JPH0156818B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for treating coal-fired boiler exhaust gas in the order of high-dust denitrification, air preheating, and low-temperature dust collection. Ammonium compounds contained in coal ash are introduced into the ash processing pipe, and high-temperature combustion exhaust gas from a coal-fired boiler is blown into the ash processing pipe to thermally decompose the ammonium compounds in the coal ash while transporting them within the ash processing pipe. The present invention relates to a method that allows ammonium compounds to be removed efficiently and economically, and that allows for a compact device.

[Conventional technology]

The exhaust gas from the coal boiler is introduced in a highly dusty state into an ammonia catalytic reduction type denitrification device to remove NOx, 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 electrostatic precipitator. When the exhaust gas is introduced into a dust collector such as a machine to remove dust, and then the exhaust gas is introduced into a desulfurization equipment for desulfurization treatment, the ammonia leaked from the denitrification equipment and the sulfur oxides (hereinafter referred to as SOx) contained in the exhaust gas are removed. ) is contained in the coal ash collected by the dust collector. This ammonium compound is expected to have an adverse effect not only on ash processing equipment but also on the dumping and utilization of coal ash. Of course, the reduction of leaked ammonia from the denitrification equipment is being considered, but the current results are insufficient, and therefore measures against ammonium compounds are needed.

The ammonium compounds contained in the coal ash collected by the dust collector are mainly (NH ₄ ) ₂ SO ₄ and NH ₄ HSO ₄
It exists in the form of Possible methods for removing ammonium compounds from coal ash include water washing and thermal decomposition. The water washing method has high solubility of ammonium compounds such as ammonium sulfate in water, and is expected to have a high removal rate.However, since the coal ash after treatment contains a large amount of water, it is difficult to use the coal ash effectively. This method has disadvantages such as the need to treat wastewater containing _NH3 (denoted as NH3). On the other hand, thermal decomposition of ammonium compounds proceeds 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 [Problem to be solved by the invention] However, thermal decomposition of ammonium compounds does not require significantly high temperatures. Therefore, a large amount of heat source had to be supplied.

At present, there is no practical technology for removing ammonia from coal ash other than thermal decomposition, and at decomposition temperatures of 350 to 700°C,
The present inventors have found that the process is completed within a residence time of several seconds to several tens of seconds at most.

On the other hand, ash handling is carried out by pneumatic transportation, and although the air used for transportation is currently at room temperature, the time required for pressure transportation is generally slightly longer than the time required for the deammonification reaction. be. Furthermore, since coal ash is generated in large quantities and requires mass processing, it is desirable that the pyrolysis furnace be compact.

In view of these points, the present invention was made based on the above knowledge, and by blowing high-temperature combustion exhaust gas into the ash treatment pipe to perform deammonia, it is possible to remove ammonium compounds without seeking other sources of thermal decomposition. , and without installing a large ammonium compound pyrolysis furnace, i.e., the ash treatment pipe plays the role of a pyrolysis furnace, making it possible to save energy in a closed system, which is more efficient and economical than coal ash. An object of the present invention is to provide a method for removing ammonium compounds.

[Means for solving problems]

In order to achieve the above object, the method for removing ammonium compounds from coal ash according to the present invention involves introducing coal-fired boiler exhaust gas in a highly dusty state into an ammonia catalytic reduction type denitrification device 2, as shown in the drawing. In this method, 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 coal ash collected by the dust collector containing ammonium compounds resulting from the reaction with sulfur oxides in the coal ash is introduced into the ash processing pipe 12 of the pneumatic conveyance type, and
High-temperature combustion exhaust gas from the coal-fired boiler 1 is blown into the ash processing pipe 12 to transport the coal ash and bring it into solid-gas contact to thermally decompose ammonium compounds in the coal ash. The cracked gas containing coal ash is introduced into the solid-gas separator 13 connected to the end of the ash processing pipe 12 to separate the cracked gas and coal ash, and the coal ash is cooled in the cooler 17 and then transferred to the ash processing equipment 20. The structure is such that the cracked gas is returned to the denitrification equipment and reused as an ammonia source.

[Effect]

The coal ash collected by the dust collector containing ammonium compounds discharged from the dust collector 4 is transferred to the coal ash transport pipe 1.
At the same time, the high-temperature combustion exhaust gas from the coal-fired boiler 1 is introduced into the ash processing pipe 12, and the coal ash is brought into solid-gas contact while being conveyed, and the ammonium compounds in the coal ash are heated. Let it break down. Coal ash and cracked gas after pyrolysis are transferred to solid-gas separator 1
3, and the cracked gas is returned to the front of denitration equipment 2.
Reuse as _NH3 source. Coal ash goes to cooler 17
After being cooled at the ash processing facility 20, the ash is transported to the ash processing facility 20.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. The drawing shows an example of a device for carrying out the method of the present invention, which includes a denitrification device 2 in which the exhaust gas duct of a coal-fired boiler 1 is filled with an ammonia catalytic reduction type denitrification catalyst in a moving bed type or fixed bed type, and an air preheater. 3. A dust collector 4 such as an electrostatic precipitator, a heat exchanger 5, a desulfurization device 6, and a chimney 7 are connected in series. Instead of an electrostatic precipitator, the dust collector may be 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. Filtration and dust collection equipment, multi-cyclone,
It is also possible to use a bug filter or the like.
Reference numeral 8 designates a economizer provided in the boiler, and reference numeral 10 designates an ammonia supply pipe connected to the upstream side of the denitrification device.

