Energy Efficiency Improvement Strategies for ...

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Energy Efficiency Improvement Strategies for Industrial Boilers: A Case Study Rahul Dev Gupta, Sudhir Ghai1, Ajai Jain2 Department of Mechanical Engineering, M.M. Engineering College, Mullana, (Ambala), 1Centre of Energy Studies, Indian Institute of Technology, Delhi, 2Department of Mechanical Engineering, National Institute of Technology, Kurukshetra, India

ABSTRACT

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In this paper, the findings of boiler house efficiency improvement study carried out in a large boiler house unit of a pulp and paper mill has been presented. The causes of poor boiler efficiency were various heat losses such as loss due to unburnt carbon in refuse, loss due to dry flue gas, loss due to moisture in fuel, loss due to radiation, loss due to blow down, and loss due to burning hydrogen, etc. The various heat losses were analyzed and a set of recommendations were made to the plant management for implementation, so that efficiency of boiler can be increased. Five important recommendations were implemented by plant management, and it has been seen that there is tremendous increase in boiler efficiency. Economic analysis reveals that the expenditure on the proposed system will be recovered in a short span of time. This work, with only five recommendations implemented, has resulted in net increase of 2% in overall boiler efficiency and an annual saving of Rs. 34,12,395. In addition, it is observed that carefulness in the operation of boiler can help a great deal in energy efficiency improvement in boiler.

Website: www.onlinejet.net DOI: 10.4103/0976-8580.74541 Quick Response Code:

Key words: Energy conservation, Boiler efficiency, Boiler heat losses

1.

INTRODUCTION

Energy is an indispensable instrument in the progress of human race. Today’s high standard living has been possible only through the judicious use of various energy resources at command. Realizing the fact that energy is the sinew of economic growth, energy management and energy conservation are of paramount importance. The above along with energy efficiency improvement are the only cost-effective and viable means of ensuring the proper use of finite natural resources, minimizing operating expenses, and increasing the profitability of enterprises. The considerable rise in plants utilizing process heat (pulp and paper, sugar mills, refineries, petrochemical, etc.) and electricity throughout the world have resulted in enormous increase in capacity and number of process heat boiler house units and thermal power plants installations. Such expansions coupled with escalating cost of fuel, have imposed an urgency to ensure that the boilers are operated as near to optimum conditions as possible. There is a need felt to carry out energy audit and efficiency test to analyze the various heat losses, with an aim to identify the major heat losses and causes of poor boiler efficiency. Efforts can then be made to minimize heat losses by proper operation 52

and modification of the boiler. Zeitz [1] has described upon the various heat loses in boilers, and these are heat losses due to unburnt carbon in refuse, heat loss due to dry flue gas, heat loss due to moisture in fuel, heat loss due to moisture from burning hydrogen, heat loss due to formation of carbon monoxide, heat loss due to sensible heat in bottom ash, heat loss due to radiation and convection, heat loss due to blow down. Energy Research Institute [2] provided information on the strategies for minimizing the heat losses. The biggest energy loss in a conventional fossil fuel fired boiler goes “up the chimney” that is, out the stack. The loss could amount to as much as 30%−35% of the fuel input in worst cases. Changnani [3] has discussed about combustion and effect of excess air in his research paper. Excess air increases the heat loss because air enters at ambient temperature and leaves the boiler at high temperature, taking a considerable amount of useful heat with it. Beer [4] has proposed a number of simple measures that could increase the energy efficiency of boiler. “Multi layer coal sorting” can sort coal particles in layers by size, with most of the larger particles on bottom of coal bed, medium size particles in the middle and smaller on top. The resulting multilayer structure leads to the reduction of unburned carbon in the slag even with a reduced excess

Journal of Engineering and Technology | Jan-Jun 2011 | Vol 1 | Issue 1

[Downloaded free from http://www.onlinejet.net on Monday, January 24, 2011, IP: 122.252.245.74] Gupta, et al.: Energy efficiency improvement strategies for industrial boilers

air supply to the grate. As a result, boiler efficiency can be improved by 5%−6%. Ozdemir [5] has discussed that operation of boilers at optimum combustion efficiency involves control of excess air supply. Ideally, excess air and stack temperature should always be maintained at the optimum levels established through the tune up procedures. This research work is focused on the improvements in boiler efficiency resulting from reduction in various heat losses [6]. The aim of this paper is not to present something new, but rather, to raise awareness and to show the tremendous energy and cost saving opportunities missed as a result of observing some simple and obvious conservation measures.

