JPH11147018A - So3 mist collection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove SO3 contained in an exhaust gas without expanding the size of a device even when an oil containing a large amount of sulfur is burned by maintaining a cooling face formed of a group of heat transfer pipes at a lower temperature than the dew point of the SO3 gas in a casing for flowing the SO3 gas, and collecting the SO3 gas through causing the SO3 gas to build up on the cooling face as an SO3 mist. SOLUTION: An exhaust gas is directed downward by straightening its flow with the help of a guide vane 3 in a casing 2 for an exhaust gas collection device 1 and then is exhausted from the lower part of the device 1 passing through the cluster of heat transfer pipes 4. Further, plural heat transfer pipes 6 for flowing a hot water 7 from a heat transfer medium into a gap between the pipes 6, are installed between barrier plates 5, 5' provided perpendicularly at a specified interval in the moving direction of the exhaust gas inside the casing 2. Thus the temperature of an SO3 gas in the inner faces of the heat transfer pipes 6 is made lower than the dew point of the SO3 gas with the hot water 7. A gaseous SO3 mist contained in the exhaust gas condensates on the inner faces of the heat transfer pipes 6 and the built-up SO3 mist is washed by an alkaline liquid from a cleaning nozzle 8. Consequently, a chemical compound 10 of sulfuric acid and the alkaline liquid is collected in a storage part 9 and the SO3 mist can be collected at a high efficiency, enabling minimize the volume of the device 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for collecting SO ₃ mist contained in flue gas or the like.

[0002]

2. Description of the Related Art FIG. 10 shows an embodiment of a conventional SO ₃ mist collecting system. In FIG. 10, after the exhaust gas from the boiler 21 is cooled by the air heater 22, it is further cooled in the cooling tower 23, and the sulfur oxide is removed in the desulfurization device 24. The exhaust gas discharged from the desulfurizer 24 is
After the dust is removed by the wet electric dust collector 26, the dust is discharged from the chimney 27 into the atmosphere.

When fuel such as heavy oil is burned in a boiler, S
O ₂ gas (sulfur dioxide) is generated, SO ₂ gas, 15
At a temperature of about 0 to 180 ° C., a part is oxidized to SO ₃ gas. This SO ₃ gas is mist when cooled by the cooling tower 23 and flows into the desulfurization device 24 in a mist state. Since the SO ₃ mist is fine particles having a diameter on the order of 0.01 to 0.1 μm, it is hardly collected in the desulfurization device 24, and most of the SO ₃ mist is discharged from the desulfurization device 24 together with the exhaust gas. When discharging the SO ₃ mist as it is from the chimney 27, Tanabiki as purple smoke, since the environmental problems normally are removed SO ₃ by a wet electrostatic precipitator 26.

[0004] However, in this system, when an oil having a high sulfur content such as a residual oil is burned, a large amount (about 100 to 100) is burned.
300ppm) fine SO ₃ mist (diameter 0.01 ~
(On the order of 0.1 μm). In conventional wet electrostatic precipitator, by the space charge effect due to the presence of the SO ₃ mist, not corona current flows, collection performance soot and dust and SO ₃ mist is extremely lowered. In order to maintain the performance of collecting dust and the like, it is necessary to increase the size of the wet electric dust collector, which increases the cost.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to remove SO ₃ mist from exhaust gas without increasing the size of a dry electric dust collector even when burning a sulfur-rich oil. It is an object of the present invention to provide an SO ₃ mist collecting device capable of performing the above-mentioned.

[0006]

The SO ₃ mist trapping device of the present invention is provided with a heat transfer tube group forming a cooling surface in a casing through which the SO ₃ gas flows, and the cooling surface is provided with a dew point of the SO ₃ gas. Means for maintaining a lower temperature are provided;
O ₃ gas is attached and collected as SO ₃ mist on the cooling surface (claim 1). A cleaning nozzle can be installed above the heat transfer tube group (claim 2). The SO ₃ mist trapping device is a boiler, an air heater, a cooling tower, a desulfurization device, and a wet flue gas treatment device including a flue gas treatment device,
It can be installed in front of the wet electric precipitator (claim 3).

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG._ThreeMist
1 shows an example of a collecting device. In FIG. 1, SO _ThreeCollection equipment
Exhaust gas supplied into the device 1 flows horizontally through the casing 2.
After flowing in the direction, it moves while being rectified by the guide vanes 3
The direction was changed and turned downward, and the heat transfer tube group 4 was provided.
After passing through the area, it is discharged from the lower part of the collecting device. here
In the casing 2, exhaust gas flowing into the casing
The blocking plate 5 is attached in the direction perpendicular to the moving direction of
Also, a blocking plate 5 'is provided below a certain distance.
Is provided. There are many transmissions between the two barriers.
Heat tube 6 is attached and surrounded by casing 2
Hot water 7 as a heat transfer medium flows through the gap between the heat transfer tubes 6.
ing.

