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
• • 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
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C17/00—Preparation of halogenated hydrocarbons
  • C07C17/38—Separation; Purification; Stabilisation; Use of additives
  • C07C17/383—Separation; Purification; Stabilisation; Use of additives by distillation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C25/00—Compounds containing at least one halogen atom bound to a six-membered aromatic ring
  • C07C25/02—Monocyclic aromatic halogenated hydrocarbons
  • C07C25/08—Dichloro-benzenes
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B11/00—Automatic controllers
  • G05B11/01—Automatic controllers electric
  • G05B11/14—Automatic controllers electric in which the output signal represents a discontinuous function of the deviation from the desired value, i.e. discontinuous controllers
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D21/00—Control of chemical or physico-chemical variables, e.g. pH value
• • 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
  • B01D3/4294—Feed stream

Definitions

• the present invention relates to a method for controlling a concentration of at least a first component of a rectification column for separating a binary mixture of the first component and a second component based on temperature measurements.
• Rectification columns are one of the most important production units in the chemical industry and are used to separate mixtures of substances. The separation is energy intensive. Both for economic and ecological reasons, energy consumption should be as low as possible. At the same time, a specification must be complied with, which may include different aspects of the column. Typical examples are:
• the specification can either result from customer requirements, environmental requirements or later production steps.
• the rectification is a thermal separation process. In the simplest case, a binary mixture is separated into its pure components. The separation can only be completed to a certain extent. In rectification, the lower vapor pressure material is called low boiler, while the higher vapor pressure is called high boiler.
• the rectification uses the physical According to the Kaiian principle, the concentration of the low boilers in the vapor phase is higher than in the liquid phase. In contrast to distillation, this process is repeated several times, ie only a portion of a condensate formed in the top of the column is withdrawn and collected, while a remaining portion of the overhead condensate is fed back into the top of the column as so-called reflux.
• a stand in a lower region of the column the so-called sump, in which the high boiler accumulates, a level in the upper region of the column, the so-called head, namely in a condensate tank provided for the low boiler and the pressure regulated.
• the stands are controlled to prevent flooding or emptying of the column and to maintain material balance.
• concentration, pressure and state the following control variables are possible:
• Achim Kienle's article "Low-order dynamic models for ideal multicomponent distillation processes using non-linear wave propagation theory” discloses a simplified model for a rectification column, the simplified model being based on a rigorous model from which a reduced “wave model "which, however, requires extensive information NEN over used substances and apparatus properties, such as, for example, assumption of ideal separation step on each floor, packing properties, etc., requires.
• a mass spectrometer can be used for measuring the concentration.
• Corresponding devices are very expensive, so that mostly temperature measurements are used for concentration control.
• a respective temperature sensor for controlling the concentration is (usually) not attached to the top or bottom of the column, since the sensitivity is too low in these areas.
• a stationary model can be used to determine where the sensitivity in terms of concentration is greatest, as in Paul S. Fruehauf, PE, Donald P. Mahoney: DISTILLATION COLUMN CONTROL DESIGN USING STEADY STATE MODELS: USEFULNESS AND LI-MITATIONS, 1993. The point is chosen where the temperature deviation in both directions is approximately equal and the sensitivity is sufficient.
• a regulation of the concentration via a temperature control by means of steam (feed in the sump) and cooling liquid (feed in the head) is often unsatisfactory.
• Many columns have temperature profiles with a high temperature gradient at the respective mass transfer zones.
• WLLuyben describes in his article "Profile Position Control of Distillation Columns with Sharp Temperature Profiles" how the temperature profile is localized with the aid of a plurality of temperature sensors and the position of the temperature profile is used as a process variable. It is now an object of the present invention to provide a further improved possibility for controlling a concentration of a component of a binary mixture of a rectification column having a sharp temperature profile.
• the present invention provides a method and a system having the features of the respective independent claims. Embodiments of the invention will become apparent from the dependent claims and the description.
• the present invention relates to a method for controlling a concentration of at least a first component of a rectification column for separating a binary mixture of the first component and a second component based on temperature measurements.
