DE3126552A1 - "METHOD FOR CONTROLLING STIRRING PROCESSES" - Google Patents

Abstract

The method allows an automatic control by means of an electronic data processing device (46) of all the parameters of a mixture process in a mixture container (10) provided with an agitator. The power absorbed is so adjusted as a function of the viscosity of the product to be mixed, measured continuously, that the mixing action is just kept up. The continuous measuring of the viscosity of the product is effected by a successive approximation based on measured values of the rotation torque of the agitator and of the number of revolutions of the agitator, as well as from the empiric relationship between the Reynolds number and the Nusselt number. To calculate the Reynolds number, a viscosity value based on experience is first taken; then, from the Nusselt number which is part of the calculated Reynolds number, the rotation torque value of the agitator corresponding to the estimated viscosity is calculated. Said value is compared with the effective rotation torque. If the two values of the rotation torque diverge, the estimated viscosity is corrected until the two values coincide.

Description

PATENT LAWYERS

Dipl.-Ing. MAX BUNKE
Dipl.-Chem. Dr. HOLGER BUNKE
Dipl.-Phys. HARTMUT DEGWERT

JOHANNES-SCHARRER-STRASSE 13 · D-BCK) O MUNICH 21

Munich, July 3, 1981 P 5025

Method for controlling stirring processes

The invention relates to a method for controlling stirring processes, in particular a method for regulating the power consumed by an agitator in a stirred tank taking into account the properties of the material being mixed, a method for determining the viscosity of a material to be stirred in a stirred tank, the stirrer of which at a given Speed emits a torque dependent on the viscosity of the material to be stirred, as well as a method for controlling the stirring parameters a stirring process in a stirred tank equipped with a stirrer by means of an electronic data processing unit icht.

In practically all areas of the chemical industry, stirring processes are used to manufacture chemical products. These agitation processes, which can take several hours or even days, require a considerable amount of energy both for the agitator drive and for the supply of heat or cooling of the agitated material in exothermic processes.The power required for the agitator drive depends on the one hand on the speed of the agitator and on the other hand on the viscosity of the material to be stirred from ₀ The viscosity of the material to be stirred changes during the various phases of the stirring process. The stirring process is only maintained if the agitator worked at a certain minimum speed for a given viscosity of the material being stirred.

The control of stirring processes is usually done by time-dependent program circuits "The for maintenance The energy supply required for the process, in particular the agitator output, is based on experience Time program controlled ο Since you essentially must use average values and maintain a sufficient safety margin from the minimum performance required for maintaining the stirring process, such control cannot be optimal Using energy «If the stirring processes are carried out with a constant speed of the agitator, must the speed can be designed in such a way that it satisfies the most unfavorable conditions, i.e. the one at a point in time during the stirring process corresponds to the highest power required or possibly the highest speed required at another point in time. This is not only a disadvantage because the agitator is unnecessary during most of the agitation process high power consumption works, but in addition, the agitator or its drive motor and gear unit must be designed for a relatively high continuous load, whereby the material and construction costs and these manufacturing costs increase.

- fj -

The object of the invention is in particular to create a method for controlling stirring processes, through which the the deficiency set out above can be remedied. The method according to the invention is intended in particular to achieve a substantial saving enable the drive energy supplied to the agitator in the course of a stirring process by increasing the speed of the The agitator is controlled in such a way that the agitator drive only delivers the optimum power that is required to keep the stirring process going. Furthermore, an automatic control of all stirring parameters should be optimized Total power consumption in the course of the stirring process; it reached will.

The process according to the invention for controlling the agitator, taking into account the power absorbed in the stirred tank the properties of the respective mix is thereby characterized in that the optimal power consumption of the agitator is determined empirically for the particular material to be stirred is the maintenance at a given viscosity value of the material to be stirred, which depends on the respective stirring phase of the stirring process taking place in the respective stirring phase with minimal expenditure of energy. Furthermore, the viscosity of the material to be stirred is continuously determined during the entire stirring process. The speed or the The torque of the agitator is then readjusted on the basis of the viscosity values determined in each case for the material being stirred until the The power consumed by the agitator corresponds to the empirically determined optimum power consumption. The invention is based So on your thoughts that the speed of the agitator depending on the viscosity of the material being stirred, it is regulated so that it is just sufficient, to keep the stirring process going.