Exhaust gas can pass through each heat transfer tube 6, and the temperature of the inner surface (cooling surface) of the heat transfer tube is controlled by hot water (heat transfer medium) 7 filled in the gap between the heat transfer tubes 6. However, the temperature is usually maintained at a temperature lower by about 10 to 20 ° C. than the dew point of the SO ₃ gas. Note that the dew point of the SO ₃ gas changes as shown in FIG. 11 depending on the SO ₃ concentration and the moisture in the exhaust gas. When the temperature of the cooling surface is excessively lowered, fine SO ₃ mist is generated and is not collected on the cooling surface.
The temperature at the cooling surface,
is important. Preferably, the flow rate of the exhaust gas passing through the inside of the heat transfer tube is also adjusted so as to be optimal for collecting SO ₃ mist.

The gaseous SO ₃ present in the exhaust gas is condensed on the inner surface (cooling surface) of the heat transfer tube whose temperature has been adjusted to form S 3.
Attaches as O ₃ mist. The attached SO ₃ mist is
In order to prevent corrosion of the heat transfer tube, it is washed away by an alkaline liquid intermittently sprayed from a cleaning nozzle 8 and accumulates as a compound (liquid) 10 of sulfuric acid and an alkaline liquid in a storage section 9 provided at a lower portion of the casing.

FIG. 2 shows an AA cross section of FIG. In FIG.
In the gap between the heat transfer tubes 6 surrounded by the casing 2,
Are filled with warm water 7 as a heat transfer medium. Exhaust gas 1
1 is an inner surface of the heat transfer tube 6 whose temperature is controlled by the hot water 7.
Contact, SO in exhaust gas 11 _ThreeBut heat transfer tubes as mist
6 on the inner surface.

FIG. 3 is a view in which the inner surface of the heat transfer tube is a cooling surface.
Unlike the above case, an example in which the outer surface of the heat transfer tube serves as a cooling surface is shown. In FIG. 3, portions other than the heat transfer tube group are the same as those in FIG.
Description is omitted. Each heat transfer tube 12 of the heat transfer tube group of FIG. 3 is provided so as to penetrate the casing 2 in a direction perpendicular to the moving direction of the exhaust gas flowing in the casing 2. Hot water 13 flows inside each heat transfer tube 12, and the outer surface (cooling surface) of the heat transfer tube is maintained at a constant temperature, that is, a temperature slightly lower than the dew point of SO ₃ . The gaseous SO ₃ in the exhaust gas comes into contact with the outer surface (cooling surface) of the heat transfer tube 12 to form dew and adhere as a mist of SO ₃ .

FIG. 4 shows a cross section taken along line BB of FIG. In FIG. 4, a large number of heat transfer tubes 12 penetrate the casing 2, and hot water 13 flows inside the heat transfer tubes. The exhaust gas 14 flowing in the casing passes through the gap between the heat transfer tubes and moves downward. In addition, in FIGS. 1 and 2, an example using hot water has been described as a method for adjusting the temperature of the heat transfer tube, but another method may be used.

FIG. 5 shows an example of a flue gas treatment apparatus provided with an apparatus for collecting SO ₃ mist according to the present invention. In FIG. 5, the combustion exhaust gas discharged from the boiler 21 is cooled by an air heater 22, further cooled by a cooling tower 23, and desulfurized by a desulfurization device 24. The desulfurized exhaust gas is
After passing through the SO ₃ mist collection device 25, dust is removed by the wet electric dust collection device 26. The exhaust gas from which dust has been removed is
It is discharged from 7.

Here, the principle of the wet type electrostatic precipitator will be described with reference to FIG. In FIG. 6, the high voltage generator 31
The discharge electrode 32 connected to the discharge electrode 32 and the dust collecting electrode 33 generate a corona discharge field 34, and the dust particles 35 are separated from the dust collecting electrode 33.
Adheres to Assuming that the SO ₃
If a mist collecting device is not provided, corona discharge is interrupted by SO ₃ mist flowing into the electric dust collecting device, and the dust collecting performance deteriorates. The phenomenon in which corona discharge is suppressed by particles existing in the space between the electrodes is called a space charge effect. The space charge effect is generally greater for higher particle concentrations and smaller particle diameters.

