Epsilon Archive for Student Projects

Abstract

In order to fulfill the Swedish national goal of achieving climate neutrality by 2045, the implementation of negative emission technologies is regarded as a vital tool, since it can compensate for emissions deemed too hard to avoid. The widespread use of district heating systems, in combination with a relatively large forest industry in Sweden, provides a unique opportunity to implement combined biochar and energy production (BCE). With BCE technology, biogenic carbon is stabilized in the form of biochar in a timespan long enough for new biomass to replace the one used for BCE, thus generating the negative emissions sought after. This project investigates the possibility of producing biochar and energy through slow pyrolysis in the three district heating systems located in the municipality of Eksjö using byproducts from local sawmills as feedstock. The different roles BCE might come to play in the local energy system and their respective effect on greenhouse gas emissions from the production of district heating are evaluated. The implementation of BCE technology in the current district heating systems is examined through simulating different scenarios with various installed pyrolysis plant heat production capacity by using a model in the software MATLAB. The results of the simulations indicate that an implementation of BCE technology in the district heating systems can cause significant reductions of greenhouse gas emissions and might lower the production cost of district heating. The lowered production cost indicate that BCE units are advantageous compared with heat only boilers that produce heat through combustion of biomass in the current systems. It should be noted that the retroactive income generated from selling the produced biochar is included in calculating production costs, and that a thorough comparison of the capital expenditures between the two technologies is outside the scope of this study. The BCE units cannot compete with combined heat and power production through energy recovery from municipal solid waste in terms of heat production cost. This leads to fewer operation hours for BCE units in the district heating system in the city of Eksjö compared to BCE units in the smaller district heating system in the municipality where BCE units would produce the base load. The three district heating systems in the municipality of Eksjö produced a total of 150 GWh district heat in 2019. The emissions of greenhouse gases caused by the current production of district heat amounts to 17,000 ton CO2-eq annually. It is estimated that BCE-units producing base load with a total installed heat production capacity of 4,1 MW are required, if the production of district heat is to be climate neutral. The heat produced from such BCE-units would amount to 36 GWh, thus 24 % of the total production of district heat. The units would produce approximately 6,180 tons of biochar and require an 88,3 GWh worth of biomass feedstock. The local sawmills contacted in this project produce approximately 271 GWh worth of biomass as byproduct, enough to enable the district heat production to achieve climate neutrality using BCE technology.