Industry Case Studies

Companies improve plant processes to reduce energy use

Energy is used at all stages of metal production – mining, beneficiation and extraction. Energy consumption at domestic integrated steel plants is typically in the range of 6.5-7 gigacalories (GCal) per tonne of crude steel as against the international norm of 4.5-5 GCal per tonne of crude steel. The higher energy consumption is mainly due to the obsolete technologies used in these plants. The industry is facing challenges in retrofitting modern technologies at old plants, and problems pertaining to old shop floor and operating practices, and poor quality of raw material such as high ash coal and coke and high alumina iron ore. Therefore, companies are working towards reducing energy consumption at their plants through technological upgradation, waste heat utilisation and better quality inputs, etc.

Power Line presents an overview of the energy efficiency initiatives taken by some of the leading iron and steel, and aluminium companies. These have also been recognised by the Bureau of Energy Efficiency in the National Energy Conservation Awards 2016.

Hindalco’s Mahan Aluminium plant, Madhya Pradesh

Mahan Aluminium is operated by Hindalco Industries Limited (Hindalco), a subsidiary of the Aditya Birla Group. Hindalco is the world’s largest aluminium rolling company and one of Asia’s biggest producers of primary aluminium. In India, the company’s aluminium units run a gamut of operations ranging from bauxite mining, alumina refining, coal mining, captive power plants (CPPs) and aluminium smelting to downstream rolling of extrusions and foils. The Mahan Aluminium plant is spread over an area of 3,357 acres near Bargawan village in the Singrauli district of Madhya Pradesh. It consists of state-of-the-art smelter units (comprising 360 pots using Aluminium Pechiney 36 technology) and a CPP with six units with 150 MW of capacity each.

Energy consumption at the plant has gone down at all levels over the past few years. Hot metal specific electrical consumption has reduced from 14,838 kWh per million tonne (mt) in 2014-15 to 13,883 kWh per mt in 2015-16, hot metal specific thermal consumption from 0.41 mkCal per mt to 0.27 mkCal per mt, ingot specific electrical consumption from 79.1 kWh per mt to 50.5 kWh per mt, and specific coal consumption at the CPP from 0.69 kg per kWh to 0.65 kg per kWh.

The company has made concerted efforts to achieve these reductions. In 2015-15, direct current power consumption was reduced to almost 130.7 MUs due to several process optimisation measures taken in the pot room. This resulted in monetary savings of Rs 44 million. During this period, ICM furnace heaters were not operated in melt mode, leading to savings of nearly Rs 2.1 million. The company also started using centralised compressed air for operating its nitrogen plant, rather than operating a dedicated, stand-alone compressor, saving 50 MWh per annum.

Nearly 3,900 MWh per annum of energy was saved by reducing the load on induced draught fans by managing the dilution damper opening based on bag filter inlet temperature. Superfluous auxiliary cooling water pumps were stopped and medium voltage variable frequency drives (VFDs) were implemented in condensate extraction pumps, saving approximately 5.2 MUs of power.

Vedanta’s Lanjigarh alumina refinery, Odisha

Vedanta Limited, Lanjigarh is a alumina refinery of global metals and mining company Vedanta Resources. Incorporated in 2001, the refinery is currently a leading producer of metallurgical grade alumina and other aluminium products, which cater to a diverse range of industries. The firm operates a greenfield alumina refinery with a capacity of 1 metric tonne per annum, and an associated 75 MW CPP at Lanjigarh, Odisha. It is the first alumina refinery in India to adopt the zero discharge system. The refinery has a high plant availability factor of 92 per cent and is driven by power supply from the CPP. The company is also the first in the country to install filtration units for red mud in order to produce red mud cake instead of using a wet red mud disposal system. Another energy conservation and efficiency initiative introduced by the company is the installation of VFDs for better process control and energy saving in critical equipment. It also installed high tension and low tension capacitor banks at all substations, which improved the overall power factor of the refinery to 0.92 from 0.84. Further, conventional lights were replaced with LED lights. Coal mill modifications were carried out for minimising rejected coal. Vacuum pump gland cooling lines were also modified. Auto drain valves were installed to separate condensate and moisture from the compressed air systems.

Main burner nozzles were replaced in areas prone to calcination, and cooling water pump motors were downsized. Wash and water spray systems in the calciner area were optimised while pulleys were modified in ball mill liquor pump motors and secondary feed pumps for single-stream operation. Idle speed control motors were replaced with energy efficient motors. The refinery also undertook rural electrification of nearby villages using solar power. Together, these initiatives reduced specific energy consumption by 0.38 GJ per mt between 2014-15 and 2015-16, furnace oil consumption from 71.6 kg per mt to 70.4 kg per mt and water consumption from 2.58 cubic metres per mt to 2.49 cubic metres per mt.

Tata Steel’s Jamshedpur plant, Jharkhand

Set up in 1907, Tata Steel is India’s largest integrated private sector steel company and the world’s tenth largest steel company with an annual crude steel capacity of 30 mt. It is also the world’s second most geographically diversified steel producer, with operations in 26 countries and a commercial presence across 50 countries. The Jamshedpur plant comprises a 9.7 million tonne per annum (mtpa) crude steel production facility and a variety of finishing mills.

Over the years, the plant’s specific energy consumption has shown a steady reduction. For this, the company undertook repair and modification of the low power steam line network in its west plant to reduce steam and energy losses. The investment in this project was nearly Rs 17 million, while the total savings were Rs 24.7 million. In addition, the company replaced high pressure nitrogen with medium pressure nitrogen at one of its blast furnaces, which generated savings of Rs 32.4 million with no significant investments. It also reduced steam and condensate losses by improving steam trap management, which resulted in annual savings of Rs 10.4 million.

Further, the optimisation of cold blast blowing to the blast furnaces through a turbo blower increased power generation and resulted in total savings of Rs 114 million. In order to reduce the compressed air loss at the plant’s compressor house, ball mill rotations per minute (rpm) were reduced from 900 rpm to 800 rpm at the pellet grinding area. This resulted in electricity savings of 6.6 MWh. Further, pulverised coal injection at the blast furnaces was improved through increased oxygen enrichment, optimisation of bosh gas volume and use of coke with higher strength. This brought the plant’s coal injection rate on par with global benchmarks, and resulted in savings of nearly Rs 2 billion.

All these initiatives helped reduce specific energy consumption at Tata Steel’s Jamshedpur plant from 6.088 GCal per tonne of crude steel (tcs) in 2011-12 to 5.767 GCal per tcs in 2015-16. The company is committed to bringing down its plant specific energy consumption to a level of 5.2 GCal per tcs by 2020-21.

JSW Steel Limited’s Bellary plant, Karnataka

JSW Steel is the flagship company of the JSW Group, which is the leading manufacturer of value-added and high-end steel in India.  As part of its commitment to improve energy efficiency, the company has taken a number of energy saving initiatives. It reduced the use of vapourised liquefied petroleum gas (LPG) in its steel plant for pilot burner operations, heating and preheating fuel for oxyfuel cutting of steel by injecting nitrogen into the LPG. This helped save 10.6 tonnes of LPG per day in 2015-16 translating into monetary savings of Rs 420,000 per day. During 2015-16, the capacity of the blast furnace was also enhanced to 1.9 mtpa from 0.9 mtpa at an investment of Rs 174 million.

Improvement in furnace availability increased top pressure recovery turbine power generation from 19.3 MW to 22.2 MW during the period. Meanwhile, the installation of variable voltage VEDs at pellet plant 2 for its updraught drying fan resulted in power savings of 0.455 MW. Further, improvements were made in converter gas recovery through corex gas holder. Strategic decisions and optimised pressure reduced oxygen venting by 17,686 Nm3 per hour from 2013-14 to 2015-16.

JSPL’s Raigarh plant, Chhattisgarh

Jindal Steel and Power Limited (JSPL), a part of the diversified O.P. Jindal Group, is one of India’s leading steel producers. The company owns a 2.4 mtpa integrated steel plant and the world’s largest coal-based sponge iron plant in Raigarh, Chhattisgarh. JSPL’s Raigarh facility houses a coal washery, a sponge iron plant, a steel melting shop, a submerged arc furnace, a blast furnace, a coke oven plant, a sinter plant, a rolling mill, an oxygen plant, a lime dolime plant, a CPP, and a lime kiln unit. Through backward integration of its captive coal and iron ore mines, JSPL conducts its operations in an economical and efficient manner to produce quality steel and power. When the plant started operations, waste heat recovery boilers (WHRBs) were installed to utilise the waste heat of rotary kilns producing sponge iron. At present, all new kilns at JSPL are fitted with WHRBs.

During 2015-16, JSPL’s various energy conservation measures resulted in financial savings of about Rs 775 million and reduced energy consumption from 9.09 GCal per tonne to 8.7 GCal per tonne. Some of these measures are replacement of cooling tower fan blades made of glass-reinforced plastic with fibre-reinforced plastic blades; installation of 15 kW photovoltaic solar power panels; deployment of control valves in instrument air header to divert air to the ash handling plant; and introduction of VFDs in induced draught fans to reduce their power consumption.

Meanwhile, the conversion of electric arc furnaces into new oxygen furnaces resulted in energy savings of 325 kWh per tonne. Further, the installation of timer controls for switching on/off shed and floodlights has resulted in savings of Rs 500,000 per year. JSPL is planning to optimise the size of pumps in the steel melting shop, and install capacitors to improve the power factor. It will also install VFDs in descaling pumps and centrifugal air fans in plate mills. From 2017 onwards, JSPL plans to achieve waste heat recovery from its sinter cooler and electric arc furnaces. It will also modify its regenerative heater furnace with a regenerative burner in its rolling mill.

Conclusion

Leading Indian companies in the metals and mining industry are proactively making improvements in their plant processes and equipment to meet international efficiency norms. This will help improve their productivity and profitability as well as their global ranking.

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