Step One
- 1. Step One (SNSCR)
- The first stage to be implemented in many applications is SNCR. In the SNCR process, ammonia is injected into the boiler, where it reacts with oxygen and NOx to form nitrogen and water. About 46-50% of the NOx can be removed. The advantages of SNCR are its simplicity and low capital cost compared to SCR.
- However, optimal SNCR efficiency has a narrow temperature window, when boiler temperatures are about 1600 to 2000oF (870 to 1090oC). At temperatures above this range, NOx conversion and ammonia utilization decrease. At lower temperatures, ammonia slips through unreacted. This ammonia slip is unacceptable in a stand-alone SNCR system, but is not a concern in Wahlco's staged system because it is itself used as the reducing agent in the SCR process.
- SNCR is a well-proven technology, successfully used in many industrial and utility applications in the United States and Europe. Unfortunately, SNCR by itself is not sufficient to meet most local regulations. However, Wahlco has adapted it for effective staged NOx reduction. SNCR provides sufficient NOx. reduction to permit the use of a smaller SCR system.
