Theoretical Analysis of a Lignite-Fired Power Plant with Pre-Drying System in Terms of Energy Efficiency and Economy

Öz

The coals with different initial moisture content to be used in the theoretical analysis were tested according to the related test standards and the results were used in the analysis. In the designed system, waste heat in the flue gas is used as the heat source. The fresh air is heated for drying in the shell-tube heat exchanger by means of flue gas. In fluidized bed dryers, the moisture of the coal was reduced by contacting the raw coal with the drying air. Due to the high initial moisture of the coals used in the theoretical analysis, the pre-drying degree could be at most 0.14 in order that the boiler feeding rate be the same as in the power plant feeding rate without pre-drying system. The system theoretically does not conform to the design parameters and the boiler feed rate is less than the flow rate of power plant without pre-drying system when the pre-drying degree is greater than 0.14. The pre-drying system had ten small capacity dryers working simultaneously to ensure the continuity of the boiler feed. In the study, the theoretical analysis was performed, and thermal performance of the power plant were formulized and graphically presented according to pre-drying degree. Thanks to the pre-drying system, owing to the decrease in the moisture content of the coal, a reduction in the flue gas flow rate and the amount of energy required to evaporate the moisture are realized. As a result, there was a decrease in the boiler losses and an increase in the efficiency of the boiler. The increase in boiler efficiency was 10.74% when coal 1 had been used and it was 7.92% when coal 2 had been used. Since the coals are dried in the same drying system under the same conditions, the moisture of coal 1 decreases more, thus the losses of the boiler decrease more. Due to the increase in the lower heating value and in the boiler efficiency, the efficiency of the power plant with pre-drying could increase by 3.04-4.34%. The coal pre-dried power plant had far more economic performance than a power plant without pre-drying system, since more electricity would be obtained thanks to the increase in efficiency of the plant. The redemption period of the system was determined as 2 years with coal 1 and it was determined as 3 years with coal 2. After the payback periods, the system makes a net profit and brings in an average of 55 million TL extra income per year. In addition, it was observed that when the degree of pre-drying was decreased, economic efficiency of the system also decreased. It is aimed that the study will provide principles of energy efficiency improvement in coal fired power plants with pre-drying system and will guide people who wants to do similar studies.

Anahtar Kelimeler

• Coal fired power plant,Pre-drying of coal,Fluidized bed dryer,Power plant efficiency improvement,Theoretical analysis

Kaynakça

1. 1. Turkish Coal Enterprises. Annual Report 2018; Ankara, Turkey, 2019. Retrieved May 9, 2019, from website: http://www.tki.gov.tr/bilgi/yayinlar/faaliyet-raporlari/228
2. 2. Turkish Coal Enterprises. Coal Sector Report (Lignite) 2016; Ankara, Turkey, 2017. Retrieved May 9, 2019, website: http://www.tki.gov.tr/bilgi/yayinlar//stratejik-plan/227
3. 3. J. Pikon, A.S. Mujumdar, Drying of coal, in: Handbook of Industrial Drying, third ed., CRC Press, Boca Raton; FL, 2006.
4. 4. Xu, C.; Xu, G.; Zhao, S.; Dong, W.; Zhou, L.; Yang, Y. A theoretical investigation of energy efficiency improvement by coal pre-drying in coal fired power plants. Energy Conversion and Management. 2016, 122, 580-588.
5. 5. Xu, C.; Xu, G.; Yang, Y.; Zhao, S.; Zhang, K.; Zhang, D. An improved configuration of low-temperature pre-drying using waste heat integrated in an air-cooled lignite fired power plant. Applied Thermal Engineering. 2015 90, 312-321.
6. 6. Xu, C.; Bai, P.; Xin, T.; Hu, Y.; Xu, G.; Yang, Y. A novel solar energy integrated low-rank coal fired power generation using coal pre-drying and an absorption heat pump. Applied Energy. 2017, 200, 170-179.
7. 7. Atsonios, K.; Violidakis, I.; Agraniotis, M.; Grammelis, P.; Nikolopoulos, N.; Kakaras, E. Thermodynamic analysis and comparison of retrofitting pre-drying concepts at existing lignite power plants. Applied Thermal Engineering. 2015, 74, 165-173.
8. 8. Xu, C.; Li, X.; Xu, G.; Xin, T.; Yang, Y.; Liu, W.; Wang, M. Energy, exergy and economic analyses of a novel solar-lignite hybrid power generation process using lignite pre-drying. Energy Conversion and Management. 2018, 170, 19-33.

