JPH1111960A - Device for producing particulate hollow glass globule and its control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely fluidize a ceramic ball at a high-temp. moreover in a short time and to highly precisely control the temp. within a specified range by heating the ceramic ball below the flash point of a ceramic ball-medium internal combustion fluidized-bed furnace to a specified temp. with gas combustion heat under variable air-fuel ratio control, direct control, variable PID control and double cross limit combustion control. SOLUTION: A ceramic ball is heated to >=900 deg.C without using an auxiliary preheating burner and automatic control within ±3 deg.C of a set temp. is conducted. Concretely, the ceramic ball (silicon carbide) is charged into a cylindrical fluidized-bed part and a gaseous mixture of propane and air is introduced. After the mixture is ignited, the ceramic ball is heated by combustion heat in a fixed air-fuel ratio under PID control. When the ceramic ball is heated to a lower temp. by 50 deg.C than the set temp., the PID control is changed and also, the control is changed to variable air-fuel ratio control. Thereby, the setting temperature can be stabilized within ±3 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic ball medium internal combustion type fluidized bed furnace type hollow glass sphere manufacturing apparatus which heat-treats a mixed gas of air and fuel gas with powder of an object to be heated. The present invention relates to a device and a control method for achieving automation and high-precision automatic temperature control to achieve automation and labor saving.

[0002]

2. Description of the Related Art Japanese Patent No. 848394 discloses a method for starting and controlling the temperature of an internal combustion type fluidized bed furnace used as an apparatus for producing a shirasu balloon or the like.
In this method, a mixed gas of air and a fuel gas is blown into a sand medium (brick powder) heated in advance to the flash point of the used fuel to form a high-temperature fluid state and maintain the temperature. This temperature is maintained by controlling the fuel gas by a motor-operated valve by a controller connected to a thermocouple, and is at a set temperature of about ± 5 ° C.

[0003]

In the prior art internal combustion type fluidized bed furnace, when a mixed gas having the same air-fuel ratio as that at the time of high temperature flow is introduced in a state where the temperature of the sand medium is lower than the flash point of the fuel gas, the sand medium is reduced. Misfire because it does not play the role of ignition source. As a countermeasure against the misfiring, it was necessary to heat the sand medium to a temperature higher than the flash point with an attached preheating device before introducing a mixed gas of air and fuel gas. Therefore, Hokkaido Industrial Development Laboratory Report 42,
As shown in (1987), it was necessary to make a side hole near the center of the flowing portion and heat it vigorously. Since this preheating burner is not used at the time of high-temperature fluidization, the backflow of sand occurs, and the amount of sand to be fluidized changes with time. In addition, there is a disadvantage that a portion having a low temperature of 10 ° C. or more is generated in the fluidized bed due to heat loss near the attachment port of the preheating burner during the flow, and the heating of the object to be heated becomes uneven. In addition, brick powder and silica sand are used as a sand medium, but these are crushed well when flowing, so that there is a drawback that fragments thereof are mixed into a product (for example, shirasu balloon). Further, regarding temperature maintenance, since only the fuel gas is fully opened and fully closed using an electrically operated valve having relatively slow controllability, the fluctuation of the optimum combustion air-fuel ratio becomes a disturbance factor, and the set temperature becomes about ± 5 ° C. Poor temperature controllability.

[0004]

In order to solve the above-mentioned problems, a fluidized bed furnace using a ceramic ball as a medium without using a preheating burner has been developed. It was examined in detail. As a result, it was clarified that the optimum combustion conditions at the time of temperature rise and at the time of high temperature fluidization were different, and that there was a high risk of a sudden rise in temperature immediately before high temperature fluidization. Therefore, as a result of repeating experiments on these solutions, variable air-fuel ratio control that precisely corresponds to combustion conditions,
It has been found that by setting the optimum output of the temperature controller by direct control, variable PID control and double cross limit combustion control, automatic startup can be achieved safely and in a short time, and high-precision temperature control during high-temperature flow Also succeeded in developing a possible control method and device.

[0005] At the time of temperature rise and at the time of high temperature flow, the optimum combustion P
Since the ID control condition and the air-fuel ratio are different, the control condition must be changed. If this change is neglected, fusion and flashback will occur due to a rapid rise in furnace temperature, causing a dangerous situation, causing wear and breakage of the fluidized bed furnace, resulting in loss of control. Therefore, at the temperature lower by 50 ° C. from the set temperature, the PID control condition is automatically changed and the variable air-fuel ratio control is switched, and the rate of change of the temperature is recognized. By programming the circuit for setting the output in advance, it has become possible to avoid a sudden rise in temperature, and to achieve a safe and quick high-temperature fluidization.

If the air-fuel ratio is made constant during high-temperature flow, the amount of air changes in accordance with the flow rate of fuel gas that fluctuates with the control output of the temperature controller, so that the amount of combustion gas passing through the fluidized bed changes. In this case, the heat history of the object to be heated (powder) fluctuates and a product of constant quality cannot be obtained. Variable air-fuel ratio control for controlling the gas flow rate was performed. Important to this temperature control is accurate control and measurement of the fuel gas flow rate and the air flow rate. Pneumatic control valves (for fuel gas and air) that can control the flow rate with high precision
Was used. Further, in order to improve the accuracy, a self-acting pressure reducing valve (for fuel gas and for air) for stabilizing the supply pressure is employed. A high-precision digital gas flow meter was used for flow measurement. As a safety measure, a system is adopted that shuts off the fuel gas in the event of an abnormality in the temperature under the furnace, air pressure, inverter and control temperature.

