Technical challenges and solutions in a closed loop MEG regeneration system for gas field offshore, UK

Abstract

Two UK gas/condensate fields are being developed as a single integrated subsea production system. Mono Ethylene Glycol (MEG) is used as a thermodynamic hydrate inhibitor. The main processes for recycling of MEG are regeneration and reclamation. Operational problems within closed MEG system are carbonate (CaCO 3) scaling deposits at MEG injection point, pipeline, and salt removal system as well as accumulation of corrosion products. This paper presents the results of prediction of precipitation of solids and corrosion in the closed MEG loop system and presents solutions for these challenges. The key points discussed in this paper are (i) The choice of acid to be used to neutralise excess alkalinity in the Lean MEG; (ii) The upper limit value of pH in order to keep a low corrosion rate and prevent scaling risk; (iii) The risk and consequences of HCl overdosage; (iv) The location of the injection point of this acid; (v) Calculation of the acid flowrate; (vi) The choice of the alkalinity source required to precipitate the divalent cations in the rich MEG pre-treatment; (vii) Calculation of the flowrate of this alkalinity source; and (viii) Monitoring of alkalinity and acid injection. The modeling methodology used as a basis for this study is a purely thermodynamic approach. The equilibrium calculations are done with the MultiScale software with the glycol add-in.

Design, optimization and economic analysis of a monoethylene glycol recovery process: salt precipitation and vacuum operation

“…The remaining CAPEX cost is shared between vacuum pumps, heaters, FLS in addition to small equipment well as piping, instrumentation general and administrative expenses. 28,[30][31][32][33]35,[37][38][39] The OPEX of P-1 was estimated to be 1.2 MMUSD/y of this 63% (~0.75 MMUSD/y) is related to the utility, and the rest 37% is shared between labor, maintenance and plant overhead and any other expenses ( Figure 2C). The utility cost was mainly related to 34% for MP steam (100 psi), 28% for Freon-12 (R-12) and 1% of electricity.…”

“…Then, a 1 N NaOH was used to precipitate calcium, magnesium and any other divalent salts. The amount of NaOH was estimated based on the alkalinity limitation 28,31‐33 . The stream was then sent to a separator (SEP) to remove divalent salts.…”

“…The amount of NaOH was estimated based on the alkalinity limitation. 28,[31][32][33] The stream was then sent to a separator (SEP) to remove divalent salts.…”

“…Vacuum FLS contributed to 9% of the equipment cost as a result of large volume sizes and high vacuum requirements. The remaining CAPEX cost is shared between vacuum pumps, heaters, FLS in addition to small equipment well as piping, instrumentation general and administrative expenses 28,30‐33,35,37‐39 …”

A systematic approach for design and simulation of monoethylene glycol (MEG) recovery in oil and gas industry

“…Injecting an amount of NaOH higher than the optimum will increase the mixture alkalinity, which in turn is not recommended as it increases the risk of calcium carbonate precipitation and scale formation in pipelines downstream MEG injection points. [22][23][24][25] Then, the MEG-water and monovalent salts are introduced to the distillation column, where water is separated from MEG and salts. The monovalent salts are then removed from MEG using a flash separator.…”