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Horizontal Vacuum Belt Filter Basics
Horizontal Vacuum Belt Filters perform well in applications that require cake washing. In a single run from slurry to dewatered cake, a HVBF can wash in multiple stages use counter current flood washing. Some benefits over Rotary Vacuum Drums and Rotary Disc Filters are visibility and reduced slurry inventory. Filtration from feed box to cake discharge can be seen on a Horizontal Vacuum Belt Filter. Since there is an overhead feed box instead of a slurry tank, the only slurry needed to operate is the slurry that will be filtered.
Slurry is introduced through a feed box above the vacuum belt and across its entire width. HVBFs can build a cake ranging from 3/16” to 6” thick. Vacuum pulls the slurry through a cloth belt and then through a rubber drainage belt. It is then pulled though the rubber drainage belt into a vacuum pan and into vacuum manifolds that separate the liquid from air.
Filter cake is formed, dewatered, washed, and dried all on the top of the belt as it travels across the filter and into the discharge zone.
Vacuum Belt Components
The rubber drainage belt is the backbone of a HVBF. Deep channels in the rubber guide slurry that has passed through the top cloth belt to a central discharge zone. National Filter Media has designed multiple vacuum rib belts to install in place of drainage/wear belt configurations, which will improve Vacuum Belt Filter performance.
Typically pulled by a variable speed gear box and motor, the drive pulley is mounted on the discharge end of the filter. Drive pulleys are diamond grooved to make better traction with the drainage belt.
One the feed end of the filter, a take-up pulley There are no diamond grooves since it doesn’t pull the belt. Sliding bearings and take-up rods put tension on the drainage belt.
The vacuum pan runs from pulley to pulley down the center of the filter. It is a box under vacuum with a slotted top. Mounted to the top, making contact with the drainage belt as it travels, slide strips reduce frictional drag on the drainage belt, extending service life. Vacuum is provided through piping in several spots down the length of the filter. Baffles within the vacuum box allow zones of vacuum and zones without to accommodate multiple process in a single run across the belt.
HVBFs utilizing fold up troughing lips have lip supports along the edges, which help direct slurry onto the middle of the belt rather than spilling off the sides. Deckle seals help to contain the cake in the form and wash zones.
Feed boxes sit over the belt on the take-up pulley end of the filter. A common design of feed box utilizes a two weir system of flow diverters to ensure even cake distribution across the face of the belt. A feed box seal sits under the bottom weir to prevent slurry from running off the take-up end of the filter.
Wash boxes, wash dams, and sprayers run along the top of the filter. Configurations vary depending upon the application.
Rubber covered rollers run the length of the filter, mounted on pillow block bearings. They support the drainage belt as it travels.
Edge trackers keep the top cloth belt wrinkle free and running on track.
Shower bars with high impact spray nozzles clean the cloth after cake discharge, ensuring consistent cake during operation.
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