JPH0548808B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a dryer, which is an aggregate heating drying device for an asphalt plant that manufactures asphalt mixture, which is a road paving material, or a dryer that heats pavement waste excavated from roads. The present invention relates to a rotation control method and apparatus for a dryer for heating aggregates, such as a dryer for recycling.

[Prior Art] A dryer for heating and drying aggregate, which is a raw material for asphalt mixture, is designed with drum size, rotation speed, blade shape, number of blades, etc. depending on desired drying performance. The rotational speed of this dryer is set to approximately 40 m/min so that the aggregate scraped up by the scraping blades falls in an ideal veil shape inside the drum and efficiently contacts the gas flow. It is determined by taking into consideration that the drive power of the dryer will not be too large. Therefore, even if the type and amount of aggregate supplied to the dryer fluctuates, the drum always rotates at a constant rotational speed.

[Problems to be Solved by the Invention] In recent years, there has been a remarkable improvement in the heating efficiency of dryers, but the heating efficiency is also at its limit due to the adverse effects caused by the decrease in exhaust gas temperature. When the exhaust gas falls below the dew point temperature, the sulfur dioxide gas and sulfuric anhydride contained in the exhaust gas cause a hydration reaction with condensed water, forming sulfuric acid mist, which corrodes equipment downstream of the drum, such as flues and bag filters. It happens. Therefore, it is necessary to maintain the temperature of the exhaust gas discharged from the dryer at around 120℃ or higher, but if the heating efficiency of the dryer is too high and the exhaust gas temperature drops below 120℃,
Since the rotation speed of the drum cannot be changed, the only option is to intentionally reduce the heating efficiency of the dryer by removing part of the drum's blades.

In view of the above-mentioned points, it is an object of the present invention to enable a dryer to be operated in a state where the heating efficiency of the dryer and the exhaust gas temperature are best balanced.

[Means for Solving the Problems] In order to achieve the above object, the present invention makes the rotation speed of a drum for heating and drying aggregates rotatably supported at an angle variable, so that the exhaust gas discharged from the drum when heating and drying aggregates is The system is characterized in that the drum rotation speed is increased when the gas temperature exceeds a preset temperature range, and the drum rotation speed is decreased when the exhaust gas temperature falls below a preset temperature range. The present invention provides a method for controlling the rotation of a dryer for heating aggregates.

In addition, the present invention uses a variable speed motor as the motor for rotating the drum for heating and drying aggregates that is rotatably supported at an angle, and a gas temperature detector for detecting the exhaust gas temperature is provided in the exhaust flue connected to the drum. , there is provided a rotation control device for a dryer for heating aggregates, characterized in that the apparatus includes a control section that controls the rotation speed of the variable speed motor of the drum according to a value detected by the gas temperature detector.

[Function] In the rotation control device for an aggregate heating dryer according to the present invention, the temperature of the exhaust gas derived from the dryer is detected by a gas temperature detector, and this detected value is taken into the control section, Compare it with the preset temperature, and if the detected value is higher than the set temperature, increase the drum rotation speed to shorten the aggregate residence time in the drum and increase heating efficiency. When the temperature is low, the drum rotation speed is lowered and the aggregate retention time is increased to prevent the exhaust gas from dropping below the dew point temperature, thereby achieving the best balance between the heating efficiency of the dryer and the exhaust gas temperature. to operate the dryer.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

A dryer 1 that heats and dries aggregates has a cylindrical drum 3 with a large number of scraping blades 2 arranged around its inner circumference.
is tilted and rotatably supported by support rollers 5 on a machine stand 4. Combustion gas is sent into the drum 3 from a burner 6 installed in a hot hopper 7 at one end of the drum 3, and an exhaust fan (not shown) installed at the end of an exhaust flue 9 connected to a cold hopper 8 at the other end of the drum 3. ) to suck exhaust gas and maintain a high-temperature gas flow passing through the drum 3, while collecting aggregate of various particle sizes from an aggregate hopper (not shown) depending on the composition of the asphalt mixture to be manufactured. A fixed amount of aggregate is cut out, fed into the drum 3 via the belt conveyor 10, and heated to a desired temperature while rolling down the drum 3 while scraping up the aggregate with the scraping blades 2.

A variable speed motor 11 is employed as a drive motor for rotating the drum 3.
By changing the rotation speed of the drum 3, the rotation speed of the drum 3 placed on the support roller 5 can be changed.

An exhaust flue 9 connected to a cold hopper 8 of the drum 3 is provided with a gas temperature detector 12 for detecting the temperature of exhaust gas led out from the drum 3. The exhaust gas temperature detected by this gas temperature detector 12 is A
- The signal is taken into the control section 14 via the D converter 13.

