Geothermal Energy at Oslo Airport Gardermoen
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Rock Energy is a Norwegian company with a patented solution for drilling deep geothermal wells, for exploitation of deep geothermal energy from Hot Dry Rocks. The concept involves a drilled sub-surface heat exchanger, referred to as cross wells. The concept is well suited for production of heat for direct heat applications. In this thesis an analysis of the existing district heating plant at Oslo Airport Gardermoen has been conducted, together with examining possibilities of implementing geothermal energy as base load at the plant. A geothermal design that could meet the needs of the district heating plant has been established, and for evaluating the geothermal system in an environmental perspective an analysis based on LCA methodology has been conducted. Hafslund operates two district heating centrals at Gardermoen (Gardermoen heating central and a smaller mobile central) for which both have been analyzed to determine the potential for implementing deep geothermal energy as base load for the systems. Gardermoen heating central is connected to the airport and to the area close to the airport. This central is again connected to the mobile heating central, which is situated near the industrial estate south-east of the airport. Based on Hafslund s production data from February 2011 to January 2012, a heat load duration curve for the two existing centrals have been established. When adding the two curves together the duration curve show a maximum load of 25,7 MW at present, and a yearly energy production of 74 GWh. The mobile central accounts for only 7,2% of the total load and heat production at present.Future heat demand in the Gardermoen area is expected to increase beyond existing capacity. Hafslund is therefore considering to increase the capacity of both their district heating centrals. The enlargement plans involves that the heating central will be expanded to a design load of 37,4 MW (24 MW at present), while the mobile central need to be increased to a design load of 15,2 MW (1,7 MW at present). Assessment of the geothermal installation showed that it is preferable to include the geothermal system in the base load of the mobile central. The additional geothermal capacity will cover 10 MW, and thus deliver 65% of the required heat load and 90% of the energy production from the mobile central. The geothermal installation was designed using the spreadsheet Geocalc . The outputs from Geocalc are used in an analysis of the environmental performance of the designed system through a Life Cycle Assessment (LCA). LCA introduces a technique to assess environmental impacts associated with all stages of a product s life from cradle to grave . The report aims at giving normative results for the environmental impacts of a geothermal installation at Gardermoen. The method provides the ability to quantitatively compare results to other sources of heat provision processes for district heating. It is important to emphasize that the analysis has provided an overview of the potential environmental impact, and not necessarily the actual results of environmental consequences. The system analyzed has a thermal output of 10 MW, lifetime of 30 years, 5000 annual operating hours. The functional unit of district heating produced is kWh. The analysis is based on the main contributing processes to construction, operation and demolition of Rock Energy s geothermal system. The district heating grid is not included in the analysis, as it is already in place at the site. Each contributing process has been systematically validated. It is however uncertainties associated with the data collection mainly due to contradictory information gathered. The information considered to be mostly uncertain is the energy consumption used for drilling purposes.Possible scenarios for the energy supply to drilling were established. These scenarios were simulated in a system model in Excel. The model is based on data and information gathered from existing literature, the database Ecoinvent, published reports and personal communication with drilling experts and specialists within the relevant fields of study. The results are assessed for the following impact categories: Climate change, metal depletion, fossil depletion, terrestrial acidification and freshwater eutrophication. The evaluated potential energy sources for the drilling operation are electricity from the Norwegian grid, electricity from the European grid, and diesel. The climate change category has especially been in focus when conducting the simulations and this category shows large spread in the results, from 0,9993 g CO2-eq/kWh for the best scenario to 23,6 g CO2-eq/kWh for the worst scenario. As expected, the analysis concludes that electricity from the Norwegian grid for the drilling is preferable. For a geothermal system in Europe, the results show that it would be advantageous to use diesel as energy supply for the drilling operation instead of European electricity mix, for which the emissions are doubled.For the metal depletion impact category, the variation of energy supply to drilling cause the least fluctuation. This is also the only impact category where the Norwegian electricity mix has higher impacts than for the diesel consumption. This can be explained by the infrastructure related to electricity transmission. The results of the study have been compared to other heat sources for district heating (waste incineration, biofuel and solar thermal). The comparison shows that from an LCA perspective geothermal energy based on Rock Energy s concept is an environmentally friendly energy supplier for district heating. The studies compared are however based on varying assumptions, and thus a generalized conclusion cannot be drawn from this.