CA1048961A - Process for the control of a continuous distillation process - Google Patents
Process for the control of a continuous distillation processInfo
- Publication number
- CA1048961A CA1048961A CA74196832A CA196832A CA1048961A CA 1048961 A CA1048961 A CA 1048961A CA 74196832 A CA74196832 A CA 74196832A CA 196832 A CA196832 A CA 196832A CA 1048961 A CA1048961 A CA 1048961A
- Authority
- CA
- Canada
- Prior art keywords
- correcting
- conditions
- control
- condition
- controlled
- 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
- B01D3/42—Regulation; Control
- B01D3/4211—Regulation; Control of columns
- B01D3/425—Head-, bottom- and feed stream
Abstract
A B S T R A C T
A process for the control of a continuous process for the separation of a feed stream into at least two product streams in a distillation column, the objective being to attain desired values for controlled conditions (G1, G2, . . . ) by adjustment of correcting conditions (C1, C2, . . . ), in which process one of the correcting conditions (C1) is chosen for the control of one of the product qualities (G1), whereupon one of the remaining correcting conditions (C2) is modified until a constraint on C1 or C2 or on one of the remaining controlled conditions (G2) is reached, care being taken to maintain the constrained condition at that limiting value, either directly if C1 or C2 is concerned or by means of C2 if G2 is concerned which process of modifiying one of the correcting conditions until a constraint on one of the correcting or controlled conditions is reached and maintaining it at the limiting value is effected simultaneously or repeated successively for the remaining conditions, and which process starts anew as soon as a change takes place in the separation process.
A process for the control of a continuous process for the separation of a feed stream into at least two product streams in a distillation column, the objective being to attain desired values for controlled conditions (G1, G2, . . . ) by adjustment of correcting conditions (C1, C2, . . . ), in which process one of the correcting conditions (C1) is chosen for the control of one of the product qualities (G1), whereupon one of the remaining correcting conditions (C2) is modified until a constraint on C1 or C2 or on one of the remaining controlled conditions (G2) is reached, care being taken to maintain the constrained condition at that limiting value, either directly if C1 or C2 is concerned or by means of C2 if G2 is concerned which process of modifiying one of the correcting conditions until a constraint on one of the correcting or controlled conditions is reached and maintaining it at the limiting value is effected simultaneously or repeated successively for the remaining conditions, and which process starts anew as soon as a change takes place in the separation process.
Description
1~1!48961 The invention relates to a process for the control of a continuous process for the separation of a feed stream into at least two product streams in a distillation column. Its specific objective is to attain desired values for controlled conditions Gl, G2,... by adjustment of correcting conditions Cl ' C2 . ' .
A distillation column may be a single column with a rectifying section and a stripping section. The said conditions Gl, G2,... and Cl, C2, ... then pertain to this entire column. If the distillation column is of a composite type such that, in addition to a top product and a bottom product stream, at least one intermediate product stream is obtained, the column may always be considered to be composed of a number of single columns, correspond-ing with the number of individual rectifying sections that can be recognized.
Every single column here has its own set of conditions Gl, G2,... and Cl, C2, .... In the following a single column will be invariably meant, except where otherwise indicated.
Controlled conditions Gl, G2,... include the quality of the top pro-duct, the quality of the bottom product, the tray load in the rectifying sect-ion, the tray load in the stripping section, the pressure, the volume of the top product stream and the volume of the bottom product stream. Correcting conditions Cl, C2,... include the amount of heat supplied to the feed stream, the amount of heat supplied to the reboiler, the amount of heat abstracted in the condenser, the amount of heat abstracted by circulating reflux, the volume of the feed stream, the volume of the reflux stream, and the volume of the circulating reflux stream. Several of these conditions are not mutually in-dependent. For example, the two reflux streams may have an additive effect, and so may the two heat streams. In a composite column the feed stream for a single column that is located higher up depends on the adjustment of the single column below it.
