Experimental and Mathematical Analysis of Energy Conservation in Iron Foundries with Critical Input Parameters of Rotary Furnace

Transcription

1 Volume 1, Issue 2, October-December, 2013, pp IASTER 2013, Experimental and Mathematical Analysis of Energy Conservation in Iron Foundries with Critical Input Parameters of Rotary Furnace Dr.R.K. Jain Professor & Head, Department of Mechanical Engineering, ITM University, Gwalior, India ABSTRACT This paper deals with Experimental Investigations and mathematical analysis of effect of critical input parameters of LDO-fired rotary furnace on energy conservation in iron foundries. Energy consumption is major problem being faced by the Indian ferrous foundries. Bureau of Energy Efficiency, The Energy and resources research Institute, Govt. of India, New Delhi & other International agencies has reported that energy consumption in Indian ferrous foundries is much more above the required limits and has to be drastically reduced. The author conducted experimental investigation on critical input parameter in a self-designed and developed 200 kg rotary furnace in an industry. The specific fuel and energy consumption of furnace, when operated under existing conditions, is 0.460liter/kg or Kwh/tone. When operated with identifying and changing critical input parameters, the specific fuel and energy consumption reduced to liter/kg or kwh/tone. The energy consumption is reduced by 35.12%. Keywords: Rotary furnace, Specific fuel, Oxygen enrichment, Energy consumption. 1. INTRODUCTION The Rotary Furnace is very simple melting unit consisting mainly of a drum of required size having a cone on each side lined with refractory fire bricks or ramming mortar generally having alumina as a constituent. This drum is placed on rollers so that they may be either locked or slowly rotated about their central axis. The rollers are driven by a small electric motor. At one end of the drum, a suitable burner is placed with appropriate blower system and combustion gases exit from other end. Two conical portions on both sides flank this drum or horizontal cylinder. One of the cones accommodate the burner whereas from the other cone hot flue gasses exit. Charging of the iron for melting is also done from this side. The cone on one side can accommodate different types of burners using the Light Diesel Oil (L.D.O.). The tap hole is located in the cylindrical wall halfway between the ends. This tap hole is used to take out the molten metal but it is kept closed during the melting of metal. There are a number of variables controllable to varying degrees, which affect the quality and composition of the out-coming molten metal. These variables, such as, revolutions per minute of the drum, melting time, fuel consumption and melting rate play significant role in determining the molten metal s properties and should be controlled throughout the melting process. However, even an experienced operator may find it difficult to select the optimum input parameters, which would yield ideal molten metal, and often he may choose them by guessing which may not be effective and economical. 108

2 The working of Rotary furnace is explained [1].The regression modeling and excel solver technique has been applied for mathematical modeling and optimization of critical parameters of rotary furnace viz. rpm, melting rate, specific fuel consumption etc [2]. An overview of energy consumption in ferrous foundry has been presented and the need of an energy efficient furnace for foundries is stressed upon [3]. The most of the units are crippled with usage of rudimentary techniques. The Indian foundry industry needs optimization of energy consumption [4].The use of newer and cleaner technology for energy conservation has been advocated [5]. The use energy efficient melting techniques are stressed upon [6]. It is emphasized to supply oxygen at 8kg/cm 2 pressure as it reduces melting time and emission levels [7]. The numerical methods to solve the linear, transcendental and polynomial equations are explained [8]. The procedures of optimization using mathematical techniques are described [9].The numerical techniques can also be applied to solve the engineering problems [10]. The statistical techniques can be used for optimization of energy consumption [11]. The present exercise is yet another attempt in energy conservation of iron foundries for melting of cast iron, through critical input parameters of rotary furnace. The critical input parameters identified are(1) Preheated air volume(2) Oxygen volume(3) Flame temperature (4) Preheated air temperature. These parameters need to be controlled for optimal specific fuel and energy consumption. Figure-1 shows the layout and accessories of a rotary furnace. 2. MELTING OPERATION Fig 1 -Layout and accessories of a rotary furnace. The process of melting the charge in rotary furnace is carried out in the following steps: (I) (II) (III) (IV) (V) (VI) (VII) Preheating of oil and furnace- Charging After pre heating, the furnace is charged. Rotation-After sufficient pre heating and charging, the furnace is rotated at desired speed. Melting- Tapping-The tape hole is slightly lowered and opened and metal is transferred into ladles, which are pre heated prior to the transfer of molten metal to avoid heat losses. Inoculation-The Ferro silicon and Ferro manganese approx. 600 grams per heat are added in molten metal contained in the ladles. Pouring The ladles are then carried to moulds and pouring is completed. 3. EXPERIMENTAL INVESTIGATIONS 3.1 Operating furnace under existing conditions of operation without oxygen enrichment Specific fuel and energy consumption The furnace was operated under existing conditions of operation without oxygen enrichment. The charge per heat is kg. In first heat, as furnace was started from room temperature, the melting time, fuel and energy consumption were more. In subsequent heats, the melting time, fuel and energy 109

