Joint Industry Project for Improved MEG Regeneration Systems

One of the key challenges for multiphase gas flow pipelines is the risk of gas hydrate formation, which may plug the pipeline and stop gas production. Hydrate formation is eliminated by injecting Mono Ethylene Glycol (MEG) into the pipeline. Due to the large volumes of MEG required, it?s high cost and the environmental restrictions, the glycol must be regenerated. This is done by re-concentrating a high water containing rich MEG solution back to a lean MEG solution that is suitable for offshore re-injection. Dissolved salts and other impurities may also be removed from the MEG in a Reclaimer by precipitating out the salts coming with the formation water. These solids formed are subsequently separated using suitable solid-liquid separation technology. NOV initiated and ran a joint industry project (JIP) together with four oil and gas fields operators to address some of the key technical challenges faced by most operators when operating a MEG Regeneration Unit (MRU). The JIP aimed to improve current MRUs by testing and qualifying solutions to three critical technical challenges: 1) Organic Acid Salts Removal Accumulation of organic acids in the MEG Reclaimer is a major challenge for many operators. Removing the organic acids from the Reclaimer liquid will reduce MEG losses and reduce operational hick-ups. 2) Hydrocarbon (HC) Separation Separation of hydrocarbons from MEG is more challenging compared water. More understanding was required for better technology selection and sizing criteria to reduce hydrocarbon carry under to the MEG regeneration unit. 3) Mercury (Hg) Handling Technologies for mercury removal from MEG were not available in the market. This JIP focused on identifying and testing candidate technologies for this purpose. A high level summary of the results from the project is given below: 1.Organic Acid Salts Removal: The JIP has qualified a technology based on distillation of organic acids by acidifying a MEG stream from MEG reclamation. The HCl-acidification step converts carboxylate salts to organic acids and these are then boiled off . The concept has been demonstrated experimentally on a pilot scale and the concept is considered ready for field deployment, such as field trials. - Pilot tests demonstrate that both acetic acid and formic acid can be removed. - Process simulation tools have been adjusted to better predict the organic acid removal efficiency from laboratory experiments and application of acquired VLE data. - It is intended to have a modularized design, and standard size and flow capacity due to low flow rate variations, with a low degree of customization on heat exchanger sizing and HCl-dosage rates. - The concept is suitable for both greenfield and brownfield applications. - Utilities are cooling and heating medium/electrical power and HCl. 2.Hydrocarbon (HC) Separation: Small scale tests showed that the hydrocarbon separability decreased with MEG concentration. Dissolved salts improved the separation; more so at higher salinity concentrations. High temperature gave a significant improvement. Separation showed improvements at lower shear and higher residence times as expected. Large-scale trials with gravity separator, inline coalescer and hydrocyclone validated the positive impact of salts in the system. Inline coalescer only provided marginal improvement in separation performance ? this was most evident in non-saline gravity separation tests. Hydrocyclone technology proved most effective at condensate levels around 2-3vol%. However, at an inlet oil of ~2500ppmw separation was poor, even at 70°C. Plate pack in the gravity separator gave no improvement in separation performance compared to tests without the plate pack. A method for screening separation performance at laboratory scale has been developed in this work including suitable analytical procedures. These can be utilised in future work for screening the impact of field-specific fluids or chemicals in an economical manner. 3.Mercury (Hg) Handling The JIP has qualified two different technologies for removing mercury from aqueous streams namely (1) adsorption technology and (2) precipitation-based technology. The efficacy of both technologies were demonstrated experimentally in presence of MEG. The specific tested adsorption based removal technology is considered suitable for treating aqueous streams as it removes both elemental and ionic mercury and can reduce impact of mercury on salts and produced water disposal strategies. The technology is effective over a wide range of conditions and can be integrated upstream or downstream the MEG regeneration unit. It is a mature technology which is scalable and commercially available. Precipitation based technology only removes ionic mercury and can only be employed upstream the MEG regeneration unit. It may therefore require additional removal of elemental mercury if this is present.

Outcomes from the project are: - Organic Acid Removal Distillation concept developed for removing organic acids from the MEG system and has been demonstrated through pilot tests. Thermodynamic data has been acquired to tune process design tools. Technology is ready for large scale deployment or field trials. - Hydrocarbon Separation Reduced knowledge gaps for MEG impact on the separation performance of the gravity separator and hydrocyclone. Theoretical models for prediction of hydrocarbon separation can be developed. Lab scale results match with the large-scale loop trials; making the bench scale apparatus and method developed a useful tool for testing. - Mercury Removal Mercury Adsorption and Precipitation-based technology has been qualified. The efficacy of technologies demonstrated experimentally. Adsorption technology removes both elemental and ionic mercury. Precipitation technology only removes ionic mercury to a satisfactory extent for a variety of conditions.