoir having in association therewith means for maintaining a liquid level within the reflux reservoir, said reflux reservoir being in liquid communi-cation with said withdrawal outlet and being adapted to direct the side stream portion of the liquid source to the withdrawal outlet, and said reflux reservoir being in liquid communication, through a first liquid conduit with the said control valve means adapted to pass a cont-rolled flowrate of said reflux portion of the liquid source, via a second liquid conduit to the said metering chamber positioned at an elevation below the reflux reservoir, said chamber having at least one flow orifice through which passes the reflux portion to the lower fractionation stage, and said chamber having in association therewith the said liquid level measuring means for monitoring of liquid level in the chamber.
B
4a An advantageous embodiment of the invention provides an apparatus for dividing liquid traffic down a distillation column having a plurality of fractionation stages through which pass liquid and vapour in countercurrent flow, an :
.., ~, .
~S736 outlet for a vapour product from the top of the column, an outlet for a liquid product from the bottom of the column, and an intermediate outlet for withdrawal of a side stream liquid product, ~aid di~iding taking place into a side stream product and a reflux flow to the fractionation ~tage below the side stream product outlet and for the measure-ment and control of reflux flowrate, said apparatu~
comprising a liquid reflux reservoir con~isting of a liquid receiver being divided by a reflux weir into a first re~ervoir and a second (side stream) reservoir~ a means for ¢ollecting all liquid traffic flowing down the distillation column from the fractionation stage above the 6ide stream outlet and for routing by gravity flow said liquid traffic into the said first reservoir of the receiver; a control valve positioned external to the column at a vertical elevation below that of the top of the reflux weir, the control valve being connected with the ~aid first reserYoir through a liquid conduit1 a metering chamber positioned at a vertical elevation below the top of the reflux weir, said chamber having one or more calibrated flow orifices in liquid communication with the next fractionation stage below the side stream outlet~ the metering chamber being connected with the oontrol valve through a liquid ¢onduit;
and a mean~ for measuring llquid level in the metering chamber, said level ha~ing a proportional relation~hip to reflux flow through said calibrated flow orifi¢es.
In it~ simplest aspects, the apparatus aocordin~ to the invention provides for oollection Or liquid source, in particular liquid traffio down a distillation ¢olumn, at th0 fractionation stage from which side stream withdrawal i8 deslred, into a liquid reflux reservoir or receiver. The liquid reflux ressrvoir or receiver maintains an essential-ly constant level sour¢e of reflux liquid by means of suitable means for maintaining a liquid level within the reflux reservoir. A reflux weir is an advantageous means , 57~6 for this service. Reflux flow pagses fxom this receiver through a conduit external to the column.
~he conduit contain~ a control valve which i~ used to control flow of the reflux. Downstream of the control val~e, - 5 reflux flow enter~ a metering chamber containing one or more calibrated orifices, preferably on one or more of its vertical walls, which orifices permit reflux flow onto the fractionation ~tage below the point of side stream with-drawal to be indirectly measured as a function of liquid level in the ¢hamber. ~hat liquid source, in particular liquid traffic which enter~ the liquid reflux reservoir (or receiver) but which iB not taken as reflux through the control and metering elements of the apparatu~ is conti-nuously withdrawn from the distillation process as ~ide stream. ~he apparatus of the invention, provides for a more stable and preoise control of reflux than wa~ hereto-fore practised. ~he control sy~tem does not attempt to respond to the fluctuations in column liquid traffic 80 a~
to reproduce these ~ame fluctuation~ in side stream flow.
Instead, the control function provided by the invention operates in a manner essentially independent of the influ3xe of suoh fluctuations.
~ he apparatus according to the invention comprises three elements, in combination with a distillation column ¢ontaining a plurality of fractionation stages. ~he three elements must be interconnected with conduits for liquid flow and positioned in such a manner that the liquid flow passes, by action of gra~ity, sequentially to each of the elements in a precise order. ~ppermost of tbe elements of the apparatus according to the inYention is a liquid reflux reservoir into whi¢h passes all liquid source, in particular liquid traffic down the distillation column at an intermediate location in the column from which a ~ide ctxeam withdrawal is desired and at which an outlet from the column ie pro~ided for said withdrawal. The liquid .....