3 consumption were reduced. 1liter of LDO is equivalent to kwh/kg of energy. Observations are given in Table 1. S N Table1- Specific fuel and energy consumption of furnace under existing conditions of operations He at no Rp m Time min Fuel liters Specific Fuel (lit/kg) Melting Rate (kg/hr) Flame temp. 0 C Preheated air cons The energy consumption of furnace under existing conditions of operations is shown in fig.2 m 3 Energy Cons. Without oxygen. Kwh/kg Fig.2-The energy consumption of furnace under existing conditions of operations 3.2 Operating furnace with oxygen enrichment of preheated air- Specific fuel and energy consumption It is thought to optimize the energy consumption by reducing the amount of air and supplying oxygen externally, required for combustion. Several experiments were conducted, gradually reducing air to its theoretical requirement and even lesser in steps of 5.0 to 10.0% and supplying oxygen externally in steps of 1.0 to 2.0 %, and its effect on flame temperature, time, fuel, melting rate, and fuel consumption was studied. The effect was significant only when air was reduced to 75.0% of its theoretical requirement and approx 7.0% oxygen was supplied externally. The experimental investigations conducted are given in following sections. 3.3 Effect of 6.9%oxygen enrichment of % of theoretically required air on flame temperature, time, fuel, melting rate, specific fuel and energy consumption- Numbers of experiments are conducted, rotating furnace at optimal rotational speed 1.0 rpm, with 6.9% oxygen enrichment of % of theoretically required air, preheating LDO to 70 0 C. The effect of above on flame temperature, time, fuel, melting rate, and specific fuel consumption are given in table

4 Table 3- Effect of 6.9% oxygen enrichment of % of theoretically required air on performance (flame temperature, time, fuel, melting rate), and specific fuel consumption. H ea t n o Rp m Preheat ed air temp 0 C Flame temp 0 C Time min Fuel liter Meltin g rate kg/hr Specif ic fuel cons. lit/kg 6.9% oxygen Specific Energy Cons. Kwh/kg Oxy gen cons. m 3 Oxy gen cons % Prehea ted air cons. m 3 Prehe ated air cons % The above experimental investigations reveal that by 6.9% oxygen enrichment of % of theoretically required preheated air, the specific fuel and energy consumption are significantly reduced. The energy consumption of furnace with 6.9% oxygen enrichment of % of theoretically required air is shown in fig.3 Fig.3 The energy consumption of furnace with 6.9% oxygen enrichment of % of theoretically required air 4. MATHEMATICAL ANALYSIS The furnace was run for maximum preheated air temperature of C,flame temperature C, time required/heat 30.5 minutes, fuel required/heat 52 liters, melting rate kg/hr, oxygen consumption/heat 36.5m3,air consumption/heat 426.5m 3 which gave the specific fuel consumption of liters/kg. 111

5 4.1 Identification of the Critical Input Parameters Based on several experimental investigations the critical input parameters are (1) Preheated air volume (2) Oxygen volume (3) Flame temperature (4) Preheated air temperature 4.2 Normalization of Critical Input Parameters - The maximum limits of each input and output is selected.the inputs and output are divided by their respective maximum limits to normalize them. Maximum limits of inputs and output are given in table 4 Table4- Maximum limits of inputs and output SN Inputs Maximum limit 1 Preheat air consumption 459m 3 2 Oxygen consumption 39m 3 3 Flame temp C, 4 Preheat air temp C Output Maximum limit 1 Specific fuel consumption liter/kg Out of the seven (7) sets of table 3 only 5 sets have been selected.the normalized values of inputs and output of above 5 sets of table 3 are given in table 5. For developing of equations the inputs (variables) have been taken as x x 4 respectively and output as y Table 5-The normalized values of inputs and output INPUTS OUTPUT Heat Preheated Oxygen Flame Preheated Specific no air cons. cons./heat. temp air fuel cons. m3 m 3 0 C temperature y x 1 x 2 x Formation and Development of Equation - As per mathematical analysis the equation has been considered as Y=a 1 x 1 +a 2 x 2 +a 3 x 3 +a 4 x 4 +a 5, Where a a 5 are constants and x 1 ---x 4 are variables. The mathematical equations as per normalized values of inputs and output are given in table 6. x 4 112

