JP2001227865A - Drier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drier where it is easy to set the target of drying to an objective percentage of contained liquid without taking time or labor more than necessary in drying. SOLUTION: This drier is equipped with a storage container 1 which stores the target of drying being solid matter, a drying means 4 which dries the target of drying within the storage container 1, a temperature detector 9 which detects the temperature of the target of drying within the storage container 1, and a control means 5 which controls the drying means 4, based on the detection result of the temperature detector 9, and the control means 5 is equipped with a computer 12 which computes the point of time of change when the target of drying changes from a constant-rate drying state to a falling-rate drying state, a memory 13 which stores the drying condition on the target of drying, and a controller 14 to the drying means 4, and the storage means 14 stores beforehand the drying conditions on and after the point of time of such a change that the target of drying comes to an objective percentage of contained liquid, and the drying means 4 dries the target of drying under the above drying condition on and after the point of time of change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drying apparatus for drying a solid object to be dried.

[0002]

2. Description of the Related Art Conventionally, the above drying apparatus is disclosed in
As disclosed in Japanese Patent No. 4271, a container for storing a solid object to be dried, a drying unit for drying the object to be dried in the container, and a temperature of the object to be dried in the container are detected. A temperature detector and a control unit that controls the drying unit based on the detection result of the temperature detector are provided, and the control unit calculates a change point at which the object to be dried changes from the constant-rate drying state to the reduced-rate drying state, The drying unit is controlled based on the change time point and the temperature of the object to be dried on the outlet side of the apparatus, so that the inside of the container is set to a predetermined temperature distribution.

[0003]

In the above-mentioned conventional configuration,
It is only possible to set the inside of the storage container to a predetermined temperature distribution. Even if the inside of the storage container is set to the predetermined temperature distribution, the liquid content of the object to be dried may be out of the target range. Was.

Incidentally, there are the following means [A] to [D] as means for drying an object to be dried.

[A] After drying, a part of the object to be dried is extracted and the amount of liquid contained therein is measured, whereby the degree of dryness of the entire object to be dried is estimated. Alternatively, it is determined whether or not the drying operation is completed.

[B] The liquid content of the object to be dried is estimated by measuring the total amount of liquid discharged from the drying apparatus, the discharge rate per hour, or the total amount of drying action given to the object to be dried. I do. Alternatively, it is determined whether or not the drying operation is completed.

[C] The drying conditions in which the liquid content of the object to be dried is within a certain range from the repeated drying conditions in the past are stored, and drying is performed under the drying conditions.

[D] The object to be dried is exposed for a certain period of time or longer under conditions of temperature and pressure (pressurized or reduced pressure) at which the liquid content of the object to be dried reaches an equilibrium value.

[0009] However, in the means of [A], the operation of extracting a part of the object to be dried and the operation of measuring the amount of liquid contained therein cannot be omitted, and the operation is troublesome.

It is also possible to extract a part of the object to be dried,
If the amount of liquid mixed therein cannot be measured, it is difficult to dry the object to be dried so that the liquid content of the object falls within a certain range.

In the means [B] and [C], the liquid content of the object to be dried is not directly measured, but the liquid content is estimated from indirect information. When the liquid content or the like is different from normal or when an unusual disturbance or the like is applied during drying, the object to be dried cannot be dried to a state where the liquid content is within a certain range. In the means [D], drying takes a long time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a drying apparatus which can easily set an object to be dried to a target liquid content ratio without taking unnecessary time and labor for drying. The point is to provide.

[0013]

The constitution, operation and effect of the invention according to claim 1 are as follows.

[Constitution] A storage container for storing a solid object to be dried, drying means for drying the object to be dried in the storage container, and a temperature detector for detecting the temperature of the object to be dried in the storage container And control means for controlling the drying means based on the detection result of the temperature detector, wherein the control means calculates a change time point at which the object to be dried changes from a constant rate drying state to a reduced rate drying state. An operation unit, a storage unit for storing drying conditions for the object to be dried, and a control unit for the drying unit are provided, and the change time point is such that the object to be dried has a target liquid content. The subsequent drying conditions are stored in the storage unit in advance, and the drying unit is configured to dry the object to be dried under the drying conditions after the change point.

[Operation] The constant-rate change state is a dry state in which the liquid contained in the object to be dried has reached the boiling point (sections AB in FIG. 2; FIG. 2 shows the drying time and the object to be dried). FIG. 2 is a diagram showing the relationship with the temperature.) The decreasing rate change state is a drying state after the drying of the liquid on the surface of the object to be dried is completed from the constant rate changing state (FIG. 2). Section B ~
C). It is known that the liquid content of the object to be dried at the transition point (B in FIG. 2) from the constant rate drying state to the rate decreasing drying state becomes a constant value depending on the composition of the drying object.

