Hydrate Management System
Cost effectively eliminate uncertainty
Achieve target MEG inhibition while preventing unnecessary overdoses.
Monoethylene glycol (MEG) is one of the most commonly used reagents for hydrate inhibition in production pipelines. It is recovered and reinjected to minimize the operating and environmental costs associated with MEG replacement and disposal.
PUREMEG MEG reclamation and regeneration systems not only regenerate the MEG by boiling off the pipeline water, they also remove salts and other solids to achieve the required outlet glycol purity. Dissolved salts in formation water, pipeline production chemicals, and pipe scale all have the potential to scale or foul both subsea and topside processing equipment. This MEG recovery system is an essential component of pipeline flow assurance.
The cost of MEG replacement can surpass millions of dollars per year. Our proprietary brine displacement and divalent salt removal systems minimize both MEG deterioration and losses, significantly reducing MEG replacement requirements compared with competing systems.
In addition to our reclamation technology, we provide everything from customized site support contracts covering training, installation, commissioning, and startup to long-term operational assistance, data acquisition, conditional monitoring, and predictive maintenance services.
The PUREMEG system is configured with either a full-stream or slipstream process. Full stream both regenerates and removes salts from the rich MEG feed. Slipstream has full-feed MEG regeneration, with a portion of the lean MEG sent for reclamation. Our experts can advise you which option best suits your process requirements. In either case, the process comprises five steps: pretreatment, MEG regeneration, flash separation, salt management, and divalent salt removal.
In the pretreatment stage, the rich MEG—containing some dissolved gas and hydrocarbon liquids—is heated and passed through a three-phase separator vessel. The gas is flashed to flare and liquid hydrocarbons are sent to the condensate recovery system. The treated MEG is sent either to storage or the downstream process.
MEG regeneration is conducted in a reflux distillation column. For a slipstream process, the column operates off the low-pressure flare backpressure and is provided with a pump-around heating loop. For a full-stream system, the distillation column operates under vacuum conditions.
The lean MEG produced at the bottom of the column is pumped to storage for reuse. For the slipstream service, a portion of the lean MEG is sent for reclamation. The vaporized water passes overhead where it is condensed and collected in the reflux drum. A portion of the water is returned to the distillation column to provide reflux while the remainder is routed to water treatment. Residual hydrocarbons in the system are generally associated with this produced water stream, and we provide a wide range of water treatment systems capable of meeting local environmental legislation for discharge.
In the flash separator, the rich MEG stream (full-stream reclamation) or lean MEG stream (slipstream reclamation), consisting of water and MEG with dissolved salts, is brought into contact with a hot recycled stream of concentrated MEG. The flash separator operates under vacuum conditions to maintain process temperatures below the degradation temperature of MEG. The feed MEG and water are vaporized and exit through the top of the flash separator. These vapors either pass to the MEG distillation column for regeneration (full-stream service) or are condensed and sent to lean MEG storage (slipstream service). The monovalent salt components, primarily sodium chloride, precipitate in the flash separator. They fall via gravity through a column of brine and are collected in the brine-filled salt tank.
The salt tank serves two primary functions. The first is to condition the salt levels for optimal performance of the salt separation process. The second is to provide a surplus of salt for converting freshwater makeup to saturated brine. Salt is removed from the brine by a hydrocyclone to produce a slurry suitable for a landfill or for redissolving for marine disposal.
Divalent salts (typically calcium, magnesium, and iron but also barium and strontium) cannot be precipitated out in the flash separator. Instead they accumulate in the process, which has an impact on system operability. For a slipstream process, the salts are often a cause of scaling within the reboiler. Removing the salts by MEG blowdown can be cost-prohibitive once disposal and replenishment costs are considered.
The divalent salt removal system precipitates out the salts by chemical reaction to form insoluble salts. Crystal size and shape directly influence the performance of the downstream filter. A dedicated reactor vessel is provided to control the temperature, time, and concentration for optimal crystal growth and morphology. Both sodium carbonate and sodium hydroxide are used for the chemical reaction to account for variations in feed conditions. The crystals, together with any other solids such as pipe scale and sand, are removed by filtration. Typically a dynamic crossflow filter is used for this service because of its tolerance for a wide range of particle sizes and distribution. The filter produces a clean MEG stream, which is returned to the process, and a concentrated slurry or cake, which is washed to recover any residual MEG. The produced slurry or cake can be further dried to provide a waste product that is easy to store and handle.
The MEG regeneration and reclamation system often demands the largest heating duty in a gas facility. Efficiency improvements in heat integration can significantly affect facility opex for heating and capex for the heating medium system.
The Schlumberger advanced heat integration process uses mechanical vapor recompression (MVR) to transform waste heat from the MEG regeneration overheads into a usable heating medium for the process.
The MVR compressor boosts overhead vapor from the MEG regeneration column, a low-grade steam, to a useable low-pressure steam, reducing heating medium demand by more than 80% which in turn reduces capex, opex, and greenhouse gas (GHG) emissions associated with the heating medium system. The compressor increases electrical demand slightly, <10% of heat duty, with the actual usage engineered for maximum savings for a specific facility.
The MVR compressor can benefit both slipstream and full-stream MEG regeneration and reclamation systems. Other industries have proved that the concept can improve process economics and sustainability.
Monoethylene glycol (MEG) is widely used in wellheads and pipelines to prevent hydrate formation, and regenerated for reuse from the produced water and MEG mixture by the PUREMEG MEG reclamation and regeneration unit.