Automation/Desalination Fresh Water from the Sea – Automating a World–Scale Desalination Plant
Water, water, everywhere - Nor any drop to drink: The Nemmeli sea water desalination plant in Tamilnadu uses reverse osmosis membranes to process sea water into drinkable water. It is also the first desalination plant to use electric actuators in redundant line topology for the automation of valves. Here’s a look at how highend technology was combined to build India’s largest seawater desalination plant...
The Nemmeli sea water plant, with the capacity to treat 100 MLD sea water a day, is the first and largest desalination plant in India on Engineering, Procurement & Construction (EPC) basis meant for 100 per cent potable use. The project has been executed by the water treatment company, VA Tech Wabag in partnership with IDE Technologies (Wabag - IDE consortium) for the Chennai Metropolitan Water Supply and Sewerage Board (Chennai Metrowater).
Auma India was the technology provider for automating flow control valves throughout the desalination plant. The plant is constructed at a cost of `1033 crore on a design, build, operate basis and is spread across 81,000 sq mt of land. It uses reverse osmosis membranes to treat the sea water into potable water, to be supplied to Southern Chennai.
Owing to repeated failure of the monsoons, increasing urbanization and population, there is shortage of water supply in several areas across the Tamilnadu state. “With a view to overcome these challenges, desalination of sea water is considered as the best option considering the fact that we as a country are blessed with long coastlines,” said Sr Manager - E&I (Construction), VA Tech Wabag, K Manickam.
An EPC Contractof World–Scale Dimensions
Wabag was entrusted with the total responsibility of building this plant on EPC basis. It was a large and complex project involving procurement of specialized process equipment from various countries across the globe such as: RO membranes from Hydranautics, Japan; intake screens from Johnson Screens, Australia; UF membranes from NORIT, Netherlands; high pressure pumps from flow serve, Spain; disc filters from Arkal, Israel; super duplex pipes and fittings from H-butting, Germany and Tubacex, Spain etc.
Agreeing and talking about the process in detail, Manickam explained, “The piping materials used are exotic in nature and are not readily available and hence it had to be planned and procured well in advance.
Moreover, the fabrication of these piping materials had to be done under controlled conditions. The whole planning for the plant was meticulous which enabled us to commission the plant in record time without any hindrance. Even the critical work of intake and outfall under water pipeline laying work was successfully done at one go despite the adverse weather conditions and rough sea conditions in the Bay of Bengal.”
Precise Water Flow is the Key to Efficient Desalination
For efficient operation of the plant, precise water flow control is required at each stage, starting from intake till the post-treatment system. This calls for speedy communication between each system for maximum plant availability.
Therefore, electric actuators enabled with latest technologies were required to operate valves to control the flow of water throughout the plant. The electric actuators in redundant line topology for the automation of valves were supplied by Auma India.
Talking of Auma’s involvement in the project, Managing Director, Auma India, Arvind K Goel averred, “Our scope of work included supplying and commissioning assistance for actuators with integral starter (274 nos.) with MODBUS communication protocol, using redundant line topology resulting in high process availability and faster response time. These actuators are connected to the DCS supplied by ABB.”
Using Electric Actuators – Automating the Flow Process
Pentair Ltd / VA Tech Wabag had awarded the contract to Auma India for the supply of electric actuators for automating all valves. This company is the only electric actuator manufacturer in India offer MODBUS enabled actuators with open protocol architecture in redundant line topology, allowing easy and hassle free integration of actuators with any DCS for this project.
“Only actuators with integral starter (274 nos.) with MODBUS communication protocol were needed in this project. The Nemmeli SWRO is a state-of-the-art desalination plant comprising of seawater intake system, pre-treatment system (disc filters and ultra filtrations), backwashing, reverse osmosis system (product treatment through RO high pressure pumping and pressure exchanger, filtering the rejected water) and posttreatment system.
Desalination With State–of–the–Art Automation Technology
These MODBUS enabled electric actuators in redundant line topology allows quick response time of about 125 ms to the DCS, resulting in optimum reliability and maximum plant availability. High degree of automation results in better efficiencies,” elucidated Goel. Conventional technologies include use of standard electrically operated valves, which can be connected in loop topology that is slower in communication speed compared to redundant line topology.
The process at Nemmeli desalination plant required fast communication to the DCS and needed to establish robust control architecture. Hence, the solution offered by the company was superior to the existing technologies.
Bringing in the Technical Expertise
Building the nation’s largest seawater desalination plant undoubtedly requires precision to the highest level. Talking about Auma’s contribution to the project, Manickam said, “Their involvement in this project pertains to the supply of actuators for various critical valves that are located in our process plant systems at UF and RO units. The precise operation of these motorized actuator valves plays a crucial role in the successful operation of the plant as it is wholly automated. The company with their vast experience and technical expertise on this job, exhibited a high degree of commitment and dedication during the installation and commissioning of the plant.”
According to Manickam the Tamil Nadu Government has announced four desalination plants in the state viz. Chennai, 150 MLD expansion project at Nemmeli; Chennai – 200 MLD new project and 200 MLD expansion at Pattipulam; Tuticorin – 100 MLD and Ramnad – 100 MLD. “Gujarat too is coming up with a 300 MLD desalination plant. All this indicates that as of today, industries are increasingly resorting to
desalination for industrial use. Afterall, desalination is a reliable, viable and sustainable alternative source of water,” concluded Manickam.