The present invention has for its object to provide a process for the control of a distillation process whereby the desired product is invariably obtained in maximum quantities of the required quality.
The invention relates to a process for the control of a continuous ~ - 2 -S '`~' 1~4t~61 process for the separation of a feed stream into at least two product streamsin a distillation column, the objective being to attain values for controlled conditions (Gl, G2,...) by adjustment of correcting conditions (Cl, C2,...), in which process one of the correcting conditions (Cl) is chosen for the control of one of the product qualities (Gl), whereupon one of the remaining correcting conditions (C2) is modified until a constraint on Cl or C2 or on one of the remaining controlled conditions (G2) is reached, care being taken to maintain the constrained condition at that limiting value, either directly if Cl or C2 is concerned or by means of C2 if G2 is concerned, which process of modifying one of the correcting conditions until a constraint on one of the correcting or controlled conditions is reached and maintaining it at the limit-ing value is effected simultaneously or repeated successively for the remain-ing conditions, and which process starts anew as soon as a change takes place in the separation process.
According to the invention, one of the correcting conditions (Cl) is chosen for control of one of the product qualities (Gl), whereupon -2a-f `
~ "
3- 1~1i48961 one of the remaining correcting conditions C2 is modified until a constraint on C1 or C2 or on one of the remaining controlled conditions (G2) is reached, care being ta~en to maintain the constrained condition at that limiting value, either directly if C1 or C2 is concerned or by means of C2 if G2 is concerned, which process of modifyin~ one of the correctine conditions until a constraint on one of the correcting or controlled conditions is reached and maintaining it at the limiting value is effected simultaneously or repeated successively for the remaining conditions, and which process starts anew soon as a chan~e t~kes place in the separation process.
In the process according to the invention first a product stream is chosen whose yield must be a maximum. This choice is dictated by external reasons such as demand and/or price. If the stream in question is the top product, G1 will stand for the requisite quality of it and C1 may be the reflux stream. Then, according to the invention other correcting conditions are successively modified until several conditions reach their limiting values, The quality G1, however, is maintained on a constant level. As a result, a maximum yield of the specific desired product is obtained. The modification of a correcting condition invariably goes in such a direction that the object of maximum yield is pursued. This implies that the correcting conditions may be either raised or lowered for the attainment of the desired optimum.
When a state of equilibrium has been established in the column, a number of automatic control systems are acting to maintain the controlled conditions at the values obtained, operating according to a definite scheme, which will as a rule be known as such. Now if a disturbance appears, these control systems will try to go on complyine with the set values which have been attsined according to the invention.
Frequently, however, the disturbance will necessitate readjustment of one or more of the correctine conditions or even of differently composed control systems. Examples of such disturbances are changes of the cooline-water temperature or of reed composition or of the desired quality Or one of the products. Then the action of the automatic control systems ensures that the - possibly modified - quality requirement is satisfied, but as a rule the column no longer gives the msximum yield of that product, because many correcting and/or controlled conditions are not at their 1~8961 limiting values any more, In that case the successive modifications to the correcting conditions according to the invention start afresh.
Modifications to a correctin~ condition are preferably effected at such a rate that the automic control systems remain approximately in equilibrium, Preferably a suitably programmed digital computer is used for the selection and modification of a correcting condition (C1, C2 , . ,) and to determine whether limiting values for a correcting condition (C1, C2, , . ,) and/or a controlled condition (G1, G2 ~ . . ) have been attained. The control of the separation process can be done at least partly by control devices which receive the set value from this computer.
Alternatively, the control may be at least partly of the direct digital type, Whether a limiting value has been reached for a correcting and/or controlled condition can be established by measurement of the relevant condition, It is also possible to determine the value of a condition such as, for example, the tray load, by computation from data that are available from other measurements, Such computations can be carried out by the digital computer which may be used for the process according to the invention.
