JPH0576329B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of operating a bubble generator in a wet flue gas desulfurization equipment, and particularly to a method for generating fine bubbles in an absorbent slurry using a propeller-type stirring blade. This invention relates to a method of operating a bubble generator.

[Background of the invention]

The mainstream wet flue gas desulfurization equipment currently in use uses calcium-based absorbents and recovers gypsum as a byproduct. In other words, limestone, which uses limestone, quicklime, and nitrate as absorbents.
This is the plaster method (or lime/gypsum method). FIG. 7 shows a conventional flue gas desulfurization device that uses limestone as an absorbent and recovers gypsum as a byproduct.
Exhaust gas 1 from a boiler, etc. is led to a dust removal tower 2, where it is cooled and dust removed and a portion is desulfurized, and then led to an absorption tower 3, where it comes into contact with circulating fluid slurry, and is removed by a demister 4. The mist is removed and discharged from the absorption tower 3. On the other hand, limestone slurry 20, which is an absorbent slurry, is supplied to the absorption tower circulation tank 5 by a limestone slurry pump 21, and the slurry is supplied to a spray nozzle 22 installed in the absorption tower 3 by an absorption tower circulation pump 7, Absorption tower 3 from here
It is sprayed into the exhaust gas 1 and comes into contact with the exhaust gas 1, absorbs and removes sulfur oxides in the exhaust gas 1, returns to the absorption tower circulation tank 5, and is used for circulation. The slurry in the absorption tower circulation tank 5 after absorption is supplied to the dust removal tower circulation tank 6 by the absorption tower bleed pump 8, and is sprayed from the spray nozzle 22 in the dust removal tower 2, and further comes into contact with the exhaust gas 1, and the exhaust gas is By removing the sulfur oxides in the slurry, the amount of unreacted limestone in the slurry is reduced and the slurry is supplied to the by-product recovery system, that is, the oxidation tower supply tank 10. Oxidation tower supply tank 10
The unreacted limestone is turned into gypsum by adding sulfuric acid, and the pH is adjusted to be suitable for oxidation. PH
The adjusted slurry is supplied to the oxidation tower 12 by the oxidation tower supply pump 11, where the calcium sulfite is air-oxidized to gypsum, and then guided to the sikuna 14 through the conduit 13, to the tank 15, and to the pump 16. After being concentrated in , the gypsum slurry is dehydrated in a centrifuge 17 and powdered gypsum 18 is recovered. The filtered water 19 from the filter 14 and the centrifugal separator 17 is recycled and reused.

As mentioned above, in lime/gypsum wet flue gas desulfurization equipment for boiler exhaust gas, it is necessary to oxidize the absorbent slurry containing calcium sulfite produced by absorbing sulfur oxides in the exhaust gas and convert it into gypsum. It is. Oxidation of this absorbent slurry has traditionally been carried out through a gas-liquid reaction using fine air bubbles.
As a means for generating air bubbles, a method generally employed is to supply air near a high-speed rotating body that stirs the absorbent slurry.

As a rotating body for atomizing air, a paddle blade, a turbine blade, or a cylindrical or umbrella-shaped atomizer is used. However, although these bubble generators have no problem in generating bubbles, they are not effective in uniformly dispersing the generated bubbles over a wide range in the absorbent slurry, and therefore, oxidation reactions may occur locally in the absorbent slurry tank. However, it was difficult to proceed with the oxidation reaction throughout the tank.

[Purpose of the invention]

The present invention attempts to eliminate such conventional drawbacks, and its purpose is to operate a bubble generator that can generate fine bubbles even in areas with a small amount of air supply and that consumes less power. It provides:

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention provides a stirring blade in a tank storing an absorbent slurry and an air supply pipe on the back side of the stirring blade to blow air into the tank to perform a gas-liquid reaction. When starting up, air is first supplied from the air supply pipe, and then the stirring blades are rotated.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic system diagram of a bubble generator according to an embodiment of the present invention, FIGS. 2 and 3 are a plan view and a side view of the experimental apparatus, and FIGS. A characteristic diagram showing the air supply amount, oxidation rate, air supply amount and reduction rate of power consumption obtained using the experimental apparatus shown in the figure. Figures 6a and b are explanatory diagrams showing the state of air bubble generation by the stirring blade. It is.

Hereinafter, before explaining the embodiments of the present invention, the experimental apparatus shown in FIGS. 2 and 3 and the experimental device shown in FIG.
We will introduce the experimental results shown in Fig. 5, Fig. 5, and Fig. 6 a and b.

In Fig. 2, Fig. 3 and Fig. 6 a, b,
22 is an absorbent slurry of Na ₂ SO ₄ aqueous solution, 23 is a tank storing the absorbent slurry 22, 24 is a propeller type stirring blade, 25 is an air supply pipe, 26 is a flow meter,
27 is an on-off valve, and 28 is a stirring shaft.

