JPS6248844B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the flow rate of a fluidized bed used as a constant temperature bath, a reactor, or the like.

In a fluidized bed, gas is sent into the powder from below a tank filled with powder, and the gas pressure causes the powder to float in the tank, creating a fluid-like state similar to that of a liquid. Therefore, if the relationship between the gravity of the granular material and the force that the granular material receives from the gas is not appropriate, a uniform temperature distribution may not be obtained, or conversely, the air cells may become too large and cause vibrations. This will cause problems such as damage to the sensor inside the tank.

In a fluidized bed, the volume and viscosity of the gas change as the temperature inside the tank changes.
This results in a change in the fluid state, that is, the relationship between the gravity of the powder and the force that the powder receives from the gas. Changes in the fluid state due to these temperature changes are
This is corrected by adjusting the flow rate of gas sent into the tank to avoid the above problems, but conventionally, when changing the temperature, the flow rate was manually adjusted while directly monitoring the inside of the tank. I was adjusting.

The reason this was done manually is that it is difficult to automate the process of detecting the flow state itself, its changes, and determining the state without using an advanced computer system. However, such conventional manual flow rate adjustment is not only complicated but also relies on the intuition of the operator, resulting in reliability problems.

As a result of various experiments and studies, the inventor of the present invention has discovered the relationship between temperature, flow rate, and pressure at the lower position of the dispersion plate with respect to changes in the flow state, and has completed the present invention. That is, an object of the present invention is to provide a control method that can maintain a constant fluid state even if the volume and viscosity of the fluid change due to changes in the temperature of the fluidized bed.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a fluidized bed controlled by the method according to the present invention, and FIG. 2 is a block diagram showing an embodiment of the present invention.

In the figure, 1 is a tank constituting a fluidized bed. This tank 1 has a substantially cylindrical shape. A ceramic filter is attached as a dispersion plate 2 to the lower opening, and a sensor insertion tube 3 is fixed to the upper opening. A lid body 4 is attached. Fine alumina powder with an average particle size of 100 μm is used as the powder 5 filled in this tank 1, its total weight is 35 kg, and its specific heat is 0.24 cal/g°C.

A heater 6 wound spirally into a cylindrical shape is installed on the outer periphery of the tank 1, and a cylindrical flow path forming plate 7 is installed on the outer periphery of the heater 6.
Further, a cylindrical outer casing 8 is provided on the outer periphery of this flow path forming plate 7.
is installed. The cross sections of the heater 6, flow path forming plate 7, and outer casing 8 are each concentric with the tank 1, and are placed at a predetermined distance from each other.
Between the outer casing 8 and the flow path forming plate 7 is an upward flow path 9a.
A downward flow path 9 is formed between the flow path forming plate 7 and the tank 1.
b. The downward passage 9b communicates with the lower opening of the tank 1, the upward passage 9a communicates with the blow pipe 10, and the upward passage 9a and the downward passage 9b communicate with each other at the upper part. has been done. On the other hand, the outer casing 8
An exhaust pipe 11 is connected to the vicinity of the lid 4 in the tank 1, and a ceramic filter 12 is attached to the middle of the exhaust pipe 11. A second temperature sensor S ₁ is attached between the tank 1 and the heater 6, that is, a second temperature sensor S ₂ is attached near the heater 6. Furthermore, a part of the tank 1 except for the lid 4 mentioned above and the entire outer periphery of the outer casing 8 are covered with a heat insulating material 13 made of ceramic wool, and the entire structure described above is supported by a support frame 14.

The first and second temperature sensors S ₁ and S ₂ are
As shown in the figure, it is connected to the input side of a temperature controller 16 via a changeover switch 15, and this changeover switch 15 changes the detection signal of the first temperature sensor _S1 from the detection signal of the second temperature sensor S1 in response to the alarm signal of the thermometer 16. Temperature sensor S ₂
The configuration is such that the input signal is applied to the temperature controller 16 by switching to the detection signal of the temperature controller 16. Reference numeral 17 denotes a heater control circuit that controls the heater 6 according to the output signal of the controller 16. The heater control circuit 17 is provided between the commercial power source 18 and the heater 6, and uses a thyristor circuit or the like. ing.

