teghout nitrogen vs inert gas tradeoff
TRANSCRIPT
-
Teghout Nitrogen vs. Inert gas Tradeoff Study
Introduction
The purpose of this high level trade-off study is to make an evaluation between the use of
covered inert gas cells and open tank cells with nitrogen addition in the Teghout Moly circuit .
The trade off study will focus on the comparison of economics, operability and metallurgical
performance, and safety issue.
Economics Comparison
With aspect of capital cost, for moly flotation using nitrogen, the additional cost is the nitrogen
plant. However the inert gas option has gas scrubber for NaSH, additional cost for
piping/support for the pressure equalizer. The covered flotation cells from inert gas option is
also more expensive than open tank cell from nitrogen option.
With aspect of operational cost, nitrogen has operational cost from nitrogen plant, while with
inert gas option the flotation cell power consumption will be higher, the NaSH consumption is
also reported lower compared with inert gas option. Additional operation cost from inert gas
includes the caustic used for NaSH scrubber. Table below summarized the capital and
operational cost of each option.
Nitrogen Inert gas
Nitrogen plan 430,000
Flotation cells 480,150 582,000
NaSH gas scrubber 200,000
Pressure equalizer ect 100,000
Total CAPEX 910,150 882,000
Nitrogen Inert gas
Nitrogen plant
operational cost 71,487
NaSH cost 498,480 598,176
Flotation cell power
cost 88,232 110,290
Caustic in gas scrubber 2183
Total OPEX 658,198 710,649
From economic comparison, the capital cost of two options are quite close, the operational cost
of nitrogen option is marginally lower than the inert gas option. based on 25 years of project
-
life, the nitrogen option is marginally favorable than the inert
the CAPEX and OPEX comparison of these two options.
Operability and Metallurgical Performance
Theoretically covered cell should have similar metallurgical performance with nitrogen supplied
flotation cell, except with a little higher NaSH consumption.
convenient to operate and observe by operators
overall flotation performance. The maintenance of covered cell is also more difficult than the
open tank cells.
Safety Issue
For covered cell with inert gas option, there will be considerable amount of H2S accumulated
inside the cell which can be potential safety risk, especially wh
not properly maintained. A fatal accident
America, one operator died from H2S exposure
cell in the moly circuit.
0
100,000
200,000
300,000
400,000
500,000
600,000
700,000
800,000
900,000
1,000,000
Nitrogen option
US
$
Economic Comparison between
Nitrogen and Inert gas option
life, the nitrogen option is marginally favorable than the inert gas option. Followed graph show
the CAPEX and OPEX comparison of these two options.
Performance
Theoretically covered cell should have similar metallurgical performance with nitrogen supplied
little higher NaSH consumption. However covered cell is less
perate and observe by operators in field, this may potentially compromise the
The maintenance of covered cell is also more difficult than the
For covered cell with inert gas option, there will be considerable amount of H2S accumulated
inside the cell which can be potential safety risk, especially when the PH level in the circuit is
fatal accident was reported in one of copper moly plant in South
America, one operator died from H2S exposure during the maintenance of covered inert gas
Nitrogen option Inert gas option
Economic Comparison between
Nitrogen and Inert gas option
CAPEX
OPEX/year
gas option. Followed graph show
Theoretically covered cell should have similar metallurgical performance with nitrogen supplied
However covered cell is less
, this may potentially compromise the
The maintenance of covered cell is also more difficult than the
For covered cell with inert gas option, there will be considerable amount of H2S accumulated
en the PH level in the circuit is
reported in one of copper moly plant in South
during the maintenance of covered inert gas
-
For open tank cell with nitrogen option, it is unlikely to accumulate very high concentration of
H2S, and sufficient ventilation insides the building, H2S monitoring and alarm system will be
enough to control the safety issue.
Conclusion
From the economic point of view, nitrogen option and inert gas option have quite similar OPEX
and CAPEX, due to the difference between NaSH savings and flotation cell power consumption,
the economic marginally favors nitrogen option.
From the plant operability and safety aspect, open tank cell with nitrogen addition is more
preferred option, especially for any green field operation where labor resource is not very
experienced.
