Title:
Exergy Anlaysis and Optimisation of a Decentralised Woodchip-Fired Cogeneration Plant
Author(s):
Strzalka, R., Aly, A., Schneider, D., Eicker, U.
Document(s):
Paper
Poster
Abstract:
In this study, comprehensive exergy analysis of a woodchips fired cogeneration system based on organic Rankine cycle (ORC) is presented. The analysis is conducted to an existing cogeneration plant located in Scharnhauser Park, Stuttgart-Ostfildern, Germany that has been in operation since 2003. This study starts with discussing the exergetic analysis methodology, and then defining the most important performance evaluation indicators based on the exergetic analysis (e.g. exergetic efficiency, exergy destruction ratio, relative exergy destruction ratio, and exergy loss ratio).In the first section of the study, the input parameters for a simulation-based analysis is defined. In following sections, a mathematic model of the energy generation process was established. The structure of the model is explained, and the mass and exergy balances of the major system components are discussed in detail. The study shows that the Fixed Bed Combustion Boiler (FBCB) and the ORC evaporator are the main sources of exergy destruction. The FBCB contributes to 58% of the total destructed exergy while the ORC evaporator contributes to 30% of the total destructed exergy. Finally, some recommendations are suggested to optimize the plant’s energy conversion process through reducing the exergy destruction within the FBCB.To achieve higher conversion efficiencies continuous development of the bioenergy systems is needed. The presented study, which is based on experience from a full-scale system, aims to increase the knowledge about the influence of process parameters on the conversion efficiency. The primary and secondary air-flow rates are employed as major controlling parameters to maintain the stability of the combustion and achieve high conversion efficiencies. Simulation results showed that the energy efficiency of the biomass furnace can be increased by more than 2% when an optimized combustion air management system is applied. The study also examines the influence of the fuel moisture on the exergetic efficiency of biomass conversion. Simulation results showed a considerable influence of the fuel moisture on the process efficiency. The evaporation process of the moisture in the combustion chamber absorbs a considerable fraction of the fuel energy, which had an important effect on decreasing the process temperature levels.Finally, clear recommendations were suggested to optimize the plant’s energy conversion process through reducing the exergy destruction within the boiler. The main two factors that seem to improve the exergetic efficiency of the FBCB and consequently of the overall exergetic efficiency of the plant are obtaining woodchips with lower moisture content and decreasing the excess air ratio.
Keywords:
cogeneration, combustion, organic rankine cycle (ORC), optimization, efficiency enhancement
Topic:
Biomass Conversion Technologies for Heating, Cooling and Electricity
Subtopic:
Biomass and bioliquids combustion for small and medium scale applications
Event:
23rd European Biomass Conference and Exhibition
Session:
2BV.2.58
Pages:
760 - 768
ISBN:
978-88-89407-516
Paper DOI:
10.5071/23rdEUBCE2015-2BV.2.58
Price:
FREE
