Thermodynamic analysis of a bubbling fluidized bed multi generation plant for industrial applications

Politic restrictions in energy assurance and extreme increase in petroleum prices have directed Turkey towards energy and environment legislation to maximize the utilization of low grade local lignites, in which the country is relatively rich. Biomass co-firing with coal exhibits great potential for large scale utilization of biomass energy in the near future. The object of this study is to design a 6,5 MWe, 2,5 t/h proses steam and 7,5 MWt district heating capacity multi-energy generation power plant for operating with low grade lignite, Kangal, and eight different types of biomass of Turkey and implementing of the various R&D studies. After modeling and simulation of the designed power plant, comprehensive energy and exergy analyses have been carried out in order to improve its energy and environmental performance. In the present work, energy and exergy analyses are carried out for a co-firing based multi energy generation power plant system to investigate the impacts of biomass co-firing on system performance and gaseous emissions of CO2 and SO2. The power generation system considered is a typical bubling fluidized bed coal-fired steam cycle system, while eight biomass fuels (corn cobs, forest resedulas, hazalnut shells, olive pits, pistachio shells, rice husk, waste papers and bigasse) and one coal (Kangal lignite) are chosen for the analysis. System performance is evaluated in terms of important performance parameters for 10% of fuel at different cofiring conditions are considered. The results indicate that plant exergy distruction decrease with biomass proportion in the fuel mixture. As shwon from results, the lowest exergy distruction is in case of Kangal and pistachio shells and Kangal and hazalnut shells. The extent of decrease in exergy distruction depends on specific properties of the chosen biomass types. The results also show that the fraction of biomass significantly reduces the net CO2 and SO emissions for all types of selected biomass. Also as shown from the results that the exergy analyses have demonstrated that 90% of the total exergy loss of the power plant occurs in the boiler, and unlike energy analyses, actual energy efficiency must be in the boiler, not in the cooling system where only 2.41% of the total exergy loss occurs. Certain coefficients have been calculated for power plants fired with low grade local lignites, in order to determine directly the approximate fuels exergies and power plants exergy efficiencies with the help of the lower and higher heating values of the fuels and power plant energy efficiencies. Therefore, an approximate but highly practical tool has been obtained for reoffering the complicated exergy analyses by engineers.