JPH08112515A - Dry desulfurizing and denitrifying method for removing sulfur oxide and nitrogen oxide in waste gas - Google Patents

Abstract

PURPOSE: To reduce the quantity of dust in waste gas fed into a dry desulfurizing/denitrifying device and to reduce driving power by recycling off gas into waste gas in the upstream side of an electrostatic precipitator. CONSTITUTION: Off gas containing SO2 and SO3 which have not been removed by a byproduct recovery device 11 is recycle-injected into inlet waste gas of an electrostatic precipitator 3. In this way, SO3 in the off gas is stuck on dust in waste gas and the dust is collected and removed by the electrostatic precipitator 3. Therefore, since the quantity of SO3 at the inlet of an adsorber 7 is remarkably decreased and the quantity of formed ammonium salt is decreased, the ammonium salt is prevented from being stuck and deposited on an inlet louver 13 to block a gas flow passage. Further, the electric resistance of the dust is lowered to improve dust collecting performance in the electrostatic precipitator 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to a dry desulfurization and denitration process for removing sulfur oxides contained in the exhaust gas from a boiler or the like (SO _X) and nitrogen oxides (NO _X).

[0002]

2. Description of the Related Art Exhaust gas containing SO _X and NO _X is led to a cross-flow type moving bed adsorption tower (hereinafter abbreviated as an adsorption tower) packed with a granular catalyst such as activated carbon, and SO _X and NO _X are granular. The catalyst is brought into contact with the catalyst, SO _x is adsorbed on the catalyst, and NO _x is N ₂
A dry desulfurization and denitration method for reducing and removing the above is conventionally known. The enhanced activity of the catalyst, in order to reduce a reaction or catalyst with NO _X is worn, it is also known to inject ammonia gas into the exhaust gas at the inlet of the adsorption tower. In these conventional desulfurization and denitration methods, as shown in FIG. 3, the exhaust gas from the boiler 1 is cooled by an air heater 2 and the dust in the exhaust gas is collected by an electric dust collector 3 and then passed through a blower 4 to obtain a dry desulfurization and denitration device. Introduced in 5. As shown in FIG. 4, the details of the dry desulfurization and denitration device are composed of an adsorption tower 7, a desorption tower 8, a conveyor 9 and an ammonia supply device 10. At the inlet of the adsorption tower 7, ammonia gas is injected into the exhaust gas. It is introduced into the adsorption tower. Then, the exhaust gas reacts with the activated carbon filled in the adsorption tower, so that the SO
_X is adsorbed on activated carbon in the form of ammonium sulfate,
O _X is reduced to N ₂ by a reduction reaction and becomes a gas from which SO _X and NO _X have been removed, and is emitted from the chimney 6. SO _X
The activated carbon adsorbing is taken out from the bottom of the adsorption tower 7 and carried into the desorption tower 8 by the conveyor 9. When the activated carbon descends in the desorption tower 8 and is heated to about 400 ° C., SO
_X is desorbed from the activated carbon, regenerates the activated carbon, and the desorbed gas becomes SO ₂ concentrated gas, which is guided to the byproduct recovery device 11 and is recovered as a byproduct (sulfuric acid or the like). However, a part of the off-gas from the by-product recovery device is recycled into the exhaust gas at the inlet of the adsorption tower 7 because some of it remains as SO ₂ and SO ₃ in the off-gas without being recovered. On the other hand, the activated carbon regenerated in the desorption tower 8 is separated into dust by a sieving machine 12, and then supplied from the top of the adsorption tower 7 into the adsorption tower 7 by a conveyor 9 for reuse.

[0003]

The conventional dry desulfurization and denitration method is performed as described above, but since the off gas is recycled into the exhaust gas at the inlet of the adsorption tower, the SO _{3 in} the off gas is ammonia. To produce an ammonium salt, which not only deposits and deposits on the flue but also deposits and deposits on the inlet louver 13 holding the activated carbon of the adsorption tower 7, blocking the gas flow path and causing pressure loss. There was a problem such as increasing. It is an object of the present invention to solve the above-mentioned problems and to reduce the amount of dust in the exhaust gas sent to the desulfurization and denitration apparatus to save the operating power of the equipment.

[0004]

Means for Solving the Problems After exhaust gas containing SO _X and NO _X discharged from a boiler or the like is dedusted by an electric dust collector, ammonia is injected into the exhaust gas and the gas is used as a granular catalyst such as activated carbon. Is introduced into the adsorption tower, the desulfurization and denitration reaction is carried out in the adsorption tower, and the granular catalyst in which SO _X is adsorbed is introduced into the desorption tower to desorb SO _X and the desorbed gas as a by-product. In a dry desulfurization denitration method in which a raw product recovery device collects by-products such as sulfuric acid and the off-gas from the by-product recovery device is recycled into the exhaust gas at the inlet of the adsorption tower, the injection point of ammonia into the exhaust gas and The off-gas injection location is upstream of the electrostatic precipitator.

[0005]

In the present invention, the off gas from the by-product recovery device 11 is recycled into the exhaust gas at the inlet of the electrostatic precipitator, so that SO _{3 in} the off gas adheres to the dust in the exhaust gas, and the dust is collected by the electrostatic collector. Since it is collected and removed by the dust device, the amount of SO _{3 at} the inlet of the adsorption tower 7 is significantly reduced, and the amount of ammonium salt produced by injecting ammonia is reduced, so that the ammonium salt adheres to the inlet louver 13. It is possible to suppress the accumulation and blocking of the gas flow path. Further, when the electric resistance value of the dust is high, SO ₃ adheres to the dust, so that the electric resistance value of the dust is lowered, and the dust collecting performance of the electric dust collector 3 is improved. Further, by changing the injection position of the ammonia gas from the inlet of the adsorption tower 7 of the dry desulfurization and denitration device 5 to the inlet of the electrostatic precipitator 3, an ammonium salt is generated in the preceding stage of the electrostatic precipitator, and the ammonium salt is generated. Since the ammonium salt is reduced in the dust at the inlet of the dry desulfurization and denitration apparatus because it can be removed by, the adhesion and deposition of dust in the adsorption tower of the apparatus hardly occur. Further, the halogen compound in the exhaust gas also reacts with ammonia to form an ammonium salt, which can also be removed by the electrostatic precipitator, so that dust is unlikely to adhere or accumulate in the adsorption tower.

[0006]

EXAMPLES Next, examples of the present invention will be described. FIG. 1 is a flowchart of the method of the present invention. The exhaust gas from the boiler 1 is about 140 at the air heater 2.
In order to collect the dust in the exhaust gas after cooling to ℃, it is introduced into the electrostatic precipitator 3. The exhaust gas dedusted by the electric dust collector 3 is guided by the blower 4 to the adsorption tower 7 of the dry desulfurization and denitration device 5. Is ammonia gas is injected into the exhaust gas at the inlet of the adsorber column 7, in the exhaust gas in the device 5 SO _X, N
O _x is removed and is emitted from the chimney 6. Then, the desorbed gas (SO ₂ concentrated gas) from the desorption tower 8 of the dry desulfurization and denitration device is guided to the byproduct recovery device 11 and recovered as a byproduct such as sulfuric acid. (Up to this point, it is the same as the known desulfurization and denitration method.) However, S that could not be recovered by the byproduct recovery device
The off gas containing O ₂ and SO ₃ is recycled and injected into the exhaust gas at the inlet of the electrostatic precipitator 3. By doing so, SO ₃ in the off-gas adheres to the dust in the exhaust gas, and the dust is collected and removed by the electrostatic precipitator 3, so the amount of SO _{3 at} the inlet of the adsorption tower 7 is greatly reduced. Since the amount of the produced ammonium salt decreases, it is possible to prevent the ammonium salt from adhering to and depositing on the inlet louver 13 and blocking the gas flow path. Further, when the electric resistance value of the dust is high, SO ₃ adheres to the dust in the form of sulfuric acid, so that the electric resistance value of the dust is reduced to a value suitable for the dust collecting property, and the dust collecting performance of the electric dust collector 3 is improved. Let

FIG. 2 is a flow chart of the method of the present invention. The present invention is the same as that of the first aspect of the invention except for the point of injecting the ammonia gas into the exhaust gas, and in this invention, the point of injecting the ammonia gas is the inlet of the electrostatic precipitator 3. According to this method, the ammonium salt is generated in the preceding stage of the electrostatic precipitator and can be removed by the electrostatic precipitator, so that the ammonium salt is reduced in the dust at the inlet of the dry desulfurization and denitration device, so It becomes difficult for dust to adhere and accumulate in the adsorption tower. Further, the halogen compound in the exhaust gas also reacts with ammonia to form an ammonium salt, which can also be removed by the electrostatic precipitator, so that dust adhesion and deposition are also less likely to occur.

[0008]

According to the present invention, it is possible to prevent ammonium salt from adhering to and depositing on the inlet louver 13 and blocking the gas flow path of the adsorption tower 7, and when dust has a high electric resistance value, it is collected. Electrostatic precipitator 3
The dust collection performance of can be improved. Further, by changing the injection position of the ammonia gas from the inlet of the adsorption tower 7 of the dry desulfurization and denitration device 5 to the inlet of the electrostatic precipitator 3, an ammonium salt is generated in the preceding stage of the electrostatic precipitator, and the ammonium salt is generated. Since the ammonium salt is reduced in the dust at the inlet of the adsorption tower because it can be removed by, the adhesion and deposition of dust on the louver at the inlet of the adsorption tower of the device are less likely to occur, and the pressure loss of the adsorption tower is reduced, The operating cost can be reduced. Furthermore, the halogen compounds in the exhaust gas also react with ammonia to form ammonium salts,
The same effect can be obtained such that this can be removed by the electrostatic precipitator.

[Brief description of drawings]

1 is a flow chart of the method of the invention as claimed in claim 1;

FIG. 2 is a flowchart of the method of the present invention.

FIG. 3 is a flowchart of a known dry desulfurization and denitration method.

FIG. 4 is a detailed explanatory view of a dry desulfurization denitration device and a by-product recovery device in FIG.

[Explanation of symbols]

 1 Boiler 2 Air heater 3 Electrostatic precipitator 4 Blower 5 Dry desulfurization denitration device 6 Chimney 7 Cross flow type moving bed adsorption tower 8 Desorption tower 9 Conveyor 10 Ammonia supply device 11 By-product recovery device 12 Sieve filter 13 Louver

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B01D 53/81 53/56 53/94 B01D 53/34 123 B 129 B 53/36 102 G

Claims (2)

[Claims] 1. An exhaust gas containing SO _X and NO _X discharged from a boiler or the like is dedusted by an electrostatic precipitator, ammonia is injected into the exhaust gas, and the gas is filled with a granular catalyst such as activated carbon. It is introduced into an adsorption tower, a desulfurization and denitration reaction is performed in the adsorption tower, and a granular catalyst having SO _X adsorbed therein is guided to a desorption tower to desorb SO _X, and the desorbed gas is a by-product recovery device. In the dry desulfurization and denitration method, in which the off-gas from the by-product recovery device is recycled to the exhaust gas at the inlet of the adsorption tower, the off-gas injection point is the exhaust gas upstream of the electrostatic precipitator. A dry desulfurization and denitration method characterized by being recycled into the inside. 2. An exhaust gas containing SO _X and NO _X discharged from a boiler or the like is dedusted by an electrostatic precipitator, ammonia is injected into the exhaust gas, and the gas is filled with a granular catalyst such as activated carbon. It is introduced into an adsorption tower, a desulfurization and denitration reaction is performed in the adsorption tower, and a granular catalyst having SO _X adsorbed therein is guided to a desorption tower to desorb SO _X, and the desorbed gas is a by-product recovery device. In a dry desulfurization and denitration method in which sulfuric acid is recovered as a by-product in the exhaust gas and the off-gas from the by-product recovery device is recycled into the exhaust gas at the inlet of the adsorption tower, the injection point of ammonia into the exhaust gas and the off-gas A dry desulfurization denitration method characterized in that the injection location is located upstream of the electrostatic precipitator.