JPS635121B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for monitoring and controlling the operation of a distillation column. More particularly, the present invention relates to the measurement and control of internal liquid reflux from a partial side stream draw tray of a distillation column.

Partitioning a fluid mixture into various component fractions according to their relative boiling points or boiling point ranges can be accomplished by fractional distillation, achieving intimate contact between the vapor flowing upward through the column and the liquid flowing downward. It is usually carried out in a vertical column containing beds or trays of packing material. Such a distillation column provides an overhead product consisting of a low boiling fraction and a bottoms product consisting of a high boiling fraction. In addition, it is often desirable to remove one or more intermediate boiling fractions as a side cut from an intermediate location in the column. When a liquid sidecut withdrawal is made, it typically involves only a portion of the liquid descending the column at the point where the withdrawal occurs. In this case of partial withdrawal, the remainder of the liquid passes as reflux to the fractionation stage of the column below the side cut draw to maintain liquid-vapor contact and achieve effective fractionation in this part of the column.

In order to obtain such a partial side cut draw, it is necessary to separate the liquid flowing down the column into a side cut and a reflux. Since the reflux liquid remains within the distillation process and affects its operation, it is often advantageous for this separation to allow measurement and control of the flow rate of the reflux. In addition, it is best to perform measurement and control functions such that liquid pressures similar to those normally available for gravity flow of liquid from the side cut draw trays of the column to the next lower fractionation stage are required. preferable. Operating within gravity flow constraints avoids the need for pumping the return flow through metering and control equipment, which is normally customary.

At least one device has been proposed for use in separating or splitting a liquid flow into a side cut and a reflux that also provides metering of the flow rate of the reflux.
This known device is a device that includes a chamber for collecting all the liquid passing down the column at the location of the desired partial side cut draw. The reflux and sidecuts each exit the chamber continuously through one of the two outlets. The reflux outlet is
It consists of a graduated orifice located at the bottom of the chamber. Since the flow through the orifice is dependent upon the liquid head above the orifice, implementation of a monitor of the liquid level within the chamber provides an indirect measure of the flow rate of the reflux.

This concept of flow measurement can be adapted to provide some degree of control of the reflux flow rate. For example, if a given constant flow rate of reflux through a chamber orifice is desired, the side cut flow rate could theoretically be varied as needed for a given constant liquid level in the chamber, and thus a constant gives a flow rate of reflux of . However, such indirect control logic is in practice preferred for providing stable control of the reflux flow rate, since the flow of liquid through a distillation column is usually characterized by constant fluctuations in flow rate. I know it's not a success. Such fluctuations are variable in amplitude and frequency so as not to allow adequate sidecut control response to prevent these fluctuations from being reflected in the chamber liquid level and thus the reflux flow rate. . In essence, certain control logics do not work in this application. This is because changes in liquid flow cannot be reproduced with the same corresponding change in side cut flow rate. As a result, small disturbances and normal variations in the distillation process above the side draw trays are transmitted to the lower section of the column via changes in the flow rate of the reflux.

Another drawback of many conventional metering chamber devices is their inability to accommodate substantial changes in column operation. The metering and control functions of conventional equipment are accomplished by the same orifice calibrated for operation under a given mode of tower operation. For example, feed material flow rate, feed material composition,
Or long-term large changes in the distillation process, including side cut flow rates, may require shutdown of column operation for orifice replacement so that the orifice can function properly in the new mode of operation.

The object of the invention is to propose a solution to the above-mentioned problem. The present invention provides separation (i.e., splitting) of liquid flowing down a distillation column between the side cut and the lower section of the column such that the flow rate of the reflux is not affected by normal fluctuations in column operation above the location of the side cut drawer. A device is provided for achieving a metered and controlled reflux flow to the The present invention serves a "liquid source" within the distillation column, including, but not limited to, "liquid traffic" flowing from the fractionation stage of the distillation column above the side draw outlet. Furthermore, use of the apparatus of the present invention allows continued control of the flow rate of the reflux during periods when the column is operated in a manner significantly different from that for which it was designed. These advantages are realized in accordance with the present invention without the need for pumping reflux flow.

