Pressure exchanger

This rotational action is similar to that of an old fashioned machine gun firing high pressure bullets and it is continuously refilled with new fluid cartridges.

The performance of a pressure exchanger is measured by the efficiency of the energy transfer process and by the degree of mixing between the streams.

Efficiency is a function of the pressure differentials and the volumetric losses (leakage) through the device computed with the following equation:

Mixing is a function of the concentrations of the species in the inlet streams and the ratio of flow volumes to the device.

The concentrate leaves the ERD at low pressure [5], expelled by the incoming feedwater flow [1].

The most advanced are the multi-stage flash distillation seawater evaporation desalinators, which make use of multiple stages and have an energy consumption of over 9 kWh per cubic meter of potable water produced.

For this reason large seawater desalinators were initially constructed in locations with low energy costs, such as the Middle East, or next to process plants with available waste heat.

These salts and impurities are discharged from the SWRO device as a concentrated brine solution in a continuous stream, which contains a large amount of high-pressure energy.

Many early SWRO plants built in the 1970s and early 1980s had an energy consumption of over 6.0 kWh per cubic meter of potable water produced, due to low membrane performance, pressure drop limitations and the absence of energy recovery devices.

An example where a pressure exchange engine finds application is in the production of potable water using the reverse osmosis membrane process.

In this process, a feed saline solution is pumped into a membrane array at high pressure.

In the pressure exchanger the energy contained in the brine is transferred hydraulically[1][2] and with an efficiency of approximately 98% to the feed.

Therefrom results an economic energy recovery, amortization times for such systems varying between 2 and 4 years depending on the place of operation.