Khaled Touati

Evaluation of the recovery of osmotic energy in desalination plants by using pressure retarded osmosis

ABSTRACT The current paper explores the possibility of using pressure retarded osmosis (PRO) as part of the post-treatment of existing desalination plants: a membrane-based PRO system would be used to transform osmotic energy of the retentate into hydraulic pressure; this pressure is then used to generate electricity in a turbine. For this, a source of water with lower osmotic pressure would be needed: municipal or industrial wastewater, brackish water, etc. From the point of view of implementation, except for the PRO membranes, this additional PRO post-treatment uses a small number of additional components, which are similar to those already standards in desalination industry. A model of the process is developed, and some feasibility studies will be discussed, to evaluate the potential for varying mixing rates.

Effect of the operating temperature on hydrodynamics and membrane parameters in pressure retarded osmosis

AbstractThe osmotic energy recovered by pressure-retarded osmosis from flows of different salinities is affected by the temperature, so its effect on hydrodynamic and membrane parameters is studied here. It is shown by models and experimental results that raising the temperature of the solutions leads to a variation in the mass transfer coefficient, the boundary layer, the diffusion coefficient, the solute resistivity, and the permeability, therefore, affecting the water flux. Consequently, the expected power density is improved at high temperatures, although, the salt flux diffusion increases. Laboratory results are presented using solutions at different concentrations and temperatures to validate the analysis.

Energy recovery using salinity differences in a multi-effect distillation system

AbstractThe use of Salinity Gradient methodologies to recover part of the osmotic energy in the brine of multi-effect distillation (MED) systems is explored here. Measurements from a membrane-based Pressure Retarded Osmosis laboratory system have been used to estimate the energy that would be recovered from this brine, when a source of low-salinity water is available locally (such as industrial or municipal wastewater). This methodology has been evaluated for a specific case study (72 m3/d solar/gas MED system) at different temperatures.

Green energy generation by pressure retarded osmosis: State of the art and technical advancement—review

ABSTRACT Pressure-retarded osmosis (PRO) is a method for converting salinity gradients to power by allowing water to flow through a semi-permeable membrane against an applied hydraulic pressure. PRO already has a long history, starting from the middle of the last century, and has rapidly improved in recent years. In this paper, we present a historical development of PRO since its inception: the development of this renewable energy process has gone through several stages, depending on technological developments, worldwide energy demands, and environmental concerns. The technological progress of the process is also studied, as well as its cost viability and environmental impact. Finally, some ideas to further develop the PRO process and mitigate its detrimental effects are discussed.

Effects of the Temperatures on PRO

The effects of the temperatures of the feed and draw solutions on the pressure retarded process are studied in detail here: the operating temperatures are known to affect the performance of membrane-based systems, as they affect the membrane permeability, the reverse salt diffusion, and some process parameters (viscosity, density, diffusion, etc.). As fluid temperatures may vary over a wide range, depending on the nature of the sources, the location, and its surrounding climate, it is important to understand the effect of these temperatures to optimize the design and operation of pressure retarded osmosis systems. Thus, in this chapter, the effects of the temperatures of the feed and draw solutions on the structural parameters of the membrane, as well as the hydrodynamics, are investigated.

Pressure Retarded Osmosis as Renewable Energy Source

Abstract This chapter presents a novel renewable energy source (pressure retarded osmosis), which uses the energy generated by differences in salt concentrations between two fluids, commonly freshwater and saltwater. Compared with other renewable energy sources, it has the advantage of controllability. An overview of the state of the art of this technique is presented, discussing also its basic operation principles and main challenges.

Water and Salt Fluxes in Pressure Retarded Osmosis

Abstract The pressure retarded osmosis (PRO) process is studied in detail in this chapter, concentrating on developing models that make it possible to predict water and salt fluxes in real PRO membranes. These models are fundamental to understand the process to obtain the best performance. A precise description is proposed, taking into account internal concentration polarization (ICP), caused by the membranes porous layer, and the external concentration polarization (ECP), building up in the fluid boundary layers on both sides of the membrane. The proposed models are validated using laboratory scale, under different operating conditions to show the prediction capacities of the model. The implications on full-scale power plants are then discussed: a good selection of operating conditions and membranes can then improve the power production by reducing ICP and ECP.