rev.1.1 Page 10-18
In order to prevent the Concentrate stream from exceeding the solubility limits, a small
amount of Concentrate is sent to drain. This water is replaced with Dilute feed water,
through the Concentrate Make-up valve. The amount of Concentrate Bleed required is
dependent on the Recovery required, which is itself dependent on the flow rates and the
feed water hardness level. For more information on Recovery and Concentrate Bleed, see
the “Concentrate Bleed” section below.
The conductivity of the Concentrate stream should be kept between 50 and 600 µS/cm. This
will allow sufficient current flow through the E-Cell Stack. For applications with very low
conductivity feed water, brine can be injected directly into the Concentrate loop to raise the
conductivity.
Note: The Recovery must never be increased in order to increase the conductivity in the
Concentrate loop. The Concentrate Bleed flow must be set to achieve the required recovery
rate. If the Concentrate Bleed flow is decreased, the maximum allowable recovery will be
exceeded and scaling of the Concentrate chamber will begin.
10.1.3 Concentrate Bleed Stream
Range – Dependent on required recovery ratio.
Ions removed from the Dilute stream must be expelled from the E-Cell Stack through the
Concentrate Bleed stream to prevent scaling. The Concentrate Bleed flow required is
dependent on the amount of hardness. Recovery ratios have been calculated to maintain
an acceptable hardness level.
Feed Hardness
(ppm as CaCO
3
)
E-Cell
Recovery
(1)
NaCl Injection into C-loop
(2)
(uS/cm)
0.0 – 0.10 95% - -
0.10 – 0.50 90% + 400 – 500
(1)
Lowering the recovery lowers the hardness level in the concentrate loop and hence
decreases the scaling potential.
(2)
NaCl injection also reduces the electrical resistance of the stack, and hence the power
consumption.
At feed hardness levels <0.1 ppm, a maximum recovery of 95% applies and periodic
cleanings are generally not required in the absence of upsets.
At feed hardness levels >0.1 ppm, the recovery is reduced to 90% and salt is injected into the
Concentrate loop as shown in the table above. Periodic cleanings are required.
Recovery ratios are provided because the amount of Concentrate Bleed required is
dependent on the feed water hardness, the Dilute flow and the Electrode flow rates (as Dilute
flow increases, the amount of hardness entering the E-Cell Stack also increases).
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