Oxygen Excess Control of Industrial Combustion Through The Use of Automotive Lambda Sensor

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The objective of this study is to present a simple and low cost method of determining the flue gases oxygen concentration. The method makes use of the Lambda sensor, a part of the fuel injection system of the modern automobile’s engine. A combustion chamber was mounted with a heated Lambda sensor installed in its chimney. Residual oxygen concentrations in the flue gases were estimated by the use of the Nernst equation and compared to a reference combustion analyser. The observed average deviation in the measurements was of about 5 % which is in the range of interest to the industrial combustion.

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Oxygen Excess Control of Industrial Combustion Through The Use of Automotive Lambda Sensor

  1. 1. 2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. International Transaction Journal of Engineering, Management, & Applied Sciences & TechnologiesInternational Transaction Journal of Engineering, Management, & Applied Sciences & Technologies http://www.TuEngr.com, http://go.to/Research Oxygen Excess Control of Industrial Combustion Through the Use of Automotive Lambda Sensor a* a a Lutero C. de Lima , Humberto A. Carmona , Cesar V. M. da Silva , and Francisco S. a Cavalcante Junior a Graduate Program on Applied Physics, State University of Ceará, BRAZIL ARTICLEINFO A B S T RA C T Article history: The objective of this study is to present a simple and low Received 30 April 2011 cost method of determining the flue gases oxygen concentration. Received in revised form 20 July 2011 The method makes use of the Lambda sensor, a part of the fuel Accepted 25 July 2011 injection system of the modern automobile’s engine. A Available online 26 July 2011 combustion chamber was mounted with a heated Lambda sensor installed in its chimney. Residual oxygen concentrations in the Keywords: flue gases were estimated by the use of the Nernst equation and Flue gases; compared to a reference combustion analyser. The observed Industrial combustion; Lambda sensor; average deviation in the measurements was of about 5 % which is Oxygen concentration; in the range of interest to the industrial combustion. Thermal control 2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Some Rights Reserved. 1. Introduction   Laws and environmental regulations for the control of air pollution are turning more stringent mainly where the combustion of fossil fuels or biomass is present. After Wulfinghoff (2000), the efficiency control of combustion generally is made through the measurement of oxygen, carbon monoxide or carbon dioxide concentration in the flue gases. The measurement of oxygen concentration is better suited for the efficiency test of a combustion process because oxygen and excess air is almost independent of the fuel type. When the optimum excess air setting is approached, the relative change in oxygen concentration is much more accentuated than the relative change in carbon monoxide or *Corresponding author (L.C. de Lima). Tel/Fax: +55-85-31019902. E-mail addresses: luterolima@gmail.com. 2011. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. 365 eISSN 1906-9642. Online Available at http://TuEngr.com/V02/365-373.pdf
  2. 2. carbon dioxide for a given change in excess air. The Orsat analyser is the pioneer ofcombustion efficiency testers. This chemical testing apparatus in which flue gases are mixedwith a liquid reagent that changes volume as a result of the reaction is simple and accurate.However, the apparatus is built of delicate glass tubing and requires a fine touch. Still after Wulfinghoff (2000), most of the modern combustion testers is based on electro-chemical sensors. For the detection of oxygen the most common sensor used is a zirconiumoxide element that develops a voltage difference across two platinum electrodes separated bya porous ceramic layer if there is a difference in oxygen concentration. The combustionprocess in the modern automobiles generally is controlled by an oxygen sensor known asLambda sensor (Figure 1). Figure 1: Commercial Lambda sensors. McDonald, et al. (1998) used unheated and heated Lambda sensors for the monitoringresidential oil burners. They observed that even being a