Energetische Integration der CO2-Gewinnung direkt aus der Luft und seiner Methanisierung mit erneuerbarem Wasserstoff
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Date
2022
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Abstract
Global warming is posing a threat to our environment and our life. The major cause of global warming is the increase global atmospheric CO2 concentration from 280 ppm in the preindus-trial era to 415 ppm in 2020. The heavy reliance on fossil fuels as the primary energy sources results in globally over 30 Gt/year of energy-related CO2 emissions in this decade. To address the global issues of the threat of climate change, a common goal for limiting global warming was set in the Paris Agreement by the Intergovernmental Panel on Climate Change (IPCC) in 2015, which aims to restrict the global average increase in temperature to 1.5-2 °C by the end of this century. Moreover, the IPCC 2018 special Report restates the consensus of reducing the global net greenhouse gas emissions to zero by 2050. This indicates that a transition to net-zero CO2 emissions by 2050 is imperative.
There are three main pathways for achieving the target of net-zero CO2 emissions. The first pathway is using renewable energy instead of fossil fuels as primary energy to reduce the sources of CO2 emissions. The second pathway is scaling up of carbon dioxide removal tech-nologies, namely the carbon capture and storage (CCS) technologies to lower current CO2 emis-sion rates from large stationary sources. The last pathway is applying the negative emissions technologies (NETs) to recapture the carbon dioxide previously released due to human activi-ties in the atmosphere.
Among all the carbon dioxide removal (CDR) technologies, direct air capture (DAC) of CO2 with chemicals is the most promising NET with advantages such as a low demand of land and water use, high flexibility for location choosing, high technical feasibility, high scalability, and low risk. DAC faces the only significant challenge of decreasing its high costs.
An attractive alternative to circumvent the intensive energy requirements for the regeneration of the adsorbents in the DAC is the coupling of the endothermic DAC process with an exother-mic process such as Power to Gas (Methane), i.e. the conversion of surplus renewable energy into chemical energy in the form of gas. The exothermic Sabatier reaction for the methanation of CO2 with renewable hydrogen is able to supply the heat to the DAC and thus reduce the cost for recapturing CO2 from ambient air.
Based on this idea, a concept of an energetic integrated DAC-PtG system has been introduced in this work. The energetic integrated processes have been modeled and simulated with the software Aspen Custom Modeler® (ACM). The heat recovery system has been optimized by using a Pinch analysis. A systematic analysis of the energy demand and an economic evaluation have been made in order to evaluate the potential value of this concepts.
Besides the energetic analysis of the integrated DAC-PtG system, the experimental studies for the DAC and methanation process were carried out separately in the laboratory. Lewatit® VP OC1065 has been selected from the adsorbent screening tests as the most suitable adsorbent for the DAC process. In order to identify its thermodynamic and kinetic performances during the ad- and desorption process, the adsorbent Lewatit® VP OC1065 has been examined in a mon-olithic and a fixed-bed adsorber. The methanation of CO2 has also been investigated with a parameter study using the method of statistical test planning on the 5 wt.% Ru/Al2O3 catalyst in an isothermal fixed-bed reactor.
The results of this work present the possibility to integrate a DAC facility with a PtG device applying heat exchange to reduce the price of CO2 recovery from ambient air and to enhance the energy efficiency.
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Keywords
CO2-Gewinnung, Energetische Integration, Direkt Air Capture, CO2-Methanisierung, Power to methan