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$.