little more expensive the heatedLambda sensor presented better accuracy and low response time when compared to theunheated one. The unheated Lambda sensor takes about 5 minutes of warm-up in order to beoperational. Unéus, et al. (1999) applied Lambda sensor for the measurement of oxygenpercentage in the range of 12 to 15 % in industrial boilers. Wiesendorf, et al. (1999) usedthis sensor for the monitoring of fluidized bed combustors. Gibson, et al. (1999) developed anew technique of working with Lambda sensor which consist of applying a potential in oneand in the opposite directions of the sensor terminal and the electrical currents measured. Theratio between forward and reverse currents presents linear correspondence to the oxygenpercentage in the combustion environment. Pickenacker, et al. (2000) determined 366 Lutero C. de Lima, Humberto A. Carmona, Cesar V. M. da Silva, and F. S. Cavalcante Junior
  3. 3. experimentally air excess in boilers and furnaces using the concept of Wobbe which wasdetermined through the use of Lambda sensor. Auckenthaler, et al. (2002) were the firstresearchers to study the transient behavior of Lambda sensor. Niklasson, et al. (2003) studiedair-fuel ratio in a fluidized bed furnace through fluctuating signals from zirconia cell probes.Eskilsson, et al. (2004) used Lambda sensor to monitor oxygen concentration, combustionefficiency and emissions in pellet burners. Johansson, et al. (2007) used a Lambda probe toindicate whether the combustion environment was in oxidizing or reducing conditions.Varamban, et al. (2005) extended the perturbation method developed by Gibson, et al. andproposed a scheme to measure the emf and short circuit current of a potentiometric (zirconia)sensor simultaneously. In the present article an automotive Lambda sensor was installed in the chimney of acombustion chamber where its voltage difference and the flue gases temperature weremonitored and the oxygen concentration determined through the use of the Nernst equation.Results indicate that it is relatively simple the construction of low cost equipment to monitorindustrial combustion.2. Materials and methods  The Lambda sensor being an electrochemical cell when inserted in a situation wherethere is a difference of oxygen concentration as, for example, between the inside of acombustion chamber and the atmospheric air, and at a temperature above 300 °C, starts toconduct oxygen ions from the region of high to the region of low electrochemical potential.The migration of oxygen ions inside the electrochemical cell generate a voltage whichdecrease exponentially with the oxygen concentration inside the combustion chamber, takingas reference the air outside with oxygen concentration of 20.96 %. The equation which relates the oxygen concentration with a voltage developed inside theLambda sensor is the Nernst equation in its inverse under the following form: / ₂ % 20.96 (1),where z is the number of electrons migrating from one electrode to another electrode inside*Corresponding author (L.C. de Lima). Tel/Fax: +55-85-31019902. E-mail addresses:luterolima@gmail.com. 2011. International Transaction Journal of Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. 367eISSN 1906-9642. Online Available at http://TuEngr.com/V02/365-373.pdf
  4. 4. the Lambda sensor, F is the Faraday constant, E is the voltage developed in the sensor, R isthe universal gas constant and T is the absolute temperature inside the Lambda sensor. A commercial Lambda sensor was installed in the chimney of the combustion chambershown in Figure 2. The combustion chamber has a Weishaupt LPG burner of 50 kW. Closeto the Lambda sensor was installed a type K thermocouple. It was developed an electroniccircuit which feed the heating element of the Lambda sensor in order to maintain constant theinside temperature of sensor no matter how is the temperature of the flue gases. Figure 2: Experimental setup. The voltage signal of the Lambda sensor was monitored by a FLUKE 189 multimeterwith resolution of 0.01 mV and accuracy of 0.4 %. The thermocouple signal was recorded bya temperature controller showing resolution of 1 °C and accuracy of 0.5 %. The oxygenconcentration was measured by the TESTO 300 XL combustion gas analyser with resolutionof 0.1 % and accuracy of 0.2 %.3. Results and Discussion  Figure 3 presents signal of a Lambda sensor in mV calculated by the Nernst equation (1) for different levels of temperature and as a function of oxygen concentration. As can be seen by that figure when the oxygen concentration comes to the extreme points, as for example, 0 % and 20.96 % the voltage signal of the Lambda sensor go to infinite and zero respectively. This behavior of the Lambda sensor limits its application to the measurement 368 Lutero C. de Lima, Humberto A. Carmona, Cesar V. M. da Silva, and F. S. Cavalcante Junior
