DE2311231C3 - Method for regulating the crystallization process of sugar solutions in a discontinuous cooking apparatus - Google Patents

Description

From DE-OS 18 12 457 is a method of regulation the crystallization process of sugar solutions in a discontinuous cooking apparatus known, With a crystal content of up to approx. 25%, the indentation depends on the supersaturation and then depends can be regulated by the crystal content. In this process, in an initial phase, the regulation of the Over-saturation only changes the water intake and when a certain crystal content of the filling compound is reached Depending on the crystal content, only the juice intake is adjusted. Even if these earlier orders in Generally working satisfactorily, it was not always the most energy-efficient and cooking-time-saving way Maintaining a balance between desugarization and evaporation performance is guaranteed.

Furthermore, an automatic cooking system is already known in which the moment of resistance is one in the cooking material moving sensor is used for regulation. This measured variable is a complex variable, not just the Viscosity, but also includes the crystal content. The measured value is dependent on the altitude The variable setpoint is compared in a controller and the syrup intake is controlled as a function of this. At the same time, the controller also acts on a condensate control valve via an addition relay. By setting The relay can be used to change the ratio of syrup to condensate. In addition, with this arrangement the supply of condensate is also automatically reduced as the level of the cooking substance rises.

It is also already known to use the conductivity to regulate the cooking process, which is the case with impure Products can serve as a substitute for oversaturation (see DE-OS 15 67 316). Analogous to the Rege-Jung the cooking process for pure products according to DE-OS 18 12 457 is in the known method in In the initial phase the level was kept constant through the intake of water and only in the later phase of the actual Crystal growth the level is raised by the juice feed programmed and according to the actual level the conductivity setpoint changes quickly in this

ίο the second phase the actual level before the target level, so will switched from juice intake to water intake, thus maintaining the pre-programmed level increase.

In the sugar crystallization process, roughly the program sections syrup feeding, thickening, sowing can be used or seeding, crystal growth phase of approx. 0-25% Crystal content, boiling up and boiling off can be distinguished.

In order to keep the circulation of the cooking substance going in the cooking apparatus, a certain water evaporation rate is necessary; it must be higher if there is no agitator supporting the circulation Heating vapor pressure.

For example, if a 50-ton white sugar brew Normal crystals with a mesh size of 0.6 mm in an apparatus with an evaporation rate of 8 tons per hour should provide and it is assumed that these crystals with unhindered crystallization 1.5 hours Need growth time, then a water evaporation of 8 · 1.5 = 12 t would be ideal. The apparatus will be but 67 t of feed syrup with 70 Brix was added, from which 17 t of water had to be evaporated. As a result, will the crystallization hindered with progressive desugarization by an excess of water, so that the Crystallization of the 0.6 mm crystals did not end after 1.5, but actually only after 17: 8 = 2.1 hours additional cubic meters of water drawn in in the initial phase of the process must also be used be vaporized. This costs additional heating energy and leads to a further handicap Crystallization, which manifests itself in an extension of the cooking time.

The situation changes when in the same apparatus, with the same evaporation capacity and the same Feed syrup coarse crystals with a mesh size of 1 mm are to be generated, with unhindered crystallization z. B. need 2.4 hours of growth time. A water intake of 2.2 t would be justified here. In the The slower-running desugarization shown in this example can also be used for manual cooking Trouble. In many cases, therefore, a lower concentration is used. Lack of water is therefore not the rule in the crystallization of white and raw sugar, but the exception.

Furthermore, water supply is justified from time to time if the concentration fluctuates due to disturbances occur in the infusion juice or the evaporation capacity increases due to fluctuations in vapor pressure.

