Desalination installations

Membrane element with pressure vessel

The desalination unit in a desalination installation consists of a number of Reverse Osmosis membranes in several pressure vessels, which are placed in a certain order. The feed water that is pumped into the module will be separated into water with a low salt content and water with a high salt content. The water with a low salt content is called ‘permeate’ and the water with a high salt content is called ‘concentrate’. The concentrate flow is regulated by a pressure vessel, which is placed within the concentrate. The pressure vessel regulates the percentage of feed water that leaves the module through the concentrate flow.

In a spiral module that consists of multiple membranes situated in a pressure vessel, the feed water flows within the pressure vessel, through the spiral channels of the element.
The spiral membranes in the pressure vessel that are interconnected will make sure that the feed water becomes more concentrated. When the concentrate passes through the last membrane, it will reach a pressure lid, which releases pressure.
The permeate of each membrane element is collected in a tube that is place centrally in each spiral membrane. Outside the pressure vessel a drain catches the permeate off the spiral membranes.

A specific benefit of spiral membrane units is the fact that they can be arranged serially within any pressure vessel. This means that the feed water flows through a membrane with one tubular system multiple times.
Hollow fiber units do not have this benefit, which means that they need separate drains for the feed water, the permeate and the concentrate. Hollow fiber installations that are built on a grand scale will have very high system costs, mainly for the built-up of the drainage system.

* graphic images come from FILMTEC membranes

Desalination

Desalination with Reverse Osmosis

Desalination installations system design

Desalination pre-treatment

Membrane technology

Scaling and antiscalants