STRATEGY FOR CONTROLLING NOX EMISSIONS AND AMMONIA SLIP IN AN SCR SYSTEM USING A NONSELECTIVE NOX/NH3 SENSOR

摘要

One aspect of the invention relates to controlling the ammonia feed rate to an SCR reactor (103) using a NOx sensor (113) cross-sensitive to ammonia. The sensor (113), positioned downstream of the reactor (103), 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 (107) enters into an ammonia slip recovery mode (58) 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.