Therefore, the drying conditions after the time point at which the object to be dried changes so as to reach the target liquid content are obtained in advance by experiments or the like, and the drying conditions are stored in the storage unit of the control means. After the change point calculated by the department,
The control unit controls the drying unit to dry the object to be dried under the drying conditions.

That is, the drying object is dried in the manner described above after the time point of the change when the liquid content of the drying object becomes a constant value. Even if the amount or the initial liquid content is different from normal, or even if an unusual disturbance is applied during drying, the liquid content of the drying target is easily set to the target value. Become.

For example, means for exposing the object to be dried under a condition of temperature and pressure (pressurized or depressurized) at which the liquid content of the object to be dried reaches an equilibrium value to a certain value for a certain period of time or longer means drying. It takes a long time, but in the configuration of the first aspect, the drying does not take a long time.

There is no need for an operation of extracting a part of the object to be dried or an operation of measuring the content of the liquid contained therein.

[Effects] Accordingly, a drying apparatus that can easily set an object to be dried to a target liquid content accurately without requiring excessive time and labor for drying can be provided.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a drying apparatus for drying a granular polyamide resin containing liquid (corresponding to a solid object to be dried).

The drying device includes a rotary drum 1 (corresponding to a storage container) for storing a polyamide resin,
A control unit 5 (corresponding to a control unit) for providing a quantitative supply mechanism 3 for measuring and supplying the polyamide resin to the rotary drum 1, providing a drying unit 4 for drying the polyamide resin in the rotary drum 1, and controlling the drying unit 4 Is provided.

The drying means 4 is provided with a heating medium temperature adjusting mechanism 7 for covering the rotating drum 1 with a heating medium jacket 6 and for adjusting the temperature of the heating medium in the heating medium jacket 6. Are connected to each other.

A first temperature detector 9 for detecting the temperature of the polyamide resin in the rotary drum 1 and a pressure gauge 10 for detecting the pressure in the rotary drum 1 are provided to detect the temperature of the heat medium. (2) A temperature sensor 11 is provided, and respective signals are sent from the first temperature sensor 9 and the pressure gauge 10 to the control device 5, and the heat medium temperature control mechanism 7 is transmitted from the second temperature sensor 11
To send a signal.

The control unit 5 includes an arithmetic unit 12 for calculating a change point when the polyamide resin changes from a constant-rate dry state to a reduced-rate dry state, a storage unit 13 for storing drying conditions for the polyamide resin, The storage unit 13 is provided with a control unit 14 and stores in advance the drying conditions (temperature, pressure, time, etc.) after the change point such that the polyamide resin has a target liquid content. After the change point, the drying means 3 is configured to dry the polyamide resin under the drying conditions.

The polyamide resin is dried in the drying apparatus having the above structure as follows.

The polyamide resin is weighed by the metering mechanism 3 and charged into the rotating drum 1. When the weight ratio of the liquid contained in the polyamide resin is less than 20%, the proportion of the liquid has little effect on the drying accuracy, and therefore, the measuring accuracy of the polyamide resin to be introduced does not need to be very high. Further, the temperature of the polyamide resin to be introduced has little influence on the drying accuracy and can be ignored.

After the polyamide resin is charged, the inside of the rotary drum 1 is depressurized by the vacuum exhaust mechanism 8 and circulated in the heat medium jacket 6 while the heat medium is heated to a constant temperature by the heat medium temperature adjusting mechanism 7.

At this time, since the pressure inside the rotary drum 1 and the temperature inside the heat medium jacket 6 have little effect on the drying accuracy, it is not necessary to increase the control accuracy so much.

By these actions, the temperature of the polyamide resin rises and eventually reaches the boiling point of the liquid at the pressure at that time (point A in FIG. 2).

At this time, the dried state of the polyamide resin is a constant-rate dried state. In the constant-rate drying state, the surface of the polyamide resin is covered with a liquid film, and the drying speed is governed by the difference between the ambient temperature and the wet bulb temperature. When the evaporation of the liquid in the rotating drum 1 is sufficiently exhausted by the vacuum exhaust mechanism 8, the wet bulb temperature is controlled by the pressure (degree of vacuum) and the temperature in the rotating drum 1. The constant rate drying rate can be represented by the following relational expression.

