FCE is Important for EDI Electrodeionization System Performance

FCE is Important for EDI System Performance. Electrodeionization systems depend on conductivity, CO2, and Silica; all brought together by using FCE, or Feedwater Conductivity Equivalent.

For an electrodeionization system to operate properly, the feed water must be high-quality Reverse Osmosis (RO) permeate. An RO permeate water analysis will provide the data that is needed to estimate FCE.

FCE (Feed Conductivity Equivalent) determines the “load” on the EDI, and predicts electrodeionization performance well.

As FCE increases, the load on the EDI system increases, and EDI product quality decreases. The theory is explained below.

FCE, normally in microsiemens (technically μS/cm), is the weighted sum of the ionic load, the load due to Total CO2 (CO2 + HCO3–+ CO3-2) in mg/l and silica (SiO2) in mg/l. This weighting correlates with water treatment experience.

FCE (μS/cm) = Conductivity (μS/cm) + 2.79*(Total CO2, ppm) + 1.94*(SiO2, ppm)

• Conductivity is the measured conductivity at 25°C, in μS/cm.
• Total CO2, in ppm, is the sum of the concentrations of CO2, HCO3–, and CO3-2. This is important for 2 reasons. First, as pH changes the Total CO2 remains the same but the species present convert from one to the other. Second, CO2 and its ionic forms are weakly absorbed on ion exchange resins and adds a significant load to the EDI.
• Silica, SiO2 in ppm, generally adds a small load but is added for emphasis.

FCE example: if there is 5 μS/cm conductivity, 3 ppm CO2, 3 ppm HCO3, and 1 ppm SiO2 then

FCE = 5 + 2.79*6 + 1.94*1 = 23.7 μS/cm

Note that in this example many users would only consider the EDI load to be 5 μS/cm, when actually it is almost 24 μS/cm. As you can see, CO2 and HCO3– contribute significantly to the load on electrodeionization. Inside the EDI, which is at pH 7.0, most of the CO2 exists as the bicarbonate ion, HCO3–.

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Taxonomy

• Water
• Electrodeionization
• Ultra Pure Water