Both the order in which the correcting conditions are modified and the choice of correcting condition to be used for a certain controlled condition will depend entirely on the particular properties of the column in question, As a rule, one will choose that correcting condition from among the ones that are still available which imparts the best dynamic properties to the control system concerned, This order and this choice may be entirely fixed for a certain column, Alternatively, when a digital computer is used, the ~ost suitable order and combination can be selected automatically by determination of the range of adjustment and mutual comparison of the dynamic properties.
The following table gives an example of combinations of correcting and controlled conditions which may pertain to a column.
These combinations have also been used in subsequent examples.
1~4~
Correcting condition Reflux streamHeat stream Heat stream to the feed to the reboiler Constrained condition ____ ______________________ _______ _________ __ Reflux stream 10 0 0 Heat stream to feed 0 10 0 Heat stream to reboiler O 0 10 _______________ _-- - ,~ _____ _______ ___ ______ Quality of top product 8 6 4 Quality of bottom prod. 4 6 8 Tray load in rectifying section 8 6 4 Tray load in stripping section 4 6 8 ___ _________ ______________________ ____ .
The numbers indicate the relative preference for the control of a controlled condition by a correcting condition. The number O denotes that control is impossible, the number 10 that that combination is the only one possible In any case, the higher the number, the better the operation of the control system.
When a condition mentioned in the left-hand vertical column reaches a limiting value - this may be either a correcting or a controlled condition -the best correcting condition out of the ones still available may be chosen from the associated horizontal row of figures.
When a correcting condition itself reaches a limiting value it must be maintained at that limiting value. As a matter of fact, the correcting condition can only be controlled by itself.
The number may differ for other columns.
In drawings which illustrate embodiments of the invention, ~igure 1 is a schematic layout of the invention and Figure 2 illustrates the positions of l;m;ting values for various controlled conditions of a distillation column on a system of axes of three correcting conditions.
~0148961 The operation of the control process according to the invention will be further elucidated by reference to Figure 1. In this Figure 1 is a distill-ation column. The feed enters at 2, the top product leaves ~he column in the vapour phase at 3, is condensed to liquid in the condenser 4 and passes to accumulator 5, whence top product 6 and reflux stream 7 are taken off.
? - 5a -1~)48''361 The bottom product leaves the column at 8. A part of the bottoms is heated in the heat exchanger 9 and then returned to the column. The feed 2 msy be preheated with the aid of the exchsnger 10.
A few automatic control systems have been represented. Controller 11 keeps the liquid level in the accumulator 5 within permissible limits by adjustment of va}ve 12, and controller 13 does the same with vr~lve 14 for the liquid level in the bottom Or the column.
Controller 15 keeps the amount of heat supplied to heat exchanger 10 at a constant value by means of valve 16, and controller 17 and valve 18 similarly regulate the supply of heat to the reboiler 9.
Controller 19 keeps the reflux stream 7 constant with valve 20. All these valves are readjusted as soon as the set values of the associated controllers change.
Also shown are a quality meter 21 for the top product 6, a quality meter 22 for the bottom product 8, a tray-load meter 23 for the stripping section and a tray-load meter 24 for the rectifying section of column 1.
EXAMPLE I
Let the column be in a certain equilibrium. ~ow one wishes to attain the maximum yield of the top product of a requisite quality.
To this end, the set values of several controllers will be modified at such a rate that the column's equilibrium is hardly disturbed.
The set value of controller 19 for the reflux stream 7 (correcting condition C1) is lowered. Then the quality of the top product (controlled condition G1), measured by meter 21, can reach the required limiting value. This quality (G1) is now regulated directly by the reflux stream (C1).
Subsequently, the amounts of heat supplied to the feed (correctine condition C2) and to the reboiler (correcting condition C3) are increased. It is assumed that the tray load in the rectifying section (controlled condition G2), measured by meter 24, thereby attains its maximum value. This value for G2 is now regulated by the amount of heat supplied to the feed; hence a control system for G2 with C~ is formed.
r1ext, the amount of heat supplied to the reboiler (C3) is further raised. This will cause the amount of heat supplied to the fee~ (C2) to decrease, because otherwise the associated tray load (G2) would become too high. The latter is, however, maintained at its maximum value.