Rc = (t−t ′) × h / λ Rc: constant rate drying rate t: ambient temperature t ′: wet bulb temperature h: film heat transfer coefficient λ: latent heat of vaporization of t ′ where constant rate drying If the temperature of the inside atmosphere is set to an appropriate value, the liquid adhering to the surface of the polyamide resin is uniformly dried, and the temperature of the polyamide resin is set to the wet bulb due to the latent heat of evaporation of the liquid. It takes a substantially constant value depending on the temperature (see FIG. 2, section AB). Alternatively, the temperature rise of the polyamide resin is much slower than before the constant-rate dry state is entered (see FIG. 2, section 0 to A).

After that, when the drying proceeds further, the drying of the liquid adhering to the surface of the polyamide resin is eventually completed, and the drying state shifts to the reduced-rate drying. It is known that the drying rate at this time is approximately proportional to the difference between the liquid content at that time and the equilibrium liquid content (hereinafter referred to as the free liquid content).

It is known that the equilibrium liquid content is proportional to the logarithm of the internal temperature of the polyamide resin. Therefore, the relationship among the drying rate, the equilibrium liquid content, and the free liquid content in the reduced-rate drying period can be expressed by the following equation.

Wc = −C × InT F = W−Wc Rd = Rc × F / Wc Wc: equilibrium liquid content T: internal temperature of polyamide resin F: free liquid content W: liquid content Rd: reduced rate drying Speed C: Constant FIG. 3 is a diagram showing the relationship between the liquid content and the drying speed when a polyamide resin is given a drying action under a certain condition. The symbols A, B, and C in FIG. 3 indicate the same time points as the symbols A, B, and C in FIG.

Sections AB in FIG. 3 are in a constant-rate dry state,
Sections B to C are in a reduced-rate dry state. The point at which the drying rate becomes 0 (C in FIG. 3) indicates the point in time when the equilibrium liquid content under that condition has been reached.

It is known that the liquid content at the transition point (B in FIG. 3) from constant rate drying to reduced rate drying takes a constant value depending on the resin composition. As the rate-of-rate drying state progresses from the point of change to the drying state, the drying speed temporarily decreases.

This means that the amount of latent heat of vaporization of the liquid per unit time is reduced. If the polyamide resin is continuously subjected to the same drying action as that at the time of constant-rate drying, the latent heat of vaporization of the liquid is generated. The amount of heat exceeding the amount will be used to raise the temperature of the polyamide resin (sections B to B in FIG. 2).
C).

The temperature of the polyamide resin during drying is detected by a first thermometer 9 installed inside the rotary drum 1, and a signal of the temperature is continuously sent to the controller 5. With this configuration, it is possible to detect an increase in the temperature of the polyamide resin at the time of transition from constant-rate drying to reduced-rate drying when a drying action under given conditions is given.

That is, at the time of this change, the amount of the polyamide resin charged is constant, the resin temperature is constant, and the liquid content is also constant.

The controller 5 controls the ripening medium temperature control mechanism 7 and the vacuum exhaust mechanism 8 so that the temperature and pressure inside the rotary drum 1 satisfy predetermined conditions from the above state.
The polyamide resin inside the rotating drum 1 keeps a predetermined liquid content at a predetermined time. For example, by changing the above conditions, it is possible to end the drying operation at an arbitrary liquid content. Become.

Since the drying speed in this section gradually decreases as the drying proceeds, the liquid content at the time of the change caused by errors in the amount of the polyamide resin charged, the temperature of the object to be dried, the content of the liquid, and the like. The rate error will also converge.

In order to further increase the accuracy of the degree of drying at the end of drying, the drying action after the change from the constant rate drying state to the reduced rate drying state or the drying action immediately before the end of drying is adjusted. This becomes possible by reducing the drying speed in that section.

[Another Embodiment] The present invention can be applied to any type of batch type drying apparatus.

If a plurality of temperature detectors are arranged in the flow direction of the polyamide resin so that the temperature of the heat source can be individually controlled in the flow direction of the polyamide resin, the present invention can be applied to a continuous drying apparatus.

In the above embodiment, the heat source is constituted by the heat medium jacket, but may be constituted by a burner or the like.

In the above embodiment, the drying device is provided with the vacuum exhaust mechanism 7, but a drying device without a vacuum exhaust mechanism may be used.

Examples of the object to be dried include carbon black, fertilizers, pigments, and synthetic resin particles such as polyamide resin. The type of the object is not particularly limited as long as the solid can contain a liquid therein.

The shape is not particularly limited as long as the balance between the specific surface area, the heating heat flow rate, the specific heat of the solid, and the latent heat of vaporization of the liquid is set within an appropriate range.

The liquid contained in the object to be dried may be not only water but also a solvent or the like.

[0052]

Next, an embodiment in which a granular polyamide resin is dried by a conventional drying apparatus and an embodiment in which a granular polyamide resin is dried by a drying apparatus according to the present invention will be described.