The control unit 14 includes a CPU 15 and a storage unit 16, and compares the detection value detected by the gas temperature detector 12 with a set temperature inputted in advance to the storage unit 16 via the setting input unit 18, and performs the detection. If the value exceeds the set temperature, a command is issued to the rotation controller 17 that controls the rotation speed of the variable speed motor 11 to increase the rotation speed of the motor, and if the detected value falls below the set temperature, the rotation controller 17 It is programmed to issue a command to lower the rotational speed of the variable speed motor 11.

The lower limit value of the set temperature, which is preset and input into the storage section 16 via the setting input section 18, is, for example, around 120.degree. C., using the dew point temperature of the exhaust gas as a guide. In addition, the upper limit of the set temperature is set in consideration of the fact that as the exhaust gas rises, the amount of heat carried away by the exhaust gas increases and the heating efficiency decreases, so the dryer is operated in a state that provides the best balance between heating efficiency and exhaust gas temperature. Determine the temperature value as appropriate.

Therefore, when heating aggregates in the dryer 1, the allowable temperature range of the exhaust gas derived from the dryer 1 is input in advance from the setting input section 18, and the control section 1
The settings are stored in the storage unit 16 of 4, and while the drum 3 is rotated at the design standard rotation speed, combustion gas is sent into the drum 3 from the burner 7 and aggregate is supplied into the drum 3 to reach the desired temperature. Heat the aggregate until .

When the aggregate heating in the dryer 1 reaches steady state operation, the temperature of the exhaust gas led out from the drum 3 is detected by the gas temperature detector 12 installed in the exhaust flue 9, and the detected exhaust gas temperature is detected from A-D. The data is taken into the CPU 15 of the control unit 14 via the converter 13. CPU
15 compares the detected value with the exhaust gas set temperature previously stored in the storage unit 16, and when the detected value is higher than the upper limit of the set temperature, the rotation controller 17 sets the rotation speed of the variable speed motor 11. A command is issued to increase the aggregate retention time in the drum, thereby increasing heating efficiency. In addition, if the detected value is lower than the lower limit of the set temperature, the exhaust gas will drop below the dew point temperature and form sulfuric acid mist, which may corrode equipment downstream of the drum such as the flue and bag filter. A command is issued to reduce the rotation speed of the variable speed motor 6, and the exhaust gas temperature is raised above the lower limit of the set temperature.

Regarding the relationship between the rotational speed of the drum 3 and the exhaust gas, the data may vary depending on the size of the drum, the shape of the blades, the number of blades, etc., but according to experiments conducted by the present inventor, When the drum rotation speed was varied from 12.7 rpm to 9.5 rpm to 6.3 rpm with the material supply amount constant, the exhaust gas temperature rose to 90℃, 110℃, and 142℃ as the drum rotation speed decreased. Ori,
It has been proven that there is a correlation.

In addition, the upper limit value is set and input as the set temperature of exhaust gas, and when the exhaust gas temperature exceeds the upper limit value, the drum rotation speed is increased, but only the lower limit value is set and input, and the exhaust gas temperature is set to When the temperature drops below the dew point temperature, the rotation speed of the drum may be lowered and the temperature of the exhaust gas may be raised to prevent the temperature from falling below the dew point temperature.

[Effects of the Invention] As described above, in the present invention, since the rotation speed of the drum is controlled according to the temperature of the exhaust gas derived from the dryer, the rotation speed of the drum is controlled according to the amount of aggregate supplied. The dryer can be operated in a state where the heating efficiency and exhaust gas temperature are most balanced.

Further, since it is possible to operate the dryer so that the exhaust gas does not fall below the dew point temperature, it is possible to prevent equipment downstream of the dryer, such as the exhaust flue and bag filter, from corroding as much as possible.

Furthermore, it is possible to control the supply amount of aggregate and the temperature of exhaust gas by simply adding a simple device, so it is inexpensive and easy to adopt to conventional dryers, making it very practical. .

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a rotation control device for an aggregate heating dryer according to the present invention. 1...Dryer, 3...Drum, 6...Burner, 9...Exhaust flue, 10...Belt conveyor,
11... Variable speed motor, 12... Gas temperature detector, 14... Control section, 17... Rotation control section, 18
...Setting input section.

Claims (1)

[Claims] 1. The number of rotations of a drum for heating and drying aggregates that is rotatably supported at an angle is variable, and when the temperature of the exhaust gas derived from the drum during heating and drying aggregates exceeds a preset temperature range, the drum is turned off. A method for controlling the rotation of a dryer for heating aggregates, characterized in that the rotation speed of the drum is increased, and the rotation speed of the drum is decreased when the exhaust gas temperature falls below a preset temperature range. 2. A variable speed motor is used to drive the rotation of the drum for heating and drying aggregates which is rotatably supported at an angle, and a gas temperature detector for detecting the temperature of the exhaust gas is installed in the exhaust flue connected to the drum. 1. A rotation control device for a dryer for heating aggregates, comprising a control section that controls the rotation speed of the variable speed motor of the drum according to a detection value detected by a detector.