The reflux stream (Cl) will change such that the quality of the top product (G1) is always maintained at the required value. The increase of C3 causes a rise of the tray load in the stripping section (controlled condition C3), measured with meter 13. When this tray load reaches its maximum value, C3 and G3 together form a control system serving to maintain the tray load in question at its maximum value. Therewith the final state has been reached.
EXAMPLE II
Again let the column be in a certain equilibrium. This time one wishes to attain the maximum yield of the bottom product of a requisite quality.
The set value of controller 17 for the supply of heat to the reboiler 9 (correcting condition C1) is lowered. Then the quality of the bottom product (controlled condition G1), measured by meter 22, can reach the required limiting value. This quality (G1) is now regulated directly by the amount of heat supplied to the reboiler (C1).
Mext, the reflux stream 7 (correcting condition C2) is increased by modifying the set value of controller 19, and the supply of heat to the feed is reduced by modifying the set value of controller 15 (correcting condition C3). It is assumed that the tray load in the rectifying section (controlled condition G2), measured by meter 24, thereby attains its maximum value. This value for G2 is now regulated by the reflux stream, hence a control system for G2 with C2 is formed.
The amount of heat suppied to the feed (C3) i8 then further reduced and assumed to go to a minimum value while the limitine values for the quality of the bottom product (G1) and the tray load in the rectifying section (G2) are maintained by automatic readjustment of the heat stream to the reboiler (C1) and the reflux stream (C2). Therewith the final state has been reached.
Figure 2 gives a picture of the positions of limiting values for various controlled conditions of a distillation column on a system of axes of three correcting conditions. The amount of heat supplied 1~48~1 to the feed stream has been plotted on the axis OA, the amount of heat supplied to the reboiler on the axis OB and the volume of the reflux stream on the axis OC. The plane ADFE contains the points where the amount of heat supplied to the feed streQm is a maximum, the plane BDFG the points where the amount of heat supplied to the reboiler is a maximum, and the plane CEFG the points where the reflux stream is a maximum.
The plane HKLM lies inside the plane ADFE, the plane KLN inside the plane OAEC and the plane TPRS inside the plane OBGC.
The body HKLMNPTSRQ represents the various constraints that are applicable to a certain column. The plane BK~1 denotes the maximum amount of heat supplied to the feed stream, the plane KLM the minimum amount of heat supplied to the reboiler, the plane HKNPT the limiting value of the quality of the bottom product, the plane NLMQRP the limiting value of the quality of the top product, the plane THMQS the maximum tray load in the rectifying section, the plane QRS the maximum tray load in the strippine section.
If the values of the correcting conditions are adjusted such that the point Q i8 reached, the quality of the top product has the required value and the tray loads in the rectifying and the stripping section are at their maximum value.
If the values of the correcting conditions are adjusted such that the point T is reached~ the quality of the bottom product has the required value~ the tray load in the rectifying section is a maximum and the amount of heat supplied to the feed stream is a minimum.
The positions of the limiting values for the controlled conditions indicated may be different for different columns.
A distillation column may be a single column with a rectifying section and a stripping section. The said conditions Gl, G2,... and Cl, C2, ... then pertain to this entire column. If the distillation column is of a composite type such that, in addition to a top product and a bottom product stream, at least one intermediate product stream is obtained, the column may always be considered to be composed of a number of single columns, correspond-ing with the number of individual rectifying sections that can be recognized.
Every single column here has its own set of conditions Gl, G2,... and Cl, C2, .... In the following a single column will be invariably meant, except where otherwise indicated.