1~57~6 -xeflux reservoir is provided with ~uitable means for maintaining a liquid level within the reflux re~ervoir and effects separation of the liquid source or traffic into a side stream and a reflux. At a vertical elevation below that of the liquid reflux reservoir i8 104ated the seoond element of the invention, a control valve. ~ocated downstream of the control valve, the third element is a metering chamber which, in effect, translates a flowrate parameter into a more readily determinable liquid level or, equivalently, a differential pressure parameter by means of the use of one or more flow orifice~. While the liquid reflux re~ervoir and metering chamber may conceivably be, at least in part, located external to the column, it i8 preferred that they are located within the column walls. As will be illustrated below, through reference to the drawing8, these element~ may be arranged within the column in a manner which necessitQtee the use of no more internal column 6pace than i8 normally provided for conventional means of side stream wlthdrawal.
~he apparatus of the invention ie intended to be applied in combination with a distillation column of any oonventional design. As the invention generally provides a means for withdrawing a side stream from a distillation column, it is to be under~tood that the column comprises fractionation stages both above and below the relative vertical position of the side stream outlet. ~ractionation stage~ as the term is used here, is intended to broadly appl~ to any conventional means of effecting vapour-liquid contact within a distillation column, common example~ of which are valve trays, sieve trays, packed column sections, and the like.
The liquid reflux reservoir provided with means for maintaining a liquid level within the reflux reservoir employed aB an element of the apparatus of the invention may be of any convenient design, so long as it provides l~s7~6 B
for collection of the entire liquid source or traffic flowing from the fractionation ~tage above the 6ide strsam draw location, for the maintenance of an es6entially constant level liquid surge capacity from which reflux flow may ~ontinually be drawn, and for the withdrawal of exce~s liquid traffic, i.e., that not taken from the re~ervoir as reflux, from the column as side stream product. In addition the liquid reflux reservoir muæt not ~ub6tantially interfere with the ~as~age of vapour traffic from the fractionation 6tage below the draw location to that above.
In one of the possible embodiment6 of the in~ention, the liquid reflux reservoir may take the general form of a conventional chimney tray. ~he tray pan is provided with two outlets, one for reflux and one for side 6tream, each of which i6 connected to a conduit for pa~sage of the respective liquid flows external to the column. ~he liquid reflux reservoir, or draw tray pan, i8 equipped with a vertical reflux weir running transversely acrosa the pan, and between the two outlets, to divide the tray into two liguid reservoirs. The reflux weir is an advantageou6 means for maintaining liquid level within the reflux re~ervoir.
~iquid traffic entering thereceiver is directed to one side of the weir and into a fir3t part of the reflux re6ervoir which is in communication with the reflux outlet through which reflux passes to the reflux control valve. That portion Or the liquid traffic which enter~ the first part of the reflux reservoir, but which iB not taken under control through the reflux outlet, overflows the reflux weir to a ~econd part, the side strsam reservoir. In oxder to assure that an essentially constant reflux re~ervoir liquid level iB always maintained by continuous flow over the reflux weir, the liquid traffic directed to the first part of the reflux reservoir must necessarily be of greater flowrate than the reflux which is drawn from the fir3t part of the reflux reservoir. While it is pos~ible to direct 114S7~6 only a portion of the liquid traffic to the first part of the reflux reservoir~ it is generally desirable that all liquid traffic enter the first part of the reflux reservoir as there is then maximum assuranoe that flow requirements for the reflux will at all times be met. Any entering liquid traffic not directed to the fir~t part of the reflux reservoir of the re¢eiver must neceesarily pa~s directly to the side stream reservoir. Division of liquid traffic in such a manner that a portion enters the first part of the reflux re~ervoir and the remainder enters the side stream reservoir would perhaps be desirable, for instance, when multipass trays with multiple downcomers are employed as column fractionation stages and when the requirements of reflux flowrate can easily be met by that portion of the total liquia traffic collected from fewer than all of the multiple passes.
The side stream reservoir, in communication with the side stream outlet, is maintained at a liquid level below the top of the reflux weir under normal operation of the apparatus. An essentially constant level source of liquid is thus provided upstream of the weir, in the first part of the reflux reservoir. If de6ired, liquid level in the side etream reservoir may be monitored by means of conventional liquid level instrumentation, and flowrate of side stream withdrawal may be controlled to maintain a given level.