The previous considerations only relate to

the sugar and water balance for the total brew. There is an approximately constant evaporation output one - largely dependent on the existing crystal attachment area - initially very small, then but as the crystallization progresses, increasingly greater desugarization is compared, which eventually soon by the given evaporation rate

'f is bordered. But also brings after observations ; ".;. Entering into the critical process start-up phase with : low desugarization compared to water intake none .X-J Disadvantages, provided that a lüistall content is reached 25% height increases of 30% are not significantly exceeded. When crystallizing With low evaporation speeds, juice intake has advantages over water intake. The circulation is less impaired as the consistencies2 of the cooking mass (magma) increase more slowly, the crystals are less restricted in their free movement and fewer conglomerates are formed.

The object of the present invention is to in a method of the type mentioned for a precise, quality-increasing process management and that energy-efficient and cooking time-saving maintenance of a balance between desugarization and evaporation capacity to care.

This object is achieved by the measures specified in the claims

The invention will be explained in more detail using a drawing; it shows

F i g. 1 the diagram of an automatic crystallization process and

F i g. 2 is a block diagram of the process automation.

In Fig. 1, the measured curves of viscosity a, consistency b and level c of the cooking mass (magma) in the cooking apparatus are plotted on a time axis.

FO the time the syrup feeding starts in the cooking apparatus 1 at the time of the radiator 1 with syrup is covered; the Siri draw-in valve 5 closes after the heating chamber is covered at time 1 1, always at the same height. In the period 1 1 to 1 2, the sugar solution is thickened up to a supersaturation number which is in the metastable range for sowing and in the intermediate range for inoculation. At time 12 , a defined amount of seed crystals is introduced or inoculated. In the period r2 to f 3, the crystals grow from zero to approx. 25% crystal content of the magma; Here, the oversaturation is achieved through the intake of juice or, in exceptional cases, through the intake of water. The increase in height when syrup is drawn in is monitored and limited. The supersaturation is determined by measuring the viscosity a . In the period f 3 to ί 4, the high boiling phase follows, in which the primary reference variable is the crystal content. This is recorded by measuring the consistency b, with the setpoint being increased in an adjustable manner in accordance with the rise in level. At f4 the maximum height is reached and the syrup intake is ended. At the time f 5 is the end of the game, which is detected and signaled by a limit value signal of the consistency. Then it is aerated and the finished brew is drained into the mash.

In the period after 1 6 the cooking apparatus is prepared for a new brew z. B. Evaporation, window flushing and evacuation.

With reference to FIG. 2, the control scheme is explained in more detail. In the schematically illustrated cooking apparatus 1, which can be heated with heating vapor, syrup can be drawn in via a control valve 5 or water can be drawn in via a control valve 6. The level c of the cooking substance in the cooking apparatus 1 is detected by a level sensor 3 which provides an electrical signal corresponding to the respective level c at its output. A transducer 2 is used to measure viscosity and consistency. The viscosity or consistency of the cooking material (magma) is detected by means of a cylindrical measuring body rotating in the syrup or in the cooking material, which is driven by measuring springs. The angle of rotation between the drive and the measuring body resulting from the moment of resistance of the cooking material is a measure of viscosity or consistency. In order to be able to cover the large measuring range up to »Sudende« and around

ίο at the same time with viscosity values between 60 and 400 cP to obtain a sufficiently high sensitivity and measurement certainty, two measuring springs are different Built-in spring constant The sensitive measuring spring forms the counter-torque in the viscosity range; the sum of both springs is the counter-torque in the consistency measuring range.

The respective angle of rotation is converted into an electrical measured variable in an amplifier part 4 (consistency b). A signal range between 60 and 400 centi-poise is cut out from this signal via an electrical threshold value stage, amplified and made available as a measurement signal for the viscosity a
Viscosity a, consistency b and level c are continuously recorded on a recorder 26. Furthermore, the measured values for level, viscosity and consistency are still used via limit indicators 27 to 31 to signal certain states; For example, the response of limit monitor 27 means "radiator covered", limit monitor 28 "seed point reached", limit monitor 29 "start boiling", limit monitor 30 "start of boiling" and limit monitor 31 "brew ready". These values are sent to the control and evaluated for corresponding commands in such a way that the control advances the device over the entire cycle.

