JPH0957150A - Method for removing sulfur oxides in combustion exhaust gas - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To appropriately control the injection amount of ammonia into combustion exhaust gas in response to load fluctuation of a boiler and to suppress excessive consumption of ammonia injection. A method for removing sulfur oxides is provided. SOLUTION: The denitration device 1 is sequentially provided on the downstream side of the boiler 10.
2. The air heater 14 and the electrostatic precipitator 16 are provided, ammonia is injected into the flue 32 between the air heater 14 and the electrostatic precipitator 16, and the sulfur oxide in the combustion exhaust gas from the boiler 10 reacts with the ammonia. To remove. At this time, the air heater is based on the difference between the total concentration of sulfur oxides contained in the combustion exhaust gas from the sulfur content in the fuel used in the boiler 10 and the SO ₂ concentration at the outlet of the air heater 14 measured by the SO ₂ automatic analyzer 26. It controls the amount of ammonia injected into the flue 32 between 14 and the electrostatic precipitator 16.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for removing sulfur oxides in combustion exhaust gas, and more particularly to a method for removing sulfur oxides in combustion exhaust gas containing a large amount of sulfur oxides.

[0002]

2. Description of the Related Art In a flue gas treatment facility for treating combustion exhaust gas from an oil-fired boiler, etc., a denitration device, an air heater, an electric precipitator, and a desulfurization device are installed in sequence on the downstream side of the boiler. nitrogen oxides in the exhaust gas (NO _X) is removed and the electrostatic precipitator to remove dust, the desulfurization unit is adapted to remove sulfur oxides in the combustion exhaust gas of the (sO _X).

When a fuel containing sulfur is combusted in the boiler, the sulfur content in the fuel is oxidized by the combustion in the boiler and becomes sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) which is discharged from the boiler. It A catalyst containing vanadium as a main component is used in the denitration device, which is operated at about 400 ° C. which is a temperature suitable for the denitration reaction, and the inlet temperature of the air heater is about the same.

By the way, there is a contact method as a denitration method used in the production process of sulfuric acid or fuming sulfuric acid. In this method, a mixed gas of SO ₂ and oxygen is brought into contact with a platinum or vanadium catalyst maintained at about 400 ° C. It is known that this contact causes SO ₂ to easily react with oxygen and be oxidized to SO ₃ . Therefore, when the combustion exhaust gas passes through the denitration device and the air heater, the inside of the denitration device and the air heater are about 400 °.
Due to the presence of C, SO ₂ in the combustion exhaust gas is converted to SO _3, and the SO ₃ concentration in the combustion exhaust gas sent to the electrostatic precipitator becomes high.

This SO ₃ remarkably raises the dew point of the combustion gas, and the operating temperature of the electrostatic precipitator is 120 to 190 °.
In the vicinity of C, a part becomes mist. As a result, if the mist adheres to the discharge wire or the dust collecting electrode of the electrostatic precipitator, problems such as enlargement of the discharge wire and defective separation of dust from the dust collecting electrode are caused. Therefore, in order to prevent this, ammonia is injected into the flue between the air heater and the electrostatic precipitator to convert SO ₃ into a solid substance of ammonium sulfate, which is then recovered and removed by the electrostatic precipitator.

[0006] Originally, the amount of injected ammonia is S of combustion exhaust gas.
It should be set based on the measurement result of measuring the O ₃ concentration, but the current technology does not allow automatic analysis of SO ₃ . Therefore, conventionally, SO ₃ was collected as mist at the outlet of the air heater, and the injection amount of ammonia was controlled based on the analysis value obtained by manually analyzing this.

[0007]

However, in the conventional method in which the ammonia injection amount is controlled based on the analysis value of the manual analysis, the analysis of the manual analysis ends from the collection of SO ₃ mist. Since it takes several hours to complete, real-time control according to changes in the SO ₃ concentration cannot be performed. For this reason, there is a drawback that the amount of injected ammonia cannot be appropriately controlled in the case where the boiler load changes and the amount of SO ₃ produced greatly fluctuates, or when the amount of SO ₃ changes during a normal steady load.

Further, when the injection amount of ammonia is small, ammonium hydrogensulfate which is an intermediate thereof is produced without proceeding to ammonium sulfate. This ammonium hydrogensulfate has a function of increasing the adhesion force of the dust, so that the peeling property of the dust attached to the discharge line of the electrostatic precipitator or the dust collecting electrode is significantly deteriorated, and as a result, the discharge line is enlarged and the discharge is increased. There is a problem that the influence on the current is adversely affected and that the dust from the dust collecting electrode cannot be removed properly. As a countermeasure against this, the amount of ammonia injection is changed to SO ₃
The current situation is that the amount is more than necessary for the reaction with, and ammonia was wasted.

