JPH10339425A - Sulfur dew point corrosion preventive duct - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent sulfur dew point corrosion by a method wherein a lining material is applied on the internal surface of the body of a duct through a reinforcing rib and the whole of the outer circumferential surface of the body of the duct is enclosed by a heat reserving material without providing the reinforcing rib on the outer circumferential surface of the body of the duct. SOLUTION: In this sulfur dew point corrosion preventing duct, a reinforcing rib 2 is mounted on the inner circumferential surface of the body 1 of a duct and a lining material 3 is applied on the whole of the inner circumferential surface provided with the reinforcing rib 2. The lining material is applied by blowing a castable onto the inner circumferential surface at a desired thickness. A heat reserving material 4 is applied on the whole of the outer circumferential surface of the body 1 of the duct without providing the reinforcing rib on the outer circumferential surface thereof. The heat reserving material herein used is kaolin wool and applied by winding it on the outer circumference of the duct. This enables preventing of sulfur dew point corrosion as caused by sulfur in an exhaust gas flowing through the duct.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas duct for a combustion gas of a sulfur-containing raw material, and more particularly to a duct for preventing dew-point corrosion due to sulfur in exhaust gas.

[0002]

2. Description of the Related Art For example, in a sintering machine, since S content is contained in fine ore, SO ₂ and SO ₃ are contained in exhaust gas of the sintering machine.
Is contained, and SO ₃ minutes combine with H ₂ O in the exhaust gas to form H ₂
There is a problem that sulfur dew point corrosion of the flue gas duct is severe due to the formation of ₂ SO ₄ and condensation as sulfuric acid. As such a countermeasure, for example, Japanese Patent Application Laid-Open No. 5-118767 discloses a method in which SO ₂ and H ₂ O in the exhaust gas of a sintering machine are detected, and the temperature at which rapid corrosion of metal by sulfuric anhydride in the exhaust gas is started is calculated. A method of preventing duct corrosion by maintaining exhaust gas temperature has been proposed. Also, Japanese Patent Application Laid-Open No.
No. 06006, the exhaust gas main pipe of the sintering machine is provided with an inlet duct connected to the desulfurization and denitration equipment and a bypass duct directly connected to the chimney, and the processing gas outlet duct passed through the desulfurization and denitration equipment is connected to the bypass duct. A method has been proposed in which the temperature of the exhaust gas is increased to maintain the internal temperature of the duct at a temperature equal to or higher than the rapid corrosion start temperature by connecting a branch pipe branched from the processing gas outlet duct to a bypass duct by joining the pipe near the chimney and connecting it to a bypass duct.

[0003]

However, the above-mentioned conventional countermeasures against dew-point corrosion have the following problems. That is, in the case of changing the operation method of the sintering machine to increase the exhaust gas temperature to maintain the internal temperature of the duct at or above the rapid corrosion start temperature (Japanese Patent Laid-Open No. 5-118767), the exhaust gas temperature is always kept high. Since the amount of heat must be maintained, an excess amount of heat is taken in the exhaust gas, and the amount of sensible heat recovery of the sinter decreases, which causes a problem that the cost of the entire sintering plant deteriorates. In addition, by providing a duct connected to the desulfurization and denitration equipment and a bypass duct directly connected to the chimney, and connecting the outlet duct and the bypass duct after the desulfurization and denitration treatment, the exhaust gas temperature is raised and the internal temperature of the duct is set to the rapid corrosion start temperature A method for maintaining the above (Japanese Patent Laid-Open No. 54-1060)
No. 06), a part of the exhaust gas is discharged into the atmosphere from the chimney without being subjected to the desulfurization and denitration treatment, and there is a problem that the environment is seriously affected.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to provide a flue gas duct capable of preventing sulfur dew point corrosion by improving the structure of the duct itself.

[0005]

A duct for preventing sulfur dew point corrosion according to the present invention has a lining material installed on the inner surface of a duct body via a reinforcing rib, and the entire outer peripheral surface is not provided on the outer surface of the duct body. Is surrounded by a heat insulating material, and a rain shield is provided on the outer surface of the duct.

