Regression Analysis of Innovative Melting Technique for Energy Conservation in Foundry Industry

Transcription

1 Regression Analysis of Innovative Melting Technique for Conservation in Foundry Industry R. K. Jain, Dean, ITM University, Gwalior, India ratanjain@itmuniversity.ac.in Introduction TERI 1 (2005), The and Resources Institute, New Delhi, expressed its deep concern on excess fuel consumed in Indian ferrous foundries and laid down the limits. It further proposed to penalise the units consuming excess energy. Malhan Rajinder 2 (2005) presented the statistics on the foundry industry and suggested measures for Indian foundries to be globally competitive. Cardona Ramon 3 (2007) detailed the status of present energy scenario and stressed to develop some other sources of energy. Panchal Subodh 4 (2006) presented an overview of the upsurge of foundry industry in new century and is very optimistic about growth of Indian foundry industry. Arasu M. 5 etal. (2006) confirmed that an appropriate melting technique in arc furnace is important for survival of a foundry. conservation in melting can be achieved by controlling melting techniques, and applying quick charging of raw material, appropriate power input, cutting down of idle time, improvement of dust collecting efficiency etc. Dhumane Sharad 6 (2008) stressed to control the air displacement during mould filling to reduce the back pressure exerted by entrapped air as it slows down the metal flow and causes casting defects which leads to wastage of energy. Mukhopadhyay M.K. 7 (2009) stressed upon control rejections in castings for energy conservation. ASME Assessment Guide 8 (2010) gives the basic guidance in fulfilling the requirements of the energy assessment standards. The energy assessment standards established procedures for assessing an entire system for energy inputs to work performed. The standards are intended to assist the plant personnel in identifying the energy savings. Singh Saurabh Kumar, Chandra Ayush, Malik Kapil 9 (2011) advocated the energy conservation in furnaces by adopting certain techniques like check against infiltration of air, using sealed doors, monitoring O 2 /CO 2 / CO and controlling excess air, improving burner design, combustion control and proper instrumentation. They are of opinion that combustion chamber should have slight positive pressure, the load should match with furnace capacity, heat exchangers to be used, and flame should not touch the stock. Kim Hak Young, Beek Seung Wook 10 (2011) used the fuel-lean re-burn system to replace conventional re-burning technique in terms of increasing efficiency. It maintained fuel lean conditions in the furnace, in oxygen- As per 47th Census of World Casting Production, the Indian foundry industry is the third largest in the world producing 9,344,400 metric tonnes of castings annually, after China 42,500,000 metric tonnes and USA 12,824,960 metric tonnes and as per metalcasting plants by nation, India has approximately 4,500 plants. The majority of foundries are in the medium and small-scale categories. The study reveals that the two-thirds of the energy consumed in a foundry is used for metal melting and holding operation. Considerable energy savings can be achieved by proper attention to this process of melting with proper energy management. According to the reports published by several national and international agencies, the energy consumption in Indian foundries is much more above the required limits and has to be drastically reduced. Conservation of energy is an essential step that can be taken toward overcoming the mounting problems of the worldwide energy crisis and environmental degradation. The developing countries and countries with economies in transition are keenly interested in addressing the issues related to the inefficient power generation and energy usage. This paper deals with LDO-fired rotary furnace. The author conducted a series of experimental investigations on the self-designed and developed, 200 kg rotary furnaces, installed at foundry industry of Agra. These experimental investigations on the rotary furnace revealed that by reducing rpm from 2 to 1, energy consumption was reduced by 8.43%. The regression analysis of energy consumption in melting was carried out to verify the experimentally investigated results which may further be applied for any size of furnace. enhanced combustion, to replace additional air system, which reduces CO and NOx emissions significantly. TERI 11 (2014) explained that in general, the melting process consumes the maximum amount of energy in a foundry. Hence, foundries can cut costs by reducing energy (fuel) consumption during the melting process. This can be done by replacing the conventional cupola with the energyefficient divided blast cupola (DBC), or by reducing heat losses in the induction furnace. The major problems being faced by Indian foundry industry are: (1) consumption and its availability; (2) Technology upgradation; and (3) Impact of Globalisation. Out of these, the most severe one is energy consumption and its availability and technology upgradation. 29

