The reverse osmosis spiral membranes from Alfa Laval are based on a unique construction of either polyester or polypropylene support material in a sanitary full-fit design that provides optimum cleaning conditions. The spiral membranes are available with different reverse osmosis membrane types and in different combinations of length, diameter and feed spacer size
Alfa Laval reverse osmosis spiral membranes use membranes with pores so minute that only small fractions of salts can pass through, along with the water that is the prime component of the permeate.
Certain organic compounds with low molecular weights can also pass - but only to a limited extent. However, it is impossible for any other components suspended or dissolved within the liquid flow (salts, sugars, etc.) to do so.
Alfa Laval reverse osmosis spiral membranes are used for the concentration of many feed streams particularly of heat sensitive products, pre-concentration prior to evaporation as well as product and water recovery from permeate streams and evaporator condensate.
Alfa Laval offers two series of reverse osmosis spiral membranes with different NaCl rejection properties. The membrane materials are thinfilm composite cast on either polyester or polypropylene backing paper.
RO PE Series
The spiral membranes of this series are the types RO99 and RO90 having a NaCl rejection of ≥ 98% and ≥ 90% respectively.
RO98 pHt™ Series
In this series you find the RO98 pHt™ spiral membrane which is characterized by its high temperature tolerance compared to the RO PE series. The RO98 pHt™ spiral membrane has a NaCl rejection of ≥ 98%.
- cost-effective operation due to low energy consumption
- cover a broad range of salt permeabilities
- available in different combinations of length, diameter and spacer size
- sanitary design with all materials in compliance with EU regulations (EC) 1935/2004 and FDA regulations (CFR) Title 21. USDA approved
- same membrane types available as both flat sheet membranes and spiral membranes
- suitable for extensive range of processes
- suitable for processing at low temperature
- manufactured by Alfa Laval's own membrane centre
How it works
The basic technology behind membrane filtration involves using a semi-permeable membrane to separate a liquid into two distinct streams.
Pumping this liquid across the surface of the membrane creates a positive trans-membrane pressure that allows any components smaller than the porosity of the membrane to pass through, forming the permeate.
Any components larger than the pore size simply cannot pass through, and remain behind in what is called the retentate. The surface of the membrane is kept free of blockages by the force of the liquid flow moving parallel to the membrane surface.
Spiral membrane construction
A spiral element comprises of a number of membrane 'envelopes' with 2 membrane sheets separated by a permeate spacer mesh, each glued to a central permeate collection tube.
Between each pair of envelopes there is a spacer which creates the feed channel, allowing the feed to flow across the length of the spiral element, whilst the permeate passing through the membrane into the membrane envelope flows in a spiral pattern to the permeate collection tube.
In the illustration above showing the flow pattern in a spiral membrane from Alfa Laval, red represents the feed/retentate. Yellow the permeate.
All materials used for the production of Alfa Laval membranes, in both spiral-wound and flat-sheet designs and configurations, comply with EU Regulation (EC) 1935/2004 and Commission Directive 2002/72/EC as well as FDA regulations (CFR), Title 21. The membranes are thus suitable for use within food and pharmaceutical processing applications.
These compliance also extend to the equipment and fittings related to membrane operations, including items such as plate-and-frame units, element housings and pumps.