Controlled conditions Gl, G2,... include the quality of the top pro-duct, the quality of the bottom product, the tray load in the rectifying sect-ion, the tray load in the stripping section, the pressure, the volume of the top product stream and the volume of the bottom product stream. Correcting conditions Cl, C2,... include the amount of heat supplied to the feed stream, the amount of heat supplied to the reboiler, the amount of heat abstracted in the condenser, the amount of heat abstracted by circulating reflux, the volume of the feed stream, the volume of the reflux stream, and the volume of the circulating reflux stream. Several of these conditions are not mutually in-dependent. For example, the two reflux streams may have an additive effect, and so may the two heat streams. In a composite column the feed stream for a single column that is located higher up depends on the adjustment of the single column below it.
The present invention has for its object to provide a process for the control of a distillation process whereby the desired product is invariably obtained in maximum quantities of the required quality.
The invention relates to a process for the control of a continuous ~ - 2 -S '`~' 1~4t~61 process for the separation of a feed stream into at least two product streamsin a distillation column, the objective being to attain values for controlled conditions (Gl, G2,...) by adjustment of correcting conditions (Cl, C2,...), in which process one of the correcting conditions (Cl) is chosen for the control of one of the product qualities (Gl), whereupon one of the remaining correcting conditions (C2) is modified until a constraint on Cl or C2 or on one of the remaining controlled conditions (G2) is reached, care being taken to maintain the constrained condition at that limiting value, either directly if Cl or C2 is concerned or by means of C2 if G2 is concerned, which process of modifying one of the correcting conditions until a constraint on one of the correcting or controlled conditions is reached and maintaining it at the limit-ing value is effected simultaneously or repeated successively for the remain-ing conditions, and which process starts anew as soon as a change takes place in the separation process.
According to the invention, one of the correcting conditions (Cl) is chosen for control of one of the product qualities (Gl), whereupon -2a-f `
~ "
3- 1~1i48961 one of the remaining correcting conditions C2 is modified until a constraint on C1 or C2 or on one of the remaining controlled conditions (G2) is reached, care being ta~en to maintain the constrained condition at that limiting value, either directly if C1 or C2 is concerned or by means of C2 if G2 is concerned, which process of modifyin~ one of the correctine conditions until a constraint on one of the correcting or controlled conditions is reached and maintaining it at the limiting value is effected simultaneously or repeated successively for the remaining conditions, and which process starts anew soon as a chan~e t~kes place in the separation process.
In the process according to the invention first a product stream is chosen whose yield must be a maximum. This choice is dictated by external reasons such as demand and/or price. If the stream in question is the top product, G1 will stand for the requisite quality of it and C1 may be the reflux stream. Then, according to the invention other correcting conditions are successively modified until several conditions reach their limiting values, The quality G1, however, is maintained on a constant level. As a result, a maximum yield of the specific desired product is obtained. The modification of a correcting condition invariably goes in such a direction that the object of maximum yield is pursued. This implies that the correcting conditions may be either raised or lowered for the attainment of the desired optimum.
When a state of equilibrium has been established in the column, a number of automatic control systems are acting to maintain the controlled conditions at the values obtained, operating according to a definite scheme, which will as a rule be known as such. Now if a disturbance appears, these control systems will try to go on complyine with the set values which have been attsined according to the invention.
Frequently, however, the disturbance will necessitate readjustment of one or more of the correctine conditions or even of differently composed control systems. Examples of such disturbances are changes of the cooline-water temperature or of reed composition or of the desired quality Or one of the products. Then the action of the automatic control systems ensures that the - possibly modified - quality requirement is satisfied, but as a rule the column no longer gives the msximum yield of that product, because many correcting and/or controlled conditions are not at their 1~8961 limiting values any more, In that case the successive modifications to the correcting conditions according to the invention start afresh.
