𝐶𝑂2+ 𝑀𝐸𝐴 + 𝐻2𝑂 ↔ 𝑀𝐸𝐴𝐻++ 𝐻𝐶𝑂3− R(2.8)
The total concentration of CO2 is the sum of all the concentrations of the different forms:
𝐶
𝐶𝑂2,𝑇𝑂𝑇= 𝐶
𝐶𝑂2+ 𝐶
𝐻𝐶𝑂3−+ 𝐶
𝐶𝑂32−+ 𝐶
𝐻𝑁(𝐶2𝐻4𝑂𝐻)𝐶𝑂𝑂− (2.1)The total concentration of amine is the sum of all the concentration of the different forms:
𝐶
𝑀𝐸𝐴,𝑇𝑂𝑇= 𝐶
𝑀𝐸𝐴+ 𝐶
𝑀𝐸𝐴𝐻++ 𝐶
𝐻𝑁(𝐶2𝐻4𝑂𝐻)𝐶𝑂𝑂− (2.2)2.6 Earlier work
Some of the relevant earlier work that has been done on simulating CO2 absorption is presented in this subchapter.
In 2007, Lars Erik Øi (USN) used Aspen HYSYS to simulate CO2 removal by amine absorption from a gas based power plant. The results showed that adjusting the Murphree Efficiency outside the simulation tool could be a practical approach when using Aspen HYSYS to simulate CO2 removal. The paper was published at the Conference on Simulation and Modelling SIMS2007 in Gøteborg. [12]
In 2007, Finn A. Tobiesen, Hallvard F. Svendsen and Olav Juliussen from SINTEF, developed a rigorous rate-based model of acid gas absorption, and a simplified absorber model. They validated the models against mass-transfer data obtained from a 3 month campaign in a laboratory pilot-plant absorber. It was found that the simplified model was satisfactory for lower CO2 loading, whiles the rigorous model had a better fit for higher CO2 loading. [13]
In 2008, Hanne M. Kvamsdal (SINTEF) and Gary T. Rochelle (University of Texas) studied the effects of temperature bulge in CO2 absorption by MEA. They compared an Aspen Plus rate based absorber with 4 sets of experimental data from a pilot plant at the University of Texas, Austin. Several adjustments were made to the model in order to create a predictable model and to study effects of change in specific parameters. [14]
In 2009, Luo et al., from NTNU, compared and validated sixteen data sets from four different pilot plant studies, with simulations in four different simulation tools (Aspen Plus equilibrium-based, Aspen Plus rate-based, ProMax, ProTreatTM and CO2SIM).
They concluded that all the simulation tools were able to present reasonable predictions on overall performance of CO2 absorption rate, while the reboiler duties, concentration and temperature profiles were less predictable. [15]
In 2011, Espen Hansen worked on his master thesis at USN. Hansen compared Aspen HYSYS, Aspen Plus and ProMAX simulations of CO2 capture with MEA. He concluded that Aspen HYSYS and Aspen Plus gives similar results, while the results from ProMAX deviated from the Aspen tools. Hansen found that Kent-Eisenberg model in Aspen HYSYS was similar to the Aspen Plus equilibrium-based model for the absorber, but there was a significant difference in the reboiler duties. [16]
In 2012, Jostein Tvete Bergstrøm worked on his master thesis at USN. Bergstrøm compared Aspen HYSYS (Kent-Esienberg and Li-Mather), Aspen Plus (Rate-based and equilibrium) and ProMAX simulations of CO2 capture with MEA. Bergstrøm found that the models gave similar results, and that the equilibrium-based model in Aspen Plus and Kent-Eisenberg model in Aspen HYSYS gave coinciding results. [17]
In 2012, Lars Erik Øi (USN) compared Aspen HYSYS and Aspen Plus (rate-based and equilibrium) simulation of CO2 capture with MEA. Øi found that there was small deviations in the equilibrium-based model in Aspen HYSYS and Aspen Plus. He found larger deviations between the equilibrium-based calculations and the rate-based calculations. [18]
In 2013, Ying Zhang and Chau Chyun Chen simulated nineteen data sets of CO2
absorption in MEA with Aspen rate-based model and the traditional equilibrium-based model. Their result show that rate-based model yields reasonable predictions on all key performance measurements, while equilibrium-based model fails to reliably predict these key performance variables. [19]
In 2013, Stian Holst Pedersen kvam worked on his master thesis at USN. Kvam compared Aspen Plus (rate based and equilibrium) and Aspen HYSYS (Kent-Eisenberg and Li-mather) simulations of CO2 capture with MEA. The primary goal was to compare the energy consumption of a standard process, a process with vapour recompression and a vapour recompression with split stream, and not to evaluate the performance of the absorber. [20]
In 2013, Even Solnes Birkelund worked on his master thesis at UIT. Birkelund compared a standard absorption process, a vapour recompression process and a lean split with vapour recompression process. He simulated the models in Aspen HYSYS and used Kent-Eisenberg as thermodynamic model for the aqueous amine solution, and Peng-Robinson for the vapour phase. All configurations were evaluated due to the energy cost. The results showed that lean split vapour recompression and vapour recompression had the lowest energy cost, while the standard absorption process was simulated to have a much higher energy cost. [21]
In 2014, Lars Erik Øi et al, simulated different absorption and desorption configurations for 85% amine based CO2 removal, from a natural gas based power plant using Aspen HYSYS. They simulated a standard process, split-stream, vapour recompressions and different combinations thereof. The simulations were used as a basis for equipment dimensioning, cost estimation and process optimization. [22]
In 2014, Lars Erik Øi and Stian Holst Pedersen Kvam from USN, simulated different absorption and desorption configurations for 85% CO2 removal from a natural gas fired combined cycle power plant, with the simulation tools Aspen HYSYS and Aspen Plus.
