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FLUE GAS DENITRIFICATION PLANT (De-NOxPLANT)

1. GeneralNOX is health hazardous chemical ingredient, same as SOX, environmental

restriction on NOX has been stringent and most of coal fired power plant in J apan there dayshave come equipped with low NOX burners and de-NOX plant. NOX is classified into two

categories; one type of NOX is mostly fuel NOX and the other is originated from Nitrogen inair, which is called thermal NOX. Nearly 95% of NOX is believed to be NO. Nitrogen contentof the coal less than 2.0% dry ash free basis is acceptable to most coal fired power stations inJ apan these days.

NOX(P

PM)

Thermal NOX

Thermal NOXChinese Coal

Domestic Coal

200

150

100

50

1100 1500 1600140013001200

Furnace Temperature (oC)

It is generally noted that NOX under the furnace temperature of less than 1400

oC is

considered fuel NOX and 25% 30% of NOX under the furnace temperature of above1600

oC is considered thermal NOX.

50

100

150

200

0.0 1.0 2.0 3.0 4.0 5.0

Fuel Ratio (Fixed Carbon/Volatile Matter)

NOX(ppm)

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Graph above shows the relationship between NOX level and Fuel Ratio with differentNitrogen content at constant furnace temperature of 1350

oC. It should be appropriate

interpretation that NOX level has something to do with Nitrogen content of the coal, but at thesame time NOX level has also something to do with fuel ratio as well. Graph above clearlyillustrates that higher the fuel ratio higher the NOX level regardless of nitrogen content of thecoal.

2. Low NOX burner (Nozzle)Basic principle of Low NOX burner is to minimize NOX generation during combustion bychanging concentration of coal particles in primary air at each burner using thecharacteristic that either ban concentration or dense concentration would normally giveless NOX generation.

3. De-NOX plantBasic principle of de-NOX plant is that NO is to be converted to N2 and H2O usingammonia gas (NH3) and its chemical reaction (reduction) is as follow :

4 NO +4 NH3 + O2Catalyst

4 N2 + 6 H2O

NO + NO2 + 2 NH3Catalyst

2 N2 +3 H2O

NH3 in liquid form is vaporized then injected into flue gas. Type of catalysis being used isnormally porous ceramic mainly made of Aluminum and Titan.

4. Location of De-NOX planta. De-NOX plant is installed after economizer where flue gas temperature would

normally be 300oC~400

oC. Flue gas after de-NOX plant is then cooled down by air

heater to approximately 150oC and goes to low temperature ESP.

NH3 150oC

Low Temperature ESP

De-NOX AH De-SOXESP

Boiler

300o~400oC

b. Low dust De-NOX plantFlue gas from economizer goes to high temperature ESP in the first place where mostof dust are collected under the temperature of 360

oC~400

oC, then flue gas containing

100~300 mg/Nm3

dust goes to De-NOX plant where NO reduction takes place underthe temperature of 300oC~400oC. No recovery efficiency would be approximately80%.

High Temperature ESP

De-NOX AH De-SOXESP

Boiler

300o~400oC

360oC~400oCNH3