[Examples of Drying with Conventional Drying Apparatus] The moisture content of the polyamide resin before the start of the drying action is as follows:
12.8% by weight ratio average for each drying, variation is σ
= 0.28.

When the drying operation is completed, 0.10 ± 0.
The goal is to dry to 02%. In addition, the input amount of the polyamide resin per drying was 4.02 t on average.
on, the variation is σ = 0.219. The temperature of the polyamide resin at the time of charging is the outside air temperature at that time and is not particularly specified.

The evacuation mechanism 8 is constantly operated during the drying operation.
0 torr to 4.5 torr (3999.66 Pa to 5
99.949 Pa), which is not specified.
The number of times of drying conducted in this study was 89 times.

FIG. 5 shows a typical temperature trend when drying is performed according to the prior art. At this time, the temperature of the polyamide resin was set to 11 after 10 hours from the start of drying.
The output of the heat medium temperature control mechanism 18 is controlled to reach 5 ° C.

The drying operation described in the embodiment is performed. When the temperature of the polyamide resin reaches 115 ° C., it is determined that the drying is completed, and the moisture content at that time is measured for each drying operation. FIG. ing.

[Examples of Drying by the Drying Apparatus According to the Present Invention] The moisture content of the polyamide resin before the start of the drying action was 12.9% by weight on average for each drying, and the variation was σ = 0. 30.

This was reduced to 0.08 ± 0.
The goal is to dry to 02%. In addition, the input amount of the polyamide resin per drying was 4.04 t on average.
on, variation is σ = 0.220. The temperature of the polyamide resin at the time of charging is the outside air temperature at that time and is not particularly specified.

The temperature control pattern of the heat medium temperature control mechanism 7 was set as shown in FIG. In this embodiment, the time when the temperature of the polyamide resin reaches 65 ° C. while the temperature of the heat medium is constant at 120 ° C. is set as the change time B at which the constant-rate drying is shifted to the reduced-rate drying, and 5.5 hours from the change time B Thereafter, the drying operation ends at a heating medium temperature of 110 ° C.

However, in order to shorten the entire drying time, the temperature of the polyamide resin is set to 55 ° C. one hour after the start of the drying action.
, And between 1 hour and 3 hours after reaching the change point B, the temperature of the heat medium is raised to 150 ° C. to rapidly heat the polyamide resin.

The pressure inside the rotary drum 1 is maintained at 30 torr (3999.66 P) until 4 hours have passed since the start of drying.
a) Hereinafter, 15 torr (1
999.83 Pa) or less, and is maintained at 5 torr (666.61 Pa) or less until 10 hours thereafter.

In the above embodiment, the target moisture content and the target range are set as shown in Table 1. However, these can be easily changed by changing the parameters of the temperature control pattern according to the present invention. Can be.

In the above embodiment, the method of controlling the temperature pattern of the heating medium from the measured temperature of the target polyamide resin was used, but the temperature pattern of the subsequent polyamide resin was determined from the measured temperature of the target polyamide resin. Can also be applied to the method of controlling

FIG. 7 shows the water content of each drying at the end of the drying operation in this embodiment. In addition, Table 1 shows a comparative example in which the drying was performed by the conventional technique and a variation in the water content of the two at the end of the drying in the example according to the present invention. The water content was measured by the Karl Fischer method.

[0066]

[Table 1] From the above examples, it was confirmed that according to the present invention, it is easy to set the liquid content of the polyamide resin to a value within a target range.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a drying apparatus.

FIG. 2 is a diagram showing a relationship between a drying state (time) and a temperature.

FIG. 3 is a diagram showing a relationship between a drying state (liquid content) and a drying speed.

FIG. 4 is a diagram showing a relationship between a drying temperature and a drying time.

FIG. 5 is a view showing a drying result of a comparative example.

FIG. 6 is a diagram showing a drying result of a comparative example.

FIG. 7 is a diagram showing the drying results of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage container 4 Drying means 5 Control means 9 Temperature detector 12 Operation part 13 Storage part 14 Control part

Claims (1)

[Claims] 1. A storage container for storing a solid object to be dried, drying means for drying the object to be dried in the storage container, and a temperature detector for detecting the temperature of the object to be dried in the storage container. Control means for controlling the drying means based on the detection result of the temperature detector, wherein the control means calculates a change time point when the object to be dried changes from a constant-rate drying state to a reduced-rate drying state. Unit, a storage unit for storing drying conditions for the object to be dried, and a control unit for the drying unit is provided, and after the change time point such that the object to be dried becomes a target liquid content rate A drying unit configured to store in advance the drying conditions in the storage unit, and to dry the object to be dried under the drying conditions after the change point.