JPH09173766A - High concentration sulfur oxide treating system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the temperature of a duct to prevent formed acidic ammonium sulfate from being melted and from being partly stuck on equipment to be an obstacle to operation by injecting water while injecting ammonia for preventing corrosion in a high concentration sulfur oxide treating system. SOLUTION: In a high concentration sulfur oxide treating system in which after waste gas which high sulfur content containing fuel is burned in a boiler 1 to form is denitrified, heat is recovered by an air heater 3 and then dust is removed by an electric precipitator 4 and further the waste gas is desulfurized, NH3 for neutralizing SO3 in the waste gas is injected into a duct 10 leading the electric precipitator 4 from the air heater 3, and also H2 O is injected into the duct 10 so as to lower the temperature of the waste gas to below a meting point of acidic ammonium sulfate formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for treating flue gas containing high-concentration sulfur oxides (SO _X ) after orimulsion has been burned in a boiler, and particularly to a system for treating SO ₃ in exhaust gas. Acidic ammonium sulphate (NH ₄ HSO ₄ ) formed as a result of ammonia added to prevent corrosion and combining with SO _3.
The present invention relates to a flue gas treatment system that prevents melted matter from adhering to equipment.

[0002]

2. Description of the Related Art A boiler in a power generation facility or the like is provided with a flue gas treatment system for treating exhaust gas containing sulfur oxide (SO _x ) generated from the boiler. The flue gas treatment system includes a boiler that burns fuel, a denitration device that removes nitrogen oxides from the exhaust gas from the boiler, an air heater (AH) that recovers heat of the exhaust gas from the denitration device, and an exhaust gas from the air heater. An electrostatic precipitator (EP) that removes dust, a desulfurization device that removes sulfur oxides from the exhaust gas from the electrostatic precipitator, a gas gas heater (GGH) that recovers heat immediately before desulfurization, and a gas that heats after desulfurization It is composed of a gas heater (GGH) and a circulation pipe that connects these two gas gas heaters and circulates a heat medium.

When exhaust gas containing a high concentration of SO ₃ is generated by burning orimulsion, etc., when the exhaust gas temperature falls below the acid dew point of SO ₃ of 160 to 170 ° C., SO ₃ is sulphated and the apparatus is oxidized. There is a risk of corroding. In conventional equipment, the exhaust gas temperature is kept above the acid dew point until it exits the air heater (AH), but after that it drops to below 160 ° C, so the electrostatic precipitator (EP)
In order to protect the gas heater (GGH) from corrosion by sulfuric acid, it is necessary to inject NH ₃ into the exhaust gas when it comes out of the air heater (AH) to neutralize SO ₃ .

[0004]

However, in this conventional method, by injecting ammonia, acidic ammonium sulfate (NH ₄ HSO ₄ ) is produced as a salt as shown by the following formula.

H ₂ SO ₄ + NH ₃ → NH ₄ HSO ₄ The melting point of this acidic ammonium sulfate is 147 ° C., while the exhaust gas temperature near the injection of ammonia is above the acid dew point (usually 170 ° C.) in order to prevent the sulfation of SO _3. ), The melting point of the acidic ammonium sulfate is higher than the melting point of the acidic ammonium sulfate, and the ammonium sulfate in the form of starch syrup is a part of the equipment such as EP (electrostatic precipitator) and GG.
It adheres to H (gas gas heater) and causes trouble in operation. However, the use of ammonia is unavoidable at this point because corrosion occurs unless ammonia is used.

Therefore, an object of the present invention is to prevent the acidic ammonium sulfate produced when injecting ammonia from being melted and to prevent the ammonium sulfate from adhering to a part of the apparatus and impeding the operation. Is.

[0007]

In order to achieve the above object, the invention of claim 1 is an electric precipitator after denitration of exhaust gas after combustion of a fuel containing a high sulfur content in a boiler and heat recovery by an air heater. In a high-concentration sulfur oxide treatment system that removes dust with, and further desulfurizes, NH ₃ for neutralizing SO ₃ contained in the exhaust gas is injected into the exhaust gas from the air heater to the electrostatic precipitator, and generated. In order to lower the exhaust gas temperature below the melting point of acidic ammonium sulfate, H ₂
It is configured to inject O 2.

According to a second aspect of the present invention, there is provided a high-concentration sulfur oxide treatment system having a boiler that burns a fuel containing a high sulfur content, in which a denitration device, an air heater, an electrostatic precipitator, and a desulfurization device are sequentially connected to the boiler. The NH ₃ injecting means and the H ₂ O injecting means are connected to a duct between the air heater and the electrostatic precipitator.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, the exhaust gas after combustion from the boiler 1 is forcibly discharged by an induction fan (IDF) 5 and guided to a denitration device 2 to be subjected to denitration treatment. Since the exhaust gas after denitration has a considerably high temperature, in order to recover heat from this, the air heater (AH) 3 exchanges heat between the high temperature exhaust gas and the combustion air at room temperature, and the heat for combustion becomes high. Air will be supplied to the boiler 1. On the other hand, the heat-exhausted exhaust gas is then guided to an EP (electrostatic precipitator) 4 for dust removal processing.