Modifications to a correctin~ condition are preferably effected at such a rate that the automic control systems remain approximately in equilibrium, Preferably a suitably programmed digital computer is used for the selection and modification of a correcting condition (C1, C2 , . ,) and to determine whether limiting values for a correcting condition (C1, C2, , . ,) and/or a controlled condition (G1, G2 ~ . . ) have been attained. The control of the separation process can be done at least partly by control devices which receive the set value from this computer.
Alternatively, the control may be at least partly of the direct digital type, Whether a limiting value has been reached for a correcting and/or controlled condition can be established by measurement of the relevant condition, It is also possible to determine the value of a condition such as, for example, the tray load, by computation from data that are available from other measurements, Such computations can be carried out by the digital computer which may be used for the process according to the invention.
Both the order in which the correcting conditions are modified and the choice of correcting condition to be used for a certain controlled condition will depend entirely on the particular properties of the column in question, As a rule, one will choose that correcting condition from among the ones that are still available which imparts the best dynamic properties to the control system concerned, This order and this choice may be entirely fixed for a certain column, Alternatively, when a digital computer is used, the ~ost suitable order and combination can be selected automatically by determination of the range of adjustment and mutual comparison of the dynamic properties.
The following table gives an example of combinations of correcting and controlled conditions which may pertain to a column.
These combinations have also been used in subsequent examples.
1~4~
Correcting condition Reflux streamHeat stream Heat stream to the feed to the reboiler Constrained condition ____ ______________________ _______ _________ __ Reflux stream 10 0 0 Heat stream to feed 0 10 0 Heat stream to reboiler O 0 10 _______________ _-- - ,~ _____ _______ ___ ______ Quality of top product 8 6 4 Quality of bottom prod. 4 6 8 Tray load in rectifying section 8 6 4 Tray load in stripping section 4 6 8 ___ _________ ______________________ ____ .
The numbers indicate the relative preference for the control of a controlled condition by a correcting condition. The number O denotes that control is impossible, the number 10 that that combination is the only one possible In any case, the higher the number, the better the operation of the control system.
When a condition mentioned in the left-hand vertical column reaches a limiting value - this may be either a correcting or a controlled condition -the best correcting condition out of the ones still available may be chosen from the associated horizontal row of figures.
When a correcting condition itself reaches a limiting value it must be maintained at that limiting value. As a matter of fact, the correcting condition can only be controlled by itself.
The number may differ for other columns.
In drawings which illustrate embodiments of the invention, ~igure 1 is a schematic layout of the invention and Figure 2 illustrates the positions of l;m;ting values for various controlled conditions of a distillation column on a system of axes of three correcting conditions.
~0148961 The operation of the control process according to the invention will be further elucidated by reference to Figure 1. In this Figure 1 is a distill-ation column. The feed enters at 2, the top product leaves ~he column in the vapour phase at 3, is condensed to liquid in the condenser 4 and passes to accumulator 5, whence top product 6 and reflux stream 7 are taken off.
? - 5a -1~)48''361 The bottom product leaves the column at 8. A part of the bottoms is heated in the heat exchanger 9 and then returned to the column. The feed 2 msy be preheated with the aid of the exchsnger 10.
A few automatic control systems have been represented. Controller 11 keeps the liquid level in the accumulator 5 within permissible limits by adjustment of va}ve 12, and controller 13 does the same with vr~lve 14 for the liquid level in the bottom Or the column.
Controller 15 keeps the amount of heat supplied to heat exchanger 10 at a constant value by means of valve 16, and controller 17 and valve 18 similarly regulate the supply of heat to the reboiler 9.
Controller 19 keeps the reflux stream 7 constant with valve 20. All these valves are readjusted as soon as the set values of the associated controllers change.
Also shown are a quality meter 21 for the top product 6, a quality meter 22 for the bottom product 8, a tray-load meter 23 for the stripping section and a tray-load meter 24 for the rectifying section of column 1.
EXAMPLE I
Let the column be in a certain equilibrium. ~ow one wishes to attain the maximum yield of the top product of a requisite quality.