2 The entire energy consumption study of foundry is divided into three parts:- (1) Availability of energy; (2) consumption in ferrous foundries and (3) Need for energy conservation. in Various Furnaces On the basis of survey conducted in various leading foundries, the energy consumption (kwh/tonne of metal produced) in different furnaces (in plants & equipments, melting charge, pollution control equipments, shot blasting, etc.) is given in Table-1. The energy consumption in rotary furnace is the highest. But it has some distinct advantages as compared to other furnaces, like (1) Graded and ductile iron can be produced; (2) The molten metal temperature achievable is higher than other furnaces; (3) The quality of metal produced is better; (4) It can be easily operated on a standby generator in case of power failure; (5) Low quality contaminated scrap can be used; (6) Due to rotation, the uniform heat transfer takes place inside the furnace which gives better melting rate; (7) Fluidity of molten metal and precision of operation can be controlled; and (8) It is economically viable. The major disadvantage is the energy consumption, which is more than the other furnaces. Hence, if energy consumption is reduced by further investigations, then it can be the most suitable furnace. investigations were carried out to achieve the optimal values for energy consumption in rotary furnace. Investigations investigations were carried out to observe the effect of identified parameters on the performance of rotary furnace. For this purpose, a kg rotary furnace was designed and fabricated. The designed rotary furnace was installed at foundry shop of Harbhajan Singh Namdhari Enterprises, Industrial Estate, Nunhai, Agra. Few experiments were also conducted on another kg rotary furnace installed at foundry shop of the Department of Mechanical Engineering, Faculty of Engineering, Dayalbagh Educational Institute (DEI), Dayalbagh, Agra. The furnace was operated at 2.0 rpm, as per existing conditions; the charge per heat was kg. In first heat, as furnace started from room temperature, more air was required, the flame temperature, preheated air temperature, and melting rate were less, but time and fuel consumption were more. In subsequent heats, the air was reduced, flame temperature, preheated air temperature and melting rate increased, whereas the time and fuel consumption decreased. Observations taken during the experiment are given in Table-2 (1 litre fuel= kwh). Table-2 : Performance of Furnace, Operated at 2 rpm S.N. H e a t No. Rpm T i m e min F u e l lit. S p e c. F u e l ( L i t / kg) kwh/kg Graphical representation of effect of operating furnace at 2 rpm (under existing conditions of operation), consumption/heat is shown in Fig. 1. RPM Fig. 1 : Effect of operating furnace at 2 rpm on energy consumption/heat. Further Investigation - The experimental investigations carried out are given in following sections: Effect of Rotational Speed on and Performance of Furnace To study the effect of rotational speed, experiments were done between 0.8 to 2.0 rpm as described below. The rotational speed was changed from 2.0 rpm to 1.6 rpm and then in steps of 0.2 rpm. Experiments were conducted at different rotational speeds varying from 0.8 to 2.0 rpm. It was difficult to rotate the furnace below 0.8 rpm. For each rotational speed, several observations were taken as given in Table-3. Table-1 : (Kwh/tonne) of Metal Produced in Various Furnaces SN Parameter Cupola Cokeless Cupola Induction Plasma Arc Rotary Crucible Oil Gas 1 consumed

3 Table-3 : Effect of Rotational Speed on Time (min), Spec. Fuel (lit/kg) and, Kwh/kg of Furnace SN Rpm Time (min) Fuel (lit.) Melting Rate kg/hr Spec. Fuel (lit/kg) Kwh/kg The graphical representation of effect of changing rpm from 2 to 1 on energy is shown in Fig. 2. Fig.2 : Effect of changing rpm from 2 to 1 on energy consumption. Results and Discussion The results of above experimental investigations of reducing rpm from 2.0 to 0.8 were studied and then the optimal values were obtained for energy consumption and emission level of pollutants. These values were obtained at 1.0 rpm. The improvements in performance of furnace by changing rpm from 2.0 to 1.0 are given in Table- 4. Table-4 : Improvement in Performance of Furnace by Changing rpm from 2.0 to 1.0 S.N. Parameters Absolute Reduction Reductions/Improvements 2.0rpm 1.0 rpm 1 (a) Melting time (minutes) % (b) Minimum Fuel (litres) % (c) Specific Fuel (lit/kg) % (d) in Melting (kwh/tonne) % 2 (a) Melting Rate (kg/hr) (b) No. of Heats per Day (200 kg) 3 Annual Savings *(a) Annual (b) Annual Fuel (litres) (c) Annual Fuel Cost % 20% x10 5 kwh 12.60x10 3 litres Rs.3.78 lakh 4 Annual Production (tonnes) % *[ Effect of rpm on Annual Savings: At 2.0 rpm, specific fuel consumption is litre/kg. At 1.0 rpm, specific fuel consumption is litre/kg Savings in fuel consumed in litres/kg = ( ) =0.035 litre/kg., For one heat of kg = 200x0.035 litre =7.0 litres/heat, 6 heats per day (at 2 and 1 rpm both) =7x6= 42.0 litres/day. Assuming 25 days /month=25x42.0=1050 litres/month. The annual savings = 12x litres = litres = 12.6 K litres The annual savings in energy consumption = 12.6 K litres x kwh/litre = kwh = x10 5 kwh Reducing rpm from 2.0 to1.0, the annual energy savings =1.247x10 5 kwh] 31