2.

DETAILS OF THE CASE STUDY

The efficiency test and energy conservation study has been conducted in the boiler house of a leading Pulp & Paper Mill. After calculation, the sum of various heat losses and boiler efficiency comes to be 19.015% and 80.98%, respectively [Table 1]. On the basis of efficiency test conducted and further analysis of various heat losses, the following recommendations were proposed for energy efficiency improvement and energy conservation. 2.1 Coal Preparation and Handling Sieve analysis of coal was carried out and the average value of Sieve analysis [7] comes to be 13.5%, which is on higher size and shows oversize coal. Because of this oversize coal, unburnt loss in bottom ash is quite high. To control this loss, Sieve analysis has to be carried out on a fixed time-frame basis (once in every shift) on coal coming out of the crusher. It is better to install one sieve analyzer in boiler house, so that sieve analysis can be

Table 1: Results of Efficiency Test Loss due to

kJ/ kg Coal

Dry flue gas 1328.53 Moisture in fuel 256.03 Moisture from burning hydrogen 843.47 Combustibles in refuse 1347.03 Formation of CO 17.62 Moisture in combustion air 56.65 Sensible heat in bottom ash 92.11 Radiation and convection − Blow down − Total losses Efficiency = 100 − total losses = 80.98%

Percentage loss 5.93 1.14 3.77 6.03 0.0785 0.255 0.41 0.7 0.7 19.015%

carried out there itself and feedback can be sent to coal crusher people. 2.2 Excess Air Boiler had been running at 75% excess air level and 8.8% oxygen in flue gas. This is on very high side. Operate boiler at lower excess air (around 40%-50%). Online oxygen analyzer [8] or oxygen trim system needs to be installed for proper control on excess air and oxygen content in flue gas. In the absence of online oxygen analyzer, it is recommended to conduct flue gas analysis after every 2 hour and adjust the combustion excess air, as condition changes. Under grate air must be properly distributed for peak burning efficiency. It is important to ensure periodic surveillance and maintenance to replace worn or broken grate sections. Air infiltration to the furnace must be minimized. It takes place through furnace wall seam areas or through the stoker. Sealing the furnace at potential leak sites reduces air infiltration. 2.3 Soot Blower Operation Installed soot blowers are not functioning since long because of soot blowers master steam control valve problem. It is recommended that the soot blower steam control valve needs immediate repair and in this regard valve supplier may be contacted and overhaul the valve, if needed. It is recommended to carry out the soot blower operation once in every shift. Soot blowing should also be carried out in economizer and air preheater. 2.4 Blow Down It is observed that blow down from boiler is on continuous basis (CBD). Usually, the blow down is excessive, just to be sure. Automatic blow down system [9] can be installed, consist of continuous monitoring of conductivity, and an automatic blow down sequence at a preset level. This automatic system can save energy wasted by continuous system. 2.5 Insulation It is observed that some boiler surfaces and valves are not properly insulated. One rule of thumb is that any surface above 120 ºF should be insulated, including boiler surfaces, steam or condesate piping, valves and fittings. All the damaged or worn out insulation should be changed on priority basis. Boiler casing should be checked for hot spots. Hot spots are an indication of excessive heat losses from the boiler enclosure. The temperature of surface of outer skin should not be more than 50 ºC.


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2.6 Periodic Training Program It is suggested that awareness on energy efficiency aspects be created among all employees; and especially boiler operators need training in energy conservation area [10]. It shall enhance overall efficiency of boiler house. Trained personnel shall also keep records, documents systematically and professionally. 2.7 On Going Sampling and Monitoring Schedule For proper control of unburnt in bottom ash and fly ash, it is suggested that in a shift of 8 hour, at least four samples of bottom ash & fly ash should be taken, and they may be sent for testing in lab for un burnt carbon [11]. This will help in reducing the unburnt carbon loss.

