Measuring up to the Desalination Challenge
Published on : Thursday 10-11-2022
Krishna H Prashanth looks at the lessons learned from innovations in the East and outlines how measurement instruments can help ensure high standards are met.
Desalination is widely seen as an answer to water scarcity in many areas of the world. Yet, with a large energy demand, desalination plants need to run as efficiently as possible to reduce their environmental impact. This article looks at the lessons learned from innovations in the East and outlines how measurement instruments can help ensure high standards are met, avoiding the need to use more energy replacing water that does not meet specifications.
Water is vital for life, yet 97 percent is in the form of seawater, making it too salty for drinking or agriculture. Only some three percent of the Earth’s water is fresh, with most of that locked up in ice caps and glaciers.
The remaining small percentage must meet all the world’s potable drinking water and agricultural needs, a world which is also experiencing a rapidly growing population. Water scarcity is thus a growing issue across the globe, encouraging water utilities and governments to turn to technological solutions like desalination.
Around 300 million people around the world now get their water from desalination plants. The number of these plants has been rising steadily over the last decade, with nearly 16,000 operational plants currently offering a combined capacity of nearly 100 million cubic meters per day.
Eastern countries lead the way
Much of the development in desalination capacity and technology is taking place in the Middle East and south Asia, in countries which have both a burgeoning water demand from increasing populations and industrialisation and a growing water scarcity.
In the arid desert region of the Middle East, desalination is often the only source of water. The water shortage and the finance available for large projects means that no other region desalinates so much water, accounting for approximately 60 percent of the world’s desalination capacity. [1]
India is looking at desalination as a possible solution to its severe water scarcity. The demand for drinking water in India is expected to be 73 billion cubic meters by 2025, reaching 102 billion by 2050. Mumbai Municipal Corporation has announced it will build a desalination plant to supply the city with 200 mega litres per day by 2025.
Meanwhile, in Chennai, a plant with a capacity to treat 150 mega litres per day (MLD) is due for completion by 2023, with another 400 MLD capacity plant to be completed by 2025. [2]
Overall, the Indian desalination systems market is expected to grow at a CAGR greater than three percent over the next five years.
With new capacity being planned and built, these markets have the opportunity to use the latest digital technology to control and monitor desalination plants, mitigating the challenges that the process involves.
Options for desalination
There are several popular methods of desalinating sea water and brackish water from estuaries. One of the best ways is thermal distillation, which uses heat and pressure to boil the water, condensing it back down to leave fresh potable water behind. The most common thermal desalination processes are multi-stage flash distillation, multiple-effect distillation and vapour-compression evaporation.
Another method is electro dialysis, which uses membranes that only allow the passage of either negatively charged or positively charged ions at a time.
Reverse osmosis (RO) is currently the most widely used method of desalination. Although offering high efficiency, efforts are continuing to improve the performance of the membranes themselves, with techniques such as increasing the diameter of the membranes to improve their capacity.
Digital devices are up for the challenge
One of the main challenges in desalination is the large amount of energy used in the process. Across the globe, desalination plants use more than 200 million kilowatt-hours (kWh) of energy each day, with energy accounting for around 55 percent of plants’ total operation and maintenance costs.
As well as cutting energy use and avoiding fossil fuels, improving the sustainability of desalination is one of the major routes to cutting costs. This can be achieved by using advanced monitoring and measurement instruments to ensure the process is efficient and that a quality product is produced with no contamination, which would require producing extra water and increase production costs.
The need to monitor both the quantity and quality of water as it passes through the desalination process calls for accurate measurement of a range of parameters. These include flow rate, water quality, pressure, level and temperature. The ability to record data for analysis and predictive maintenance is another essential facility.
Flowmeters play a key role throughout desalination processes, measuring the quantities of both raw water entering the plant, and treated water leaving it. As well as being robust and accurate, flowmeters need to be easy to manage and maintain and the most advanced digital based units incorporate features to enable this. These features include menus to guide easy set-up, even for inexperienced operators.
Modern units such as the ABB WaterMaster flowmeter uses advanced diagnostic functions to monitor both its own operability and the process. Limit values for the diagnostic parameters can be set by users, with an alarm being tripped when these limits are exceeded. In the event of an error, the flowmeter will display easily readable messages such as 'Maintenance Required', 'Check Function', and 'Failure'.
Water quality counts
Water quality factors include turbidity, pH level, conductivity and chlorine levels. Here again, digital water analysers can bring benefits. In contrast to legacy 4-20mA systems that give very little insight into what is happening in that instrument, digital devices can report a wealth of information. They can be interrogated to gain answers to queries such as: Is everything working as expected? What are the levels of the diagnostics? What is the process variable? When was this last calibrated?
For example, knowing the exact value of pH when the instrument was last calibrated assures the operator that that measurement will be correct, as well as providing the temperature of the sample.
Similarly, modern pressure transmitters use digital capabilities to provide a wealth of other data, from totaliser data through to diagnostic data. For example, ABB’s Plugged Impulse Line Diagnostic (PILD) function compares the current performance of a pressure device to that set during commissioning. Any differences in these figures could indicate a blocked impulse line, allowing corrective action to be taken.
Another key role in desalination plants is played by data recorders, which are used throughout the process to ensure that water is correctly treated and also correctly billed for as it enters the water distribution network.
An example of a plant taking advantage of digital instrumentation is the world’s first dual mode desalination facility, the Keppel Marina East Desalination Plant (KMEDP) in Singapore. Designed to produce 136 mega litres of potable water from both sea and rainwater, the plant will support the national water company’s wider water security strategy of ensuring 30 percent of supply comes from desalination.
The plant uses a combination of ABB instruments and analysers to monitor the quality and quantity of water being treated by the plant. Equipment employed includes electromagnetic and swirl flowmeters, continuous water analysers to measure fluoride, turbidity, pH and conductivity, plus instruments to measure level, temperature and pressure.
Overall, digital instrumentation provides accurate readings to ensure that the produced water is up to the required quality. Accuracy is also vital to keeping costs low. As an inherently expensive process, desalination needs to work as expected if the use of energy is to be optimised, and expensive maintenance or reprocessing avoided.
Making operations and procedures easier for inexperienced technicians is another advantage, while instruments can also send performance and condition data to the vendor for online support. The result is more effective and efficient operations that ensure desalination can be a more sustainable way of solving the water crisis.
For more information about ABB’s products for desalination applications, visit https://bit.ly/ABB_Desal.
References
[1] https://eu.azcentral.com/story/news/local/arizona-environment/2019/11/29/middle-east-oman-water-desalination-reliance-costs/2123698001/
[2] https://www.mordorintelligence.com/industry-reports/india-desalination-systems-market
Krishna H Prashanth, ABB Instrumentation Global Product Line Manager, is a change agent, creative thinker, imagineer and a passionate innovation enthusiast with global experience in strategy and execution. He brings to the table: Rich experience in building sustainable solutions in Industrial automation along Product Line Strategy, Product development process, roadmap Management, Operational Expertise along Profit and Loss accountabilities, demand management, supply management, sales & marketing.
