Energy and exergy analysis of a circulating fluidized bed boiler

Coal reserves and exploit of this reserves plays a vital role for countries such as Turkey depending on energy imports. In this point, quality of coal is a decisive factor. Especially, Turkey's coal reserves have properties such as low calorific value and high ash, humidity and SO2 rate. Fluidized bed combustion technology is the most effective solutions for efficiently burning of this coals. Even if this combustion system has the higher technology than other combustion systems, inefficient points in combustor are determined by applying energy and exergy analysis at certain times. Therefore, operational costs can be decreased and more energy can be produced against consumed per unit mass fuel. In this study, energy and exergy analyses of 75 t/h steam capacity circulated fluidized bed combustor in Kırka Boron Production Plant located Seyitgazi district of Eskişehir was made. When boiler was operated at full load, real data was obtained by making measurements for to use in calculations. Moreover, chemical analyses of flue gas and coal was made. In the energy and exergy analyses of FBC, combustor was considered as a whole rather than examined in case of sections. Besides, energy and exergy analyses of air heater was separately made from boiler. Node points were determined for both CFBC and air heater. Energy and exergy calculations were implemented for determined node points. These calculations were made for death state conditions (25℃, 101.325 kPa and 17.27℃, 89.4 kPa), respectively. Input and output energy and exergy values to CFBC and air heater were calculated for these reference environmental conditions. After that energy losses and exergy destruction were determined by creating energy and exergy balances. At the end of the analysis, energy and exergy efficiencies of CFBC and air heater, which based on the first and second laws of the thermodynamic. In this study has demonstrated that exergy efficiency of CFBC and air heater are significantly affected from reference environmental conditions. Consequently, decline in the reference environmental conditions give rise to increase in exergy efficiency. When we evaluate in terms of energy efficiency, it is seen that input and output values of the CFBC are independent of reference environmental conditions in energy efficiency calculation. However, input and output values used in energy efficiency of air heater are affected by reference environmental conditions. According to this result, change in efficiency have been detected.