Improving Gas Dehydration Using Pre-Inhibited Glycol

Abstract

Abstract A report is presented on natural gas dehydration performance of dehydration units in two different plants using a pre-inhibited glycol/antifoam/pH adjuster blend versus neat glycol with periodic injection of anti-foam and pH adjuster inhibitors. To investigate the effect of using pre-inhibited glycol, two plants, each containing two gas dehydration trains (modules) were utilized such that while one train employed neat glycol with periodic chemical injection, the other employed the pre-inhibited blend with both trains running simultaneously. The two facilities were selected based on their history of poor dehydration and glycol regeneration performance and internal corrosion while using neat glycol. Performance was assessed based on resulting gas dew point, dissolved iron content, pH stability and glycol loss rate (in form of top-up frequency). In all four KPIs selected for this study, the pre-inhibited blend out performed its counterpart significantly despite initial concerns that the fixed inhibitive properties of the blend may not be robust enough to address varying operational conditions. Glycol loss rates decreased by 67% and this led to a corresponding reduction in operating cost. Gas dew point was further depressed by more than 5°C thereby restoring the two facilities to within gas export specifications in compliance with Gas Sales Agreements (GSA). pH stability remained within the buffered zone of 8.5 – 10. As evinced by the decreased loss rates, foaming did not occur at this pH range as opposed to typical experience with neat glycol. Corrosion, being inherently more chronic than acute was not measured in this trial, although there was a progressive decrease in dissolved iron content with the pre-inhibited blend. These results imply that not only can dehydration performance be increased and operating costs decreased, but also that the traditional installation of pH adjuster and antifoam injection skids may prove unnecessary for future facilities The insights made with this new pre-inhibited glycol blend approach presents strong evidence of an opportunity for significant reduction in both operating and capital costs for existing and future gas processing plants as well as a decrease in corrosion rates with prolonged plant life.