Energy Efficiency in Iron Ore Mining

The study aimed at assessing energy (electrical) performance of various equipment and systems having significant energy consumption and find scope for reduction in Iron ore open cast mines. - Kishor H. Bhusal, Avijit Nayak

Energy Efficiency in Iron Ore Mining - Electrical India Magazine on Power & Electrical products, Renewable Energy, Transformers, Switchgear & Cables | Energy Efficiency in Iron Ore Mining - Electrical India Magazine on Power & Electrical products, Renewable Energy, Transformers, Switchgear & Cables
Energy Efficiency in Iron Ore Mining

The fourth common element and second most abundant metal on Earth’s crust is iron. About five per cent of the Earth’s crust is composed of iron. The metal is chemically active and is found in nature combined with other elements in rocks and soils. In its natural state, iron is chemically bonded with oxygen, water, carbon dioxide, or sulphur in a variety of minerals.

Iron ore mining is basically cascade array of ore extraction, ore preparation (crushing and grading/sizing), storage and transportation. To carry out extraction operation mines division is equipped with various classes of machineries ranging from deep bore driller, explosives and blasting equipment, earth movers like dozers, loaders, dumpers etc. Ore preparation is about bring the ore within a range of particular size or grade suitable for downstream operation. The preparation plant is equipped with crushers, screens, and conveyors etc. The transportation involves use of loaders, trucks, dumpers, rail etc.

The operation support services ranges from maintenance facility for earth movers and other vehicles, electrical supply to crusher and belt drives, water pumping and distribution for sprinklings in operation areas and domestic use, Operation Control Centre, Mines Admin Offices etc. The study aimed at assessing energy (electrical) performance of various equipment and systems having significant energy consumption and find scope for reduction in Iron ore open cast mines.

Iron ore mining industry in India

The production of iron ore consisting of Lumps, Fines and Concentrates at 192 million tonnes in 2016-17 increased by 21.5 per cent as compared to the previous year.

Odisha was the leading producer of iron ore accounting for 52 per cent of total production followed by Chhattisgarh (16 per cent), Karnataka (14 per cent), Jharkhand (11 per cent) and remaining (7 per cent) production was also reported from Andhra Pradesh, Goa, Madhya Pradesh, Maharashtra and Rajasthan. Public sector mines contributed about 36 per cent of total production and share of private sector in the total production was 64 per cent in 2016-17. (Source: IBM)

Production and Consumption of Iron and steel products is a direct indicator of development index of any country. Though Iron/ Steel is technically an infinite times recyclable element the process of production/recycle is highly energy intensive and calls for immediate attention as huge scope exists in the life cycle of iron for energy efficient technological intervention.

About iron ore mining process

The forms of Iron Minerals, Ores, and Rocks Iron occur mainly in iron-oxide ores. Some ores are a mixture of minerals rich in iron. Other iron ores are less rich and have a large number of impurities. The most important iron ore forming minerals are:

  • Magnetite – Magnetite (Fe3O4) forms magnetic black iron ore.
  • Hematite – Hematite (Fe2O3) is a red iron ore
  • Goethite – Goethite (Fe2O3.H2O), a brown ore, contains iron.
  • Limonite – Limonite (Fe2O3.H2O) is a yellow-brown iron ore. Limonite is a collective term for impure goethite and a mixture of hydrated iron oxides.

Process Overview: There are two basic methods of mining iron ore:

  • Surface mining or open-cast mining
  • Underground or shaft mining.

To be competitive, iron mining must be done on a very large scale. Surface mining is the preferred choice, although there are exceptions. The mines under energy audit study are open cast mines. The entire manufacturing is termed as ‘Mining’, where Iron ore is produced by open-cast mining. After removal of over-burdens, the ore is crushed to suitable size for further process.

Extraction

Explosives of high and mild intensity are used by drilling deep bore into earth surface to blast off in order to loosen and dislodge the iron ore deposit to be easily collected using various classes Dozers and Loader available at the site and subsequently the discharge is loaded onto Dumper to be transported to the crusher house. Forms of Energy utilised: Diesel.

