Paper For Thailand

‘Opportunities of Energy Conservation in Steel Rolling Mill’ A Case study Shreekant Tare 1 Madhu Sharma 2 Department of Mechanical Engg, Faculty of Engg, SKSInstitute of Tech and Science, Indore (India) 452 012 E-mail: [email protected] 2 Department of Electrical Engg, Faculty of Engg, University of Petro & Energy, Dehradun (India) 248001 E-mail: [email protected]

1

Abstract The iron and steel industry presents one of the most energy intensive sectors within the Indian economy .The steel is mainly used for the infrastructural development in the form of plain/torsteel bars, popularly known as torbars.Most of the energy consumption in the rolling of the steel is in the form of thermal energy however the importance of electrical energy is no way less important.The opportunity of the energy saving is tremendous in the said industry .The aim of the study is to calculate actual energy consumption, and the measures for the energy savings.

Introduction The iron and steel industry presents one of the most energy intensive sectors within the Indian economy and is therefore of particular interest in the context of both local and global environmental discussions. Six industries in India have been identified as energy intensive industries: They are, Aluminum, cement, fertilizer, glass, paper and iron and steel, . Together they account

for 16.8% of manufacturing value of output (VO) and consume 38.8% of all fuels consumed in the manufacturing sector. The iron and steel sector holds a considerable share within these energy intensive industries. In 1993 it accounted for 46.5% of value of output within the six industries and for 7.8% in the manufacturing sector. Energy accounts for about 15% of the total manufacturing cost for steel.

Production Scenario In 1992, the total consumption of finished steel was 14.84 million tones in India . In 2008, the total amount of domestic steel consumption was 47.525 million tones. With the increased demand in the national market, a huge part of the international market is also served by this industry. Today, India is in seventh position among all the crude steel producing countries. However it is expected that upto year 2020 India will be the second largest country in the world in manufacturing of finished steel.In the year 2004, the global steel production has made a record level by crossing the 1000 million tones. China ranked 1 in the world in steel production among the top producers in the steel production .

Blowers - Two blowers to supply the air into the furnace for complete combustion of coal,each having capacity of 400 kg air per minute assisted by 25 kw motor. Coal Pulveriser – Pulverised coal is fired to the furnace.The pulveriser consumes 50 kwh. Rolling Mill – The rolling mill is having 4 rollers each supported by gun metal bushes at two ends.The rolling mill is driven by a power supply unit having capacity of 1000 kw. FIG 1

Production of Steel In India

Unit Under Observation

The chain of the production in the rolling plant is as under.

The company under observation, which is a mini steel plant produces torsteel bar of various sizes like 10 mm,12 mm,16 mm,and 25 mm.having total production of 15,000 Ton per year.

1) Sizing of

The floor is equipped with the setup containing following important setups.

Coal Furnace – The steel ingots are passed through a controlled temperature zone upto 1200 oC. The furnace is about 15 m long in which the ingot travels @ 6 m/ Hr.

Ingots – The ingots receied from the steel section is the raw material for a rolling mill.The ingots are batched in various sizes depending upon the final required size of the torbars. bring the ingot temperature to the plastic state, maintaining at 950o C. 2) Heatimg – The ingots are fed to the coal furnace,where they travel on a conveyer from low temperature to the high temperature region.The highest temperature maintained to 1200 o C to

3) Rolling – The red hot ingot is rolled in various stages,normally four number of stages reducing the size from 80 mm to 12 mm.

4) Cooling - The rolled plain cylindrical bars of about 10 meter in length are allowed to cool naturally.The bars are cooled from 450o C. to the atmospheric temperature.

FIG 2- STANDARD CF BLOWER

No doubt, the risk of scale formation is much high incase of hot rolling and thus in case where the accuracy is the criterion, the

cold working of the metal is preferred, however the uniformity of the material, liberty to go for relatively high percentage of carbon in the steel,low power required, smooth outer surface and avoidance of annealing makes the hot rolling process most preferred rolling process worldwide. FIG 3 - An Ingot Traveling in Furnace

Observations taken in the Steel Rolling Unit

Hot Rolling Process To fulfill the objectives as stated ,the following observations are recorded . Hot rolling is a fairly simple process .The steel is well above it's recrystalisarion temperature of 750 degrees C at 1000 degrees C. A slab or billet or ingot is passed or deformed between a set of work rolls and the temperature of the metal is generally above its recrystallization temperature, as opposed to cold rolling, which takes place below this temperature. Hot rolling permits large deformations of the metal to be achieved with a low number of rolling cycles. As the rolling process breaks up the grains, they recrystallize maintaining an equiaxed structure and preventing the metal from hardening. Hot rolled material typically does not require annealing and the high temperature will prevent residual stress from accumulating in the material resulting better dimensional stability than cold worked materials. Hot rolling is primarily concerned with manipulating material shape and geometry rather than mechanical properties. This is achieved by heating a component or material to its upper critical temperature and then applying controlled load which forms the material to a desired specification or size.

* Temperature of incoming air to the coal furnace * Temperature of the coal furnace. * Temperature of the ingot going in to the coal furnace. * Temperature of the ingot coming out of the coal furnace * Temperature of the ingot fed to the rolling mill. * Temperature of the torbars kept for natural cooling. * Velocity of the incoming air to furnace. * Number of turns to form torbars from the plain bars

* Additional Heating of Material =50 oC * Specific heat of Steel = 0.5 kJ/Kg/oC * Extra heat for extra heating per day = 16000 *0.5*50 = 4,000,00 KJ/Day * Furnace Efficiency =25% * Additional heat supplied = 4,00,000/0.25 = 16,000,00 kJ/Day

FIG 4- Rolling of Ingots into Plain Steel Bar As shown in the figure, the pair of rollers press the plastic state steel ingot section and reduces its size to half. The required final size can be obtained after 4 to number of operations forming the plain cylindrical bars.

Instruments Used * Tongue tester. * Laser beam remote temperature recorder. * Air flow Velocity meter

Loss Due to Extra Heating of the Material in Furnace

* Calorific Value of coal = 24360 kJ/kg

Saving potential :* Extra coal burnt = 16,00,000/24360 = 66 kg/day * Extra coal burnt @Rs.5.50 per kg = 363 /- Rs/day * Saving potential = 363 Rs/day* 300 days = Rs 1,08,900/- PA * Cost of sensor and monitor along with the installation = Rs 1,15,000/* Payback period = 115000/1,08,900*12 = Approx 13 months

Extra Air Supply to Furnace * Average Raw Material Charged in the furnace = 4800Ton/year * Average number of days running 300Days/Year * Average Raw Material Heating per Day = 16Ton per Day * Desired furnace temperature for the rolling =1200 oC * Actual temperature Maintained =1250 oC

* 12 kg carbon requires 32 kg oxygen for complete combustion * For a sample of Indonesian coal for complete combustion it requires about 16 kg of air/kg * For assured complete combustion and the heat to pass for about 10 meter furnace, about 5 times extra air to be supplied = 16*5 = 80 kg air/ kg of coal is required

* For burning of 3.5 ton coal in a day total quantity of air = 3500 kg* 80 kg of air/kg of coal = 2,80,000 kg/day * For 16 hrs operation per day,air required = 2,80,000/16= 17,500 kg/hr * The standard 25 kw blower supplies 375 m3/min of air at 2000 rpm at 90% efficiency. * Quantity of air measured at the blower output = A*V At area = 0.5 m2 and velocity measured by anemometer=520 m/s Q= 0.5 m2* 520 m/min = 210 m3/min Also V= 3.4 √∆P m/sec where ∆P is the average differential pressure. *Thus total air supplied by 2 blowers in 1 hour = 210*2*60 = 25,200 m3/hr *As above, the air required for combustion is 17,500 kg/hr where the actual quantity of air being supplied is 25,200 kg/hr ie. 25,200/17,500 = 1.44 times extra air (25,200-17,500=7,700 kg/hr) is being thrown into the furnace which is causing heat loss unnecessarily.

Saving Potential :For the supply of 17,500 kg air per hour,two blowers having capacity of 16.5 kw can work .However the calculations are shown as under. * Saving in power expected is (25-16.5)*2 = 13 kwh approx * Net saving of 13*5.5 = 71 Rs/hr = 71*16 Rs/day = 1,136 Rs/day * At average working of 300 working days an year,net saving be 1136*300= Rs 3,40,800 PA.

* Cost of two blowers = Rs 2,50,000 * Recovered cost of the two existing blowers = Rs.50,000 Approx * Net amount payable = Rs 2,000,00 * Pay back period = 2,000,00 *12/ 3,40000 = 7 months

Table 1 –Heating of Ingots in Furnace

Extra Heating in Coal Desired Condition 1200 oC Actual Condition 1250 oC Extra Heating 400000 kJ/day Additional Heat Supplied 1600000 kJ/day Extra Coal Burnt 66 kg/day Saving Potential Rs 108000.00 pa Saving Potential in % 5% Cost of Sensors Rs 105000.00 Installation Cost Rs 10000.00 Total Cost Rs 1,15,000.00 Payback Period 13 Months

Table 2 –Air Supplied to Furnace

Extra Air Supplid Desired Air

280000 kg/day

Actual Air Supplied 403200 kg/day Extra Air Supplied 123200 kg/day Extra Air in % 44% Blowers Installed 2 No 25 kW each Blowers Reuired 2 No 18 kW each Saving Potential 13 kWh per day Net Saving Rs 340800.00 pa Extra Amount Involved in New Blowers Rs 200000.00 Payback Period 7 Months

Conclusion

The project was undertaken to study the process of rolling of ingots to the cylindrical bars of different size and various parameters related to consumption of electrical and thermal energy were studied by taking the actual data on the job. The following points can be discussed at the conclusion . * Multiple leakage points are observed in the blower line.This is responsible for the pressure drop and finally affects the complete combustion of the coal inside the furnace. * The coal consumption in the rolling plant is about 78 kg/Ton of torsteel which is much higher compared to the recommended consumption of 70 kg per Ton of rolled steel for coal of 6000 kJ/kg calorific value. * The rolling mill runs on electrical energy at 1000 kwh,which consumes @135 kwh per Ton of rolled steel.This is to be compared with the standard electrical energy consumption of 110 kwh as the national average. The major reason of such a high consumption is the old rollers running on gun metal bushes.A strong recommendation of replacement of bushes with the roller bearings is given through this project report. * Instrumetation should be a regular culture of the energy intensive industry. The unit under observation found to be negligent towards the periodical collection of data, monitoring the measuring systems. * Finally,regular maintainance of the various machinery and plant is recommended. Also the cleaning of furnace is required more frequently than the existing schedule.

Acknowledgement

This project work was held in the premises of a mini steel plant and rolling mill M/s Ramdarshan Steel Rolling Mill situated at Indore city of the central Indian State of India.-452012 and well supported by the staff and engineers of the industry.

References:* Thermal Engineering by Domkundwar * Applied Thermodynamics by Rajput * Thermodynamics by P.K.Nag * Engineering Chemistry by Jain and Jain * www.millennium-steelstorage.com *http://productsearch.machinedesign.com /mdproducts/air_blower_design http://www.gidonline.com/catalogue/Blow ers.htm * www,wikipedia.org * www.energymanagertraining.com * www.bee-india.nic.in