Natural Gas vs. Electricity for Solvent-Based Direct Air Capture

Abstract

Removing CO2 from the air with chemicals (Direct Air Capture, DAC) requires a significant amount of energy. Here, we evaluate the cost of co-constructing a solvent DAC process with its energy system. We compare eight energy systems paired with two alternative designs for a liquid-solvent DAC system capturing 1 MtCO2/year, which requires roughly 240 to 300 megawatts of steady power equivalent, 80% thermal and 20% electric. Two energy systems burn natural gas onsite for heat and electricity, capturing nearly all the CO2 released during combustion, and six are all-electric non-fossil systems. The cost of the DAC facility alone contributes $310/tCO2 for a conventional process-based design and $150/tCO2 for a more novel design. When the decomposition of calcium carbonate occurs within a natural-gas-heated calciner, the energy system adds only $80/tCO2 to these costs, assuming $3.25/GJ ($3.43/MMBtu) gas. However, leakage in the natural gas supply chain increases the cost of net capture dramatically: with 2.3% leakage (U.S. national average) and a 20-year Global Warming Potential of 86, costs are about 50% higher. For the all-electric systems, the total capture cost depends on the electricity cost: for each $/MWh of levelized cost of electricity, the total capture cost increases by roughly $2/tCO2. Continuous power is required, because the high-temperature calciner cannot be cycled on and off, so solar and wind power must be supplemented with storage. Our representative capture costs are $250–$440/tCO2 for geothermal energy, $370–$620/tCO2 for nuclear energy (two variants–a light water reactor and small modular nuclear), $360–$570/tCO2 for wind, $430–$690/tCO2 for solar photovoltaics (two variants assuming different daily solar capacities), and $300–$490/tCO2 for a hybrid system with a natural-gas-powered electric calciner.

The impact of binary water-CO2 isotherm models on the optimal performance of sorbent-based direct air capture processes.

“…Figure S14 show how the results from the model compare to work by Joss et al 65 The profiles shown are at the end of the column for a TSA cycle, involving open heating, closed cooling, pressurisation, and adsorption in that order. The slight difference in temperature profiles could be because the work by Joss et al includes a wall energy balance, whereas this study just considers overall heat transfer from the jacket fluid to the column inside.…”

“…The heat transfer coefficient, ℎ , was a value found when validating the model against work by Joss et al and this is assumed to be a reasonable value for the modelling study considered here. 65 The heat transfer coefficient mainly affects the heating and cooling times, which would impact the productivity of the process. Hence the productivity values calculated in this work should be taken with caution.…”

Current status and pillars of direct air capture technologies

“…Each of these sources will result in a different price per ton of CO 2 , affecting the overall cost examined in the previous sections. The following sources result in various capture costs: Solar would result in a cost of $430–690/30tCO 2 , wind results in a cost of $360–570/tCO 2 , natural gas results in a cost of $88–228/tCO 2 , coal results in a cost of $88–228/tCO 2 , and nuclear results in a cost of $370–620/tCO 2 ( McQueen et al., 2021a ; National Academies of Sciences, 2018 ). Evidently, the several listed energy sources can greatly affect the capture cost of DAC systems, and therefore, its appeal to the public.…”

Life cycle and techno‐economic assessments of direct air capture processes: An integrated review

“…The cost of the DAC facility itself was estimated to be €264/tCO 2 for a conventional DAC-based design and €128/tCO 2 for a more innovative design, while the total capture costs including the energy system range from €213 to €587/tCO 2 , depending on the energy source. 68 Various DAC costs estimations are also detailed in the literature regarding the adsorption approach, as highlighted in Table 3. Efimova 63 and Fasihi et al 9 provide costs estimations and pointed out that as for absorption technology, adsorption process costs could be potentially reduced by 2050 to 67 and €38/tCO 2 respectively, while current DAC costs are evaluated at €222/ tCO 2 by Fasihi et al 9 Compared with the absorption technology that needs high temperature (900 C for the Carbon Engineering's technology), the adsorbent regeneration energy could be supplied by relatively cheaper low-grade heat.…”