Investigating the performance of reciprocating high-pressure pumps in constant recovery small RO desalination plants

Small-scale reverse osmosis plants that can produce less than 50 m ³ /d are vital for small communities in villages located in remote areas. The design parameters of such plants involve low flow rate and high-pressure feed. For such operating conditions, reciprocating pumps are more favorable than centrifugal pumps because the efficiency of centrifugal pumps in such conditions is reduced extensively. Recently, reciprocating pumps with energy recovery are presented by several pump companies for desalination applications. The concept of energy recovery in these pumps is quite similar to that used in pressure exchangers. In these pumps, the pressurized brine is directed to the back of the pumping pistons which reduces the pumping motor required power. This work presents a numerical simulation and experimental analysis for such pumps. The numerical simulation includes a computational fluid dynamics transient analysis for the used pump. The analysis is presented using both two-dimensional and three-dimensional models. The effects of the operational and design parameters on the performance of the pump and its volumetric efficiency are investigated. The results show that increasing the valve spring stiffness increases the volumetric efficiency. It also shows that increasing the outlet pressure and piston speed reduces the volumetric efficiency. The most striking result to emerge from the data is that reducing the valve spring stiffness below a specific value results in large reduction on the volumetric efficiency. Results of pump’s testing at different operating conditions are evaluated. The results of the presented numerical simulation were compared with the experimental results at several operating conditions, and the deviation was less than 10%.