Accordingly, the present invention provides a multi-stage counter-current distillation column having an upper separating stage above the draw-out outlet and a lower separating stage below the draw-out outlet used for withdrawing a liquid side draw from the multi-stage counter-current distillation column. In an apparatus for separating a liquid source, the separation divides the liquid source into a reflux portion with a measured and controlled flow rate which passes by gravity flow to a downward fractionation stage and a side cut portion which is withdrawn from the distillation column through the withdrawal outlet. comprising a liquid reflux sump adapted to collect the liquid source and further comprising a metering chamber, a control valve and liquid level metering means, the sump being separated from the upper separation stage. located at an intermediate height with said lower separation stage, said reflux sump having associated retaining means for maintaining a liquid level within said reflux sump, said reflux sump being located at said withdrawal outlet; and is in fluid communication with the first reflux reservoir and is suitable for directing a side cut portion of the liquid source to the withdrawal outlet.
is in fluid communication with the control valve via a second liquid conduit means located below the reflux sump, the control valve directing a controlled flow rate of the reflux portion of the liquid source through a second liquid conduit means located below the reflux sump. suitable for passage into said metering chamber, said chamber having at least one flow orifice for passing a reflux portion to a lower separation stage, and said chamber comprising:
A device for isolating said liquid source is provided, characterized in that said liquid level metering means is associated with said chamber for monitoring the liquid level within said chamber.

An advantageous embodiment of the invention provides a plurality of fractionation stages with countercurrent flow of liquid and gas, an outlet for the vapor product from the top of the column, an outlet for the liquid product from the bottom of the column, and Apparatus for separating a downwardly proceeding liquid stream from a distillation column having an intermediate outlet for withdrawal of sidecut liquid product, said separation comprising separating said liquid stream from sidecut product and reflux; the reflux is sent to a fractionation stage below the side cut product outlet;
The reflux flow rate is measured and controlled, and the device consists of a liquid reflux reservoir consisting of a liquid receiver divided by a reflux weir into a first reservoir and a second (side cut) reservoir; means for collecting all the liquid stream flowing down the distillation column from the upper fractionation stage and directing the liquid stream by gravity flow to the first sump in the receiver; below the top of the reflux weir; a control valve located external to the column and connected to the first sump via a liquid conduit; one or more control valves located below the top of the reflux weir and in liquid communication with the next fractionation stage below the outlet of the side cut; a metering chamber having a graduated flow orifice of not less than or equal to or more and connected to said control valve via a liquid conduit; and a liquid level in the metering chamber having a proportional relationship to the flow rate of reflux through said graduated flow orifice; A device for separating said liquid flow is provided, characterized in that it has measuring means for measuring the liquid flow.

In its simplest aspect, the apparatus according to the invention collects the liquid stream proceeding downward through a liquid source, in particular a distillation column, into a liquid reflux sump or receiver at a fractionation stage where sidecut withdrawal is desired.
The liquid reflux sump or receiver maintains a substantially constant level source of reflux liquid by suitable means for maintaining the liquid level within the reflux sump. Reflux weir provides an advantageous means for this action. The reflux stream passes from this receiver via a conduit out of the column. The conduit includes a control valve that is used to control the flow rate of the reflux. Downstream of the control valve, the reflux flow enters a metering chamber that preferably includes one or more graduated orifices in one or more of the vertical walls, the orifices disposed in the compartment below the location of the side cut drawer. The reflux flow to the stage is then measured indirectly as a function of the liquid level in the chamber. This liquid source,
In particular, the liquid stream that enters the liquid reflux reservoir (or receiver) but is not taken as reflux through the control and metering elements of the apparatus is continuously withdrawn from the distillation process as a side cut. The device of the present invention provides more stable and precise control of reflux than previously possible. The control system does not attempt to cause the same variations in sidecut flow in response to variations in column liquid flow. Instead, the control functions provided by the present invention operate substantially independently of the effects of such variations.

