JPS6332494B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for treating coal-fired boiler exhaust gas in the order of highly dust-based denitrification, air preheating, and low-temperature dust collection. The present invention relates to a method for efficiently and economically removing ammonium compounds contained in the coal ash collected by the dust collector by preheating the coal ash collected by the dust collector while transporting it and introducing it into a decomposition furnace.

Exhaust gas from a coal-fired boiler is introduced in a highly dusty state to an ammonia catalytic reduction type denitrification device for denitrification, then the exhaust gas is introduced to an air preheater to preheat the combustion air, and then the exhaust gas is sent to a low-temperature electrostatic precipitator. When introducing the exhaust gas into a dust collector such as the
Ammonium compounds resulting from the reaction between leaked ammonia from the denitrification equipment and sulfur oxides (hereinafter referred to as SOx) contained in the exhaust gas are 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, countermeasures 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. There are problems 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 However, thermal decomposition of ammonium compounds requires quite high temperatures, and the supply of a heat source is therefore a major problem. It was hot.

The present invention was made as a result of intensive research by the present inventors in order to solve the _above -mentioned problems. The coal ash collected by the device is put into an ammonium compound pyrolysis furnace, and high-temperature combustion exhaust gas from a coal-fired boiler is blown into this decomposition furnace to bring it into solid-gas contact at a temperature of 250 to 700°C to remove the ammonium compounds in the coal ash. The cracked gas containing coal ash from the cracking furnace is introduced into a solid-gas separator, where the cracked gas and coal ash are separated.The coal ash is cooled with air in a cooler and then transported to an ash processing facility. After exchanging heat with high-temperature coal ash in the cooler, the heated air is blown into the coal ash transport pipe on the upstream side of the cracking furnace and used as air for feeding the ammonium-containing coal ash into the cracking furnace and air for preheating the ammonium-containing coal ash. By returning the cracked gas from the gas separator to the front of the denitration equipment and reusing it as a _NH3 source,
The present invention aims to provide an efficient method for removing ammonium compounds from coal ash that can save energy in a closed system without requiring any other heat source for thermal decomposition of ammonium compounds.

Hereinafter, the configuration of the present invention will be explained based on the drawings. The drawing shows an example of a device for carrying out the method of the present invention, which includes a denitration device 2 in which the exhaust gas duct of a coal-fired boiler 1 is filled with an ammonia catalytic reduction denitration 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 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 filtration and dust collectors, multi-cyclones, bag filters, etc. 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 an ammonium compound thermal decomposition furnace 13 via an ash hopper 12, and an upper part of this decomposition furnace 13 is connected to a coal ash and cracked gas discharge pipe 14. It is connected to a solid-gas separator 15 consisting of a multi-cyclone, a bag filter, a gravel type filtration and dust collector, or a combination thereof. Solid gas separator 1
The cracked gas outlet of No. 5 is connected to the upstream side of the denitrification device 2 via a cracked gas pipe 16, and the coal ash outlet of the solid-gas separator 15 is connected to a cooler 18 which is cooled by air via a coal ash transport pipe 17. The coal ash outlet of this cooler 18 is further connected to ash processing equipment 21 via a coal ash transport pipe 20. In addition, a high-temperature combustion exhaust gas pipe 22 is connected to the upstream or downstream side of the economizer 8 of the boiler, and this exhaust gas pipe 22 is connected to the cracking furnace 1.
Connect to the bottom of 3. It is preferable that the cracking furnace 13 employs a fluidized bed, a transport bed, a spouted bed, or the like. Note that an auxiliary exhaust gas heating furnace 23 may be connected to the exhaust gas pipe 22 to raise the exhaust gas temperature to a desired temperature when the exhaust gas temperature is low. 24 is a cooling air supply pipe for supplying cooling air to the cooler 18 that cools the coal ash, and 25 is a heating air pipe for extracting heated air by exchanging heat with the high-temperature coal ash in the cooler 18. Then, this heated air pipe 25 is connected to the decomposition furnace 13.
It is connected to the coal ash transport pipe 11 on the upstream side, and configured to transport ammonium-containing coal ash using heated air, preheat it, and charge it into the decomposition furnace 13.

