2. |
Corporate Overview – Vedanta Resources Plc.
1
Vedanta Aluminium Ltd is an associate company of the London Stock Exchange listed, FTSE 100 diversified
resources group Vedanta Resources Plc. Originally incorporated in 2001, VAL is a leading producer of
metallurgical grade alumina and other aluminium products, which cater to a wide spectrum of industries.
ABOUT Vedanta Aluminium Limited, Jharsuguda
VAL has invested in a 0.5 MTPA aluminium smelter and 1215 MW captive power plant supported by highly
modern infrastructure at Jharsuguda, Orissa.
In addition to this, construction of 1.25 MTPA aluminium smelter expansion project at Jharsuguda is under
process. The company intends to expand the fully integrated aluminium smelting capacity to around 2.75
MTPA in near future.
Jharsuguda is also the site of the 2400 MW Independent Power Plant being set up by group company
Sterlite Energy Ltd to meet the growing demand for power from both urban and rural consumers.
5. |
To produce 1 kg of aluminium the following
amounts of raw materials are needed:
2 kg 0.415 Kg 20 g 2 g
Alumina Carbon Aluminium fluoride Cryolite
+ =
13 - 15 kWh 1 kg
Electrical energy Aluminium
+ + +
4 kg bauxite
+ CO2 + CO + HF + CF4 + Coke + Other gases
Raw material Consumption – Production of Aluminium
7. |
Reasons for High Voltage drop across the Electrolyte
6
CO2, CO Released during Aluminium
Smelting - Accumulation of gases
beneath anode Increases Bubble
resistance – Voltage
Drop increases
voltage fluctuation –
Noise may occur
Current efficiency
Decreases – Hot metal
volume Decreases
Energy consumption
for production of
Aluminium increases
Gas Bubble reacts
with Carbon and
Reduces Anode Life
Increases Energy
Consumption and Green
House Gas emissions
During Aluminium smelting, CO2 gases are evolved.
CO2 bubbles get accumulated under the anode – forms a high
resistance film.
8. |
Impact of reduction of bubble resistance.
7
Minimizing of the anode gas bubble voltage drop -
One of the most economical ways to reduce
energy consumption.
Modification of the anode surface/Introducing
slots can effectively reduce both the bubble
voltage drop and anode overvoltage
Evacuate
the
gases
Reduces the cell bubble
resistance - Reduce
insulation of anode from
bath
Increase
surface area
of anode
Increases
Current
Efficiency. Pot
Voltage can be
reduced.
Increases
production
of metal
Anode Surface Slots
Reduces Energy
Consumption
and Green
House Gas
emissions
9. | 8
Risk Assessment – Press Forming
Disadvantages
Makes green anodes more fragile
Variable anode quality (decrease in anode
density, increase in air permeability -
tendency to carbon dust, Spikes which
ultimately leads to reduction in CE
Limitation to increase the slot height.
Wide slots are made using the slot plates.
Packing Coke tends to clog the slots,
requiring more cleaning.
Reduces the mass of carbon and the life
of anodes
Scrap Generation increases in GAP and bake
oven.
Advantages
▪ Negligible Capital and Operating costs
Crack initiation from a
slot in a green
anode, damaged
during handling
Anode breakage
influenced by slot
location.
Excessive
consumption at
slots during cell
operation.
Slot slumping
during baking
Spikes during Cell
Operation
POSSIBLE FAILURE MODE
11. |
Conceptualization & Design Engineering
11
Anode surface slots were not present in the initial design by O&M.
In house design engineering - Calculate the appropriate slot height and slope
Straight slots may be a problem in gas evacuation.
Design of experiment and data analysis was performed
Result was slanted slots are better in case of gas evacuation
Press forming which is the most common method – sometimes lead to the formation of
Low density green anodes - results to excess coke dusting.
recipe for preparation of green anodes analysed with varied anode density.
Optimum Density and minimum coke dusting - Specific anode preparation recipe
formulated
Design modifications have been made in the anode forming equipment (Vibro-
compactor). Slot blades of variable height and slope was fabricated into the equipment.
Packing coke is used as the heat transfer mode in bake oven when green anodes are
heated to form baked anodes which if not removed will lead to excess coke dusting in
pots
Slot cleaning machine was installed in bake oven to remove this packing coke.