The ongoing determination of the viscosity of the material to be stirred is basically possible with existing equipment difficult, and in addition, common viscosity

BATH ORIGIN /

measuring devices very expensive. The invention therefore provides Furthermore, a method for the ongoing determination of the viscosity of the material to be stirred in a stirred tank in the course of the stirring process, that is, the use of conventional viscosity measuring equipment makes redundant. The method according to the invention for continuous measurement of the viscosity of the material being stirred is as follows Process steps marked:

a) the Reynolds number of the mix is calculated from

- the values characteristic for the dimensioning of the agitator;

- the specific weight of the material to be mixed;

- the measured speed of the agitator; and

- an approximate value of the viscosity estimated on the basis of empirical values;

b) the one belonging to the calculated Reynold number due to Nusselt number known from empirical studies is determined;

c) from the Nusselt number determined in this way, the speed of the agitator, the specific weight of the material to be mixed and the values characteristic for the dimensioning of the agitator the associated theoretical torque is calculated;

d) The theoretical torque is measured with the actual Torque of the agitator compared;

e) depending on the difference between the theoretical and the actually measured torque, the corrected estimated approximate value of viscosity; and

f) the calculations according to process steps a) to e) are based on the corrected viscosity values

BATH ORIGINAL

repeated until the difference between the theoretical and then actually measured torque is less than a is the specified limit value.

The method according to the invention thus enables the ongoing Determination of the viscosity of the material to be stirred in the course of the stirring process solely on the basis of the measured speed of the stirrer plant and the torque with which the agitator is driven, as well as due to the easily determined specific Weight of the mix and due to the known dependence of the Reynolds number on the nuts from empirical studies number. The calculations required in the course of a continuous viscosity determination carried out according to the method according to the invention by successive approximation can be slightly medium a suitable data processing device. Microprocessor or microcomputer systems are particularly suitable, all other control and monitoring functions in addition to the ongoing calculation of the viscosity of the agitator of the agitation system.

In a further embodiment of the invention, a method for controlling the stirring parameters of a stirring process by means of an electronic data processing device created, which invention :. is characterized in that the Stirring parameters, in particular the composition of the material to be stirred, as well as temperature and pressure in the stirring vessel, at the beginning of the Stirring process via a data input station in the data processing device be entered; the data processing facility Depending on the data entered, Ei controls directions which determine the stirring parameters, in particular Inlet valves for charging the stirred tank with the material to be stirred, heating device of the stirred tank and Pressure control; the data processing device taking into account the agitation parameter from the measured speed of the agitator and the torque output by this under utilization the empirically determined relationship between Reynolds number and Nusselt number, the viscosity of the mix continuously

BATH ORIGINAL

calculated during the various stirring phases? and depending on the calculated viscosity of the mix the torque or the speed of the agitator is controlled so that the power consumption of the agitator is equal to one empirically determined optimal power consumption is at which the maintenance for the calculated viscosity value the ongoing stirring process is still guaranteed "

This inventive method enables the automatic Control of the entire stirring process: - · Esses, starting with the entry the mix composition at an input station of the data processing device, ZoBo on a keyboard until the end the stirring process, which is achieved when a predetermined period of time has elapsed or when a certain target value for the viscosity of the material to be stirred has been set.

In the course of the entire stirring process, the data processing device takes on the control functions assigned to it all monitoring functions, which ensure safe operation of the agitation system «

Advantageous further developments of the invention are set out in the subclaims marked.

Further advantages and features of the invention emerge from the following description of exemplary embodiments and from the drawing referred to. In the drawing show:

Fig. 1 is a schematic view of a stirring system used for Implementation of the method according to the invention is suitable is, with the stirred tank shown in vertical axial section and in plan view?

Fig. 2 is a flow chart of a subroutine for calculation the viscosity of the material to be stirred via successive approximation; and

^BAD ORlGt _NAL

- .. '■''Υ'ι JI Ό J. 312655;

Fig. 3 is a flow chart of a complete control program to explain the method according to the invention.

