(431c) Comparative Techno-Economic and Life Cycle Assessment of Reactive CO2 Capture to Synthetic Natural Gas

Reactive CO₂ Capture (RCC) is an emerging class of carbon management technologies that aim to efficiently produce low carbon fuels and chemicals. RCC is a process intensification approach integrating CO₂ capture and conversion to a value-added product in one system. RCC is particularly advantageous because i) it avoids intermediate CO₂ purification (reducing thermal energy demand) and ii) creates a marketable product in addition to CO₂ capture (additional revenue incentivizing CO₂ capture technologies), leading to potential energy and cost competitiveness. In this analysis, RCC is designed to capture and convert CO₂ to produce synthetic natural gas (SNG) as a method of long-duration energy storage. The production of natural gas is especially favorable because it has a wide range of uses, such as heat, electricity, transportation fuel, chemical production and an energy carrier in the power-to-gas framework. SNG is a promising energy carrier primarily because it has long-term storage capacity, and it can be used to overcome intermittency issues with renewable energy coupled grid systems. Additionally, unlike hydrogen, SNG can utilize readily available and existing natural gas infrastructures and therefore, has locational flexibility when deployed. SNG produced via RCC is considered a renewable and potentially carbon-neutral energy source that can be used to decarbonize multiple economic sectors.

In this contribution, I will discuss our comparative system analysis, which includes process modeling, techno-economic, carbon footprint and sensitivity analysis, to identify key metrics and evaluate the technical viability of RCC. Through RCC, CO₂ can be captured and directly converted into SNG in one system, with renewable hydrogen and a dual-function material. We compared RCC to a separated CO₂ to SNG process which involves two steps – i) CO₂ is first captured via Direct Air Capture, then ii) converted to SNG in a methanation facility. Our analysis suggests that RCC has 56-66% energy savings compared to a separated process. This resulted in a minimum SNG selling price of $2.17/kg, 12-13% lower than the cost of a separated two-step process. The overall cost is dominated by sorbent and hydrogen operating costs (also evident in the sensitivity analysis). Compared to existing technologies such as conventional natural gas production offset with Direct Air Capture with Storage and anaerobic digestion of waste feedstocks, SNG via RCC costs 12-21% less. As an energy storage option, SNG from RCC is a low-cost option; it costs 6-79% less than other systems such as batteries, geothermal, hydropower, hydrogen, and others. The carbon footprint analysis resulted in around 8-10 g CO_2e/MJ when powered by renewable energy, but the carbon intensity is 15-17x greater if the process is powered by the US grid mix, suggesting that we must use renewable energy to drive these technologies. Our analysis suggests that RCC is a promising technology for energy generation, as it avoids the continued use of fossil fuels while offsetting carbon emissions, but it is not without its challenges.