Postcombustion Capture or Direct Air Capture in Decarbonizing US Natural Gas Power?

This analysis investigates the cost of carbon capture from the US natural gas-fired electricity generating fleet comparing two technologies: postcombustion capture and direct air capture (DAC). Many of the existing natural gas combined cycle (NGCC) units are suitable for postcombustion capture. We estimated the cost of postcombustion retrofits and investigated the most important unit characteristics contributing to this cost. Units larger than 400 MW, younger than 14 years, more efficient than 45%, and with a utilization (capacity factor) higher than 0.5 were found to be the most promising for retrofit. Counterintuitively, DAC (which is usually not considered for point-source capture) may be cheaper in addressing emissions from nonretrofittable NGCC units. DAC can also address the residual emissions from retrofitted units. Moreover, the economic challenges of postcombustion capture for small natural gas-fired units with low utilization, such as gas turbines, make DAC look favorable for these units. After considering the cost of postcombustion capture for the entire natural gas-related emissions and incorporating the impact of learning-by-doing for both carbon capture technologies, our results show that DAC is the cheaper capture solution for at least 1/3 of all emissions.

Sorbents for the Direct Capture of CO2 from Ambient Air.

The urgency to address global climate change induced by greenhouse gas emissions is increasing. In particular, the rise in atmospheric CO2 levels is generating alarm. Technologies to remove CO2 from ambient air, or "direct air capture" (DAC), have recently demonstrated that they can contribute to "negative carbon emission." Recent advances in surface chemistry and material synthesis have resulted in new generations of CO2 sorbents, which may drive the future of DAC and its large-scale deployment. This Review describes major types of sorbents designed to capture CO2 from ambient air and they are categorized by the sorption mechanism: physisorption, chemisorption, and moisture-swing sorption.