Steam Purity Monitoring Using Statistical Process Control

Abstract

Steam purity and steam quality must be controlled to minimize degradation of geothermal steam turbines. Poor steam purity and quality may be the result of inadequate separation and scrubbing systems, sub-optimal operating practices, or upset conditions during operational transitions. All operators monitor chemical indicators of steam purity by taking steam samples at regular intervals near the turbine inlet. Any deviation from the normal is explained by deviations in operating conditions. We have experimented with a statistical approach, borrowed from the discipline of experimental design and process control that required acquiring all operational data corresponding to the steam purity data from the turbine and statistically determining the optimal combination of operating parameters.

Such experiments were run at Satellite Station 4 (SS-4) in the Mak-Ban Geothermal Field and not surprisingly, running steamwash at a high rate was the single major factor in maintaining high steam purity. The other operational parameters shown to significantly affect steam purity were separator level and separator pressure. When all these three operational parameters were controlled within the recommended limits, chloride readings never exceeded 0.1 ppm in the power plant