JPS5819280B2 - 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 batch process in the latter stage, which are often combined in a complex manner, but looking at the individual processes, there is no difficulty in automating the sugar decoction process, which involves crystallizing sucrose.

Frozen sugar is made in a vacuum crystallizer (hereinafter simply referred to as a crystallizer), and has a long history.Although there have been many attempts to automate the process, it still has complicated dynamic characteristics. 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.

Traditionally, crystal edges 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.

Through this operation, the vapor within the crystal edge is led to the barometric condenser 6, condensed with cooling water, and drained.
Non-condensable components are removed from the vacuum system by a positive displacement vacuum pump (not shown).

This initiates a vacuum in the end.

(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 passes from the pan tank (not shown) to the crystal 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 within the crystal edge, the suction valve is closed.

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

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

Pressure inside the end is 50-150 HgAb and temperature 50-60℃
to hold.

(4) When the concentration of the ultra-high 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 for generating crystals include: (i) A method of excessively concentrating and naturally generating crystals (Natural 1, Seeding) (10 Inhaling air or a small amount of seed crystals with air) There is a method of inducing crystals by shock (shock seeding), 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 seeding, a method is also used in which the seeds are added as an alcohol slurry without inhaling air.

In the present invention, any of the above-mentioned superhigh methods may be used.

(5) Within the edge immediately after the super high front height, the surface area of the crystal is extremely small compared to the evaporation rate, and the crystallization rate is slow, so naturally occurring pseudocrystals other than seed crystals and crystal redissolution 1 are likely to occur. , 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 inside the crystal edges, 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, increase the end internal pressure, suppress the evaporation rate, and 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 the ultra-high temperature has passed, the above measures are returned to normal 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 it is within a reasonably stable range.

That is, as the surface area of the crystal increases, the length and speed of sugar crystallization and the crystallization rate 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) Pre-clamping When the crystal grain size reaches the desired value, the supply of sugar solution is cut off, heating is continued, and pre-clamping is performed.

This is to achieve a 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 gleaning valve 14 at the lower part of the gleaning crystal can and send the white bottom inside the end 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 release valve 15 and the laundry can hot water valve 16 to clean the inside of the crystal end using steam and hot water in preparation for the next round of brewing.

Here, 17 is an orifice provided in the steam inflow path, 18 is a differential pressure transmitter that is connected to the orifice and detects the pressure difference before and after the orifice, and 19 is a differential pressure transmitter that uses 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; 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 which is operated by the 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.

1. When extremely high. Supersaturation degree of sugar solution in can 1.00-1.25
By maintaining the crystal in the metastable range of □, it is possible to stably grow a crystal from a seed crystal.

From this very high stage to the middle of the pre-high stage, the degree of supersaturation serves as a guideline for crystal growth.

Next, after the pre-high and middle stages, hardness becomes an important guideline for brewing sugar for the following reasons.

(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 type crystallizer, the amount of evaporation decreases, so it is necessary to reduce the circulation speed. It will lower it.

However, a decrease in the circulation rate causes the formation of crystallization, ie, twinning and crystallization.

(2) However, if the crystal volume fraction is lowered, the circulation speed increases, but the crystal gaps become wider and pseudocrystals are 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 best to set the temperature to about 2mvt. However, the crystal gap at the time of high temperature is not constant, and (1) when the temperature is very high, the amount of sugar liquid that is sufficient to cover the heat exchanger must be reduced in the concentration stage of the previous process. Naturally, the amount determines the crystal gap at the time of seeding, and since this value is usually larger than the gap at the end, it is necessary to gradually narrow it down to the desired gap in the subsequent steps.

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

Therefore, when preparing the crystal, it is necessary to take these matters into account and plan the growth of the crystal while maintaining the best conditions.

Figure 2 summarizes the above results and shows the front height model considered to be optimal.

The front height model was obtained using the following method.

In addition, it has been demonstrated that the following Maeda model simulates actual roasting 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 crystal g: Crystal gap, then Q=N(a+g,)'' ・・・・・・・・・
...It can be expressed as (1).

. Also, the ratio of the crystal volume to the total volume is φ: Volume fraction of crystal 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 described on pages 71 to 7-81, "Characteristics and control of sugar refining crystal cans," : If it is a constant, 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 by applying these relationships to the above equation, the front height 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 within the edge, it is necessary to specify the time course of the 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 above-mentioned calculation formula because the crystal gap is constant and the sugar is not boiled.

As shown in the previous model, the state of humility requires two independent programs.

Theoretically, it is possible 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 grain size and crystal volume fraction are program-controlled using the end liquid level and hardness.

This will be explained with reference to FIG. 1. 31 is a liquid level detector for detecting the liquid level in the end, 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 edge is a complex system that is related to each other, priority was given to the control system.

Normally, the amount of sugar solution supplied is controlled based on the internal liquid level program 34, and the liquid level controller is operated according to the deviation between the specified value and the input from the liquid level detector 31 from the program 34, and the liquid level controller is operated via the selector 37. Operate the sugar solution supply control valve.

However, the converter 3
If the hardness input from 3' becomes lower than the specified value output from the program 35, the selector 37 selects the hardness control program 3' with priority over the liquid level adjustment signal.
The amount of sucrose solution supplied is controlled by the regulation signal from 5.

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 1 liquid level recovers while the program progress is temporarily held is that during that period, the crystal edge operation and control continues, and the - inside the edge grows. As crystals form, the amount of sugar solution supplied is controlled and the liquid level recovers.

This function also applies to hardness control.

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.

In such a case, the progress of the program can be automatically interrupted and restarted to perform automatic operation of the crystal edge, as described above.

In this way, since disturbances during crystal growth caused by disturbances etc. 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 edge according to the present invention as described above satisfies all the necessary conditions for automatic operation of the crystal edge, and makes it possible to completely change the automation of the crystal edge, which conventionally required constant operator intervention. The present invention can be applied to processes other than sugar refining that include a crystallization process, such as monosodium glutamate and chemicals.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows an example of a high front model. 1...□Crystal-131...Liquid level detector, 32...
Hardness snoring, 33... Converter, 34... Liquid level control program, 35... Hardness control program, 36...
Liquid level controller, 37... Selector, 39... Hardness controller, 30... Sugar solution supply controller, 11... Sugar solution supply valve.

Claims (1)

[Claims] 1. Measure the liquid level and hardness of the raw material within the crystal edge in the crystal can control direction where the crystal can is automatically controlled according to the steps of depressurization - suction - concentration - super-high-temperature - pre-high - brewing - sugar reduction - washing. Then, programs indicating the change process of the liquid level and hardness are provided independently in advance, the deviation values between the programs and the corresponding measurement signals are determined, and one of the deviation values of each of the deviation values is determined. One is selected, and the raw material supply amount is controlled based on the selected deviation value, and the supersaturation degree and hardness program is used from the ultra-high to the previous high-medium stage, and the hardness and hardness program is used from the previous high-medium stage onward. A crystal can control method characterized in that the control is performed based on the following: