Bench scale electrodeionization for high pressure boiler feed water

In this paper, a bench scale RO/EDI system for high pressure boiler feed water is reported. Technical and economical aspects were evaluated to determine whether RO/EDI system is feasible to replace existing ion exchange bed. The EDI module used in this study was all filled electrodeionization type with mixed bed ion exchange filler. All product quality of demin water produced by RO/EDI during bench scale test shows good water quality (conductivity: 0.3–0.4 μs/cm; pH: around 6.3; silica: 0.00–0.01 ppm; and Na: < 0.003 ppm), even better than existing demin water system specification (conductivity: < 5 μs/cm; pH: 6.5–8.5; silica: < 0.12 ppm; and Na: < 0.3 ppm), except pH. Dissolved CO2 in water (HCO3−) is a suspected substance which is present in RO/EDI product water that influences the pH. The specific water cost of RO/EDI was US$0.53/m3 lower than existing ion exchange beds, US$0.66/m3. The main operating costs were membrane replacement and electricity cost. Long term performance of the RO/EDI system showed stable and high product quality even during periods when the feed solution has relatively high conductivity.

► Long term performance of bench scale EDI showed stable and high product quality.
► Technical and economical aspects were evaluated for high pressure boiler feed water.
► Dissolved CO2 in water (HCO3 −) is a suspected substance that influences the pH.
► The specific water cost was US$0.53/m3, lower than existing ion exchange bed.
► The main operating costs were membrane replacement and electricity.