Novel Process for the Separation and Regeneration of Methanol from Hydrocarbon Condensate on an FPSO

Abstract Industry experience in the removal of methanol from condensate is limited and the methanol regeneration process is energy intensive, and a solution has been required to overcome both issues. Because methanol is a polar molecule, the quality of separation from condensate that will be achieved in the presence of another polar molecule, water, is difficult to predict. In this project, these challenges were successfully overcome through the development of a robust process scheme that incorporated counterflow mixing of condensate with washwater, customized separator internals, and an electrostatic treater. This scheme was specifically designed to efficiently remove methanol from light condensates, even in the presence of floating production, storage, and offloading (FPSO) unit motion, and subsequently regenerate the methanol. This methanol recovery and regeneration package was designed to separate gas, condensate, and aqueous methanol, and the objective was to reduce the concentration of methanol in condensate to 50 ppmv or less. The process uses multiple separator stages to separate water and methanol from the condensate, water, and methanol mix. The water and methanol mix then goes to the regeneration unit, concentrating methanol to 98 wt% and recycling the water. Condensate then moves to the stabilization unit. The initial design approach included three separators arranged in series with cross-current water injection followed by a methanol regeneration unit. To mitigate the limited industry experience and associated risks, a comprehensive analysis reviewed technical information and the available literature and used three process software programs, each with distinct equations of state (EOSs), for system simulation. Comparing the results from each software program and the EOSs provided a high level of uncertainty in the prediction of methanol removal. Several performance-enhancing improvements were suggested by the analysis. First, the water-injection method was switched from cross-current to countercurrent flow, leading to washwater savings of 67% and a carbon footprint reduction of 57%. Second, a customized electrostatic treater was introduced to efficiently remove water from condensate. To improve the mixing of washwater and condensate for efficient methanol transfer from the condensate phase to the water phase, a combination of mixing valves and static mixers was proposed and implemented. Computational fluid dynamics (CFD) studies confirmed the mixing efficiency of each static mixer. Third, enhanced process schemes and high-performance separator internals were added to enhance separation efficiency, substantially reducing the weight and space required for the methanol regeneration module. These enhancements increased system efficiency, lowered the environmental impact by 17,000 metric tons of carbon dioxide equivalent (CO2e) annually, equivalent to 49% of the initial design, and ensured adherence to stringent methanol content regulations.