Used Filters

Filtration is the separation of a fluid-solids solution involving the passing of this mixture through a porous barrier which retains most of the solid particulates contained in the mixture. The various terms used in filtration processes include: Media – the filtration cloth or barrier to collect the solids, Liquor – the solution containing the liquid and solids, Filtrate – the liquid that has been filtered clear, Cake – the solids filtered out of the liquid, Polishing – the removal of the last bit of solids for a finished liquid product, Washing – pumping water or a wash liquid over the cake, Pre-coat – coating the filter cloth with a material like diatomaceous earth to aid in the filtering.

The liquor is either pushed through the filter under pressure or pulled through the filter under vacuum. The types and configurations of filters vary widely; each has its own method of filtering, its own method of discharging the filtrate and discharging the cake. Depending on the product, sometimes the filtrate is the desired product and other time the cake is the desired product.

Filters are measured by the square foot surface area available for filtering, and the cubic foot cake capacity.

Type of Filters:

• Plate and Frame Filter Press – this is an assembly of plates covered with a filter cloth and frames designed to collect the cake, held together in a press with that has a head plate and tail plate – the press is closed by a hydraulic pump, or manually in small presses. The plates and frame can be made of many types of materials, polypropylene is popular. Many times the press has “recessed plates” where two plates form a cavity for collecting cake eliminating the frame. Filter presses must be opened and the plates separated to remove the cake.
• Pressure Filters – These are batch filters that push the liquor through the filter under pressure. Once the cake capacity is reached the cake must be removed before you continue the process. All pressure filters consist of a vessel with internal filter plates or cloths.
  • Basket, Candle, & Cartridge filters - This type of filter has a tank with an internal basket with a cloth bag, or filter cartridges, mounted inside the tank.
  • Vertical Tank with Horizontal plate filters - Once the plates are full of cake the cake must be removed. In smaller filters like a Sparkler filter, the plate bundle is remove manually, in larger filters like a Shenk or Funda filter the plate bundle is rotated at a high rpm to use centrifugal force to throw the cake off the plates and remove cake from the bottom of the tank.
  • Horizontal Tank Vertical plate filters – the cake can be removed by shaking the plates, spraying the plates with high pressure water, or scraping the cake off as the plate bundle rotates.
• Vacuum filters – These include rotary drum filters and horizontal belt filters. Both are continuous operations.
• Rotary Drum filters – these are horizontal drums with perforated exteriors covered with a filter cloth and internal vacuum pipes that are designed to be partially submerged in a trough of liquor. The internal vacuum pipes create suction on the outside of the drum. As the drum rotates the liquor is pulled through the filtrate cloth and the cake is form on the outside of the drum. Before the cake dips back into the trough it is removed from the drum by a scraper or belt discharge.
• Horizontal Belt filters – The liquor is spread onto one end of a horizontal perforated belt covered with a filter cloth. A vacuum is pulled under the belt creating suction on top. As the product is conveyed along the moving belt the filtrate is pulled through the belt perforations, leaving the cake on top. When the cake reached the end of the belt it basically drop off or is scrapped off the filter cloth.
• Pan filters – Like a belt filter with a moving filter cloth and suction underneath, this filter replaces the belt with a series of vacuum pans that extract the filtrate while the cake is conveyed along the filter cloth.
• Rosenmund Type – The major manufacturers of this type of filter are Cogiem and Rosenmund. Also known as Filter/Dryers and Nutche filters. This type of filter is typically pressure and vacuum rated internally, heated with a jacket, and has an agitation system that double as a cake discharge screw, and for added drying, the shaft of the agitator can be cored for heating and cooling. Depending on the process this type of filter can take the place of a reactor, a filter, and a dryer, all in one machine. The basic design is a large diameter tank, with a screen in the bottom head, top mounted agitator drive that can raise and lower the internal blades during different cycles. When the process is finished the agitator is lowered to scrape along the filter screen, a cake discharge valve is opened, the agitator scrapes the cake out of the filter/dryer. The newer machines have a removable bottom head so the filter screens can be removed and the bottom head cleaned without any type of tank entry. Filter/dryers are measured by the Square Meter of filter screen area.
• Tower Filters – Similar to a filter press in filtration techniques. The tower press has horizontal plates with a continuous cloth woven in and out of the plates. During filtration the plate stack is closed and during discharge the plate stack is opened and the cake is conveyed out of the pres by the filter cloth. Eliminates the manual labor use to clean filter presses.