JPS6357095B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for treating coal-fired boiler exhaust gas in the order of high-dust denitrification, air preheating, and low-temperature dust collection. The present invention relates to a coal ash processing method that efficiently and economically removes black coal ash whose main components are ammonium compounds and unburned carbon contained in the coal ash.

[Conventional technology]

When treating coal-fired boiler exhaust gas with a technically and economically superior high-dust system of denitrification, air preheating, and low-temperature dust collection, combustion of coal types with a high fuel ratio (fixed carbon/volatile matter) and two-stage combustion are recommended. Black coal ash, which is mainly composed of unburnt carbon, generated by implementing combustion measures to reduce nitrogen oxides (NOx) such as combustion and exhaust gas mixing, and the reaction between leaked ammonia from the denitrification equipment and sulfur oxides (SOx) in the exhaust gas. The ammonium compounds responsible are contained in the coal ash collected by the dust collector. In normal ash processing at coal-fired power plants, coarse powder is dumped, and fine powder is sold as fly ash and used in cement admixtures.

[Problem that the invention seeks to solve]

However, when black coal ash is generated, it cannot be sold as a product, so the entire amount must be dumped, which poses a problem. In addition, ammonium compounds generate ammonia odor and elute ammonia into water systems, so
Negative effects are expected when dumping and using coal ash.

The main component of black coal ash contained in coal ash is unburned carbon, and in addition to unburned carbon, Fe ₃ O ₄ is thought to be the cause of blackening. Unburned carbon and Fe ₃ O ₄ can be removed by combustion at a high temperature of 500°C or higher as shown in the following equation.

C+O ₂ →CO ₂ 4Fe ₃ O ₄ +O ₂ → 6Fe ₂ O ₃ On the other hand, ammonium compounds are (NH ₄ ) ₂ SO ₄ ,
It is contained in the form of NH ₄ HSO ₄ and can be removed by washing with water or thermal decomposition. The water washing method focuses on the high solubility of ammonium compounds such as ammonium sulfate in water, and is expected to have a high removal rate.
Since treated coal ash contains a large amount of water, it is difficult to commercialize coal ash, and there are also problems such as the generation of ammonia odor and the elution of ammonia into water. On the other hand, the thermal decomposition of ammonium compounds occurs at
It progresses quantitatively at temperatures above 300°C according to the following formula.

(NH ₄ ) ₂ SO ₄ →NH ₃ +NH ₄ HSO ₄ NH ₄ HSO ₄ →NH ₃ +SO ₃ +H ₂ O However, the burning of black coal ash and the thermal decomposition of ammonium compounds require high temperatures, and the supply of this heat source is It was a big problem.

The present invention was made as a result of intensive research by the present inventors in order to solve the above-mentioned problems. Focusing on the fact that most of the coal ash is contained in fine powder, in the method of treating coal-fired boiler exhaust gas by high-dust denitrification and low-temperature dust collection, black coal ash and coal ash collected by a dust collector containing ammonium compounds are used. First, it is put into a classifier and classified into fine powder containing ammonium compounds and coarse powder containing black coal ash such as unburned carbon. After solid-gas separation, it is commercialized as flyash, and the cracked gas containing ammonia is reused as an ammonia source for the denitrification equipment.
The purpose of the present invention is to provide a coal ash processing method that can effectively utilize coal ash by efficiently and thermoeconomically removing black coal ash and ammonium compounds by calcining and decolorizing at a temperature of ~1100°C. It is something.

[Means for solving problems]

In order to achieve the above object, the coal ash processing method of the present invention, as shown in the drawing, introduces coal-fired boiler exhaust gas in a highly dusty state into an ammonia catalytic reduction type denitrification device 2 to denitrify it, Next, the exhaust gas is introduced into the air preheater 3 to preheat the combustion air, and then the exhaust gas is introduced into the low-temperature dust collector 4 for dust removal. The ash is charged into a classifier 11 and classified into fine powder containing ammonium compounds and coarse powder containing black coal ash such as unburned carbon, and the fine powder is transferred to an ammonium compound pyrolysis furnace 12.
At the same time, high-temperature combustion exhaust gas is blown into this cracking furnace 12 and brought into solid-gas contact at a temperature of 300 to 500°C to decompose ammonium compounds in the fine powder, and the cracked gas containing coal ash from the cracking furnace 12 is After solid-gas separation, the cracked gas containing ammonia is returned to the front of the denitrification equipment and reused as an ammonia source, while the classified coarse powder is fed into the decolorization furnace 16 and
It is fired and decolored at a temperature of 1100℃.

