JPH0472152B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a device for controlling the temperature and volume of hot air from a burner in a grain dryer. In conventional dryers, the temperature and volume of hot air remain constant from the start to the end of drying, so as the grain dries, the temperature of the exhaust air increases and the humidity decreases, allowing the hot dry exhaust air to remain dry with sufficient drying capacity. As a result, the drying rate of the grains gradually slows down and the thermal efficiency is also poor. In the present invention, the hot air temperature is set constant according to the amount of grain to be dried, and the actually measured amount of water removed is used as the calculation standard until the humidity of the exhaust air reaches a preset value after drying starts. The drying speed of grains is kept constant by controlling the volume of hot air to match the amount of water removed, and when the humidity of the exhaust air decreases to a preset value, the volume of hot air is reduced to The purpose is to prevent humidity loss and improve the thermal efficiency of dryers. The present invention will be described based on an embodiment shown in the drawings. Reference numeral 1 denotes a storage chamber of a dryer, and a chevron plate 2 having an inverted V-shaped cross section is provided at the center of the bottom of the storage chamber 1. Direction swash plates 3, Install 3. Perforated plates 4 are connected to both side edges of the chevron-shaped plate 2 and the lower edges of the guiding swash plates 3, 3, respectively, and a pair of opposing perforated plates 4 form a drying chamber 5, 5. The discharge ports at the lower ends of the drying chambers 5 and 5 are connected to a gutter-like grain flow chamber 7 through a rotary valve 6, and the output end of a grain feeding helix 8 suspended horizontally in a groove in the center is connected to a grain hoist 9.
Connect to the bottom intake of the A grain feeding helix 10 is connected to the upper part of the grain raising machine 9,
Its terminal end is opened above the diffusion plate 11 suspended from the center of the ceiling plate of the storage chamber 1. Then burner 1 is placed opposite the front and back of the dryer.
2 and a suction fan 13 are installed, and the burner 12 is exposed to the hot air chamber 14 inside the left and right drying chambers 5, 5, and the fan 13 is attached to the outside of the drying chambers 5, 5 and the exhaust area surrounded by the outer wall of the dryer. Connect to the wind chamber 15.
16 is a shield plate that closes off the side of the hot air chamber 14 opposite to the burner 12. The grains pass through a grain hoist 9 and a grain feeding helix 10, are spread evenly into a storage chamber 1 by a diffusion plate 11, and flow down a drying chamber 5. At this time, the hot air from the burner 12 enters the left and right drying chambers 5 from the central hot air chamber 14 and dries the grains flowing down, and the exhausted air containing moisture is sent to the exhaust chamber 15.
The air is then exhausted to the outside of the machine by a fan 13. The dried grains fall into the flow grain chamber 7 by rotation of the rotary valve 6, and are returned to the storage chamber 1 by the grain feeding helix 8 and the grain raising machine 9. However, in this embodiment, temperature sensors Sa and Sb are installed inside the hot air chamber 14 and exhaust air chamber 15 of the dryer, respectively, to measure the actual hot air temperature Ta and exhaust air temperature Tb. A grain amount setting circuit 17 is provided to set the grain amount Ao loaded into the dryer, and this is connected to the hot air temperature setting circuit 18. When the grain amount A is large, the hot air temperature is set high, and when the grain amount A is small, the hot air temperature is set high. The hot air temperature setting circuit 18 sets the hot air temperature by calling the optimum hot air temperature data from the hot air temperature data determined and stored in advance according to the grain amount A, such as by setting the hot air temperature low. Reference numeral 19 denotes a comparator circuit, to which a hot air temperature setting circuit 18 and a hot air temperature sensor Sa are connected to the input side of the comparator circuit. The control device 20 is operated to control the fuel flow rate and burn the burner 12 so that the actual hot air temperature becomes equal to the set temperature. Next, the grain amount setting circuit 17 is connected to the reference water removal amount setting circuit 21, and by this circuit 21, the grain amount A,
A calculated water removal amount Q to be used as a reference is calculated from the values of the water content and a predetermined drying speed based on (Equation 4) described later, and a voltage proportional to the calculated value is output. First, the drying rate is the decrease in the moisture content (%) of grains per unit time, so if the moisture content at a certain time is a, and the moisture content a unit time after that is b, then
The drying rate P (%/hour) at that point is as follows: P=a-b (Equation 1). The weight of water evaporated from the grain per unit time when the drying rate is P, that is, the amount of water removed Q (Kg/hour)
If the weight of the grain at a certain time is A (Kg), and the weight of the grain after a unit time is B (Kg), then Q=A-B (Equation 2). By the way, since the individual weight of the grain excluding water does not change before and after drying, the following equation holds. A-Aa/100=B-Bb/100 (3 equations) Find b and B from (1 equation) and (3 equations) and substitute them into (2 equations), Q=A(1-1-a/100 /1-a-P/100) (Equation 4) The reference water removal amount setting circuit 21 calculates the reference water removal amount Q based on this (Equation 4). On the other hand, the temperature sensors Sa and Sb are connected to the actually measured water removal amount calculation circuit 22, and this circuit 22 calculates the hot air temperature.
The actual water removal amount q is measured from the values of Ta, exhaust air temperature Tb, and initially set air volume W based on (Equation 8) described later, and a voltage proportional to the measured value is output. In the first place, the value of the measured water removal amount q is determined by the difference between the absolute humidity of the hot air and the exhaust air and the air volume per unit time W (Kg) of the hot air, since the water evaporated from the grains is included in the exhaust air and discharged outside the machine. It is found by the product of Since absolute humidity is the number of grams of water contained in 1 kg of air, when this is converted into kilograms, the following equation holds true for the measured water removal amount q. q = (Absolute humidity Mb of exhaust air - Absolute humidity Ma of hot air) × 0.001 × W (Kg/hour) (Equation 5) Since the absolute humidity difference between hot air and exhaust air is proportional to the temperature difference between the two, the ratio is k Then, k = absolute humidity difference between hot air and exhaust air/temperature difference between hot air and exhaust air (
Equation 6). Therefore, when actually operating the dryer, the normal hot air temperature is between 40℃ and 50℃, and the absolute humidity of the hot air is 4 to 8 (g/Kg), and the exhaust air temperature is
Assuming that the temperature is between 21°C and 27°C, the absolute humidity at the exhaust air temperature at that time is determined as shown in Table 1, as shown by the broken line in the moisture-air diagram in Figure 4.