-
Appendix A: Cost Estimate
Estimate of Nitrogen Plant
Robinson Copper moly plant treat 120 mtph of bulk concentrate, the nitrogen plant built in
2005 costs approximately 726, 000 US$. The designed feed rate for Teghout project is roughly
25 mtph (18.7 mtph nominal rate for 12 million tons case during phase 2). Considering scale up
factor with power index of 0.6 and assumed 5% annual inflation, the nitrogen plant for Teghout
at this time may is estimated around 430,000 US$.
Operational Cost of Nitrogen Plant
The operational cost of nitrogen plant is estimated as below;
Maintenance: 3% of total nitrogen capital cost, around 12,900 US$/year.
Power cost: mainly from one 150 HP compressor, annual power consumption is 53,587
US$/year based on 0.07 US$/kwhr.
maintenance, US$/yr 12,900
consumerable, US$/yr 5000
power, US$/yr 53,587
Total 71,487
When nitrogen option is chosen, the cell can be open tank cell with forced air, which is typically
cheaper than covered cell, the estimated capital cost reduction is estimated 70,000 US$ lower
with open tank cell with nitrogen option.
Inert gas option also requires gas scrubber, additional piping and support, and caustic used for
the gas scrubber, this corresponds to 302,000 US$.
-
Appendix B: Comparison of NaSH Consumption
Nitrogen plant can supply gas with maximum 1% oxygen, while the inert gas typically contains
5-10% oxygen. The pressure equalizer incorporated in the covered flotation cell with inert gas
option will draw fresh air into the flotation cell when the pressure inside flotation cell is less
than atmospheric pressure. These two factors cause nitrogen option consumes less NaSH than
inert gas option. For inert gas flotation cell, it is reported the NaSH consumption typically
reduce 30% to 50%; while for the nitrogen supplied flotation, the NaSH consumption is
reported 50% to 70% reduction. Additional bench scale test conducted by FLSmidth for La
Caridad indicated Nitrogen option save 7% to 13% more NaSH than inert gas option.
It is conservative to assume nitrogen option can save at least 10% more NaSH than inert gas
option in commercial scale. Current Teghout moly testworks indicated NaSH consumption is
about 3.5 kg/mt of bulk concentrate, if we assume 4.0 kg/mt of NaSH consumption in
commercial scale, based on current price of NaSH around 15,000 $ per short ton of 46% NaSH
solution, the annual cost from NaSH for the inert gas is 598,176 US$, and the nitrogen option
will cost 498,480 US$ for NaSH.
-
Appendix C: Flotation Cell and Associated Cost
Flotation Cell Capital Cost
Based on covered inert gas flotation cells, we quoted 375,100 GBP, which roughly corresponds
to 582,000 US$. Typically the open tank cell is 25% less expensive than covered cell, and for
open tank cell, the blower typically is about 5-10% of the flotation cell itself. Based on this
number, the open tank cells with blower is estimated roughly 480,150 US$.
Energy Cost from Flotation Cells
The Wemco mechanism typically consumes more power than open tank cell, roughly 20% to
30% more. The total motor power rating of the Wemco flotation cell for Teghout is 230 kw,
based on 85% load factor and 92% plant availability, the annual power consumption from the
moly flotation cells is estimated 1,575,574 kwhr per year. Assuming 0.07 US$/kwhr electricity
cost, the energy cost from the moly flotation cell with inert gas option is about 110,290
US$/year. Assuming the open tank cells with blower from nitrogen option consume 20% less
power than covered inert gas cell, the power cost for open tank cells with blower is estimated
at 88,232 US$/year.
-
Appendix D: Additional Miscellaneous Cost
For covered flotation cells with inert gas option, a pressure equalizer will be required to balance
the pressure inside the flotation cell, in addition a gas scrubber will be required to treat the H2S
gas coming out from the flotation cells. Caustic is also required in the gas Scrubber to treat the
H2S gas coming out of flotation cells.
Gas Scrubber for H2S
Typical gas scrubber to treat the H2S coming out from moly flotation circuit is estimated around
200,000 US$.
Pressure Equalizer
The pressure equalizer consists all the piping and support for system, the installed cost for this
additional portion is estimated around 100,000 US$.
Caustic
It is estimated every metric ton of moly circuit feed will consume 0.056 Kg of NaOH solution.
Based on the price of 260 US$/mt of caustic solution, the annual caustic cost is about 2,183
US$.