Economic and Technical Analysis of a Reverse-Osmosis Water ...

Figure 7. Effect of seawater salinity on water production cost and quality.Case 4. Effect of inlet temperatureLiterature shows that with higher temperatures, the salt passage increases, flux (permeate flow)increases, and operating pressure required is lower. With lower temperatures, the inverse occurs,in that salt passage decreases (reducing the total dissolved solids (TDS) in the product water),whereas operating pressures increase. When operating pressures do not increase, then the amountof permeate or product water is reduced. In general, RO systems are designed for raw watertemperatures of 25 o C. Higher temperatures or lower temperatures can be accommodated withappropriate adjustments in the system design. In this study, because the Gulf surface watertemperature always remains higher than 20 o C and goes up to higher than 30 o C [11], atemperature range between 33 o and 20 o C is used to estimate its effect on RO systemperformance. The analysis shows that at constant permeate flow (2,000 m 3 /day), the fresh watercost increased slightly by 2.5%, power consumption increased by 12.6%, feed water pressureincreased by 16.9%, while the fresh water quality improved by 31.6%. This is shown in Table 5and Figure 8.Table 5. Effect of RO inlet temperature on water production cost and qualityTemperature( o C)Fresh watercost($/m 3 )Fresh waterquality(ppm)Powerconsumption(kWh/m 3 )Recoveryratio(%)Feed flow(m 3 /day)Feed waterpressure(bar)Brine flow(m 3 /day)Brinesalinity(ppm)33 0.982 301 2.90 0.42 4,800 54.3 2,800 60,00032 0.983 294 2.92 0.42 4,800 54.9 2,800 60,00031 0.985 286 2.94 0.42 4,800 55.5 2,800 60,00030 0.986 279 2.97 0.42 4,800 56.1 2,800 60,00029 0.988 272 2.99 0.42 4,800 56.8 2,800 60,00028 0.989 265 3.02 0.42 4,800 57.6 2,800 60,00027 0.991 257 3.05 0.42 4,800 58.4 2,800 60,00026 0.993 250 3.08 0.42 4,800 59.2 2,800 60,00025 0.995 243 3.12 0.42 4,800 60.1 2,800 60,00020 1.007 206 3.32 0.42 4,800 65.4 2,800 60,000