[Table] From this, it turns out that the value of k within that range is 0.42. Therefore, from (Equation 5) and (Equation 6), q = (Temperature of hot air - Temperature of exhaust air) x 0.42m x W
(Equation 7) becomes. Here, m is the efficiency obtained by subtracting the amount lost due to temperature increases between the dryer and the grain, and is a constant compensation coefficient determined by the model and specifications of the dryer, the type and quality of the grain, etc. Since 0.42m is a constant, it is set as k1, and if the temperature of the hot air is Ta (°C) and the temperature of the exhaust air is Tb (°C), equation (7) can be rewritten as follows. q=(Ta-Tb)×k1×W (Formula 8) The actually measured water removal amount calculation circuit 22 calculates the actually measured water removal amount q based on this (Equation 8). Next, the output sides of the reference water removal amount setting circuit 21 and the actual water removal amount calculation circuit 22 described above are connected to the comparison circuit 23, and the output side of the circuit 23 is connected to the width increasing circuit 24.
These circuits 21 to 24 constitute a first air volume setting circuit 25. Reference numeral 26 denotes an air volume measuring device that measures the air volume from static pressure, and its pressure measuring unit is attached to the hot air chamber 14 to convert the static pressure in the hot air chamber into the air volume W of hot air and output it. And the first stage air volume setting circuit 25 and the air volume measuring device 2
6 is connected to the comparison circuit 27, and its output side is connected to the rotation speed control circuit 28 of the motor 29 of the suction fan 13, and in the first air volume setting circuit 25,
The value of the air volume W is set so that the outputs of the circuits 21 and 22 match, that is, the measured water removal amount q is equal to the reference water removal amount Q, and the actual air volume by the circuit 26 is equal to this reference air volume W. The control device 28 is operated so that the motor 2 of the suction fan 13
Rotate 9. Next, a humidity sensor that measures the absolute humidity Ma of the outside air.
Install Ha outside the dryer and connect it to the humidity sensor Sa,
It is connected to the exhaust air humidity determination circuit 30 together with Sb. By the way, since there is no water in and out of outside air and hot air, and their absolute humidity is equal to each other, in (Equation 6), k =
If it is 0.42, the absolute humidity Mb of the exhaust air is Mb = Ma + (Ta - Tb) x 0.42m (Equation 9). According to this equation (9), the exhaust air humidity determination circuit 30 determines the absolute humidity Mb of the exhaust air from the absolute humidity Ma of the outside air detected by the humidity sensor Ha, the hot air temperature Ta detected by the temperature sensors Sa and Sb, and the exhaust air temperature Tb. Calculate. The output side of this circuit 30 is connected to the reference water removal amount setting circuit 21 and the actual water removal amount calculation circuit 22 of the early air volume setting circuit 25, and is also connected to the latter air volume setting circuit 31, and the output side of the circuit 31 is connected to a comparison circuit. Connect to 27. Therefore, in the latter air volume setting circuit 31, the upper limit value Wp and lower limit value Wq of the set air volume W are determined in advance according to the grain amount A as shown in FIG. In the first half of drying, the standard set air volume W is determined by the first stage air volume setting circuit 25 as described above, but when the absolute humidity Mb of the exhaust air falls to a predetermined value in the second half of drying,
This is detected by the exhaust air humidity determination circuit 30, and the reference set air volume W is determined by the latter air volume setting circuit 31 so that the absolute humidity Mb of the exhaust air does not fall below a predetermined value. It goes without saying that even in the latter half of the drying period, the comparison circuit 27 operates the rotation speed control device 28 so that the set air volume W becomes equal to the actual air volume, as in the first period. In this way, the set air volume W is changed to circuit 2 in the early drying period.
