forward osmosis tubular module

Tubular modules made from tubular forward osmosis membranes

Tubular module summary

Packing density Up to 500 m2/m3
Advantage ease of modularization and ease operation when wastestreams contain high amounts of fouling agents and/or solutions entering the module have high viscosities
Disadvantage tube wall thickness might limit the water flux performance of tubular FO membrane modules to a level where the modules are not economically viable

 

Detailed description

forward osmosis tubular module
Image from trihigh.com

Membrane modules based on tubular membranes are well-know in the water treatment industry for ultra-filtration applications with high fouling / high viscosity waste water streams. Briefly, porous tubes with inner diameters ranging from 5mm to 15mm are coated with micro-porous layers of PVDF or PES on either the inside or outside walls. Depending on the orientation of the micro-porous layer, tubular modules – consisting of individual tubular membranes fitted into a cylindrical housing – are either operated in outside-in (waste water stream flowing outside individual tubes) or inside-out (waste water stream flowing inside individual tubes) configurations.

From a forward osmosis module point of view, tubular modules should be seen as an alternative to plate and frame modules in applications with high fouling / high viscosity waste water streams. Compared to plate and frame modules, tubular modules offer two main advantages compared to plate and frame modules:

  1. Up to 4-5 times higher packing densities (refer to the table below) significantly reduce the overall footprint of tubular forward osmosis modules
  2. Tubular modules are inherently easier to produce since they only require sealing at either end of the module

However, there are also drawbacks to using tubular forward osmosis membranes. First of all such membranes are currently not commercially available and most R&D efforts are directed towards flat sheet and hollow fibre FO membranes. Secondly, the overall thickness of the porous tube wall – including the PVDF or PES micro-porous layer –  might render the tubular configuration unfit for forward osmosis processes due to severe build-up of internal concentration polarization.

Parameter Value
Tube length 1m
Tube wall thickness 0,4mm
Tube inner diameter 10mm
Tube inner area 0,031m2
Inner diameter of module 220mm
Number of tubes in module 319**
Internal volume of module 0,038m3
Active area per module 10m2
Packing density 260

** See engineeringtoolbox.com for an online calculation tool of how many small circles fit into a large circle

Please follow the links below for descriptions of other design variants of forward osmosis modules

  1. Plate and frame forward osmosis membrane modules
  2. Spiral wound forward osmosis membrane modules
  3. Hollow fiber forward osmosis membrane module

 

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