3.

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ii.

iii.

iv.

v.

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IMPLEMENTATION OF VARIOUS RECOMMENDATION MADE FOR IMPROVED ENERGY EFFICIENCY OF BOILER On the basis of recommendation made, the plant management instructed the boiler operators to send the coal sample for sieve analysis, once in every shift. [Earlier they used to do it, twice in a week]. Because of this, now there is proper control on coal size and any deviation in coal size can be checked timely. Because of regular and more frequent coal sieve analysis, the average reading of sieve analysis reduced from 13% to 7.5%. Because of this, the heat loss due to unburnt in front ash reduced from 3.48% to 3.08% and boiler efficiency also improved by 0.40%. On the basis of recommendation made, the plant management instructed the boiler operators to carry out the flue gas analysis, in every 2 hour. Now boiler operators adjust the combustion excess air, on the basis of flue gas analysis. Because of this, now the boiler is running on low excess air and heat loss due to dry flue gas has reduced from 5.93% to 4.97% [Figure 1]. And boiler efficiency has improved by 0.96%. It was recommended to repair the installed soot blowers. They have started the process of repairing of installed soot blower. On the basis of recommendation made, the boiler operators have started varying the amount of blow down as per quality of water, e.g., total dissolved solids (TDS) in water [12]. Although the blow down is still on continuous basis, but its quantity has reduced, and by doing this, the heat loss due to blow down, has been reduced.

7 %age Heat Loss

6 5 4 3 2 1 0 Dry flue gas

Moisture in fuel

Moisture Combustibles Formation Moisture in Sensible of CO combustion heat in from in refuse air burning Bottom Ash hydrogen

Before implementing Energy Conservation Techniques After implementing Energy Conservation Techniques

Figure 1: Comparison of heat losses

vi On the basis of recommendation made, all the cracks in the furnace insulating materials have been repaired. All the damaged or worn out insulation has also been changed. This has resulted in reduction of heat loss due to radiation and convection [13]. viii. On the basis of recommendation made, the boiler operators started taking samples of bottom ash and fly resulted in proper control on heat loss due to unburnt in bottom and fly ash [14]. Because of this and other measures, the heat loss due to unburnt in refuse reduced from 5.98% to 5.08% and boiler efficiency has increased by 0.9%.

4.

RESULT

During the efficiency test, the efficiency of boiler comes out to be 80.98%. To improve the boiler efficiency, various losses were identified. Their relative magnitude was calculated and then various recommendations were made to the plant management for improving the boiler efficiency. After implementing some of the recommendations made, efficiency test was again conducted. The efficiency of boiler has increased from 80.98% to 82.98% [Table 2]. i. By controlling excess air (air-flow rate), boiler efficiency improved from 80.98% to 81.94%. ii. By sifting and segregating coal fines, carbon content in front and fly ash was reduced from 13% to 12.1% and 30% to 26.34%, respectively. This meant saving in coal consumption of 444.6 tons per annum. iii. By employing better insulation on steam pipes, and by employing other recommendations, there was further improvement in boiler efficiency and boiler house efficacy.



Table 2: Efficiency Test of Boiler after Implementing the Recommendations Loss due to

(kJ/kg) Coal

Dry flue gas 1113.74 Moisture in fuel 252.4 Moisture from burning hydrogen 846.50 Combustibles in refuse 1139.39 Formation of CO 17.23 Moisture in combustion air 46.93 Sensible heat in bottom ash 88.40 Radiation and convection − Blow down − Total losses Efficiency = 100 − total losses= 82.98%

Percentage loss 4.97 1.12 3.77 5.08 0.0769 0.209 0.394 0.7 0.7 17.02%

improvement techniques in boilers (particularly coal fired). It is hoped that energy efficiency improvement techniques, as embedded in this work, would go a long way in improving efficiency of boilers. If immediate steps are taken to create energy efficiency consciousness in industries and a national policy program on energy conservation is implemented, it is hoped that the major problems associated with energy and fuel can be brought under control. This will lead to an economy with higher productivity and sustained growth.