[0006] Dew point corrosion of the duct due to sulfur contained in the exhaust gas is mainly caused by a decrease in the internal temperature of the duct and direct contact of the gas with the inner surface of the duct. Therefore,
In order to prevent sulfur dew point corrosion inside the duct, it is necessary to prevent the temperature inside the duct from lowering and to prevent the exhaust gas from coming into direct contact with the inside of the duct. Therefore, in order to prevent the temperature of the inner surface of the duct from lowering and prevent the exhaust gas from coming into direct contact with the inner surface of the duct, the present invention applies a lining material to the inner surface of the duct via a reinforcing rib. Instead of providing a means to surround the entire outer peripheral surface with a heat insulator,

Usually, reinforcing ribs are provided on the outer peripheral surface of the smoke exhaust duct, and since the ribs serve as fins, a large amount of heat is radiated from the ribs, thereby lowering the duct inner surface temperature. Therefore, in the present invention, the reinforcing rib is provided inside the duct, and a means for surrounding the entire outer peripheral surface of the duct with a heat insulating material is employed. Thereby, the amount of heat radiation from the ribs can be reduced, and the temperature of the inner surface of the duct can be prevented from lowering by the action of the heat insulating material. Further, the reason why the lining material is applied to the inner surface of the duct is to prevent dew of sulfuric acid in the exhaust gas from occurring on the inner lining so as not to corrode the duct body. As the heat insulating material, a material having a thermal conductivity of about 0.03 is selected, and as the lining material, a material capable of withstanding a high-temperature exhaust gas (temperature of 120 ° C. or more) and an acidic atmosphere (pH 2 to 3) is selected. Specifically, as a heat insulating material, for example, kao wool (trade name) having a thickness of 50 mm manufactured by Isolite Industry Co., Ltd. is used, and as a lining material, a thickness of 50 m manufactured by Toko Construction Co., Ltd. is used.
m FC-SS (trade name) is preferred.

In the case of a duct having a square cross section,
In a conventional duct in which reinforcing ribs are provided on the outer peripheral surface, since the upper reinforcing ribs have a lattice shape, rainwater that accumulates in the lattice portion lowers the duct inner surface temperature. For this reason, in the present invention, the reinforcing ribs on the outer surface of the duct are removed, and a rain shield is further provided on the outer surface of the duct whose entire outer peripheral surface is surrounded by a heat insulating material. By providing a rain shield on the outer surface of the duct in this way, the inner surface temperature of the duct without reinforcing ribs surrounding the entire outer peripheral surface with a heat insulating material can be kept at a higher state, and the effect of preventing sulfur dew point corrosion inside the duct is improved. Can be enhanced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a longitudinal sectional view showing an example of a sulfur dew point corrosion prevention duct corresponding to claim 1 of the present invention, and FIG. 2 is a sulfur dew point corrosion prevention duct also corresponding to claim 2 of the present invention. FIG. 1 is a longitudinal sectional view showing one example of a duct body, 1 is a duct body, 2 is a reinforcing rib, 3 is a lining material, 4 is a heat insulating material,
Is a rain shield. Here, a duct having a square cross section will be described as an example.

That is, as shown in FIG. 1, a duct for preventing sulfur dew point corrosion according to claim 1 of the present invention has a reinforcing rib 2 attached to the inner peripheral surface of a duct body 1 by welding or the like. The lining material 3 is applied to the entire inner peripheral surface provided with 2. This lining material is applied by, for example, spraying a castable on the inner peripheral surface to a desired thickness. On the other hand, without providing a reinforcing rib on the outer peripheral surface of the duct body 1,
The heat insulating material 4 is applied to the entire outer peripheral surface. As the heat insulating material, for example, the above-mentioned kao wool having a thickness of 50 mm is used, and is wound around the outer periphery of the duct for construction.

FIG. 2 shows an example of a sulfur dew point corrosion prevention duct according to a second aspect of the present invention.
For example, a roof-shaped rain shield 5 is attached to the ceiling side of a duct having the cross-sectional structure shown in FIG. The rain shield 5 can be installed on the upper surface of the duct main body 1 via a column or the like.

In the case of the sulfur dew point corrosion prevention duct having the structure shown in FIG. 1, since there is no reinforcing rib on the outer surface of the duct, a temperature drop due to the fin effect of the reinforcing rib is prevented, and the heat insulating material 4 applied to the entire outer peripheral surface is provided. By the action of the above, the outer surface of the duct is kept warm and the temperature inside the duct is prevented from dropping. Furthermore, by applying the lining material 3 to the inner surface of the duct,
The exhaust gas contacts the surface of the lining material, and dew condensation of sulfuric acid in the exhaust gas occurs on the inner lining surface. By these effects, sulfur dew point corrosion due to sulfuric acid in exhaust gas flowing in the duct can be prevented. In the case of the sulfur dew point corrosion prevention duct having the structure shown in FIG. 2, since the rain does not directly hit the duct due to the action of the rain shield 5, the temperature drop inside the duct can be suppressed even in rainy weather, and the temperature inside the duct can be increased. Can be held.