The generally cylindrical stirred tank shown schematically in vertical axial section and in plan view in FIG 10 has an agitator with a coaxial agitator shaft 12 and agitator blades arranged thereon at a distance from one another 14 on. The agitator shaft 12 is at its upper end of driven by an agitator drive 16 which is installed in a housing 18 and, in addition to the drive motor, a gear unit includes. The agitator shaft 12 is rotatably mounted in a main bearing 20 at the upper end of the agitator container 10. That too Housing 18 is rotatably mounted on the stirred tank 10. It has a radially outwardly projecting arm 22 which rests on one of two pressure cells arranged opposite one another 24, 26, which are rigidly connected to the stirred tank 10. Through the pressure cells 24, 26 of the Agitator drive torque delivered to the agitator shaft can be measured in both directions of rotation.

The stirred tank 10 has on its upper side two inlet connections 28, 30 which have different cross-sections. before the inlet port 28, 30 is each an inlet valve 32 and 34 is arranged. The inlet valves 32, 34 are provided with a suitable one Provide drive for automatic remote control. On the underside of the stirred tank 10 there is an outlet nozzle 36, to which an outlet valve 38, which can also be automatically operated remotely, is flanged.

The stirred tank 10 is surrounded by a heating jacket 40 over most of its height. The temperature inside the Stirring container 10 is monitored by a thermometer 4 2, the is arranged on the underside of the stirred tank and the heating jacket 40 penetrates. Above the heating jacket 40 is Furthermore, a level indicator 44 is arranged on the outer wall of the stirred tank 10.

A digital data processing device is used to control the stirring process 46 provided, which in Fig. 1 only seemingly as a housing with a digital display and with an input keyboard is shown »The data processing device 46 is via a plurality of lines with the Pressure cells 24c 26, the valves 32, 34, the agitator drive 16, the level indicator 44, the heating jacket 40, the thermometer 42 and the outlet valve 38 connected. It controls the actuation of the inlet and outlet valves through the heating jacket formed heating and the speed of the agitator drive 16 due to a stored in their program memory Program which, in addition to these control functions, also continuously monitors all operating values that are important for the stirring process guaranteed. The mode of operation of the agitation system shown schematically in FIG. 1 is described below under Referring to Fig. 3 will be explained in detail.

Referring to FIG. 2, a subroutine of the complete control program shown in FIG. 3 for the Execution of a complete stirring test explained.

The subroutine shown in FIG. 2 enables the viscosity of the material to be stirred in the stirred tank to be determined on an ongoing basis due to the measurement of the agitator drive from dom on the agitator shaft output torque and the speed of the agitator, which is preferably photoelectrically by means of a the agitator shaft 12 attached slotted or perforated disk and one attached to the container wall, with this disk cooperating photodetector arrangement is measured. This in The subroutine shown in FIG. 2 is used to calculate the viscosity of the material to be stirred according to a method of successive approximation. This calculation is based on generally known physical laws that make up the dependency the viscosity of the material to be stirred from the individual stirring parameters results. The viscosity η is a function of the speed n des

BATH

312655:

Agitator, the Nusselt number Ne, the Reynold number Re, des Agitator torque Md, the diameter d of the agitator and the specific weight g of the material to be stirred. So the following applies:

η = F (n, Ne, Re, Md, d, o).

Here the Reynold number is again a function of the Nusselt number. The following applies:

R = F (Ne).

The above relationships show that the viscosity of the mix cannot be calculated directly from the speed of the agitator and its torque. Rather, have to In addition, the Reynold number and the Nusselt number for the conditions given in the agitator must be known. Is the Reynolds number known, the associated Nusselt number can only be determined empirically. The dependence of the Reynolds number on the The Nusselt number is a complicated relationship, which in practice for given agitator conditions is only empirical can be determined and recorded in diagrams. An important feature of the invention is that this relationship between the Reynold number and the Nusselt number for the given agitator conditions is determined empirically and in is stored in a data memory of the data processing device. If the Reynold number is known, then stands for each Viscosity calculation, the associated Nusselt number is immediately available.

