Abstract: In an absorption tower of a wet lime-gypsum process desulfurization plant which desulfurizes an exhaust gas by bringing an incoming exhaust gas into contact with an absorbent liquid circulated therethrough by means of a plurality of pumps, an optimum pH value of the absorbent liquid and an optimum number of working pumps are set according to an amount of an exhaust gas load of the absorption tower, and a feed rate of the absorbent liquid and a number of working pumps are controlled on the basis of these set values. According to one mode of embodiment of the invention, a variation rate of the exhaust gas load and a desulfurization ratio are detected, and when the amount of exhaust gas load is constant or rising and also the desulfurization ratio is lower than a desired desulfurization ratio, the number of working pumps is correctively increased.

Abstract: A tri-electrode probe consisting of a central electrode and a pair of measuring electrodes on the opposite sides of the central electrode disposed so as to symmetrically cover an immaginary surface having a plane of symmetry, is connected to a measuring system including minute current ammeters and a variable D.C. voltage source, the tri-electrode probe is positioned at a measuring point within an electric field where both positive and negative ions coexist as oriented in such direction that the plane of symmetry is directed in perpendicular to the direction of the electric field with one of the measuring electrodes opposed to a negative ion source and the other measuring electrode opposed to a positive ion source, a current flowing through the minute current ammeter connected to the central electrode is made substantially zero by varying the voltage of the variable D.C.