Energy and Exergy Analysis of Wood-based CHP. Case Study

The paper presents use of energy and exergy analyses for the assessment of input and output flows in a cogeneration plant, shows points of exergy degradation in a system and allows to make a quantitative evaluation of energy quality changes. The objective of the study is to determine the essential points and values of exergy destruction in a biomass combined heat and power (CHP) plant in Jelgava, as well as to define boundaries of the method's use. A mathematical model is elaborated, used and evaluated as suitable for its application for the real plant and may be used in the plant's further operation for efficiency assessment and improvements. The results are shown with Sankey and Grassmann diagrams; the largest exergy destruction occurs in the boiler (steam generator) and represents 63.7% of input fuel exergy; second largest exergy destruction is observed in heat exchangers of district heating (DH) system. Exergy efficiency of the plant is influenced by the power to heat ratio (α) and potential of the produced heat (temperature). Increased heat load or decreased temperature of heat delivered to the consumer lowers the value of exergy efficiency of the plant.