In such a structure, the experimental apparatus is equipped with four propeller type stirring blades 24 on the side wall of the tank 23 as shown in FIGS. 2 and 3, and Na ₂ SO ₃ inside the tank 23. An aqueous solution was oxidized, and bubbles were observed, the power required for stirring was measured, and the oxidation rate of Na ₂ SO ₃ was measured, which is a measure of the fineness of the oxidizing air.

The experimental equipment consists of four propeller-type stirring blades 24 at a height of 0.1 m from the bottom of a cylindrical tank 23 with a diameter of 0.8 m.
Attach a stirrer with a
It was placed eccentrically at an angle of 15 degrees from the center of 3.

The outer diameter of the propeller type stirring blade 24 is 120 mm,
A blade with a width of 30 mm is attached to the stirring shaft 28 at an angle of 30 degrees. One air supply pipe 25 is attached to each stirring blade 24, and a flow meter 26 and an on-off valve 27 are used to allow any amount of air to be vented to the propeller type stirring blade 24.

In the experiment, a concentration of 40 mmol/ was placed in tank 23.
Add 250 ml of the absorbent slurry 22 of Na ₂ SO ₃ aqueous solution, rotate the propeller type stirring blades 24 at a rotation speed of 1000 rpm, and connect the air supply pipe 25 to each stirring blade 24.
The experiment was started by evenly ventilating a predetermined flow rate of air. Note that the state of bubbles and gas-liquid stirring was observed visually and by taking strobe photography, and the power required for stirring was measured with a rotating torque meter (not shown) attached to the stirring shaft 28. The state of bubble refinement was also measured by changing the Na ₂ SO ₃ concentration in the tank 23.

According to the observations of the inventors, when the propeller-type stirring blades 24 are ventilated through the air supply pipe 25, the bubbles become finer and at the same time the bubbles are pushed out into the tank 23. It was seen that the gas-liquid reaction was progressing throughout the tank 23.

However, the present inventors further proposed a propeller-type stirring blade 2.
As a result of examining the aeration stirring according to No. 4, it was found that depending on the operating conditions of the propeller-type stirring blade 24, the generation of fine bubbles is poor, that is, the air blown from the air supply pipe 25 as shown in FIG. We learned that there is a region A where the propeller-type stirring blade 24 simply passes over the center axis, and furthermore, in this region A, the required power for stirring by the propeller-type stirring blade 24 is the same as when no air is blown, and the required power is lower. I learned that it does not deteriorate. Normally, the method of generating fine bubbles in a liquid to perform a gas-liquid reaction is used in the fermentation industry, synthetic chemical industry, and wastewater treatment industry when the amount of gas to be reacted is small compared to the amount of liquid. If the amount of is small, fine bubbles will not be formed, so the propeller type stirring blade 24 was not used.

However, the present inventors further investigated the formation of air bubbles by the propeller-type stirring blades 24, and found that the phenomenon in which air passes through without being atomized, as shown in FIG. , once a phenomenon similar to so-called cavitation (hereinafter simply referred to as cavitation-like phenomenon) occurs, in which air passes through this region A and clings to the propeller-type stirring blade 24, as shown in FIG. 6b, the air supply is stopped again. The inventors discovered that even if the amount of air from the pipe 25 is reduced, the cavitation-like phenomenon B continues as it is, and the propeller-type stirring blades 24 continue to generate fine bubbles, resulting in the present invention.

In other words, the results of measuring the oxidation rate of the Na ₂ SO ₃ aqueous solution and the required stirring power of the propeller-type stirring blades 24 by varying the amount of air supplied from the air supply pipe 25 are shown in the fourth table.
As shown in FIG. When the air supply amount is increased from point C to point D in Figure 4, cavitation-like phenomenon B, which was explained in Figure 6b, occurs around 5 m ³ /h, and the air flow increases from point E to point F in Figure 5. The power required for stirring rapidly decreases, and the oxidation rate of Na ₂ SO ₃ rapidly increases. However, when this cavitation-like phenomenon B occurs, the air supply amount is
When decreasing from 10 m ³ /h to 5 m ³ /h or less, cavitation-like phenomenon B continues to occur, and the required stirring power does not increase to point E in Figure 5, and Na ₂ The oxidation rate of SO ₃ also does not decrease to point C in FIG. This phenomenon revealed that the history of temporarily increasing the amount of air supplied according to the present invention is effective in oxidation, that is, the formation of fine bubbles, in areas where the amount of air supplied is small. Furthermore, as is clear from the above experimental data, the state of bubble formation depends on the required stirring power, that is, the propeller type stirring blade 2.
In addition to the method of changing the air supply amount over time, it is also possible to control the air supply amount using the detected value of the rotational torque, since it is closely related to the rotational torque of No. 4. In other words, in the examples shown in Figs. 4 and 5, when the oxidation reaction is being performed at an air flow rate of 5 m ³ /h to generate bubbles due to cavitation-like phenomenon B, the air flow rate may change due to fluctuations in the air supply amount due to failure of the motor, etc. If air blow-through occurs, the oxidation rate decreases by about half and the rotational torque of the propeller-type stirring blade 24 increases by about 1.5 times. Therefore, if you increase the air supply amount until the rotational torque decreases to about half of that amount to ensure cavitation-like phenomenon B occurs, then reduce the air supply amount until the rotational torque or air supply amount returns to the original state. good. Note that the power required for stirring is determined not only by the rotational torque of the stirring shaft 28 but also by the power consumption of the stirring power source or the propeller type stirring blade 2.
Since there is a close relationship with the strength of the liquid flow caused by 4, these detected values may also be used as control factors in the same way as the detected value of rotational torque.