[Effect]

The exhaust gas from the coal-fired boiler 1 is introduced in a highly dusty state to the ammonia catalytic reduction type denitrification device 2 to be denitrified, and then the exhaust gas is introduced to the air preheater 3 to preheat the combustion air, and then to the low-temperature dust collector. It is introduced into the device 4 to remove dust. Black coal ash generated in coal-fired boiler 1 and denitration equipment 2
The coal ash collected by the dust collector, which contains ammonium compounds generated by the reaction between leaked ammonia and SOx in the exhaust gas, is collected by a classifier such as an air classifier 1.
Fine powder containing an ammonium compound is added to 1,
It is classified into coarse powder containing black coal ash such as unburned carbon. Ammonium compound thermal decomposition furnace 12
At the same time, high-temperature combustion exhaust gas is blown into the decomposition furnace 12 and brought into solid-gas contact at a temperature of 300 to 500°C to thermally decompose ammonium compounds in the fine powder.

Next, the cracked gas containing coal ash from the cracking furnace 12 is introduced into the solid-gas separator 14 for solid-gas separation, and then the cracked gas containing ammonia is returned to the front of the denitrification device 2 and reused as an ammonia source. The coal ash separated by the solid-gas separator 14 is transported to an ash cooling facility via the ash cooler 15 and is effectively used as fly ash. On the other hand, the coarse powder classified by the classifier 11 is put into the decolorization furnace 16, where the black coal ash is calcined and decolorized at a temperature of 500 to 1100°C, and then transported to the ash processing equipment via the ash cooler 17 for effective use. be done.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. Fig. 1 shows an example of an apparatus for carrying out the method of the present invention. A preheater 3, a dust collector 4 such as an electrostatic precipitator, a heat exchanger 5, a desulfurizer 6, and a chimney 7 are connected in series. Instead of an electrostatic precipitator, the dust collector is replaced by another device, such as a gravel type, in which a granular filter material such as sand, gravel, or ceramics is movably filled between supports such as louvers, wire mesh, or punched metal. It is also possible to use filter dust collectors, multi-cyclones, bag filters, etc. Reference numeral 8 designates an economizer provided in the boiler 1, and reference numeral 10 designates an ammonia supply pipe connected to the upstream side of the denitrification device.

