Temperature Raise Control of Super Critical Boiler Using Derivative Digital Filter

Summary

A DDC algorithm for raising the temperature of water wall outlet fluid of super critical boilers at the start up is proposed and some results of its implementation to a super critical boiler for the test purpose are presented.

Because of radical change of the constant-pressure specific heat of water through the transition zone at the start up of these type boiler, the range of variation in the dynamics is very large. Thus in order to raise it on the desired rate the algorithm proposed in this paper composes two parts: one is the feed-forward part which is product of preset raise rate and a constant, and the other is feed-back part which is product of another constant and the raise rate approximated by the output of derivative filter.

These constants are estimated by off-line identification of the boiler dynamics using a few observed variables.

Derivative filter is realized as a finite impulse response digital filter and its characteristics is designed in the frequency domain.

By using this filter the useful changes of the temperature for the raise control was extracted and smooth control performance was also proved.