Strategy for controlling NOx emissions and ammonia slip in an SCR system using a nonselective NOx/NH3

摘要

One aspect of the invention relates to controlling the ammonia feed rate to an SCR reactor using a NOx sensor cross-sensitive to ammonia. The sensor, positioned downstream of the reactor, is interrogated by introducing a pulse in the ammonia feed rate. A positive response to a positive pulse indicates ammonia slip. A negative response to a positive pulse indicates NOx breakthrough. Another aspect of the invention related to a combination of feed-back and feed-forward control. Upon detecting ammonia slip, the controller enters into an ammonia slip recovery mode in which the ammonia feed rate is reduced for a period to restore the reactor's ammonia or NOx buffering capacity. After the recovery period, feed-forward control is restored, optionally with an updated control objective. A further aspect of the invention relates to a learning probabilistic model for feed-forward control trained according to the occurrence or non-occurrence of NOx breakthrough and ammonia slip.