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SCR (Selective Catalytic Reduction) technology for denitrification

SCR (Selective Catalytic Reduction) technology reduces NOx in flue gas to nitrogen and water by allowing reducing agent NH3 to selectively react with NOx in flue gas under the effect of catalyst. Its reactor is located between the outlet of boiler economizer and the inlet of air preheater, with effective reaction temperature ranging from 320℃ to 400℃. The most commonly used chemical reactant (reducing agent) is ammonia.

With its maximum denitration efficiency more than 90%, the SCR technology for denitration is the most mature and reliable denitration technology. The key to this technology lies in controlling NH3 escape rate and SO2 conversion rate while guaranteeing denitration efficiency to ensure the SCR system runs safely and stably.

I. Reaction principle

Chemical reaction equation under SCR condition

4N4NH3+4NO+O2=4N2+6H2O

It also removes NO2 under the effect of appropriate catalyst:

4NH3+2NO2+O2=3N2+6H2O

6NO2+8NH3→7N2+12H2O

Catalyst is the core and key to the entire SCR system. Its design and selection depends on flue gas condition and components. Its design is affected by three interactional factors: NOx removal rate, NH3 escape rate and catalyst volume. Catalyst is of three major forms: plate type, honeycomb type and corrugated plate type.

II. Process flow diagram

III. Features of SPC's SCR technology for flue gas denitration

(1) This technology offers a set of effective catalyst selection methods for key parameters of different projects including flue gas composition and dust content. By optimizing catalyst selection, it extends the service life of catalyst and prevents dust accumulation on the catalyst as well as reducing system resistance.

(2) A number of EPC projects involving this technology give us abundant experience in steel structure design, construction and erection management.

(3) We have developed a set of SCR process calculation software based on longtime research on reaction principle, process calculation and configuration of the denitration system.

(4) On the basis of numerical simulation of the system, optimized design of flue arrangement, deflector arrangement, ammonia homogenization device and ammonia-air mixer has improved the system's reaction efficiency and reduced ammonia consumption.


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