JPS6135893B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention uses ash containing a compound of NH ₃ and sulfuric acid, such as NH ₃ obtained by collecting dust from ash in coal combustion exhaust gas.
This relates to the treatment of ash containing a compound of NH 3 and sulfuric acid (hereinafter referred to as NH ₃ sulfate).

Coal combustion exhaust gas contains nitrogen oxides, ash, and sulfur oxides. To prevent pollution, denitrification, dust collection, and desulfurization equipment will be installed. For denitrification, a catalytic reduction method using NH ₃ as a reducing agent is used. In this case, approximately 5 to 20 ppm of NH ₃ remains in the exhaust gas after denitrification. Further, the exhaust gas contains 10 to 20 ppm of sulfuric anhydride and ash content of several g/Nm ³ to several tens of g/Nm ³ .

Heat is recovered from the exhaust gas from denitrification using an air heater to bring the temperature down to about 200°C or less, and then dust is collected using an electrostatic precipitator.

Below this temperature, NH ₃ and sulfuric anhydride in the exhaust gas condense, producing sulfates of NH ₃ (ammonium sulfate, acidic ammonium sulfate, etc.), which adhere to the ash and are collected by an electrostatic precipitator.

Ash with NH ₃ sulfate adhering to it poses a major problem in which conventional usage and disposal methods cannot be applied.

In order to use the above ash as a raw material for fly ash cement, if it is mixed with Portland cement to make fly ash cement, the free lime of the cement will be mixed with water and mixed at the site where it is used.
The sulfate of NH ₃ reacts to form gypsum and liberate NH ₃ , causing NH ₃ odor pollution in the working environment.

On the other hand, when dumping or landfilling, a similar reaction occurs due to the elution of alkaline content contained in the ash itself.
Causes pollution problems.

In order to solve the above problems, the present invention aims to
A new method for removing NH ₃ and an apparatus for carrying out the method are proposed. The present invention separates the exhaust gas from the inlet of the economizer of the boiler and converts the high-temperature gas into _NH3.
The boiler outlet and the denitrification device inlet are connected to each other, and an air heater and an electric precipitator are arranged in this order on the downstream side of the denitrification device in the flow direction of the boiler exhaust gas. The outlet for the ash collected by the dust collector is communicated with the ash treatment reactor through a pipe line for introducing ash, and a portion of the high temperature boiler exhaust gas on the upstream side of the denitrification device is extracted and transferred to the ash treatment reactor. The present invention is characterized in that a pipe line is provided that leads to the ash treatment reactor, and a pipe line that returns the treated exhaust gas treated in the ash treatment reactor to the upstream side of the denitrification device inlet. By heating the ash with boiler exhaust gas at 350-450°C, the sulfate of _NH3 is thermally decomposed and becomes sulfuric anhydride and _NH3 . Sulfuric anhydride reacts with alkaline components such as calcium in the ash to form gypsum, which is fixed in the ash. NH ₃ becomes a gas and is included in the exhaust gas, and NH ₃ is removed from the ash. The exhaust gas containing NH ₃ is returned to the boiler exhaust gas at the inlet of the denitrification equipment.

According to the present invention, since NH ₃ is not contained in the treated ash, the above-mentioned secondary pollution does not occur. Furthermore, since boiler exhaust gas is used for heating in the present invention, no new fuel is required. further separated and removed
NH ₃ gas can be used as an ammonia source for denitrification, and there is no need to clean up after exhaust gas.

Denitrification equipment removes nitrogen oxides from boiler exhaust gas. It adds NH ₃ to the boiler exhaust gas in an amount equivalent to the nitrogen oxides in it, causes a catalytic reaction between nitrogen oxides and NH ₃ , and removes nitrogen. This is a device that converts oxides into nitrogen and water and removes nitrogen oxides.

The NH ₃ generated by ash treatment is returned to the main exhaust gas and used for denitrification.

