CO2-Abtrennung aus Prozessen der Zellstoff- und Papierindustrie zur Produktion synthetischer Kraftstoffe

The objective of this work is the ecological and techno-economical investigation and evaluation of potential production routes for synthetic fuel from industrially captured carbon dioxide (CO2). The CO2 is being captured from processes in the industry sector and is used for the production of a synthetic fuel applicable in the same industry sector. The approach aims at finding a technological combination of carbon capturing and synthetic fuel production that is practicable, ecologically advantageous and economically feasible.
The works methodological approach is based on an extended literature research regarding the core aspects of the topic. From that, a technology pre-selection is made regarding one theoretically suitable system of carbon capturing and subsequent synthetic fuel production for the industrial sector. The potential process route is technologically simulated, modelled and analysed ecologically and economically as well as being compared to the also modelled reference situation in the industrial sector. For the ecological analysis the concept of life cycle assessment (LCA) is used and the software Umberto ® LCA+ serves for the modelling and calculation of the systems LCAs. The models are analysed regarding their performance in the life cycle impact categories climate change [kg CO2-Eq.] and fossil depletion [kg oil-Eq.].
The analysed reference activity from the pulp and paper production chain is the natural gas fired lime kiln that regenerates calcium oxide needed in the pulping process. In the synthetic process chain synthetic natural gas (SNG) replaces the fossil natural gas applied to the lime kiln. The SNG is produced from a Power-to-Gas (PtG) approach using renewable power to capture CO2 from the lime kiln emissions and convert it to SNG in a methanation reactor using hydrogen separately produced from water electrolysis.
The life cycle assessment of the PtG-process chain results in values of 566.06 kg CO2-equivalents (CO2-Eq.) for the life cycle impact category climate change and 152.02 kg oil-equivalents (oil-Eq.) for the category fossil depletion. The LCA of the reference situation delivers 1,458.77 kg CO2-Eq. (climate change) and 764.72 kg oil-Eq. (fossil depletion). The results state an ecological net advantage of the proposed PtG-chain in comparison to the reference state for both considered life cycle impact categories. The economic assessment results in a net profit of 651,56 € for the reference state and -213,68 € for the synthetic production chain. The results deliver net costs instead of profits for the proposed PtG-chain and state its economical disadvantage in comparison to the reference state. The most significant influences on both ecological and economical performance of the synthetic production chain result from power delivering processes to satisfy the energy demand of the water electrolysis for hydrogen production. The power delivering processes are investigated in a scenario analysis to further analyse their impact. The to be reduced power demand of the water electrolysis is identified as the central scale-up condition of the synthetic production chain from technological perspective.