The sensible heat of the exhaust gas after dust removal is recovered by the heat recovery gas gas heater (GGH) 6 and then desulfurization absorption tower 7
And is desulfurized. The exhaust gas after desulfurization is
The sensible heat recovered by the heat recovery gas gas heater (GGH) 6 is applied in the reheating gas gas heater (GGH) 8. The exhaust gas after the application of sensible heat is discharged from the chimney 20. The heat recovery gas gas heater (GGH) 6 and the reheating gas gas heater (GGH) 8 are connected by a heat medium circulation pipe 9 so that the heat medium circulates through both heaters 6 and 8 through the circulation pipe 9. Has become.

The duct 10 extending from the air heater (AH) 3 to the electrostatic precipitator (EP) 4 has an upright tubular shape.
NH ₃ injection means 11 and H ₂ O injection means 12 are provided (see FIGS. 2 and 4). The NH ₃ injecting means 11 has an NH ₃ injecting means nozzle 13a, and the H ₂ O injecting means 12 has H ₂ O.
The injection means nozzles 13b are installed at equal intervals. Ammonia is injected from the nozzle 13a and water is injected from the nozzle 13b into the duct 10. A propeller for stirring or a wire mesh for stirring (not shown) may be provided close to the injection means 12 so that the injected water is evenly scattered in the duct 10.

In the present embodiment, the injection direction of ammonia and the injection direction of water may be either counter-current direction or co-current direction with respect to the exhaust gas flow. Considering this, it is preferable to inject in a countercurrent direction with the exhaust gas.

Due to the injected water, the temperature of the duct 10 is initially about 170 ° C. and the melting point of acidic ammonium sulfate (NH ₄ HSO ₄ ) is changed.
It is cooled to 140-145 ° C, which is lower than 147 ° C. Then
The acidic ammonium sulfate produced by the combination of ammonia and SO ₃ becomes a powdery solid and is collected and removed by the electrostatic precipitator 4.

At the time of injecting the above water, it is necessary to pay attention to the amount of water to be infused. FIG. 5 is a diagram showing the relationship between the temperature and the humidity of the exhaust gas, and this explains how much water may be injected in the present embodiment.

In the figure, first, the exhaust gas emitted from the air heater (AH) 3 is in the state (temperature 160 ° C.) shown at point a,
By injecting water, the temperature drops to 140 ° C and the humidity rises as shown at point b, and then the gas gas heater (GG
H) 6, heat is recovered and the temperature drops to 100 ° C as shown at point c. Then, in the absorption tower 7, the absorption liquid is sprayed to the point d.
The humidity is 100%, the temperature is lowered to 55 ° C. as shown in FIG. 3, and then the temperature is raised to 95 ° C. by reheating by the gas gas heater (GGH) 8 and then discharged from the stack 20.
In the graph of FIG. 5, the amount of water to be injected is 1) to lower the exhaust gas temperature to below the melting point (147 ° C.) of the generated acidic ammonium sulfate.

2) The determination is made by paying attention to the two points that the amount of heat required for reheating by the gas gas heater (GGH) 8 can be recovered by the gas gas heater (GGH) 6 without lowering the exhaust gas temperature too much. .

That is, when exhaust gas discharged from the absorption tower 7 is exhausted by the chimney, it is necessary to secure a sufficient amount of heat to reheat the exhaust gas so that the exhaust gas does not turn into white smoke. Therefore, the temperature rise (in the case of this embodiment) It is necessary to secure (recover) a sufficient amount of heat (about 40 °) by the gas gas heater (GGH) 6. Therefore, in the case of the present embodiment, the exhaust gas temperature after injection must be 140 ° C or higher. I won't. On the other hand, since the exhaust gas temperature should be lower than the melting point of acidic ammonium sulfate (147 ° C), the desirable exhaust gas temperature after injection is 140 ° C to 145 ° C.
It will be ℃. That is, in the present embodiment,
The amount of water injected is such that the exhaust gas temperature after injection is approximately 140 ° C to 14 ° C.
Adjusted to 5 ° C.

Specifically, as shown in FIG. 5, when the humidity and temperature of the exhaust gas leaving the air heater (AH) 3 are at point a, the maximum amount of water to be injected reaches saturation (point f). △ E
However, by injecting about 10% to 20% of water with respect to this maximum injection amount, the melting point of acidic ammonium sulfate is maintained while maintaining the exhaust gas temperature at a sufficiently high temperature (140 ° C) for subsequent heat recovery. Can be lower.

