JPH06273043A - Moisture content adjusting method of ventilation belt dryer - Google Patents

Abstract

PURPOSE:To control the moisture content of a dried product in an automatic mode by controlling the supply temperature of hot air in conformity with the difference between the moisture content of a raw material and a target moisture content. CONSTITUTION:A temperature detector 39 detects the discharged temperature of hot air ejected from an eight air supply box 5h. A control part 36 calculates the moisture content of a raw material at the current time based on a preliminarily stored relative relation and controls the supply temperature of hot air in conformity with the difference between the moisture content and a target moisture content, thereby controlling the moisture content. More specifically, when the detected moisture content is larger than the target moisture content, drying operation is continued as it is. Especially when it is considered necessary, a cooled air supply source 34 is halted while a temperature controller 28 of a heat exchanger 28 is adjusted so as to increase the supply temperature of hot air. On the other hand, when the moisture content is smaller than the target moisture content, the release volume of cooled air valves 35h and 35i is controlled so that a proper amount of cooled air may flow into a terminal supply passage 31h and 31i.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting the water content in an aeration belt dryer for drying solid matter such as shredded kelp, vegetables and small fish mainly under normal pressure.

[0002]

2. Description of the Related Art An aeration belt dryer is one in which a raw material is placed on a conveyor belt and hot air is passed through the raw material to dry the raw material under normal pressure.

Incidentally, depending on the type of raw material, a relatively large water content may be required after the drying operation (for example, in the case of shredded kelp, about 20 wt%). Conventionally, as shown in FIG. 6, a constant hot air supply temperature (70/60/50
The correlation between the water content and the drying time is detected for each temperature, and various conditions such as the hot air supply temperature and the drying time are determined from this relationship to obtain the desired water content.

[0004]

However, the correlation shown in FIG. 6 largely changes depending on the type of raw material and the level of the initial water content, so that the operator ultimately depends on his intuition and experience. The hot air supply temperature and drying time must be determined. Therefore, the conventional method has a problem that the water content of the product tends to vary and the work efficiency also decreases.

Therefore, an object of the present invention is to provide a method of adjusting the water content in a ventilation belt dryer which can automatically control the water content of a dried product.

[0006]

[Means for Solving the Problems] To achieve the above object,
In the present invention, when hot air is passed through the raw material placed on the conveyor belt to dry the raw material under normal pressure, the humidity of the hot air that has passed through the raw material is detected, and the moisture content in the raw material is calculated from this detected value. After that, the hot air supply temperature is controlled according to the difference between the water content and the target water content.

[0007]

OPERATION An example of a ventilation belt dryer is shown in FIG. This is one in which a mesh-shaped conveyor belt (3) is brought into close contact with a blower box (5) whose upper surface is open. The blower port (7)
The hot air blown into the air blowing box (5) from the air passes through the raw material (8) on the conveyor belt (3) and dries it. Using this dryer, the hot air supply temperature is changed (70/60/50 ° C, 3 types), the water content in the raw material (8) at regular intervals and the hot air immediately after passing through the raw material (8) When the humidity (exhaust humidity) of is measured as shown in FIG. 5 (however, FIG. 5 shows the case where shredded kelp is used as the raw material (8)).

From this figure, there is a correlation that approximates a proportional relationship between the water content and the exhaust humidity, and at a constant exhaust humidity (for example, 20 RH%), regardless of the hot air supply temperature. It can be seen that the water content in the raw materials also shows a substantially constant value (≈20 wt%). That is, by successively measuring the exhaust humidity, the water content in the raw material can be specified regardless of the hot air supply temperature.

In the present invention, this characteristic is utilized to automate the water content management. Specifically, the humidity (exhaust humidity) of the hot air that has passed through the raw materials is detected, and this detected value is shown in FIG.
After determining the water content in the raw material by applying the correlation shown in (4), the hot air supply temperature is controlled according to the difference between this water content and the target water content. Generally, the relative humidity of air decreases when the temperature rises, and the relative humidity increases when the temperature decreases.
Therefore, if the supply temperature of the hot air is controlled, the relative humidity of the hot air is increased or decreased accordingly. When the relative humidity of the hot air rises or falls in this way, the humidity after passing through the raw material (exhaust air humidity) rises or falls in proportion to this, and as a result, the water content also increases or decreases.

[0010]

EXAMPLES An example of applying the present invention to a ventilation belt dryer previously proposed by the present applicant (see Japanese Patent Application No. 3-275126) will be described with reference to FIGS. 1 to 3. To do.