4 The graphical representation of effect of changing rpm from 2 to 1 on time, fuel, energy, specific fuel, and on melting rate (per heat) is shown in Fig.3. RPM Table-7 : Values of Constants SN Constant Value 1 a a a a a Putting these values, the general equation becomes Y = x x x x (1) Fig. 3 : Absolute reduction in energy consumption on changing rpm from 2 to 1. Regression Analysis It is clear that rpm of furnace affects the energy consumption. The data given in Table- 5 was used for analysis. Table-5 : Data Used for Regression Analysis S.N. Rpm (kwh/kg) It was converted into polynomial form of equations, taking X= rpm and Y= energy consumption. The equation becomes Y=a 0 x 4 +a 1 x 3 +a 2 x 2 +a 3 x, where a 0 a 1 a 2 a 3 a 4 are constant. The equations are given in Table-6. Table-6 : Equations for Regression Analysis S.N. rpm Equations a 0 + 8a 1 + 4a 2 + 2a 3 + a 4 = a a a a 3 = a a a a 3 = a a a a 3 = a 0 +a 1 +a 2 +a 3 = The values of constants were evaluated using several techniques as given below: Using Elimination of Simultaneous Equation The values of constants evaluated are given in Table Comparative Evaluation of using Equation (1) Comparative evaluation of calculated energy consumption and actual experimental energy consumption, with percentage variation is given in Table-8. Again this equation (1) was used to evaluate the values of Y putting X= 2,1.6,1.4,1.2,1, and 0.8 respectively. Table-8 : Comparative Evaluation of using Equation (1) S.N. rpm Calculated Actual Percentage (%) Variation Average % variation method Using Matrices The values of constants evaluated using matrices method is given in Table-9. Table-9 : Values of Constants Evaluated using Matrices Method S.N. Constant Value 1 a a a a a Putting these values, the general equation becomes Y=a 0 x 4 +a 1 x 3 +a 2 x 2 +a 3 x Y= x x x x (2)

5 Comparative Evaluation of Eenergy using Equation (2) The comparative evaluation of calculated energy consumption (with this equation) and actual experimental energy consumption, with percentage variation is given in Table-10. Table-10 : Comparative Evaluation of Using Equation (2) S.N. rpm Calculated Actual Percentage (%) Variation Method Average % variation method Comparison of - The comparison of energy consumption, based on both equations and experimental is given in Table-11. Graphical Representations The graphical representation of comparison of energy consumption, based on both equations and experimental is shown in Fig.4. It is clear from above experimental analysis that RPM of rotary furnace plays a significant role in energy conservation in foundry. ly, it reveals that reducing rpm from 2.0 to 1.0, the annual energy savings is 1.247x10 5 kwh. Further, the regression analysis as carried Fig.4 : Comparison of, based on both equations and experimental. out by using elimination method reveals average variation is % and by using matrices methods reveals the variation to be %. The overall average variation is %. This variation is well within acceptable limits and coincides with experimental analysis. Hence, this analysis is acceptable. Conclusion At 1 rpm, the rotary furnace is an innovative melting technique for energy conservation in foundry industry. It has been proved experimentally and by regression analysis. References 1. TERI, New Delhi, Report 2002,, Vol. 48, Issue 6, p Malhan Rajinder., 2005, Global Opportunities for Indian Foundry,, Vol.51, Issue 3, p Cardona Ramon, 2005, International Conference on Security in the Age of Globalization, World Federation of Trade Union, New Delhi. Table-11 : Comparison of, based on both equations and experimental S.N. Rpm Calculated Calculated Actual Percentage (%) Variation Percentage (%) Variation Average % variation Overall average % variation

6 4. Subodh Panchal, N. Ramamurthy (2006), Foundry Industry Resurgence in the New Millennium, Indian Foundry Journal,Vol.52, No.3, March.2006, p Arasu M., 2006, Melting & Conservation Techniques in Arc Furnace,, Vol.52, Issue 6, p Dhumane Sharad., 2008, Methoding of Cast Iron Automotive Castings,, Vol. 54, Issue 8, p Mukhopadhyay M.K., 2009, Conservation in Foundries by Controlling Rejections, Indian Foundry Journal, Vol. 55, Issue 3, p ASME Assessment Guide ASME EA- 1G-2010, Assessment for Process Heating System. 9. Singh Saurabh Kumar, Chandra Ayush, and Malik Kapil., A Perception for Conservation in Indian Industries, RAME Recent Advances in Mechanical Engineering, B.S.A.C.E.T. Mathura, March 25-26, 2011, Proceed,p Hak Young Kim, and Seung Wook Beek, 2011, Study of Fuel Lean Re-burn System for NOx Reduction and CO Emission in Oxygen Enhanced Combustion, International Journal of Research, Vol. 35, Issue 8, p The and Resources Institute (TERI), (2014), Promoting Efficiency in Foundry Industry by Strengthening Business Development Services, A Case Study in Rajkot Engineering Cluster, The booklet of Small Industries Development Bank of India (SIDBI) under the MSME Financing and Development Project and funded by Department for International Development (DFID), UK., January