Klimatpåverkan av att pyrolysera dränerad torv : en konsekvens-LCA för användandet av biokol i betong

Detta är en Uppsats för yrkesexamina på avancerad nivå från SLU/Dept. of Energy and Technology

Sammanfattning: In Sweden there is approximately 6.4 million hectares of peatlands, which is about 15 % of the total land area. A significant proportion of peatlands, 2,4 million hectares, is affected by human drainage to promote agriculture and forest production. The drained peatlands in Sweden emits a total of 15-25 million tons of carbon dioxide equivalents (CO2eq), which is in line with emissions from all domestic traffic, 14.5 million tons of CO2eq, and one third of Sweden’s reported emissions in 2014, a total of 54.4 million tons CO2eq. The purpose of this study was calculating the climate impact of pyrolysis of drained peat with the use biochar in concrete. There the pyrolysis would start 2021 in Brista in a planned slow pyrolysis plant. The biochar was first used to adsorb CO2 flue gas from combustion plants and thereafter three different uses of biochar was studied. The first one biochar substitute sand and smaller quantities of cement in concrete, the second one to substitute aggregate and smaller quantities of cement, and the last is to substitute only cement in smaller quantities. Smaller quantities in cement means that biochar substitute 0.1 % of the weight of the concrete. Life cycle assessment were used as the method to calculate the climate impact. The result in this study is that drained peat can lead to a climate benefit and reduce global warming in a 100-year perspective. This happens when biochar adsorbs CO2 from combustion gas and substitutes cement in smaller quantities. Biochar that is used to substitute aggregate and cement can lead to climate reductions, only when the peat was pyrolyzed from nutritious peatlands without forest and after-treated with afforestation with growth measures. The climate benefit is -34.7-(-22,6) kg CO2eq/MWhheat. Treating drained peatlands without forests to wetlands provide a climate benefit with -111.8-(- 82.9) kg CO2eq/MWhheat and -137.6-(-125.5) kg CO2eq/MWhheat for nutrient-poor respectively nutritious peatlands. The total climate benefit biochar has is -661,9 kg CO2eq/tonne dry peat when biochar substitutes cement, -225,6 kg CO2eq/tonne dry peat when biochar substitutes aggregate and cement, and -203,7 kg CO2eq/tonne dry peat when biochar substitutes sand and cement. More studies need to be researched in the subject of peat biochar and its uses in concrete. To pyrolyze peat from peatland Vännmuren can provide climate benefits in a 100-year perspective only if the peatland is after-treated with afforestation with growth measures, and biochar is used to replace cement in smaller quantities. The climate benefit is -109.3-(-59.2) kg CO2eq/MWhheat.

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