JPS584919B2 - Crystal can control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling crystallization cans used, for example, in sugar refining processes.

The sugar refining process involves a continuous process in the first stage and a patch process in the second stage, which are often combined in a complex manner, but looking at the individual processes, there is no part that is more difficult to automate than the sugar decoction process that crystallizes sucrose. .

Pre-saccharification is carried out in a vacuum crystallizer (hereinafter simply referred to as a crystallizer), and has a long history.Although many attempts have been made to automate the process, many attempts have been made to automate it; Since it is a process, there have been few success stories, and it has generally been operated by hand with many years of experience.

Furthermore, all of the successful examples mentioned above were capable of automatic operation under certain conditions, and none of them had been established as generalized automatic operation of crystal cans.

The object of the present invention is to eliminate elements that have been an obstacle to the automated operation of conventional crystal cans, and to make general automated operation of crystal cans possible.

Conventionally, crystal cans were operated according to the following sequence.

(1) Depressurization Close the vacuum break valve 2 attached to the crystal can 1 shown in the first figure, and open the vacuum source valve 4 and cooling water valve 5 of the barometric condenser connected to the crystal can 1 via piping 3.

By this operation, the vapor in the crystal can is guided to the barometric condenser 6, condensed by cooling water, and drained, and non-condensable components are removed from the vacuum system by a positive displacement vacuum pump (not shown).

This starts reducing the pressure inside the can.

(2) When the internal pressure of the suction can reaches a predetermined value (approximately 400 mmHgAbs), the sugar solution concentrated to nearly a saturated solution in the previous step flows from the pan tank (not shown) to the crystallization can 1 via piping 7 and sugar solution suction valve 8. It gets sucked in.

When the sugar solution is sucked in until it slightly exceeds the upper surface of the heat exchanger 9 in the crystal can, the suction valve is closed.

(3) Open the concentrating heat exchanger steam valve 10 and start heating the sugar solution in the crystal can.

In order to prevent the volume of the sugar solution from decreasing due to steam and the upper surface of the heat exchanger coming out above the liquid level, the sugar solution is gradually supplied from the sugar solution supply valve 11 to keep the liquid level constant.

The inside of the can is maintained at a pressure of 50 to 150 miHgAbs1 and a temperature of 50 to 60°C.

(4) When the concentration of the crystallized sugar solution progresses and the concentration increases to a supersaturated state, the valve 12 is opened to introduce seed crystals that will become the nuclei of crystals.

Other methods of generating crystals include: (1) excessive concentration to generate crystals naturally (natural, sheeting); (11) air or a small amount of seed crystals are inhaled with air and then subjected to impact. There is a method of inducing crystals (shock seating), but it is difficult to determine the number of crystals, and currently the common method is to introduce seed crystals corresponding to the number of crystals mentioned above.

In order to avoid shock and seating, a method is also used in which the seeds are made into an alcohol slurry and are injected without inhaling air.

In the present invention, any of the above crystallization methods may be used.

(5) Crystal Growth In the can immediately after crystallization, the surface area of the crystals is extremely small compared to the evaporation rate, and the rate of crystallization is slow, so naturally occurring crystals other than seed crystals and redissolution of the crystals occur. easy and extremely unstable.

As a countermeasure, (1) Reduce the heat exchanger steam flow rate to suppress the evaporation rate.

At this time, if the crystal can is not equipped with a stirrer for the sugar solution in the crystal can, the stirring of the liquid cannot be reduced below the guaranteed limit.

(2) Hot water corresponding to the difference between the evaporation rate and the crystallization rate is supplied to the valve 13.
Open and supply.

(3) Reduce the amount of cooling water to increase the can internal pressure and suppress the evaporation rate, as well as lower the crystallization rate by increasing the temperature of the liquid and lowering the degree of supersaturation.

Take such methods.

When the growth of the crystals progresses and the unstable state immediately after crystallization has passed, the above measures are returned to their original state and the supply of sugar solution is started.

The crystals grow gradually, and the volume of Shiroshita (a slurry of crystals and honey) gradually increases.

During this period, the crystal surface area increases and self-equilibrium occurs, so the range is fairly stable.

That is, as the surface area of the crystal increases, the speed at which sugar crystallizes and the rate of crystallization increase.

The crystallization rate is related to the degree of supersaturation; as the degree of supersaturation increases, the rate of crystallization increases, and as the degree of supersaturation decreases, it decreases, so changes in the rate of crystallization will reduce changes in the degree of supersaturation.

However, care must be taken during this period as crystal pecking, twinning, and crystal formation are likely to occur.

(6) Roasting When the crystal grain size reaches the desired value, the supply of sugar solution is cut off and heating is continued to perform roasting.

This is to make the fluidity suitable for centrifugation in the next step and to increase the rate of crystallization. At the desired fluidity, the heat exchanger steam valve 10 is closed and the vacuum breaker valve 2 is opened. Perform vacuum destruction.