The exhaust gas from the coal-fired boiler 1 is introduced in a highly dusty state to the ammonia catalytic reduction type denitrification device 2 to be denitrified, and then the exhaust gas is introduced to the air preheater 3 to preheat the combustion air, and then to the low-temperature dust collector. It is introduced into the device 4 to remove dust. In the coal-fired boiler 1, a type of coal with a high fuel ratio is burned,
When NOx reduction combustion measures are taken, such as two-stage combustion or exhaust gas mixing, black coal ash, which is mainly composed of unburned carbon, is produced. This black coal ash and the coal ash collected by the dust collector containing ammonium compounds produced by the reaction between leaked ammonia from the denitrification equipment 2 and SOx in the exhaust gas are fed into a classifier 11 such as an air classifier to collect ammonium compounds. It is classified into fine powder containing black coal ash and coarse powder containing black coal ash such as unburned carbon. The fine powder is put into the ammonium compound pyrolysis furnace 12, and high-temperature combustion exhaust gas is blown into the decomposition furnace 12 to
The ammonium compound in the fine powder is thermally decomposed by solid-gas contact at a temperature of 350 to 450°C. As the ammonium compound pyrolysis furnace 12,
Air flow conveyance types such as spouted bed, fluidized bed, and transport bed are used. The heat source of the ammonium compound pyrolysis furnace 12 is the high-temperature combustion exhaust gas before or after the economizer 8 of the coal-fired boiler 1, or the high-temperature combustion exhaust gas that has been further heated in the auxiliary combustion furnace 13 (hot air generation furnace), or hot air. High-temperature combustion exhaust gas from only the generation furnace 13 and/or high-temperature exhaust gas from a decolorization furnace (described later) is used. Next, decomposition furnace 1
The cracked gas containing coal ash from No. 2 is transferred to a solid-gas separator 14.
After solid-gas separation, the cracked gas containing ammonia is returned to the front of the denitrification device 2 and reused as an ammonia source. As the solid-gas separator 14, an electrostatic precipitator, a bag filter, the above-mentioned gravel filter dust collector, a multi-cyclone, etc. can be used.
It is preferable to use a gravel filtration device. The coal ash separated by the solid-gas separator 14 is transported to an ash cooling facility via the ash cooler 15 and is effectively used as fly ash. On the other hand, the coarse powder classified by the classifier 11 is fed into the decolorization furnace 16.
The black coal ash is calcined and decolorized at a temperature of 500 to 1100°C, preferably 700 to 900°C, and is transported to an ash processing facility via an ash cooler 17 for effective use. As the decolorizing furnace 16, an air flow conveyance type furnace such as a spouted bed, a fluidized bed, a transport bed, a kiln type furnace, etc. are used.The decolorizing furnace 16 is heated by installing a burner 20 in the decolorizing furnace and using fuel. A method of directly combusting the decolorizing furnace, a method of connecting a hot air generating furnace 21 to the decolorizing furnace and supplying high-temperature combustion exhaust gas, and/or a method of supplying high-temperature combustion exhaust gas of the coal-fired boiler 1 as it is, etc. are used. Since black coal ash is fired at a very high temperature, it is also possible to utilize and recover the exhaust heat by inputting the exhaust gas after firing and solid-gas separation into an ammonium compound thermal decomposition furnace. Further, as the ash coolers 15 and 17, it is desirable to use fluidized bed type coolers in order to recover waste heat. Decolorization furnace 16
Since a large amount of heat is generated by burning the black coal ash, this heat is recovered by the fluidized bed type ash cooler 17.

〔Effect of the invention〕

As explained above, according to the method of the present invention, the black coal ash and ammonium compounds contained in the coal ash collected by the dust collector can be removed very efficiently, and the cracked gas can be used as an ammonia source for the denitration equipment. It has the following effects: it can be reused as coal ash, it can save energy as a whole, and it can contribute to the effective use of coal ash.

[Brief explanation of the drawing]

FIG. 1 is a systematic explanatory diagram showing an example of an apparatus for carrying out the method of the present invention. 1...Coal-fired boiler, 2...Denitration equipment, 3...
... Air preheater, 4 ... Dust collector, 5 ... Heat exchanger, 6 ... Desulfurization device, 7 ... Chimney, 8 ... Carbon economizer, 10 ... Ammonia supply pipe, 11 ... Classifier, 12... Ammonium compound thermal decomposition furnace, 13
... auxiliary combustion furnace (hot air generating furnace), 14 ... solid-gas separator,
15... Ash cooler, 16... Decolorization furnace, 17... Ash cooler, 20... Burner, 21... Hot air generating furnace.

Claims (1)

[Claims] 1 Coal-fired boiler exhaust gas in a highly dusty state is introduced into an ammonia catalytic reduction type denitrification device for denitrification, then the exhaust gas is introduced into an air preheater to preheat the combustion air, and then the exhaust gas is sent to a low-temperature dust collector. In the method of introducing dust removal, coal ash collected by a dust collector containing black coal ash and ammonium compounds is fed into a classifier to separate fine powder containing ammonium compounds and coarse coal ash containing black coal ash such as unburned carbon. The fine powder is charged into an ammonium compound thermal decomposition furnace, and high-temperature combustion exhaust gas is blown into the decomposition furnace to cause solid-gas contact at a temperature of 300 to 500°C to decompose the ammonium compounds in the fine powder. After separating the cracked gas containing coal ash from the cracking furnace into solid and gas, the cracked gas containing ammonia is returned to the front of the denitrification equipment and reused as an ammonia source, while the classified coarse powder is fed into the decolorization furnace. A coal ash processing method characterized by firing and decolorizing at a temperature of ~1100℃.