Process gases containing acid gases are generated in many industrial processes. Such an industrial process may be the combustion of a fuel such as coal, oil, peat, waste, etc., in a combustion plant such as a power plant, whereby a hot process gas or “flue gas” is generated containing pollutants including acid gases. The process gas needs to be treated for removal of at least a portion of the acid gases. Such treatment may be provided in a wet scrubber such as disclosed in EP 0 162 536. The disclosed wet scrubber comprises an absorption liquid, which is brought into contact with the process gas to absorb at least a portion of the acid gases. For example, the absorption liquid may be atomized through nozzles to react with the process gas.
The treatment process may be controlled based on a feedback of information concerning the status of the treatment process. Such information may include measured properties of the absorption liquid. A common manner of controlling a wet scrubber is to measure the pH level in the absorption liquid and thereby provide information that may be used for controlling the supply of fresh absorbent, such as limestone, to the absorption liquid.
However, measurements of the pH level in an absorption liquid are not reliable. The pH measurement is a difficult procedure that may provide unreliable information on the properties of the absorption liquid. This reduces the accuracy of the control of the treatment process and the efficiency of the wet scrubber.
Consequently, there is a need for a more reliable measurement of the properties of an absorption liquid in a gas cleaning device for controlling the treatment process of cleaning a process gas.