How to Design an RO / NF System

Step 6 - Calculate the Number of Pressure Vessels Needed

Step 1: Consider Feed Source, Feed Quality, Feed / Product Flow, and Required Product Quality
Step 2: Select the Flow Configuration and Number of Passes
Step 3: Select Membrane and Element Type
Step 4: Select Average Membrane Flux (Design Flux)
Step 5: Calculate the Number of Elements Needed
Step 6: Calculate the Number of Pressure Vessels Needed
Step 7: Select the Number of Stages
Step 8: Select the Staging Ratio (Array Ratio)
Step 9: Balance the Permeate Flow Rate
Step 10: Example

Calculate the Number of Pressure Vessels Needed

A) Total number of pressure vessels needed = (total number of elements) / (number of elements in pressure vessel)

B) Round up to the nearest integer.

C) For large systems, 6-element vessels are standard, but vessels with up to 8 elements are available. For smaller and / or compact systems, shorter vessels may be selected.

D) Although the approach described in the following sections apply for all systems, it is especially applicable for 8-inch systems with a larger number of elements and pressure vessels, which then can be arranged in a certain way. Small systems with only one or a few elements are mostly designed with the element in series and a concentrate re-circulation for maintaining the appropriate flow rate through the feed / brine channels.

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