JPH02197791A - Drying of granular body - Google Patents

Abstract

PURPOSE:To permit economical drying as well as the securing of stabilized quality at all times even when the conditions of granular body and atmosphere are changed by a method wherein a drying temperature is changed and set based on the output signal of a regulating meter except the regulating meter of the drying temperature while the supplying amount of heat source and/or the supplying amount of the granular body are regulated so as to coincide with the set drying temperature. CONSTITUTION:When the moisture content of dried granular body becomes higher than a set value in a moisture regulating meter 23, the output of the regulating meter 23 sets a drying temperature at a temperature higher than the present set temperature while the set value of the drying temperature is reduced when the moisture content has become smaller than the set value on the contrary. On the other hand, when a difference between the wall surface temperature of a drying device and the dew point of hot exhaust gas, which is detected by a dew point regulating meter 20, is smaller than a set value or the relation of both temperatures is reversed, a dew point regulating meter 20 shifts the set value upward to elevate the drying temperature so as to avoid dewing on the wall surface. On the contrary, when the temperature difference is larger than the set value, the output of the regulating meter 22 shifts the set value so as to reduce the drying temperature. A selector 21 selects higher value between the set drying temperatures outputted from the moisture regulating meter 23 and the dew point regulating meter 20 at all times and outputs the higher value as the set value indicated by a drying temperature regulating meter 19.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a method for continuously drying powder and granular material that can ensure stable quality of dried powder and granular material and can be operated economically. Regarding the method.

<Conventional technology> When continuously drying powder or granular materials such as synthetic resins, the powder or granules mixed in water, etc. are dispersed in a fine state using a sprayer or the like in a drying tank, and then hot air and There is a method in which, after evaporating moisture through contact, a collector provided at a later stage collects the powder and granules entrained in the exhaust gas (thermal exhaust gas) of the hot air used for drying.

In this case, as a method of controlling the operation, the drying temperature, that is,
The temperature of the hot air used for drying and/or the supply amount of the powder has been controlled so that the temperature of the powder or the hot exhaust gas inside or exiting the drying device is a predetermined value.

<Problems to be Solved by the Present Invention> However, what is ultimately required of the granular material discharged from the drying device is not temperature but moisture.

For this reason, in the past, while operating a drying temperature set to a certain degree depending on the type of powder or granule, workers would periodically take out a part of the powder as a sample and verify the moisture content. The drying temperature has been changed if it is outside the specified value.

However, since the moisture testing process is carried out periodically, the drying equipment must be run blind during the testing process, and manual work is required to measure the moisture content. There was a problem that became a bottleneck in doing so.

Furthermore, the drying temperature and the amount of moisture entrained in the supplied powder and granules,
Depending on the atmospheric conditions, the amount of moisture in the hot exhaust gas can reach near saturation, causing dew to condense on the inner walls of the drying equipment due to the cooling effect of the outside air. There were problems in that the powder particles would clump or adhere to the inner wall, making it difficult to remove them, and also corrode and wear out the equipment.

In order to solve this problem, it is possible to set the drying temperature high, but if the temperature setting is too high, the amount of moisture entrained in the powder and granules to be dried will be reduced, even if the product is of the same type. Since the temperature is different each time, the temperature of the dried powder or granular material may become too high, deteriorating its quality, and there may also be problems such as uneconomical operation.

In view of these conventional problems, the present invention aims to provide a method for drying powder and granular materials that is economical and always ensures stable quality even when the conditions of the powder and the atmosphere change. purpose.

<Means for Solving the Problems> The present invention provides a method for continuously drying powder or granular materials using a drying device, in which, in addition to the drying temperature, the dew point of the exhaust gas of the hot air contributing to drying or an alternative One or more of the humidity or the amount of moisture contained in the exhaust gas, the amount of moisture in the dried powder, and the wall temperature of the drying device are measured together, and a single or multiple signals of these are set in advance. The drying temperature is changed and set based on the output signal of the controller other than the drying temperature controller, and the supply amount of the heat source and/or the powder/granular material is changed to match the drying temperature. It is characterized by adjusting the supply amount of.

Effect> In the present invention, in addition to the drying temperature, for example, the temperature of the hot air exhaust gas that contributed to drying, the dew point of the hot air exhaust gas or humidity in place of this, the amount of moisture contained in the exhaust gas, and the dried powder or granular material Measure one or more of the moisture content of the dryer and the wall temperature of the drying device, input these single or multiple signals to the corresponding controller, and set the settings based on the moisture content of the powder or granular material in these controllers, for example. Set a target value for the drying temperature based on the temperature difference between the wall temperature of the device and the dew point of the heat exhaust gas, and change the drying temperature to the highest temperature among these target values. Set. Adjust the temperature of the hot air introduced into the drying device to meet this setpoint (target) by increasing or decreasing the supply of the heat source and/or adjusting the amount of powder or granular material supplied to the device. As a result, the moisture content in the dried powder and granules can be satisfied,
In addition, problems such as equipment corrosion and wear due to dew condensation can be avoided, allowing stable and economical operation, and unmanned operation is also possible.

