Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 97 (2014) 2064 – 2071
12th GLOBAL CONGRESS ON MANUFACTURING AND MANAGEMENT, GCMM 2014
Enhancing effectiveness of Shell and Tube Heat Exchanger through Six Sigma DMAIC phases K.Srinivasana,*,S.Muthub, S.R.Devadasanc, C.Sugumarand a
Associate Professor, Department of Mechanical Engineering, Adhiyamaan College of Engineering, Hosur 635109, Tamilnadu, India Professor and Dean, Department of Mechanical Engineering, Dr N G P Institute of Technology, Coimbatore 641048,Tamilnadu,India c Professor, Department of Production Engineering, P S G College of Technology, Coimbatore 641014, Tamilnadu, India d Principal, Vel Tech (Owned By RS Trust), Chennai 600 062, Tamilnadu, India
b
Abstract This research portrays the pilot implementation of Six Sigma DMAIC (Define-Measure-Analyze-Improve-Control) phases to improve the effectiveness of shell and tube heat exchanger in a small sized furnace manufacturing company. Shell and tube heat exchanger is one of the critical components of the furnace. The imperative objective is to improve the quality of the furnace through DMAIC phases. In define phase, the critical to quality (CTQ) parameter was identified as effectiveness in shell and tube heat exchanger through the voice of the customer (VOC) and Pareto Chart. In measure phase, the present effectiveness was measured as 0.61. In analysis phase, the reason for the reduction of effectiveness was identified as less heat transfer area through cause and effect diagram. In improve phase, the existing design was modified through various alternative solutions by conducting brainstorming sessions. In this phase, the solution was identified with the introduction of circular fins over the bare tubes to improve the effectiveness in the shell and tube heat exchanger. Consequently, the effectiveness has been enhanced from 0.61 to 0.664. In control phase, the control strategies were recommended to sustain the improvements in shell and tube heat exchanger. In the end, the annual monetary savings of Rs.0.34 million were achieved through the implementation of DMAIC phases in the furnace manufacturing company. © Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2014 2014The TheAuthors. Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Organizing Committee of GCMM 2014. Selection and peer-review under responsibility of the Organizing Committee of GCMM 2014
Keywords:Six Sigma; DMAIC; CTQ; quality; effectiveness; furnace; shell and tube heat exchanger.
*Corresponding author. E-mail address:
[email protected]
1877-7058 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Organizing Committee of GCMM 2014
doi:10.1016/j.proeng.2014.12.449
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1. Introduction In the modern era of business practice, furnace plays an imperative role in metal extraction, metal forming and heat treatment process. The furnace products manufacturers maintain global competitiveness through strategic energy management by using energy efficient technologies. The performance of the furnace strives to enhance the quality by considering efficiency and performance of the furnace together. Among the various methods available to improve the furnace performance, a systematic approach should be used for achieving impetus improvement at an affordable cost. In engineering arena, the complexity reduction of the functional unit can be achieved through either break down of the system or process. The furnace has some basic performance influential components namely heat exchanger, nozzle, burner and control valve. The performance of individual components can be evaluated and integrated to embark the total performance of the furnace. The strict investigation was taken over to identify and eliminate the vital parameters that affect the efficiency of the furnace through a systematic approach namely Six Sigma DMAIC (Define, Measure, Analyze, Improve, and Control)phases. Six Sigma is a quality management tool introduced by Bill Smith of Motorola in 1980 [1]. It is said to be fierce approach that directly hits imperative woes faced in customer end, by reducing the variation to achieve 3.4 defects per million opportunities (DPMO) that subsequently enhance the quality, market share of the manufacturing organization. The variations are controlled by using a hierarchical approach of Six Sigma DMAIC, which have been derived from Deming’s improvement cycle namely PDCA (Plan-Do-Check-Act). This case study narrowly performs investigations on improving current performance of heat exchanger that improves the overall efficiency of the furnace by using the Six Sigma DMAIC approach. In this regard, the atmospheric air is preheated for complexity reduction through exhaust flue gas of a furnace. The preheating of combustion air illuminates to reduce energy loss in the furnace by improving overall efficiency. This preheating process provides 10–30 percentage monetary savings with the economical fuel usage [2]. 