In the device configured as described above, coal-fired boiler exhaust gas is denitrified with high dust content, air preheated, and
When processing with a system consisting of low-temperature dust collection and desulfurization, the dust collector-collected coal ash containing ammonium compounds discharged from the dust collector 4 is fed into the ammonium compound thermal decomposition furnace 13 via the ash hopper 12. High-temperature combustion exhaust gas from the coal-fired boiler 1 is introduced as a heat source to the decomposition furnace 13, and the ammonium compound is thermally decomposed at a temperature of 250 to 700°C, preferably 350 to 700°C, and more preferably 350 to 500°C. Coal ash and cracked gas after pyrolysis are transferred to solid-gas separator 1
5, and the cracked gas is returned to the front of denitrification equipment 2.
Reuse as _NH3 source. Coal ash goes to cooler 18
After being cooled with air at the ash processing facility 21, the ash is transported to the ash processing facility 21. After heat exchange with high temperature coal ash in cooler 18
Air heated to around 200 to 500°C is blown into the coal ash transport pipe 11 on the upstream side of the cracking furnace 13, and is used as a source for transporting ammonium-containing coal ash. Since the ammonium compound-containing coal ash is transported using heated air in this way, the coal ash can be preheated during transportation, and the heated air and high-temperature combustion exhaust gas collide in the cracking furnace 13 to mix the coal ash. , the dispersion is improved, and the coal ash is uniformly dispersed, making it suitable for thermal decomposition. Therefore, the decomposition furnace can be made compact.

As explained above, according to the method of the present invention, the ammonium compounds contained in the coal ash collected by the dust collector can be thermally decomposed extremely efficiently, and the cracked gas from the ammonium compound thermal decomposition furnace can be The high-temperature combustion exhaust gas within the system can be reused as a _source of decomposition heat, and the high-temperature combustion exhaust gas within the system can be used without requiring a source of decomposition heat outside the system. Therefore, it is possible to save energy in a closed system, and the processing Since there is almost no effect on other exhaust gas treatment configuration technologies such as an increase in system volume, there are effects such as stable coal-fired boiler exhaust gas treatment.

[Brief explanation of the drawing]

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...scorch device, 5...heat exchanger, 6...desulfurization device, 7...chimney, 8...coal economizer,
10...Ammonia supply pipe, 11, 17, 20...
... Coal ash transport pipe, 12 ... Ash hopper, 13 ... Ammonium compound pyrolysis furnace, 14 ... Coal ash/cracking gas discharge pipe, 15 ... Solid gas separator, 16 ... Cracking gas pipe, 18 ... Cooler, 21... Ash processing equipment, 22... High temperature combustion exhaust gas pipe, 23... Auxiliary furnace for heating exhaust gas, 24... Cooling air supply pipe, 25
...Heated air pipe.

Claims (1)

[Claims] 1 Coal-fired boiler exhaust gas is introduced in a highly dusty state to an ammonia catalytic reduction type denitrification device for denitrification, then the exhaust gas is introduced to an air preheater to preheat the combustion air, and then the exhaust gas is passed to a low-temperature dust collector. In the method of introduction and dust removal, the coal ash collected by the dust collector containing ammonium compounds resulting from the reaction between leaked ammonia from the denitrification equipment and sulfur oxides in the exhaust gas is introduced into an ammonium compound pyrolysis furnace. At the same time, high-temperature combustion exhaust gas from a coal-fired boiler is blown into this decomposition furnace and brought into solid-gas contact to decompose ammonium compounds in the coal ash.
The cracked gas containing coal ash from the cracking furnace is introduced into a solid-gas separator to separate the cracked gas and coal ash.The coal ash is cooled with air in a cooler and then transported to an ash processing facility. The heated air that has undergone heat exchange with the high-temperature coal ash is blown into the coal ash transport pipe on the upstream side of the cracking furnace and used as air for charging the ammonium-containing coal ash into the cracking furnace and as air for preheating the ammonium-containing coal ash.
A method for removing ammonium compounds from coal ash, characterized in that the cracked gas from the solid-gas separator is returned to the front of the denitrification device and reused as an ammonia source.