Furthermore, since the heat contained in the treated exhaust gas is returned to the main exhaust gas, the heat is ultimately recovered by the air heater, resulting in less heat loss.

Next, the present invention will be specifically explained based on an embodiment example shown in FIG.

The coal-fired boiler exhaust gas treatment system according to the present invention includes a boiler 1, a denitration device 2, an air heater 3, an electrostatic precipitator 4, and a denitration device 5.

The NH ₃ sulfate-adhered ash is collected by an electrostatic precipitator 4 and sent to an ash treatment reactor 6. A portion of the boiler exhaust gas 8 is bypassed and supplied to the ash treatment reactor 6 .

The ash treatment reactor 6 is a kiln-type or pneumatic conveyance-type gas-solid reactor, and heat and mass transfer are performed therein. The temperature of boiler exhaust gas is about 350 to 450°C.
The temperature of the ash is about 100℃. In the ash processing equipment, the ash is heated to 300℃ by boiler exhaust gas.
That's all. At the same time, the sulfate of _NH3 is thermally decomposed,
NH ₃ is dissipated into the exhaust gas, and sulfuric anhydride becomes gypsum.

Exhaust gas containing NH ₃ is shown in Figure 9. The treated exhaust gas 9 is
The temperature reaches 300°C, and if necessary, dust is collected using a cyclone (not shown) and returned to the inlet of the denitrification equipment. The NH ₃ -free ash 10 is discharged from the ash treatment device.

Experimental Example An experiment was conducted using the apparatus shown in Figure 1 to treat ash obtained from coal-fired boiler exhaust gas.

Ash at 110℃ contains 0.2wt% of NH ₃ as ammonium sulfate.

NH ₃ and SO ₃ at the air heater outlet were 10 ppm and 20 ppm, respectively.

The above ash was supplied to a kiln with a diameter of 2 m and a length of 6 m at a rate of 50 Kg/hr, and the boiler exhaust gas at 450°C was fed at a rate of 300 Nm ³ /hr.
hr supplied. A cyclone was installed at the kiln outlet to collect the scattered ash. As a result of analyzing the ammonium sulfate concentration in the collected ash, the ammonium sulfate concentration was 0.004 to 0.006 wt%. The residual rate of NH ₃ was 2-3%.

Effects of the present invention By bypassing the exhaust gas at the inlet of the denitrification equipment, NH ₃ sulfate-adhered ash could be treated.

Since there is little residual NH ₃ in the treated ash, there is no problem with post-treatment. The treated NH ₃ is used for denitrification. Because exhaust gas is used as the heating source, utility costs are saved and no secondary pollution occurs.

[Brief explanation of the drawing]

The figure is a block diagram showing an example of an embodiment of the present invention. 1...Boiler, 2...Denitration device, 3...Air heater, 4...Electrostatic precipitator, 5...Desulfurization device, 6
...Ash treatment reactor, 7... _NH3 sulfate adhering ash,
8...Boiler exhaust gas, 9...Processed exhaust gas containing _NH3 , 10...Ammonia-free ash.

Claims (1)

[Claims] 1. Ash containing a compound of NH ₃ and sulfuric acid is heated with high-temperature gas at the inlet of a boiler economizer to thermally decompose adhering ammonium salts and obtain a gas containing NH ₃ .
The gas is returned to the inlet of the denitrification device.
Method for processing ash containing compounds of NH ₃ and sulfuric acid. 2. The boiler outlet and the denitrification equipment inlet are communicated, and an air heater and an electrostatic precipitator are arranged in order on the downstream side of the boiler exhaust gas flow direction of the denitrification equipment, and the ash discharge port and the ash collected by the electrostatic precipitator are arranged in order. The processing reactor is connected to the ash processing reactor through a pipe line that leads ash, and a pipe line is provided to extract a part of the high temperature boiler exhaust gas upstream of the denitrification device and lead to the ash processing reactor, An ash processing device characterized in that a pipe line is provided for returning the treated exhaust gas to the upstream side of the denitrification device inlet.