[0015]

FIG. 7 shows the relationship between the temperature of the cooling surface of the heat transfer tube and the collection efficiency of the SO ₃ mist, and the SO flowing through the heat transfer tube.
₃ shows an experimental device for examining the relationship between the gas flow rate of _three gases and the collection efficiency of SO ₃ mist. In FIG. 7, water 42 whose temperature can be controlled is stored in a water tank 41.
A tube 43 is submerged in the water 42, and the SO ₃ gas passes through the tube 43.

EXPERIMENTAL EXAMPLE 1 Using the above apparatus, the temperature of water was raised to 65 to 85 ° C. while maintaining the SO ₃ gas flow rate in the tube at 2 liter / min.
Within the range of S, the S trapped on the inner surface of the tube
The amount of O ₃ mist was measured, and the collection efficiency of SO ₃ mist was determined. FIG. 8 shows the result. The SO ₃ mist collection efficiency (η) was determined by measuring the SO ₃ mist concentration at the inlet and the outlet of the tube and calculating from the following equation. η = (1-Co / Ci) × 100 (%) Ci: SO ₃ concentration at the inlet (ppm) Co: SO ₃ concentration at the outlet (ppm)

EXPERIMENTAL EXAMPLE 2 Using the above apparatus, while maintaining the temperature of water at 85 ± 5 ° C., the amount of SO ₃ gas passing through the tube was changed within the range of 0.5 to 10 liter / min. Then, the amount of SO ₃ mist collected on the inner surface of the tube was measured, and the collection efficiency of SO ₃ mist was determined. FIG. 9 shows the result. From the results of Experimental Example 1 and Experimental Example 2, the collection efficiency of SO ₃ mist was reduced to 9 by setting the water temperature and the gas flow rate to optimal conditions.
It turned out that it can improve to 0% or more.

[0018]

According to the mist collecting device of the present invention, SO ₃ mist can be collected from exhaust gas with high collecting efficiency. In addition, by disposing the mist collecting device on the upstream side of the wet-type electrostatic precipitator, the capacity of the wet-type electric precipitator can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an SO ₃ mist collecting device of the present invention.

FIG. 2 is a diagram showing a cross section taken along line AA of FIG. 1;

FIG. 3 is a diagram showing an example of the SO ₃ mist collecting device of the present invention.

FIG. 4 is a view showing a BB cross section of FIG. 3;

FIG. 5 is a view showing an example of a combustion exhaust gas treatment apparatus provided with the SO ₃ mist trapping device of the present invention.

FIG. 6 is a diagram showing the principle of a wet electric precipitator.

FIG. 7 is a diagram showing an experimental device for measuring the collection efficiency of SO ₃ mist.

FIG. 8 is a diagram in which the horizontal axis represents the temperature of water in the water tank and the vertical axis represents the efficiency of collecting SO ₃ mist.

FIG. 9 is a diagram in which the abscissa is the amount of gas passing through the tube and the ordinate is the collection efficiency of SO ₃ mist.

FIG. 10 is a view showing a conventional flue gas treatment apparatus.

FIG. 11 is a diagram showing the relationship between the dew point and the concentration of SO ₃ gas.

[Explanation of symbols]

1 SO ₃ collecting device 2 casing 3 guide vane 4 tube banks 5,5 'blocking plate 6,12 heat transfer tubes 7 and 13 hot water 8 washing nozzle 9 accommodating portion 10 the liquid 11 exhaust gas 21 boiler 22 air heater 23 cooling tower 24 desulfurizer Reference Signs List 25 mist collecting device 26 wet electric dust collecting device 27 chimney 31 high voltage generator 32 discharge electrode 33 collecting electrode 34 corona discharge field 35 dust particles 41 water tank 42 water 43 tube

Claims (3)

[Claims] 1. A provided with a heat transfer tube group forming a cooling surface in the casing to flow SO ₃ gas, the cooling surface SO ₃
Providing means for maintaining the temperature below the dew point of the gas,
An SO ₃ mist collecting device, wherein SO ₃ gas is adhered and collected as SO ₃ mist on the cooling surface. 2. The SO ₃ mist collecting device according to claim 1, wherein a washing nozzle is provided above the heat transfer tube group. 3. A flue gas treatment apparatus comprising a boiler, an air heater, a cooling tower, a desulfurizer, and a wet-type electrostatic precipitator, wherein the apparatus is disposed upstream of the wet-type electrostatic precipitator.
A combustion exhaust gas treatment device comprising the SO ₃ mist collection device described in 1 above.