3
screen bowl effluent streams. Although not the subject of
this paper, it is noteworthy that Arch Resources has success-
fully implemented high pressure filtration with plate and
frame presses to overcome the inherent screen bowl losses
of ultrafine coal.
StackCell Flotation Technology
The innovative StackCell high-intensity flotation technol-
ogy was developed to provide the metallurgical benefits of
column flotation cells while addressing the challenges of
cell size, foundation loads, and capital and operating costs.
The StackCell technology de-couples the particle collection
process from the froth recovery process, thus allowing for
optimization of each process independently.
As depicted in Figure 2, slurry and air are introduced
to the bottom of the StackCell contacting chamber through
the feed inlet and air inlet. The pulp and air are subjected
to intense mixing while traveling up through the contact-
ing chamber and the mixture is discharged into a quies-
cent separation chamber where a phase separation occurs
between the slurry and froth. The froth depth is maintained
sufficiently deep to facilitate froth washing, thus providing
similar metallurgical performance to column flotation cells.
The system is specifically designed to have both a small foot-
print and a gravity-driven feed system. This allows multiple
units to be installed in series for new circuits or to supple-
ment existing column or convention flotation circuits. The
performance of the StackCell flotation cell is governed by
the distribution of hydrodynamic parameters in the pulp
phase such as turbulent kinetic energy, turbulent dissipa-
tion rate, air bubble size distribution and air void fraction
[9]. The StackCell rotor and stator blades are designed with
many slots to create strong shear layers in the wake regions
(downstream) of the slots. The high shear rates in wake
regions between the blades enhances the bubble breakup
process and reduce the bubble diameter, which enhances
the collisions and attachment of fine and ultrafine particles
with air bubbles. The shear layers in the wake region of
slots interact in a non-linear fashion and generates large
turbulent fluctuations that increase the turbulent dissipa-
tion rates. The high turbulent dissipation rates inside the
contacting chamber are needed for efficient collisions and
attachment rates of fine and ultrafine particles with air bub-
bles [10-13].
The high-intensity hydrodynamic conditions in the
StackCell flotation cell result in roughly a 50% reduc-
tion in required cell volume compared to column cells,
thereby reducing both equipment and installation costs
while achieving similar flotation performance. Structural
steel requirements are considerably less due to the reduc-
tion in tank weight and live load. For a typical installa-
tion, the overall space requirement for a StackCell is half
the volume of an equivalent column circuit. Moreover, the
energy input per unit ton processed is typically lower for
the StackCell since energy is only expended for the pur-
pose of creating bubbles and for bubble-particle contacting,
and not for particle suspension like conventional flotation
cells. In addition, the StackCell contact chamber operates
at low pressure, which facilitates the use of a low-pressure
and maintenance-friendly blower as opposed to a compres-
sor [14].
The success of the StackCell technology in fine coal
cleaning applications is documented by nearly 50 StackCell
installations in coal circuits throughout North America,
Australia, and Asia. Examples of the economic advantages
of StackCell technology are well documented [15-16]. One
Figure 2. Illustration of Eriez StackCell high-intensity flotation machine
screen bowl effluent streams. Although not the subject of
this paper, it is noteworthy that Arch Resources has success-
fully implemented high pressure filtration with plate and
frame presses to overcome the inherent screen bowl losses
of ultrafine coal.
StackCell Flotation Technology
The innovative StackCell high-intensity flotation technol-
ogy was developed to provide the metallurgical benefits of
column flotation cells while addressing the challenges of
cell size, foundation loads, and capital and operating costs.
The StackCell technology de-couples the particle collection
process from the froth recovery process, thus allowing for
optimization of each process independently.
As depicted in Figure 2, slurry and air are introduced
to the bottom of the StackCell contacting chamber through
the feed inlet and air inlet. The pulp and air are subjected
to intense mixing while traveling up through the contact-
ing chamber and the mixture is discharged into a quies-
cent separation chamber where a phase separation occurs
between the slurry and froth. The froth depth is maintained
sufficiently deep to facilitate froth washing, thus providing
similar metallurgical performance to column flotation cells.
The system is specifically designed to have both a small foot-
print and a gravity-driven feed system. This allows multiple
units to be installed in series for new circuits or to supple-
ment existing column or convention flotation circuits. The
performance of the StackCell flotation cell is governed by
the distribution of hydrodynamic parameters in the pulp
phase such as turbulent kinetic energy, turbulent dissipa-
tion rate, air bubble size distribution and air void fraction
[9]. The StackCell rotor and stator blades are designed with
many slots to create strong shear layers in the wake regions
(downstream) of the slots. The high shear rates in wake
regions between the blades enhances the bubble breakup
process and reduce the bubble diameter, which enhances
the collisions and attachment of fine and ultrafine particles
with air bubbles. The shear layers in the wake region of
slots interact in a non-linear fashion and generates large
turbulent fluctuations that increase the turbulent dissipa-
tion rates. The high turbulent dissipation rates inside the
contacting chamber are needed for efficient collisions and
attachment rates of fine and ultrafine particles with air bub-
bles [10-13].
The high-intensity hydrodynamic conditions in the
StackCell flotation cell result in roughly a 50% reduc-
tion in required cell volume compared to column cells,
thereby reducing both equipment and installation costs
while achieving similar flotation performance. Structural
steel requirements are considerably less due to the reduc-
tion in tank weight and live load. For a typical installa-
tion, the overall space requirement for a StackCell is half
the volume of an equivalent column circuit. Moreover, the
energy input per unit ton processed is typically lower for
the StackCell since energy is only expended for the pur-
pose of creating bubbles and for bubble-particle contacting,
and not for particle suspension like conventional flotation
cells. In addition, the StackCell contact chamber operates
at low pressure, which facilitates the use of a low-pressure
and maintenance-friendly blower as opposed to a compres-
sor [14].
The success of the StackCell technology in fine coal
cleaning applications is documented by nearly 50 StackCell
installations in coal circuits throughout North America,
Australia, and Asia. Examples of the economic advantages
of StackCell technology are well documented [15-16]. One
Figure 2. Illustration of Eriez StackCell high-intensity flotation machine