Optimization and energy efficiency measures in modified combined heat and power plant processes : A case study of changed processes in Mälarenergi power plant

Abstract: The EU energy efficiency directive is driving the EU member states to set ambitious goals to increase energy efficiency. Mälarenergi AB is one of the Swedish energy companies, affected by the directive, that have taken an active role in order to increase efficiency within their energy production. This study was initiated to perform energy analysis and find energy optimization measures in the systems attached to one of Mälarenergi’s CHP-units, called P5.The operating conditions of the bio fueled combined heat and power plant, P5, recently changed when the connected boiler, P4, was decided to be shut down. The two boilers shared turbine, steam, feed water, condensate and oil systems, and the operating conditions of these systems changed radically when the mass flow decreased as P4 was shut down. The changed operating conditions affects the efficiency and the performance of the plant. The changed mass flow affects the capacity demands, efficiency in components and the technical conditions of the plant.The general approach through this thesis and the used methodology is based on initial analysis of the system changes, review of the necessary functions in the system and identification of the differences between the needed functions and the existing system. Optimization potential were identified where there were large differences and as a final step, technical and economic feasibility of implementing identified optimization measures was analyzed. The results shows that feasible optimization potential is identified in removing pumps without adjustable speed drives from the system, installing adjustable speed drives to the warm condensate pumps, replacing the dilution water pumps and detaching the atomization steam tank for P4. The economic feasibility to invest in a new direct heater, better adjusted to the operating conditions of P5, is small but could be an option to Mälarenergi if the alternative production cost remains high. Without the already installed adjustable speed drives in Mälarenergi’s plant the efficiency of the operations would be much lower than what it is today and the optimization potential essentially larger. The efficiency potential in the plant increases further when the attached turbine, G4, is to be dismantled and the operating conditions changes again. More extensive simplifications and rearrangements of the system can be made to decrease the energy demand for operations with 745 MWh/year.