5, the measured water removal amount q is determined to be equal to the reference water removal amount Q, and in the latter stage of drying, the absolute humidity Mb of the exhaust air is determined by the circuit 31 so that it does not fall below a predetermined value. On the other hand, once the hot air temperature Ta is set according to the amount of grain A, it remains constant until the drying is completed. The difference, ie (Ta-Tb) in (Equation 8), becomes smaller. Therefore, in the first half of drying, in order to make the measured water removal amount q match the reference water removal amount Q, the set air volume W of hot air is controlled to increase as the drying progresses. In addition, the humidity of the exhaust air tends to decrease as the drying progresses, so in order to maintain the absolute humidity Mb of the exhaust air so that it does not fall below a predetermined value in the late drying stage, the set air volume W of the hot air must be set at the upper limit. It is controlled to gradually decrease from the value Wp to the lower limit value Wq. In the embodiment shown in the drawings, the humidity sensor Ha is installed outside the dryer to measure the humidity of the outside air, but since the humidity of the outside air and the hot air are the same since no water enters or exits, the humidity sensor Ha is installed inside the hot air chamber 14 to measure the humidity of the hot air. You may also measure the humidity. If the humidity sensor Ha is installed outside the dryer, the measurement accuracy will be improved because the sensor is not affected by heat, and if the humidity sensor Ha is installed inside the hot air chamber, the humidity sensor Ha and the hot air temperature sensor will be
It has the advantage that the sensor can be manufactured at low cost because Sa can be integrated. Note that the gist of the invention does not change even if relative humidity is used instead of absolute humidity. In short, in the present invention, the hot air temperature of the burner 12 is set constant according to the amount of grain to be dried, and in the early drying period when the humidity of the exhaust air is greater than a predetermined value, the actually measured water removal amount q is set according to the amount of grains. The drying speed is kept constant by controlling the hot air volume to match the calculated reference water removal amount Q, and the hot air volume is reduced in the late drying period when the humidity of the exhaust air decreases to a predetermined value. Therefore, according to the present invention, since the drying rate is constant in the first stage of drying, which actually accounts for most of the drying time, grains of good quality can be dried without shell cracking, and the humidity of the exhaust air is reduced. In the latter stage of drying, the amount of hot air is reduced and the time it takes for the hot air to cross the drying chamber 5 is increased, allowing it to contact the grains for a long time and fully utilize its drying ability, resulting in high thermal efficiency and reduced burner fuel consumption. This has the effect of saving money.

[Brief explanation of drawings]

Fig. 1 is a sectional front view of a grain dryer embodying the present invention, Fig. 2 is a cross-sectional plan view thereof, Fig. 3 is a block diagram of its control system, and Fig. 4 is a hygrodynamic diagram showing the relationship between hot air and hot air. Shows the relationship between exhaust air temperature and absolute humidity. FIG. 5 is a graph showing the relationship between the upper limit value Wp and lower limit value Wq of the set air volume of hot air and the amount of grain A in the latter stage of drying according to the present invention.

Claims (1)

[Claims] 1 Burner combustion is controlled so that the hot air temperature is set according to the amount of grain to be dried, and in the early drying period when the humidity of the exhaust air is higher than a predetermined value, the actual amount of water removed is determined in advance based on the amount of grain, moisture content and drying. The drying speed is kept constant by controlling the hot air volume to match the standard water removal amount calculated from the speed, and the hot air volume is reduced in the late drying period when the humidity of the exhaust air decreases to a predetermined value. Features: Hot air control device for burner in grain dryer.