Crushing

Since by the primary extraction of iron ore the lump size is often very big which poses difficulty for transportation through belt, thus it is imperative to reduce the size of lumps to a grade which becomes readily transportable and ready for use in integrated or secondary steel production plants. Forms of Energy utilised: Electricity.

The Crusher house has two streams of crushing lines where lump size is reduced by jaw crusher and Cone crusher. This charge is then ready for transportation through. Conveyor lines, vibrating mesh are operated in series for size segregation and storage.

Transportation to stock yard/rail siding for dispatch

(-) 10 mm size is termed as fines while 10 to 40 mm size is lump. All size of materials contains >60 per cent Fe. Recovery percentage of (-) 10 mm size is 47.39 per cent by weight while the balance 52.61 per cent by weight is 10 to 40 mm size. The finished products are transported by road to yard area and Railway siding for final dispatch to buyers. Wherever the mines not having railway siding facility the entire dispatch are done through roadways. Forms of energy utilised is diesel.

Major energy consumption area in iron ore mining

The electrical energy accounts for less than 5 per cent of energy used in iron ore production. The major energy consumption is contributed by diesel used for transportation. Though scope exists for energy performance improvement in both forms of energy consumption, Diesel consumption is highly dependent on driving practices apart from proper maintenance of earth movers. This requires periodic sensitisation about energy consumption among drivers and performance assessment of engines.

Though electrical energy consumption quantitatively less, it does not lose priority being the most sophisticated form of energy available today. The average price of electricity at mines range between Rs.7.80 – Rs. 8.03 per kWh. The major electrical energy requirement for mining is accounts for following heads:

  • Prime movers of crusher house and conveying systems
  • Lighting (outdoor and indoor)
  • Water pumping system
  • Other industrial support services like electric motors, drive systems and transformer compressors, ACs etc.

The energy consumption per tonne of ore varies from mines to mine as it is completely dependent on level of mechanisation and distance of stockyard from mining area. While the study team has witnessed highly mechanised mine having Ore Handling plant and transporting conveyor of more than 3km distance, in other mines portable crusher units are deployed for ore preparation at mining site only. Hence it is difficult to define a range of SEC.

Water Pumping System

Identified scope for energy conservation options

Savings by improving load side power factor for distribution loss reduction

For the mine under study had the present operating power factor at incoming main distribution panel of the plant is maintained at 0.68 levels. The operating power factor and loads at these panels were measured and it is proposed to partly increase the capacity of the installed capacitors from LT incoming panel to load- side panels as per operating load and PF to maintain consistent 0.97 PF in the system for effecting annual distribution loss reduction.

Transformers load distribution and replacement

The loading (average and observed) in various transformer were substantially low, under these conditions the equipment are subjected to high Iron or No load losses, which can be eliminated by either merger/load sharing or equipment resizing. It was found that various transformers are substantially under loaded due to over rated design parameters thus existing high Iron loss/No load loss. Most of the transformers were found to be in operation for more than 4 decades. Phase wise replacement also has been suggested with energy efficient transformers.

Water Pumping System

During the study, trials were conducted on all the pumps where water flow, discharge and suction heads and electrical power consumption for each of the pumps were measured and their specific power consumption and combined efficiency were computed. It was found that pumps were performing by far from design parameters and were in very dilapidated condition. The pumps were in operation more than 4 decades. Immediate replacement was suggested with energy efficient pump sets.

Lighting system

One major load in mines division are of lighting system, used for indoor illumination in office cabins, control rooms, crusher and drive house, store and workshop etc as per requirement and outdoor illumination in form of streetlight or high mast lights used for night operation. Separate Trials were carried out on lighting systems for Indoor and Outdoor lighting system including area wise lux survey of the entire plant area and after thorough analysis few recommendations were made in the lighting system for proper lighting requirements and replacement with efficient lighting.

Air-conditioning system

Air-conditioning in mines division is limited to window and split ACs of different ratings. Trial runs were conducted on various AC units on sample basis under which the thermal load and electrical load were measured by using instruments like digital thermometer, hygrometer, and anemometer and power analyser ultimately computing their efficiency parameters kW/TR. The analysis found various ACs if replaced with new energy efficient ACs would return payback within acceptable period.

All the above recommendations for five mines attract a saving potential up to 5 MU given the required investments expected payback less than three and a half years.


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