Container solution eases transfers of water purifiers

Oct. 1, 2003
Enwa has introduced standard 20-ft contain- ers to simplify installation offshore of its desalination system, which purifies water through reverse osmosis (RO).

Enwa has introduced standard 20-ft contain ers to simplify installation offshore of its desalination system, which purifies water through reverse osmosis (RO). According to the company, the new solution should appeal to vessel operators and to drilling rig contractors in particular, as the latter often need to relocate their RO units quickly to different rigs. An order has already been received from Dolphin Drilling, Aberdeen, for two RO/containers operating at 105 cu m/d.

The compact RO units are claimed to be far smaller than conventional evaporators typically installed on ships, and can also produce fresh water, even when the main engines are not running.

Osmosis is a natural process that involves inducing water to flow from a diluted saline solution through a membrane to a more concentrated salt solution. The concentrated salt solution is also then diluted. Flow of pure water through the membrane continues until the concentration of salt in both solutions is equal. The difference between the water level in the container, on each side of the membrane, is the osmotic pressure. By applying pressure greater than the osmotic pressure to the concentrated salt solution, the process can be reversed. Pure water subsequently passes through the membrane, flowing into the weaker salt solution. Desalinated water is thus obtained through dilution.

A containerized reverse osmosis desalination unit.
Click here to enlarge image


The Enwa system works as follows. A low-pressure pump directs the feed water into a pre-treatment section, where the larger particles and other contaminants are filtrated. This section is designed to suit the properties of the water. A high-pressure pump then forces the water through one or more membranes. Two streams are issued from the module – one, consisting of brine, is discharged as waste. The other, comprising desalinated and purified water, passes through a conductivity meter for quality control.

Recently, Enwa also received an order from the Iranian shipyard Sadra for a 40 cu m/d RO unit for a new semisubmersible drilling rig under construction for the National Iranian Oil Co. This unit is designed to treat raw water from the Caspian Sea, where the rig will soon be operating.

For more information, contact Ingela Ivarsson, Enwa. Tel: +4631 742 9250, Fax: +46 31 742 9260, [email protected],