2. Literature review Furnace efficiency can be refined by concentrating on overload and heat transfer for diminishing the heat loss from flue gas [2]. In order to save the process industry economically, attention must be given to heat transfer improvement instead of reducing the size of equipment [3]. [4] Stated that, for improving performance and efficiency of the compact cross flow heat exchanger with affordable cost, the velocity of the air should not be higher. [5] Investigated the performance level of plain tube and finned tube that the heat transfer can be improved by using fins when comparing with plain tubes that produces high thermal performance and found the efficiency of the fin to be increased by43%.[6] Made a qualitative analysis of the heat transfer capacity on various fin configurations. Elliptical fins are suitable for lower pressure, and circular fins can withstand higher pressure after carry out various analysis and optimization process on their parameters and geometry. However, the staggered arrangement provides better performance improvement than inline arrangement for most cases. [7] Carried out an analysis and comparison of thermal performance of plate fin sinks and pin fin sinks, which is usually used in electronic equipment industry and explains that the increasing heat sink length reduces thermal resistance of the pin fin and the same increases in plate fin. [8] Illustrate about the advantages of circular fin in various fields and given the important aspect that should be concentrated when fins are getting contact with gas/fluid. The fin efficiency or performance is improved by the optimization of fin thickness and fin radii, also focused on one and two dimensional solutions of fin performance. By implementing Six Sigma DMAIC (a revolutionary approach) with its statistical tools and techniques in different process industries, fuel energy along with monetary savings can be achieved [9]. Six Sigma is the statistical breakthrough tool which improves the existing performance level of business strategy and controls the variations in the processing stage to less than 3.4 DPMO. The reputations of the Six Sigma are gained by identifying defects and insinuate their root cause [10]. [11] Clearly reckoned that, the primary objective of Six Sigma is the elimination of non-value added process activities along with continuous improvement. [12] Enumerated that Six Sigma is a data driven approach for reducing variation, by eliminating defects and errors such
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that the efficiency and quality were improved. [13] Enlightened the Six Sigma phases for improving and designing the process as DMAIC and DMADV (Define, Measure, Analyze, Design, and Verify) which are employed in a systematic project-oriented fashion of removing the root causes of customer quoted defects. [14] Systematic approach of the Six Sigma DMAIC methodology which has been derived from Deming’s PDCA cycle and Juran’s seven steps on quality was adopted to identify and reduce the defect rate for constructing the road proposed for a wind farm whose maintenance cost was in a perilous situation in that way process improvement was achieved with the reduced expenses in maintenance cost. [15] Illustrated the emerging importance of process capability analysis (PCA) and the statistical tool of Six Sigma in manufacturing sector for reducing the defects caused in the crankcase due to air pressure and feed, by embarking the Six Sigma level. 3. DMAIC Methodology 3.1. Define phase In this case study, the define phase evaluates the furnace performance, through identifying and reducing multiple operational energy losses to improve the overall efficiency. The Pareto chart in Fig.1 reveals that, numerous opportunities for improving the performance of the furnace. Among numerous opportunities, the waste heat recovery system saves up to 30% energy by transferring excess thermal energy to essential parts, especially for the combustion chamber to reduce high fuel consumption for obtaining required operating temperature. The heat generation parameter which includes proper air fuel ratio, reducing the excess air, enriching oxygen and preheating combustion air provides 25% energy savings. Heat containment saves 15% of energy by the reduction of energy loss to the surroundings, through inspecting convection, radiation and opening losses. The heat transfer saves 10% of energy loss by the removal of carbon deposits and maintaining a clean surface [2].
