Concentration and Separation Processes for FOREST PRODUCTS
When process engineers need to separate effluent streams, clarify or fractionate and where they demand reliable and repeatable performance, membrane filtration systems are often their first choice. At its most basic level membrane filtration involves separating a single flow stream into two separate streams, one more concentrated than the other, by passing it through a membrane filter. These streams can then either undergo further processing, or in the case of a waste-stream be diverted to an appropriate outlet.
Typical Applications
Effluent Control in the Pulp Industry
- Bleach effluent processing for colour, OD/BOD and toxicity removal
- Mechanical pulping effluent prior to recycling processes
- Chemical pulping effluent prior to recycling processes
- Evaporator acid condensate for effluent treatment and water recycle
- Deresining of pulp washwater
- Debarking water for colour/COD removal
Membrane Filtration
A membrane is defined as an interface between two liquid phases. In membrane separation processes this interface is usually a physical barrier that is permeable to some of the species present in one of the streams. In order to carry out the process, a driving force is necessary, in this case pressure. There are in essence four overlapping pressure-driven, cross flow membrane technologies:
- Reverse Osmosis (RO)
- Nanofiltration (NF)
- Ultrafiltration (UF)
- Microfiltration (MF)
PCI Membranes' systems can be based on any of the above technologies. In 'crossflow' membrane filtration, liquid flow tangential to the membrane surface inhibits the formation of deposits. The membrane retains dissolved and suspended solids. The retained fraction is known as the concentrate or retentate, the fraction passing through the membrane is the permeate or filtrate. The product may be the permeate (e.g. wastewater purification) or the concentrate (e.g. concentration of spent sulphite liquor) or both.
The Membranes
For a given separation requirement, Aquious chooses the optimum solution from its range of products. Systems are based on tubular membranes for liquids containing suspended or colloidal materials, spiral-wound membranes for clear liquors and ceramic membranes for high temperature long-life applications. PCI Membranes, with its own membrane manufacturing facility and in-house research and development group, can develop customised membranes
Effluent Control in the Paper Industry
- White water treatment for water recycling and toxicity removal
- De-inking effluent for colour removal
- Concentration of fibreboard effluent
Recovery of Valuable Products
- Spent sulphite liquor for lignosulphonate fractionation
- Kraft black liquor for lignin separation and colour removal
- Concentration of spent sulphite liquor prior to alcohol production
- Recovery of paper coating materials from effluent streams
(Above) Aquious ultrafiltration plant consisting of six stages in series in two lines giving a total membrane area of 1120 m2. Installed at Borregaard Industries, Norway it separates and concentrates spent sulphite liquor.
(Left) Aquious ultrafiltration plant consisting of 1784 PCI 3.6 m long B1 modules giving a total membrane area of 4740 m2. It is installed in the Stora Nymölla AB pulp and paper mill, Sweden, where it reduces 300 tonnes/ hour of bleach plant effluent to 6 tonnes/hour.