The viscosity signal proportional to the oversaturation is fed to a comparison point 8 and here compared with the target value for the viscosity supplied by a setpoint generator 25. The setpoint is at Sowing set to a supersaturation value lying in the metastable zone, to which the cooking mass at the start of sowing via regulator 9 and actuators 7 acting on syrup or water intake valves 5 and 6 should be adjusted. If this is the case and the crystal seeds have been introduced into the cooking apparatus, it changes As a result of the growing crystals now in the juice, the relationship between the measured viscosity value the cooking mass and oversaturation of the

so mother syrups. The necessary correction is made by continuously increasing the target value for the viscosity performed. For this purpose, a motorized setpoint adjuster 18, 19 is started from time f2, which is adjustable in Time a potentiometer moves from the start to the end position. The measuring amplifier 20 detects the Change in resistance of the potentiometer and convert it into a current. This is in the multiplier circuit 10 multiplied by the viscosity gradient that can be set on the setpoint adjuster 32 and used as a Time-dependent increasing setpoint voltage added for correction of the setpoint value for the viscosity. The control deviation formed at the reference junction 8 acts in this phase via the controller 9 and Positioner 7 on the syrup intake valve 5 and stops

as a result, the oversaturation at the desired value.

In the high boiling phase, the regulation is always and in the growth phase from 0 to 25% crystal content

Balance between desugarization and evaporation capacity act on the syrup intake valve 5.

Is the balance between desiccation and evaporation in the growth phase between O to 25% crystal content disturbed, in the sense that the evaporation capacity or the nature of the feed syrup fluctuates, this can result in a hurrying away from the crystallization process express a large increase in the level of the cooking substance in the cooking appliance 1. In this case a safety device is used effective, which ensures that even with coarse brews, too high evaporation capacity or too highly concentrated drawing syrup the process does not get out of control and the set cooking time is adhered to will. This ensures that no more water has to be evaporated than for a specified one Cooking time is required for a given evaporation capacity. The safety device works Monitoring and, if necessary, maintaining an adjustable level rise appropriate to the crystallization in the growth phase up to boiling point. For this purpose, the motorized setpoint adjuster 18,19 over the measuring amplifier 20 time-dependent increasing current signal used in a multiplier circuit 11 is multiplied by the gradient of the height of the cooking compound supplied by a setpoint generator 33 will. This so-formed, time-dependent and possibly program-dependent increasing setpoint for the altitude is compared with the actual value supplied by the altitude sensor 3 in a comparison point 12 and the difference is fed to a limit value indicator 14 acting as a height limiter. This does not intervene as long as the actual level of the cooking material corresponds to the setpoint specified by the schedule lags behind. If, however, the specified target value is overtaken by the actual value, the limit value indicator 14 switches over the switch 22 the controller 9 so long via position controller 7 on the water intake valve 6, until the setpoint and actual value correspond to each other. If necessary, the limit monitor 14 is thus switched between Juice and water intake to regulate the level rise. In order to maintain the same control action when changing, is It should also be noted that for the two intake valves 5 and 6, the design ratio given by the juice concentration What is essential is instead of a limit value indicator acting as a two-position controller there is also a constant regulator that changes the ratio of the control interventions for water and syrup.

In this phase of the process, the planted seeds are carefully developed further, with precise adherence to them the oversaturation by the oversaturation control described above. With the growing size of the crystals, the crystal attachment surface increases to an even greater extent, which in the further course of the crystallization itself has an increasingly stronger control function on the oversaturation of the cooking material From a certain point in time after the seed has been planted, the regulation can be based on the crystal content be made if it is ensured that on the one hand the free movement of the crystals in the juice does not limited, on the other hand, the crystal gaps in the cooking mass are not too large. This is through It is possible to maintain and regulate the correct consistency values for the cooking material.

