JPH11151424A - Waste gas treating device for boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the volume of a waste water discharging section and to reduce the use of ammonia by providing a vaporizer for vaporizing ammonia contained in a desulfurization waste water fed to the waste water discharging section from a desulfurization apparatus and re-injecting to the upstream side of an electric dust collector as ammonia gas. SOLUTION: The waste gas discharged from the boiler 1 is successively passed through a denitrification equipment 2, an air preheater 3, the electric dust collector 4 and the desulfurization apparatus 5 and discharged from a chimney stack 6. When the waste gas discharged from the boiler 1 contains SO3 , SO3 is converted to ammonium sulfate to be collected with the smoke and soot and removed by injecting ammonia to the upstream side of the electric dust collector 4. In such a case, a part of the desulfurization waste water is introduced into the vaporizer 8 and heated by an auxiliary steam to vaporize ammonia contained in the desulfurization waste water. The vaporized ammonia is re-injected to the upstream side of the electric dust collector 4. The remaining desulfurization waste water is biologically treated in the waste water discharging section 7 to be denitrificated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a boiler exhaust gas treatment facility.

[0002]

2. Description of the Related Art Generally, as shown in FIG.
Downstream of the boiler 1, a denitration device 2 for removing nitrogen oxides (NOx) contained in exhaust gas discharged from the boiler 1 and a combustion air (not shown) supplied to the boiler 1 are preheated. An air preheater 3 for removing dust, an electric precipitator 4 for removing dust contained in the exhaust gas from which nitrogen oxides have been removed by the denitration device 2, and an exhaust gas from which the dust has been removed by the electric dust collector 4. A desulfurization device 5 for removing contained sulfur oxides (mainly SO ₂ ) by spray cleaning or the like and a chimney 6 are provided, and exhaust gas generated by burning fuel in the boiler 1 is: Denitration equipment 2
After the nitrogen oxides are removed in the above, heat exchange is performed with the combustion air supplied to the boiler 1 in the air preheater 3,
The dust is removed in the electric precipitator 4 and the desulfurizer 5
, Sulfur oxides such as SO ₂ are removed by spray cleaning or the like, and are discharged from the chimney 6 to the atmosphere.

When a high sulfur content coal such as high sulfur content coal or orimulsion asphalt is used in the boiler 1, a considerable amount of SO ₃ is entrained in the exhaust gas together with SO ₂ . The mist of SO ₃ has a very special property, and cannot be sufficiently absorbed and removed even if spray-cleaning is performed as in the desulfurization apparatus 5, so that the mist is discharged from the chimney 6 as purple smoke.

[0004] Therefore, by injecting ammonia (NH ₃ ) into the upstream side of the electric dust collector 4, SO ₃ contained in the exhaust gas is collected and removed together with the dust in the electric dust collector 4. ing.

Here, on the upstream side of the electric dust collector 4,
Theoretically SO_ThreeAmmonia at twice the molar ratio of
In this case, an acidic ammonium sulfate (NH_FourHS
O_Four) Is generated, and the electrodes of the electrostatic precipitator 4 are corroded.
Ammonia, the theoretical ratio
And excess ammonium sulfate ((NH_Four)_TwoS
O _Four) Is generated, and the electrodes of the electrostatic precipitator 4 are
Corrosion is prevented.

On the other hand, if the ammonia is injected in excess of the stoichiometric ratio, unreacted ammonia will be contained in the exhaust gas introduced into the desulfurization unit 5, and the unreacted ammonia will be added to the absorbent sprayed in the desulfurization unit 5. Since the ammonia of the reaction dissolves and the desulfurization effluent discharged from the desulfurization unit 5 contains a large amount of nitrogen and exceeds the water quality standard of the effluent,
The desulfurization effluent discharged from the desulfurization unit 5 is subjected to denitrification by biological treatment using nitrifying bacteria or the like in a wastewater treatment unit 7 and has a high content of reducing substances represented by COD (chemical oxygen demand). After being adsorbed by an adsorption resin made of a molecular material, the water is discharged to the sea or the like as purified treated water.

[0007]

However, as described above, desulfurization wastewater containing unreacted ammonia dissolved and containing a large amount of nitrogen is sent to the wastewater treatment apparatus 7 and desulfurized by biological treatment using nitrifying bacteria or the like. In denitrification of wastewater,
The capacity of the wastewater treatment apparatus 7 is increased, leading to an increase in equipment costs, and also an increase in the use of various chemicals and the like for denitrification, leading to an increase in operating costs.

In order to collect SO ₃ as ammonium sulfate,
Since excessive ammonia must be injected and the amount of ammonia used increases, there is a problem that the operating cost is further increased from this point.

In view of the above, the present invention can reduce the capacity of a wastewater treatment apparatus, reduce the amount of various chemicals and the like used for denitrification, and reduce the amount of ammonia used. It is an object of the present invention to provide a boiler exhaust gas treatment facility capable of reducing costs and operating costs.

[0010]

SUMMARY OF THE INVENTION The present invention provides an electric precipitator for removing dust contained in exhaust gas discharged from a boiler, and a sulfur oxide contained in exhaust gas from which dust is removed by the electric dust collector. a desulfurization apparatus for removing, and a waste water treatment apparatus for treating the desulfurization waste water discharged from the desulfurization apparatus, inject ammonia to remove SO ₃ in the exhaust gas on the upstream side of the electrostatic precipitator In the exhaust gas treatment equipment of the boiler, a part of the desulfurization effluent sent from the desulfurization device to the wastewater treatment device is introduced, and ammonia contained in the desulfurization effluent is vaporized to form an ammonia gas upstream of the electric dust collector. The present invention relates to a boiler exhaust gas treatment facility provided with a vaporizer for re-injection.