In this ventilation belt dryer, as shown in FIG. 1, three endless conveyor belts (3a) to (3c) made of mesh belts are stacked and arranged in a drying chamber (1). A plurality of air blow boxes (5a) to (5i) are arranged between the transport side (4a) and the return side (4b) of each transport belt (3). The blower boxes (5a) to (5i) are arranged three by three on the conveyor belts (3a) to (3c) of each stage, and the upper surface thereof is a perforated plate (6) as shown in FIG. ing. The perforated plate (6) is in close contact with the transport side (4a) of the transport belt (3).

The raw material dropped from the terminal end of the supply belt (9) is supplied onto the uppermost conveyor belt (3a) through the first hopper (11a). The raw material reaching the end of the conveyor belt (3a) is supplied to the intermediate conveyor belt (3b) through the second hopper (11b), and so on. After being sequentially passed through the conveyor belt (3c), the sheet is discharged to the outside of the apparatus. Each conveyor belt (3a)
During the transportation of the raw material (8) by (3c) to (3c), hot air is supplied from the air blowing port (7) provided in each of the air blowing boxes (5a) to (5i). The hot air thus supplied passes through the perforated plate (6) and the conveyor sides (4a) of the conveyor belts (3a) to (3c) and is jetted upward to dry the raw material (8).

The first to third hoppers (11a) to (11)
The stirring mechanism (15) already proposed by the present applicant is arranged in c) (see Japanese Patent Application Nos. 4-12214 and 4-20212, etc.). As shown in FIG. 2, the stirring mechanism (15) includes a pair of rotating rollers (16) arranged opposite to each other, and both rotating rollers (16).
The stirring member (17) radially attached to the cover and a large number of fixing members (19a) to (19c) fixed to the cover (18) are provided, and the stirring members (17) themselves, and the stirring member (17) and the fixing member. Conveyor belt (3a) by meshing (19a) to (19c)
The raw material (8) falling from the terminal end of is properly solved.

FIG. 3 shows the intake and exhaust system pipelines of the ventilation belt dryer. In the following description, the blower boxes (5a) to (5i) will be first described in the order of passage of the raw material (8).
The blower box (5a) to the ninth blower box (5i).

The air sucked from the outside by the intake fan (21) is divided into two systems, a first hot air supply passage (23) and a second hot air supply passage (24), and both supply passages (23) ( It is heated by the heat exchangers (25) provided in the middle of 24) to become hot air. At this time, the heating temperature on the first hot air supply passage (23) side is set to be slightly higher than that on the second hot air supply passage (24) side. A temperature controller (28) having a control valve (26) on the primary side and a heat-sensitive sensor (27) on the secondary side is attached to both heat exchangers (25). By the temperature controller (28), the temperature of the hot air flowing through the hot air supply passages (23) (24) can be independently adjusted arbitrarily.

The hot air flowing through the first hot air supply passage (23) is
The first half of the drying process, that is, the first to fifth blower boxes (5a)
To (5e) and pass through the perforated plates and the conveyor sides (4a) of the conveyor belts (3a) and (3b) to dry the raw materials as described above. On the other hand, the hot air flowing through the second hot air supply passage (24) is
The latter half of the drying process, that is, the sixth to ninth blower boxes (5
f) to (5i), and similarly conveyor belts (3b) (3c)
Dry the above ingredients. As a result, a relatively high temperature hot air is supplied to the first half of the drying process and a lower temperature hot air is supplied to the latter half of the drying process, so that excessive drying of the raw material (8) is prevented and the heat contained in the raw material is reduced. Weak nutrients (eg,
The decrease of vitamins etc.) is suppressed to the minimum. The hot air blown out from each of the blower boxes (5a) to (5i) is collected from a plurality of exhaust ports (29) and is exhausted outdoors by an exhaust fan (30).

Among the second hot air supply passages (24), the cold air supply passages (31h) (31i) connected to the eighth and ninth air supply boxes (5h) (5i) respectively 32h)
(32i) is connected. This cold air supply channel (32h) (32
i) is connected to a cold air supply source (34) for inhaling indoor air, and the amount of cold air flowing into the terminal supply paths (31h) (31i) is supplied to both cold air supply paths (32h) (32i). The flow rate control valves (35h) (35i) provided can be independently adjusted. The opening amount of the cold air valves (35h) (35i) is automatically controlled by the control unit (36) based on the detection value of the humidity detector described later.