In order to obtain the Reynold number, an estimated approximate initial value is first based on empirical values the viscosity is entered into the data processing device, e.g. by means of a keyboard or another data input station. This is in Fig. 2 as the initial step 100 of the subroutine shown. In the subsequent steps 102 and 104, the speed n of the agitator and its torques

Md measured. Since the "agitator diameter d and the viscosity of the material to be stirred are previously known for a given stirring process, the Reynolds number can now be calculated according to the following relationship Re measured;

• 60 «η '

Where η is the estimated approximate initial viscosity value, and the factor 60 is based on the specification of the speed n in revolutions / minute.

The calculation of the Reynolds number Re is shown in FIG. 2 as a subroutine step 106 specified = Subsequent to the calculation of the Reynolds number Re, the Nusselt number Ne im is determined Step 108.

An associated torque can be derived from the Nusselt number by using known physical laws Calculate the Md ^ of the agitator according to the following relationship: κ

Md _R = -2 ^ 2. _No

This calculation is shown in FIG. 2 as subroutine _{step 110. In the following program step 112, it is then checked whether the torque Md R} calculated in this way corresponds to the actual torque Md of the agitator measured in step 104. This is generally not due to the rough estimate of the initial value of the viscosity entered in step 100; be the case, and then in step 114 the assumed initial value of the viscosity is corrected by a step of a predetermined size in the appropriate sense. The subroutine then returns to step 104 and runs through steps 104 to 112 again, specifically until the check carried out in this step 112 confirms that the measured torque value Md corresponds to the

BATH ORIGINAL

- yi -

calculated torque value Md _R results. The initial value of the viscosity specified in the immediately preceding calculation of the torque Md _R then corresponds to the actual value of the viscosity of the material to be stirred. The viscosity η of the stirring material has thus been found and can be displayed on a display board in step 116 and at the same time or alternatively stored in a working register of the data processing device in order to be used in the control program shown in FIG. 3 for regulating the optimal speed n of the stirrer will.

Referring to Fig. 3, the method according to the invention will now be described for controlling the stirring parameters of a stirring process by means of the electronic data processing device.

The data processing device preferably contains a microprocessor / a working memory, a data memory and a program memory comprising a fixed program memory part and a programmable program memory part. By doing Fixed-program memory section stores those control and monitoring functions that are required for each stirring process are, while specific program steps are stored in the programmable program memory part, which are adapted to the agitator used, the individual agitation parameters, etc. At the beginning of a stirring process, the individual stirring parameters via an input keyboard, a program card or the like. in the programmable program memory part can be entered.

The method begins with the start step 200 shown in FIG. 3, whereupon it is checked in step 202 whether the previously entered The mixing program is to be repeated. If the program is not to be repeated, in step 204 the new Entered stirring parameters, i.e., in particular the composition of the material to be stirred, temperature curve during the entire stirring process

.BAD ORiGINA!

ι *

process, duration of the stirring process or predetermined final viscosity of the material to be stirred, pressure conditions inside the stirred container, etc. If, on the other hand, a program is to be repeated, program step 204 is bypassed. In step 206 it is then checked whether the entire stirring process should run automatically. If not, the required control functions are set manually in step 208. If automatic operation is desired, the stirring process is started in step 210. In step 212, the specific weight g of the material to be stirred is then calculated from the composition entered in step 204. Step 212 is now followed as program step 214 by the subroutine shown in FIG. 2 with subroutine steps 100 to 116, ie it becomes dU; Viscosity η of the material to be stirred was measured. Then, in step 216, that torque value Md ,, / which corresponds to the calculated viscosity value η is fetched from the data memory. The setpoint Md _c ,, of the agitator torque is the value that is required to maintain the agitation process with minimal energy consumption by the agitator drive. The dependence of this nominal torque value on the various viscosity values was previously determined empirically and stored in the data memory. This dependency is the same for all stirring processes and therefore only needs to be determined once. In step 218 it is then checked whether the measured torque Md ^{agrees with the nominal value M (} 3 oll of the torque. If there is agreement, readjustment of the agitator is not necessary Senses readjusted by a predetermined step o By readjusting the speed, the torque of the agitator increases or decreases, depending on whether the speed has been increased or decreased. Following the readjustment of the speed of the agitator, the viscosity η is then first recalculated again, and the associated target torque is fetched from the data memory and then again with the in step 218

BATH ORIGINAL

measured torque compared. The speed readjustment takes place in that formed from steps 214 to 220 Program loop until, in step 218, there is agreement between the measured torque and the target torque of the Agitator is determined. In this state, the agitator system works with minimal energy consumption by the agitator a maintenance of the stirring process is just guaranteed. The agitator works during the whole Stirring process with optimal power consumption, which means savings in the Order of magnitude of up to 40% can be achieved. Furthermore, the entire agitation system can be used for a significantly short period of time load can be designed.