It follows from the above that if the grain growth phase is correctly managed, the change from the process control variables viscosity to consistency is relatively uncritical; the change can therefore be made depending on the consistency or time and will coincide approximately with the start of the boil-up phase. In the present circuit, the arrangement is such that the switch 21 is switched over by the limit indicator 29, so that the consistency control is now effective. To control the consistency, the signal proportional to the measured consistency b is compared in the comparison junction 13 with the consistency setpoint. In order to take into account the amount by which the target value of the consistency must be brought up with the increase in the filling compound level, a signal proportional to the measured level c is multiplied by a gradient of consistency derived from the target value adjuster 24 in a multiplier 34 and supplied as the target value to the comparison junction 13 . The signal formed here acts exclusively on the juice intake valve S via the controller 9. As already mentioned, the control deviation "consistency" is fed to the controller 9 at the beginning of the process phase "boiling up" and the switch 21 is switched at the same time , adjusted the motorized setpoint adjuster 16, 17 via switch 23 so that the setpoint for the consistency is tracked to the actual value of the consistency, ie the control deviation between the 1st and the setpoint consistency is kept equal to zero. The automatic tracking device achieves, on the one hand, a smooth, seamless transition from viscosity control to consistency control and, on the other hand, switching over without manual adjustment when "brewing".

In summary, the following regulation of the crystallization process results:

After being drawn in until the radiator is covered, the syrup is concentrated up to the seed or inoculation point, see above that depending on whether it is sown or vaccinated, corresponding curves result. The controller performs the Oversaturation to the initial setpoint and correspondingly the increase set on the viscosity gradient so that in the phase of crystal growth between 0-25% (grain formation phase) the supersaturation remains at the desired value

In the phase of crystal growth from 0-25%, the level rise is also monitored carried out Here, the setpoint and actual value are compared, the resulting system deviation is recorded by a limit monitor, If the actual value is too high, the controller switches to water intake and if the actual value is too low, it switches to juice intake switches. By interpreting the control values of the juice and water valves in relation to the water foule the gain in the control loop remains the same for syrup.

In addition to this solution, the system deviation that is formed can also be fed to a continuous controller which, depending on this system deviation, determines the ratio of the control interventions of the juice and water valve continuously changed For this purpose, the output signal of the oversaturation controller could, for example via a potentiometer, the motorized drive of which is controlled by a continuous level regulator is adjusted proportionally depending on the controller deviation. You can use this potentiometer then voltages are tapped, converted into impressed currents in amplifiers and via electropneumatic Interlockings act on both control valves.

At approx. 25% crystal content, which is caused by a time or

consistency-dependent signal are determined, is based on the crystal content / consistency measuring range of the

switched over. The tracking of the consistency setpoint to the actual value ensures that the Switching process takes place smoothly. Depending on the level of the cooking substance and the set Gradients for the height, the target value for the consistency is increased.

1 sheet of drawings

Claims (3)

Claims: • ■ • '■!' (Γ. .- · ■ " 1. Method for regulating the crystallization process of sugar solutions in a discontinuous manner working cooking apparatus, with up to approx. 25% crystal content, the intake depends on the oversaturation by measuring the viscosity and then, depending on the crystal content, by measuring the consistency is controllable, characterized in that that in the phase of oversaturation control with essentially syrup intake with increasing Viscosity is worked that the measured value for the level of the cooking mass with the after a program increased setpoint of the altitude is compared and that the ratio of Water to syrup intake is then increased as long as the setpoint of the level is exceeded is. 2. The method according to claim 1, characterized in that the setpoint for regulating the crystal content the actual value of the crystal content measured during the pauses in the crystal content control is tracked. 3. The method according to claim 1, characterized in that viscosity and consistency with one the moment of resistance of the cooking mass detecting transducer are measured, the one im Relative to the consistency range, has great sensitivity in the viscosity range and across channels different amplification the measurement signals for viscosity and consistency to the controls supplies.