Next, the results obtained by simulating the effect of the sulfur dew point corrosion prevention duct of the present invention by heat transfer calculation are shown below. These results were obtained by calculation taking the case of a sintering exhaust gas temperature of 100 ° C. as an example. FIG. 3 is a diagram showing changes in the inner surface temperature of a duct in which a heat insulating material (thermal conductivity 0.03) is applied to the outer surface of the duct, in comparison with the inner surface temperature of a duct on which anticorrosion measures have not been taken. In other words, while the inner surface temperature of a general duct without anticorrosion measures changes as shown in Fig. 1 depending on the outside air temperature, in the case of a duct in which a heat insulating material (thermal conductivity 0.03) is installed on the outer surface of the duct, As shown in FIG. 1, it can be seen that the inner surface temperature of the duct is almost the same as the exhaust gas temperature and can be maintained at a high temperature.

FIG. 4 shows an example of comparing the inner surface temperature of the duct when the reinforcing rib is provided on the outer surface of the duct and the case where the reinforcing rib is provided on the inner surface of the duct. As is clear from the data in FIG. 4, the provision of the reinforcing ribs on the inner surface of the duct can keep the inner surface temperature of the duct higher.

FIG. 5 shows the effect of extending the life of the duct due to the construction of the inner lining material in comparison with a duct in which no anticorrosion measures have been taken. The inner lining was castable. From the simulation results in FIG. 5, it can be seen that when the lining is provided on the inner surface of the duct, the effect of extending the life of the duct is greatly improved.

[0016]

FIG. 6 shows the results of measuring the inner surface temperature of the duct by applying the present invention to a sintering exhaust gas duct of a sintering plant and comparing the duct inner surface temperature with that of a non-corrosion preventive duct. Table 1 shows the specifications of the duct in this embodiment, and Table 2 shows the operating conditions.

As is clear from the results shown in FIG. 6, according to the duct of the present invention, the inner surface temperature of the duct can be kept almost equal to the temperature of the sintering exhaust gas, and the inner surface temperature of the duct is always kept higher than the rapid corrosion start temperature. It can be seen that the duct life can be greatly extended by doing so.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

As described above, the duct for preventing sulfur dew point corrosion of the present invention can prevent the temperature of the inner surface of the duct from being lowered by the action of the heat insulating material installed on the outer surface, thereby keeping the inner surface temperature of the duct substantially equal to the exhaust gas temperature. It is possible,
In addition, the inner surface lining constructed with reinforcing ribs on the inner surface prevents corrosion of the duct body due to dew condensation of sulfuric acid in exhaust gas, so it is resistant to sulfur dew point corrosion and can greatly extend the life of the duct, greatly reducing duct repair costs Can be measured.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a sulfur dew point corrosion prevention duct according to claim 1 of the present invention.

FIG. 2 is a vertical sectional view showing an example of a sulfur dew point corrosion prevention duct according to a second aspect of the present invention.

FIG. 3 is a diagram showing changes in the inner surface temperature of a duct in which a heat insulating material is applied to the outer surface of the duct, in comparison with the inner surface temperature of a duct on which anticorrosion measures have not been taken;

FIG. 4 is a diagram comparing the inner surface temperature of the duct when the reinforcing rib is provided on the outer surface of the duct and the case where the reinforcing rib is provided on the inner surface of the duct.

FIG. 5 is a diagram showing the effect of extending the life of the duct by applying the internal lining material in comparison with a duct in which anticorrosion measures have not been implemented.

FIG. 6 shows the duct inner surface temperature in the embodiment of the present invention.
It is a figure shown in comparison with a normal anticorrosion measure non-implemented duct.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Duct main body 2 Reinforcement rib 3 Lining material 4 Heat insulation material 5 Rain shield

Claims (2)

[Claims] 1. A flue gas duct for preventing dew point corrosion due to sulfur in a combustion gas, wherein a lining material is provided on an inner surface of the duct body via a reinforcing rib, and a reinforcing rib is provided on an outer surface of the duct body. A sulfur dew point corrosion prevention duct characterized in that it has no structure and the entire outer peripheral surface is surrounded by a heat insulating material. 2. A duct for preventing sulfur dew point corrosion according to claim 1, wherein a rain shield is provided on an outer surface of the duct.