Patent ID: 6029100
Filing Date: 2000-02-22
Classification: B01D,Y10S

Abstract:
A method for controlling oxidation in flue gas desulfurization which comprises bringing a flue gas into contact with an absorbent liquid containing a calcium compound for removal of at least sulfur dioxide from the flue gas, while maintaining a concentration of sulfurous acid in the absorbent liquid within a low level range close to zero by a feed back control process, comprising continuously detecting a flow rate of an oxidation-reduction potential of the absorbent liquid and increasing or decreasing a flow rate of an oxygen-containing gas to be blown into the absorbent liquid so that the detected oxidation-reduction potential matches a predetermined target (oxidation reduction potential (ORP)) value, wherein when the flow rate of the oxygen containing gas is to be incrcased, a proportional sensitivity in the feed back control process, which determines a control input, F1, for regulating the flow rate of the oxygen-containiing gas based on a deviation obtained from a difference between the target (ORP) value and a detected (ORP) value, is increased depending on the increase of the deviation in a region where the detected (ORP) value is below the target (the predetermined ORP target value) in correspondence with a characteristic change of the oxidation-reduction potential against the concentration of sulfurous acid, wherein the control input, F1, is given by the equation (4) as follows: ##EQU4## wherein K is the proportional gain or sensitivity and .epsilon. is the final deviation, TI is an integer time and TD is a differentiation time, and wherein K of equation (4) is calculated from a deviation .epsilon.1 obtained by reversing the polarity of .epsilon. and utilizing equation (5) to obtain a computational intermediate sensitivity KA, to wit; ##EQU5## wherein a, b and m are constants, wherein the intermediate sensitivity KA is used to form a computational intermediate sensitivity KB and the proportional sensitivity K is obtained by multiplying KB by a proportional coefficient KO.