Study On Cyclic Capture Of CO₂ In Flue Gas By Modified Calcium-based And Magnesium-based Pellets

In recent years,the excessive emission of greenhouse gas CO₂ has seriously affected the living environment of human beings.For this reason,carbon capture and storage?CCS?technology has attracted attention.The key issue of CCS is the capture and storage of CO₂ after fuel combustion.Calcium oxide and magnesium oxide-based sorbents have the characteristics of cheap and wide sources,large theoretical sorption capacity,and low secondary pollution to the environment.They have become potential high-temperature/medium-temperature CO₂ capture materials.In order to further increase the development and application potential of calcium-based and magnesium-based sorbents,corresponding improvement techniques are proposed.In this paper,the calcium-based sorbent has a low adsorption capacity,and the cycle sorption performance declines with the increase of the number of cycles.The organic acid and the mixing ratio are used to modify it.The magnesium-based sorbent has a low capture rate during the sorption process and the cycle sorption capacity is low.Problems such as the use of sodium nitrite and sodium nitrate mixed modification,and two kinds of sorbent in the system application is easy to break and wear mechanical performance is not good granulation modification.First,modification of calcium-based ore?limestone and dolomite?powder with organic acids,followed by two-step calcination and extrusion-spheronization granulation,to simulate the real calcination environment?100%high purity CO₂?Desorption,CO₂ cycle sorption performance test using a fixed bed,the experimental results are close to the actual working conditions.The following conclusions were reached:After citric acid modified Ca²⁺:Mg²⁺molar ratio of 9:1 powder sorbent,the average sorption capacity can reach 0.59g/g after 20 carbonation cycles;After carbamic acid-modified Ca²⁺:Mg²⁺molar ratio of 9:1 to 300?,the adsorbent pellets granulated after 20 carbonation cycles,the average sorption capacity can still be maintained at 0.57g/g,and the cycle sorption is stable.The particle size of the internal crystals of the sorbent pellets prepared by this method is smaller,the specific surface area and porosity are higher,and the sorption stability is improved.The prepared sorbent pellets have certain mechanical properties and can be applied to fluidized bed reactor.A simple wet-mixing method was used to prepare a sodium nitrate/sodium nitrite-coated or co-coated magnesium-based sorbent,and extruded-rolled into pellets;CO₂ sorption test found,The powdery magnesium-based sorbent coated with sodium nitrite as a coating agent has a higher adsorption capacity and better cycle stability than sodium powder coated with a sodium nitrate;The prepared sodium nitrate and sodium nitrite have a mass ratio of 1:1 and are co-coated with a magnesium-based sorbent,which further improves the sorption cycle stability and the maximum sorption capacity;The sorption rate of powder samples increased to some extent after extrusion-spheronization;At the optimum sorption temperature of 340?,the maximum sorbed CO₂ sorption capacity of the 1:1 co-coated sorbent powder and pellets can reach 0.66g/g and 0.57g/g,respectively.But after extrusion-spheronization granulation,the 1:1 co-coated sorbent pellets have a faster sorption rate,more stable cyclic sorption,higher total cyclic sorption,and have certain mechanical properties.The paper has 34 pictures,5 tables and 91 references.