To this end, the set values of several controllers will be modified at such a rate that the column's equilibrium is hardly disturbed.
The set value of controller 19 for the reflux stream 7 (correcting condition C1) is lowered. Then the quality of the top product (controlled condition G1), measured by meter 21, can reach the required limiting value. This quality (G1) is now regulated directly by the reflux stream (C1).
Subsequently, the amounts of heat supplied to the feed (correctine condition C2) and to the reboiler (correcting condition C3) are increased. It is assumed that the tray load in the rectifying section (controlled condition G2), measured by meter 24, thereby attains its maximum value. This value for G2 is now regulated by the amount of heat supplied to the feed; hence a control system for G2 with C~ is formed.
r1ext, the amount of heat supplied to the reboiler (C3) is further raised. This will cause the amount of heat supplied to the fee~ (C2) to decrease, because otherwise the associated tray load (G2) would become too high. The latter is, however, maintained at its maximum value.
The reflux stream (Cl) will change such that the quality of the top product (G1) is always maintained at the required value. The increase of C3 causes a rise of the tray load in the stripping section (controlled condition C3), measured with meter 13. When this tray load reaches its maximum value, C3 and G3 together form a control system serving to maintain the tray load in question at its maximum value. Therewith the final state has been reached.
EXAMPLE II
Again let the column be in a certain equilibrium. This time one wishes to attain the maximum yield of the bottom product of a requisite quality.
The set value of controller 17 for the supply of heat to the reboiler 9 (correcting condition C1) is lowered. Then the quality of the bottom product (controlled condition G1), measured by meter 22, can reach the required limiting value. This quality (G1) is now regulated directly by the amount of heat supplied to the reboiler (C1).
Mext, the reflux stream 7 (correcting condition C2) is increased by modifying the set value of controller 19, and the supply of heat to the feed is reduced by modifying the set value of controller 15 (correcting condition C3). It is assumed that the tray load in the rectifying section (controlled condition G2), measured by meter 24, thereby attains its maximum value. This value for G2 is now regulated by the reflux stream, hence a control system for G2 with C2 is formed.
The amount of heat suppied to the feed (C3) i8 then further reduced and assumed to go to a minimum value while the limitine values for the quality of the bottom product (G1) and the tray load in the rectifying section (G2) are maintained by automatic readjustment of the heat stream to the reboiler (C1) and the reflux stream (C2). Therewith the final state has been reached.
Figure 2 gives a picture of the positions of limiting values for various controlled conditions of a distillation column on a system of axes of three correcting conditions. The amount of heat supplied 1~48~1 to the feed stream has been plotted on the axis OA, the amount of heat supplied to the reboiler on the axis OB and the volume of the reflux stream on the axis OC. The plane ADFE contains the points where the amount of heat supplied to the feed streQm is a maximum, the plane BDFG the points where the amount of heat supplied to the reboiler is a maximum, and the plane CEFG the points where the reflux stream is a maximum.
The plane HKLM lies inside the plane ADFE, the plane KLN inside the plane OAEC and the plane TPRS inside the plane OBGC.
The body HKLMNPTSRQ represents the various constraints that are applicable to a certain column. The plane BK~1 denotes the maximum amount of heat supplied to the feed stream, the plane KLM the minimum amount of heat supplied to the reboiler, the plane HKNPT the limiting value of the quality of the bottom product, the plane NLMQRP the limiting value of the quality of the top product, the plane THMQS the maximum tray load in the rectifying section, the plane QRS the maximum tray load in the strippine section.
If the values of the correcting conditions are adjusted such that the point Q i8 reached, the quality of the top product has the required value and the tray loads in the rectifying and the stripping section are at their maximum value.
If the values of the correcting conditions are adjusted such that the point T is reached~ the quality of the bottom product has the required value~ the tray load in the rectifying section is a maximum and the amount of heat supplied to the feed stream is a minimum.