On the other hand, the blow pipe 10 has a flow rate adjustment valve 19
A pressure gauge 20 is connected to the air pipe 10 or flow paths 9a and 9b on the downstream side of the flow rate adjustment valve 19.
is installed. 21 is this pressure gauge 20
This is a flow rate controller that opens and closes the flow rate adjustment valve 19 according to the detected value of the flow rate adjustment valve 1.
Feedback control is performed so that the pressure on the downstream side of the dispersion plate 9, that is, the pressure below the dispersion plate 2, is always kept constant.

Next, the operation of the device configured as described above will be explained.

When gas is sent through the blast pipe 10, the gas ascends from the blast pipe 10 through the upward passage 9a, is turned back at the upper position, descends through the downward passage 9b, and reaches the lower position of the dispersion plate 2. The gas is preheated by the heater 6 while flowing through the downward flow path 9b. Furthermore, the gas passing through the dispersion plate 2 and rising inside the tank 1 is
An upward force is applied to the granular material 5, and the force is applied to the granular material 5.
When the powder or granular material 5 is in balance with the gravity of In this way, the powder 5
Convection occurs, and the powder and granules 5 are agitated by air cells generated within the powder and granules 5, so that the entire powder and granules 5 have a substantially uniform temperature distribution.

If the temperature inside the tank is desired to be, for example, 650°C, the target set temperature of the temperature controller 16 is set to 650°C, and the alarm signal generation temperature, that is, the switch switching set temperature is set to 600°C. At this time, if the temperature inside the tank is 600°C or lower, the changeover switch 15 turns on the first temperature sensor S ₁ and turns on the heater according to the detected value of the first temperature sensor S ₁ installed in the tank. 6 is controlled.

Therefore, as shown in FIG. 3C, when the heater temperature and the temperature inside the tank rise and the temperature inside the tank exceeds the switching set temperature of 600°C, the temperature controller 16 generates an alarm signal and switches the switch. Switch switch 15 and
This time, the second temperature sensor _S2 located near the heater 6 is turned on. At this time, since the heater temperature exceeds the target temperature of 650° C., the current to the heater 6 is turned off, and the off state is maintained until the temperature drops to the target temperature. On the other hand, the temperature inside the tank is raised by the amount of heat generated by the heater 6 that exceeds the target temperature, and reaches the target temperature.After that, the temperature in the tank is controlled based on the detected value of the second temperature sensor _S2 , and the target temperature is maintained constant. be done.

The switching setting temperature for the above-mentioned target temperature changes depending on the amount and material of the granular material 5, and it is necessary to conduct an experiment for each fluidized bed to obtain the value. This can be easily obtained by setting an arbitrary target temperature and operating the fluidized bed only with the first temperature sensor _S1 installed in the tank without operating the changeover switch 15. That is, when operating only with the first temperature sensor _S1 , a temperature curve in the tank as shown in FIG. 3B is obtained, and the target temperature used in the experimental operation is set as the switching setting temperature, The apex temperature of the tank internal temperature curve may be set as the target temperature.

In addition, even when using the fluidized bed by changing the temperature of the fluidized bed sequentially, it is possible to perform the above experiment for each temperature in advance and express the switching set temperature for each target temperature in a graph etc. There is no risk of overshoot, and the target temperature can be quickly reached. Incidentally, since the fluidized bed has a large heat capacity and requires time to cool down, it is preferable to raise the temperature in order from a low temperature.

As mentioned above, when the temperature inside the tank is changed, a change in the volume and viscosity of the gas occurs, which changes the flow state of the powder and granules, and the gravity of the powder and the force that the powder receives from the gas If the balance is out of balance, problems may occur such as not being able to obtain a sufficient flow state and uniform temperature distribution, or the air bubbles becoming too large and causing vibrations that can damage the sensor inside the tank. Become.

Therefore, it is necessary to change the flow rate of gas flowing into the tank depending on the temperature.

Now, considering the temperature inside the tank and the flow state of the powder and granular material, the pressure P at the lower position of the dispersion plate 2 will be Since it can be regarded as the sum of the pressure loss △P ₁ and the pressure loss △P ₂ due to the dispersion plate 2, the following formula holds true.