Alternatively, side stream liquid may be allowed to drain freely from the side stream re6ervoir. A conduit is general~
ly provided for communication of the side stream liquid from the side stream reservoir to the side stream outlet.
In some embodiments of the invention in which the side stream reservoir is in dire¢t contact with the outlet, the reservoir itself serves as a means to channel side stream to the outlet and no other oonduit is required. It is considered most significant that fluotu2tions in side ~5 stream reservoir level and in 6ide stream flowrate are of ll~S7~6 no conoern in the operation of the apparatus of the inven-tion as they have no influence upon the control of the reflux flow.
It may al~o be desirable that the ~ide stream reservoir of the liquid reflux re~ervoir, in an advantageou~
embodiment, i~ equipped with an outlet overflow weir and an overflow downcomer to the fractionation ~tage below. ~he overflow weir extend~ to a height above the normal liquid level in the side ~tream reservoir. ~uring periods of extreme upset in column operation or of instrument mal-function, when more liquid traffic enter~ the liquid reflux re~ervoir than i~ withdrawn a~ reflux and side stream, the excess liquid overflows the overflow weir and i6 directed to the lower fractionation stage.
The apparatus of the invention comprises a ~onduit to route reflux from the liquid reflux reservoir to the control valve9 located external to the column at a vertioal elevation below the top of the reflux weir. ~he control valve may be operated manually or automatically in response to signal~ from appropriate instruments provided for main-tenance of a desired distillation proce3a parameter, for example, temperature on the fractionation stage below the metering chamber, flowrate of reflux through the metering chamber, etc. It is necessary that the control valve be specified so as to operate under the relatively low differential pressure provid0d by the gravity flow of the reflux from the receiver to the metering chamber. Normal tray spacing in a trayed distillation column, i.e., about two feet, will generally provide sufficient driving force for operation of a control valve. A~ a practical matter it is advisable thatthe control valve be physically located at a relative vertical elevation no higher than that of the metering chamber liquid level, in order to prevent flashing of reflux liquid to a vapour/liquid mixture downstream of the valve. An advantageou~ embodiment of the invention ~Si7~6 involves the arrangement of the control function 80 that the valve automatically provide~ conetant reflux flowrate in respon~e to signals generated by the flow metering chamber element.
A conduit i8 provided for communicating reflux liquid from the control valve into the metering chamber. The metering chamber element of the invention generally compri-8e8 a box of any convenient shape. ~he chamber i8 equipped with an inlet opening for interconnection with the conduit from the control valve and with one or more outlet - openings, in the form of calibrated flow orifices, for the flow of reflux onto the fractionation stage below the receiver. Since the flow into the chamber ie controlled and the flow out of the chamber i~ metered, and further since it is desired to meter and control the eame flow, it is - critical that the chamber have ess2ntially no other openings through which liquid may be communicated into or out of the chamber during normal operation of the apparatu~.
~his, how~ver, does not preclude a chamber open at the top, and located inside the column 80 long as the column and the apparatus of the invention are of ~ch a de~ign that liquid doe~ not normally pass into the chamber through eaid opening. It i~ generally desirable that the chamber have ~ome opening at or near the top to permit vapour to freely enter and exit the chamber vapour spaoe as the liquid level in the chamber rises and falls.
~ he one or more calibrated outlet flow oririces may be provided in one or more of the metering chamber walle, in particular the side walls. While the apparatus will be operable if some or all of the orificea are located on or near the bottom of the chamber, a wider range of effective flow mea~urement may generally be obtained if the orifice or orifices extend substantially across the full vertical dimenbion of one or more chamber ~ide walls. ~hrough appropriate sizing and vertical poeitioning of the orifices, ~57:~6 it is possible to obtain es6entially any desired functional relationship between liquid level in the chamber and flow-rate of reflux liquid out of the chamber through the orifices. Liquid level in the chamber is suitably monitored by means of any one of the many types of conventional devices known for such service, for instance, liqu~d float, sight glass, or differential pre~sure instrumentation.
The present invention will now be described by way of example in more detail with reference to the drawings, in which: -Figure 1 i~ a side view of an advantageous embodimentof the apparatus according to the invention in partial cross ~ection.
~ igure 2 ie a top sectional view of the liquid reflux reservoir and metering chamber from line 2-2 of ~iguxe 1.
Figure 3 is a side sectional view of the metering chamber from line 3-3 of Figure 2.
Figure 4 is a side sectional view of the metering ¢hamber from line 4-4 of Figure 2.
Referring now to figures 1-4, wherein the sQme referen-ce numbers indicate the eame components, the cylindrical wall of a distillation col~mn ie designated as 1. In figuree 1-4, only a portion of the vertically extending column, above and below the liquid reflux reservoir or receiver, in this example a conventional draw tray designated 31, ie pictured. One single-pas~ fractionation tray, 32, above tha draw tray, iB shown equipped with a weir 2 to maintain liquid levsl on the tray and a down¢omer 3 to direct liquid overflowing the weir to the draw tray.
~ere, the tray 32 fun¢tione to aid in collecting the liquid traffic down the distillation column and in directing the ~low onto the receiver. ~he draw tray 31 iB supplied with one or more chimneys 4 to bypase vapour flow upward through the draw tray 31 without fractionation contact with liquid thereon. In addition, the draw tray 31 i~ equipped with a ' ll~S7 ~6 reflux weir 5 which divides the tray pan 80 a~ to provide two distinct liquid reservoirs. ~he first part of the liquid reflux reservoir upstream of the reflux weir 5, i.e.
on the side of the weir in direot communication with liquid from the downcomer 3, is generally de~ignated 6, while the second part, the side 6tream reservoir, on the other ~ide of the weir i8 generally designated 7. In operation, liquid flowing from the tray 32, through the downoomer 3, is directed into the first part 6 of the reflux reservoir to provide a constant-level ~ource of liquid from which reflux may be drawn. ~hat portion of the liquid traffic entering the draw tray 31 from the tray 32 which is not taken as reflu~ overflows the weir into the reservoir 7 from which it iB removed as side ~tream via a conduit 17 to a side stream outlet 18. ~he draw tray is further provided with an overflow weir B and an overflow downcomer 9, in order that under ma~or upseta in column operation large quantities of liquid traffio may overflow the receiver without the constraint of reflux or side stream control.
A conduit 10, in liquid communioation with the re~ervoir 6, runs external to the oolumn to a oontrol valve 11. A conduit 12 extends from the control valve 11 to an inlet into a metering ohamber having an internal spaoe generally designated 13. ~he metering ohamber floor may be ~5 coinoident with the deck of a tray 30, the fraotionation stage below the reoeiver. ~his is shown in figures 1-4. The chamber i8 further defined by at least three vertioal wall~, two of whioh are~ in figures 1-4, the oolumn wall 1 and the reoeiver overflow downoomer 9. One or more of the other vertioal wall~, 14, oontain a flow orifioe in the form of a rectangular vertioal ~lit (~lotted weir) 15 extending across ~ubstantially the full vertioal dimension of the wall 14. A liquid level monitoring and control means 16 is affixed to the metering chamber and provides a signal which direot~ the operation of the oontrol valve 11 to provide -:
.
~57~6 a metered reflux of a controlled, and here constant~ flow-rate.
~ he conduit 17 extends from the side stream reservoir 7 through the side ~tream outlet 18 to the destination of the side stream draw external to the distillation column. Mean~
for optional control of 6ide stream flo~ through the conduit ~~ 17 and measurement of liquid level in the reeervoir 7 are not shown.
Figure~ 2 and 3 particularly illustrate the disposition of the metering chamber 13 within the ~pace d~fined by the column wall 1 and the overflow downoomer 9. In the embodi-ment of the invention depicted, a third vertical wall, 14, defining the metering chamber ic shown a~ viewed from the top and from the center of the column in ~igures 2 and 3, respectively. Figure 4 indicates an orifice ~lit 15 in the wall 14 (~lotted weir).
~ he drawing depicts an application of the invention to a oonventional distillation ¢olumn containing single-pass fraotionating trays. Appropriate arrangements for manifol-ding of conduits and placement of metering chamber and¢hamber orifices wlll be apparent to those skilled in the art and may for example permit application of the invention to multipa~s trays.
Various modifications of the invention will become apparent to thoee skilled in the art fxom the foregoing description and accompanying drawing~.
Such modifications are intended to fall withln the scope of the appended claims.
