Scientists from Global Water Sustainability Centre (GWSC), Texas A&M University at Qatar (Tamuq) – a QF partner university – and University of Technology Sydney (UTS) have been working together to use produced water to generate 'blue energy', sometimes also called osmotic power or salinity gradient power.
Produced water (PW) is a term used in the oil industry to describe water that is produced as a byproduct during the extraction of oil and natural gas. Funded by Qatar Foundation’s (QF’s) Qatar National Research Fund, this innovative project is based on the phenomenon of osmosis, which is the movement of water molecules from a region of low solute concentration to a region of high solute concentration, through a semi-permeable membrane.
The technology being pursued by the group is called Pressure Retarded Osmosis (PRO). In simpler words, imagine you have two solutions of water, one with high salt content and the other with little or no salt. If these two solutions were placed side by side, with only a thin semi-permeable membrane between them – which means it only allows water molecules to pass through and not salt ions – water molecules will move from the side with low salinity to the side with high salinity. This movement of water molecules across the membrane will build up pressure which can eventually be used to drive turbines and generate power.
“Since aging is inevitable, the amount of PW generated is only expected to increase. With that in mind, we are trying a different approach wherein instead of trying to find new ways to dispose PW, we are looking at it as a resource rather than a nuisance. For the past 2-3 years, we have been exploring the possibility of generating energy using PW,” said Dr Samer Adham, head of ConocoPhillips GWSC at the Qatar Science and Technology Park.
“The challenge with PW is its complex composition, in addition to being hypersaline, it also consists of dispersed oil, hydrocarbons and suspended solids. Its complex composition means it does not make economic sense to treat this water for use in irrigation or such. It is typically reinjected into disposal wells so it can help maintain reservoir pressure and enhance oil recovery via waterflooding,” said Dr Adham.
While its high salinity is perhaps what hinders its reuse the most, it is also what gives it potential in 'blue energy' generation. Since the amount of energy generated is dependent on the salinity difference – a greater salinity difference will mean more energy produced. This is exactly what the group is trying to do.
However, using PW comes with its own share of challenges. The first challenge is pre-treatment of PW before it can be used as its constituents can quickly block the pores of the membrane and greatly reduce its efficiency. The second challenge is that because of the larger salinity gradient, the osmotic pressure that will be created is much higher than currently used membranes are able to withstand.
“At GWSC, we are working to find a pretreatment method that is cost and more importantly energy efficient. Quite simply because if pretreatment is more intensive than necessary, it costs more energy which reduces the overall efficiency of the process,” said Dareen Dardor, chemical engineer, GWSC.
Collaborators in Sydney are working on developing new and stronger PRO membranes that are chemically treated and/or reinforced with nanomaterials.
“At Tamuq, we are developing a model that can predict lab and full-scale PRO performance to help optimise operating conditions and costs," added Dr Ahmed Abdel-Wahab, lead project investigator and Professor of Chemical Engineering, Tamuq.