Konvertering av oljelager till värmelager : I Sundsvalls fjärrvärmesystem

Sammanfattning: This study has examined how an oil storage could be converted into a thermal heat storage (TES). Focus was put on the transient thermal heat flow that occurs during the early years when using a rock cavern as a TES. First existing literature were studied to learn from earlier experiences. Crucial steps of a conversion were identified as well as important mistakes that have been made in the past. Simulations of Sundsvall’s district heating (DH) system were made to see what impact a large TES would have. These simulations showed the importance of being able to transfer enough amount of heat. Then heat simulations were preformed to study the transient heat flow. This showed that much of the heat will be heating the rock around the cavern. Over time, the losses decrease as the rock around the cavern remains heated, due to its thermal inertia. This means that some energy needs to be considered an investment cost as it will not be used in the DH-grid but will increase the efficiency of the TES. 4 different heating strategies were analysed and the heat losses during 25 years were measured. The results showed that a conversion would save between 0,7 – 1,55 million SEK annually depending on how many caverns were converted and cost approximately 6 million SEK for one cavern, 10,5 million SEK for two caverns and 15 million SEK for three caverns.