  5. 5. of oxygen concentration outside of such range. Figure 3: Output signal of a Lambda sensor as calculated by the Nernst equation. The relationship between the temperatures of the heating element of the Lambda sensoragainst its electrical resistance is shown in Figure 4. It was permitted to the combustionchamber to warm until 300 ºC. The burner was turn off and the electrical resistance of theheating element inside the Lambda sensor was recorded during the cooling period. It is veryimportant to know the electrical resistance of the heating element of the Lambda sensor as afunction of temperature because the electronic circuit responsible for the maintenance ofconstant temperature inside the sensor works controlling its resistance feeding more or lesspower.*Corresponding author (L.C. de Lima). Tel/Fax: +55-85-31019902. E-mail addresses:luterolima@gmail.com. 2011. International Transaction Journal of Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. 369eISSN 1906-9642. Online Available at http://TuEngr.com/V02/365-373.pdf
  6. 6. Figure 4: Curve of electrical resistance of the heating element against temperature. Figure 5: Flue gases oxygen percentage against measurements of the reference monitor. Figure 5 presents the percentage of oxygen in flue gases calculated by equation (1) withthe input of the voltage furnished by the Lambda sensor and temperature given by thethermocouple for different situations of combustion of LPG against measurements taken from 370 Lutero C. de Lima, Humberto A. Carmona, Cesar V. M. da Silva, and F. S. Cavalcante Junior
  7. 7. the reference combustion monitor. The average deviation of the set of measurements wasabout 5 %. The correlation factor was of 0.97 demonstrating good agreement between themeasurements of the proposed method of determining oxygen concentration of combustionflue gases and the measurements made by the reference monitor. In the range higher than 15% of oxygen concentration the deviation was more accentuate (about 10%) and this is due thelogarithmic nature of the sensor’s output, as can be seen in the Figure 3.Figure 6: Output of the Lambda sensor at the constant temperature of 500 °C as a function of the oxygen concentration. Figure 6 presents the evolution of the output of the proposed method as a function of theoxygen concentration while the temperature inside the Lambda sensor was maintainedconstant at about 500 °C and independent of the flue gases temperature. As it is shown in thatfigure the measurements follow very closely the Nernst law equation.4. Conclusion  In this work it was presented a simple method of determining oxygen concentration in theexhaust gases of combustion particularly the industrial combustion. Results demonstrated the*Corresponding author (L.C. de Lima). Tel/Fax: +55-85-31019902. E-mail addresses:luterolima@gmail.com. 2011. International Transaction Journal of Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. 371eISSN 1906-9642. Online Available at http://TuEngr.com/V02/365-373.pdf
  8. 8. feasibility of the proposed method when the Lambda sensor is operated inside a usualcombustion chamber. The heating time of about 5 minutes and the logarithmic response ofthe Lambda sensor are its main drawbacks if it is wanted to develop the herewith presentedmethod of measuring oxygen concentration in flue gases of industrial combustion.5. Acknowledgements  The authors thank the Brazilian National Council for Scientific and TechnologicalDevelopment (CNPq) for financial support. A very special thank you is due to Dr.JoãoBatista Furlan Duarte for insightful comments, helping clarify and improve the manuscript.6. References Auckenthaler, T.S., C. Onder, and H.P. Geering. (2002). Control- oriented investigation of Switch-type air/fuel ratio sensor, in: Proceedings of the IFAC World