I. Introduction

The dust of the flue gas produced in coal-fired boiler is removed by the electric or bag dust collector. After reaching standard, the above flue gas containing sulphur is fed into the absorption tower by the induced draft fan. Several layers of high-pressure water mist combined spray heads are installed in the tower. The high pressure water (ammonia water) pumped by the high reassure pump from the ammonia water tank in the absorption tower is sprayed out by the spray heads. Then in the absorption tower, the rising original flue gas encounters the water mist sprayed downward at high speed and the gas, liquid and solid contact sufficiently. The SO_x and NO_x will react with the ammonia water as following:

(1) SO₂+H₂O+2NH₃+1/2O₂=(NH₄)₂SO₄   

 (2) 2(NH₄)₂SO₃+SO₃+H₂O=(NH₄)₂SO₄+2NH₄HSO₃

(3) 4NH₃+2NO+O₂→6H₂O+3N₂             

(4) 4NH₃+2NO₂+O₂→6H₂O+3N₂

In the absorption tower, the resultant from the reaction of flue gas and absorption solution is fed into thickener after oxidation and crystallization, dried after separated by separator, and finally made into the ammonia fertilizer (ammonia sulfate). While the filter liquor flows back to the ammonia water tank and mixed with the concentrated ammonia water to a certain concentration for cyclic utilization; the flue gas will be discharged into the air from the chimney after its water of super saturation removed with mist eliminator. 

If the dust collection effect of the dust collector in the previous stage is poor, in order to produce high quality fertilizer, a high-pressure water mist dust scrubber special for refined dust collection can be added. The water mist sprayed form the above tower doesn’t contain the desulphurization and denitration agent like ammonia water. The high-pressure water mist can realize the desulphurization and denitration and reduce the emission of ammonia to adapt to the increasingly high environmental protection requirements. The process requires that the prophase dust collection must reach standard, then the high quality nitrogenous fertilizer can be obtained; or the nitrogenous fertilizer quality will be affected. 

II. Process Technical Indexes：

1.Desulphurization Efficiency（SO₂ Reduction Rate）：≧99.5%

2.Denitration Efficiency（NO_x Reduction Rate）：≧50%

3. NH₃ Escapement Rate：≧15 mg/Nm³

4.Hot State Resistance:≦1200 Pa