In Aspen Plus, both an equilibrium-based model including Murphree Efficiency and a rate-based model were used. The results show that all simulation models calculate the same trends in the reduction of equivalent heat consumption, when the absorption process configuration were changed from the standard process. [23]
In 2014, Inga Strømmen Larsen worked on her master thesis at USN. Larsen simulated a rate based Aspen Plus model and compared the results to experimental data from TCM. Larsen found that the Aspen Plus model TCM used was in general agreement with the experimental data. Larsen found temperature and loading profiles similar to the experimental data by adjusting parameters. She also did comparison of mass transfer correlations in Aspen Plus. [24]
In 2014 Espen Steinseth Hamborg et al, published a paper with the results from the MEA testing at TCM during the 2013 test campaign. The paper reveals CO2 removal grade, temperature measurement, and experimental data for the process. [7]
In 2015 Espen Steinseth Hamborg from TCM presented some of the results from the campaign in 2013 and the results from USN-student Inga Strømmen Larsen’s master thesis from 2014, at the PCCC3 in Canada. A v.7.3 Aspen Plus rate-based model was compared to the experimental data. The temperature and loading profile from Aspen Plus presented in this paper gave a good reproduction of the experimental data. [25]
In 2015, Solomon Aforkoghene Aromada and Lars Erik Øi studied how reduction of energy consumption can be achieved by using alternative configurations. They simulated standard vapour recompression and vapour recompression combined with split stream configurations in Aspen HYSYS, for 85% amine-based CO2 removal. The results showed that it is possible to reduce energy consumption with both the vapour recompression and the vapor recompression combined with split-stream processes. [26]
In 2015, Coarlie Desvignes worked on a master thesis at Lyon CPE. Desvignes evaluated the performance of the TCM flowsheet model in Aspen Plus, and compared with the data obtained in the 2013 and 2014 test campaign at TCM. Desvignes found that the Aspen Plus model TCM used performed quite well for 30 and 40wt% MEA, but not for higher flue gas temperature and solvent flowrate. [10]
In 2015, Ye Zhu worked on his master thesis at USN. Zhu simulated an equilibrium model in Aspen HYSYS, Based on the data from TCM 2013 campaign published in Hamborg et al [7]. Zhu adjusted the Murphree Efficiency to fit the CO2 removal grade and temperature profile from the experimental results. Zhu found that linear decrease in Murphree efficiency from top to bottom gave good temperature predictions. [27]
In 2016, Kai Arne Sætre worked on a master’s thesis at USN. Sætre simulated seven sets of experimental data from the amine based CO2 capture process at TCM, with Aspen HYSYS (Kent-Eisenberg and Li-Mather) and Aspen Plus (rate-based and equilibrium). He found that it is possible to fit a rate-based model by adjusting the IAF and equilibrium-based model by adjusting the EM, both Aspen HYSYS and Aspen Plus will give good results if there are only small changes in the parameters. [28]
In 2016, Babak Pouladi, Mojtaba Nabipoor Hassankiadeh and Flor Behroozshad, studies the potential to optimize the conditions of CO2 capture of ethane gas in phase 9 and 10 of south pars in Iran, using DEA as absorbent solvent. They simulated the process in Aspen HYSYS and found the effect of temperature to be significant. [29]
In 2017, Monica Garcia, Hanna K. Knuutila and Sai Gu, validated a simulation model of the desorption column built in Aspen Plus v8.6. They used four experimental pilot campaigns with 30wt% MEA. The results showed a good agreement between the experimental data and the simulated results. [30]
In 2017, Mohammad Rehan et al., studied the performance and energy savings of installing an intercooler in a CO2 capture system based on chemical absorption with MEA as absorption solvent. They used Aspen HYSYS to simulate the CO2 capture model. The results showed improved CO2 recovery performance and potential of significant savings in MEA solvent loading and energy requirements, by installing an intercooler in the system. [31]
In 2017 Leila Faramarzi et al, published a paper with the results from the MEA testing at TCM during the 2015 test campaign. The paper reveals CO2 removal grade, temperature measurement, and experimental data for the process. [32]
In 2018, Ole Røsvik worked on his master thesis at USN. Røsvik simulated the TCM data from the test campaign in 2013, published by Hamborg et al [7]. And the data from TCM’s test campaign in 2015, published by Faramarzi et al [32] in Aspen HYSYS and Aspen Plus (equilibrium and rate-based). He found that both Aspen HYSYS and Aspen Plus will give good results if there are only small changes in the parameters. [33]
In 2018, Lare Erik Øi, Kai Arne Sætre and Espen Steinseth Hamborg, compared four sets of experimental data from the amine based CO2 capture process at TCM, with different equilibrium-based models in Aspen HYSYS and Aspen Plus, and a rate based model in Aspen Plus. The results show that equilibrium and rate-based models perform equally well in both fitting performance data and in predicting performance at changed conditions. The paper was presented at the Conference on Simulation and Modelling SIMS 59 in Oslo. [34]