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Mixed Bed Units:-
Are an Excel Filtration method used wheresuperior water quality is needed. They are typically the last treatment step inthe water treatment process train. They are normally positioned downstream ofeither individual two-bed working ion exchange units or reverse osmosissystems, further treating the effluent of these demineralizers.
For low TDS(Total Dissolved Solids) waters, they can be used as standalone ion exchangeunits. In this application they are often referred to as Working Mixed Beds.
In condensate polishing applications, you can use Mixed Bed Ion Exchange toremove condensate contamination before reuse Mixed Beds are ion exchangers thathave both Cation and Anion resins, mixed in a single vessel.
The resin bed isin the both H-OH form.
These units are normally designed so that they can beautomatically operated, with all the necessary internals, instruments,components and controls.
Each unit is mounted on a rigid, structural steel skidbase.
The last traces of TDS and silica can be removed on a resin bed wherehighly regenerated strong acid cation and strong base anion resins are mixed.
Mixed bed units deliver an excellent treated water quality, but are complicatedto regenerate, as the resins must first be separated by back washing beforeregeneration. Additionally, they require large amounts of chemicals, and thehydraulic conditions for regeneration are not optimal.
Therefore, mixed bedsare usually only used to treat pre-demineralised water, when the service run islong. Mixed bed polishing produces water with less than 1.0 µS/cm conductivitya conductivity of less than 1.0 µS/cm.
With a sophisticated design andappropriate resins, the conductivity of pure water.
During the service cycle, water enters the unit through the inlet distributorat the top of the vessel, and is evenly distributed across the resin bed.
Asthe water flows through the resin bed, its ionic contaminants are exchanged forH and OH ions on the resin beads.
This removes the ionic contaminants from thewater, producing highly purified Demineralized water. The treated water thenpasses through the false bottom under drain strainers to the outlet piping atthe bottom of the Unit. When the units capacity is exhausted, regenerationbegins.
The resin is backwashed and hydraulically classified based on theirdensities, and after the bed settles, regeneration is carried out. CausticSodium hydroxide is introduced through the down flow.
Regenerate distributor and acid is introduced through the upflow regenerator header. The interface collector receives spent acid andcaustic for disposal.
A slow rinse displaces regenerate acid and caustic, thenthe full bed is rinsed with service water. The vessel is drained until thewater level is just above the bed surface.
The resins are then re-mixed withair. The vessel is refilled and the bed is rinsed before the unit is returnedto service.