high pressure pumps
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Reverse osmosis (RO) systems have made enormous progress in terms of commercial significance in recent years, both in seawater desalination applications and in the general conditioning of drinking water (potabilization). In the desalination sector, the equipment spectrum extends from small, portable units (camping, boats) to huge plants for industrial and municipal water supply applications (‘water factories’). With increasing size of plant, the specific cost of generating the product ‘water’ becomes increasingly decisive. The central element of what is referred to as the ‘core hydraulic system’ of an RO plant is the high pressure pump, the task of which is to push the seawater up against the membranes at a pressure that exceeds the osmotic pressure (60–90 bars). Due to its high power requirement, the pump accounts for most of the energy consumed by the facility and, as such, are a critical determining factor with respect to the system’s overall economic efficiency. Hence, the purpose of this paper is to compare the theoretically achievable efficiencies of two different types of high pressure pump.
high pressure pump types
Figure 1 is a conceptual diagram of the core hydraulic system of a reverse osmosis plant
high pressure pumps.
Depending on which, if any, energy recovery system is employed, the high pressure pump will either have to handle at high pressure the full flow of raw seawater (100%) or only the permeate (approx. 40%) obtained from the seawater. Basically, the choice of pumps is limited to two types of single-entry, multistage sets: Type a – with back-to-back impellers and an axially split casing, and Type b – vertically split, ring-section design with impellers arranged in series. Type a was originally designed for heavy-duty processing applications, most notably for use as pipeline pumps in the oil industry. The characteristic feature of this design is a high level of axial force compensation resulting from appropriately arranged impellers. Such pumps also have an axially split casing with suction and discharge nozzles on the bottom half. At least in pipeline applications, this yields advantages in terms of integration into the piping and ease of maintenance. The Type b high pressure pump is basically a ‘classic’ vertically split ring section pump that is used in large numbers in power engineering applications. Its impellers are arranged in series, and it has a centralized axial thrust