| Abstract [eng] |
District heating systems are an important part of urban energy infrastructure, therefore their efficiency, flexibility and reliability are becoming increasingly more important. Due to energy price fluctuations, the need to reduce fossil fuel use and the aim to use biomass heat more efficiently, thermal energy storage tanks can be applied as a practical solution for reducing the mismatch between heat production and demand. Such a tank can store surplus heat during lower-load periods and supply it later when the network demand increases or when expensive peak-load production has to be reduced. This Master’s Final Degree Project analyses the integration of a thermal energy storage tank into the Kaunas district heating system. The object of the project is the planned thermal energy storage tank in the territory of Petrašiūnai boiler house and its possible operation under real conditions of the Kaunas district heating network. The aim of the project is to evaluate the technical, operational and economic effect of this tank on the Kaunas heat supply system. The project reviews thermal energy storage technologies, their operating principles, the importance of stratification, heat losses and control strategies. The computational model uses 2025 hourly data of the Kaunas district heating network load and heat producer operation. Three scenarios are analysed: replacement of natural gas heat production with biomass heat, compensation of short-term power ramping gaps, and the combination of both functions into one control strategy. The results showed that the thermal energy storage tank can improve system flexibility and reduce the need for gas-fired units, but its benefit directly depends on the selected control logic. In scenarios A and C, approximately 5.9–6.4% of the measured natural gas heat production in 2025 is replaced. The avoided CO₂ emissions reach approximately 152–155 t per year. The highest annual discharge is obtained in scenario C with a fully charged initial state, reaching 864.3 MWh per year. The same case also gives the highest number of equivalent full cycles, 3.9 cycles per year. In conclusion, the thermal energy storage tank has technical potential in the Kaunas district heating system. It can help reduce natural gas use, compensate load fluctuations and increase network flexibility. However, its economic feasibility depends on the intensity of tank utilisation, market prices, charging opportunities and the selected control strategy. Therefore, the tank should be considered not only as a reaction to separate gas production events, but as an active optimisation tool for the whole district heating system. |
