Development of typical processes and key devices for direct air CO2 capture
Conventional carbon capture and storage technologies and carbon capture,utilization and storage technologies mainly target CO2 emissions from fixed sources,while direct air capture CO2(DAC)technology,as an emerging negative carbon emission technology,can capture CO2 emissions from distributed sources and further reduce the global atmospher-ic CO2 concentration.In this paper,the development process of DAC's typical liquid absorption process,solid adsorption process and the construction of relevant demonstration projects are introduced,the technical characteristics of emerging DAC processes are analyzed,and the key equipment schemes and future development trends of existing DAC processes are discussed.The DAC liquid absorption process has the characteristics of low cost of absorbent raw materials and high selectivity,which can realize a large-scale continuous capture,but high energy consumption in the regeneration process.The DAC solid adsorption process has the characteristics of modularity,low investment cost,and relatively low energy consumption in the regeneration process,but requires a regular replacement of adsorption materials and maintenance of adsorption equipment,which is suitable for small-scale DAC application scenarios.Two typical DAC process absorption/adsorption materials are reviewed.In the DAC electric oscillation adsorption process,CO2 is chemically cap-tured in the solid electrode,and CO2 desorption is achieved by changing the polarity of the solid electrode with applied electric field.This process has a higher efficiency than that of the heat or pressure-based separation process.The CO2 in the air is selected through the DAC separation membrane to achieve an efficient carbon capture.The DAC process achieves the CO2 absorption and desorption through the change of humidity,which breaks through the high energy con-sumption limit of conventional variable temperature/pressure swing adsorption.The DAC bio-absorption process absorbs and fixes CO2 through the photosynthesis of algae organisms.The DAC process based on bifunctional catalyst can cap-ture and catalyze CO2 in one integrated process,saving the transportation and storage cost of CO2 capture.The key devices of DAC liquid absorption process are air contactor,particle reactor,calciner and curing device,among which the core of air contactor development is to improve gas-liquid contact efficiency,reduce water loss during spray process and reduce equipment corrosion,while the key of particle reactor and curing development is to improve the contact efficiency of solid-liquid two-phase materials and the solid-liquid separation efficiency after reaction.The DAC solid adsorption process is composed of a modular device consisting of an induced air module,an adsorption/regeneration module,an energy supply regeneration module and a CO2 compression module.The core of optimizing the adsorption module is to improve the gas-solid mass transfer rate,adjust the CO2 capture efficiency and reduce the pressure drop.It is very important to select suit-able regeneration system or use clean energy based on the process requirements of different application scenarios,optim-ize DAC process and develop high-performance DAC core devices.
direct air capture technologycarbon neutralliquid absorptionsolid adsorptionadsorbent regenerationadsorption device
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