A humidity detector (39) is provided above the eighth blower box (5h). The output wiring of the humidity detector (39) is connected to the control section (36). The control unit (36) stores in advance a correlation between exhaust gas humidity and water content as shown in FIG. 5 for each type of raw material.

The specific procedure for adjusting the water content in the ventilation belt dryer will be described below.

First, the humidity detector (39) detects the exhaust humidity of the hot air blown from the eighth blower box (5h). The control unit (36) calculates the water content in the raw material at the present time from the input detected value based on the correlation stored in advance (see FIG. 5). Then, the supply temperature of hot air is controlled according to the difference between this water content and the target water content, and the general characteristic of air, that is, the relative humidity decreases when the temperature rises, and conversely, the relative humidity increases when the temperature falls. The water content is controlled by utilizing the characteristics.

More specifically, when the water content is higher than the target water content, the drying operation is continued in that state. If necessary, the cold air supply source (34) is stopped and the temperature controller (28) of the heat exchanger (25) is adjusted to increase the hot air supply temperature. Then, the relative humidity of the hot air supplied to each of the blower boxes (5a) to (5i) decreases, so that the exhaust humidity also decreases and the water content of the raw materials also decreases. On the other hand, when the water content is smaller than the target water content, the control unit (36) controls the opening amount of the cold air valves (35h) (35i) according to the difference, and an appropriate amount of cold air is supplied to the end supply path (31h). ) (31i). Then, the supply temperature of the hot air supplied to the eighth and ninth air blowing boxes (5h) (5i) is lowered, and the relative humidity of the hot air is increased due to the general characteristics. As a result, the exhaust humidity increases and the water content of the raw materials also increases. Hereinafter, the moisture content is determined while sequentially measuring the exhaust humidity with the humidity detector (39), and the above-described procedure is repeated to match the moisture content with the target value.

According to the present invention, the above-mentioned many air blowing boxes (5a) to (5i) and the mesh-shaped transport belt (3a).
It can be applied not only to a dryer formed by combining (3c) to (3c) but also to any type of ventilated belt dryer that performs normal pressure drying of raw materials placed on a conveyor belt.

Further, in this embodiment, the cold air is used at the final stage of the drying process, that is, the eighth and ninth air blowing boxes (5h) (5h).
Although it is supplied to i), cold air may be supplied to either one of the air blowing boxes or the other air blowing boxes (5a) to (5g). Further, the humidity detector (39) is provided above the eighth blower box (5h), but the humidity is detected on the other blower boxes (5a) to (5g) and (5i) to which cool air is supplied. It is also possible to provide a container (39).

Further, in this embodiment, hot air is taken in from the outside and cold air is taken in from the inside. This is because the indoor humidity is usually slightly higher than the outside, and the effect of increasing the water content by the cold air is increased. Is more efficient,
If there is no particular inferiority in efficiency, the air may be taken from indoors or outdoors.

[0025]

As described above, in the present invention, noting that the water content in the raw material can be specified from the humidity (exhaust air humidity) of the hot air after passing through the raw material, the exhaust water humidity is sequentially detected to determine the water content in the raw material. After the indexing, the temperature control of the hot air is performed according to the difference between the water content and the target water content, so that the water content management, which was conventionally performed by the operator's eyes or touch, can be automated. Therefore, it becomes possible to obtain a desired moisture content accurately and efficiently.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a ventilation belt dryer proposed by the present applicant (a) and a cross-sectional view taken along the line AA in the (a) diagram (b).

FIG. 2 is a side view of a stirring mechanism arranged between a terminal end portion of an upper conveyor belt and a starting end portion of a lower conveyor belt.

FIG. 3 is a circuit diagram of an intake system and an exhaust system of the ventilation belt dryer according to the present invention.

FIG. 4 is a sectional view of a ventilation belt dryer.

FIG. 5 is a graph showing a correlation between water content and exhaust humidity.

FIG. 6 is a graph showing a correlation between water content and drying time.

[Explanation of symbols]

 3a to 3c Conveyor belt 8 Raw materials 39 Humidity detector

Claims (1)

[Claims] 1. When hot air is passed through a raw material placed on a conveyor belt to dry the raw material under atmospheric pressure, the humidity of the hot air that has passed through the raw material is detected, and the moisture content in the raw material is detected from this detected value. After indexing, the method for adjusting the water content in a ventilation belt dryer is characterized in that the supply temperature of hot air is controlled according to the difference between this water content and the target water content.