Solar-assisted temperature vacuum swing adsorption for direct air capture: Effect of relative humidity

Abstract

Direct air capture (DAC) has emerged as a promising tool to address the sizeable non-point sources of CO2 emissions. However, energy penalty of its regeneration process is extremely high due to the low CO2 concentration in the atmosphere. This paper aims to explore the potential of a temperature vacuum swing adsorption (TVSA) system for DAC which utilizes solar energy and condensation heat recovered from air conditioners. The effect of indoor environmental parameters especially for relative humidity (RH) is targeted for carbon removal processes. It demonstrates that 40% RH is the optimal value with regard to the minimum heat consumption of 12.16 MJ/kg. Then four representative cases with different energy supply methods for the regeneration processes, i.e., solar-assisted condensation heat recovery, solar energy, condensation heat, and electricity, are compared and analyzed in terms of techno-economic aspects to seek the best system configuration. The effects of various indoor environmental conditions, e.g., temperature, RH, and CO2 concentration are also counted. The results demonstrate that the levelized cost of DAC (LCOD) and the cost calculated via net present value (NPV) increase with the increased temperatures and the reduced CO2 partial pressure. Due to a tradeoff between the increased adsorption capacity and regeneration heat in the presence of water, a minimum value of economic performance could be obtained at 30% RH. It reveals a novel and cost-effective TVSA combined system for DAC, which may bring more merits to approach carbon mitigation shortly.