JPH03100439A - Method for controlling microwave heating and drying machine - Google Patents

Abstract

PURPOSE:To stably dry a substance to be heated by detecting the weight of the substance to be heated, calculating a weight decreasing speed, discriminating a shifting time to decreasing rate drying from constant rate drying and lowering microwave output from the shifting time. CONSTITUTION:The substance to be heated in a sample dish 4 is rotated by a turntable 5 and irradiated with the microwave which is radiated from a microwave generator 2 and dispersed by a microwave dispersion plate 3 so as to be heated and dried. Then, the weight of the substance to be heated which is decreased by heating is measured momently by a scale 6 and a weight signal is transmitted to a controller 10. The controller 10 momently calculates the weight decreasing speed of the substance to be heated from the weight of the substance to be heated and compares it with the maximum value of the weight decreasing speed. When the weight decreasing speed becomes equal to or below a proper value which is <=90% of the maximum weight speed, the controller 10 lowers the microwave output. Furthermore, when it becomes <=75% thereof and a decreasing rate drying area is obtained, the controller 10 lowers the microwave output to 35% of the maximum output. Thus, stable drying without burning the inflammable substance to be heated is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling a microwave heating dryer applied to drying coal and the like.

[Conventional technology]

In the conventional method of controlling a microwave heating dryer, there has been a method of controlling the drying time by calculating the heating time from the weight reduction rate detected by a weight sensor. There is also a method of controlling microwaves by detecting the temperature of the object to be heated using an infrared thermometer.

[Problem to be solved by the invention]

In the conventional dryer control method, the method of controlling the heating time based on the rate of weight loss is effective for heating foods, cooking rice, etc. where evaporated moisture is known in advance. However, when drying something whose moisture content is unknown, 1. It is impossible to set the drying time in the drying area, and when the lapse rate drying area is entered, the temperature of the heated object increases and the heated object decomposes.
It had the disadvantage of being a horizontal mine.

Furthermore, the method of detecting the temperature of the object to be heated using infrared rays and controlling the microwave output is effective when the surface of the object to be heated is smooth and the moisture content is uniform.

However, if the object is grainy, clumpy, or uneven on the surface, the surface temperature will not be constant and a temperature distribution will occur, so when the object to be heated on the turntable is detected with an infrared thermometer, there will be large temperature fluctuations. Temperature is not suitable as a microwave control signal, and appropriate control may not be possible depending on this temperature.

The present invention seeks to solve the above problems.

[Means to solve the problem]

The microwave heating dryer control method of the present invention detects the weight of the object to be heated by microwaves, calculates the weight loss rate from the detected weight, and determines the point at which the transition from constant rate drying to decreasing rate drying occurs. The system is characterized in that it is determined based on the change in the rate of weight loss, and the microwave output is reduced from the point at which the weight changes.

[Effect]

In the above, the weight, which is heated by microwaves and decreases moment by moment, is detected by a weighing scale, and a weight signal is sent to a control device. The control device calculates the rate of weight decrease from moment to moment based on the weight signal, and determines the point in time when the drying state of the heated object shifts from constant rate drying to decreasing rate drying based on changes in the same weight decrease rate. When the controller determines the transition point, it sends a control signal to the microwave generator to reduce the microwave output.

As a result of the above, when the drying state of the heated object shifts to lapse rate drying, the microwave output is lowered, making it possible to stably dry the flammable heated object without causing it to cross.

〔Example〕

An apparatus used in an embodiment of the present invention will be explained with reference to FIG.

In the apparatus used in this embodiment shown in FIG. 1, l is a heater main body provided with an air outlet 9 having an exhaust fan 7, an air intake port 8, and an infrared thermometer 11, and 2 is an interior of the heater main body l. 3 is a microwave generator which is a heat source for heating the sample, and 3 is a microwave dispersion plate, which is a rotary blade, which is installed below the microwave generator to prevent concentration of microwaves. 6 is the above-mentioned A weighing scale 5 is provided at the lower part of the heater body 1, and a turntable 5 is provided on the upper part of the weighing scale 6, and a sample plate 4 for placing the object to be heated is disposed on the upper surface to uniformly heat the object. , and IO is the weight scale 6 mentioned above.
Input the weight signal to the microwave generator 2.
? This is a control device that outputs a 111 signal.