• a controlled system defined by temperature sensors arranged in the longitudinal direction of the column is linearized with the aid of an estimate of a temperature profile, a real temperature profile T * (h) determined by the temperature sensors being approximated by a function T (h) as a function of a column height h , where the column along the column height h is divided into two sections and the function T (h) is defined in sections based on a logistical function.
• T * (h) determined by the temperature sensors being approximated by a function T (h) as a function of a column height h , where the column along the column height h is divided into two sections and the function T (h) is defined in sections based on a logistical function.
• the position of a mass transfer zone serves as a controlled variable in order to produce a desired charge associated with a desired product concentration. Adjustment of the mass transfer zone.
• Product concentration can be understood as meaning the concentration of the first component (for example head product), the concentration of the second components (for example bottom product) or both components.
• the estimated temperature profile for example, the temperature can be estimated at the top and based on this the concentration of the low boiler or of the top product can be determined.
• the binary mixture results in two mass transfer zones, namely a first in the lower region of the column, ie below an inlet or in the stripping section and a second in the upper region of the column, ie above the inlet or in the reinforcing section.
• Actuating variable for the rectifying section is a quantity of coolant; the actuating variable for the stripping section is a quantity of steam.
• PI / PID controllers can be used as a controller standard PI / PID controllers can be used.
• the inventive method in a rectification column for the separation of 1, 2-dichlorobenzene (ODB) and COCI 2 (phosgene) is applied.
• the advantage of the invention is firstly the significantly lower modeling effort compared to model approaches known from the prior art, since only relatively few material data (boiling temperatures) and column data (packing type, etc.) are required, and secondly the thus less required computing power.
• a rigorous process model, as known from the prior art, can easily contain several hundred differential equations, while the simplified process model presented here, depending on the number of installed measuring points or temperature sensors, is one to two orders of magnitude lower. This makes it possible to use it in a production system without using dedicated hardware. Rigorous models represent a technical mecha- nism with exact scientific methodology.
• the estimated temperature at the top or bottom of the column can be used for concentration calculation.
• the prerequisite is that the concentration of secondary components is "small".
• the concentration to be determined may have a lower con- centering than that of the minor components.
• the temperature profile can be visualized in an embodiment in a control panel associated with the installation or the column, so that, for example, effects on the head temperature of disturbances of possible temperature increases in the middle of the column can be better estimated.
• a rectification column for separating a mixture of phosgene and ODB, where phosgene is the first component and the low boiler of the mixture and ODB is the second component and the high boiler of the mixture. Accordingly, when the rectification is carried out, phosgene preferably accumulates in the upper region of the column, ie in the top of the column, and thus constitutes the top product. ODB as high boiler is enriched in the bottom of the column and accordingly constitutes the bottoms product Temperature profile is based on the example of the rectification column for the separation of phosgene and ODB on observations during jump tests on a simulated system.
• a jump test is understood to mean a sudden change in a manipulated variable, such as, for example, the amount of coolant at the top or the amount of steam at the bottom.
• a manipulated variable such as, for example, the amount of coolant at the top or the amount of steam at the bottom.
• a temperature profile obtained therefrom along the column, ie along the column height are in particular characteristic zones (or fronts, ie locations with a high temperature gradient - see "Jörg Raisch: Multi-variable control in the frequency domain.” Oldenbourgmaschinesverlag, Berlin, 1994., Chapter 9.18). to be seen with a high temperature gradient (in relation to the height). At these a strong mass transfer takes place, which is why these sites are also referred to as mass transfer zones.
• the temperature characteristic can be represented as static non-linearity.
• Characteristic of the course are two S-shaped temperature curves. The first covers the reinforcing part between the head of the column (100% of the column height) and feed (about 24% of the column height), the other the stripping section between inlet and bottom of the column (0%). The characteristic S-shapes are preserved during the jump attempts and are only shifted along the column height. This results in the approach of approximating the behavior of the column during the jump tests, ie in particular the temperature behavior along the column height by a displacement of a static characteristic curve.