Fig.1. Pareto chart of furnace performance
It is clear that, increasing heat transfer subsidizes in enhancing the quality of the furnace and preheating the combustion air plays an active part in fuel economy. The Pareto chart clearly illustrates that the heat exchanger is primary subsystem that highly contributes in waste heat recovery and heat transfer that improves the overall
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performance of the furnace. Thus, the effectiveness of heat exchanger is the critical-to-quality (CTQ) factor that should be considered for improving its performance.
3.2. Measure phase The measure phase involves data collection and data evaluation processes to find the factors that identify the impact on performance of a heat exchanger. In order to identify the severity of each factor, Pareto chart was constructed as shown in Fig. 2.
Fig.2. Pareto chart for heat exchanger problems
The Pareto chart reveals that, the various parameters which influence the heat exchanger performance. It is evident that the effectiveness of shell and tube heat exchanger is having high potential value of impact on the overall performance of the furnace among the various parameters. From this interpretation, the effectiveness of the present heat exchanger was found to be 0.61.[16] Recommends that prior to the enhancement of the processing stages, process capability should be thoroughly measured to identify the path for improvement. Hence, the PCA for heat exchanger effectiveness was plotted to facilitate the current level of Six Sigma. The PCA clearly explains that, the current sigma level of the shell and tube heat exchanger as 1.34 by engendering PCA curvature using the MINITAB 16 software. Hence, the effectiveness of the heat exchanger must be improved to meet the customer expectation and accentuate the sigma level of the shell and tube heat exchanger. 3.3.Analyze phase In analyse phase, the identification of the root cause, makes an impact on the effectiveness of the shell and tube heat exchanger. In this regard, various subcritical factors were illustrated by cause and effect diagram in Fig. 3.
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Consequently, the brainstorming sessions were conducted to identify the major critical factor that makes an impact on the shell and heat exchanger effectiveness. It is clear that, the convective heat transfer area is less and identifies the best solutions for improving the convective heat transfer area were gathered through brainstorming sessions. Subsequently, various solutions were identified namely, increase in volume of the shell, increase in surface area of the tube, decrease in the flue gas velocity [3] and increase in a number of passes. The strict investigation reveals unanimously that, increase in surface area of the tube by implementing fins over bare tubes. This implementation shows that, the improvement on overall efficiency of the furnace by enhancing the effectiveness of shell and tube heat exchanger [17, 18]. 3.4. Improve phase In improve phase concentrates on embarking the current system configuration, which enlightens the sigma level. In this regard, the brainstorming session was made-up with the charter team that discussed the current status of the system. After fierce investigation, the consensus reveals that, the idea of introducing the fins over the bare tubes could intensify the heat transfer by protecting energy losses and enhances the effectiveness of shell and tube heat exchanger.
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Fig.4. Implementation of fins over the bare tubes
The Fig.5 illustrated that, the implementation of finsincrease the effectiveness of shell and tube heat exchanger. Pilot implementation revealed that the improvement in shell and tube heat exchanger effectiveness from 0.61 to 0.664. The continuous assessment on improvisation was assessed by taking the heat exchanger with optimal sample size of 10. The results obtained were evaluated by generating the PCA. The effectiveness of the finned tube heat exchanger found to be satisfied which embarks the sigma level to 2.01 from 1.34. 3.4.1.Fuel consumption and monetary saving calculation for finned tube heat exchanger The furnace consists often burners each with a fuel capacity of 10 liters. The furnace consumed totally 100 liters /hour. Heat exchanger acquires 50% of burner capacity and assuming seven hours/day (one cycle/day), where it runs 300 cycle/year. Improved heat exchanger model with fins has effectiveness of = 0.664, and the air temperature was elevated from 414 to 443 . The effectiveness improvement after the implementation of fins over the bare tubes was found to be 0.054. 50 liters / hr 0.054 = 2.7 liters/hr 2.7 liters / hr 7hrs/day = 18.9 liters/day 18.9 liters /day 300 days = 5670 liters/year 5670liters/year Rs. 60 = Rs.0.34 million per year In improve phase, monetary savings of about Rs.0.34 million per year was achieved from the shell and tube heat exchanger with fins. Finally, the enhancement of the effectiveness in CTQ parameter had been consummated. 3.5. Control phase In control phase, the gains have been achieved by the team personnel through refined process that yield maximum remunerations. In improve phase, the furnace manufacturing company implemented the optimal solution to achieve continuous improvement on effectiveness of the heat exchanger. Consequently, the overall effectiveness of heat exchanger enhanced by analysing and identifying the critical components of the furnace in theproper way.