The present invention has been made in view of such circumstances, and it is possible to appropriately control the amount of ammonia injected into the combustion exhaust gas in response to the load fluctuation of the boiler, and at the same time, to consume excessive ammonia injection. It is an object of the present invention to provide a method for removing sulfur oxides in combustion exhaust gas that can suppress the above.

[0010]

In order to achieve the above-mentioned object, the present invention is provided with a denitration device, an air heater, and an electrostatic precipitator in sequence on the downstream side of a boiler. In the method for removing sulfur oxides in combustion exhaust gas by injecting ammonia into a flue between the exhaust gas and reacting with ammonia to remove sulfur oxides in combustion exhaust gas from the boiler, the fuel used in the boiler is used. The total concentration or amount of sulfur oxides contained in the combustion exhaust gas is calculated from the sulfur content in the exhaust gas, and the concentration or amount of sulfur dioxide in the combustion exhaust gas in the flue between the air heater and the electrostatic precipitator. Of the sulfur oxides, and the ammonia injected into the flue between the air heater and the electrostatic precipitator based on the difference between the total concentration or amount of the sulfur oxides and the concentration or amount of the sulfur dioxide. And controlling the A amount.

According to the present invention, the total concentration (or total amount) of sulfur oxides calculated from the sulfur content of the fuel,
From the difference between the concentration (or amount) of sulfur dioxide (SO ₂ ) in the flue gas, which is sequentially measured in the flue between the air heater and the electrostatic precipitator, the sulfur trioxide (SO ₂ in the flue gas in the flue gas)
The concentration (or amount) of ₃ ) can be calculated sequentially. Therefore, even impossible automatically measuring the SO ₃ concentration in flue gas, it is possible to control the ammonia injection amount in real time based on the change in the SO ₃ concentration.

Incidentally, sulfur dioxide (S
Automatic measurement of O ₂ ) concentration is well known.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a method for removing sulfur oxides from combustion exhaust gas according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is an example of a configuration diagram of a flue gas treatment facility to which the method for removing sulfur oxides in combustion exhaust gas according to the present invention is applied.

As shown in FIG. 1, the flue gas treatment facility has a denitration device 12, an air heater 14, an electrostatic precipitator 16, a fan 18, a desulfurization device 20, and a chimney 22 in order from the outlet of the boiler 10.
It is composed of Then, the combustion exhaust gas generated in the boiler 10 is sequentially sent to the denitration device 12, the air heater 14, the electrostatic precipitator 16, and the desulfurization device 20, and the nitrogen oxides (NO
_X ), dust, and sulfur oxide (SO _X ) are removed and exhausted from the chimney 22. Here, the air heater 14 uses the high-temperature waste heat from the boiler 10 and exchanges heat between the high-temperature waste heat and the air supplied to the boiler 10, thereby increasing the combustion efficiency of the boiler 10.

The SO ₂ automatic analyzer 26 includes an air heater 1
The SO ₂ concentration in the combustion exhaust gas that is communicated through the sampling pipe 34 in the middle of the flue 32 that connects the electric dust collector 16 and the electric dust collector 16 and sequentially measures the SO ₂ concentration at the outlet of the air heater 14. . In addition, in the middle of the flue 32 connecting the air heater 14 and the electrostatic precipitator 16, the sampling pipe 34
An injection pipe 36 for injecting ammonia is connected between the communication section and the electrostatic precipitator 16, and the injection pipe 36 is connected to an ammonia tank 40 via a valve 38. In addition, it is desirable that the distance between the communicating portion of the sampling pipe 34 and the communicating portion of the injection pipe 36 (indicated by A in the figure) is about 1 m or more.

The SO ₂ automatic analyzer 26 is connected to a computing unit 46 via a signal cable 44. This computing unit 46 is connected to the valve 38 via a signal cable 48, and the boiler load signal 50 is transmitted to the signal cable 4
It is output to the computing unit 46 via 2. In addition, the computing unit 46
And a rotation speed detector (not shown) of the fan 18 are connected by a signal cable 30 so that the amount of combustion exhaust gas flowing through the flue can be known. The weight ratio of components such as carbon, hydrogen, oxygen, nitrogen, sulfur, and water in the fuel used in the boiler 10 is input and stored in the calculator 46 in advance, and the combustion amount of the fuel of the boiler load signal 50, function of calculating the total concentration of sulfur oxides in the combustion exhaust gas from the component of the air ratio and fuel (T-SO _X) is provided.
If the lot of fuel changes and the above components change,
A new numerical value is input to the calculator 46.

