Drum level control device null of exhaust heat recovery

摘要

PURPOSE: To save can water blow at the time of swelling of boiler start by inserting a differentiator for drum level detection signal, a function generator for correcting the differentiation signal and an adder for adding the correction signal and a drum set signal between a drum level detector and a comparator. CONSTITUTION: Since daily start/stop operation is always hot start, a low level signal setter 11 selects a low level set signal when gas is conducted. Level fluctuation increases abruptly when swelling is started and a differentiator 24 produces a differentiation signal 25 and a function generator 26 produces a correction signal 27 which is provided as a bias signal to an adder 28. A drum level set signal 19 becomes a the differentiation signal 25 from a drum level detection signal 20 and the bias signal of the correction signal 27. Since the signal 20 is higher than the set signal 19, a can water reduction valve 8 opens to blow can water to the outside of system. When inclination in the drum level fluctuation disappears, the signal 27 goes zero and the control set signal of the valve 8 becomes the set signal 19 thus ending can water blow to the outside.