Design And Process Economics Of A Monoethylene Glycol (Meg) Recovery System From Produced Water

Abstract

Monoethylene glycol (MEG) is a widely used hydrate inhibitor in the oil and gas industry to reduce the risk of hydrate formation in pipelines that could cause a blockage. Large volumes of MEG are used annually as an effective hydrate control strategy adding an extra cost on oil and gas industries. The spent MEG is disposed of afterward by injection in wells. The environmental impact of the disposal of MEG has not been well studied yet, but it is expected to gain importance in the near future. The development of an effective process for MEG recovery has been gaining importance to reduce its purchase cost and eliminate the environmental concern of its disposal after use. Hence, the present study was performed to develop and optimize MEG recovery process based on a simulation method and to evaluate the economic feasibility of recycling and reusing the recovered MEG. The simulation process was carried out using Aspen Plus and a built-in ELEC-NRTL thermodynamic package, while the process economics was investigated using the economic analyzer tool add-in to estimate the cost of the design developed. The process simulation was conducted in two distinct designs with four scenarios. The results revealed that an optimized process consists of a flash separator and a distillation column operated under vacuum pressure recovering 99.7% of high purity (99.7wt%) MEG. The capital expenditures (CAPEX) and operating expenses (OPEX) associated with the optimized process reported as present worth, project lifetime of 20 years and annual interest rate of 8%, were estimated to be 11.5 and 35 MMUSD, respectively. All studied scenarios achieved the required MEG recovery and purity reaching values up to 99.7% as per the requirement of the Qatari industry in general and ConocoPhillips in specific. The similarity in the trends for all scenarios is due to the homogenous water chemistry as well as the low amount of total dissolved solids (TDS). Applying the proposed MEG recovery system can save at least 50% of the MEG purchase cost if MEG passes through one regeneration cycle in the unit. Moreover, this study shows that 80% of MEG purchase cost can be saved when MEG is regenerated up to 5 times. Finally, an environmental benefit is achieved due to the considerable reduction in the disposal of spent MEG.