DE3420001A1 - METHOD FOR REGULATING THE VACUUM COOKING PROCESS FOR PRODUCING CRYSTALLINE SUGAR - Google Patents

Description

Name: Procedure for regulating the vacuum cooking process for the production of crystalline sugar

Description:

The invention relates to a method for regulating the vacuum cooking process for the production of crystalline sugar, woüei setting the consistency of the filling during cooking and Crystallization process by regulating the syrup supply depending on given values for the consistency the filling compound takes place, the level of the filling compound being continuously measured in the cooking apparatus after the inoculation and the target value for the consistency depending on the level measured value is changed according to a predetermined course until a maximum level is reached.

Crystalline sugar is usually produced in cooking equipment in which sugar-containing plants are pressed or extracted, then purified and pre-concentrated syrup so far under the action of heat and Dehydration is thickened so that a supersaturated sugar solution is formed. This oversaturated sugar solution becomes

usually rait finely ground sugar (slurry) or with a crystal suspension (crystal base) added (inoculated) from the production process, so that the sugar from the crystallize supersaturated reading on the presented crystals can. As it crystallizes out, further pre-concentrated syrup is continuously drawn into the apparatus, whereby in order to maintain the optimal supersaturation state for the crystal formation additionally condensate, i.e. water can be drawn in. The supply of

IQ of further filling compound and possibly of condensate takes place depending on the continuously measured consistency of the filling compound. As soon as the maximum filling level is reached in the cooking apparatus, every syrup and condensate intake is stopped and the entire filling is boiled with additional heat until a specified maximum value for the consistency is reached. After the boiling process has ended, the crystal suspension is separated into crystals and drainage using a centrifuge.

^The term consistency in the present case includes the so-called rheological value of the filling of the cooking apparatus, which is described at the beginning of the syrup intake by the viscosity of the crystal-free syrup and in the further course of the cooking process by the consistency of the filling compound consisting of mother syrup and crystals. From DE-AS 22 14 850 an automatic control method is known in which this rheometer value is used as a reference variable for automatic control of the cooking process. After thickening a basic filling quantity on the for

go to a degree of supersaturation required for crystal formation, which can be determined on the basis of empirical tests by a certain rheometer value, is the filling inoculated and, after inoculation, the setpoint of the reference variable while continuing to draw in syrup and condensate "Rheometer value" as a function of the increase in the level according to a predetermined program changed to increasing the maximum level is reached and the other

Syrup and condensate intake stopped and continued supply of heat the filling is boiled down until a specified maximum value for the reference variable "rheometer value" is achieved. After the boiling process has ended, the crystal suspension is converted into crystals using centrifuges Separate process.

The aim of all automatic control processes is to check the degree of supersaturation in the cooking appliance after the inoculation To keep the filling compound constant in a narrow range with further addition of syrup, in order to achieve as much as possible on the one hand to bring about rapid but uniform crystal growth of the seed germs, but on the other hand a further increase to prevent the degree of oversaturation, namely not only to irregularities in the crystal structure of the already existing crystals, for example twin formation, would lead, but also in the further course of the cooking process would lead to spontaneous crystal formation from the supersaturated solution, so that At the time of boiling, there are crystals with considerable grain differences in the filling compound. The fine grain fraction however, it is undesirable. Therefore, the crystal content of the filling compound must be limited, otherwise the resulting Impermeability of the crystal slurry in the centrifuge does not provide sufficient separation of the drain from the crystal cake and also no specific rewashing of the crystal cake is possible. But this means a lower one Crystal yield from the pre-concentrated syrup used and a correspondingly higher return from the drain in the manufacturing process. The fine grain fraction contained in the centrifuged crystals must then be expensive Separate sieving systems, dismantled again and returned to the crystallization process.

With the previously known method, attempts have now been made to reduce this narrow range for uniform crystal formation to achieve the necessary degree of oversaturation by

that in addition to a linearly increasing rheometer value, based on empirical studies, only the one with increasing Crystal growth in the filling compound also increasing consistency of mother syrup and crystals filling compound also takes into account condensate in addition to the syrup intake, i.e. water is drawn in in order to avoid excesses here to prevent the degree of oversaturation, which would lead to fine grain formation. With such an energy-intensive one The process of boiling sugar has every addition of additional water during boiling and cooking Crystallization process results in an additional expenditure of energy. Attempts have therefore been made to have automatic regulations to be designed on the basis of the previously known method, but in this case to reduce the energy requirement the condensate intake has been omitted to support the control. However, this immediately had the one described above undesired fine grain formation as a result. To avoid fine grain formation, attempts have been made, for example, by the additional installation of agitators a greater homogeneity of the contents of the apparatus and thus a more uniform crystal growth to reach. Furthermore, efforts were made to do this through the use of quickly responding measurement, control and To ensure control systems through a linear link between the syrup intake and the reference variable. These However, measures did not lead to the desired success.