6 Table 6- The mathematical equations as per normalized values of inputs and output SN Equations 1 a 1 +a a a 4 +a 5= a a a a 4 +a 5 = a a a a 4 +a 5 = a a a a 4 +a 5 = a a 2 +a a 4 +a 5= Evaluation of Constants -Mat Lab - The values of constants a a 5 are evaluated using Mat lab. The programme run is shown below and values are given in table 7 M-file script A= [ ; ; ; ; ]; b= [1.000; ; ; ; ]; X=A\b Solution: X = Where, X= [a1; a2; a3; a4; a5] Table 7 -The values of constants a a 5 using Mat lab SN Constants Value 1 a a a a a Comparison of Calculated and Experimental Outputs - Putting values of constants as per table 7 in equations 1 to 5, (table 6) and comparison of calculated and experimental outputs is given in table 8. Table8- Comparison of calculated and experimental outputs Sn Equation Calcula ted Y Experim ental Absolute variation % Absolute variation Mean average %variation 1 a 1 +a a a 4 +a 5 = % a a a a 4 +a 5 = a a a a 4 +a 5 = a a a a 4 +a 5 = a a 2 +a a 4 +a 5= Presentation of Variations - The variations between experimental and calculated output y (specific fuel consumption) is presented graphically in fig 4 113

7 Fig 4 -The variations between experimental and calculated output 5. RESULTS 5.1 Experimental analysis- The comparison of performance, fuel and energy consumptions under existing conditions of operation and with 6.9% oxygen enrichment are given in Table 9. Table 9- The comparison of performance, fuel and energy consumptions under existing conditions of operation and with 6.9% oxygen enrichment Parameters Operating furnace Operating furnace with 6.9% Percentage without oxygen oxygen enrichment of 75.3%- reductions/ enrichment of 75.4% of theoretically required increments preheated air preheated air Time minutes % Flame temperature0c % Melting rate kg/hr % Fuel liters % Specific fuel cons.lit/kg % Specific energy cons. kwh/kg Preheated Air consumption % m 3 Oxygen consumption m 3 /tone - The comparison of energy consumptions is presented graphically in figure 5 Fig. 5 The comparison of energy consumptions under existing conditions of operation and with 6.9% oxygen enrichment 114

8 5.2 Mathematical analysis- The variations between actual and modeled specific fuel consumption is from % to The mean average percentage variations is %.It lies within the acceptable limits of ±10%. 6. CONCLUSIONS The above experimental investigations reveal that by 6.9% oxygen enrichment of % of theoretically required preheated air, not only the specific fuel and energy consumption are significantly reduced but performance of furnace is also improved significantly. The mean average percentage variation between experimental and theoretically calculated results is %. It lies within the acceptable limits of ±10%.It is concluded that Mathematical Techniques are capable of analyzing the experimentally investigated results of specific fuel/energy consumption in iron foundries with sufficient accuracy and further can be utilized for energy conservation analysis in any sector. REFERENCES [1] Baker EHW Rotary furnace Modern Workshop Technology, part -1, Clever Hummer Press Ltd., London nd Edition, Chap 4, [2] Jain R.K., Singh R, Modeling and optimization of rotary furnace parameters using Regression & Numerical Techniques proc. 68 th world Foundry Congress 2008, Chennai [3] Jain R.K., Singh R., Gupta B.D.- Energy considerations in Indian ferrous foundries Indian foundry journal, 2008, 54(8), [4] Baijya Nath, Pal Prosanto, Panigrahi K. C.- Energy conservation options among Indian foundries-a broad overview Indian foundry Journal 2007,53(8)27-30 [5] Singh Kamlesh Kumar, Energy efficiency in foundry process and casting rejection control Indian foundry Journal, 2007, 53(11) [6] Arjunwadkar S.H. Pal Prosanto, et al- Energy savings and carbon credits- opportunities and challenges for Indian foundries Indian foundry Journal, 2008, 54(10) [7] Pandey G.N., Singh Rajesh & Sinha A.K,- Efficient energy measures in steel foundry Indian foundry Journal, (10) [8] Grewal B.S.- Numerical Methods in Engineering and Science Text Book, Khanna publishers, New Delhi, 2008, [9] Rao Singiresu S - Engineering Optimization Theory and Practice Text Book, New Age International (P) Limited Publishers, New Delhi, [10] Shastry S. S - Introductory Methods of Numerical Analysis Third edition, Text Book, Prentice Hall of India. New Delhi, 2008, [11] Das H.K, Verma Rama - Introduction to Engineering Mathematics Volume II, Text Book, S. Chand &Co. ltd, New Delhi