The Development Of Phase Change Absorbent For CO₂ Chemical Absorption And Pilot Test

Carbon capture,utilization and storage is an important technical support for achieving large-scale carbon reduction and carbon neutrality during the process of fossil fuel utilization.Chemical absorption technology is highly concerned by various industries for its merits of good flue gas applicability,high technical maturity and wide industrial application.At present,the key technical bottleneck of traditional chemical absorbent is high energy consumption of regeneration,which results in high capture costs and limits their large-scale industrial applications.After absorbing CO₂,the solution was stratified into rich and lean phase and only the rich phase was regenerated in the process of desorption,thus greatly reducing the amount of liquid entering the regeneration tower and reducing the energy consumption of regeneration.In this paper,different phase-change absorption systems are screened,phase separation phenomenon and mechanism,absorption/desorption thermodynamic and kinetic characteristics,regeneration cycle stability and other aspects are thoroughly researched.1000 tons/year phase-change CO₂ capture pilot plant was built in Huaneng Changchun Thermal Power Plant and the operation of absorbent is also verified.Finally,the world’s largest carbon capture project,1.5 million tons/year carbon capture project,was carried out with the flue gas emission of 1000MW domestic efficient ultra-supercritical coal-fired air cooling unit as the carbon source.After determining the screening criteria of the important performance indexes of the new absorbent and the physicochemical characteristics of several main absorbent types,17 absorbent formulations of 6 categories were allocated using different characteristics of organic amines,amino acid salts,physical solvents,and etc,.Large scale screening was carried out via rapid evaluation device experiment test.The test results indicated that,40wt.%DMAC+20wt.%DETA solution（40wt.%H₂O）,40wt.%DMSO+20wt.%DETA solution（40wt.%H₂O）,40wt.%NMP+20wt.%DETA solution（40wt.%H₂O）and 40wt.%DMF+20wt.%DETA solution（40wt.%H₂O）and other four phase-change systems containing DETA（referred to as DMAC,DMSO,NMP,DMF systems）can form a clear phase separation interface after absorbing CO₂.The critical phase separation loading,rich phase content and component redistribution behavior of this four systems（DMAC,DMSO,NMP and DMF systems）were deeply studied.The experimental results showed that CO₂ was mainly absorbed by DETA molecules in this phase change system and carbamate was formed.Therefore,the DETA content in the lean phase gradually decreased with the increase of CO₂loading.The content of DETA in the rich phase gradually increased with the increase of CO₂ loading.Under the condition of 40℃and the loading of 1.3mol CO₂/mol DETA),the mass ratio of rich phase to total solution of this four phase change systems is 46.23%,67.81%,48.13%,and 50.21%,respectively.The maximum quality of regenerated solution is reduced by more than 50%.DMAC system has the lowest mass ratio of rich phase to total solution and the energy saving potential is the highest.Real heat flow reaction calorimeter was used to determine the molar absorption heat of CO₂,relative apparent absorption rate and CO₂ cycling loading of this four systems.The experimental results showed that the molar absorption heat of this four systems was less than 20wt.%DETA aqueous solution.Under different loading conditions,DMF system shows the fastest absorption rate,followed by DMAC system,and then the DMSO and NMP system.The CO₂ loading capacity of DMAC and DMSO systems was up to 0.7 mol/mol.The desorption enthalpy changes by the entirety desorption and the rich phase desorption after phase separation were investigated by double-desorption method.The experimental results showed that under the condition of 120℃,compared to 20%MEA aqueous solution,the reduction rates of desorption enthalpy by rich phase desorption of 4 phase change systems（DMAC,DMSO,NMP and DMF system）are 61.60%,56.84%,55.26%and 38.42%,respectively.Particularly,DMAC system has the highest reduction rate of desorption enthalpy.In conclusion,DMAC system has the best performance in CO₂solubility,relative apparent absorption rate,desorption rate and desorption enthalpy change.The recycling stability of DMAC system absorbent was also studied.The experiment results showed that DMAC system absorbent has the excellent CO₂ absorption performance,good regeneration ability and recycling performance.Based on the above solvent system screening results and key index test of phase change solvent,the phase change CO₂ capture process and efficient new multi-level horizontal phase separation clarifier were developed.The real coal flue gas CO₂ capture pilot test was carried out on China’s first 1000t/year phase-change CO₂ capture pilot plant built in Huaneng Changchun Thermal Power Plant,which achieved continuous and stable operation for 72 hours.During the operation of the pilot plant,the absorbent rich liquid was continuously and dynamically divided into two phases,the amount of solution entering the regeneration system was reduced by 40%-45%,and the energy consumption of regeneration was less than 2.3GJ/ton CO₂,which was 40%lower than the 30wt.%MEA solution.The 1.5 million tons/year carbon capture engineering design scheme was carried out with the flue gas emitted by the 1000MW domestic efficient ultra-supercritical coal-fired air cooling unit as the carbon source based on the phase change absorption system developed in this paper.The development of the first million-ton phase change carbon capture process package in the world and the design of parameters for key equipment were completed.