Next, the operation of the method for removing sulfur oxides from combustion exhaust gas of the present invention using the flue gas treatment facility constructed as described above will be described. By the boiler load signal 50, the combustion amount of fuel in the boiler 10 and the air ratio are output to the calculator 46,
Total concentration of the above components of the stored fuel sulfur oxides in the combustion exhaust gas (T-SO _X) is calculated in advance.
On the other hand, the SO ₂ concentration in the combustion exhaust gas at the outlet of the air heater 14 is sequentially measured by the SO ₂ automatic analyzer 26, and the measured result is output to the calculator 46. Further, the rotation speed of the fan 18 is output to the calculator 46, and the gas amount of the combustion exhaust gas passing through the flue 32 is calculated. The calculator 46 calculates the total concentration of sulfur oxides (T-S
From O _X) and the difference between the SO ₂ concentration measured by the SO ₂ automatic analyzer _{26 [(T- SO X) -SO} 2], calculates the SO ₃ concentration in the combustion exhaust gas in the air heater 14 outlets. The calculator 46 calculates the injection amount of ammonia to be injected into the flue 32 from the calculated SO ₃ concentration and the gas amount calculated from the rotation speed of the fan 18, and controls the opening / closing degree of the valve 38. That is, S measured as the total concentration of the sulfur oxides
The difference between the O ₂ concentration corresponds to SO ₃ concentration in flue gas, the calculated SO ₃ content in the combustion exhaust gas from the SO ₃ concentration and the amount of gas, ammonia injection amount based on the SO ₃ content is calculated Will be.

Here, the SO ₃ concentration (calculated value) in the combustion exhaust gas calculated from the difference between the total concentration of sulfur oxides and the measured SO ₂ concentration, and the combustion exhaust gas at the outlet of the air heater 14 are sampled. S in flue gas analyzed by analysis
The relationship with the O ₃ concentration (analytical value) is shown in FIG. As can be seen from FIG. 2, although the calculated value tends to be slightly higher than the analytical value, the calculated value and the analytical value show a clear linear relationship. Therefore, the amount of SO ₃ in the combustion exhaust gas can be accurately obtained by correcting with a constant proportional constant.

In controlling the amount of injected ammonia, SO ₃ in the combustion exhaust gas is usually about 20 to 200 ppm, but ammonia is uniformly mixed with the combustion exhaust gas in the flue for efficient removal of SO _3. It is desirable to do so. Thus, according to the present invention, the boiler 10
The amount of ammonia injected into the combustion exhaust gas can be controlled accurately according to the change in the SO ₃ concentration due to the change in the load of the fuel, and real-time control is possible, so that the amount of ammonia required for the reaction of SO ₃ can be smoked. Can be injected into the road.

The distance between the sampling pipe 34 and the injection pipe 36 communicating with the flue 32 (shown by A in the figure).
Are separated by about 1 m or more, so sampling pipe 3
Ammonia from the injection pipe 36 does not enter the 4 side, and the accuracy of SO ₂ concentration measurement by the SO ₂ automatic analyzer 26 is not reduced.

[0021]

As described above, according to the method for removing sulfur oxides in the combustion exhaust gas according to the present invention, ammonia is injected into the combustion exhaust gas according to the change in the SO ₃ concentration accompanying the load fluctuation of the boiler. Since the amount can be controlled accurately and in real time, troubles in the electrostatic precipitator can be prevented.

Further, since the amount of ammonia required for the reaction of SO ₃ can be injected, it is possible to suppress the excessive consumption of ammonia injection and reduce the running cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a flue gas treatment facility to which a method for removing sulfur oxides from combustion exhaust gas according to the present invention is applied.

FIG. 2 shows the total concentration of sulfur oxides calculated from the sulfur content of fuel and SO ₂ measured by an SO ₂ automatic analyzer.
Relationship between the SO ₃ concentration in the combustion exhaust gas calculated from the difference with the concentration (calculation value) and the SO ₃ concentration in the combustion exhaust gas analyzed by manual analysis of the combustion exhaust gas at the air heater outlet (analysis value)

[Explanation of symbols]

10 ... Boiler 12 ... Denitration device 14 ... Air heater 16 ... Electrostatic precipitator 18 ... Fan 20 ... Desulfurization device 22 ... Chimney 26 ... SO ₂ automatic analyzer 38 ... Valve 40 ... Ammonia tank 46 ... Computing unit 50 ... Boiler load signal

Claims (1)

[Claims] 1. A denitration device, an air heater, and an electrostatic precipitator are sequentially installed on the downstream side of the boiler, and ammonia is injected into a flue between the air heater and the electrostatic precipitator to discharge the ammonia from the boiler. In a method of removing sulfur oxides in combustion exhaust gas by reacting sulfur oxides in combustion exhaust gas with ammonia to remove sulfur oxides contained in the combustion exhaust gas from sulfur content in fuel used in the boiler. Calculate the total concentration or total amount, sequentially measure the concentration or amount of sulfur dioxide in the combustion exhaust gas in the flue between the air heater and the electrostatic precipitator, the total concentration or total amount of the sulfur oxides And controlling the amount of ammonia injected into the flue between the air heater and the electrostatic precipitator based on the difference between the concentration or amount of the sulfur dioxide. Method for removing sulfur oxide.