Retro-fitting existing SWRO systems with a new energy recovery device

A new pressure exchanger (PX) device transfers the energy from the concentrate stream directly to the feed stream. This direct, positive displacement approach results in a net transfer efficiency of over 95%. This efficiency advantage makes it possible to dramatically improve the performance of existing SWRO plants by reducing their energy consumption by as much as 75% or by expanding their capacity as much as 300%. Detailed system designs, parameters, and recommendations are provided in this paper for several retro-fit configurations and will be accompanied with case data from operating plants that have been retro-fitted using these new devices. There has been a recent proliferation of commercially available energy recovery devices based on the positive displacement direct pressure exchange approach. This increased interest is driven by the fact that the technology can significantly reduce the energy consumption of new and existing SWRO systems. Since energy costs are rising and can consume, as much as 75% of the total operating costs of an SWRO plant, it is important that the technology be encouraged and disseminated throughout the industry. Although the author of this paper is directly associated with Energy Recovery, Inc., a leading supplier of pressure exchanger technology, the principles and theories presented in this paper will be applicable to all devices that are based on the positive displacement, isobaric chamber approach.

The extremely high efficiency of pressure exchanger technology makes it is possible to significantly increase the capacity of existing systems and/or reduce the power consumption of existing systems even when the best of yesterday’s energy recovery technologies are already in place. We have shown several approaches to retro-fitting existing SWRO systems with pressure exchanger technology, which include the power reductions, the expansions, and the multiple train power reduction. These real case examples have been applied around the world and many other approaches are possible. As the market tries to maximize Table 12 Multiple train power reduction comparative power consumption and production Description Before After PX PX kW requirement main HP pump(s)* kW requirement n/a PX booster pump* kWh/m3 2.88 2.25 kWh/1000 gal 10.9 8.53 Permeate production, m3/h 6501 6578 % difference