Based on the above experimental data, a system diagram of the bubble generator of the present invention will be explained using FIG. 1.

In FIG. 1, 22 is an absorbent slurry, 23 is a tank, 24 is a stirring blade, 25 is an air supply pipe, 27
is an on-off valve, 28 is a stirring shaft, 29 is an air supply pipe 25
30 is a sub-opening/closing valve of the sub air supply pipe 29, 31 is an air tank, 32 is a motor, 33 is a timer, and 34 is an air supply port.

In such a structure, the feature of the present invention is to control the flow rate of air supplied to the air supply port 34, and the air supply pipe 2 from the air tank 31 to the air supply port 34 is controlled.
5 and auxiliary air supply pipe 29 are arranged, and timer 3
3, the on-off valve 27, and the on-off valve 30, the tank 2
This is to increase or decrease the amount of air supplied to No. 3. When the timer 33 is activated at startup, the on-off valve 27 and the auxiliary on-off valve 30 are first opened by a signal from the timer 33, and air from the air tank 31 passes through the air supply pipe 25 and the auxiliary air supply pipe 29 to the air supply port. 3
Sent to 4. Then, from the timer 33 to the motor 32
A signal is sent to the stirring blade 24 and the rotation of the stirring blade 24 is started. When the rotational speed of the stirring blade 24 increases after a certain period of time has elapsed, a signal from the timer 33 is sent to the auxiliary on-off valve 30, which closes and the air supply from the auxiliary air supply 29 is stopped, thus reducing the air flow rate. is operated with the flow rate reduced to a predetermined flow rate.

Furthermore, if the cavitation-like phenomenon B described in FIG. 6b does not occur due to an accident such as a temporary interruption of the air supply during operation, the motor 32
Since the motor 32 becomes overloaded and the power consumption increases, the signal from the motor 32 generated in the case of overload is transmitted to the timer 3.
3, and the state of the timer 33 returns again to the time of startup. The auxiliary on-off valve 3 is activated by the signal from the timer 33.
0 opens, air supply by the sub air supply pipe 29 is resumed, and the amount of air from the air supply port 34 increases. Since the on-off valve 27 is open at this point, timer 3
Even if an opening command is sent by a signal from 3, the state remains as it is, and the motor 32 also continues to rotate in the same manner.

In this way, in order to form fine bubbles by the stirring blades 24, the cavitation-like phenomenon B explained in FIG. It is important to surround yourself with

However, this cavitation-like phenomenon B does not occur when the amount of air is small, but if air is supplied from both the air supply pipe 25 and the auxiliary air supply pipe 29 to temporarily increase the air amount, the cavitation-like phenomenon B If this is generated, that state will be maintained even if the amount of air is reduced, so fine bubbles will be generated, and the stirring blades 24 and power consumption will also be reduced.

〔Effect of the invention〕

Since the present invention is configured as described above,
A method of operating a bubble generator that can generate fine bubbles even in a region where the amount of air supplied is small and that consumes less power can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic system diagram of a bubble generator according to an embodiment of the present invention, FIGS. 2 and 3 are a plan view and a side view of the experimental apparatus, and FIGS. 6A and 6B are explanatory diagrams showing the state of bubble generation by the stirring blade, and FIG. 7 is a schematic system diagram of the wet flue gas desulfurization device. 22... Absorbent slurry, 23... Tank, 24
... Stirring blade, 25... Air supply pipe, 27... On-off valve, 29... Sub-air supply pipe, 30... Sub-on-off valve.

Claims (1)

[Claims] 1. In a tank storing absorbent slurry, a stirring blade is provided, and an air supply pipe is provided on the back side of the stirring blade, and air is blown into the tank to perform a gas-liquid reaction. A method of operating a bubble generator, comprising rotating the stirring blade after supplying air from an air supply pipe. 2. A sub-air supply pipe having a sub-on/off valve is provided in parallel with the air supply pipe, and both the on-off valve attached to the air supply pipe and the sub-on/off valve attached to the sub-air supply pipe are operated. 2. The method of operating a bubble generator according to claim 1, wherein both valves are opened to supply air, then the stirring blades are rotated, and after a predetermined period of time, one of the on-off valves is closed.