(7) Open the dropping sugar valve 14 in the lower part of the dropping sugar crystal can and send the white sugar in the can to the next separation process.

The white sap is separated into crystals and honey by centrifugation.

After that, the crystals are dried in a dryer and cooler, and then placed in a silo.
It is stored in sugar bins, packaged and shipped.

(8) Open the laundry can steam valve 15 and the laundry can hot water valve 16 to clean the inside of the crystal can with steam and hot water in preparation for the next batch of brewed sugar.

Here, 17 is an orifice installed in the steam inflow path, 18 is a differential pressure transmitter connected to the orifice and detects the pressure difference before and after the orifice, and 19 is based on Bernoulli's theorem based on the output from the differential pressure transmitter. This is a calculator that calculates the steam flow rate.

20 is a steam flow rate program, and a signal from the program 20 is outputted to a steam flow rate controller 22 via a selector 21, and the heat exchanger is controlled based on the deviation value between the specified value from the program and the output from the calculator 19. The opening degree of the steam valve 10 is adjusted.

23 is a pressure transmitter that transmits the absolute pressure inside the crystal can,
24 is a temperature measuring element for measuring the boiling temperature of the sugar solution in the crystal can;
Reference numeral 5 denotes a pressure-temperature calculator, which calculates the corresponding temperature from the measured absolute pressure inside the crystal can using the pressure-temperature characteristics of the solvent (water in this case).

26 is a supersaturation computing unit that computes the supersaturation based on the input signal from the temperature measuring element 24 and the input signal from the computing unit 25.

27 is a cooling water valve 5 based on an input signal from the pressure transmitter 23.
This is a cooling water controller that controls the

Reference numeral 28 indicates an electromagnetic flowmeter, which sends an output proportional to the flow rate of the sugar solution to a computing unit 29, and a sugar solution flow rate measurement signal from 29 is inputted to a sugar solution supply controller 30.

Next, the instrumentation principle of the present invention will be explained.

During crystallization, crystals can be stably grown from seed crystals by maintaining the supersaturation degree of the sugar solution in the can in a metastable range of 1.00 to 1.25.

From the time of crystallization to the middle of crystal growth, the degree of supersaturation serves as a guideline for crystal growth.

Next, after the middle stage of growth, hardness becomes an important guideline for brewing sugar due to the reasons for the second half.

(1) During this period, the liquid level in the can rises and the hardness increases, so the circulation speed under the whites decreases.

A decrease in the circulation speed of the white rice lowers the heat transfer amount of the heat exchanger, which increases the time for roasting sugar, and in a natural circulation crystal can, the amount of evaporation decreases, so the circulation speed is further reduced. I'll let you.

In addition, a decrease in the circulation speed causes the combination of crystals, that is, twinning and crystallization.

(2) However, if the crystal volume fraction is lowered, the circulation speed increases, but the crystal gaps become wider and crystallization is more likely to occur, which deteriorates the particle size distribution of the product.

Empirically, the crystal pores are gradually narrowed during the process of boiling sugar, and at the end of the process, it becomes 0.
It is said that it is good to set it to about 2 mm.

However, the crystal spacing during crystal growth is not constant; (1) during crystallization, the amount of sugar solution needed to cover the heat exchanger is required in the concentration stage of the previous process; Since this value is normally larger than the gap at the end, it is necessary to gradually narrow it down to the desired gap in subsequent steps.

(2) When the crystal grain size is small, crystallization is relatively difficult to occur even if the crystal volume fraction is small, and the crystal growth rate can also be increased, so it is advantageous to grow the crystals in a state with a high circulation rate. be.

Therefore, when cultivating cans, it is necessary to take these things into consideration and plan the growth of crystals while maintaining the best conditions.

Figure 2 summarizes the above results and shows the crystal growth model considered to be optimal.

The crystal growth model was obtained using the following method.

In addition, it has been demonstrated that the following crystal growth model simulates actual decoction sugar with high accuracy.

Here, it is assumed that the crystal is cubic.

Q: Total volume N: number of crystals a: Length of one side of the crystal g: crystal gap Then, Q=N(a+g)3 (1) It can be expressed as

Also, the ratio of the crystal volume to the total volume is If φ is the volume fraction of the crystal, then becomes.

Although the volume fraction of crystals cannot be measured directly, it is known that it can be measured indirectly using a hardness meter.

In other words, 7 of "Measurement and Control" published in November 1962.
According to the paper by Mr. Umetani and Mr. Mori, “Characteristics and Control of Sugar Refining Crystal Cans,” described on pages 71 to 781, Then, it can be expressed as .

It has been empirically known that the crystal size and total volume are expressed by a linear equation that increases in proportion to time, so when these relationships are given to the above equation, the crystal growth model shown in Figure 2 can be obtained. I can do it.

From the above results, the following can be inferred.

(1) In order to determine the state inside the can, it is necessary to specify the time course of two quantities independently.

That is, in this example, the growth rate of the crystal and the rate of increase in volume of the underwhite area are specified, and everything is defined thereby, but both can be specified independently of each other.

(2) The change in hardness over time is actually different from the optimal program obtained based on the calculation formula described above.

The cause is that the crystal spacing is constant and sugar is not boiled.

As shown in the above growth model, the conditions inside the can require two independent programs.

Theoretically, it is conceivable to programmatically control the average grain size and crystal volume fraction of the crystals.

Further, as described above, the crystal volume fraction is a value related to the crystal gap, and it is also possible to directly measure the crystal gap using industrial television or pattern recognition, and program control based on the crystal gap and average grain size.

Here, the average particle size and crystal volume fraction are program-controlled using the liquid level and hardness inside the can.

This will be explained with reference to FIG. 1. 31 is a liquid level detector for detecting the liquid level in the can, and 32 is a hardness meter.

33 is a converter that converts the hardness meter output into hardness.

34 is a program for liquid level control, and 35 is a program for hardness control.

The present invention is characterized by the following configuration in order to further widen the stability range.

(1) Since the crystal can is a complex system that is interrelated,
The control system is given priority.

Normally, the amount of sugar solution supplied is controlled based on the program 34 of the liquid level in the can, and the liquid level controller is operated according to the deviation between the specified value from the program 34 and the input from the liquid level detector 31. Operate the liquid supply control valve.

However, at a time when supersaturation is a better guideline before seed crystal injection and hardness is a better guideline after seed crystal injection, the hardness input from converter 33 is lower than the specified value output from program 35. If this happens, the selector 37 controls the amount of sugar solution supplied using the adjustment signal from the hardness control program 35, giving priority to the liquid level adjustment signal.

Here, 38 is a supersaturation degree controller, and 39 is a hardness controller.

The hardness controller is adapted to issue an output signal based on the deviation value between the output from the program 35 and the output from the converter 33.

Reference numeral 40 indicates a switch that is switched when the hardness before and after seed crystal injection becomes a better guideline.

Note that the hot water supply control valve 13 is controlled by a program 35.

(2) Next, in the present invention, when the liquid level deviates from a predetermined program to a certain value due to a disturbance caused by a change in the type of sugar solution supplied, the progress of all programs is interrupted and the This state is temporarily maintained, and the program is started again when the liquid level returns to a value in accordance with the program based on changes in the degree of supersaturation and hardness.

The reason why the liquid level recovers while the program progress is temporarily held is because the operation and control of the crystal can continues during this period, and the crystals inside the can grow. As the plant grows, the amount of sugar solution supplied is controlled and the liquid level recovers.

This function also applies to hardness braking.

That is, when the concentration of the supplied sugar solution or the pure sugar rate is low, the hardness may deviate from the predetermined programmed value.

Even in such a case, the progress of the program can be automatically interrupted and restarted to carry out automatic operation of the crystal can, as described above.

In this way, since disturbances during crystal growth caused by disturbances or the like during the crystal growth period are automatically corrected by interrupting the progress of the program, stable automatic control during crystal growth is possible.

The structure of the crystal can according to the present invention as described above satisfies all the necessary conditions for the automatic operation of the crystal can, and it is possible to achieve the automatic operation of the crystal can, which conventionally required constant operator intervention. It can be carried out without any problems.

The present invention can be applied to processes other than sugar refining, such as monosodium glutamate and chemicals, which involve a crystallization process.

[Brief explanation of drawings]

FIG. 1 shows an example of the present invention, and FIG. 2 shows an example of a growing crystal model. 1... Crystal can, 31... Liquid level detector,
32... Hardness meter, 33... Converter, 3
4...Liquid level control program, 35...
・Hardness control program, 36...Liquid level controller, 37...Selector, 39...Hardness controller, 30...Sugar liquid supply Controller, 11...
...Sugar liquid supply valve.

Claims (1)

[Claims] 1. In a crystal can control method in which a heat exchanger exchanges heat with a raw material to generate crystals from the raw material and grow the crystals, the liquid level and hardness of the raw material in the crystal can are measured, and the liquid level and a program indicating the hardness change process is provided independently in advance, each of the deviation values between the program and the corresponding measurement signal is determined, and one of the deviation values is selected, The raw material supply amount is controlled based on the selected deviation value. When the deviation value between the value of the unselected program and the corresponding measurement signal exceeds a predetermined value, all of the programs are controlled. When the progress is interrupted and the deviation value between the value of the unselected program and the corresponding measurement signal returns to the original value, the raw material supply amount is controlled again based on the deviation value of the selected side. A crystal can control method, characterized in that: