Abstract
Direct air capture (DAC) of CO 2 is a key solution for balancing hard-to-abate carbon emissions and plays a crucial role in achieving net zero. Common DAC methods typically employ fixed bed reactors packed with granular adsorbents, which suffer from high gas pressure drop, poor heat and mass transfer, and long cycle durations. Additionally, multiple reactors are required for continuous operation, resulting in bulky systems and complex control. This study proposes a novel rotary adsorber-based DAC strategy, where powdered adsorbents are shaped into structured adsorbents, enabling rapid carbon capture in a single reactor via a steam-assisted temperature swing adsorption cycle. A ton-scale-potential DAC prototype was constructed. Experimental results exhibit a CO 2 capture rate of 50%-85%, producing high-purity CO 2 ( > 90%) with remarkable CO 2 productivity of 0.235 -0.352 kg CO2 /kg adsorbent /day. A mathematical model was developed to reveal the dynamic variations of key parameters within the rotor. On this basis, optimization strategies were proposed, showing that by implementing heat recovery, the total energy consumption of carbon capture could be reduced to 7.41-9.64 MJ/kg CO2 . Further enhancement of the adsorbent performance could lower the energy consumption to 2.50-3.14 MJ/kg CO2 . These findings demonstrate the rotary adsorber's outstanding carbon capture capability, offering an efficient and attractive DAC solution. Abbreviations: Symbol, Description; a , channel half height; As 1 , specific surface area for the bulk gas; As 2 , specific surface area for the adsorbent; b , channel half width; C CO2 , CO 2 concentration; CRF , CO 2 recovery fraction; C H2O,sat m, water vapor saturation molar concentration; C inert , inert gas concentration; c p , constant pressure heat capacity; C T mol/m 3 , mol/m 3 total gas molar concentration; D ax , axial diffusion coefficient; DSAR , desorption section area ratio; E blower , blower energy consumption; EC , CO 2 capture energy consumption; E comp , compressor energy consumption; E elec , electrical energy consumption; E motor , motor energy consumption; E ther , thermal energy consumption; E ther,rec MJ/kg, thermal energy consumption when adopting heat recovery; F air m, air flow rate; F des , desorption gas flow rate; F steam , steam flow rate; f gas , ratio of the gas flow channel's cross-sectional area to the total area; f water , water effect factor; h , convective heat transfer coefficient; h steam , steam enthalpy; h water , kJwater enthalpy; k LDF , LDF kinetic coefficient; L , rotor thickness; m ads , kadsorbent mass; M CO2 k, kg/mCO 2 molecular weight; n rot r/h, rotor rotation speed; P blower , blower power; P channel , channel perimeter; p CO2 , CO 2 partial pressure; PGC , product gas concentration; P motor , motor power; PR , CO 2 productivity; R , ideal gas constant; rate CO2 , adsorption/desorption rate of CO 2 ; rate condense , condense rate; rate H2O , adsorption/desorption rate of H 2 O; R eq m, channel equivalent radius; S gas , gas flow cross-sectional area; Sh , Sherwood number; sto CO2 , stoichiometric ratio of CO 2 (equal to 1 for CO 2 and 0 for other gases); sto H2O , stoichiometric ratio of H 2 O (equal to 1 for H 2 O and 0 for other gases); S total , channel total cross-sectional area; t , operation time; T , thermodynamic temperature; T air , air temperature; T gas , thermodynamic temperature in the gas side; Tq , motor torque; T sol , thermodynamic temperature in the solid side; T steam , steam temperature; v , gas velocity; V m , ideal gas molar volume; x , molar fraction; x RH , relative humidity; x RH,air , air relative humidity; z , spatial coordinate of the axis; δ, channel wall thickness; ΔH , heat of adsorption; λ, heat conduct coefficient; µ, dynamic viscosity; ρ, density.
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