The Measurement of SO2 Concentration in Flue Gases Using Ionization Techniques

The recent concern with the problem of SO2 removal from flue gases has indicated that a need exists for some type of inexpensive yet reasonably accurate instrument to be used as a stack monitor for coal-fired power stations. This paper describes work that was carried out to demonstrate the feasibility of such an instrument based upon the fact that SO2 gas has a very strong affinity for free electrons. This property enables the SO2 concentration to be related to the current flowing in a specially designed ionization chamber that may use either a corona or a radioactive emitter as the ionization source. When used in a differential mode, it is possible to separate interfering effects caused by the broad range of variables encountered in flue gas, such as temperature, gas composition, fly ash, etc. Results are presented showing that excellent sensitivity is obtained in the crucial concentration range of < 1500 parts per million (ppm) SO2 and that the resulting instrument should be ideally suited to direct monitoring of flue gases.