Special Report No. 76-06: An Investigation of H2S and SO2 Calibration Cylinder Gas Stability and Their Standardization Using Wet Chemical Techniques

The definition of sample integrity of TRS compounds during the collection and transfer of samples in source gas monitoring systems has been a problem of long standing. A reliable source of stable reduced sulfur calibration gas suitable for use at the mill level to determine sample integrity and calibrate sensors has also been needed if the quality of TRS monitoring is to be significantly upgraded. The attached Special Report is based on an investigation of the stability of hydrogen sulfide (H2S) and sulfur dioxide (SO2) calibration gases stored in specially treated aluminum cylinders.  It showed that H2S stored in air and H2S stored in nitrogen both have the necessary stability, if stored in the special cylinders, to satisfy the calibration needs of source gas monitoring systems. Laboratory investigations were conducted and suitable wet chemical analytical procedures selected, for use at the mill level in the routine periodic recalibration of the cylinder gases. These procedures were demonstrated to be adequately sensitive for calibration of systems used for monitoring at well controlled recovery furnace systems. Similar investigations and findings were made regarding SO2. Procedures have also been developed for integrating the use of these cylinder gases in routine sampling system sample integrity determinations and for sensor calibration. The cost for setting up a gas sample handling and sensor calibration system is about $900, of which $350 is for the laboratory cylinder gas recalibration setup and $550 for the monitoring system calibration setup. The moderate initial equipment cost, and relatively small amount of time required for cylinder gas recalibration and weekly monitoring system calibration, make it possible to upgrade and maintain most existing TRS monitoring systems at a level which would significantly improve the quality of monitoring data now generated. Those mills now operating and those planning TRS monitoring systems should include this or another system calibration scheme of equal quality at the earliest time.