Congress, Barcelona, Spain, CD-ROM.Eskilsson, D., M. Ronnback, J. Samuelson and C. Tullin. (2004). Optimisation of efficiency and emissions in pellet burners. Biomass and Bioenergy, 27, 541-546.Gibson, R.W., R.V. Kumar and D.J. Fray. (1999). Novel sensors for monitoring high oxygen concentrations. Solid State Ionics, 121, 43-50.Johansson, A., F. Johnsson, F. Niklasson and L.E. Armand. (2007). Dynamics of furnace processes in a CFB boiler. Chemical Engineering Science, 62, 550-560.McDonald, R.J., T.A. Butcher and R.F. Krajewski. (1998). Development of self tuning residential oil burner – oxygen sensor assessment and early prototype system operating experience. Brookhaven National Laboratory, Informal Report BNL- 66045, 26 pages, Upton, NY, USA.Niklasson, F., F. Johnsson and B. Leckner. (2003). Local air ratio measured by zirconia cell in a circulating fluidised bed furnace. Chem. Eng. J. , 96, 145-155.Pickenacker, K., D. Trimis and K. Wawrzinek. (2001). Development of a Wobbe number sensor for controlled combustion of gaseous fuels with varying quality, in: Proceedings of International Conference on Technologies and Combustion for a Clean Environment (Clean Air VI), Porto, Portugal, V.1, 1-11.Unéus, L., P. Ljung, M. Mattson, P. Martensson, R. Wigren, P. Tobias, I. Lundstrom, L.G. Ekedahl and A. Lloyd Spetz. (1999). Measurements with MISIC and MOS sensors in flue gases, in: Proccedings of Eurosensors XIII, Hague, Netherland, 521-524.Varamban, S.V., R. Ganesan and G. Periaswami. (2005). Simultaneous measurement of emf and short circuit current for a potentiometric sensor using perturbation technique, Sensors and Actuactors B, 104, 94-102. 372 Lutero C. de Lima, Humberto A. Carmona, Cesar V. M. da Silva, and F. S. Cavalcante Junior
  9. 9. Wiesendorf, V., E.U. Hartage, J. Wether, F. Johansson, J. Sternéus, B. Leckner, D. Montat, and P. Briand. (1999). The CFB boiler in Gardanne – an experimental investigation of its bottom zone, in: Proceedings of the 15th Int. Conf. On Fluidized Bed Combustion, Savannah, Georgia, USA, May 16-19, ASME, Paper FBC99-0151.Wulfinghoff, D. R. (2000). Energy Efficiency Manual. Published by Energy Institute Press, USA. Dr.Lutero Carmo de Lima graduated in Physics by the University of Santo Amaro, M.Sc. and Dr. Eng. in Mechanical Engineering by the Federal University of Santa Catarina and University of São Paulo, respectively. He is presently Adjunct Professor at the State University of Ceará and basically works in fundamental problems of the thermal science, clean energy and instrumentation. He was awarded a Fulbright Fellow and inducted as Vice President of PHI BETA DELTA, Chapter Beta Theta, Honour Society for International Scholars, USA.  Dr.Humberto de Andrade Carmona is an Adjunct Professor in the Program for Applied Physical Science at the Ceara State University working mainly with alternative energies, particularly with material science applied to problems involving thermal science and solar energy. He holds a PhD in Physics from the University of Nottingham, England, as well as MS and graduation from the Federal University of São Carlos, Brazil. He has vast experience with electronic transport in semiconductor devices, and computer modeling of materials. César Vinicius Mota da Silva graduated in Physics by the State University of Ceará. He is presently colaborating at the State University of Ceará working in fundamental problems of the thermal science, clean energy and instrumentation. He is currently also working as a monitor of the project Science Traveling with experiments in various areas of Physics. Francisco dos Santos Cavalcante Junior holds a degree in physics from the State University of Ceará. He is currently a student at the Master Program in Applied Physics of that university. In that program he conducts research related to renewable energy with emphasis on biomass combustion.Peer Review: This article has been internationally peer-reviewed and accepted for publication according to the guidelines given at the journal’s website.*Corresponding author (L.C. de Lima). Tel/Fax: +55-85-31019902. E-mail addresses:luterolima@gmail.com. 2011. International Transaction Journal of Engineering,Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. 373eISSN 1906-9642. Online Available at http://TuEngr.com/V02/365-373.pdf

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