P=ΔP ₁ +ΔP ₂ ... The pressure loss ΔP ₁ due to the powder 5 is always constant as long as the powder 5 is in a fluidized state as a characteristic of a fluidized bed, so the following formula is obtained.

△P ₁ = constant... This is because when considering a grain of powder 5, the gravity mg applied to the powder and the force F that the powder receives from the gas are balanced, and the The relationship between the force F that the body receives from the gas, the viscosity μ of the gas, the surface area A of the granular material, the gas velocity V, and the distance x between the granular materials can be expressed by the following equation.

mg=F=μAV/x=constant... A constant flow state means a state in which the distance x between powder and granules is constant, so the following equation is obtained from the equation, and this equation is under the condition of a constant flow state. be.

μ・V=constant...Since the viscosity μ of this gas is determined by the temperature, it can be understood that a constant flow state can be obtained by adjusting the gas velocity V, that is, the flow rate of the gas flowing into the tank 1, according to the temperature. .

By the way, regarding the dispersion plate 2 as well, the sum of the surface areas in the ventilation holes of the dispersion plate 2 is
Considering A' and the average gap x' between the ventilation holes, the following equation can be obtained from the relationship between the force F' applied to the dispersion plate 2, the pressure loss ΔP ₂ due to the dispersion plate 2, and the area S of the dispersion plate.

F′=△P ₂・S=μA′V/x′ … Here μ・V= which is the condition of constant flow state
The sum of the surface areas of the vents if constant is realized.
Since A', the average gap x' of the ventilation holes, and the area S of the dispersion plate are constants, the pressure loss ΔP ₂ can be expressed by the following equation.

ΔP ₂ =constant... From the above equation, it can be understood that if μ·V=constant, the pressure P at the lower position of the dispersion plate 2 will be constant regardless of the temperature.

Therefore, if the flow rate is adjusted so that the pressure P at the lower position of the dispersion plate 2 is always constant,
A constant flow state can be obtained under any temperature conditions. This flow rate control is independent of temperature as shown in Figure 2, so once a predetermined pressure value is set in the flow rate controller 21, there is no need to reset it when the temperature setting is changed. This can be done with a simple feedback loop in which the flow rate adjustment valve 19 is controlled so that the detected value of the pressure gauge 20 is constant.

As explained above, according to the present invention, the pressure at the lower position of the dispersion plate of the fluidized bed is detected, and the flow rate adjustment valve is feedback-controlled so that the detected pressure value becomes a constant value. Regardless, since the pressure at the lower part of the distribution plate is held constant, even if the volume and viscosity of the fluid change due to changes in the temperature of the fluidized bed, the fluidized state can be held constant.

Therefore, according to the present invention, even if the temperature is changed, an appropriate flow rate for that temperature can be automatically obtained, which has the effect of maintaining a uniform temperature distribution in the fluidized bed. There is an effect that there is no risk of damaging the sensor, and there is also an effect that there is no risk of wasting energy because unnecessary fluid is not sent.

Furthermore, according to the present invention, the process can be carried out without relying on human labor and with a simple feedback loop, resulting in high reliability and extremely low cost burden.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a fluidized bed controlled by the method according to the present invention, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 A, B, and C show the temperature rise characteristics of the fluidized bed. It is a graph diagram for explanation. 1... Tank constituting a fluidized bed, 2... Dispersion plate, 1
9...Flow rate adjustment valve, 20...Pressure gauge, 21...
...Flow rate controller.

Claims (1)

[Claims] 1 A method of controlling the fluid state, which fluctuates due to changes in the volume and viscosity of the fluid due to changes in the temperature of the fluidized bed, to a constant level, by detecting the pressure at the lower position of the distribution plate of the fluidized bed, and ensuring that this pressure detection value remains constant. 1. A flow rate control method for a fluidized bed, characterized in that the pressure at a lower position of a dispersion plate is held constant regardless of temperature changes by feedback controlling a flow rate adjustment valve so as to maintain a constant pressure at a lower position of a dispersion plate regardless of temperature changes.