RamdounPURE CEDI Continuous Electrodeionization                               

CEDI System Design

RamdounPURE®With the “all-filled” module construction described above, salt injection or recirculation pumps are not necessary, therefore reducing system complexity and potential maintenance downtime. The operating cost is also lower because a concentrate recirculation pump can use nearly as much electricity as the CEDI modules themselves. The modules typically use only about one megajoule (MJ) of electricity per cubic meter (m3) of product water, compared to 20 to 50 MJ/m3 for the high-pressure RO pump.

CEDI systems often use smaller modules in parallel to obtain high product flow rates. Therefore, if a problem occurs with one particular module, that module can simply be isolated from the system and the other modules can process a slightly higher flow until a replacement can be installed. Following the same approach, the rectifier can be designed to operate each module individually. Individual DC power controllers allow some degree of operational flexibility and additional individual module monitoring capabilities. The controllers are cost-effective for small and medium sized systems up to about 100 m3/h. The CEDI control system’s main requirement is that the DC power be shut off if insufficient water flow occurs. This feature prevents overheating and potentially permanent damage to the CEDI modules and can be accomplished by using flow switches on both the product and concentrate streams, as well as a “run signal” from the RO system or CEDI feed pump.

Proces Considerations with RO/CEDI

The CEDI process has gradually evolved into a polishing demineralization step that is almost always used downstream of an RO system. This has occurred mainly because CEDI devices are susceptible to hardness scaling, organic fouling and physical plugging by particulates and colloids. It also occurs because CEDI product water quality is somewhat dependent on feed water quality. While some CEDI devices may be able to produce “two-bed quality” water directly from softened feed water, most power plant applications now require “mixed-bed quality” water. This typically cannot be produced by CEDI alone. By using RO as pretreatment to the CEDI, the dissolved solids are reduced to a level that allows the CEDI to meet the feed water quality requirements of a high-pressure boiler (Table 1). Also, RO removes organics that could foul the ion exchange resins in the CEDI modules and it removes particulates that could clog the narrow flow channels in the resin compartments (spacers) or the resin bed itself.

Features:

Reliable, compact design. 

Elimination of possible regenerate contamination.

Truly chemical free. No brine feed to CEDI system compare to competitor 

Does not produce CL2 at anode, the concentrate can be recycled. 

Patented use of ion exchange resin in the concentrate channel.

No concentrate circulation pump.

Lower operating cost.

Easy installation; easy design and maintenance.