BOKELA DYNO Filter for Dynamic Cross Flow Filtration - Function Principle
Dynamic crossflow filtration with the BoCross Dynamic filter is a unique process for microfiltration and ultrafiltration of microfine to nanoscale suspensions. Tasks such as thickening, washing and clarifying are performed by the BoCross Dynamic filter in continuous operation with permanently high throughput rates.
The dynamic shear gap principle ensures almost ideal physical conditions for the separation process. The process and machine principles allow an exceptionally high concentration of suspensions to be processed in one run. Under the influence of the shear forces, the concentrate still remains flowable even with high thickening. Therefore, highly viscous and highly concentrated suspensions can still be processed. Compared with conventional crossflow filtration, five to six times higher concentrations are achieved with the BoCross Dynamic filter.
The BoCross Dynamic filter has a modular and hermetically sealed construction. It is available with filter sizes from 0.1 m² to 8 m² and can be used for an operating pressure of up to 6 bar (a). and an operating temperature up to 100 °C.
Applications of the BoCross Dynamic filter:
BoCross Dynamic filters are characterized by:
- separation and washing of solids in the particle range of 0.01–200 μm
- high flow rates even with high feed concentration or high viscosity up to 25,000 mPas
- very high final concentration of up to 80 wt.- %
- pasty, spreadable solids discharge
- no segregation or classification in the apparatus
- absolute filtration – 100 % solids separation and particle-free filtrate
- processing of slimy, gel-like particles
- hermetic process – filtration without air contact
- continuous or batch operation
Modular construction & functionality
The BoCross Dynamic filter consists of disc-shaped filter modules arranged in a row, forming a completely closed system of process chambers. Each filter module is equipped with filter media on both sides. The modules have central openings for the filter shaft, which carries the rotors of the individual suspension chambers. The suspension flows from chamber to chamber in a meandering manner, whereby the concentration increases successively, since filtrate drains off in each chamber. The thickened concentrate is discharged controlled in the last chamber by means of an exhaust valve. In each chamber separately washing liquid or other process liquids can be supplied.
Dynamic Crossflow Filtration
The tangential overflow of the filter surface is induced by rotors in the suspension room and the transmembrane pressure difference is generated by the feed pump. The liquid flows over the filter medium in a shear gap with a high velocity gradient. This prevents blocking of the filter medium. The rotors ensure a uniform homogenization of the suspension and excellent mixing, e.g. with the washing liquid.
Washing out of residues and contaminations
In each chamber wash liquid or other process liquids can be introduced separately. The rotors cause an intensive mixing of suspension and wash liquid and thus, an efficient washing out. It is also possible to replace the mother liquor with another process fluid.
Gentle operation & high flexibility
The BoCross Dynamic filter is very gentle on the product. The desired process result is achieved not only after several circulations with circulating streams but in only one run with short residence times. The variable rotor speed ensures that no particle destruction takes place. A heating/cooling system which is integrated in the modules allows a tempering of the product by cooling or heating during filtration.
The BoCross Dynamic filter reacts flexibly on changes in the product characteristics – for example, in terms of viscosity or solids concentration in the feed or as a result of product changes – and thus, ensures reliable operation and constant operating results. This is particularly important for multi-purpose plants.
Continuous small batch production
Due to the process and apparatus principle, the BoCross Dynamic filter also enables continuous operation with very small production volumes in the range of 1 kg/h.
Filter media
The BoCross Dynamic filter can be used with a variety of filter media such as:
- micro filtration membranes in the range of 0.1–1.0 μm
- ultrafiltration membranes
- sintered plastic or ceramic membranes
- specially developed sieve composite sheets
- metallic media
Automatic operation
BoCross Dynamic filters work fully automatically and can be easily integrated into process automation. Startup and shutdown procedures as well as cleaning procedures are automated.
Technical data
| Filter Type [–] | XS01 | S04 | M2 | L8 |
| Filter Area [m²] | 0.13 | 0.4 | 1.8 | 8 |
| Filter Diameter [mm] | 145 | 200 | 375 | 555 |
| No. of modules [–] | 5 | 8 | 10 | 20 |
| Drive [kW] | 3 | < 5.5 | < 15 | < 55 |
