(194d) Challenges in SCR Operation

Selective Catalytic Reduction (SCR) systems are becoming more common as environmental regulations apply to more and more sources. To achieve desired results, a fundamental understanding of the SCR system and its limitations is needed. Mathematically, most process parameters are measured directly and then used to calculate the values that have permitted limits. Ammonia slip is often a calculated value using a material balance. A stack test is used to verify actual values. Any biases in the system are absorbed into a D-factor. These biases will likely be different in different modes of operation. Physically, the requirement to meet emission limits may lead to a design with operational challenges. This paper will explore the learnings of SCR operation: sensitivity of various inputs on the ammonia slip in different modes of operation, common errors with the calculations, dynamic effects, and industry trends that are addressing operational issues.