Control and Monitoring of MSF-RO Hybrid Desalination Process. Kumar. 2013. IEEE

Control and Monitoring of MSF-RO hybrid desalination process Brajesh Kumar [email protected] Dr. M. L. Dewal [email protected] Dr. S. Mukherjee [email protected] Dept. of Electrical Engg. Indian Institute of Technology Roorkee, Roorkee, India Abstract — The growing demand for making the seawater desalination process more and more cost effective call for the two leading desalination technologies namely Multi-Stage Flash brine recirculation (MSF-BR) and Reverse Osmosis (RO) to be hybridized at various levels to complement each other. This paper demonstrates development of supervisory control and data acquisition (SCADA) based process control and instrumentation of the hybridized system. The hybridized system focuses on the use of MSF reject cooling seawater to feed reverse osmosis unit. FactoryTalk View Site Edition (SE), a real time platform for industrial automation by Rockwell Automation, is used for development and simulation of entire process. The entire process control and monitoring take place through human machine interface (HMI). Keywords — MSF-BR; SCADA; hybridized system; process control and instrumentation; HMI. I. I NTRODUCTION The reverse osmosis (RO) desalination technology is leading in terms of market share [1] due to its energy efficiency, yet multi-stage flash (MSF) plants are also in use due to their own advantage of time tested reliability [2] [3][4][5]. Hence, at this point, two major technologies exist in the desalina tion market : MSF and RO [6]. The large sc ale (50,000 – 75,000 m 3 /day) MSF brine recirculation (MSF-BR) plants are almost as cost efficie nt as reverse osmosis plants [7], but the smaller (27,000 – 32,000 m 3 /day) conventional MSF plants are lagging in terms of cost efficiency . For RO plant water flux rate through the membrane increase with the feed water temperature due to decrease in the viscosity of the solution [8]. However, it also increases salt diffusion rate through membrane and also accelerate membrane degradation rate. So optimized RO feed temperature is found to be in the range of 30ºC t o 35ºC [9]. It decreases the energy cost for reverse osmosis process as the applied pressure decreases. In this regard research has also been done at the Nuclear Desalination Demonstration Project (NDDP), Kalpakkam, India [10] and gave a clue to the use of MSF rejected cooling seawater. So there is a motivation to hybridize conventional MSF-BR plant with RO unit to make the use of MSF rejected cooling seawater, having temperature betwe en 40ºC to 45ºC, as RO feed. Nowadays, SCADA/HMI is being popular due to its capability to reduce cost, reduce manpower, increase production, and improve safety working conditions. The MSF- RO hybridized desalination plant being a large application requires SCADA/HMI system for the above said reasons. It facilitates the operator at higher hierarchy level to monitor and control the hybridized part of the desalination plant. This paper demonstrates a configuration scheme of SCADA based control and monitoring for MSF-RO hybridization. Here, a controller based on programmable logic controller (PLC) is considered to configure remote terminal unit (RTU) with human machine interface (HMI). II. SCADA CONFIGURATION SCADA refers to a whole system that gathers data from diverse sensors at a plant, factory or in other distant locations and then sends these data to a central computer which then controls, monitors and manages the data. HMI (Human Machine Interface) is a part of SCADA system. The basic components of SCADA systems are: Multiple remote terminal units (RTUs) Master terminal unit (MTU) Communica tion infrastructure s: there are two types of communication system. One is MTU-RTU communication system and another is RTU-Field device communication system. The process has typical inter-connection among field sensors, controller, and HMI for hybridized MSF-RO desalination plant as shown in figure 1. It depict a s ection of controlled plant with analog values (AV), set points (SP), status information (SI), control command (CC) with their corresponding RTU-Plant interface and feedback (FB) with the corresponding feedback controller. MTU-RTU communica tion uses LAN for industrial/process plant applications. It may be wireless or wired. Commonly used technologies are Ethernet, RS485/Modbus and Foundation Field bus for wired type while Wi-Fi and ZigBee for wireless type. On the other hand RTU- Field device communication may be of two types: analog or digital. Digital communication uses wired LAN while 4-20 mA

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Control and Monitoring of MSF-RO Hybrid Desalination Process. Kumar. 2013. IEEE