Modeling And Simulation Of CO₂ Absorption In Amine Solutions By Using ASPEN Simulators

In the past few years,large human emission of greenhouse gases has become one of the most crucial environmental concerns around the world.This has motivated intensive research on CO₂capture about which more energy-efficient absorbents and cutting-edge methods are essential.For technical,economical,and environmental reasons,aqueous solutions of alkanolamines are widely applied to the industrial CO₂absorption processes as a prominent method.This technique is commonly used for acid gases（CO₂,H₂S）removal in the process of natural gas sweetening in addition to CO₂capture from fossil-fuel-fired power plants or from other important industries such as chemical and petrochemical plants,steel,aluminum,and cement production.The major constituents of CO₂absorption process including CO₂,the types of amine solutions,the concept of mass transfer and the relevant reactions as well as the conventional and new equipment for the absorption process have been described in chapter I.As the first step of this research,the absorption efficiency of the selected amine solutions have been assessed in chapter II.The high pressure CO₂absorption from a specific gas in a conventional column has been evaluated by the Aspen HYSYS simulator using a wide range of single and blended amine solutions to estimate the outlet CO₂concentration,absorption efficiency and CO₂loading to choose the most proper blended solutions in terms of reactivity and CO₂removal efficiency.The property package of“Acid Gas-Chemical Solvent”built in Aspen HYSYS which is consistent with all the applied solutions for the simulation in this study,has been employed to estimate the properties based on an electrolyte non-random two-liquid（E-NRTL）model for electrolyte thermodynamics and properties in addition to Peng-Robinson equation of state for the vapor and liquid hydrocarbon phases.Among all the investigated single amines as well as blended solutions,piperazine（PZ）and the mixture of piperazine and monoethanolamine（MEA）have been found as the most effective absorbents for CO₂absorption with high reactivity based on the simulated operational conditions.As the second step of this study,both absorption and regeneration efficiency of the single amine absorbents and the blended PZ solutions have been examined in chapter III.The high pressure CO₂absorption from the specific off-gas in a conventional column has been assessed by the Aspen HYSYS simulator using a wide range of single amine absorbents and PZ-activated solutions to estimate the outlet CO₂concentration,CO₂loading,reboiler power supply and regeneration heat duty to choose the most efficient solution in terms of CO₂removal and required heat duty.The same property package including E-NRTL model and Peng-Robinson equation of state was applied.The blended amine solutions with low PZ concentrations（5 wt%and 10 wt%）were considered and compared to reduce the cost of process.The results of the simulation indicate that the blended solution of PZ+MDEA（methyldiethanolamine）with a specific concentration was the most appropriate solution in terms of CO₂concentration in the outlet gas,rich-CO₂loading and regeneration heat duty.The kinetics,thermodynamics as well as the physical and transport properties of the PZ+MDEA solution were further investigated,and modeling and simulation of CO₂absorption using the mixed absorbents（PZ and MDEA）in various concentrations and different types of equation of states were explored in the next chapters.In the third part of this study,a pilot plant with a closed cycle of the absorption/desorption process has been taken into account in chapter IV,for the simulation of CO₂capture by PZ+MDEA solution using rate-based model in Aspen Plus with all the design and operational parameters such as the hydraulic specifications of absorber and stripper in addition to the inlet flue gas conditions which are present in a commercial gas-fired burner for heating houses.Metal FLEXIPAC 250Y has been considered as the packing type and the proposed correlations in Aspen Plus were applied to the calculation of mass transfer coefficients,flooding and pressure drop in the model.In order to simulate the process,a new property package has been developed using all the required parameters in E-NRTL model and perturbed-chain statistical associating fluid theory（PC-SAFT）equation of state which are used for the estimation of activity and fugacity coefficients respectively.The model has been compared with some experimental data such as CO₂absorption efficiency and CO₂loading and demonstrated good agreement with them.In the fourth part of this study,the high pressure absorption of CO₂from a distilled ethane stream at the Phase 19 of the South Pars Gas Complex（in Iran）has been simulated in chapter V,with the application of Aspen Plus using E-NRTL and Peng-Robinson models in addition to the technical and operational data to evaluate the solution of PZ+MDEA in an industrial gas treatment unit.The plant employs 40 wt%diethanolamine（DEA）solution as the actual absorbent in a conventional column.The potential single and blended absorbents including MDEA,PZ+MDEA,and DEA+MDEA have been applied to the modeling to estimate the outlet CO₂and sulfur compounds concentrations,CO₂loading,reboiler power supply and regeneration heat duty to determine the most efficient substitute for DEA.The last part of this research has focused on the modeling of CO₂absorption using the blended amine solution of PZ+MDEA by a rotating packed bed（RPB）in chapter VI.CO₂removal by the blended amine solution of PZ+MDEA with the various molar concentration ratios in the RPB was modelled using MATLAB linked to Aspen Plus.All the required correlations of the RPB in addition to the mass and energy balances were written in MATLAB while the demanded physical and transport properties were extracted from Aspen Plus.The similar operating conditions and compositions in the reported experiments were used to run the rate-based model by the two-film theory for mass transfer as steady state based on the zwitterion mechanism,while the impact of five different parameters namely,rotational speed,PZ concentration,MDEA concentration,liquid flow rate and liquid temperature on the CO₂absorption efficiency was examined to validate the model.The modeling results are in good agreement with the experimental data for which the average absolute deviation（AAD）is less than7.0%.The process analysis revealed that rotational speed and PZ concentration have the most significant effects on CO₂absorption efficiency.The modeling of CO₂absorption using a blended amine solution in an RPB was implemented for the first time in this research.In addition,the novel method of integrating MATLAB and Aspen Plus was also applied for the first time in this kind of modeling using PC-SAFT and E-NRTL equation of states in Aspen Plus.