In this embodiment, the object to be heated in the sample dish 4 is rotated by the turntable 5 and irradiated with microwaves emitted by the microwave generator 2 and dispersed by the microwave dispersion plate 3, and then heated and dried. be done.

The microwave heating dryer for heating and drying the object to be heated is controlled by the following procedure. First, the weight of the object to be heated, which decreases due to heating, is measured moment by moment by a weighing scale 6.
A weight signal is sent to the control device 10. The control device 10
calculates the weight reduction rate of the heated object from time to time based on the weight of the heated object transmitted from the scale 6, compares it with the maximum weight reduction speed, and determines that the weight reduction speed is 90% of the maximum weight reduction speed.
A control signal for reducing the microwave output is sent to the microwave generator 2 at the point when the value falls below the appropriate value below, thereby reducing the microwave output. Furthermore, at the point when the weight reduction rate becomes 75% or less of the maximum weight reduction rate and enters the reduction rate drying area from the constant rate drying area, the microwave output is increased to 35% of the maximum output in order to prevent the heated material from decomposing and collapsing. %.

As a result of the above, stable drying without causing combustible materials to be heated is allowed to occur.

Next, a drying test conducted using the apparatus used in this example and its results will be explained.

The object to be heated used in the drying test was 1,500 g of granular coal with a size of 50 m1φ or less, and the test results are shown in FIG. 2. The weight loss rate is calculated from the weight change every minute, and when the weight decrease rate is 75% or less of the maximum weight loss rate, the microwave output is reduced to 80% (120OW, maximum 1500OW).
Microwave generator 2 with a method of reducing W) to 35%
The figure shows a weight loss curve and a temperature curve of the heated object when the output of the heated object is controlled, and it is seen that it is possible to make the temperature of the heated object extremely stable even in the lapse rate drying region.

Note that FIG. 3 shows the results of a drying test in which the microwave output was controlled by the temperature detected by an infrared thermometer, which is a conventional control method. In the above drying test, the control temperature of the heated object was set at 150°C, and the microwave output limit was set at 8°C.
It was set to 0%. When the object to be heated reaches the lapse rate drying region and microwave control is started, the microwave output changes greatly due to slight temperature changes, and the change in microwave output causes radio waves to concentrate on the backfill, causing the temperature distribution to change. Things have changed so much that it's out of control. In addition, areas where radio wave concentration occurred caused decomposition and smoke, making normal drying impossible.

As shown in Figures 2 and 3 above, heating and drying of the heated object is performed while calculating the weight loss rate, and when it enters the loss rate drying region, it is determined and the microwave output is lowered, which is difficult to do in the past. It can be seen that stable drying can be performed without causing damage to the flammable heated object.

〔Effect of the invention〕

The microwave heating dryer control method of the present invention detects the weight of the object to be heated, calculates the weight reduction rate, and determines the transition point from constant rate drying to lapse rate drying based on the change in the weight reduction rate, By lowering the microwave output from this transition point, stable drying of flammable objects to be heated without burning them became possible.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an apparatus used in an embodiment of the present invention;
Figure 2 is an explanation of the heat drying results according to the above example;
The figure is an explanatory diagram of the results of heat drying by a conventional method. 1... Heater main body, 2... Microwave generator, 3
...Microwave dispersion plate, 4...Sample dish, 5...
Turntable, 6... Weight scale, 7... Exhaust fan, 8... Air intake port, 9... Air outlet port, 1
0...Control device, 11...Infrared thermometer. 1 close

Claims (1)

[Claims] Detects the weight of the object heated by microwaves,
The microprocessor is characterized in that the weight loss rate is calculated from the detected weight, the time point of transition from constant rate drying to loss rate drying is determined from the change in the same weight loss rate, and the microwave output is reduced from the time of the same transition point. Wave heating dryer control method.