Water shortages and drought are becoming more common and longer-lasting throughout the world in places as far apart as California and China. Desalination is being hailed as one of the most effective solutions to the global water crisis.
Litre Meter has identified a number of its products as suitable for use in a number of flow control applications 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 significant water stress. It is practiced in 150 countries including Kuwait, Oman 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 currently stands at 80 million m3 and it is expected to grow substantially over the next five years.
Construction is nearing completion in Carlsbad, California, to create the Western hemisphere's largest desalination plant, estimated to produce 50 million gallons of drinking water every day. Over 200 plants are also under construction, many of them in 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 (6Mo) 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 the ecological impact of returning brine to the ocean.
VFF flowmeters are suitable for measuring liquids at pressure ratings up to 4,000 bar (60,000 psi) and flow rates from 0.0004 l/min (0.5 litres per day) to over 270 l/min (16,200 l/hr). They are of intrinsically safe design and are manufactured to operate reliably at temperatures ranging from -40 to 100°C.
Litre Meter CEO Charles Wemyss said: “Litre Meter’s VFF flowmeter is ideally suited for use in the desalination industry and in particular for low flow/high pressure applications.
“Years of experience in water and chemical injection applications onshore and offshore have confirmed the instrument’s capability to reliably measure fluids under extreme conditions of both temperature and pressure.
“The instruments are also versatile enough to be used in high flow applications as well.”