• the fluctuation range of the stationary gain of the temperature ie the fluctuation range of the temperature at a respective column height
• T (h) The fluctuation range of the stationary gain of the temperature
• a transition of the logistic functions is determined in the embodiment of the invention by a temperature at an inlet of the column.
• a logistic function of the following form is selected as the respective logistic function:
• h 0 is a support vector that shifts the inflection point of the logistic function from 0 to h 0 .
• the on-line determined parameter h 0 can be used to control the column, as this shows a less pronounced nonlinear behavior, k describes a compression in the direction of the height of the column, T 0 describes a support vector of the temperature (T min ) and v a range of the temperature (T max - T min ).
• the function T (h) is defined as follows:
• T ab (h) and T v (h) are defined on the basis of a respective logistic function and h ZvXaU f defines the column height on which the binary mixture, in particular a solution of the column consisting of the first and the second component in equal parts is supplied. Further embodiment of the method according to the invention IS applies:
• T (h) T ab (h) for he [0%, x%] in an output region from the column with 0 ⁇ x ⁇ 100, and where T 0, v and T 0, from respective support vectors of the temperature, v v and v from a respective one
• Span of the temperature, k v and k from a respective compression in the direction of the column height h and h 0, v and h 0, represent a respective support vector of the height h.
• h 0, v and h 0, ab correspond to the respective mass transfer zones in the enrichment section or in the stripping section of the column.
• x is chosen as 24. This corresponds to the relative height at which the inlet valve is arranged. The actual feed height depends on a design of a respective column and can be calculated exactly with knowledge of the column design.
• the inlet height defines the transition of the "subfunctions" T ab (h) and T v (h).
• the inlet temperature determines the transition between the logistical functions.
• T v (h) The range of values of T v (h) is therefore intended to include only functional values between the boiling point of the first component, ie the low boiler and the inlet temperature, ie the temperature at the inlet. This is followed by the support vector and the span:
• T inlet is normalized to the boiling temperature of the second component and the boiling point of the first component is set to "0". Furthermore, in a further embodiment, it is assumed that a value range of T ab (h) lies between the feed temperature T feed and the boiling point of the second component.
• the logistic function in the stripping section T ab (h) should be a Value range between T inlet and the boiling point of the second component, ie the high boiler have. This results in:
• a respective compression k v or k decreases in the direction of the respective height from a comparison of a slope of the logistic function f (x) in its inflection point and of the measured temperature profile T * (h) in it Determines inflection point, wherein the inflection point of T * (h) is calculated from an average of respective slopes in a respective inflection point of temperature curves determined from jump tests.
• the compression in the direction of the height k v or k ab thus results from a comparison of the slope of the logistical function and the real temperature profile at the point of inflection.
• h 0, v and h 0, ab can be calculated via an arbitrary temperature point T at a position h in the respective region or part of the column, ie in the amplification part or in the output part by conversion of a respectively corresponding one of the above equations.
• h 0, v and h 0, ab can be calculated via an arbitrary temperature point T at a position h in the respective region or part of the column, ie in the amplification part or in the output part by conversion of a respectively corresponding one of the above equations.
• h 0, v and h 0, ab can be calculated via an arbitrary temperature point T at a position h in the respective region or part of the column, ie in the amplification part or in the output part by conversion of a respectively corresponding one of the above equations.
• measurement inaccuracies such as measurement noise and drift
• the present invention proposes, in a further embodiment, to supplement the method described above with a parameter estimation in order to compensate for the mentioned disadvantages, where h 0, v and h 0, ab are respectively determined by a parameter estimation become.
• the running parameter i indicates the respectively existing temperature measuring points in the gain region or part or in the output region or part.
• the parameter h 0 , ie h 0, v for the amplification part and h 0, ab for the output part shall be estimated. This is a nonlinear minimization problem because the parameter is in the exponent.
• the Gauss-Newton method is used for the estimation.
• a residual vector describes the actual deviation from estimated to measured temperature and forms as follows
• step size s is then calculated as follows:
• D is a vector. Therefore, among other things, the inversion from equation (15) with (13) simplifies to:
• control variables the coolant quantity and the amount of steam are used.
