Selective Non-Catalytic Reduction (SNCR)
The SNCR + SCR Hybrid system utilizes the advantages of the SNCR system as well as those of the SCR concept.
The objective of the hybrid system is to allow the SNCR section to operate at the top of the optimum curve to achieve maximize possible NOx removal, while NH3 slip is purposely kept high.
The excessive NH3 slip allows for the installation of an SCR catalyst layer downstream, however, as a relatively high NOx removal efficiency is already being achieved by the upstream SNCR section (compared with conventional SNCR system), a significantly lower NOx removal efficiency is required by the SCR section.
Advantages of the hybrid system
An SNCR + SCR Hybrid system can be the ideal solution in applications where there is a need for a high NOx reduction but where there are space limitations and economical constraints (CAPEX & OPEX).
With a lower NOx removal efficiency required in the SCR section, the required catalyst volume can be significantly lower compared with a conventional SCR system. The ability to install a significantly lower catalyst volume provides additional benefits such as a smaller SCR reactor housing and less supporting structural steelwork.