The apparatus according to the invention comprises three elements in combination with a distillation column containing a plurality of fractionation stages. The three elements must be interconnected with conduits for liquid flow and arranged so that the liquid flow follows each element in the correct order. At the top of the elements of the apparatus according to the invention there is a liquid reflux sump into which all liquid sources lead, especially for columns where a side cut drawer is desired and an outlet from the column is provided in said drawer. At an intermediate location, the liquid flow down the distillation column passes to this liquid reflux sump. The liquid reflux sump is provided with suitable means for maintaining the liquid level in the reflux sump and dividing the liquid source or flow into a side cut and a reflux. A control valve, which is the second element of the present invention, is located below the position of the liquid reflux reservoir. The third element, located downstream of the control valve, is a metering chamber that converts flow parameters into more easily measurable liquid level or differential pressure parameters through one or more flow orifices. Convert by using . The liquid reflux reservoir and the metering chamber may be located at least partially outside the column, but are preferably located within the walls of the column.
As further discussed in connection with the drawings, these elements may be arranged within the column to require use of internal column space similar to that normally provided in conventional means of sidecut withdrawal.

The apparatus of the invention is intended to be applied in combination with distillation columns of conventional design. The present invention
It will be appreciated that the column comprises fractionation stages above and below the relative vertical position of the outlet of the sidecut to provide a means for withdrawing the sidecut from the distillation column. As used herein, fractionation stage is intended to apply broadly to conventional means of providing vapor-liquid contact in distillation columns, such as conventional means such as valve trays, sieve trays, packed column sections, etc. be.

A liquid reflux sump provided with means for maintaining the liquid level in the reflux sump used as an element of the apparatus of the invention is such that the liquid reflux sump is the source of the total liquid flowing from the fractionation stage above the side cut draw position, i.e. collection, maintenance of a substantially constant level of liquid surge capability so that the reflux stream is continuously withdrawn, and the removal of excess liquid flow from the column as a sidecut product rather than being taken from the sump as reflux. It may be of any convenient design as long as it provides a drawer. In addition, the liquid reflux sump must not substantially interfere with the passage of vapor flow from the fractionation stage below the draw location.

In one possible embodiment of the invention, the liquid reflux reservoir may take the conventional form of a conventional chimney tray. The tray pan is provided with two outlets, one for reflux and one for side cuts, each connected to a conduit for the passage of the respective liquid stream outside the column. ing. The liquid reflux sump, or draw tray pan, is provided with a vertical reflux weir extending across the pan and between the two outlets to separate the tray into two liquid sumps. A reflux weir is an advantageous means of maintaining liquid level within the reflux reservoir. Liquid flow entering the receiver is directed to one side of the weir and enters a first portion of the reflux sump that communicates with a reflux outlet through which reflux flows to a reflux control valve. Reflux reservoir 1st
This portion of the liquid flow which enters the section but is not under control passing to the reflux outlet overflows the reflux weir and passes into the second section, the side cut sump. To ensure that a substantially constant reflux sump liquid level is always maintained by continuous flow over the reflux weir, the flow of liquid directed to the first part of the reflux sump is directed to the first part of the reflux sump. The flow rate needs to be greater than the reflux drawn from part 1. While it is possible to direct only part of the liquid flow to the first part of the reflux sump, there is maximum guarantee that the flow rate requirements for reflux will always be met, so that all the liquid flow is directed to the reflux sump. It is usually preferred to enter the first part. The incoming liquid flow directed to the first portion of the receiver reflux sump must necessarily proceed directly to the side cut sump. Separation of the liquid streams, such that a portion enters the first part of the reflux sump and the remainder enters the side cut sump, is probably preferred.
For example, when a multipass tray with multiple descenders is used as a column fractionation stage, and the reflux flow requirements are facilitated by a portion of the total liquid stream collected from less than all of the multiple passes. This is the time when it can be matched.

The side cut sump, which is in communication with the side cut outlet, is maintained at a liquid level below the top of the reflux weir under normal operation of the device. A source of substantially constant level of liquid is provided upstream of the weir in a first portion of the reflux reservoir. If desired, the liquid level in the sidecut sump can be monitored by conventional liquid level measurements and the flow rate in the sidecut drawer can be controlled to maintain a given level. Alternatively, sidecut liquid may flow freely from the sidecut sump. The conduit is
Provided for communication of side cut liquid from the side cut reservoir to the side cut outlet. In some embodiments of the invention where the sidecut reservoir is in direct contact with the outlet, the reservoir itself serves as a means for conveying the sidecut to the outlet and no other conduit is required. It seems most significant that sidecut sump level variations and sidecut flow rate variations do not affect the operation of the apparatus of the present invention since they do not affect the control of the reflux flow rate.

Preferably, the side-cut sump of the liquid reflux sump in the advantageous embodiment has an overflow descender to the lower fractionation stage and an outlet overflow weir. The overflow weir extends to a height above the normal liquid level in the side cut sump. During periods of extreme turbulence in column operation or equipment malfunctions, when more liquid flow enters the liquid reflux sump than as reflux and sidecuts, the excess liquid overflows the overflow weir and drains downward. Directed to the separation stage.

The apparatus of the invention comprises a conduit directing reflux from a liquid reflux reservoir to a control valve located external to the column below the top of the reflux weir. The control valve is operated manually in response to signals from suitable devices provided for the maintenance of desired distillation process parameters, such as the temperature of the fractionation stage below the metering chamber, the flow rate of the reflux through the metering chamber, etc. or may be operated automatically. The control valve needs to be specialized to work under the relatively low differential pressure provided by the gravity flow of reflux from the receiver to the metering chamber. In tray distillation columns, the typical tray spacing, about 2 feet, can usually provide sufficient driving force for control valve operation. As a practical matter, the control valve should be physically located at a relative position no higher than the position of the liquid level in the metering chamber to prevent flashing of the reflux liquid into the vapor/liquid mixture downstream of the valve. That makes sense. An advantageous embodiment of the invention includes a control function device in which the valve automatically provides a constant reflux flow rate in response to a signal generated by the flow metering chamber element.

A conduit is provided to communicate reflux liquid from the control valve to the metering chamber. The weighing chamber element of the invention typically comprises a conveniently shaped box. The chamber has one in the form of a graduated flow orifice for flow of reflux to the fractionation stage below the receiver.
It has an inlet opening for interconnection with one or more outlet openings and with a conduit from the control valve. Liquid enters and exits the chamber during normal operation of the device, both because the flow into the chamber is controlled and the flow out of the chamber is metered, and because it is desirable to meter and control the same flow. It is important that the chamber has substantially no other openings. However, this does not mean that a chamber located within the column and open at the top, as long as the apparatus and column of the present invention are designed such that liquid does not normally pass into the chamber through the opening. It does not exclude. When the liquid level in the chamber rises or falls,
It is usually preferred that the chamber have an opening at or near the top so that steam can freely enter and exit the chamber vapor space.

One or more graduated outlet flow orifices may be provided on one or more of the walls, particularly the side walls, of the metering chamber. Although the device can be operated with some or all of the orifices located at or near the bottom of the chamber, a wide range of effective flow measurements require that the orifices be located at or near the bottom of the chamber. This is usually obtained when it extends over substantially the entire vertical dimension of. By suitable dimensions and vertical positioning of the orifice, it is possible to substantially obtain the desired functional relationship between the liquid level in the chamber and the flow rate of the reflux liquid through the orifice and out of the chamber. The liquid level within the chamber is suitably monitored by any of the many types of known and conventional devices contemplated, such as, for example, liquid floats, sight glasses, or differential pressure gauges.

The present invention will now be described in more detail with reference to the accompanying drawings.

