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Electrodialysis Principle Setup of a 20 m3/h ED/RO plant to produce pure water from river water. A case study focusing on the electrodialysis process and the compatibility with RO pretreatment by Rudolf E. Brunner and Dr. Patrick Altmeier Ioncontract GmbH PCCell GmbH Znaimer Straße 34 Lebacher Straße 60 71263 Weil der Stadt 66265 Heusweiler [email protected] www.electrodialysis.de Electrodialysis principle • Anions move towards anode • Cations move towards cathode • Cation exchange membranes let cations through and block anions • Anion exchange membranes let anions go through and block cations • Electroneutrality 1 Electrodialysis Model Principle of electrodialysis is a stack of alternating cation and anion exchange membranes. Model: A tower block with alternating red and blue floors, filled with people Looking down, youmay see either blue or red floors. Electrodialysis Rules • Yellow: go up! Do not pass blue ceiling! • Green: go down! Do not pass red floor! 2 Apply Rules • All have moved until the blocking rule apply. • Result is: blocking rule apply in each second floor. • Note: We ignored the electroneutrality, for instance. An ED stack scheme 3 Continuous ED processing • A Diluate enter the cell, DC will be processed and Diluate Electrodialyzer out leave the cell as the finished product. Concen- trate out • The solute for the uptake of the ions enter the cell and leave it as the final concentrate. Electrode rinse Diluate • Electrode rinse will be in circulated (option: use of concentrate stream) Concen- trate in continuous mode Batch ED process DC • Each process solutionis Electrodialyzer hydraulical sealand cirulated often. • Ionic concentration shift slowly; each solution remain the same. Concen- Diluate trate Batch mode 4 Minimum process requirements PCCell ED64 0 02 PCCell B-ED1-2 External liquid tanks Batch desalination: conductivity of concentrate and diluate 22 20 18 16 14 12 LF Conc 10 8 LF Dil 6 4 2 0,8 0,6 Drinking water quality Conductivity / mS cm 0,4 0,2 0,0 00:02 00:04 00:06 00:08 00:10 00:12 00:14 00:16 00:18 00:20 00:22 Time / h 5 Batch desalination: voltage / current characteristic 4,0 24 U 3,5 20 3,0 16 2,5 12 2,0 1,5 Current / A Voltage / V 8 1,0 4 0,5 0 0,0 00:02 00:04 00:06 00:08 00:10 00:12 00:14 00:16 00:18 00:20 00:22 Time / h Batch desalination: The charge in course of the process 160 140 n(NaCl) in Diluate 120 100 80 60 Charge / mF 40 20 0 00:02 00:04 00:06 00:08 00:10 00:12 00:14 00:16 00:18 00:20 00:22 Time / h 6 Batch desalination Power consumption 8 7 6 5 4 3 2 Consumed Power / Wh 1 0 00:02 00:04 00:06 00:08 00:10 00:12 00:14 00:16 00:18 00:20 00:22 Time / h Starting point of a batch desalination 7 Sizing an ED unit Key parameters for ED cell layout • Membrane area need (How • 20.000 l / h from 6 mmol/l to 3 much salt at what current mmol/l = about 60 moles = density)? about 1600 Ah • What is the conductivity level of • 10 A / m2 = 160 m2 anion diluate? membrane area (=460 cell • How much desalination per pairs) single pass (What charge has to • 3 mmol/l = about 290 As/l be taken up)? • => At a cell with 3,5 A, a minimum flow of 42 l/h is • What is the Amperage and flow needed minimum. per cell? • The cell needs 50 l/h minimum. • As EDR is used, some time • What is the final layout? interrupts are not available: • Two cells with 400 cell pairs in series have to be set up. 8 The Setup of a 20 m3/h ED/RO plant to produce pure water from river water. Task: • Produce a pure water <20mS cm with a maximum recovery rate • Use also boiler outlet water for recycling 9 Water quality at the different proecessing steps DIAGRAMM 01 60 700 600 50 Chlorid - Konz. mg/l 500 40 Chlorid mg/l Leitfähigkeit µS/cm 400 30 300 20 Leitfähigkeit µS/cm 200 pH-Wert ; TEMP. °C Härte °dH; Härte °dH 10 pH - Wert 100 0 0 0 10 20 30 40 50 60 10 MAINWASSER 20 nach MS-Filter - 30 REINWASSER - 40 DILUAT - 50 PERMEAT Temp [°C] GH °dH pH-Wert LF µS/cm Pump unit of the 20 m2 plant with sample valve battery at the right side and ED Stack 10 RO modules + pretreatment tanks RO pretreatment to prevent scaling. The pretreatment chemicals remain in the RO concentrate. RO concentrate recycling need a proper adaptionof the pretreatment chemicals. 10 square meter pilot production unit for pharmaceutical applications 11.
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