JP3304613B2 - Method for removing sulfur oxides from flue gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates relates to a method for removing sulfur oxides in the combustion exhaust gas, in particular to a method for removing sulfur oxides in the combustion exhaust gas containing a large amount of SO _2.

[0002]

2. Description of the Related Art In a flue gas treatment facility of an oil-fired boiler, a denitration device, an air heater, an electric dust collector,
Desulfurizer is provided, in denitrator removes nitrogen oxides in the combustion exhaust gas of (NO _X), electrostatic in dust removes dust, desulfurization apparatus, sulfur oxides in the combustion exhaust gas (SO _X ) is to be removed.

[0003] A catalyst containing vanadium as a main component is used in the denitration apparatus, but this catalyst partially wears out due to passing gas and scatters and adheres to an air heater or the like on the downstream side. The denitration apparatus is operated at about 400 ° C. as a temperature suitable for the denitration reaction, and the inlet temperature of the air heater is also about the same. On the other hand, as a denitration method used in the production process of sulfuric acid or fuming sulfuric acid, there is a contact method. In this method, about 40
It is known that when a mixed gas of SO ₂ and oxygen is brought into contact with a platinum catalyst or a vanadium catalyst kept at 0 ° C., SO ₂ easily reacts with oxygen and is oxidized to SO ₃ .

When a fuel containing sulfur is burned in a boiler,
The sulfur content in the fuel is oxidized by the combustion in the boiler, resulting in SO ₂
And discharged from the boiler. When the SO ₂ passes through the denitration device or the air heater, the temperature of the denitration device or the air heater is about 400 ° C., and therefore, as described above, S 2 is generated by the catalyst in the denitration device or the catalyst attached to the air heater.
Converted to O ₃ .

[0005] Since this SO ₃ is partially mist near 150 ° C., which is the operating temperature of the electric precipitator, when it enters the electric precipitator, the discharge wire is enlarged and dust is not peeled off from the dust collecting electrode. Cause troubles. Therefore, in order to prevent this, ammonia is injected into the flue between the air heater and the electrostatic precipitator, converted into ammonium sulfate, and collected by the electric precipitator.

[0006] ammonia injection amount is set based on the concentration of SO ₃ is, SO ₃ is because it can not automatically analyze, the SO ₃ was collected as a mist in the air heater outlet, based on analysis values of which were manual analysis To determine the amount of ammonia injected.

[0007]

However, in this method, it takes several hours to determine the injection amount of ammonia from the measurement of SO ₃ . As a result, the boiler load changes and SO ₃
There is a problem that the injection amount of ammonia cannot be optimized with respect to the case where the generation amount of methane greatly fluctuates or the fluctuation at the time of normal steady load.

In addition, when the injection amount of ammonia is small, ammonium hydrogen sulfate is generated. Since the melting point of this ammonium hydrogen sulfate is about 150 ° C., which is close to the operating temperature of the electrostatic precipitator, ammonium hydrogen sulfate is produced. If there is too much, the adhesion of dust will increase, and the releasability of the dust from the discharge wire and the collection electrode in the electrostatic precipitator will worsen, resulting in enlargement of the discharge wire and poor dust removal from the collection electrode. There is a problem to cause. For this reason, conventionally, the injection amount of ammonia is set to SO
_At present, it is in excess of the amount required for the reaction with ₃ .

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and to remove sulfur oxides from exhaust gas by quickly responding to load fluctuations of a boiler and adjusting an ammonia injection amount to an optimum amount. Another object of the present invention is to provide a method for removing sulfur oxides in combustion exhaust gas, which can suppress excessive consumption of ammonia.

[0010]

According to the present invention, in order to achieve the above object, SO _{2 in} flue gas is converted into SO ₃ by a catalyst of a denitration device or a catalyst attached to an air heater. air heater was measured SO ₂ concentration at the outlet side, focusing on the point that it is possible to determine the concentration of SO ₃ which was converted by knowing the difference, autoanalyzer each SO ₂ concentration at the boiler outlet and the air heater outlet Etc.,
This is a method of removing SO _{3 in} combustion exhaust gas by controlling the injection amount of ammonia based on the difference value.

[0011]

According to the present invention, the difference between the values detected by the automatic analyzer such as the SO ₂ formed in the boiler outlet and the air heater outlet side corresponds to SO ₃ concentration, the air heater and an electric current based on the SO ₃ concentration Since it controls the amount of ammonia injected into the flue between the dust collectors, it is possible to optimize the reaction between SO ₃ and ammonia against fluctuations in SO ₃ due to fluctuations in boiler load. it can be efficiently removed sO ₃ from.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method for removing sulfur oxides from flue gas according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a system diagram showing one embodiment of the method for removing sulfur oxides in combustion exhaust gas of the present invention. The flue gas treatment system shown in FIG.
It comprises an air heater 14, an electric dust collector 16, a fan 18, a desulfurizer 20, and a chimney 22.