The positions of the limiting values for the controlled conditions indicated may be different for different columns.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the control of a continuous process for the separation of a feed stream into at least two product streams in a distillation column, the objective being to attain desired values for controlled conditions (G1, G2,...) by adjustment of correcting conditions (C1, C2,...), in which process one of the correcting conditions (C1) is chosen for the control of one of the product qualities (G1), whereupon one of the remaining correcting conditions (C2) is modified until a constraint on C1 or C2 or on one of the remaining controlled conditions (G2) is reached, care being taken to maintain the con-strained condition at that limiting value, either directly if C1 or C2 is concerned or by means of C2 if G2 is concerned, which process of modifying one of the correcting conditions until a constraint on one of the correcting or controlled conditions is reached and maintaining it at the limiting value is effected simultaneously or repeated successively for the remaining condi-tions, and which process starts anew as soon as a change takes place in the separation process.
2. A process according to claim 1, in which process the rate at which a correcting condition (C1, C2,...) is modified is such that the control systems remain approximately in equilibrium.
3. A process according to claim 1, in which process a suitably program-med digital computer is used for the selection and modification of a correct-ing condition (C1, C2,...) and to determine whether limiting values for a correcting condition (C1, C2,...) or a controlled condition (G1, G2,...) or a combination thereof have been attained.
4. A process according to claim 3, in which process the control of the separation process is done at least partly by control devices which receive the set value from the computer.
5. A process according to claim 3 or 4, in which process the control is at least partly of the direct digital type.
6. A process according to any one of claims 1 to 3, in which process one chooses that correcting condition C1, C2 . . . from among the ones that are still available for the control of a controlled condition G1, G2, . . .
which imparts the best dynamic properties to the control system concerned.
which imparts the best dynamic properties to the control system concerned.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7306022A NL7306022A (en) | 1973-05-01 | 1973-05-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1048961A true CA1048961A (en) | 1979-02-20 |
Family
ID=19818763
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA74196832A Expired CA1048961A (en) | 1973-05-01 | 1974-04-04 | Process for the control of a continuous distillation process |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5014574A (en) |
| BE (1) | BE813930A (en) |
| CA (1) | CA1048961A (en) |
| DE (1) | DE2420699A1 (en) |
| FR (1) | FR2237660B1 (en) |
| GB (1) | GB1469545A (en) |
| IT (1) | IT1011804B (en) |
| NL (1) | NL7306022A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2916175A1 (en) * | 1979-04-21 | 1980-10-23 | Krupp Koppers Gmbh | METHOD FOR CONTROLLING THE AMOUNT OF HEAT SUPPLIED TO AN EXTRACTIVE DISTILLATION COLUMN |
| JPS6038001A (en) * | 1983-08-09 | 1985-02-27 | Nippon Zeon Co Ltd | Controlling method of distillation tower |
-
1973
- 1973-05-01 NL NL7306022A patent/NL7306022A/xx not_active Application Discontinuation
-
1974
- 1974-04-04 CA CA74196832A patent/CA1048961A/en not_active Expired
- 1974-04-19 BE BE1005893A patent/BE813930A/en unknown
- 1974-04-27 JP JP4716274A patent/JPS5014574A/ja active Pending
- 1974-04-29 GB GB1857174A patent/GB1469545A/en not_active Expired
- 1974-04-29 DE DE19742420699 patent/DE2420699A1/en active Pending
- 1974-04-29 FR FR7414818A patent/FR2237660B1/fr not_active Expired
- 1974-04-29 IT IT6833874A patent/IT1011804B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5014574A (en) | 1975-02-15 |
| NL7306022A (en) | 1974-11-05 |
| IT1011804B (en) | 1977-02-10 |
| FR2237660A1 (en) | 1975-02-14 |
| GB1469545A (en) | 1977-04-06 |
| BE813930A (en) | 1974-10-21 |
| DE2420699A1 (en) | 1974-11-21 |
| FR2237660B1 (en) | 1978-08-04 |
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