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Further improvement in overall efficiency of the furnace can also be done by analyzing and improving efficiency of various critical components of the furnace. 4. Results and discussion Six Sigma DMAIC methodology was used in this case study to improve the efficiency of the furnace. In measure phase, severity of the problem was found in the heat exchanger. In analyze phase, various parameters have been analysed to improve the effectiveness of the heat exchanger through cause and effect diagram and brainstorming sessions. In improve phase, the performance comparison was listed in Table1, either with or without fins. Table.1. Performance comparison before and after implementation of fins Description
Existing heat exchanger
Finned tube heat exchanger
414
443
Heat transfer surface area Actual heat transfer rate Preheated air temperature Effectiveness
= = primary surface area of the tube (bare tubes). = fin surface area.
5. Conclusion It is essential to enhance the efficiency of the furnace through the reduction of high fuel consumption for obtaining required temperature of the furnace. A significant improvement in one of the furnace components that will improve overall efficiency of the furnace. Six Sigma DMAIC methodologies were implemented in the furnace manufacturing company to reduce the thermal energy in exhaust flue gas which extremely impacts the efficiency of the furnace. Thus, DMAIC phases revealed that, the best solution to the shell and tube heat exchanger by increasing heat transfer rate and reducing thermal energy in the waste flue gas through implementation of circular fins over bare tubes. The sigma level was improved from1.34 to 2.01. The monetary savings was achieved about Rs.0.34million per year. References [1] Shing-HanLi, Chi-Chuan Wu, C. David and Ming-Chih Lee, Improving the efficiency of IT help-desk service by Six Sigma management methodology(DMAIC) – a case study of C company, Production Planning and Control, Taylor and Francis, 2011, Vol.22 No. 7, pp. 612-627. [2] Mark Atkin son, John Barry, Improving Process heating system performance, second edition, Washington,2007. [3] E. Bergles Arthur, High-flux process through enhanced heat transfer, 5-th International Conference on boiling Heat transfer, (2003), Montego Bay, Jamaica, May 4-8. [4] IsakKotcioglu, SinanCaliskan, MuammerZirzakiran, Heat transfer in a cross-flow heat recovery ventilator with fin, ErciyesUniversitesi Fen BilimleriEnstitusuDergisi, (2009), 25 (1-2) 272-286, ISSN 1012-2354. [5] AlaHasan, Kai Siren, Performance investigation of plain and finned tube evaporative cooled heat exchanger, Elsevier Science Applied Thermal Engineering, (2003) 23 (3),pp. 325-340. [6] Denpong Soodphakdee, Masud Behnia, David Watabe Copeland, A Comparisonof Fin Geometrics for Heatsinks in Laminar Forced Convection: part I- Round, Elliptical, and Plate Fins in Staggered and In-Line configurations, The International Journal of Microcircuits and Electronic Packaging, (2001), Volume 24, Number 1, First Quarter (ISSN 1063-1674). [7] Dong-Kwon Kim, Sung Jin Kim, Jin-Kwon Bae, Comparison of thermal performance of plate- fin and pin- fin heat sinks subject to animpinging flow, International Journal of Heat and Mass Transfer, (2009), 52, 3510-3517. [8] M. M.Yovannovich, J.R.Chlham and F.Lemczyk, Simplified Solutions to Circular Annular Fins with Contact resistance and End Cooling, The AIAA 24-th Aerospace Science Meeting, Reno, 1987, Vol.2, No.2. [9] PrabhakarKaushik, Dinesh Khanduja, Application of Six Sigma DMAIC methodology in thermal power plants: A case study, Total Quality
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