An optimization in itself would only be possible by strictly adhering to a characteristic crystal spacing, whereby the crystals that form during the cooking process must serve as "regulators" for the course of the process. Because for this however, there are no sensors, the object of the invention is based on the previously known Method, namely the regulation of the cooking process depending on the consistency of the filling compound, but below Avoidance of the previously known disadvantages of creating a control method that does not require additional condensate to support the control for a higher crystal yield with a considerable reduction in the fine grain

'tr

part leads.

The object according to the invention is achieved in that, in order to change the setpoint value for the consistency, as a function of an exponential function of the measured level value

^{= k} 1 " ^ex P <VV ^{+ k} 3

it is specified that each time a starting point is reached

levels h., the actual value Rh of the consistency of the filling compound is measured in the cooking apparatus before the inoculation / that, according to the measured actual value Rh _a, the starting point of the setpoint curve relevant for the regulation by changing the constants k .. and k, depending on from the fair IJ

nen consistency actual value Rh is automatically adapted and after the relationship

k ₁ = a * Rh _A + b
and

k ₃ = c · Rh _Ä - d.

The advantage of this control method is that by specifying the exponential function specified above for the management of the rheometer setpoint of the crisis

installation process can be carried out so that the crystals produced have a much narrower particle size distribution spectrum have than in the previously customary processes, with the additional supply of as a further advantage Water to compensate for excess concentrations

can be completely dispensed with during the regulated crystallization process. The constant k n given in the formula is an apparatus constant / which takes into account the characteristics of the cooking apparatus in question and the corresponding sensor (rheometer, V / K transmitter, radiometric DicntemeiistrecKe). This constant is determined by a series of experimental _{tests in which the parameter Ic 9} , which specifies the steepness of the expnential function, is varied until an optimum crystal yield is achieved

and uniformity of the crystals produced is achieved. The cooking process is now divided into two phases / namely a first controlled phase, in which one is controlled by corresponding Minimum filling quantity kept constant by water evaporation thickened to the degree of supersaturation which then enables crystal formation by seeding with crystal nuclei. This degree of oversaturation is, as already stated above, determined by an empirically determined rheometer value. To After the inoculation, the regulated cooking phase follows, i.e. the further syrup supply into the cooking apparatus up to the specified The maximum filling level is dependent on the specified course for the rheometer setpoint. An exponential curve, which only takes into account the apparatus constant k "would presuppose that the initial value of the rheometer setpoint corresponds exactly to the rheometer value at the time of vaccination. However, this can be done in practice not achieve because the consistency of the syrup ZUIu vaccination time due to different initial compositions can be different. The transition from the controlled phase to the regulated phase is therefore in a A number of cases result in a "jump" in the rheometer setpoint, which would immediately lead to disturbances in the crystallization process. Accordingly is in the exponential curve A correction option is provided for the course of the rheometer setpoint during the regulated phase the constants k .. and k_, which indicate the state of the cooking appliance filling at the time of the transition from the controlled phase to the regulated phase. These constants are immediately before the transition to the regulated phase via auxiliary functions depending on the one to this The actual rheometer value measured at the time is determined and then inserted into the exponential curve. With the With modern technical aids in data processing it is possible to set the rheometer starting value practically time-synchronously Rh as a data signal correspondingly constructed arithmetic blocks of the control circuit, which then accordingly

the input measurement signal to the specified computer program
"Rh" transform accordingly and then as constants Jc ₁ and
Ic, enter into the control module for the management of the rheometer setpoint so that the rheometer value Rh equals the

Rheometer value Rh ,, at the starting point of the exponential curve
is.

The constants a, b, c and d of the auxiliary functions for adaptation the initial value of the exponential curve can in turn be determined empirically by appropriate test samples.

Is used after determining the constants specified above
the regulated crystallization process over the specified
Exponential curve for the rheometer setpoint performed, see above

As already explained above, the crystallization process can be carried out without the addition of condensate
and still offers the advantage that what used to be common
Boil the filling mass without adding any further syrup except for
a given rheometer end value can be omitted. at

In the process according to the invention, when the specified fill level is reached, the crystallization process is also completed, and with regard to an optimal, ie
uniform grain size distribution that of the previously known
Process possible irregularities in the crystal formation are avoided.

