Combined heat and power plants – efficient energy generation and clean emissions

Ammonia slip refers to ammonia that passes through the SCR catalyst unused and is released into the environment with the exhaust gas. It occurs when more reducing agent is dosed than can react with nitrogen oxides on the catalyst. Causes include overdosing, uneven distribution of the reducing agent across the exhaust gas cross-section, exhaust gas temperatures that are too low, rapid load changes or a catalyst whose activity has declined. Ammonia slip is undesirable for several reasons: ammonia is itself an air pollutant, it can form deposits in combination with sulphur compounds, and it means unnecessary consumption of urea solution. It can be avoided with load-dependent dosing control, a sufficient mixing section upstream of the catalyst, an appropriate catalyst design and regular checks of the dosing equipment. In addition, a downstream oxidation catalyst can convert remaining ammonia. If your measurement reports show ammonia or your urea consumption is rising, send us the data so that we can assess the dosing and catalyst condition together with you.