Glycol reclaiming

Large glycol reclamation plants that recover mono-ethylene glycol (MEG) used for hydrate inhibition typically apply flash vaporisation under vacuum to remove dissolved and suspended solid contaminants. Heat is transferred to the salty rich glycol feed at the lowest possible temperature by direct contact with hot recycled liquid, followed by distillation to recover clean salt-free reconcentrated glycol.

Proprietary technology based on fundamental research into how glycol, water and salt interact has been developed by the authors to improve the design and performance of these plants, resulting in the following refinements to the basic process:

• design of the main separator vessel reduces the population of erosive and fouling salt particles in the recycle circuit by 90+%

• unusually high fluid velocities and heat transfer rates result in a more compact plant with substantially less risk of fouling or MEG thermal degradation

• on-line separation of MEG from the waste salt without the need for large tanks, filter presses, centrifuges or the like, enables safe disposal of the waste salt into the sea without further treatment

The new technology is built into the glycol reclamation package on Enterprise Products Partners LP’s Independence Hub platform about to be deployed in Mississippi Canyon block 920. This plant will process 7,800 bpd of salty rich MEG and is the largest glycol reclaiming plant in the world.

For many small projects other technologies have been applied for reclaiming MEG such as falling film or scraped surface evaporators, ion exchange and electro-dialysis. This paper does not address these technologies but notes that the attractions of superior performance and simple equipment may broaden the range of application of the latest flash vaporisation concepts to include smaller projects.