<Examples> Examples of the present invention will be described below based on the drawings, but the present invention is not limited thereto unless it exceeds the gist thereof.

The drying device is equipped with a drying tank main body 1, an air filter 2, a blower 3, an air heater 4, etc. as equipment for supplying hot air in order to dry the powder and granular material, and is accompanied by moisture, which is the material to be dried. As equipment for supplying powder and granules,
Tank 5, pump 6, sprayer 7 in drying tank 1, drying tank 1
It is equipped with a collector 8, an exhaust fan 9, a discharger 10, etc. for processing the hot exhaust gas and dried powder and granular material.

The powder or granular material to be dried is fed from the tank 5 by the pump 6, and the flow rate is controlled by the control valve 11, and the powder is sent to the drying tank 1.
The hot air introduced from the hot air supply equipment is sprayed by the centrifugal force of a disk rotating at high speed, and moisture is evaporated.

On the other hand, the temperature of the hot air decreases due to the evaporation of moisture, and it becomes hot exhaust gas containing a large amount of moisture.When it comes into contact with the hot air, it entrains dry powder and granules, and passes through the pipe 1a to the collector 8 in the latter stage. After the powder and granules are collected by a furnace cloth tube or the like, the hot exhaust gas is discharged into the atmosphere through the pipe 9a by the haiku P119. A dew point meter 12 is installed near the pipe 9a, and a part of the hot exhaust gas is extracted from the pipe 9a to measure the dew point. The powder and granules collected in the collector 8 are
It is discharged out of the system via the discharger 10 and sent to the next process as shown by the arrow, for example, via the cylindrical discharge pipe 13, but the powder and granules remain at the bottom of the discharge pipe 13. As if falling continuously without any interruption,
Tilt at an appropriate angle to the horizontal plane. A moisture meter 15 is installed in an opening 14 provided in a part of the upper surface of the discharge pipe 13 so as to be perpendicular to the discharge pipe 13, and falls down the bottom of the discharge pipe 13. Moisture content is measured by observing powder and granules.

Next, the control system will be explained.

After the volume of the hot air is adjusted by a damper 16, the blower 3 supplies the hot air from the outlet of the air heater 4 to the drying tank l. In order to keep the temperature constant at the set value, the temperature of the hot air supplied to the drying tank 1 is measured with a thermometer 17', and this is input to the hot air temperature controller 17, and the control valve is adjusted based on this. 18 to increase or decrease the amount of steam supplied from a steam generator (not shown) to the air heater 4, thereby controlling the temperature of the hot air and supplying it to the drying tank 1.

In the drying tank 1, the hot air evaporates the moisture in the powder and granules, the temperature of which decreases, and the hot air flows into the collector 8 through the pipe 1a as hot exhaust gas containing a large amount of water and moisture. , conduit 1
A part of it is taken out from a and its temperature is measured with a thermometer 19', and this is taken as the drying temperature.The drying temperature is 1ft! f
A control valve 11 that manually controls the f meter 19 and controls the amount of powder and granular material supplied so that this value becomes a set temperature (target value) to be described later.
It outputs an output signal to.

The dew point meter 12 installed near the conduit 9a extracts some of the gas from the conduit 9a, passes it over a mirror surface (not shown) inside the dew point meter 12, and cools this mirror surface from the back side. , a dew condensation phenomenon occurs on the mirror surface, and at this time, the light reflectance on the mirror surface is significantly reduced by detecting the light from the light emitter installed on the top with the light receiver also installed on the top. The mirror surface temperature at this time is measured as the dew point.

A dew point controller 20 is provided to prevent the dew point from becoming higher than the wall temperature of the device and condensation on the wall surface.
A signal from the thermometer 24 that measures the wall temperature of the collector 8 as the wall temperature of the device is input manually, and the thermometer 19'
A drying temperature signal is also input, and a drying temperature set value (target value) that makes the wall temperature of the device higher than the dew point by the set temperature (θ~5°C) is output to the selector 21, which will be described later. ing.

On the other hand, the moisture meter 15 installed at the upper part of the discharge pipe 13 has an infrared light emitter and a light receiver built inside, and because the wavelength of the infrared light in a certain range emitted from the light emitter is absorbed by moisture. Utilizing the fact that the amount of light that is reflected and returns to the receiver is different compared to the surrounding wavelength, a signal indicating the amount of moisture entrained in the powder or granular material is output based on the difference in attenuation.
Since the output value (attenuation amount) varies depending on the substance to be measured and is not proportional to the moisture content, a conversion formula is created based on known values measured in advance.
A signal proportional to the moisture value is output to the moisture controller 23 according to this conversion formula. Same controller 2
At the same time, the drying temperature signal from the thermometer 19' is input to 3, and the set value (target value) of the drying temperature is changed from the current drying temperature so that the moisture value matches the set value (target value).
is output to the selector 21.

The selector 21 includes the dew point controller 20 and moisture controller 2 described above.
3 are input, and the higher value of both is automatically selected and outputted as the set value of the drying temperature controller 19.

Next, the effect will be explained.

