Application of Optimal Periodic Control Theory to Catalytic Denitrification Control of Refuse Incinerator Plant

Abstract

Aiming to reduce consumption amount of ammonia (NH₃), which is blown into the catalytic denitrification process of the refuse incinerator plant, application of the periodic control method has been studied.
Through a step response examination in an actual plant, remarkable process dynamic characteristics have been observed: namely, that time-constant (T_u) of blowing in NH₃ is smaller than (T_d) of blowing off.
Applying the optimal periodic control theory to the process, the following analytical results are obtained: (i) Optimal bang-bang type periodic control of NH₃ blowing is more effective in reducing NH₃ consumption than optimal continuous steady state control, and (ii) The NH₃ consumption reduction rate depends on the T_d/T_u ratio and the ζ parameter (ζ=aimed denitrification rate/process capable denitrification rate)
Because the theoretical solution of the optimal control period is approximately zero, a practical finite periodic control has been examined on an actual catalytic denitrification process. Results of the examination have shown that the NH₃ reduction level is acceptable but lower than the theoretical value.
In actual plants, because of wide fluctuation of nitrogenoxide (NO_x) generation, simple periodic control cannot maintain exhaust NO_x concentration under the required NO_x concentration for a long time. The periodic control with feedback correction of control timing has been proposed and demonstrated to be effective by simulation.