Epsilon Archive for Student Projects

Abstract

Härnösands Energi och Miljö AB (HEMAB) provides district heating in Härnösand and is owned by Härnösand municipality. The fuel mixture of the district heating plant mainly consists of forest residuals, but also some peat. Whether peat is to be considered a fossil fuel or not is debated, however in most cases it is regarded as a fossil fuel. Therefore, HEMAB is interested in evaluating other types of fuel to replace peat, and therefore be able to claim that their district heating is carbon neutral. Peat is however regarded as a good fuel from a combustion perspective, mainly because it contains large amounts of sulphur, which counteracts corrosion inside the combustion chamber. The purpose of this report is therefore to evaluate and compare other types of fuel that can be used instead of peat. The proposed fuel mixtures were compared with respect to their combustion properties, CO2-emissions, and economic aspects. In addition to this a minor analysis of how an increased domestic production of biofuels may affect district heating companies were made. The proposed fuel mixtures are shown below:

Mix 1 represents a proposal where the peat is replaced by increasing the amount of bark and log wood chips. Sulphur will be added in the form of sulphur granules. This alternative should not need a new environmental permit nor any renovation of the plant. Mix 2 represents a proposal were HEMAB make use of the collected white wood residues in Härnösand, Kramfors and Sollefteå. The peat is replaced by increasing the amounts of log wood chips and bark as well as including white wood residues in the fuel mixture. Sulphur will be added in the form of sulphur granules. The current environmental permit will be enough.
Mix 3 represents a proposal where HEMAB includes wastewater and brown wood residues, in their fuel mixture. The new fuels are being collected at HEMAB:s existing facilities, in addition to this waste water and brown wood residues will be bought from Kramfors and Sollefteå. Since wastewater contains a lot of sulphur there is no need to add it. For this alternative, a new environmental permit will be needed, and the combustion plant may need to be modified. The results from the calculated key figures indicated that all the proposed fuel mixtures have good combustion properties. Mix 3 had the best results. For Mix 1 and Mix 2 sulphur needs to be added. All the proposed fuel mixtures are cheaper than the current fuel mixture. Mix 1 and Mix 2 should not require any modifications of the plant with exception of the system for adding sulphur. These two fuel mixtures can also be considered renewable whether mix 3 cannot. Mix 3 also comes with the lowest fuel costs. However additional investment costs will be needed and the maintenance costs may increase. An increased domestic production of biofuels is considered to only have a minor impact on the district heating sector. The reason for this being that the biofuels using the same raw materials as the district heating sector is not yet fully commercial developed.