When operating at a certain drying temperature, if the amount of moisture accompanying the powder increases or the amount of water supplied increases, the temperature of the hot exhaust gas, that is, the drying temperature, decreases. In this case,
The controller 19 controls the control valve 11 so that the set temperature is reached.
Reduce the amount of powder and granular material supplied by narrowing the opening. Conversely, when the drying temperature becomes higher than the set value, the control valve 11 opens more to increase the supply amount of powder and granules, thereby keeping the drying temperature constant. Here, even if the drying temperature is constant, the moisture content of the dried powder and granules changes depending on the amount of moisture entrained in the powder and the type of powder and granules, so the setting value of the moisture controller 23 may vary. When the moisture content increases, the output of the controller 23 attempts to set the drying temperature to a higher value than the current value. Conversely, if the moisture content of the dried powder is less than the set value, the set value of the drying temperature is lowered.

In addition, in the dew point controller 20, if the difference between the wall temperature of the device and the dew point in the hot exhaust gas is smaller than the set value or if the two temperatures are reversed, condensation will occur on the wall surface, so this should be avoided. In order to increase the drying temperature, the output of the controller 22 shifts the set value upward. Conversely, if the temperature difference is greater than the set value, the drying temperature is shifted to lower.

The selector 21 selects the highest value among the set drying temperatures output from the moisture controller 23 and the dew point controller 20 and outputs it as the set value of the controller 19. Drying is carried out at the lowest economical temperature that satisfies both conditions, without causing the amount to exceed the specified value, and without condensation of water vapor in the hot exhaust gas within the apparatus.

In this embodiment, as a method of controlling the drying temperature, the output of the controller 19 is used to open and close the 3Ji1 control valve 11 to control the flow rate supplied to the drying tank l. Adopts a volumetric type proportional to the number of tanks and 5
The rotation speed of the pump 6 may be controlled by making the amount of return to zero or constant.

Alternatively, the supply amount of the powder or granular material may be kept constant and the control valve 18 may be controlled by changing the set value of the controller 17 using the output of the controller 19, or the output of the controller 19 may be used to directly control the control valve 18. The temperature of the hot air introduced into the drying tank 1 may be adjusted by controlling the valve 18, and further,
Both the supply amount of the powder and the temperature of the hot air may be adjusted.

In addition, the moisture content of the dried powder and granules is not measured near the exhaust pipe 13, and some of the powder and granules are collected from inside the collector 8 or along the path of the hot exhaust gas introduced into the collector 8. You can also pull it out and measure it.

It is also possible to use the temperature of the thermal exhaust gas instead of the wall surface temperature as the input value of the dew point controller 20, and it is also possible to input only the dew point and adjust it so that the dew point does not fall below a certain value. good.

Furthermore, instead of measuring the dew point, measure the humidity and make sure that this value does not exceed a certain level, or measure the moisture content and keep the percentage of the saturated moisture content output by a separate converter below a certain level. Adjust the drying temperature 3I!
The set temperature of the meter 19 may be changed.

Furthermore, as the drying temperature, the temperature of the powder after drying may be measured instead of the temperature of the hot exhaust gas.

Furthermore, the measurement points of the wall temperature and dew point of the device are not limited to the positions shown in Figure 1, and instead of using multiple controllers as shown above, a controller with multiple functions can be used. Needless to say, it is also possible to use a process computer or the like.

Furthermore, the present invention can be utilized for drying powder and granular materials using other drying apparatuses, for example, drying apparatuses equipped with a fluidized bed.

<Effects of the Invention> As explained above, according to the present invention, even if the amount of moisture accompanying the powder or the difficulty of drying changes, or the atmospheric conditions (e.g. temperature, humidity) change, The powder and granules are always dried at the optimum drying temperature, and moisture does not condense inside the device, dampening the dried powder or corroding or wearing out the device. In addition to economical operation that satisfies the moisture content of powder and granules, it also eliminates the need for workers to test the moisture content, making unmanned operation and labor saving possible, and has extremely high industrial utility value.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention. 1--Drying tank body, 3--Blower 4--1 air heater, 5--tank. 6---Bomb, 71---Sprayer. 8--1 collector, 9--1 wind machine. 10--11 discharger, 11-- control valve. 12-m--dew point meter, 13---discharge pipe. Moisture meter. -Thermometer. Drying temperature 11 meters weighing Dew point controller. Converter. thermometer 17--Hot air temperature controller 18-4Ji1 section valve 19'-m-thermometer. 21-m-selector. 23-m-Moisture controller. teenager Reason Man

Claims (1)

[Claims] In a method of continuously drying powder or granular materials using a drying device, in addition to the drying temperature, the dew point of the exhaust gas of the hot air that contributed to the drying, or the humidity in place of this, or the amount of moisture contained in the exhaust gas, and the amount of moisture contained in the exhaust gas, The drying temperature is determined by measuring one or more of the moisture content of the powder and the wall temperature of the drying device, and inputting these single or multiple signals to the appropriate controller that adjusts them to preset values. The drying temperature is changed and set based on the output of a controller other than the controller, and the supply amount of the heat source and/or the supply amount of the powder or granular material is adjusted to match the drying temperature. Drying method.