According to the above means, the following effects can be obtained.

Exhaust gas generated by burning fuel in the boiler is subjected to dust removal in an electric precipitator and sulfur oxides such as SO _{2 in a} desulfurization device. To S
When O ₃ is contained, ammonia is injected into the upstream side of the electric dust collector, and SO ₃ contained in the exhaust gas is collected and removed together with dust in the electric dust collector as ammonium sulfate.

Here, the desulfurization effluent discharged from the desulfurization unit contains a large amount of nitrogen because unreacted ammonia is dissolved, and a part of the desulfurization effluent is introduced into a vaporizer. Ammonia contained in the desulfurization effluent is vaporized in the vaporizer and re-injected as ammonia gas into the upstream side of the electrostatic precipitator, while the remaining desulfurization effluent is subjected to treatment such as denitrification in a wastewater treatment device as in the prior art. It is discharged to the sea etc. as purified treated water.

[0014] As a result, the desulfurization effluent containing unreacted ammonia dissolved therein and containing a large amount of nitrogen does not need to be sent to the wastewater treatment apparatus in its entirety. Therefore, it is not necessary to increase the capacity of the wastewater treatment apparatus, thereby reducing equipment costs. In addition, the use of various chemicals for denitrification is reduced, leading to a reduction in operating costs. In addition, it is possible to recover and reuse unreacted ammonia, thereby reducing the amount of ammonia used. Therefore, the operating cost is further reduced.

[0015]

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

FIG. 1 is an example of an embodiment of the present invention. In the figure, the portions denoted by the same reference numerals as those in FIG. 2 represent the same components, and the basic configuration is the same as that of the conventional device shown in FIG. As shown in FIG. 1, a part of the desulfurization effluent sent from the desulfurization unit 5 to the wastewater treatment unit 7 is introduced and included in the desulfurization effluent. Ammonia that is vaporized and converted into ammonia gas
Is provided with a vaporizer 8 for re-injecting the gas into the upstream side.

The vaporizer 8 heats a part of the desulfurization effluent by auxiliary steam to vaporize ammonia, and drains the waste to the outside as appropriate.

Next, the operation of the illustrated example will be described.

Exhaust gas generated by burning fuel in the boiler 1 is subjected to removal of nitrogen oxides in a denitration device 2 and heat exchange with combustion air supplied to the boiler 1 in an air preheater 3. The dust is removed in the electric precipitator 4, and sulfur oxides such as SO ₂ are removed in the desulfurization device 5 by spray cleaning or the like, and released into the atmosphere from the chimney 6. When SO ₃ is contained, ammonia (NH ₃ ) is injected into the upstream side of the electric precipitator 4, and SO ₃ contained in the exhaust gas is collected and removed together with dust in the electric precipitator 4 as ammonium sulfate. Is done.

Here, the desulfurization effluent discharged from the desulfurization unit 5 contains a large amount of nitrogen because unreacted ammonia is dissolved, and a part of the desulfurization effluent is introduced into the vaporizer 8. Heated by the auxiliary steam in the vaporizer 8, the ammonia contained in the desulfurization wastewater is vaporized and re-injected into the upstream side of the electric precipitator 4 as ammonia gas, while the remaining desulfurization wastewater is drained as in the prior art. Processing unit 7
In the above, denitrification is performed by biological treatment using nitrifying bacteria or the like, and the reducing substance is adsorbed by an adsorption resin made of a polymer material, and then discharged to the sea or the like as purified treated water.

As a result, the entire amount of desulfurized wastewater containing unreacted ammonia dissolved and containing a large amount of nitrogen does not need to be sent to the wastewater treatment apparatus 7, so that it is not necessary to increase the capacity of the wastewater treatment apparatus 7, and equipment costs are reduced. In addition to reducing the amount of ammonia used, the amount of various chemicals used for denitrification is reduced, leading to a reduction in operating costs. Unreacted ammonia can be recovered and reused, thus reducing the amount of ammonia used. As a result, operating costs are further reduced.

In this way, the capacity of the wastewater treatment apparatus 7 can be reduced, and the amount of various chemicals and the like used for denitrification and the amount of ammonia can be reduced. I can figure it out.

The boiler exhaust gas treatment equipment of the present invention
It is needless to say that the present invention is not limited to the illustrated example described above, and various changes can be made without departing from the scope of the present invention.

[0024]

As described above, according to the exhaust gas treatment equipment for a boiler of the present invention, the capacity of the wastewater treatment equipment can be reduced, the amount of various chemicals and the like used for denitrification and the amount of ammonia can be reduced. It is possible to achieve an excellent effect that the usage amount can be reduced and the facility cost and the operation cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall schematic configuration diagram of an example of an embodiment of the present invention.

FIG. 2 is an overall schematic configuration diagram of a conventional example.

[Explanation of symbols]

 Reference Signs List 1 boiler 4 electric precipitator 5 desulfurization device 7 wastewater treatment device 8 vaporizer

Claims (1)

[Claims] 1. An electric precipitator for removing dust contained in exhaust gas discharged from a boiler, and a desulfurization device for removing sulfur oxide contained in exhaust gas from which dust is removed by the electric dust collector. , and a waste water treatment apparatus for treating the desulfurization waste water discharged from the desulfurization apparatus, the exhaust gas treatment of a boiler which is adapted to inject ammonia to remove sO ₃ in the exhaust gas on the upstream side of the electrostatic precipitator In the equipment, a part of the desulfurization wastewater sent from the desulfurization device to the wastewater treatment device was introduced, and a vaporizer for vaporizing ammonia contained in the desulfurization wastewater and re-injecting it as ammonia gas upstream of the electric dust collector was provided. An exhaust gas treatment facility for a boiler, characterized in that: