Positive displacement meters suited to use in desalination plants

17 September 2013

Litre Meter has identified a number of its flowmeter products as being suitable for use in the growing desalination plant market.

Desalination is the process of removing salt and minerals from water to make it potable. This is mainly necessary in countries suffering water stress such as Oman, Kuwait and Saudi Arabia in the Middle East and in Australia, North Africa, Spain, the USA and China. Desalination is also used on ships, submarines and offshore facilities.

According to the International Desalination Association water production from desalination plants operated worldwide has been increasing 12.3% year-on-year. Production is expected to reach 120 million m3 by 2020; some 40 million m3 of which is planned for the Middle East.
The two main methods of desalination are reverse osmosis – forcing water through a membrane to collect contaminants (the reverse of this process known as forward osmosis) – and multistage flash.

The multistage flash method uses heat to convert salt water into fresh water. ‘Flash' refers to rapidly bringing the water to a boil multiple times or in stages. As the salt water enters each stage of the conversion unit it is subjected to externally supplied steam heat and pressure. During each stage, fresh water vapour forms and is collected.

Litre Meter flowmeters are useful in two areas of the desalination process – to monitor the use of chemicals to control costs and to monitor and control the environmental impact of desalination.

Chemical pre-treatment and cleaning are a necessity in most desalination plants. This typically includes treatment against bio fouling, scaling, foaming and corrosion in thermal plants and against bio fouling, suspended solids and scale deposits in membrane plants.
VFF meters already used to great effect in chemical injection in the oil and gas industry are suitable for measuring the flow of chemical pre-treatment in the desalination process. For example, VFF positive displacement flowmeters are used on a potable water chlorine dosing skid for a North Sea gas platform.

These meters are designed to measure the flow of water in a range of 1,470 to 5,000 l/hr at a pressure of 8.5 bar. The meters are both accurate and robust over long periods of continual use. All the process wetted and pressure retaining parts are constructed from 6 Moly Austenitic Stainless Steel to deal with the sodium hypochlorite content.

VFF meters can also be used in monitoring the impacts of desalination in measuring the flow and concentration of brine being returned to the sea in the multistage flash process for example. This entails measuring the mixture of brine in the ‘mixer zone' to minimise ecological impact of returning brine to the ocean.

VFF flowmeters are suitable for measuring liquids at pressure ratings up to 4,000 bar and flow rates from 0.0004 l/min to over 270 l/min. They are of intrinsically safe design and are manufactured to operate reliably at temperatures ranging from -40 to 100°C.

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