DE1812457C3 - Procedure for regulating the crystallization process in A and R sugar boilers - Google Patents

Description

25th

The invention relates to a method for regulating the crystallization process in A- and /? - sugar boilers by drawing in juice and / or water, in which the supersaturation calculated from the temperature of the filling compound and negative pressure in the kech apparatus and that determined in a measuring device from the filling compound Crystal content as a rule.

Sugar boiling processes of the kind mentioned react due to the high purity of the processed Juices and the associated higher rate of crystallization react relatively quickly to changes in the cooker. In automatic mode, they are very precise in a narrow metastable To lead a supersaturation zone, otherwise grain dissolution or fine grain formation occurs very quickly.

To assess the stage of crystallizing cooking masses one must have two quantities at any one time know:

The degree of oversaturation of the mother syrup and the amount of crystals in the cooking mass. Since you Cannot measure these quantities directly, the following quantities can be recorded indirectly and a system for using them automatic monitoring of the crystallization can be set up:

Temperature difference / between the boiling crystal mass and its saturated steam; electrical Conductivity of the cooking mass; Consistency of the cooking mass and level (see magazine for the sugar industry 1967, No. 3, p. 164, left paragraph).

On this basis, an automatic control system is known, in which from the temperature of the filling compound and the Negative pressure in the cooking apparatus in a computing device is more proportional to the oversaturation of the filling compound The value is continuously determined and then the water or juice intake is regulated (compare, for example, the designed Documents of the Austrian patent application A 11 411/65).

This well-known regulation is only available in the initial phase se of the cooking process satisfactory values for the course of the crystallization process, the cause lies in that even when determining the supersaturation on a favorable measuring location (corresponding to a Average value for the contents of the cooking appliance) There are deviations from this value at various points in the apparatus. In order to As the process progresses, the circulation in the filling compound gets worse and worse, the different ones give way Set certain supersaturation values more and more from each other, so that finally the supersaturation as Controlled variable for guiding the process no longer usable isL The task of the present invention is to provide a relatively simple method by which the crystallization process in each phase the cooking process can be optimally performed. This object is achieved according to the invention in that in the initial phase (grain foot phase) the oversaturation is regulated by water intake and that after Achieving a crystal content of approx. 25% of the crystal content through juice intake corresponding to one The value is adjusted depending on the altitude.

In this way, a favorable syrup layer thickness is achieved very quickly thanks to the oversaturation control to reach the crystals, which then has the consequence that one is maintaining the supersaturation of the crystal itself can be left to if the achieved syrup layer thickness is kept constant via the crystal content control or is carried out within reasonable limits. This exploitation of the self-regulating property of the crystals is before especially with unfavorable circulation conditions more effective and better than any external intervention Oversaturation control.

Like the supersaturation, the syrup layer thickness is also a calculation variable and cannot be measured directly. the However, the syrup layer thickness is related to the continuously detectable crystal content - that is the percentage by weight of grown crystals in the filling compound - in close relationship and thus also stands for the Boil phase a good controlled variable available.

The invention is explained in more detail below using an exemplary embodiment with the aid of FIGS. 1 and 2 explained.

Fig. 1 shows a cooking apparatus K , which consists essentially of a closed container BH, which is used to receive the filling compound FM. In its lower half there is a heating element HE, which is acted upon with saturated steam SD via the supply line Zl. The juice and water intake line SA + W opens into the cooking apparatus K under the heating element HE . Lines Z2 and ZX are used for sucking off cooking vapors KB . They are generally connected to a central vacuum station with the lines of other cooking appliances. The finished filling compound FM is drained off via the line ZA . Line Z5 is used to ventilate the cooking apparatus K. The SAT seed pot is used to hold the seed powder suspended in isopropyl alcohol. A line Z6 that can be acted upon by steam is used to evaporate the cooking apparatus K.

The filling compound temperature is measured with a resistance thermometer WT and the negative pressure in the cooking apparatus is measured with an absolute pressure transducer U. From these two measured values and from the purity of the syrup set on the quotient divider QS (potentiometer), the supersaturation calculator R forms an output signal A, which can be calibrated in a boiling point increase from Ö to 15 ° G or directly in supersaturation. The output signal A forms the oversaturation ACTUAL value and is compared in the measuring unit MEi with a nominal value 5VKl. This nominal value SWX is to that in the

metastable zone lying supersaturation value set to which the syrup is to be regulated at the start of the process. It can be kept constant, but also to take into account the slightly decreasing purity of the mother syrup in the course of the grain root phase (initial phase), it can be increased automatically by a program control unit PS in steps or continuously (see also FIG. 2).

In the grain base phase, the control deviation B , which is formed in the measuring unit MEi for oversaturation, is switched to the electropneumatic feed controller P1. At this time it acts with its pneumatic output signal on the control valve RX in the water pipe W.

Serves for measuring the height Riümasse object a transmitter H, which is flanged laterally on the cooking apparatus K The crystal content is such that with a meter KH. B. evaluates the conductivity difference between mother syrup and filling compound, measured. In a second measuring unit ME2 , the control deviation D is formed from the output signal C of the crystal content meter KH and the values set on the setpoint dials “Zero point N” and “Gradient Ca”. The crystal content value that is aimed for at the beginning of the boil is set at the setpoint adjuster »Zero point N«. The change amount proportional to the rise in the level in the cooking apparatus K , by which the crystal content is to be increased when boiling up, is set on the "Gradient G" setpoint adjuster.

The measurands crystal content. Height and boiling point increase (or oversaturation) are recorded on chart recorders 51 ... 53. This letter; Si ... S3 contain an adjustable minimum and maximum limit contact 1 ... 6 for each measured variable. All limit contacts 1 ... 6 are connected to a signal and control device ST. With the switch »manual / automatic« HA and the button »process start« T you create the conditions for the automatic switching of the automatic devices in this relay combination. This is how the program switching mechanism P5 is started, the control deviations ßbzw. D of the two measuring units MEi and ME 2 are switched via the relay L 1 and the four three-way solenoid valves Mi ... M4 in the control pressure lines of the control valves R I and Λ 2 for the water and juice line SA are actuated.

When a crystal content of approx. 25% is reached, the grain foot boil is ended and boiling begins. The limit contact "crystal content" minimum 4 switches anseile the Error B "oversaturation" the Flegel deviation D "crystal content" übe- the relay L 1 on the feed regulator Pl, now acting on the control valve R2 in the Saf (circuit SA.

The supersaturation calculator R is pressure-corrected in the range from 150 to 250 Torr. ie, absolute pressure fluctuations in this range do not affect the measurement result. According to practical experience, disturbances due to slight fluctuations in negative pressure in the grain base phase can be corrected by the catchment control alone. If, due to the conditions in the vacuum station, major disruptions are to be expected, additional negative pressure control is required.It is advantageous to use a controller PJ 1 for this purpose, the control deviation E _{1 of} which is formed from the actual value / the negative pressure in the cooker K and a setpoint S2, via an interlocking 5IVaUf the pneumatic operation Λ 3 of a control flap RK in the vapors line / ifl acts.

When the control device ST interacts with the draw-in regulation, the operating sequence shows the results in the diagram in FIG. 2 drawn bar sequence.

In this diagram, the measured variables height, crystal content and supersaturation are plotted over the time of the process sequence. The time axis is divided into different cycles 1 ... 9. At cycle i, the start button Pan of the control device 5T is pressed and the process begins. Juice is drawn into the cooking apparatus K via the solenoid valve M4 and control valve R 2 in the juice line SA until the heating element HE is covered

The control pressure for the juice valve R 2 is taken from the reducing station DR. After the heating element HE lsi has been covered, a minimum level is reached in the cooking apparatus K , and the minimum contact 1 of the recorder 52 responds (cycle 2). The juice valve R 2 is closed via the solenoid valve M4 and the heating vapor line Zi is opened via the valve Vi . During the evaporation of water from the filling compound FM that now follows, the level drops again. The minimum contact 1 opens again (via the control device ST and the solenoid valve M4) the juice valve Rl until the restart ^; ~ g of the height and exceeding the minimum value the oafteinzug is again interrupted. With such repeated switchings, contact 1 works as a two-point controller for the ride height.

If the oversaturation has risen to a minimum value, (cycle 3) the contact 2 of the recorder S 3 closes and sends the signal “seed point” to the control device ST . The valve V2 is opened and the seed powder suspension is drawn in from the seed pot 5/4. In addition, the closing of contact 2 ends the intake of juice via the two-point control with contact 1 for good. The oversaturation of the filling compound FM increases up to the setpoint 5VKl, which corresponds to a maximum value. In addition, the contact 3 of the recorder 53 closes (cycle 4). The program switching mechanism PS is started, which increases the setpoint 5Wl for the oversaturation to a constant value (solid curve) or gradually by small values (dashed curve). Accordingly, the altitude remains constant or decreases in stages (solid and dashed curve). At the same time the draw-in regulator Pl works - the relay L 1 has switched the control deviation B to the draw-in regulator PI - only on the water valve R 1 and thus maintains the oversaturation at the setpoint 5Wl.

From cycle 3 the crystal content increases and reaches a minimum value at cycle 5. The contact 4 of the recorder 51 sends a signal to the control unit 57 "<. Which switches the intake regulator P / via the relay L i from the MEi unit (oversaturation) to the measuring unit ME2 (crystal content). The single regulator output is supplied by water (Ri ) reversed to salt valve R2 The high boiling process begins, with the crystal content and the level increasing.

If the hearing level has reached a maximum value, then contact 5 of the recorder 5 2 closes (cycle 6). The crystalline content regulation and the juice intake via the juice valve R 2 are ended, and the boiling phase begins. The crystal content increases while the altitude drops.

When a maximum value of the crystal content is reached the contact 6 of the recorder 51 closes (cycle 7) and gives the signal "Sud finished". The filling compound FM is

drained, the level naturally falling, but the crystal content of the filling compound FM remaining in the cooking apparatus K remains constant. When the cooking appliance is empty, cycle 8 begins with evaporation (cleaning). The end of the process is signaled at the end of the Aus (Lampfcns) (bar 9).

For this purpose 2 sheets of drawings

Claims (2)

Patent claims: 1. A method for regulating the crystallization process in A and ft sugar boilers by drawing in juice and / or water, in which the upper saturation calculated from the temperature of the filling compound and negative pressure in the cooking device and the crystal content determined from the filling compound in a measuring device serve as control variables, characterized in that in the initial phase (grain base phase) the upper saturation is regulated by water intake and that after reaching a crystal content of approx. 25% the crystal content is regulated by juice intake according to a value that is changed depending on the altitude. 2. The method according to claim 1, characterized in that the respective crystal content from the Conductivity difference between mother syrup and filling compound is.