[0007] Further, since the present apparatus is not provided with a preheating burner, the fluidized bed portion is completely cylindrical, and has a structure suitable for uniform temperature distribution. By combining these devices and structures with high-performance temperature controllers, fuel gas controllers, air flow controllers, and air-fuel ratio setting devices, highly accurate temperature control has become possible. By automating the above operations, a stable high-temperature fluidized state was successfully formed in a short time. Furthermore, in order to prevent mixing of the medium fragments into the product, silicon carbide balls and cordierite balls having excellent thermal shock resistance were used as the medium. Thereby, the crushing of the medium during the high temperature fluidization was almost eliminated, and the production of a high quality product became possible.

[0008]

[Example] In a fluidized bed part consisting of an inner cylinder with an inner diameter of 132 mm,
17 ceramic balls (silicon carbide) with a diameter of 1.5 mm
Load 50g. A mixed gas of propane gas and air is introduced into the fluidized bed portion, and after ignition, PID control is performed at a constant air-fuel ratio to raise the temperature of the ceramic balls by the heat of combustion. Then, the ceramic ball is heated from the set temperature (1000 ° C.) to 50 ° C.
When the temperature reached a low temperature (950 ° C.), the PID control conditions were changed and the system was switched to variable air-fuel ratio control, and the temperature was stabilized at a set temperature of 1000 ° C. ± 3 ° C. or less. The time required from ignition to stabilization at the set temperature was 12 minutes.
As the powder to be heated, shirasu fine powder having an average particle diameter of 4 μm (produced from Yoshida-cho, Kagoshima Prefecture) was supplied to the fluidized bed at 1.0 kg / h in association with the mixed gas before combustion. Foamed by rapid heating with an average particle diameter of 6.2 μm and a bulk specific gravity of 0.
A fine and lightweight Shirasu balloon of No. 3 could be manufactured. Even during the supply of the fine shirasu powder, the variable PID temperature control and the variable air-fuel ratio control maintained the temperature at or below the set temperature of ± 3 ° C., thereby producing a high-quality shirasu balloon free of impurities.

[0009]

According to the present invention, high-temperature fluidization, which has been manually or intuitively performed, can be automatically performed in a short time by the present invention, and high-precision fluidized-bed temperature control becomes possible.
As well as labor saving, high quality products can be manufactured. Further, even when silica sand or brick powder is used as a medium, similar automation and labor saving are possible. Regarding the technology of an internal combustion type fluidized bed furnace that heat-treats a mixed gas of air and fuel gas with accompanying powder, its industrial use was limited due to the danger and complexity at the time of startup, but according to the present invention, It was found that the startup of the high-temperature fluidized-bed furnace and the high-precision temperature control can be operated automatically and safely. Therefore, anyone can easily test the production of shirasu balloons using an internal combustion type fluidized bed furnace,
Since heat treatment experiments and the like become possible, academic research is also promoted, and the widespread industrial use of high-temperature fluidized-bed furnaces is expected. Further, since the apparatus according to the present invention hardly contains impurities, it can be used not only as an experiment for producing an inorganic foam such as a shirasu balloon, but also as a reaction apparatus such as a heat treatment apparatus for powder or a surface treatment apparatus. As a raw material of the inorganic foaming substance used in the present invention, there is natural glass such as vitreous volcaniclastic material and vitreous volcanic rock, and artificial glass having a foaming source can be foamed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an internal combustion type fluidized bed furnace using ceramic balls as a medium.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshitaka Kamino 1445-1, Oda, Hayato-cho, Aira-gun, Kagoshima Prefecture Inside the Kagoshima Industrial Technology Center (72) Kazuto Hamaishi, Inventor 1445-1, Oda, Hayato-cho, Aira-gun, Kagoshima Kagoshima Prefectural Industrial Technology Center (72) Inventor Keinori Yoshimura 1049 Kawahara Iwasaka, Kokubu City, Kagoshima Prefecture (72) Inventor Shunji Tone 2--15-12 Katano, Kokurakita-ku, Kitakyushu-shi

Claims (2)

[Claims] In an internal combustion type fluidized bed furnace using ceramic balls as a medium, variable air-fuel ratio control, direct control,
By variable PID control and double cross limit combustion control, without using the attached preheating burner, the temperature of ceramic balls below the flash point is raised to 900 ° C or more by the heat of gas combustion, and the automatic temperature control within the set temperature ± 3 ° C A production apparatus for a fine-grained hollow glass sphere. 2. An internal combustion type fluidized bed furnace using ceramic balls as a medium, wherein variable air-fuel ratio control, direct control,
By variable PID control and double cross limit combustion control, without using the attached preheating burner, the temperature of ceramic balls below the flash point is raised to 900 ° C or more by the heat of gas combustion, and the automatic temperature control within the set temperature ± 3 ° C A method for controlling an apparatus for producing a fine-grained hollow glass sphere, comprising: