Power Savings

Cement manufacturers take measures to reduce energy consumption

India is the second largest producer of cement in the world and the cement industry is a vital part of its economy. The real estate sector, which includes commercial, domestic and industrial infrastructure, is the biggest demand driver for cement. The industry is energy intensive in nature and, therefore, power is an important cost factor. A major portion of the total expenses are spent on the energy needs of plants, which, of late, have been working towards efficient energy use and energy conservation.

Power Line highlights the energy conservation measures undertaken by some leading cement companies…

Prism Cement Limited, Unit II, Satna, Madhya Pradesh

Prism Cement Limited is India’s largest integrated building materials company offering a wide range of products  like cement, ready-mix concrete, tiles, and bath and kitchen products. It has three divisions – Prism Cement, H&R Johnson (India), and RMC Readymix (India). The cement division of the company operates one of the largest single-kiln plants in the country at Satna, Madhya Pradesh. Prism Cement primarily caters to demand from Uttar Pradesh, Bihar and Madhya Pradesh. Its first line was commissioned in 1997 with a clinker production capacity of 6,000 tonnes per day (tpd). It was increased to 13,200 tpd after the commissioning of the second line in January 2011. Currently, it produces 5.6 million tonnes per annum (mtpa) of cement .

As a result of its energy conservation measures, the unit achieved electrical savings of 8.52 million kWh (a saving of 5.41 per cent over the previous year) and fuel savings of 202,107 million kCal (a saving of 14.75 per cent over 2013-14) in 2014-15. The unit’s specific thermal consumption also reduced by 15.19 per cent in 2014-15, from 0.64 million kCal per tonne in 2013-14 to 0.55 million kCal per tonne.

A key initiative that made this possible was the replacement of the cooler electrostatic precipitator (ESP) fan slip ring induction motor with a direct current (DC) motor. Previously, its kiln-hood draught was controlled by a damper as the SPRS could not reduce the revolutions per minute below 70 per cent. With the DC motor, the kiln-hood draft was controlled by the motor’s speed control feature, even at speed requirements below 40 per cent. The damper was subsequently removed, which helped achieve power savings of 200 kW per hour and annual savings of 158,400 kWh.

The unit has also optimised the running of cooling tower fans through temperature interlock with program logical controllers. Initially, two cooling tower fans of 22 kW each were running continuously in the local mode. With the temperature interlock in place, one fan runs continuously, while the other starts/stops based on temperature variations. If the temperature is less that 25 °C, one fan stops and when it is more than 30 °C, the fan starts revolving. The initiative has led to annual energy savings of 76,650 kWh.

Other initiatives include increasing the cement mill output by changing the grinding media pattern and by using pet coke in the process heating mix with coal, optimising the PH outlet temperature by reducing the speeds of both the PH sting fans and the bag house fans, optimising the shell cooling fan running by kiln shell temperature, the speed control of P&V blowers of load centre substations by installing variable frequency drives (VFDs), and the use of light-emitting diodes (LEDs) in place of conventional lights.

Mangalam Cement Limited, Kota, Rajasthan

Established in 1976 as a wing of the B.K. Birla Group, Mangalam Cement Limited produces 43 grade, 53 grade and Portland pozzolana (PPC) cement. The company started commercial production in March 1981 with an installed capacity of 0.4 mtpa of cement, which it subsequently increased to 3.25 mtpa. All the units of the company, namely, Managalam Cement and Neer Shree Cement, are located in Kota, Rajasthan. The company also owns two captive thermal power plants of 17.5 MW capacity each and 13 wind mills at Jaisalmer, Rajasthan.

Since 2011-12, the company’s specific heat consumption (SHC) has been showing a declining trend. The SHC decreased from 798 kCcal per kg clinker in 2011-12 to 739 kCcal per kg clinker in 2014-15. During the same period, the specific power consumption too decreased by 5.18 per cent, from 82.55 kWh per million tonnes of (mt) cement to 78.27 kWh per mt of cement.

The company has adopted a number of measures for the improvement and reduction of specific energy consumption both in electrical and thermal energy. The measures include process optimisation through in-house modifications of equipment for the enhancement of energy efficiency, the use of medium voltage drives and grid-resistance regulators in all high tension motors of most of the process fans (that is, preheater fans, ESP fans, coal mill fans), arresting of leakages to reduce fan electrical loads and process thermal loads, and the replacement of old and inefficient motors with IE-3 energy efficient motors. The company has also used energy-efficient compressors (screw compressor) and compressors with VFD, energy efficient lighting fixtures, and dedusting cones in place of conventional cyclones for reducing fan load and better efficiency of cyclones.  It has shown a higher utilisation of fly ash (31.11 per cent in 2014-15 as compared to 27.47 per cent in 2013-14).

Some other initiatives that the company undertook for reducing energy consumption are expanding its Unit 1 from 1,750 – 3,000 tpd with a six-stage pre-heater having an in-line calciner and a modern SF crossbar clinker cooler, the installation of a more efficient vertical raw mill (VRM) for raw-meal grinding, the installation of a more efficient vertical coal mill for coal grinding, the elimination of two belt conveyors from the lime stone-feeding circuit of VRM 1 by providing a direct chute to the hopper and replacing the reciprocating feeder by sector gates for clinker extraction from the clinker stock pile in CM 2.

Ramco Cements Limited, Madras Grinding Plant, Kancheepuram, Tamil Nadu

Ramco Cements Limited’s Madras Grinding Plant, with a capacity of 0.75 mtpa, is located in Kancheepuram district of Tamil Nadu. The plant was commissioned in May 2009 and manufactures PPC under the brand name Ramco Super Grade.

It has an online demand monitoring system, through which the entire plant’s operations and power drawn are closely monitored. There is an energy conservation task force that was formed under the unit head’s leadership with cross-functional members.

The plant has taken a number of initiatives to reduce its energy  consumption over the years as a result of which power consumption decreased from 38.01 kWh per tonne of cement in 2012-13 to 35.44 kWh per tonne in 2014-15 (till October 2015).

The measures included the installation of 42 W LED well glass fittings and 70 W LED street light fittings in place of 70 W and 250 W metal halide fittings respectively, replacing the 70 W metal halide lamps with 35 W compact fluorescent lamps (CFL), providing individual switches for all areas to reduce idle running, the installation of 65 W CFL street light fittings in place of 250 W metal halide fittings, replacing the lower diameter pulley with a mill vent bag filter and a separator vent bag, and the installation of a water high-level sensor switch in the overhead water tank.

The unit also installed a 250 kVA lighting transformer on the main lighting distribution board and 2 VFDs (30 kW each) for the compressor motor.

Other measures included the elimination of one cement bag transporting belt conveyor (2.2 kW) from the circuit by installing a direct chute arrangement at the truck loading, changing the motor connections of the packing plant belt conveyors from Delta to Star, increasing mill productivity by optimising the separator and recirculation fan, and providing a silo top bag filter interlock with an unloading compressor.

Conclusion

Given that the cement industry consumes a considerable amount of energy, improving its cost effectiveness through various energy efficiency initiatives is crucial for industry players. These case studies highlight how even small energy saving initiatives can go a long way in meeting the industry’s energy needs in a sustainable manner.

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