Settling Tanks

Question 1

what is the basic principle that settling tanks are created on?

Answer 1

terminal settling velocity

Question 2

where are settling tanks used?

Answer 2

mining (slurries, large amount of liquid to filter)

Question 3

Thickener

Answer 3

desired product is settled particles at bottom

Question 4

Clarifier

Answer 4

desired product is clear liquid off the top

Question 5

purpose of rake in settling tank

Answer 5

to push solids towards underflow exit

Question 6

purpose of a well in settling tanks

Answer 6

prevents solids from flowing to the sides immediately, usually (1-2 m)
Can also be where add floculants which causes particles to agglomerate
Can also be used to remove surface charges (charged particles will repel each other causing increased settling time)

*tank depth usually 3-3.5m (so large portion of tank)

Question 7

Solid exiting concentration

Answer 7

typically less than 10 wt% (too high concentration means increased settling area, and more costs)

Question 8

Settling assumption

Answer 8

Stokes regime (particles moving slowly)

Question 9

Methods of estimating settling velocity

Answer 9

empirical correlations for terminal velocity

batch testing (necessary for porous or agglomerating particles as empirical estimates are not good)