A coal ash transport pipe 11 connected to the lower part of the dust collector 4 is connected to one end of an ash processing pipe 12, and the other end (end) of this ash processing pipe 12 is a multi-cyclone, bag filter, or a combination thereof. It is connected to a solid-gas separator 13 consisting of, etc.
The cracked gas outlet of the solid-gas separator 13 is the cracked gas pipe 14
The lower part of the solid-gas separator 13 is connected to the intermediate tank 15.
Furthermore, the lower part of the intermediate tank 15 is a coal ash transport pipe 16.
is connected to the cooler 17 via the cooler 17.
The coal ash outlet of is connected to ash processing equipment 20 via a coal ash transport pipe 18. In addition, a high-temperature combustion exhaust gas pipe 21 is connected to the upstream or downstream side of the economizer 8 of the coal-fired boiler 1, and this exhaust gas pipe 21 is connected to the ash processing pipe 1.
Connect one end of 2. Note that an auxiliary exhaust gas heating furnace 22 may be connected to the exhaust gas pipe 21 so as to raise the exhaust gas temperature to a desired temperature when the exhaust gas temperature is low.

In the device configured as described above, coal-fired boiler exhaust gas is subjected to high nitrogen denitrification, air preheating,
When processing with a system consisting of low-temperature dust collection and desulfurization, the coal ash collected by the dust collector containing ammonium compounds discharged from the dust collector 4 is fed into the ash processing pipe 12 via the coal ash transport pipe 11, and this High-temperature combustion exhaust gas from the coal-fired boiler 1 is introduced into the ash processing pipe 12, and the coal ash is transported and brought into solid-gas contact to thermally decompose ammonium compounds in the coal ash. The temperature inside the ash processing tube 12 is 250 to 700°C,
Preferably 350~700℃, more preferably 350~
The temperature is adjusted to 500℃. In order to achieve sufficient solid-gas contact within the ash processing tube 12, the ash processing tube 12 must be longer than a certain degree. The coal ash and cracked gas after pyrolysis are separated in the solid-gas separator 13, and the cracked gas is returned to the front of the denitrification device 2 to become NH ₃
Reuse as a source. The coal ash is cooled in a cooler 17 and then transported to an ash processing facility 20. Note that air is used as a transport source in the coal ash transport pipes 11, 16, and 18. In this case, it is possible to use either a pressure feeding type or a suction type, but it is more suitable to use a pressure feeding type.

In carrying out the method of the invention, readsorption of stripped NH ₃ is very likely to occur;
It is necessary to perform at least solid-gas separation at 250°C or higher. Therefore, it is essential in the method of the present invention that the solid-gas separation step is followed by the cooling step.

Furthermore, since the exhaust gas after pyrolysis contains water vapor, this water vapor is likely to be adsorbed by the ash, and problems such as sticking may occur during ash storage in the ash processing equipment 20. This tendency is particularly noticeable with deammoniated ash, so by cooling the ash after solid-gas separation, handling troubles during pressure transportation can be avoided, and the ash can be made into a grade that can be used effectively. becomes possible.

Furthermore, by configuring the pressure transport time to be slightly longer than the deammonification reaction time, the thermal decomposition temperature can be lowered to 250°C or higher, compared to the conventional 350°C or higher.

〔Effect of the invention〕

As described above, the present invention thermally decomposes ammonium compounds in coal ash while transporting coal ash within the ash processing pipe, so the ash processing pipe plays the role of an ammonium compound thermal decomposition furnace, and a large ammonium A compound thermal decomposition furnace is not required, and the installation area is reduced accordingly, and the entire device is made more compact and inexpensive. In addition, since a cooling process is provided after the solid-gas separation process, it is possible to prevent NH ₃ from being re-adsorbed into the ash and from sticking to the ash, and the resulting ash can be effectively used as it is. can.

As explained above, according to the method of the present invention, ammonium compounds contained in coal ash collected by a dust collector can be thermally decomposed extremely efficiently and inexpensively, and the decomposed gas can be recycled as an NH ₃ source in the denitration equipment. The high-temperature combustion exhaust gas within the system can be used without requiring a decomposition heat source outside the system, making it possible to save energy in a closed system and increase the amount of gas to be processed. Since this method has almost no effect on other exhaust gas treatment configuration technologies, such as stable coal-fired boiler exhaust gas treatment, it is effective.

[Brief explanation of drawings]

The drawing 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, 16, 1
8...Coal ash transport pipe, 12...Ash processing pipe, 13...
... solid gas separator, 14 ... cracked gas pipe, 15 ... intermediate tank, 17 ... cooler, 20 ... ash processing equipment, 21 ... high temperature combustion exhaust gas pipe, 22 ... auxiliary furnace for heating exhaust gas.

Claims (1)

[Claims] 1 Coal-fired boiler exhaust gas in a highly dusty state is introduced into an ammonia catalytic reduction type denitrification device 2 for denitrification, then the exhaust gas is introduced into an air preheater 3 to preheat combustion air, and then the exhaust gas is passed through a low-temperature dust collector. In the method of removing dust by introducing it into the device 4, the coal ash collected by the dust collector containing ammonium compounds resulting from the reaction between the leaked ammonia from the denitrification device 2 and the sulfur oxide in the exhaust gas is transported by a pneumatic transport method. The coal ash is introduced into the ash processing pipe 12, and high-temperature combustion exhaust gas from the coal-fired boiler 1 is blown into the ash processing pipe to transport the coal ash and bring it into solid-gas contact to thermally decompose the ammonium compounds in the coal ash. The cracked gas containing coal ash from the ash processing pipe 12 is introduced into the solid-gas separator 13 connected to the end of the ash processing pipe to separate the cracked gas and coal ash, and the coal ash is passed through the cooler 17. A method for removing ammonium compounds from coal ash, which comprises transporting the coal ash to an ash processing facility 20 after cooling, and returning the decomposed gas to the front of the denitrification device 2 to reuse it as an ammonia source.