Double Pass Configuration

Adding a second pass in CCRO is the same as RO/NF/ROSC. Designers should assume a break tank between the passes.

The flow calculator, and user inputs, for a two pass configuration are a duplicate of the single pass fields. The second pass recovery will default to 90% (to improve permeate quality). Additional input changes are generally not required: Feed Ratio, Recovery and Conc. Recycle default to 120%, 20% and 20 gpm (4.54 m3/h) per PV respectively (See Figure 1).

Figure 1: Double Pass Flow Calculator

Additional notes regarding above inputs:

  1. Adjust second pass recovery if required (recommend default 90%).
  2. The System Recovery is automatically calculated and displayed in the System Recovery field in the top right corner of the Flow Calculator. Increase Pass 1 recovery to increase System Recovery (to match target system/overall recovery).
  3. It is typical to recycle 100% of the concentrate from Pass 2 to the feed of Pass 1.
  4. While the pressure vessels in a first pass (or single pass) CCRO are typically sized to allow for one element spacer, it is typical for second pass pressure vessel length to match the number of installed elements. No spacers are needed as the second pass will always be run at high recovery (and as such there is no need to increase sequence time).
  5. Select OK.

Note:  The permeate split feature is not available with CCRO. However, as the permeate conductivity increases from the first to last CC Cycle, permeate from the start of the batch (with higher permeate quality) may be diverted.