Energy and exergy of a cogeneration plant in a paper mill analysis

In this study, an energy and exergy based analysis has been carried out for the cogeneration plant of Varaka Paper Mill located in Balıkesir province. In order to perform the calculations, certain points are defined and thermodynamic properties are utilised based on the pressure, temperature and mass flow data of these points. In the exergy analysis, physical and chemical exergies are considered, but potential and kinetic exergies are neglected. Exergy efficiencies and exergy destruction of system components are calculated. In the analysis, EES (Engineering Equation Solver) program was used for thermodynamic calculations. A general flow diagram of the system was created and the components of the system such as boiler, turbine, condenser, pumps, deaerator, water heaters and steam collector were detailed. Heating steam is supplied to the factory from the steam collector. In this study, 25 ℃ and 101,325 kPa are assumed as reference environmental conditions. As a result of the calculations, mass balance, energy balance and exergy balance are obtained. The mass balance confirms that the mass flows of all components in the system are in equilibrium. Energy balance shows that energy inputs and outputs are balanced in the system. Exergy balance reveals the exergy destruction in the system and the exergy efficiency of each component. The Varaka Paper Cogeneration Plant in Balıkesir produces 35185 kW of electricity in this study and sends 40 tonnes of steam per hour to the mill. Steam generation in the plant is fluidized takes place in a boiler with a bed. According to the results, the boiler has an exergy efficiency of 43.77% and has the highest loss rate with 69513 kW exergy destruction. The turbine is highly efficient in energy utilization with 81.39% exergy efficiency and 8044 kW exergy loss. The spray system has an exergy efficiency of 98.76% with 182.7 kW of exergy loss, while the degasser offers potential for improvement with an exergy efficiency of 75.51% and a loss rate of 7713 kW. The condenser stands out as the component with the lowest exergy performance, having an efficiency of 4.939%, and it accounts for an exergy loss of 10761 kW. These analyses provide important information for evaluating the thermodynamic performance of the cogeneration system and identifying improvement potentials. The obtained results provide guidance on improvements that can be made to increase the efficiency of the system and minimize energy losses. The numerical results obtained here should be summarized. In particular, numerical results for the main parameters should be mentioned. The feed water pump operates close to its ideal performance with an isentropic efficiency of 74.34%, but the condenser pump shows a lower performance with an isentropic efficiency of 56.75%. In real operating conditions, the exergy efficiency of the feedwater pump is 44% and the exergy efficiency of the condenser pump is 13%. This indicates higher energy losses especially in the condenser pump.