Study On The Intensification Of The Hydrogen Chloride Absorption Process Using A Rotor-Stator Reactor

HCl is usually generated in chlorination processes as a by-product and also widely exists in the combustion exhaust of various chlorine-containing fuels.Emission levels of HCl range from 10 to 10³ mg·m^-3.However,HCl can pose health risks,causing respiratory problems,eye and mucous membrane irritation,etc.Furthermore,it presents significant environmental hazards,contributing to pollution in water,soil,and the atmosphere.Recognizing these risks,the Chinese government has progressively tightened HCl emission standards.The HCl limits in flue gas of hazardous waste incineration have decreased from 60-100 mg·m^-3 in 2001 to 50-60 mg·m^-3 in 2021.Consequently,there is a growing need to develop efficient methods for HCl removal from flue gas.High-gravity technology has garnered increasing recognition in academia and industry for its effectiveness in process intensification,attributed to its excellent mass transfer performance.However,the absorption of HCl is limited by gas-side mass transfer,which is not good in the rotating packed bed（RPB）.The rotor-stator reactor（RSR）stands out as a novel high-gravity device,featuring a configuration of rotor rings and stator rings arranged radially in alternation instead of the traditional packing in RPB.The distinctive stator and rotor arrangement of RSR is anticipated to generate stronger gas turbulence,leading to superior gas-side mass transfer performance compared to RPB and improve the absorption of HCl.In this study,the gas-side mass transfer performance of an RSR was explored.Subsequently,in response to the constraints associated with traditional HCl absorption processes,four innovative HCl absorption processes based on the RSR were proposed,and the absorption/transfer behaviors and mechanisms in these processes were studied,including“Removal of HCl from flue gas using water in the RSR”,“Selective absorption of HCl from a gas mixture with CO₂ by alkali solution in the RSR”,“Integrated high-gravity process for HCl removal and CO₂ capture using carbide slag slurry in the RSR”and“HCl absorption using choline chloride-glycerol deep eutectic solvent in the RSR”.The key findings of this study are outlined as follows:（1）The effective mass transfer area（a）and local gas-side mass transfer coefficient（k _G）in the RSR were studied.It was found that a can be determined by using the 1 mol·L^-1 Na OH-10%CO₂ system with the gas radial velocity in the RSR greater than 0.108 m·s^-1.Based on the obtained a,k _G in the RSR was determined via the absorption of 2000 ppm SO₂ with 1 mol·L^-1 Na OH.The effects of key operating parameters on a and k _G in the RSR were explored,and it was found that a and k _G in the RSR with stator rings were higher than those without stator rings by 17%-30%and 1%-9%,respectively.a in the RSR with stator rings was 3.4%lower than that in an RPB,but k _G in the RSR was higher than that in the RPB by 78.6%,suggesting that RSR has a great potential for industrial applications in the processes limited by gas-side mass transfer.In addition,a and k _G in the RSR were modelled.（2）The performance and masss transfer behavior of HCl absorption by water in the RSR were investigated and the effects of key operation parameters on HCl absorption efficiency and overall volumetric gas-phase mass-transfer coefficient（K_Ga）were explored.It was found that the absorption efficiency of HCl rose with higher water flowrate and high-gravity factor,but declined with the increase of gas flowrate,temperature and inlet HCl concentration.K_Ga increased with higher high-gravity factor,gas flowrate and liquid flowrate,but decreased with the increase of temperature and inlet HCl concentration.In addition,comparisons with conventional column indicated that the RSR had better mass-transfer performance.Notably,under identical operating conditions,the K_Ga in the RSR was found to be 10.9%to 45.2%higher than that in the RPB.（3）To address the issue of excessive alkali consumption by CO₂ in the treatment of flue gas containing HCl and CO₂ in conventional columns,a process for the selective absorption of HCl from the flue gas in the RSR was proposed.Firstly,the absorption performances of HCl and CO₂ by different absorbents in the RSR were explored.It was observed that the absorption of HCl by Na OH,Na₂CO₃,Na HCO₃solutions and water reached 98.7%-99.3%.According to these findings,a selective absorption process for HCl from a gas mixture containing CO₂ employing alkali solution by a recycle operation in the RSR was implemented.This process facilitated desorption of CO₂ absorbed in the initial stage by lowering the final p H in the recycling operation,resulting in a zero consumption of alkali by CO₂.Under the premise of ensuring that the HCl in flue gas meets the discharge standard,the alkali consumption of the flue gas treatment process can be significantly reduced.（4）An integrated high-gravity process employing carbide slag slurry for HCl removal and CO₂ capture in the RSR was proposed,and the absorption performance of HCl and CO₂ by a simulated carbide slag slurry were investigated.The experiments indicated that the larger solids content,high-gravity factor and liquid flowrate were advantageous for the absorption of HCl and CO₂,while a larger gas flowrate was found to be unfavorable for absorption.And the absorption of CO₂ was more significantly influenced by gas-liquid contact time,liquid flowrate,and solid content compared to HCl.Furthermore,the simultaneous absorption of HCl and CO₂ by the actual carbide slag slurry in a recycle operation in the RSR was explored.It was found that the efficient HCl absorption,CO₂ reduction and environmentally friendly utilization of carbide slag slurry were achieved.In addition,two mechanistic mass-transfer models were established based on surface renewal theory and penetration theory,respectively,to depict the process.The predicted values aligned well with the experimental results,with deviations generally less than 25%.（5）The absorption process of HCl by choline chloride-glycerol（Ch Cl-Gly）was investigated in three aspects:molecular mechanism,experimental and modeling studies.The molecular mechanism of HCl absorption into Ch Cl-Gly was explored by theσ-profiles,binding models,and it was revealed that the H atom of HCl binds with O and Cl of Ch Cl-Gly to form hydrogen bonds,leading to a high solubility of HCl in Ch Cl-Gly.In view of the absorption characteristics,the process intensification of HCl absorption into Ch Cl-Gly was proposed by using the RSR.The influences of the high-gravity factor,gas flowrate,liquid flowrate and inlet HCl concentration on the absorption efficiency of HCl and K_Ga by Ch Cl-Gly in the RSR were investigated,and it was found that a larger high-gravity factor and liquid flowrate led to a higher HCl absorption efficiency,while a greater gas flowrate brought about a lower HCl absorption effect,and inlet HCl concentration had little effect on HCl absorption.In addition,a mass-transfer model was developed to describe the process of HCl absorption into Ch Cl-Gly in the RSR,and the model predictions agreed well with the experimental data,and the deviations between experimental and predicted K_Ga were generally less than±25%.This process can achieve the efficient removal of HCl from flue gas,recycle utilization of the absorbent and recovery of pure HCl gas simultaneously,exhibiting good economic benefits and the potential to replace conventional absorption methods for HCl.