Ex-ante Life Cycle Assessment of carbonating Green Liquor Dregs for CCUS An early assessment on the prospects of using direct aqueous carbonation on green liquor dregs from the pulp industry for carbon capture, utilization and storage

Sammanfattning

Since pre-industrial time, the temperature on earth has risen with over 1°C due tohuman activities. To limit the temperature rise to less than 2°C there is a need ofCarbon Capture, Utilization and Storage, CCUS, technologies that collect and storeor use CO2 from the atmosphere. However, the existing CCUS technologies are eitherexpensive or ineffective, therefore there is a need to develop new CCUS technologies.This thesis aims to show the possible prospects for CCUS by direct aqueous carbonationof green liquor dregs, GLD, using flue gas from pulp mills. With data from labexperiments and from Smurfit Kappa mill in Pite˚a, a scaled-up model was built toevaluate the maximum yield of sequestered CO2, electrical energy needed to run thecarbonation process and the possible avoided emissions from product replacementusing the carbonated GLD, cGLD. The results was then scaled up to the total GLDproduction in Sweden in 2022.Three scenarios were studied, 1.The cGLD was only filtered and assumed to beland-filled, 2.The cGLD was dried and used to substitute clinker and 3.The cGLDwas dried and used to substitute gravel. The results show that scenario 2 has thehighest negative emissions of -0.756 ton CO2 per ton of input GLD, compared withroughly -0.176 ton CO2 per ton input GLD for both scenario 1 and 3, using Swedishelectricity mix for the emissions from electricity generation. The most energy intensiveprocess step was drying, which in case 2 and 3 stood for 96% of the electricityuse. When scaled up to incorporate carbonating all GLD produced in Sweden in2022, the maximum negative emissions for the 2nd scenario summed up to 0.31%of all emissions from Sweden and 24% of the emissions from the total Swedish pulpand paper industry. A sensitivity analysis was performed by changing the electricitygeneration to be from general EU-mix. The impact on scenario 1 was minimal butfor scenarios 2 and 3, the electricity mix had significant impact with total negativeemissions of -0.627 and -0.005 ton CO2 per ton input GLD respectively, due to thehigh energy use in the drying step.Since this is a novel technology, no earlier studies regarding carbonation of GLD hasbeen published. This report should therefore only be viewed as an indication thatthere could be noteworthy benefits of carbonating GLD for CCUS, with significantnegative emissions of 0.31% of Sweden’s total emissions.