12. |
Trial & Full Implementation - Impact on Energy consumption
12
14547
14587
14521
14422 14411
14608
14551
14376
14344
14303
14282
May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct-12 Nov-12 Dec-12 Jan-13 Feb-13 Mar-13
Normal Anodes used
Normal Anodes
Slotted Anodes –
trail
Slotted Anodes – After
Stabilization Period
Normal Anodes
Slotted Anodes –
Full Implementation
stabilization Period
322.5
324.0
323.3
324.1
324
324 324.2
324.55
325.4
325.66
325.89
May-12 Jun-12 Jul-12 Aug-12 Sep-12 Oct-12 Nov-12 Dec-12 Jan-13 Feb-13 Mar-13
Normal Anodes used
Normal Anodes
Slotted Anodes –
trail
Slotted Anodes – After
Stabilization Period
Normal Anodes
Slotted Anodes –
Full Implementation
stabilization Period
Consumption increased
due to external factors
13. |
Slotted Anode Trial (Line 1-Section 7)
Trial period – 27th July to 25th Oct
Benefit realized
• Reduction in Pot Voltage - a net reduction of 11 mV
• Reduction in AEF - net reduction of 0.19 no./pot day.
• Reduction in Noise - a net reduction of 1.66 mV.
• Net saving in Power Consumption of 35.2 kWh/MT. (190 MU/Year)
• Reduction in PFC & CO2 Emissions – Net reduction by 50% in trial
section
All benefits shown are excluding the benefits realised in section 8.
14. |
Pot room Parameter Analysis for Slotted Anodes on Full line
Implementation
Implementation period – 23rd Oct’12 to 13th Jan’13
Benefits observed
• Reduction in Pot Voltage - a net reduction of 21 mV.
• Reduction in AEF - 0.21 no./pot day.
• Reduction in Noise - a net reduction of 3.9 mV
• Net saving in Power Consumption of 67.3 kWh/MT. (344 MU/Year)
• Amperage Ramp – Net increase of 3.1 KA. Production Volume
Increased by 0.106 T/Day
• Reduction in PFC & CO2 Emissions – Net reduction by 50% in
whole pot line.
15. |
Intangible Gains - Impact on Environment
15
Conservation of non renewable resources of energy.(Coal & Oil)
Power consumption reduced by 344 MU/Year.
Emissions of green house gases (PFC) has been reduced by 50%.
Manpower productivity has improved.
Anode effect frequency has been decreased to a large extent -
productivity has increased.
Reduction trend was seen in consumption of green poles
AEF had reduced by 50%.
Elimination of Safety and health hazard
reduced anode effect frequency and immediate auto quenching
methods - operators are now less exposed to hot furnace
conditions.
16. |
Future Readiness of Slotted Anodes
17
Increasing Slot Depth
Slot Cutting
Other Energy Reduction
initiatives
17. |
Other Smelters Slot Heights
18
Benefits of Slotted Anodes enjoyed by other smelters:
• For a slot depth equal to half the anode’s life, the voltage benefit is estimated between 35-66mV for Rio
Tinto Aluminium managed plants.[2]
• Voltage reduction of 45mV/pot by implementation of Slotted Anodes (HINDALCO, Renukoot)[3]
It can be seen that increasing slot depth from 10 to 20cm is
worth approximately 20mV in reduced bubble resistance
Smelter
Slot Height
(mm)
Anode
Height
(mm)
% Slot
Height
NALCO * (Press forming) 120,100 560 21.40%
HINDALCO 180,160 645 27.90%
BALCO 182,176 580 31.40%
ALBA 215,190.5 650 33.10%
MOZAL 250,230 650 38.50%
EMAL (Phase-1) 250,200 650 38.50%
Hill Side 290,270 650 44.60%
EMAL (Phase-2)* 320,300 685 46.70%
VAL (Press Forming) 207.5,200 575 36.00%
VAL (Slot Cutting) 300,280 575 52.00%
* Note: NALCO and EMAL Phase-2 are using On line Slot cutting technique
18. | 19
Online Slot Cutting
High Capital Cost
Life time of Saw
Blade
Advantages
No Variation in anode quality
Higher Slot height than press forming
More slots possible, more closely spaced
Increases active area
Disadvantage
Initial investment on Slot Cutting Machine
and operating cost
Life time of a saw blade is a potential
problem (45000 Anodes per blade is
reported as per Brochot – Supplier of
Machine to NALCO)
Handling and recycling of granular
carbon dust.
Scrap Generation increases in bake
Oven.
On Line Anode Slot
Cutting
