Filtration Flashcards

1
Q

What are the potential driving forces for filtration?

A
  • gravity
  • vacuum
  • pressure
  • centrifugal force
    (only last 3 are used on an industrial scale)
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2
Q

Filter Press

A
  • 2 plates squeeze together to form a filter cake
  • slurry distributed between 2 plates and the plate compression removes liquid
  • often operated in parallel so that one can be cleaned while other is used
  • uses vibration to remove cake
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3
Q

Belt Press

A
  • completely continuous
  • belt is a filter material, so liquid from slurry falls through belt (slight vacuum (0.8-0.5 atm) under belt or gravity used to pull liquid from system)
  • cannot get very dry filter cake, but can handle very large flowrates.
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4
Q

Rotary Drum

A
  • drum rotates with rotating material being the filter
  • slurry is fed at the basin (slight vacuum at centre of drum which pulls liquid into it)
  • can handle very large flowrates, but expensive
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5
Q

Filter theory 2 types of filters:

A
  1. Surface filter (particles collected at surface as size of solids > pore size of filter) (used for solid concentration greater than 1% by volume)
  2. depth filter (small particles can penetrate into filter media)
    - want solid concentration less than 1% by volume (otherwise can be very expensive to replace)
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6
Q

Necessary properties of a filter media

A
  • must remove solids with certain size (to give clear filtrate)
  • pores should not become plugged enough that filtration becomes too slow
  • must be strong enough not to tear
  • must be chemically resistant (not react with slurry)
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7
Q

What are the 2 properties that may be kept constant when filtering

A

1.constant pressure
- reduce rpm of pump to get lower flowrate

  1. constant flowrate
    - increase rpm of pump to get higher pressure
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8
Q

Cycle Time

A
  • the total time for filtration to occur (time to cycle, time to filter and dead time - wash time, disassembly/assembly time)
  • is cyclical
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