Environmental awareness and cost saving features
Environmental awareness has been the major driving force in the rapid development of the filtration and dewatering technology. Also increasing energy and personnel costs have made tougher demands on efficiency and automation of processes.
This development requires reliable automatic operation and simple maintenance from heavy industry. Metso's vertical plate pressure filters VPA are developed to meet these requirements.
- Light weight construction with machined polypropylene filter chambers.
- Compact design with pulling hydraulic cylinders for reduced space requirement.
- Filter cloth change, a one minute operation.
- Available in several pressure ratings for different applications.
- Few moving parts for low maintenance and high availability.
- "Smart" PLC-control system for fully automatic filter operation
- Load cell weighing system integrated to the PLC, for process control of the filter performance.
Mechanical dewatering by pressure
As particles get finer the resistance against removing water increases. Gravity dewatering can no longer be used, pressure has to be used.
By creating a differential pressure Dp across a cake of solids, liquid can be removed by
“Compression before through blow reduces cycle time, forms a homogenous cake, and does mechanically remove filtrate by squeezing of the cake”
Air through blow
“Dewatering by through blow means replacing the water in a cake with air, and during air through blow the cake remains under compression”
For vertical plate pressure filters either compression or a combination of compression and air through blow is used. The VPA pressure filter basically consists of a fabricated head stand and an end frame, joined by two side beams, which support the movable head (pressure piece) and the filter plates, which are fitted between the fixed and movable heads.
Pulling type hydraulic cylinders, 2 for VPA 10 size and 4 for VPA 15 and VPA 20 size filters, are used to open and close the filter and to provide the necessary closing force during filtration.
Filter cloths are suspended from tubular supports and hang between the filter plates. The cloth support bars are carried on an upper frame to which vibrator motors are fitted.
These can be activated during cake discharge to ensure full removal of cake from the cloths. The filter plates are linked together and to the movable head, so that the filter plates are opened “concertina” style and to provide accurate spacing between the plates during opening. Similarly the cloth support bars are also linked together to ensure that the cloths are always located between filter plates. The filter cloth support bars also serve as spray pipes, being fitted with spray nozzles and being fed from a fixed header pipe and flexible hoses. As the spray nozzles are located between the filter cloths, the cloth wash water is contained between the cloths and over spray is eliminated.