In one embodiment of the method according to the invention it is also provided that the temperature of the filling compound is regulated according to a temperature setpoint during the regulated management of the crystallization process, the is changed as a function of the level measured value, namely according to the relationship

T ,, = k. · H .. + k, -,
should 4 N 5

where k. proportional to the available cooking time is and kj- the temperature measured at the time of vaccination

corresponds to the filling mass in the cooking appliance, k. is here the temperature gradient / through which the evaporation capacity, i.e. the cooking time or the applied supersaturation potential, is implicit is specified / while the constant k, - again, the bumpless transition when switching is effected from the controlled to the controlled phase / because this is the starting temperature value for the controlled phase is given. The constant k «is specified in such a way that it is available within the range for the cooking apparatus in question standing boiling time the necessary water evaporation is also provided. It should be noted that Usually there is not one cooking apparatus in a cooking station, but that several cooking apparatuses one cooking station form / so that despite the batch-wise operation for the individual cooking apparatus for the entire cooking station overall results in a quasi-continuous mode of operation. The temperature setpoint management according to the invention takes into account here / that the initial phase, which is so important for the crystallization, in which the available The crystal surface is still relatively small / a the highest possible cooking temperature can be specified in order to avoid an excessively high oversaturation potential. With increasing Growth of the crystals in the filling compound can then be achieved by a regulated lowering of the temperature of the filling compound the evaporation capacity can be increased. This is done in usually via a corresponding regulation of the vacuum applied to the respective cooking appliance. (Cascade control)

The method according to the invention is based on an exemplary embodiment explained in more detail. The schematic drawings show:

1 shows a cooking apparatus with a control circuit,

Fig. 2 schematic cooking curves with different

Initial values that show the relationship between the rheometer value and the filling level in the cooking apparatus specify in%,

* Λλ 3420Q01 Fig. 3 shows the crystal growth curve with a control according to the invention compared to the control according to the prior art.

The crystal size distribution was used on an existing cooking apparatus and yield optimal operating points are determined. A maximum cooking time of 4.5 hours, a parboiling volume of 35% of the level output signal and a boiling point at 80% of both the level height in the cooking apparatus as well as the rheometer value. The cooking apparatus was used to generate a RZ 2 product, which was cooked over of an accumulating RZ 1 effluent with a dry matter content between 70 and 78%. The constant k ~ was then determined by experimental broth with regard to an optimum of yield and crystal size distribution, resulting in a value of 0.0185.

The temperature control was also determined by experiments, whereby the course of the temperature setpoint curve the constants k. = - 0.1333 and the constant k, - with 86.67, i.e. the starting temperature of the cooking mass revealed.

The tests resulted in the following values for the auxiliary functions for determining the constants k .. and k _3:

k ₁ = - 0.4 * Rh _A + 31.6

and

k = 1.8. Rh - 60.2.

ό Ά.

When comparing the control method according to the invention with the previously usual control method, which showed a linear link between the rheometer value and the measured level value, revealed in terms of the factors

a) Crystal yield

b) Crystal size distribution
c) Cooking time (batch duration)

with a cooking apparatus without a stirrer and a pre-concentrated syrup with a sugar content of 82 percent by weight The following values in relation to the dry matter:

a) Crystal yield:

linear leadership: average yield = 40% exponential leadership:
average yield = 50%.

b) Crystal size distribution: (according to RRSB):

starting from a crystal base with η = 3.3 and d ¹ = 0.42 mm

linear guidance: η = 3.4, d ¹ = 0.89 mm exponential guidance: η = 4.8, d ¹ = 0.98 mm

This result is in the crystal growth curves shown in FIG reproduced.

c) Cooking time (batch duration):

starting from the same crystal quality and crystal yield, the cooking time could be reduced by 30% be reduced.

In Fig. 1, the control according to the method according to the invention is shown in the form of a block diagram. A Cooking apparatus 1 is connected to a syrup supply line 2 in its lower area. In the syrup feed line 2 a control valve 3 is installed, which can be adjusted with respect to its open position via a positioner. in the In the lower area of the cooking apparatus there is a heating chamber 5 which is acted upon by heating steam and via which the heat of evaporation is generated is introduced into the cooking apparatus filling. The interior of the cooking appliance 1 is in the upper area

connected to a vacuum line 6, with a control flap 7, which is provided with an actuator 8, the vacuum acting on the interior of the cooking appliance and thus the evaporation capacity can be regulated.

The measurement data that are important for the control are once via a level measuring device 9, a sensor 10 for measuring the viscosity or consistency of the cooking apparatus filling and a temperature sensor 11 measured. 10

The position of the individual measuring elements is only schematic here and is based on the measuring principle on which the respective measuring device is based.