The SO ₂ analyzers 24 and 26 are respectively connected to a flue 28 connecting the boiler 10 and the denitration device 12, and are connected to a sampling pipe 30 for sampling exhaust gas, and a flue 32 connecting the air heater 14 and the electric dust collector 16. Samplink pipe 34 connected to sample exhaust gas
It is interposed in. A pipe 3 for injecting ammonia is located on the downstream side of the flue from a communication part between the air heater 14 and the sump pipe 34 of the flue 32 connecting the electric precipitator 14.
The pipe 36 is connected to an ammonia tank 40 via a valve 38. It is desirable that the distance (indicated by A in the figure) between the communicating portions of the sump link pipes 34 and the pipes 36 with the flue 32 be separated by about 1 m or more.

The SO ₂ analyzers 24 and 26 are electrically connected to a calculator 46 via output cables 42 and 44. The arithmetic unit 46 is electrically connected to the valve 38 via an output cable 48. The fan 18 is provided with a detector for detecting the number of rotations. Is output to the arithmetic unit 46 via the.

Next, the operation of the method for removing SO _{3 in} the flue gas configured as described above will be described. The flue gas discharged from the boiler 10 passes from the flue 28 and the flue 32 to the SO ₂ analyzer ₂ via the sump pipes 30 and 34, respectively.
Samples are partially sampled at 4, 26, and the respective SO ₂ concentrations are detected. The detection values (analysis values) of the SO ₂ analyzers 24 and 26 are transmitted to a calculator 46 via cables 42 and 44.
Further, a signal of the rotation speed of the fan 18 is transmitted to the arithmetic unit 46 via the cable 44. In the arithmetic unit 46, the SO ₂ analyzer 24 is used.
In the difference between the detected SO ₂ concentration has been SO ₂ concentration detected by the SO ₂ analyzer 26 is computed, also gas amount of the exhaust gas passing through the flue from the rotational speed of the fan 18 is calculated,
The injection amount of ammonia is calculated from the difference between the SO ₂ concentration and the gas amount. Based on the calculation result of the injection amount of ammonia, a signal is transmitted to the valve 38 via the cable 48, and the injection amount of ammonia is controlled by opening and closing the valve 38.

The difference in the SO ₂ concentration is determined by the difference between the S
Since it corresponds to the O ₃ concentration, the SO ₃ amount in the combustion exhaust gas is calculated from the SO ₃ concentration and the gas amount, and the ammonia injection amount is calculated based on the SO ₃ amount. Usually, the SO ₃ concentration in the combustion exhaust gas is about 20 to 140 ppm, and the actual amount of injected ammonia is preferably about 2.2 in equivalent ratio to SO ₃ . The pressure at the time of injecting ammonia is desirably substantially atmospheric pressure.

Further, the sump link pipe 34 and the pipe 36
The distance (indicated by A in the figure) between the communicating portions with the respective flue 32 is separated by about 1 m or more, so that ammonia from the pipe 36 does not enter the sample pipe 34, The detection accuracy of the SO ₂ concentration in the _two analyzer 26 is not reduced. In the above-described embodiment, in order to confirm that SO ₃ has been removed by the injection of ammonia, it can be determined from the NH ₄ and SO ₄ components in the collected dust. Of (NH ₄ ) ₂ SO ₄ and (NH ₄ ) HSO ₄
You can judge. That is, the higher the ratio of ammonium sulfate [(NH ₄ ) ₂ SO ₄ ] to ammonium hydrogen sulfate [(NH ₄ ) HSO ₄ ], the higher the SO ₃ removal rate.

In this embodiment, the SO ₂ concentration is automatically measured,
The injection of ammonia is automated on the basis of this analysis value, so that even if the amount of SO ₃ generated fluctuates according to the load fluctuation of the boiler, it is possible to always remove SO ₃ optimally.

[0019]

As described above, according to the present invention, the injection amount of ammonia can always be optimized in accordance with the amount of SO ₃ generated in response to the load fluctuation of the boiler, and the amount of ammonia used can be reduced. Can be planned.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a method for removing SO _{3 from} combustion exhaust gas according to the present invention.

[Explanation of symbols]

10 ... boiler 12 ... denitrator 14 ... air heater 16 ... electrostatic precipitator 18 ... fan 24 ... SO ₂ analyzer 26 ... SO ₂ analyzer 46 ... operator 40 ... ammonia tank

Continuation of the front page (56) References JP-A-2-265618 (JP, A) JP-A-59-160552 (JP, A) JP-A-63-175653 (JP, A) JP-A-63-111953 (JP) , A) JP-A-7-308601 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B03C 3/00-3/88

Claims (1)

(57) [Claims] 1. A denitration device, an air heater, and an electric precipitator are sequentially provided on the downstream side of a boiler. Ammonia is injected into a flue between the air heater and the electric precipitator to oxidize sulfur in the gas. In a method for removing sulfur oxides in flue gas by reacting with ammonia to remove substances, the SO ₂ concentration in the flue gas at the outlet side of the boiler and at the outlet side of the air heater is detected, and the value of each SO ₂ concentration is determined. A method for removing sulfur oxides from flue gas, comprising controlling an amount of ammonia injected into a flue between an air heater and an electrostatic precipitator based on the difference.