Design, modeling and optimization of a seawater reverse osmosis desalination plant.
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Potable water is one of the major needs for human, animals and plant survival. But recently, due to the growth in population and industrialization, fresh water shortage has escalated to alarming levels particularly in the Middle East and Africa. South Africa has not been spared in this predicament. Recently, Cape-town and its surrounding areas have been hard hit by water shortages and in one of the years, the region almost got to day zero, where all water sources were about to run dry, yet the region is surrounded by vast amounts of sea water. Research and development of several methods to mitigate this problem is still ongoing. Desalination of seawater is one of the several ways which have been used to ease this problem, and Reverse Osmosis (RO) is generally taking over as the preferred technique of desalination because of its generally higher efficiency and better quality of water produced using generally lower energy. Research has also shown that the limitations and concerns of using RO technique on water productivity are membrane fouling and high energy consumption in these plants. Design, modeling and optimization using modelling and simulation softwares and experiments on seawater reverse osmosis (SWRO) desalination plant is one of the ways in which this water shortage crisis may be alleviated. This dissertation seeks to attend to the limitations of the available plants in use through experimentation, coming up with mathematical models and simulations to increase throughput and efficiency of the system. Theoretical data analysis and membrane modeling of a SWRO desalination unit was done on the design and undertaken using Hydranautics Nitto Group Company powered Integrated Membrane Solutions Design (IMSDesign) software, a membrane modeling software that allows users to design a reverse osmosis (RO) system based on Hydranautics membranes. The experiments were done on the Victoria and Alfred (V&A) Waterfront desalination unit, a seawater desalination plant located along the Atlantic Ocean coastal city of Capetown, South Africa. Extracted data from experiments was collected and statistically analyzed using Microsoft excel and different relationships of parameters were plotted. Some of the design input and output parameters that were studied using include feed and permeate TDS, pressure, temperature, pH, energy consumption and conductivity. The effects of different fee parameters were compared against their permeate variables in the month of November 2018, and several relationships and correlations were plotted. Experimental data showed that an increase in feed temperature resulted in a decrease in permeate TDS, whereas and increase in feed pressure resulted in a general increase in permeate TDS. Finding the optimum compromise between the two input variables was done and optimum values were found. Energy efficiency and reducing energy consumption of the plant while not compromising on product quality is also one of the parameters that were studied and the relationships between feed TDS, feed temperature, feed pressure and feed pH against energy consumption were modelled. Modeling and simulation using ROSA and IMSDesign softwares was undertaken and several equations and correlations of specific energy and input temperature, feed temperature and permeate TDS, feed TDs and permeate TDS were produced. Optimization of the V & A desalination plant was performed using experimental data extracted from the plant and some assumed data. Simulation and optimization was accomplished using Water Application Value Engine simulation software and improvements in specific energy consumption, permeate TDS and permeate productivity were observed.