Feedback control method in v-shaped characteristic system, and NH3 injection rate control method for NOx removal apparatus using the same

摘要

The present invention relates to an NH3 injection rate control technique for suppressing an NOX concentration to below a desired NOX concentration through the use of an NH3 injection rate reaching a minimum. In the NH3 injection rate control method for an NOX removal apparatus according to the invention, an operating area of the NOX removal apparatus is divided into a first area (I) in which a molar ratio (K', 240) of an NH3 injection rate (210) with respect to an NOX flow rate (204) at an inlet of the NOX removal apparatus is smaller than a molar ratio (K0) at a minimum point where an NOX concentration (PV, 221) assumes a minimum value and a second area (II) in which the molar ratio (K', 240) is equal to or larger than the minimum point molar ratio (K0), and a virtual NOx concentration (231) with respect to the molar ratio (K', 240) is set according to a virtual characteristic line which varies monotonically to stride across a desired operating point without rising with an increase of the molar ratio (K',240) from the first area (I) to the second area (II). Moreover, feedback control is implemented for adjusting the NH3 injection rate (210) with respect to the NOX flow rate (204) on the basis of a deviation between a desired NOX concentration (SV, 222) and the virtual NOX concentration (231) in a direction that the virtual NOX concentration (231) is brought close to the desired NOX concentration (SV, 222).