The HEI sludge thickener is an efficient method to gravity
concentrate and decant waste sludges.
Liquid sludges pumped from a clarifier will have a solids
content of 0.5% from cone bottom clarifiers to 2% - 4% from
rake bottom clarifiers.
The sludge thickener must have sufficient capacity to accumulate
and thicken the sludges between filter press cycles. To
efficiently operate a filter press, the solids concentration
in the filter press feed should approach 10% solids by weight.
A typical filter press will produce a filter cake having
a solids concentration of 30% by weight. If the filter press
has 20 cubic feet capacity and the concentration of the
filter press feed is 10%, then three volumes of sludge must
be pumped through the press before the solids concentration
of the cake reaches 30%. In this case, 10 cubic feet times
3 equals 30 cubic feet or 225 gallons. The total cycle of
the press would be less than 2 hours. If the concentration
is on 0.5%, as from a typical cone bottom clarifier, the
volume would be 60 times or 600 cubic feet - 4,500 gallons
and the cycle time for the press may be 12-24 hours. Utilizing
a properly designed sludge thickener will enable the press
to be sized smaller, cycled more frequently and produce
a better filter cake.
The sludges must be given time for the solids to gravity
compact. The net thickening forces is the aggregate weight
of the solids, not the water. A column of solids 6 - 8 feet
high will compact most sludges to 8 - 10% by weight.
The rake, as it moves through the sludges, provides avenues
for the liquid supernatant to move upward as the solids
settle downward.
HEI thickeners are constructed with flat bottoms and heavy
duty rake drive mechanisms to move the sludge to the center
outlet. The flat bottom cylindrical thickener provides 3
times the volume of an equivalent cone and, hence, 3 times
the retention time.
The flat bottom thickener is elevated on integrally constructed
channels. The recessed center cavity provides a central
outlet for the thickened solids. The HEI thickener’s
compact design provides greater storage capacity and more
retention time for greater thickening of solids with less
height. An equivalent cone bottom tank would add an additional
10 feet of height. For example, an HEI 8’Ø
x 12' high thickener contains 4,520 gallons. A typical 8’
diameter cone bottom unit having 4,500 gallons storage capacity
would be 18’ high.
The heavy duty rake not only thickens the solids but also
positively moves the heavy solids to the center drain. The
constant movement prohibits the formation of a "rat
hole". Since the supernatant is more fluid than the
sludge, when the center outlet is opened, the sludge immediately
above the opening is removed. The sludge immediately above
collapses into the hole formed by the solids removal. This
in-turn is replaced by the more fluid supernatant, draining
the supernatant, and creating the formation of a rat hole.
Even a 60° cone will not prohibit the formation of the
‘rat hole’. The motorized rake is the only positive
method to move the sludge and prohibit the formation of
the ‘rat hole’.
Hoffland environmental constructs its factory assembled
sludge thickener in readily transportable sizes. Available
sizes are:
Nominal Diameter |
Height |
6' |
8' |
12' |
16' |
|
|
|
8' |
8' |
12' |
16' |
|
|
|
10' |
8' |
12' |
16' |
18' |
|
|
11'10'' |
|
12' |
16' |
18' |
24' |
32' |
13'10'' |
|
|
16' |
18' |
24' |
32' |
|
Sludge Thickener Specification