• FIG. 1 shows a schematic representation of a rectification column which can be regulated in accordance with an embodiment of the method according to the invention.
• FIG. 2 shows exemplary temperature profiles of a rectification column after carrying out jump tests, wherein a coolant quantity has been changed in each case as an abrupt change in each case in accordance with a changed manipulated variable.
• the rectification column shown in FIG. 1 is, for example, incorporated in a plant for the production of toluene diisocyanate (TDI).
• the column shown has the task of supplying TDI reaction lines with vaporous phosgene.
• the column has an upper area, ie a head area and a lower area, ie a sump area or sump.
• phosgene accumulates in the top as the top product and in the bottom ODB as the bottoms product.
• the resulting overhead product is, unlike a standard column, not total condensed, but withdrawn in vapor form. Therefore, the column shown in Figure 1 contains no condensate tank. Instead, a plug-in capacitor is used.
• the phosgene is filled on the one hand in the form of phosgene solution via an inlet F2 with inlet valve Y3. On the other hand, it is applied to the top of the column Fl as liquid phosgene in pure form.
• the phosgene solution consists of approximately equal parts of phosgene and the solvent ODB.
• coolant Via a valve Yl at the top, coolant is fed via a coolant inlet F3. supplied keit or coolant.
• the cooling liquid can be removed from the column again via a drain G3. Via a pressure gauge PI, the pressure is measured, which is to be kept substantially constant.
• the column is divided into two parts, namely an upper rectifying section, which lies between inlet F2 and the top of the column, in the case shown here in the range of 24% to 100% of the column height, and a lower stripping section between inlet F2 and bottom of the column, ie in the case shown here between 0% and 24%, divided.
• phosgene is enriched as a low-boiling component.
• the phosgene is dissolved from the solvent ODB.
• the position of the temperature sensors is particularly important. As a rule, neither the head nor the sump temperature is normally used directly for the control, but temperatures between the inlet F2 and the respective product outlet. In this case, the temperatures of the temperature sensors T2 to T4 for the control of the overhead product concentration and in the stripping section the temperature of the temperature sensor T6 for the regulation of the bottoms product concentration come into question in the amplification part.
• FIG. 2 shows a temperature profile T * (h) of the rectification column from FIG. 1 before and after it has been carried out
• Characteristic of the respective courses shown are per temperature profile per jump test in each case two S-shaped temperature curves. The first covers the enrichment section between head of the column (100%) and feed F2 (24%), the other the stripping section between inlet F2 and bottom of the column (0%).
• the characteristic S-forms are conserved during jump attempts and are only along the column height, i. moved along the abscissa. This results in the approach of approximating the behavior of the column in the jump tests by shifting a static characteristic curve. From the observations of the jump tests, the following can be seen: The fluctuation width of the stationary gain of the temperature (along the ordinate 20) is greater than the fluctuation width of the displacement of the characteristic (along the abscissa 10).
• a temperature measurement point at 40% of the column height changes dramatically by about 20% only in the last jump.
• a temperature for example 40% on the abscissa 10
• an approximately linear course can be recognized.
• the height step
• the temperature whose height is to be monitored must be between the boiling points of the pure substances, i. of phosgene and ODB. It lends itself to the temperature, which describes the position of the fronts in Figure 2.

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• Chemical & Material Sciences (AREA)
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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Automation & Control Theory (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
• Investigating Or Analyzing Materials Using Thermal Means (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 2017
  • 2017-08-01 KR KR1020197003091A patent/KR102416360B1/ko active IP Right Grant
  • 2017-08-01 CN CN201780049010.6A patent/CN109562302A/zh active Pending
  • 2017-08-01 WO PCT/EP2017/069397 patent/WO2018024711A1/de unknown
  • 2017-08-01 JP JP2019505500A patent/JP2019524436A/ja active Pending
  • 2017-08-01 EP EP17751062.5A patent/EP3493888A1/de active Pending
  • 2017-08-01 US US16/322,990 patent/US11235260B2/en active Active
• 2022
  • 2022-06-08 JP JP2022092696A patent/JP7391141B2/ja active Active

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