9. 9. Liu, M.; Yan, J.; Chong, D.; Liu, J.; Wang, J. Thermodynamic analysis of pre-drying methods for pre-dried lignite-fired power plant. Energy. 2013, 49, 107-118.
10. 10. Liu, M.; Wu, D.; Xiao, F.; Yan, J. A novel lignite-fired power plant integrated with a vacuum dryer: System design and thermodynamic analysis. Energy. 2015, 82, 968-975.
11. 11. Kızıl, H. Experimental Analysis of Coal Drying in Fluidized Bed Dryer, Post Graduate Thesis, Zonguldak Karaelmas University Institute of Science and Technology, Zonguldak, Turkey, 2011, 43-66.
12. 12. Liu, M.; Yan, J.; Bai, B.; Chong, D.; Guo, X.; Xiao, F. Theoretical Study and Case Analysis for a Predried Lignite-Fired Power System. Drying Technology. 2011, 29(10), 1219-1229.
13. 13. ASTM D4239-18e1, Standard Test Method for Sulfur in the Analysis Sample of Coal and Coke Using High-Temperature Tube Furnace Combustion, ASTM International, West Conshohocken, PA, 2018.
14. 14. ASTM D5373-16, Standard Test Methods for Determination of Carbon, Hydrogen and Nitrogen in Analysis Samples of Coal and Carbon in Analysis Samples of Coal and Coke, ASTM International, West Conshohocken, PA, 2016.
15. 15. ASTM D7582-15, Standard Test Methods for Proximate Analysis of Coal and Coke by Macro Thermogravimetric Analysis, ASTM International, West Conshohocken, PA, 2015.
16. 16. TS ISO 1928, Solid mineral fuels - Determination of gross calorific value by the bomb calorimetric method and calculation of net calorific value. Turkish Standards Institution. Ankara, Turkey, 2014.
17. 17. ASTM D5865-13, Standard Test Method for Gross Calorific Value of Coal and Coke, ASTM International, West Conshohocken, PA, 2013.
18. 18. TUBITAK. Metrology, UME, 1st; Istanbul, Turkey, 2013.
19. 19. Europen Co-operation for Accreditation. Expression of the Uncertainty of Measurement in Calibration, EA 04-2; 1999.
20. 20. Kakaç, S.; Pramuanjaroenkij, A.; Liu, H. Heat exchangers: Selection, rating, and thermal design. Boca Raton, FL: CRC Press, 2012.
21. 21. Çengel, Y. A.; Tanyıldızı, V. Heat and Mass Transfer: A Practical Approach. İzmir: Güven Kitabevi, 2011.
22. 22. Gnielinski, V. New equations for heat and mass transfer in turbulent pipe and channel flow, Int. Chem. Eng., 1976, 16, 359.
23. 23. McAdams, W. H., Heat Transmission, 3rd ed., McGraw-Hill, New York, 1954.
24. 24. Kurtuluş, O. Investigation of fluid bed drying process, Post Graduate Thesis, Yildiz Technical University Institute of Science and Technology, Istanbul, Turkey, 2007, 31.
25. 25. Agarwal, P.K.; Mitchell, W.J.; La Nauze, R.D. Transport phenomena in multiparticle systems-III. Active particle mass transfer in fluidized beds of inert particles. Chemical Engineering Science, 1988, 43, 2511-2521.
26. 26. Harimi, M.; Sapuan, S.; Ahmad, M.; Abas, F. Numerical study of heat loss from boiler using dif ferent ratios of fibre-to- shell from palm oil wastes. Journal of Scientific and Industrial Research, 2008, 67, 440-444.
27. 27. TS EN 304, Heating boilers - Test code for heating boilers for atomizing oil burners. Turkish Standards Institution. Ankara, Turkey, 2017.
28. 28. General Directorate Of Renewable Energy. Optimization in Industrial Systems; Fan Systems, Ankara, Turkey, 2017.
29. 29. Özdemir, M.B.; Yatarkalkmaz, M.M. Energy, Exergy and Economic Analysis of Different Types of Collectors. Gazi Journal of Engineering Sciences ,2015, 1 (2), 235-251.