?（SCR=selective catalytic reduction）

Theories:

SCR is a means of converting nitrogenoxides, also referred to as NO_x with the aid of a catalyst intodiatomic nitrogen (N₂) and water. The catalyst used is typicallyaqueous ammonia or urea.

SCR is reduction of NO_x underrelatively low temperature (300~450℃). A gaseousreductant is absorbed on the catalyst. NO_x is removed when the fluegas passes through the catalyst chamber. SCR is shown to reduce NO_xby at least 85%. As a mature NO_x removing method, it is typicallyfound on power plants in China and abroad.

Process flow:

Boiler  ammonia injection nozzles  aqueous ammonia storage  vaporizer   pressure accumulator   mixer  SCR reduction module   airheater   forced draft fan   ESP   induced draft fan    stack   desulfurization   booster fan

Formulas:

4NO+4NH₃+O₂=4N₂+6H₂O

2NO₂+4NH₃+O₂=3N₂+6H₂O

?

Features:

     1.Complicatedstructure, but operates conveniently.

     2.Fewmoving components, high reliability.

     3.Noside reaction consuming catalyst.

     4.HighNOx reduction: 80%~90%.

     5.Highinvestment cost.

SNCR：

     In SNCR, NH₃ and urea areinjected into the boiler to react with NO_x without catalyst.Therefore, reductant should be injected at the high temperature zone, where is850~1100℃. NH₃ reacts rapidly with NO_x to produce N₂and H₂O. The boiler is the reactor for this method.

Features:

     1.Low total cost of ownership—investment& maintenance cost;

     2.High-efficiency NO_xremoval, 50-70%;

     3.Take up small space;

     4.No catalyst used;

     5.to different coalcategory.

Process flow: