The Selective Non-Catalytic Reduction system is a proven technology to that converts NOx into N2 and H2O by injection reagents at high temperature without the need of a catalyst. The system can achieve surprisingly high reduction rates without the use of additional catalyst provided the process offers the correct temperature range.
In an SNCR, the reagents, typically aqueous ammonia or urea are injected directly into the existing flue gas duct or fire box using water as a carrier in order to cover the entire cross section in the correct temperature range.
The SNCR is the simplest and most economical form of NOx-reducing technology and is best suited for applications where a modest NOx reduction of 30-40% is required together with tight schedules and limited plot space where the flue gas temperatures are high enough (1650°F-2000°F) to promote the reactions. The SNCR can be further used in combination with a SCR system where the ammonia slip is used in a downstream SCR bed, so called “slip barrier”.
SNCR is the reaction of ammonia releasing reduction agents (ammonia water or carbamin) with nitrogen monoxide (NO) and nitrogen dioxide (NO2) at temperatures of usually 850-1050°C directly into the firebox and according to the following overall reaction:
or
2NH3 + 2NO + 1/2O2 → 2N2 + 3H2O
Spraying nozzles are injecting the NH3-Water solution into the flue gas. The water will evaporate and leave the gaseous NH3 to react with the NOx.
Advantages: The lances are not inside of the furnace / flue gas duct and remain protected in vicinity of the wall. Retrofit easily possible.
Disadvantages: NH3 distribution difficult to predict. Large quantities of water are required, leading to loss of energy.
Equipment Features
NOx Reduction with Few Components
“Easy” Technology
Rapid Installation
No Operating Costs or Expensive Catalyst to Replace
Very High Reduction Rates in Appropriate Conditions