Claims (17)
1. An apparatus, for dividing a liquid source in a multi-stage countercurrent distillation column having an upper fractionation stage above a withdrawal outlet for use in withdrawing a liquid side draw from the column and a lower fractionation stage below said withdrawal outlet,/said dividing taking place into a reflux portion of measured and controlled flowrate that passes by gravity flow to the lower fractionation stage, and a sidestream portion that is withdrawn from the distillation column through said withdrawal outlet, said apparatus comprising/
a liquid reflux reservoir adapted to collect said liquid source, said apparatus further comprising a metering chamber, a control valve and a liquid level measuring means, and said reservoir positioned at an elevation intermediate to that of the upper and the lower fractionation stages, said reflux reservoir having in association there-with; means for maintaining a liquid level within the reflux reservoir, said reflux reservoir being in liquid communication with said withdrawal outlet and being adapted to direct the side stream portion of the liquid source to the withdrawal outlet, and said reflux reservoir being in liquid communication, through a first liquid conduit with the said control valve means adapted to pass a controlled flowrate of said reflux portion of the liquid source, via a second liquid conduit to the said metering chamber positioned at an elevation below the reflux reservoir, said chamber having at least one flow orifice through which passes the reflux portion to the lower fractionation stage, and said chamber having in association therewith the said liquid level measuring means for monitoring of liquid level in the chamber.
a liquid reflux reservoir adapted to collect said liquid source, said apparatus further comprising a metering chamber, a control valve and a liquid level measuring means, and said reservoir positioned at an elevation intermediate to that of the upper and the lower fractionation stages, said reflux reservoir having in association there-with; means for maintaining a liquid level within the reflux reservoir, said reflux reservoir being in liquid communication with said withdrawal outlet and being adapted to direct the side stream portion of the liquid source to the withdrawal outlet, and said reflux reservoir being in liquid communication, through a first liquid conduit with the said control valve means adapted to pass a controlled flowrate of said reflux portion of the liquid source, via a second liquid conduit to the said metering chamber positioned at an elevation below the reflux reservoir, said chamber having at least one flow orifice through which passes the reflux portion to the lower fractionation stage, and said chamber having in association therewith the said liquid level measuring means for monitoring of liquid level in the chamber.
2. The apparatus as claimed in claim 1, for dividing liquid traffic down a distillation column having a plur-ality of fractionation stages through which pass liquid and vapour in countercurrent flow, an outlet for a vapour product from the top of the column, an outlet for a liquid product from the bottom of the column, and an intermediate outlet for withdrawal of a side stream liquid product, said dividing taking place into a side stream product and a reflux flow to the fractionation stage below the side stream product outlet and for the measurement and control of reflux flowrate, said apparatus comprising a liquid reflux reservoir consisting of a liquid receiver being divided by a reflux weir into a first reservoir and a second (side stream) reservoir, in such a way that all liquid traffic flowing down the distillation column from the fractionation stage above the side stream outlet is collected into the said first reservoir of the receiver and the said liquid traffic is routed by gravity flow into the said first reservoir of the receiver, a control valve positioned external to the column at a vertical elevation below that of the top of the reflux weir, the control valve being connected with the said first reservoir through a liquid conduit, a metering chamber positioned at a vertical elevation below the top of the reflux weir, said chamber having one or more calibrated flow orifices in liquid communication with the next fractionation stage below the side stream outlet, the metering chamber being connected with the control valve through a liquid conduit, and a means for measuring liquid level in the metering chamber, said level having a proportional relationship to reflux flow through said calibrated flow orifices.
3. The apparatus as claimed in claim 2, wherein the liquid receiver is transversely divided by a vertical reflux weir into a first reservoir and a second (side stream) reservoir.
4. The apparatus as claimed in claim 2 or 3, wherein the said first reservoir of the receiver is adapted in such a way, that all liquid traffic flowing down the distillation column from the fractionation stage above the side stream outlet, is collected and that a portion of said liquid traffic is routed by gravity flow into the said first reservoir of the receiver, said portion being of greater flow rate than the reflux flow, and wherein all liquid traffic with the exception of said portion is routed by gravity flow into the side stream reservoir of the receiver.
5. The apparatus as claimed in claim 2, wherein the receiver and the metering chamber are contained within the distillation column walls.
6. The apparatus as claimed in claim 5, wherein the calibrated flow orifices are located in one or more of the side walls of the metering chamber.
7. The apparatus as claimed in claim 2, wherein the side stream reservoir of the receiver is equipped with an outlet overflow weir and an overflow downcomer to the fractionation stage below.