Referring to FIGS. 1-4, in which like reference numerals indicate like components, the cylindrical wall of the distillation column is designated by the reference numeral 1. In Figures 1-4, only the portion of the column that extends vertically above and below the liquid reflux sump or receiver (in this example a conventional draw tray designated by the reference numeral 31) is shown. One single pass distillation tray 3 above the draw tray
2 is a weir 2 that maintains the level of liquid on the tray
and a lowering member 3 which directs liquid overflowing the weir into a draw tray. Here, tray 32 serves to collect liquid traveling down the distillation column and to assist in directing the flow to a receiver. The draw tray 31 has one or more chimneys 4 to bypass vapor flow through the draw tray 31 without separate contact with the liquid on the draw tray. In addition, the draw tray 31 has a reflux weir 5 that divides the tray pan to provide two distinct reservoirs. The first part of the liquid reflux sump upstream of the reflux weir 5, i.e. on the side of the weir which is in direct communication with the liquid from the descending member 3, is generally designated by the reference numeral 6.
The second part on the other side of the weir, namely the side cut sump, is designated generally by the reference numeral 7. During operation, the tray 3 passes through the lowering member 3.
The liquid flowing from 2 provides a constant level source of liquid from which reflux can be drawn and directed to the first part of the reflux sump. The portion of the liquid flow entering the draw tray 31 from the tray 32 that is not taken as reflux overflows the weir and enters the sump 7;
It is removed from the reservoir 7 as a sidecut via a conduit 17 to a sidecut outlet 18. Additionally, the draw tray has an overflow weir 8 and an overflow drop member 9 so that during major turbulences in column operation, large liquid streams can overflow the receiver without reflux suppression or side cut control. It's getting old.

A conduit 10 in fluid communication with the reservoir 6 extends from outside the column to a control valve 11. A conduit 12 extends from the control valve 11 to an inlet to a metering chamber having an interior space indicated generally by the reference numeral 13.
The weighing chamber floor may coincide with the deck of trays 30, which is the lower sorting stage of the receiver.
This is illustrated in Figures 1-4. The chamber is further defined by at least three vertical walls, two of which in Figures 1-4 are the tower wall 1 and the receiver overflow drop member 9. One or more vertical walls 14 that are other vertical walls are:
It includes a flow orifice in the form of a rectangular vertical slot 15 extending substantially over the entire vertical dimension of the wall 14. Liquid level monitoring and control means 16 are attached to the metering chamber and provide signals directing the operation of control valve 11 to provide a controlled, in this case constant, flow metered return.

A conduit 17 passes from the side cut sump 7 through the side cut outlet 18 and is directed outside the distillation column to the side cut draw. Means for optional control of side cut flow through conduit 17 and measurement of liquid level in sump 7 are not shown.

2 and 3 particularly show the arrangement of the metering chamber 13 within the space defined by the column wall 1 and the overflow lowering member 9. FIG. In the illustrated example of the invention, the third vertical wall 14 defining the metering chamber is shown as viewed from the top and center of the column in FIGS. 2 and 3, respectively.
FIG. 4 shows the orifice 15 (slotted weir) in the wall 14.

The drawing shows the application of the invention to a conventional distillation column containing single-pass fractionation trays. Suitable arrangements for installing chamber orifices and metering chambers and forming a manifold of conduits will be apparent to those skilled in the art and may, for example, allow the invention to be applied to multipass trays. let's.

[Brief explanation of the drawing]

FIG. 1 shows a side view, partially in section, of an advantageous example of a device according to the invention. Figure 2 shows
2 is a cross-sectional view from above of the metering chamber and liquid reflux reservoir taken along line 2--2 of FIG. 1; FIG. 3 is a side cross-sectional view of the metering chamber taken along line 3--3 of FIG. 2; FIG. Figure 4 shows line 4 in Figure 2.
Figure 4 is a side cross-sectional view of the weighing chamber taken along -4; 1... Cylindrical wall, 2... Weir, 3... Descending member, 4... Chimney, 5... Reflux weir, 8...
Overflow weir, 9... Overflow descending member, 11... Control valve, 14... Vertical wall, 16...
. . . liquid level monitoring and control means, 30 . . . tray, 31 . . . draw tray, 32 . . . single pass distillation tray.

