Performance Degradation of the Monoethylene Glycol Regeneration Process in the Presence of Electrolytes: Pilot-Scale Experiments and Dynamic Simulations

Abstract

Safe production of natural gas from offshore gas fields would rely on the injection and regeneration of mono-ethylene glycol (MEG) to inhibit hydrate formation as well as corrosion and scale issues in subsea flowlines. In this study, we investigated the solubilities of NaCl and the vapor pressure of aqueous MEG solutions experimentally with a laboratory-scale apparatus. A thermodynamic model adopting the electrolyte NRTL-RK was developed using newly obtained experimental data and by adjusting binary interaction parameters. Then, we constructed and operated the pilot-scale MEG regeneration plant with a feed flow rate capacity of 200 kg/h to investigate the concentration of MEG solution. We varied the reboiler temperature at the bottom of the packed distillation column and the concentration of NaCl in the feed stream. It was observed that the MEG concentration decreased with decreasing reboiler temperature but with increasing NaCl concentration. The enhanced electrolyte NRTL-RK model was verified using the operation data from the pilot-scale MEG regeneration system, which was in good agreement with both steady-state and dynamic operation data from the pilot-scale experiments. Based on the developed simulation model, case studies were carried out to manage the risk of NaCl precipitation in the MEG regeneration system while achieving the target lean MEG concentration. The safe operation window, avoiding the risk of NaCl precipitation, was developed using the relationship among the distillation temperature, MEG concentration, and amount of NaCl based on the developed model. When 50 wt % rich MEG solution was regenerated to 90 wt % lean MEG solution, no precipitation of NaCl was predicted by the enhanced model until the total dissolved salt (TDS) reached 100 g/L; however, the default model predicted the precipitation of NaCl at the bottom of the distillation column above the TDS of 85 g/L, which suggested that the inaccuracy model can overestimate the risk of NaCl precipitation.