Thermodynamic Performance Assessment of a Bio-gasification Based Small-scale Combined Cogeneration Plant Employing Indirectly Heated Gas Turbine

Abstract

Thermodynamic model development of biomass gasification based indirectly heated combined cogeneration plant and its simulated performance is reported in this present study. Saw dust is considered as biomass feed, which undergoes gasification in a downdraft gasifier and the producer gas is combusted in a combustor-heat exchanger duplex (CHX) unit. The CHX unit heats up air for a 100 kWe Gas Turbine (GT) and the exhaust heat of CHX unit is utilized in generating bottoming steam turbine work output and utility steam. The performance of the plant is assessed over a wide range pressure ratio (rp) and turbine inlet temperature (TIT) for the GT block, as well as, by varying the steam turbine inlet pressure and temperature along with the outlet gas side temperature of the economizer. For the base case configuration (rp= 4 and TIT=1000 deg C) the plant gives an overall electrical efficiency of about 41% and, at the same time, produces utility steam at a rate of about 180 kg/hr. Its cogeneration performance, expressed in terms of fuel energy saving ratio (FESR), is found to optimize at particular values of topping cycle pressure ratio for different TITs. The study also includes discussion on the sizing of the major plant components. Further, a Second law analysis of the plant concludes that maximum exergy destruction takes place at the gasifier, followed by the CHX unit, together accounting for nearly 40% of the fuel exergy input.

Keywords

• Bio-gasification; Indirectly heated; Combined cogeneration; Fuel energy saving ratio; exergy

References

1. B. Buragohain, P. Mahanta, and V.S. Moholkar, “Biomass gasification for decentralized power generation: The Indian perspective”, Renewable and Sustainable Energy Reviews, Vol. 14, pp. 73-92, 2010. (Article) doi:10.1016/j.rser.2009.07.034
2. Ankur Scientific Energy Technologies Pvt. Ltd. Website: http://www.ankurscientific.com/ (website)
3. C. Syred, W. Fick, A. J. Griffiths, and N. Syred, “Cyclone gasifier and cycle combustor for the use of biomass derived gas in the operation of a small gas turbine in co-generation plant”, Fuel, Vol. 83, pp. 2381-2392, 2000. (Article)
4. A. Bhattacharya, D. Manna, B. Paul, and A Datta, “Biomass integrated gasification combined cycle power generation with supplementary biomass firing: Energy and exergy based performance analysis”, Energy, Vol. 36, pp. 2599-2610, 2011. (Article) doi:10.1016/j.energy.2011.01.054
5. Yap, and M. Roy, Biomass integrated gasification combined cycles (BIGCC), University of New Orleans Theses and Dissertations, Paper 206, 2004. (Report)
6. N.S. Barman, S. Ghosh, and S. De, “Gasification of biomass in a fixed bed downdraft gasifier-A realistic model including tar”, Bioresource Technology, Vol. 107, doi:10.1016/j.biortech.2011.12.124 2012. (Article)
7. A. Datta, R. Ganguli, and L. Sarkar, “Energy and exergy analyses of an externally fired gas turbine (egft), cycle integrated with biomass gasifier for distributed power generation”, Energy, Vol. 35, pp. 341-350, 2010. (Article)
8. P. Mondal, and S. Ghosh, “Biomass based indirectly heated combined cycle plant: Energetic and exergetic performance analyses”, International Journal of Innovative Research in Science, Engineering and Technology, Vol. 3, Issue 2, pp. 9285-9294, 2014. (Article)

9. K.A. Al-attab, and Z.A. Zainal, “Performance of high- temperature heat exchangers in biomass fuel powered externally fired gas turbine systems”, Renewable Energy, Vol. 35, pp. 913–920, 2010. (Article) doi:10.1016/j.renene.2009.11.038
10. S. Soltani, S.M.S. Mahamoudi, M. Yari, and M.A. Rosen, “Thermodynamic analyses of an externally fired gas turbine combined cycle integrated with biomass gasification plant”, Energy Conversion and Management, Vol. 70, pp. 107-115, 2013. (Article) doi:10.1016/j.enconman.2013.03.002
11. Cycle-Tempo Software, Release 5 (TU Delft), 2012 (Available: http://www.cycle-tempo.nl/.) (Website)
12. J. H. Horlock, Cogeneration-Combined Heat and Power (CHP), Pergamon Press, New York, 1987. (Book)
13. S. Ghosh, and S. De, “First and second law performance variations of coal gasification fuel-cell based combined cogeneration plant with varying load”, Proceedings of the Institution of Mechanical Engineers, Part A, Journal of Power and Energy, pp. 477-485, 2004. (Article)
14. M. J Moran, “Availability Analysis: A Guide to Efficient Energy Use”, Prentice-Hall, Englewood Cliffs, New Jersey, 1982 (Book)