8. The apparatus as claimed in claim 7, wherein the receiver is a draw tray equipped with a vertical trans-verse reflux weir, at least one vapour chimney, an over-flow weir and an overflow downcomer.
9. The apparatus as claimed in claim 7 or 8, wherein the metering chamber is located in the overflow downcomer space of the draw tray.
10. The apparatus as claimed in claim 5, wherein the control valve responds automatically to a control signal generated by an operating parameter of the distillation column.
11. The apparatus as claimed in claim 10, wherein the means for measurement of liquid level in the metering chamber also serves a control function by generating signals in response to which the control valve is auto-matically operated to maintain a constant liquid level in the metering chamber.
12. The apparatus as claimed in claim 3 or 6, wherein the metering chamber is provided with at least one vertical wall, containing a flow orifice in the form of a rectangular slit (slotted weir) extending across substantially the full vertical dimension of said wall.
13. The apparatus as claimed in claim 7, 8 or 11, wherein the metering chamber is provided with at least one vertical wall, containing a flow orifice in the form of a rectangular slit (slotted weir) extending across substantially the full vertical dimension of said wall.
14. The apparatus as claimed in claim 3 or 6, wherein said means for collecting all traffic flowing down the distillation column from the fractionation stage above the side stream outlet and for routing by gravity flow the liquid traffic into the first reservoir of the receiver consists of a liquid downcomer to the receiver.
15. The apparatus as claimed in claim 7, 8 or 11, wherein said means for collecting all traffic flowing down the distillation column from the fractionation stage above the side stream outlet and for routing by gravity flow the liquid traffic into the first reservoir of the receiver consists of a liquid downcomer to the receiver.
16. The apparatus as claimed in claim 2, 3 or 6, wherein the metering chamber floor is coincident with the deck of the fractionation stage below the receiver.
17. The apparatus as claimed in claim 7, 8 or 11, wherein the metering chamber floor is coincident with the deck of the fractionation stage below the receiver.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US94688678A | 1978-09-28 | 1978-09-28 | |
| US946,886 | 1978-09-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1145706A true CA1145706A (en) | 1983-05-03 |
Family
ID=25485121
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000336369A Expired CA1145706A (en) | 1978-09-28 | 1979-09-26 | Apparatus for distillation column side stream withdrawal |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5547102A (en) |
| BE (1) | BE879009A (en) |
| CA (1) | CA1145706A (en) |
| DE (1) | DE2939023A1 (en) |
| FR (1) | FR2437234B1 (en) |
| GB (1) | GB2031746B (en) |
| IT (1) | IT1119181B (en) |
| NL (1) | NL7907143A (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2254182A (en) * | 1939-08-12 | 1941-08-26 | Lummus Co | Distillation process |
| US3053521A (en) * | 1959-10-01 | 1962-09-11 | Phillips Petroleum Co | Fractional distillation apparatus |
-
1979
- 1979-09-26 NL NL7907143A patent/NL7907143A/en not_active Application Discontinuation
- 1979-09-26 BE BE0/197323A patent/BE879009A/en not_active IP Right Cessation
- 1979-09-26 CA CA000336369A patent/CA1145706A/en not_active Expired
- 1979-09-26 JP JP12273579A patent/JPS5547102A/en active Granted
- 1979-09-26 FR FR7923929A patent/FR2437234B1/en not_active Expired
- 1979-09-26 DE DE19792939023 patent/DE2939023A1/en active Granted
- 1979-09-26 IT IT68871/79A patent/IT1119181B/en active
- 1979-09-26 GB GB7933363A patent/GB2031746B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2939023A1 (en) | 1980-04-17 |
| GB2031746A (en) | 1980-04-30 |
| BE879009A (en) | 1980-03-26 |
| DE2939023C2 (en) | 1989-06-22 |
| IT7968871A0 (en) | 1979-09-26 |
| GB2031746B (en) | 1982-08-25 |
| JPS635121B2 (en) | 1988-02-02 |
| FR2437234B1 (en) | 1987-03-20 |
| IT1119181B (en) | 1986-03-03 |
| JPS5547102A (en) | 1980-04-03 |
| FR2437234A1 (en) | 1980-04-25 |
| NL7907143A (en) | 1980-04-01 |
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