A mathematical investigation into the limited use of energy recovery devices in brackish water reverse osmosis processes

Energy recovery devices (ERDs) play a critical role in our current world, where enhancing energy efficiency is a top priority. These devices come in various designs and operate on different principles, leading to varying levels of efficiency. However, the economic cost of ERDs can be quite high. To reduce the capital costs of ERDs, self-boosting devices have been proposed as a potential solution. In this study, we aimed to assess the effectiveness of self-boosting ERDs by developing a model that calculates the normalized energy saved in reverse osmosis (RO). Several factors were taken into consideration, including the range of energy efficiency (ranging from 60 to 90%) and the operating conditions of the RO system. These operating conditions encompassed an operating pressure range of 20-60 bar, permeate recovery rates of 30-50%, and system pressure drops of 2-6 bar along the feed flow direction. Our findings revealed that the performance of ERDs varied based on operating conditions. Specifically, ERDs utilized in seawater conditions demonstrated a higher return on investment, with a normalized energy saving of up to 80% within the design space. In contrast, the normalized energy savings achieved in brackish water conditions were as low as 14%. This discrepancy suggests that optimizing the use of ERDs can lead to significant energy savings and substantial financial benefits, particularly when applied in seawater conditions. These findings underscore the importance of considering operating conditions and selecting appropriate ERDs to maximize energy savings and economic advantages in different contexts.