Claims (1)

[Scope of Claims] 1. In the multi-stage counter-current distillation column, the multi-stage counter-current distillation column has an upper separate stage above the draw-out outlet used for drawing liquid side draw from the multi-stage counter-current distillation column, and a lower separate stage below the draw-out outlet. In an apparatus for separating a liquid source, the separation comprises separating the liquid source into a reflux portion of a measured and controlled flow rate which passes by gravity flow to a downward fractionation stage and a side cut which is withdrawn from the distillation column through the withdrawal outlet. comprising a liquid reflux sump adapted to collect said liquid source and also comprising a metering chamber, a control valve and liquid level metering means, said sump being separated into said upper separate stage. and said lower separation stage, said reflux sump having associated retaining means for maintaining a liquid level within said reflux sump, said reflux sump being located at an intermediate height between said drawer and said reflux sump. the reflux reservoir is in fluid communication with the control valve via a first liquid conduit means and is suitable for directing a side cut portion of the liquid source to the withdrawal outlet; , the control valve is suitable for directing a controlled flow rate of the reflux portion of the liquid source through a second liquid conduit means to the metering chamber located below the reflux sump; a chamber having at least one flow orifice for passing a reflux portion to a lower separation stage; and said chamber having said liquid level metering means associated therewith for monitoring the liquid level within said chamber. A device for isolating the liquid source, characterized in that the device comprises: 2 multiple fractionation stages with countercurrent flow of liquid and gas;
of the liquid proceeding downward through the distillation column having an outlet for the vapor product from the top of the column, an outlet for the liquid product from the bottom of the column, and an intermediate outlet for withdrawal of the liquid product in the side cut. Apparatus for separating streams, said separation comprising dividing said liquid stream into a sidecut product and a reflux, the reflux being sent to a fractionation stage below the outlet of the sidecut product, the reflux flow rate being is measured and controlled, and the device has a first reservoir and a second reservoir.
A liquid reflux sump consisting of a liquid receiver divided by a reflux weir into a sump (side cut); collects all the liquid flow flowing down the distillation column from the fractionation stage above the outlet of the side cut into a gravity flow a control valve located external to the column below the top of the reflux weir and connected to the first reservoir via a liquid conduit; one or more graduated flow orifices located below the top of the reflux weir and in fluid communication with the next fractionation stage below the outlet of the side cut, and connected to said control valve via a fluid conduit; and measuring means for measuring the liquid level in the metering chamber proportional to the flow rate of reflux through the graduated flow orifice. Device. 3. The device of claim 2, wherein the liquid receiver is transversely divided into a first sump and a second (side cut) sump by a vertical reflux weir. 4 The first sump of the receiver collects all the liquid stream flowing down the distillation column from the fractionation stage above the outlet of the side cut, and the receiver collects a portion of the liquid stream that is greater than the reflux flow rate. suitable for directing by gravity flow into said first sump of said liquid and configured to direct all liquid flow, apart from said portion, by gravity to said first sump of said receiver. An apparatus according to claim 2 or 3. 5. Apparatus according to any one of claims 2 to 4, wherein the receiver and the metering chamber are contained within the walls of the distillation column. 6. Apparatus according to claim 5, wherein the graduated flow orifice is arranged on one or more of the side walls of the metering chamber. 7. The side cut reservoir of the receiver has an overflow descending member to the lower sorting stage and an outlet overflow weir.
Apparatus according to any one of clause 5. 8. The apparatus of claim 7, wherein the receiver is a draw tray having a vertical transverse reflux weir, at least one steam chimney, an overflow weir, and an overflow lowering member. 9. Apparatus according to claim 7 or 8, wherein the metering chamber is located in the overflow lowering member gap of the draw tray. 10. The apparatus of claim 5, wherein the control valve responds automatically with a control signal generated by the operating parameters of the distillation column. 11. Claim in which the means for measuring the liquid level in the metering chamber fulfills the function of control by generating a signal in response such that the control valve is automatically operated to maintain a constant liquid level in the metering chamber. The device according to item 10. 12. The metering chamber has at least one vertical wall including a flow orifice in the form of a rectangular slit extending substantially across the entire vertical dimension of the wall. An apparatus according to any one of claims 2 to 11. 13 Means for collecting all the flow flowing down the distillation column from the fractionation stage above the outlet of the side cut and directing the fluid stream by gravity flow to a first sump in the receiver is provided. 13. A device according to any one of claims 2 to 12, comprising a lowering member. 14. Claim 2 in which the weighing chamber floor coincides with the deck of the sorting stage below the receiver.
The device according to any one of Items 1 to 13.