5
demonstrates the reduced volume of water handled by the
pipeline as a result of improved dewatering.
Duty Conditions, Absorbed Power and Water Usage.
The pump duty for the current situation is calculated using
the modified Wasp method. The results proved to be in line
with field observations. The same method was then used
to calculate the pump duty for the scenario in which only
the pumping technology was changed. Increasing the solids
concentration of the tailings to 65% initiates non settling
behavior, hence the tailings can be pumped at a lower flow
velocity. Pumping through the current 450NB pipe assures
turbulent flow, preventing (laminar) flow settling. On the
TSF 500 NB pipe is installed which at low flow veloci-
ties might induce settling, but operational risk is minimal
due to the relative short pumping distance. In the upgraded
scenario the increased duty head requires the use of sched-
ule 80 pipe on the bottom part of the pipeline. Increasing
the pipe diameter in conjunction with the higher class pipe
results in reduced pressure losses within an acceptable flow
velocity interval.
The calculated duties are given in Table 2.
The pump selections for the upgrade scenarios were
made following Weir’s proprietary pump selection pro-
cedures. The absorbed power is known for the current
installed base. Power usage for dewatering is based on
assumed power usage of 1 kWh/t of dry solids for normal
thickening and 1.5 kWh/t for improved thickener opera-
tion (Kruyswijk, 2021). The cumulative absorbed power is
presented in Table 3.
For this comparison, it has been assumed that the
volume of interstitial water is equal for all scenarios. The
underlying argumentation is that the tailings are assumed
to consolidate to equal in situ bulk densities in each sce-
nario. Site-specific data indicated that approximately 40%
of water released at the TSF is lost to the environment
through seepage and evaporation. In the current situation,
approximately 50% of the water in the tailings is reclaimed
from the pond for re-use in the plant. Increasing the sol-
ids concentration of the tailings reduces the volume of
water pumped out to the TSF by 75%. The result is that
the loss of water to the environment through seepage and
evaporation is reduced by 89%. The combined effect of the
reduced losses and improved thickening is 81% reclama-
tion of water from the tailings stream (see Figure 4).
Burning fossil fuels—whether for electricity generation
or diesel-powered equipment—generates CO2 emissions.
Emissions are calculated using an average CO2 emission of
0.46 kg per kWh absorbed power (Kruyswijk, 2021). In
Figure 5, the total annual production for each of the con-
sidered scenarios is given. Based on these calculations, it
Figure 3. The effect of improved dewatering. Left the current
slurry at 32% solids concentration by weight, on the right
the slurry at 65% solids concentration by weight
Table 2. Head requirements
Pumping Scenario C
w
Pump station Total pressure /
pipeline
Raise
PS 1 PS 2 PS 1
Centrifugal -Current 32% 21 bar 48 bar 69 bar NA
PD -1 PS 32% 60 bar 60 bar 63 bar
PD -1 PS -dewatered 65% 63 bar 63 bar 67 bar
Table 3. Absorbed Power. (base case without raise)
Current PD PD +Dewatering
Pumping 6,529 kWh 4,829 kWh 1,764 kWh
Thickening 969 kWh 969 kWh 1,454 kWh
Total absorbed power 7,498 kWh 5,798 kWh 3,218 kWh
demonstrates the reduced volume of water handled by the
pipeline as a result of improved dewatering.
Duty Conditions, Absorbed Power and Water Usage.
The pump duty for the current situation is calculated using
the modified Wasp method. The results proved to be in line
with field observations. The same method was then used
to calculate the pump duty for the scenario in which only
the pumping technology was changed. Increasing the solids
concentration of the tailings to 65% initiates non settling
behavior, hence the tailings can be pumped at a lower flow
velocity. Pumping through the current 450NB pipe assures
turbulent flow, preventing (laminar) flow settling. On the
TSF 500 NB pipe is installed which at low flow veloci-
ties might induce settling, but operational risk is minimal
due to the relative short pumping distance. In the upgraded
scenario the increased duty head requires the use of sched-
ule 80 pipe on the bottom part of the pipeline. Increasing
the pipe diameter in conjunction with the higher class pipe
results in reduced pressure losses within an acceptable flow
velocity interval.
The calculated duties are given in Table 2.
The pump selections for the upgrade scenarios were
made following Weir’s proprietary pump selection pro-
cedures. The absorbed power is known for the current
installed base. Power usage for dewatering is based on
assumed power usage of 1 kWh/t of dry solids for normal
thickening and 1.5 kWh/t for improved thickener opera-
tion (Kruyswijk, 2021). The cumulative absorbed power is
presented in Table 3.
For this comparison, it has been assumed that the
volume of interstitial water is equal for all scenarios. The
underlying argumentation is that the tailings are assumed
to consolidate to equal in situ bulk densities in each sce-
nario. Site-specific data indicated that approximately 40%
of water released at the TSF is lost to the environment
through seepage and evaporation. In the current situation,
approximately 50% of the water in the tailings is reclaimed
from the pond for re-use in the plant. Increasing the sol-
ids concentration of the tailings reduces the volume of
water pumped out to the TSF by 75%. The result is that
the loss of water to the environment through seepage and
evaporation is reduced by 89%. The combined effect of the
reduced losses and improved thickening is 81% reclama-
tion of water from the tailings stream (see Figure 4).
Burning fossil fuels—whether for electricity generation
or diesel-powered equipment—generates CO2 emissions.
Emissions are calculated using an average CO2 emission of
0.46 kg per kWh absorbed power (Kruyswijk, 2021). In
Figure 5, the total annual production for each of the con-
sidered scenarios is given. Based on these calculations, it
Figure 3. The effect of improved dewatering. Left the current
slurry at 32% solids concentration by weight, on the right
the slurry at 65% solids concentration by weight
Table 2. Head requirements
Pumping Scenario C
w
Pump station Total pressure /
pipeline
Raise
PS 1 PS 2 PS 1
Centrifugal -Current 32% 21 bar 48 bar 69 bar NA
PD -1 PS 32% 60 bar 60 bar 63 bar
PD -1 PS -dewatered 65% 63 bar 63 bar 67 bar
Table 3. Absorbed Power. (base case without raise)
Current PD PD +Dewatering
Pumping 6,529 kWh 4,829 kWh 1,764 kWh
Thickening 969 kWh 969 kWh 1,454 kWh
Total absorbed power 7,498 kWh 5,798 kWh 3,218 kWh