In the exemplary embodiment shown, the consistency is measured using a so-called rheometer. The measurement signal emanating from the rheometer is now fed to a control circuit 12 and processed there. Since a setpoint curve dependent on the measured initial rheometer value is to be specified, the actual rheometer value Rh measured at a certain point in time is fed to a computation module containing the auxiliary function for determining the constant k and a processing module 14 containing _{the auxiliary function for determining the constant k 3.} The constants k determined by the arithmetic modules. and k ₃ are then fed to a target value computer 15 which defines the target value curve applicable for the respective batch with its starting point. As soon as the target value curve is fixed, which is indicated here schematically by block 16, the rheometer 10 is switched to this part of the control circuit, so that the difference between the target and actual value of the rheometer value required for the regulation is formed while the measuring signal from the level sensor 9 is switched on at the same time Output signal is generated, which is connected to the actuator 4 of the syrup intake valve 3 and adjusts this according to the sign of the output signal in the opening or closing direction.

The temperature sensor 11 is connected to a temperature controller 17 switched on / to which the level measurement value is supplied as a reference signal is / with the help of which the setpoint curve for the temperature control is changed depending on the level. 5

Fig. 2 shows schematically different cooking curves of the same cooking apparatus / thus with constant k_ for the exponential function of the rheometer setpoint but different initial values, as they result directly from the adjustment process before initiating the regulation phase, taking into account of the measured actual rheometer value during the transition from open-loop control to closed-loop control. In the diagram is the boiling phase until the time of inoculation is marked with I and the crystallization phase after inoculation until the end of the brewing with II. The same markings are also given in Fig. 1 in relation to the level of the cooking apparatus. The strongly drawn-out rheometer setpoint curve in FIG. 2 also shows the course of the rheometer value for phase I added. For this phase the cooker is filled to 35% of the maximum level for each batch, i.e. filled so high that the heater 5 is covered with syrup at a certain height. That running out of the syrup evaporating water is now supplemented by continuous syrup while keeping the level constant, so., jdaß this Filling quantity is concentrated and has finally reached a certain degree of supersaturation. Due to many years It is known from experience that a certain rheometer value indicates the most favorable degree of supersaturation for vaccination. As soon as this rheometer value is reached, in the diagram according to FIG. 2, this is point 18, this measurement signal becomes first fed to the arithmetic units 13 and 14 to determine the auxiliary function, the result signal of which is then the setpoint computer 15 is supplied, which adapts the setpoint curve relevant for the regulation so that the initial value the setpoint curve corresponds to the actual rheometer value measured at the time of vaccination, so that when switching from the control in phase I to the control in phase II the transition takes place smoothly.

Claims (2)

Maxton · Maxton · Langmaack Patentanwälte Patentanwalts Maxion & Langmaack - Plerdmengesstr. 50 - 5000 Cologne 51 Alfred Maxton sr. (1943-1978) Applicant: Pfeifer & Langen Alfred Maxton Linnicher Str. 48 Jürgen Langmaack Graduated Engineers rru) 5000 Cologne 41 Admitted to the European Patent Office 5000 Cologne 51 Our reference date 646 ρ 841 28.05.84 Designation; Method for controlling the vacuum cooking process for the production of crystalline sugar claims; 1. Procedure for regulating the vacuum cooking process Manufacture of crystalline sugar, adjusting the consistency the filling mass during the cooking and crystallization process by regulating the syrup supply as a function of the specified Values for the consistency of the filling compound takes place and wherein after inoculation during the regulated leadership During the crystallization process, the level of the filling compound in the cooking apparatus is continuously measured and dependent on it From the level measured value, the target value for the consistency according to a specified course until it is reached of a maximum level is changed, characterized in that to change the setpoint for the consistency as a function of the measured level value an exponential function ^{= k} 1 * ^{exp (k} 2 * V ^{+ k} 3 Telephone: (0221) 380238 Telegram: Inventator® Cologne Telex: 8883555 max d Postgirokonto-CCP Cologne (BLZ 37010050) Account No. 152251-500 Deutsche Bank AG Cologne (BLZ 37070060) Account No. 1236181 it is specified that when an initial level h is reached in the cooking apparatus, the actual value Rh of the consistency of the filling compound is measured before the inoculation, so that the starting point of the setpoint curve relevant for the control is changed by changing the constant k _{according to the measured actual value Rh A.} . and k ~ is automatically adapted as a function of the measured actual value Rh, namely according to the relationship k = a * Rh + b 1 A k_ = c · Rh - d. 2. The method according to claim 1, characterized in that in addition the temperature of the filling compound during the regulated Management of the crystallization process is regulated according to a temperature setpoint, which is dependent on is changed by the level measured value, according to the relationship ^T should ^{= k} 4 * \ ⁺ V where k. proportional to the available cooking time and k- is the temperature measured before the time of vaccination corresponds to the filling mass in the cooking appliance.