After a correspondence between the measured torque and the setpoint torque of the agitator has been determined in step 218, a check is made in step 222 as to whether a program-controlled automatic temperature switch should take place. If necessary, it is then checked in step 224 whether the viscosity value calculated in step 214 is one for which a temperature switch is provided in the stirring program. If necessary, the temperature is then readjusted in step 226 in accordance with the temperature jump provided in the stirring process, whereupon the program returns to step 214. However, if an automatic temperature changeover is not provided, or if the total viscosity value is not one at which a temperature changeover is to be carried out, a check is made in step 228 to determine whether the stirring process should be ended by making the viscosity value of the material to be stirred a predetermined value Value Hf _ert: has reached y. If this is not the case, a check is made in step 230 as to whether the stirring process should be ended by the lapse of a predetermined stirring time. When the intended stirring process time has elapsed, the stirring process is ended in step 232. If the intended stirring process duration has not expired, the program returns to step 214 '! If the test in step 228 has shown that the stirring process should be terminated, if

BATH ORIGINAL

312655,

If the intended end value t \ g _{& t} ±. ± has been reached, then in step 234 it is checked whether the viscosity value determined in step 214 _meets the desired end value -; _CT matches. Is that the case? So the program goes to the already mentioned end step 232 "If the viscosity end value is not reached, however, various monitoring functions of the agitation system are carried out in step 236." After the monitoring functions have ended, the program returns to step 214.

The program steps 204, 210, 212, 214, 216, 220, 226, 232 and 236 shown in FIG. 3 are subroutines, only one of which, namely the program step 214, was explained in detail with reference to FIG.

In the program step or »subroutine 204 z. B. the keyboard the data processing device is queried, or suitable program carriers are read out »The read out Data are then transferred to the main memory of the data processing device.

All control functions are grounded in program step or subroutine 210 carried out, which are necessary to start the stirring process. In particular, the intake valves 32, 34 controlled in order to charge the agitator container 10 with the desired material to be stirred. Further be the heating device provided in the heating jacket 40 and dai> Agitator controlled in a suitable manner.

In the program step or subroutine 212, the im Step 204 entered the composition of the stirred tank filling, the average specific gravity of the material to be stirred calculated, and the result is saved in order to remain available for the entire stirring process.

The program step or dv.s subroutine 236 also has special features. In it, the signals of the thermometer 4 and the level indicator 44 as well as other signals are monitored which are important for the operational safety of the agitator system, in particular the barrier pressure of the agitator bearing 20, the temperature of this agitator bearing and the power consumption of the agitator drive. If one of the monitored signals indicates a malfunction, the stirring system can be stopped automatically to take remedial action.

BAD ORJGlNA!

Claims (15)