REFERENCES 1.

iv. Total monetary gains of Rs. 34 12 395 per annum could be achieved which comprised of Rs. 16 56 332 savings due to reduction of excess air supply to boiler furnace from 68.9% to 40.04%, Rs 15 56 115 savings from separating coal fines and controlling coal size prior to the process of conveying of coal to the boiler furnace. And Rs. 1 99 948 savings on account of all other recommendations that were implemented.

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CONCLUSION

7.

This work determines and concludes that, tremendous positive gains can be attained by employing above approach in a given energy intensive activity, in this case in boiler house of a large paper mill. Overall boiler efficiency on account of all improvement recommendations has increased by 2% from 80.98% to 82.98%, which is a remarkable increase given the facts that no new equipment has replaced old boiler house equipment. This increase in efficiency speaks volumes about use of energy management which is need of hour. The monetary benefits thus accrued, can be gainfully used elsewhere, which shall help in providing vitality to the industry. There is a great scope of application of energy efficiency

8. 9. 10.

11. 12. 13.

14.

R. A. Zeitz, Energy Efficiency Handbook, Council of Industrial Boiler Owners (CIBO- Burke VA), pp. 25-65, 2003. R. Virendra, Energy Conservation Potential in Coal Handling Plants of Thermal Power Stations, J Ener Mgmt, pp.11-22, July-Sept 1997. D. Chnangani, Monitoring & Controlling the Stack Gas Temp, Available from: http://www.energymanagertraining.com, [last cited in 2004]. J. M. Beer, A Proposed Industrial Boiler Efficiency Improvement In Shanxi, Potential Carbon DioOxide Mitigation- Health Benefits And Associated Costs, J of Appl Ener, vol. 71, pp. 275-285, 2002. E. Ozdemir, Energy Conservation Opportunities with a Variable Speed Controller in a Boiler House, J of Appl Therm Engg, vol. 24, pp. 981-993, 2004. ASME, Power Test Code- PTC 4.1 (American Society of Mechanical Engineers USA) 1964. I. P. S. Paul, Performance Monitoring in Indian Thermal Power Stations, J of Ener Mgmt, pp. 17-24, Oct-Dec 1993. Pacific Gas & Electric Company, Boilers- Improving Energy Efficiency, Workshop Handbook (The Combustion Institute, Pittsburgh) 1994. P. Kumar, and A. K. Tyagi, Managing Energy Efficiency in Hotels and Commercial Buildings (TERI- New Delhi) 2002. P. Bowonder, Energy Audit in Manufacturing Industries, Energy conservation and Management (Administrative Staff College of India, Hyderabad) 1996. P. W. Callaghan, Energy Management (McGraw Hill Book Company Limited, Berkshire, England) 1996. P. Dockrill, Boilers & Heaters-Improving Energy Efficiency (Federal Industrial Boiler Program, Canada) 2001. G. Hain, Boiler Efficiency And Steam Quality- The Challenge Of Creating Quality Steam Using Existing Boiler Efficiencies (The National Board of Boiler & Pressure Vessel Inspectors, USA) 2004. D. Jaber, and G. A. McCoy, Steam System Management – Best Practises (Alliance to Save Energy, Washington State University, USA) 2001.


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Authors Biography Rahul Dev Gupta is presently serving as a faculty member in Mechanical Engineering Department of M.M. Engineering College, Mullana. His areas of interest include industrial engineering, cellular manufacturing systems & energy management. He is a Life Member of the Indian Society of Technical Education (ISTE) and an Associate Member of Institution of Engineers. He has 17 publications in international and Indian journals and conferences. E-mail: [email protected] Dr. Sudhir Ghai has done his Ph. D from Centre of Energy Studies of IIT Delhi. He has about 18 years of teaching experience. His areas of interest include energy conservation & management and alternate fuels for IC engines. He has more than 20 publications in international and Indian journals and conferences. E-mail: [email protected] Dr. Ajai Jain is presently serving as a faculty member in the Mechanical Engineering Department of National Institute of Technology, Kurukshetra, India. He has about 17 years of teaching experience. His areas of interest include computer aided design, flexible and automated manufacturing systems. He has more than 30 publications in international and Indian journals and conferences to his credit. E-mail: [email protected]

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