No abstract

This study was conducted to investigate the operation of a packed distillation column and analyse its performance during the separation of mono-ethylene glycol from water. The column was designed and constructed by the Curtin Corrosion Engineering Industry Centre (CCEIC) and operated in collaboration with a reputable oil company to generate experimental field data. A secondary investigation was then performed into the impacts of dissolved salts within the rich MEG feed upon the purity of the lean MEG product. It was observed through application of the FUG shortcut distillation design equations that six equilibrium stages were required to attain the experimental separations reported under continuous operation of the column. It was further determined that the packing utilised within the column had a Height Equivalent to a Theoretical Plate (HETP) of approximately 0.34 metres when no dissolved salts were present corresponding to an estimated packing height of approximately 1.7 metres. The impact of dissolved salts upon the performance of the column was evident through lower lean MEG purities observed during experimental operation of the column in comparison to salt free trials. The reduction in column performance was reaffirmed by Aspen HYSYS and Aspen Plus simulations of the field data, where salt trials resulted in lean MEG purities noticeably less than corresponding salt free experimental trials and simulated predictions. Overall, it was observed that the presence of dissolved salts during operation led to a reduction in MEG mass fraction of the final lean MEG product by on average 7.2%. The impact of dissolved salts on lean MEG purity was successfully predicted by Aspen Plus simulation with an average accuracy of 1.61% through the inclusion of monovalent salt cations using the ELECNRTL equation of state with modified binary parameters. The reduction in lean MEG purity was attributed to boiling point elevation of the MEG-Water solution and the impact of the dissolved salts on the systems vapour liquid equilibrium.

Gas hydrate formation and corrosion within gas pipelines are two major flow assurance problems. Various chemical inhibitors are used to overcome these problems, such as monoethylene glycol (MEG) for gas hydrate control and methyl diethanolamine (MDEA) and film formation corrosion inhibitor (FFCI) for corrosion control. As an economical solution, MEG is regenerated due to the large volume required in the field. MEG regeneration involves thermal exposure by traditional distillation to purify the MEG. During this process, MEG is subjected to thermal exposure and so might be degraded. This study focuses on evaluating six analytical techniques for analyzing the degradation level of various MEG solutions consisting of MDEA and FFCI that were thermally exposed to 135 °C, 165 °C, 185 °C, and 200 °C. The analytical techniques evaluated are pH measurement, electrical conductivity, change in physical characteristics, ion chromatography (IC), high performance liquid chromatography–mass spectroscopy (HPLC-MS), and gas hydrate inhibition performance (using 20 wt % MEG solutions with methane gas at pressure from 50 to 300 bar). Most of the analytical techniques showed good capability, while electrical conductivity showed a poor result for solution without MDEA and IC showed poor results for solution exposed to 135 and 165 °C. The primary aim of this paper is thus to provide the industry with a realistic evaluation of various analytical techniques for the evaluation of degraded MEG solutions and to draw attention to the impact of degraded MEG on gas hydrate and corrosion inhibition as a result of the lack of quality control.

Gas hydrate blockage and corrosion are two major flow assurance problems associated with transportation of wet gas through carbon steel pipelines. To reduce these risks, various chemicals are used. Monoethylene glycol (MEG) is injected as a hydrate inhibitor while methyl diethanolamine (MDEA) and film-forming corrosion inhibitor (FFCI) are injected as corrosion inhibitors. A large amount of MEG is used in the field, which imposes the need for MEG regeneration. During MEG regeneration, rich MEG undergoes thermal exposure by distillation to remove the water. This study focuses on analyzing the kinetics of methane gas hydrate with thermally exposed MEG solutions with corrosion inhibitors at 135−200 °C. The study analyses the hydrate inhibition performance of three different solutions at selected concentrations and pressures (50−300 bar), using a PVT cell and isobaric method. Results established that thermally degraded solutions cause hydrate inhibition drop. However, the inhibition drop was found to be lower than that of pure thermally degraded MEG, which is caused by the additional hydrate inhibition effects of MDEA and FFCI. In addition, hydrate phase boundaries and regression functions were reported to provide a deep insight into the operating envelope of thermally degraded MEG solutions.

Coatings can protect metallic substrates (e.g., piping, vessels, tubes, etc.) against corrosion attack. The adhesion strength of a coating to its substrate is an essential factor that defines the overall coating integrity and performance. A pull-off adhesion test is commonly performed to determine the coating adhesion strength. This study evaluated the effect of various vital influencing factors on the pull-off adhesion test, including surface preparation of the loading fixture (dolly) and coating surface, types, curing durations and conditions of glue, and scoring of coating around the dolly. Test results were systematically analysed with non-subjective tools such as Image-J software for failure mode assessment and statistical analysis (t-Test) to compare adhesion values.