At this time, the injection means 12 and the nozzle 13
However, it goes without saying that it is arranged so that the exhaust gas temperature can be effectively lowered to 140 ° C with a minimum amount of water. The approximate amount of water spray is about 1% of the amount of exhaust gas.

Regarding the injection of ammonia and water in the duct 10, the modification shown in FIG. 3A and FIG.
The modification shown in is possible.

That is, in the example shown in FIG. 3A, after ammonia and water are mixed in the common injection means 11a to become ammonia water, they are simultaneously injected into the duct 10 from the common nozzle 13. In this case, the ammonia water is injected countercurrent to the exhaust gas flow.

On the other hand, in the example shown in FIG. 3B, ammonia and water are introduced into the duct 10 by separate injection means 11 and 12 as in the first embodiment. Are finally integrated into one nozzle to form a two-phase fluid nozzle 13c (see FIG. 3C). The water sent from the injection means 11 is guided to the flow path outside the two-phase fluid nozzle 13c, and the ammonia sent from the injection means 12 is guided to the flow path inside the two-phase fluid nozzle 13c. Then, both are mixed and scattered at the moment of injection. In addition,
The mixed ammonia and water are injected in the direction of alternating current into the exhaust gas stream as in the previous variant.

The details of these two modifications other than those described above are the same as those of the first embodiment, and therefore the description thereof is omitted.

In summary, according to the present invention, when exhaust gas passes through the duct connecting the air heater (AH) and the electrostatic precipitator (EP), not only ammonia but also water is injected at the same time. By utilizing the latent heat of vaporization, the temperature of the exhaust gas can be made lower than the melting point of the acidic ammonium sulfate, the generated acidic ammonium sulfate can be prevented from melting, and the failure of the device can be prevented.

[0026]

In summary, according to the high-concentration sulfur oxide treatment system of the present invention, ammonia is injected into the duct extending from the air heater (AH) to the electrostatic precipitator (EP) so that the SO ₃ in the exhaust gas is removed. At the same time, inject not only ammonia but also water at the same time. Thereby, the temperature of the exhaust gas can be made lower than the melting point of the acidic ammonium sulfate generated as a salt (due to the latent heat of vaporization of water), and the melting of the acidic ammonium sulfate can be prevented. In other words, the melted ammonium sulphate is mixed with air heater (EP) and gas gas heater (G
GH) It has an excellent effect in preventing a device failure or the like caused by the adhesion to the inside.

[Brief description of the drawings]

FIG. 1 is a diagram showing a high-concentration sulfur oxide treatment system of the present invention.

2 is a cross-sectional view of a duct connecting an air heater (AH) and an electrostatic precipitator (EP) of the high-concentration sulfur oxide treatment system of FIG.

FIG. 3 (A) is a cross-sectional view of a duct that connects an air heater (AH) and an electrostatic precipitator (EP) in a first modified example of the high-concentration sulfur oxide treatment system of the present invention. (B) The air heater (AH) and the electrostatic precipitator (E) in the second modified example of the high-concentration sulfur oxide treatment system of the present invention.
It is a cross-sectional view of the duct which connects with P). (C) is a side sectional view of a two-phase fluid nozzle in a second modified example of the high-concentration sulfur oxide treatment system of the present invention.

4 is a horizontal sectional view of a duct connecting an air heater (AH) and an electrostatic precipitator (EP) of the high concentration sulfur oxide treatment system of FIG.

FIG. 5 is an explanatory diagram for explaining the amount of water to be injected in the present invention.

[Explanation of symbols]

1 Boiler 2 Denitration device 3 Air heater (AH) 4 Electrostatic precipitator (EP) 5 Induction fan 6 Heat recovery gas gas heater (GGH) 7 Desulfurization absorption tower 8 Reheating gas gas heater (GGH) 9 Heat medium circulation pipe 10 Duct 11 NH ₃ injection means 12 H ₂ O injection means 13a NH ₃ injection means nozzle 13b H ₂ O injection means nozzle 20 chimney

Claims (2)

[Claims] 1. A high-concentration sulfur oxide treatment system for denitrifying exhaust gas after burning a fuel containing a high sulfur content in a boiler, recovering heat with an air heater, removing dust with an electric dust collector, and further desulfurizing the air heater. To the exhaust gas from the above to the electrostatic precipitator, while injecting NH ₃ for neutralizing SO ₃ contained in the exhaust gas, in order to lower the exhaust gas temperature below the melting point of the acidic ammonium sulfate to be produced, H in the exhaust gas A high-concentration sulfur oxide treatment system characterized by being injected with ₂ O. 2. A boiler that burns fuel containing a high sulfur content, wherein a denitration device, an air heater, an electrostatic precipitator,
In a high-concentration sulfur oxide treatment system in which desulfurizers are sequentially connected, a duct between the air heater and the electrostatic precipitator is connected with an NH ₃ injecting means and an H ₂ O injecting means. Concentrated sulfur oxide treatment system.