Simulation of Optimal Input/output expectations under 3kW Load of Single Stage BWRO Unit at Different Feed TDS

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1 Simulation of Optimal Input/output expectations under 3kW Load of Single Stage BWRO Unit at Different Feed TDS NURUL AIDA MOHAMED1, M.A. ALGHOUL 1*, ASSIM FADHIL¹, P. POOVANAESVARAN, MAYS ABDULRAZZAQ, NILOFAR ASIM, K.SOPIAN Solar Energy Research Institute, Universiti Kebangsaan Malaysia, Bangi, Selangor, MALAYSIA *Corresponding author: Abstract: - Reverse osmosis (RO) is an appropriate process to be applied in areas where brackish water is available. This study simulated the optimal input/output that can be expected under 3kw load of single stage BWRO unit at different. The range of TDS is ppm. The simulation has been carried out using ROSA (Reverse Osmosis System Analysis) software. The obtained results showed that the energy requirement, amount and quality of fresh water are strongly depending on the concentration of TDS. The specific energy range required to operate the BWRO system is kWh/m³. The operating pressure range is bar. The results also showed that the recovery range and the desalination cost are 30-50% and $/m3 respectively. Overall, 3kW load of single stage RO desalination system is enough to treat brackish water of high salinity and to produce appropriate amount of fresh water (40-50 m 3 /day with reasonable water quality and price. Keywords: desalination, brackish water, reverses osmosis,, 3kW load, ROSA software, optimal expectations 1 Introduction The necessity of fresh water for people drinking and consuming are important. World Water Council reported that by 2020, the world will loose 17% of fresh water needed to sustain the world population. Approximately 1.76 billion people had to face with water crisis [1-2]. Desalination is a water treatment process to remove salts, dissolved mineral and contaminants from high salinity water to fresh water that suitable to drink. Freshwater is defined as water that containing less than 1000 mg/l of salts or total dissolved solids (TDS) [3, 4]. The most widely used technology for desalination is phase-change/thermal and membrane process. Reverse osmosis (RO) is categorized under membrane category. This research will focus on the effect of feed TDS on designing small scale RO desalination system in terms of simplicity of the design, the energy consumption and the cost. The cost of water production is mainly influenced by initial investment on equipment, cost of maintenance and cost of operation. Energy also plays an important role to power high pressure pump and pre-feed pump which are chosen based on feed water salinity. Besides that, RO desalination system design configuration should be as simple as possible. Other than that, monitoring of TDS is necessary because the different of TDS can give different results. The main components in reverse osmosis (RO) system consist of feed pump, high pressure pump and membrane modules. High pressure pump is imperative since it is enabling removing the total dissolved solid (TDS). Much more energy is required to remove higher. Single stage BWRO system would be the best choice for brackish water to consume the lowest amount of energy [5]. 2 MATERIALS AND METHODS 2.1 Type of Membrane TDS concentration affects both the system flux and the salt rejection of BWRO unit. When the increases, the driving force decreases (under constant applied pressure), and causes ISBN:

2 increasing of osmotic pressure. This will decrease of the flux. Membrane plays an important role in the design of reverse osmosis (RO) system. The membrane used in drinking water industries must have certain properties such as high flux, high rejection rate (to remove TDS in water), fouling resistance (high endurance) and can be operated at low pressure. These properties will increase the efficiency of the RO system as well as its flexibility. In this study, FILMTEC BW type of reverse osmosis membrane manufactured by DOW Company has been used. 2.2 Reverse Osmosis System Analysis (ROSA) The simulation will be carried out using reverse osmosis system analysis (ROSA) software developed by Dow Chemical Company. ROSA has been used successfully to evaluate the performance of membranes and energy requirements for desalination [6-10]. 2.2 Design assumptions and output expectations 1. The RO design is one stage with un limited number of pressure vessels. 2. The load of the RO unit is 3 kw only. 3. The permeate TDS is as high as possible but less than 500ppm. 4. The type of membrane that used in this research is BW The optimal output: 1. Maximum recovery 2. Maximum permeate flow 3. Minimum Specific Energy 4. Minimum Pressure 4 RESULTS AND DISCUSSION The design assumptions in the studied BWRO system are single stage RO system, 3 kw load, concentration range of ppm, permeate TDS must be lower than 500ppm [11-12]. The brackish water is chosen in this study since it is suitable to be applied in remote locations in Malaysia. Table 1 describes the optimal input and output values under 3kW load of single stage BWRO unit at different feed TDS. TDS (ppm) Table 1 summary of optimal input/output of 3kW single stage BWRO unit at different Feed flow (m 3 /day) System Recovery (%) Permeate Flow (m 3 /day) Power (kw) Pressure (bar) Specific Energy (Kwh/m 3 ) PV Elements Permeate TDS (ppm) Cost ($/m 3 ) optimal system recovery Based on the load assumption of 3kW, and maximum permeate TDS below 500 ppm. As shown in figure 1, at 10000ppm, the optimal recovery is found 30% and permeate TDS is ppm. When is ppm, the optimal recovery is found 40% with permeate TDS , , 290, and respectively. At 15000ppm, the optimal recovery is found 50% and permeate TDS is ppm. However, System recovery is optimized to balance productivity, energy consumption, membrane life, fouling and cost [13]. ISBN:

3 kw BWRO system Permeate TDS ( ) ppm low, this will help to increase the membrane life time. 30 System Recovery (%) Pressure (Bar) kw BWRO system PermeateTDS ( ) ppm 25 Figure 1: Optimal system recovery at different Optimal feed flow and permeate flow As shown in figure 2, feed flow and permeate flow decrease when increases under the assumption of this study. At of ppm, the range of optimal feed flow and permeate flow are (80-167m 3 /day) and (40-50m 3 /day) respectively. Although the feed flow range is wide, but the range of permeate flow is almost narrow under studied. Flow rate (m 3 /day) kw BWRO system Permeate TDS ( ) ppm Figure 3: Optimal pressure at different 4.4 Optimal specific energy Salinity of feed water has significant effect on energy consumption for a reverse osmosis system. So, the energy issue should be addressed in the planning of the design of the RO system. In theory, the high concentration of TDS requires more energy compare to the low TDS which has been proved in this research from ppm. The relationship between the and optimal specific energy is shown in figure 4. The range of specific energy with ppm is kWh/m Feed flow Permeate flow Figure 2: Optimal feed flow and permeate flow at different 4.3 Optimal feed pressure Specific energy (kwh/m 3 ) kw BWRO system Permeate TDS ( )ppm As shown in figure 3, the feed pressure increases when the increases. The range of working feed pressure is bar under the different. However, the simulated feed pressure is optimal because it is considered 1.3 Figure 4 Optimal specific energy at different ISBN:

4 4. 5 Optimal desalination cost The cost of water depends on the capital cost of the initial membrane elements, pressure vessels, pumps, operational and maintenance costs for membrane replacement and electricity. In this study, the membrane replacement price was assumed around $300 while the replacement rate per year was set at 25%. The life time for the BWRO system is estimated for 12 years while the interest rate is estimated to be as high as 8% per year. The production cost of produced water in this study is shown in figure 5. The cost to desalinate water with TDS value ppm is ranged from 0.41 $/m3 to 0.48 $/m3. The production cost is different due to the different system design parameters used in this research such as the TDS concentration, feed flow, flow rate, specific energy and number of elements in order to present the 3 kw of power and permeate TDS less than 500ppm (290 ppm to 408 ppm). There are several factors that will also affect the production cost of water such as feed flow and flow rate (water volume). [14] Reported that the two similar RO systems that used water of different volume of TDS have significantly different cost. Production Cost of Water ($) kw BWRO system Permeate TDS ( ) ppm Figure 5 Optimal desalination cost at different [7] Reported that the desalination cost of 3000 ppm of brackish water is 0.32 $/m3 which is lower than the production cost obtained in this study because of the low salinity of their brackish water. 5 Conclusions The results of this simulation study are evaluated under 3kW load of single stage BWRO system and allow the permeate TDS to be as maximum as possible but less than 500 ppm. The results of this study showed good agreement with previous researches. In general, design configuration of BWRO desalination system should be as simple as possible. However, this study showed that using more than one pressure vessel can significantly reduce the pressure and consequently increase the membrane life time but at the same time increase the complexity of the system. 3kW RO load is considered a good choice in terms of specific energy, amount and quality of permeate flow, and desalination cost as a small scale single stage deal with BW of high salinity ( ppm). Monitoring of TDS is necessary because, different can give different results. References:- [1] Gilau, A. M., & Small, M. J., Designing cost-effective seawater reverse osmosis system under optimal energy options, Renewable Energy,Vol. 33,2008,pp [2] Vorosmarty, C. J., Green, P., Salisbury, J., Lammers, R.B.,Water stress in to today s and tomorrow s world. Global water resources: vulnerability from climate change and population growth, Science, Vol.289, 2000, pp [3] Greenlee, L.F., Lawler, D. F., Freeman, B. D., Marrot, B., Moulin, P., Reverse osmosis desalination: Water sources, technology, and today s challenges, Water research, Vol. 43, 2009, pp [4] Sandia. Desalination and Water Purification Roadmap A Report of the Executive Committee. DWPR Program Report 95. U.S. Department of the Interior, Bureau of Reclamation and Sandia National Laboratories. Available from: [5] Poovanaesvaran, P., Alghoul, M.A., Sopian, K., Sulaiman, M.Y., Amin, N., Yahya, M., Design aspects of small-scale photovoltaic ISBN:

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