Water. desalination + reuse

TECHNOLOGY systems' overall weight and dimensions including increasing the individual pump unit size and/or increasing the number of pumps per motor through a double motor shaft configuration. Figure 3. Total 20-year life-cycle costs Table 5. Weight and Dimensional Comparison pumping system some parameters assume that the pumps are working in combination with an isobaric energy recovery system. For a full listing of the cost parameters and assumptions for the CF and AP pump, readers should consult the paper Modular Pumps Bring Efficiencies presented by the authors at the International Desalination Association's 2013 World Congress in Tianjin, China. TwENTY-YEar LifE-CYCLE COsTs Looking at Figure 3, CF energy costs on average consume 98% of their total 20-year life-cycle costs. Energy consumed by the high-pressure pump typically consumes as much as 50% of the total operating cost to produce water within the overall SWRO process 1. Therefore, high pressure pumping efficiency is of utmost importance when targeting ways to improve the overall efficiency and operating costs for SWRO. PrEsENT wOrTH aNd rETurN ON iNvEsTmENT (rOi) Both the Present Worth Costs and Payback Period show that the AP system holds a strong advantage over traditional CF pumps. Even in the extreme case at 1,136 m3/hr payback is less than three years. Payback is less than one year for the 318 and 568 systems. wEiGHT aNd dimENsiONs Looking at the overall installed weight and dimensions shows that CF systems still possess an advantage over the AP system. However, just looking at the pump weight, the AP pumps are significantly lighter below 568 m3/h. Less weight should correlate to lower materials and consequent manufacturing costs as the volume of AP pumps being applied in the marketplace increases. Possibilities exist for improving the AP | 30 | Desalination & Water Reuse | November-December 2013 sENsiTiviTY aNaLYsEs Using the standard set of costs and conditions established in Tables 1-5, the Figures 4-7 show how varying energy costs, RO feed pressure, CF capital costs and AP spare parts costs impacts the return on investment for the AP system. Energy costs obviously play a significant role and give the AP system a decisive advantage where power costs are high. Even at US$ 0.10/kWh the AP system yields a less than five-year return on investment over the entire flow range considered. However as the pump flow rate increases to 1,136 m3/h, the AP system's diminished efficiency advantage and added spare parts burden pushes the ROI to beyond 12 years at US$ 0.065/kWh. Another important factor that impacts energy consumption and thus the payback period for an energy-saving high-pressure pump is the RO feed pressure. RO feed pressures typically range between 45-69 bar depending on membrane technology, age, condition and other operating conditions. With the introduction of nano-based membranes and competition between membrane manufacturers, RO feed pressures between 45-55 bar are common today. Figure 5 shows that, at the lowest feed pressures, the AP system still provides a quick return when compared to CF pumps. Even the 1,136 m3/h AP system yields a 20% return on investment (5-year payback) over the CF system at a feed pressure of 40 bar. The installed AP system costs were 45% more expensive than the CF system on average over the three scenarios. The estimated installed capital expenditure (capex) costs were based on engineering estimates and actual quotations from the pump manufacturers and other major component suppliers. Manufacturers' quotations are subject to significant variations from initial budgetary pricing to final/best firm fixed price quotations in addition to volatility in commodity materials pricing. Therefore, we also considered the sensitivity of payback versus the Total 20-year CF Installation and Capex Costs. In Figure 5, a multiplier of 0-1 was applied to the Total 20-year CF Installation and Capex Costs and plotted against the payback period on the vertical axis.

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