PATENT LAWYERS Dipl.-Ing. MAX BUNKE
Dipl.-Chem. Dr. HOLGER BUNKE
Dipl.-Phys. HARTMUT DEGWERT JOHANNES-SCHARRER-STRASSE 13 · D-BOOO MUNICH 21 Munich, July 3rd, 1981 P 5025 PATENT CLAIMS Method for regulating the power consumed by an agitator in a stirred tank, taking into account the properties of the respective mix, characterized in that; - The optimal power consumption of the agitator is determined empirically for the respective material to be stirred at a given viscosity value of the agitated material, which depends on the respective stirring phase, a maintenance the stirring process taking place in the respective stirring phase with minimal expenditure of energy guaranteed; . - the viscosity of the material being stirred is continuously determined during the various stirring phases; - The speed or the torque of the agitator due to the particular viscosity value of the The material to be stirred is readjusted until the power consumed by the agitator is empirically determined optimal power consumption. 2. Method for determining the viscosity of a material to be stirred in a stirred tank / whose agitator delivers a torque that is dependent on the viscosity of the material to be stirred at a given speed,
characterized by the following process steps: a) the Reynolds number of the mix is calculated from - the values characteristic for the dimensioning of the agitator; - the specific weight of the material to be mixed; - the measured speed of the agitator; and - an approximate value of the viscosity estimated on the basis of empirical values; b) the Nusselt number belonging to the calculated Reynold number and known from empirical investigations becomes determined; c) from the Nusselt number determined in this way, the speed of the Agitator, the specific weight of the material to be mixed and the characteristic for the dimensioning of the agitator The corresponding theoretical torque is calculated; d) the theoretical torque is compared with the measured actual torque of the agitator; e) as a function of the difference between the theoretical and the actually measured torque corrects the estimated approximate value of the viscosity; and f) the calculations according to process steps a) to e) are repeated on the basis of the corrected values of the viscosity until the difference between the theoretical and the actually measured torque is less than a specified limit value. 3. Method for controlling the stirring parameters of a stirring process in a stirred tank equipped with a stirrer by means of an electronic data processing device, characterized in that - the stirring parameters, in particular the composition of the material to be stirred as well as temperature and pressure in the stirred tank, at the beginning of the stirring process via a data input station in the data processing device be entered? - the data processing device as a function of the data entered controls devices which determine the stirring parameters, in particular inlet valves for charging the stirred tank with the material to be stirred, heating device of the stirred tank and pressure control; - The data processing device taking into account the stirring parameters from the measured speed of the Agitator and the torque delivered by it, taking advantage of the empirically determined dependency between the Reynold number and the Nusselt number, the viscosity of the material to be stirred during the various phases of stirring calculated; and - depending _; The calculated viscosity of the material to be stirred, i.e. the torque or the speed of the agitator, is regulated in such a way that the power consumption of the agitator is equal to an empirically determined optimum power consumption at which the ongoing agitation process is still guaranteed for the calculated viscosity value. 4. The method according to any one of the preceding claims, characterized characterized in that the calculation and control functions for the agitator and / or for those determining the agitation process Mixing parameters carried out by a microprocessor to which a program memory and a non-volatile data memory are assigned. 5. The method according to claim 4, characterized in that the empirically determined dependence of the optimal line -A- Stungsaufnahme the agitator on the viscosity of the material to be mixed is stored in the data memory. 6. The method according to claim 4 or 5, characterized in that that the empirically determined dependence of the Reynold number on the Nusselt number is stored in the data memory will. 7. The method according to any one of the preceding claims, characterized in that from the composition of the material to be stirred its specific weight is calculated. 8. The method according to any one of the preceding claims, characterized characterized in that the torque of the agitator is measured by measuring the power consumption of the electric drive motor and converting the analog measurement signal into a digital signal. 9. The method according to any one of claims 1 to 7, characterized in that that the torque of the agitator is measured by means of a pressure cell, which is between that on the housing of the agitator tank rotatably mounted agitator drive and a part attached to the housing of the stirring vessel is arranged. 10. The method according to any one of the preceding claims, characterized in that the speed dea agitator photoelectrically is measured. 11. The method according to claim 3, characterized in that the data processing device allocates the material to be stirred controls gravimetrically in the stirred tank. 12. The method according to claim 3, characterized in that Jaß the data processing device allocates the material to be mixed controls volumetrically in the mixing tank. BAD OR / G / NAt mm C mm 13. The method according to any one of claims 3 to 12, characterized in that the data processing device the Output signals from sensors monitored, which are characteristic of the operational safety of the stirring system Measure sizes » 14. The method according to any one of claims 3 to 13, characterized in that the control and monitoring functions common to all stirring processes are controlled by a fixed program stored in a read-only memory and that the individual stirring processes and stirring systems associated control and monitoring functions are controlled by a programmable one Read / write memory stored program can be controlled ₀ 15. The method according to any one of claims 3 to 14, characterized in that that, following the calculation of the viscosity, depending on the calculated viscosity value, a temperature switch is made.