Clathrate desalination method applied to Produced Waters: Methodology & Results
Author: Patrick Baldoni-Andrey
Co authors: Hervé Nabet, Matthieu Jacob, Pierre Pédenaud (Total) Pascal Le Melinaire, Bruno Mottet (BGH)
The oil and gas industry generates large volumes of produced water. The quantities of water are constantly increasing because mature fields have much larger water-to-oil ratio than new fields in production. The produced water is usually saline (30 - 300 g/L of Total Dissolved Solids). The high salinity can prevent several disposal options on shore, but also be an obstacle to recycling or reuse of the water. This is the reason why Total is looking for new desalination techniques.
Total R&D department and BGH have started a partnership in 2015 in order to evaluate a new desalination process developed by BGH. To do so, a series of tests on real produced waters have been carried out at lab scale in Lacq (South West France).
The process is based on the crystallization of clathrate, most commonly known as “Gas Hydrate, or Snow Burning”. Indeed, the forming of crystals of gas hydrate within a liquid solution is a way to discriminate and sequester pure molecules of H2O. Those pure water molecules, now in solid form, can be recovered and separated which leads to desalination.
Such process has been long studied in the past using methane hydrate or carbon dioxide hydrate. For different technical and economic reasons, no real industrial solutions emerged at that time using such gas host molecules.
Recent advanced research in the field of clathrate promoter opens the door to more adequate, robust, cheaper solution than methane or carbon dioxide, for a type of application such as desalination.
The technology developed by BGH relies on two major technology breakthroughs:
- Use of cyclopentane-hydrate: it allows hydrate precipitation at atmospheric pressure and at a temperature up to 7°C higher than ice.
- Activated carbon is used in combination of cyclopentane: it acts as a reaction facilitator by (i) increasing the surface contact between cyclopentane and brine, (ii) initiating the reaction and (iii) promoting the crystal growth.
This process offers the following advantages:
- It applies to all kind of brines or salinity content, beyond the usual limit of reverse osmosis. It does not require an extended pretreatment as for reverse osmosis.
- The energy footprint is significantly less than the one for evaporation as the desalination happens at cold and ambient temperature.
- Salts can be concentrated up to salt saturation what can be an opportunity for using this technology also as a crystallizer.
TOTAL and BGH will present the results obtained on a series of tests on raw produced waters coming from different fields in production. The results indicate the performances on salinity as a global parameter, and the efficiency of the process on major ionic species in solution.
The conclusions will include the perspectives of the coming work engaged in this partnership, in order to increase the maturity level of the technique and eventually to fulfill the constraints of an industrial application case.
Keywords : desalination; hydrate; clathrate; produced water; environmental footprint, water reuse