Regeneration Of Potassium-based Sorbents Supported By Petroleum Coke-based Activated Carbon For Co₂ Capture Using Co₂/Steam Fluidization

Among the numerous CO₂ capture technologies,the alkali metal base sorbents has great advantages in CO₂ capture in recent years.The main principle is that alkali metal-based carbonate reacts with CO₂ and H₂O in flue gas at a certain temperature,so as to capture CO₂ in flue gas of coal-fired power plants.This technology has the characteristics of simple equipment structure,low energy consumption,high cycle performance,no corrosion and no pollution,so it has a wide application prospect.The CO₂ absorption of petroleum coke-based sorbents is high and the reaction rate is fast.At the same time,hexagonal K₂CO₃ obtained by thermal decomposition of KHCO₃ has the advantages of high absorption and conversion rate?up to 85%?,fast conversion rate and good cycling performance,so KHCO₃ is selected as the active component of potassium absorbent.Activated carbon from petroleum coke has a good pore structure and stable properties,with a specific surface area of 500¹000 m²/g.It has a strong loading capacity for active ingredients,and can greatly improve the contact area between KHCO₃ and CO₂ and provide a good reaction site.At the same time,the cost of petroleum coke is low,the output is large,and the source is wide,so the activated carbon of petroleum coke is a good carrier of potassium based CO₂ sorbents.The specific surface area of the prepared petroleum coke based activated carbon measured by nitrogen adsorption test is 429.79 m²/g,and the specific pore volume is 0.68 cm³/g,while the specific surface area of the commonly used K⁺sorbents carrier is generally about 100-200m²/g,so the activated carbon based on petroleum coke as the carrier has great advantages.A new type of K⁺sorbents supported by petroleum coke activated carbon was prepared by loading KHCO₃ on petroleum coke activated carbon.Firstly,the carrier material of the sorbents,petroleum coke-based activated carbon,was prepared.The original sample of petroleum coke is ball-ground and sieving to size of 100?m.The activator KOH is mixed with petroleum coke according to the KOH/petroleum coke mass ratio of3:1.The mixed material is placed in a horizontal tubular furnace.Then,a novel K⁺absorbent based on petroleum coke-based activated carbon was prepared.After stirring,standing,drying and calcining,petroleum coke-based K⁺absorbent samples with load ratios of 20%,25%,30%,35%and 40%were prepared by mixing KHCO3 and carrier materials at 5 ratios of 2:8,2.5:7.5,3:7,3.5:6.5 and 4:6,respectively.Secondly,the carbonation performance of CO₂ fluidized petroleum coke-based K⁺sorbents was studied.Different from the traditional fluidized bed test methods,which takes nitrogen as the carrier gas,CO₂ is innovatively adopted as the fluidized state gas,which saves the energy consumption of system gas separation and realizes the recycling of CO₂.The results show that when nitrogen is used as carrier gas,the increase of KHCO₃ load ratio is beneficial to improve the carbonation reaction performance of petroleum coke-based K⁺sorbents.At a loading rate of 35%,the maximum CO₂ penetration time and carbonation conversion rate of the absorbent reached6min and 92.4%,respectively.However,considering the limited load capacity of carrier materials,35%load rate is the most appropriate;The increase of reaction atmosphere temperature will increase the rate of CO₂ collection,but because the absorption reaction is exothermic,high temperature will be adverse to the forward reaction.Reaction temperature was 60?when actual reaction termination time longest and biggest CO₂ uptake,were 12.6 min and 61.2 mg/g;The higher the inlet concentration of CO₂,the shorter the penetration time of carbonation reaction and the shorter the reaction duration.When the CO₂ concentration is 16%,the shortest penetration time is 2.5 min and the shortest duration is 12.7 min.When water vapor is used as carrier gas,CO₂permeation time decreases with the increase of water vapor concentration.At the concentration of92%,the CO₂ penetration time was the minimum,which was 0.9 min.As the concentration of water vapor molecules is too high,it will occupy the pores and pores of the carrier,prevent the molecules of CO₂ gas from entering the sorbents to contact and react with the active components,and even cause the sorbents to bond and form into blocks.Therefore,the concentration of water vapor is too high,which will inhibit the ability of the sorbents to capture CO₂,and it should be controlled below 40%.When CO₂ is used as the carrier gas,as the concentration of CO₂ in the fluidized atmosphere increases,the CO₂ penetration time of the sorbents and the duration of carbonation reaction will decrease accordingly.Especially,when the CO₂ concentration exceeds40%,the amount decreases more and the trend of decrease is more obvious.The concentration of CO₂ should not be too high,and 20%⁴0%is more appropriate.Thirdly,the regeneration characteristics of K⁺absorbent supported by water vapor fluidized petroleum coke-based activated carbon were studied.The results show that the petroleum coke-based K⁺absorption agent when the temperature is above 120?for regeneration.Too high concentration of water vapor will make water vapor coagulate in the reactor and inhibit the regeneration reaction of sorbents.When the concentration of water vapor is 80%,the minimum peak reaction rate and average reaction rate are 112.8mL/min and 57.6mL/min,respectively.In addition,the volume of regenerated CO₂ is the least and the regeneration conversion rate is the lowest.When the temperature of water vapor increases,the rate of CO₂ removal of the sorbents increases,and the rate of regeneration conversion increases.This is because the superheated water vapor with high enthalpy value provides heat energy for the reaction and accelerates the process of regeneration reaction.Finally,using Malek method to determine the mechanism of oil sorbent regeneration of petroleum coke-based K⁺reaction model for random nucleation and subsequent growth,the most probable mechanism function integral form for??=-ln??1-?.Kinetic parameters of regeneration reaction of petroleum coke-based K⁺sorbents with nitrogen and water vapor as fluidized gas were solved by Coats-Redfern method.