Thermodynamic interpolation for the simulation of two-phase flow of non-ideal mixtures

This paper describes the development and application of a technique for the rapid interpolation of thermodynamic properties of mixtures for the purposes of simulating two-phase flow. The technique is based on adaptive inverse interpolation and can be applied to any Equation of State and multicomponent mixture. Following analysis of its accuracy, the method is coupled with a two-phase flow model, based on the homogeneous equilibrium mixture assumption, and applied to the simulation of flows of carbon dioxide (CO2) rich mixtures. This coupled flow model is used to simulate the experimental decompression of binary and quinternary mixtures. It is found that the predictions are in good agreement with the experimental data and that the interpolation approach provides a flexible, robust means of obtaining thermodynamic properties for use in flow models

Simulation of CO2 capture process from power plant flue gases

220 σ.Τα τελευταία χρόνια η κλιματική αλλαγή εξαιτίας του φαινομένου του θερμοκηπίου φαίνεται να απασχολεί όλο και περισσότερο, με αποτέλεσμα τη δημιουργία έντονου ενδιαφέροντος για εφαρμογή τεχνολογιών μείωσης των εκπομπών αερίων τα οποία είναι υπεύθυνα για το φαινόμενο αυτό. Από τα αέρια του θερμοκηπίου, βασικό υπαίτιο θεωρείται το διοξείδιο του άνθρακα του οποίου οι ατμοσφαιρικές συγκεντρώσεις αυξάνονται σταθερά εξαιτίας της γενικευμένης χρήσης του γαιάνθρακα για την παραγωγή ενέργειας. Η πιο ώριμη τεχνολογία μείωσης των εκπομπών διοξειδίου του άνθρακα και η οποία έχει τις μεγαλύτερες πιθανότητες για ευρεία εφαρμογή στο μέλλον είναι η δέσμευση διοξειδίου μετά την καύση από απαέρια ηλεκτροπαραγωγικών μονάδων, κυρίως με τη χρήση αλκανολαμινών ως διαλύτες για τη διεργασία. Βασικό πρόβλημα εξαιτίας του οποίου η συγκεκριμένη διεργασία δεν βρίσκει γενικευμένη εφαρμογή σε κλίμακα κατάλληλη για ενσωμάτωση σε μονάδες ηλεκτροπαραγωγής είναι το υψηλό της κόστος, το οποίο οφείλεται κυρίως στην κατανάλωση ενέργειας για την αναγέννηση του διαλύτη. Σκοπός της συγκεκριμένης εργασίας ήταν η μελέτη, βελτιστοποίηση και οικονομική αξιολόγηση της διεργασίας απορρόφησης και συμπίεσης διοξειδίου του άνθρακα από ρεύμα απαερίου προερχόμενο από εργοστάσιο ηλεκτροπαραγωγής, καύσης λειοτρειβημένου γαιάνθρακα, δυναμικότητας 500 MW. Για το σκοπό αυτό αναπτύχθηκαν διαγράμματα ροής με το λογισμικό προσομοίωσης διεργασιών Aspen Plus. Με χρήση του λογισμικού αυτού πραγματοποιήθηκαν αναλύσεις ευαισθησίας, μεταβάλλοντας κύριες σχεδιαστικές παραμέτρους της διεργασίας για να διαπιστωθεί πως κάθε μία από αυτές επιδρά πάνω σε άλλες υπολογιζόμενες μεταβλητές οι οποίες έχουν άμεση σχέση με το τελικό κόστος. Αφού πραγματοποιήθηκαν οι αναλύσεις ευαισθησίας, έγινε διαστασιολόγηση του χρησιμοποιούμενου κάθε φορά εξοπλισμού και οικονομική αξιολόγηση διαφορετικών περιπτώσεων λειτουργίας της ίδιας μονάδας. Στόχος ήταν η εύρεση των βέλτιστων συνθηκών λειτουργίας με χρήση των οποίων επιτυγχάνεται η ελαχιστοποίηση του τελικού κόστους. Συνολικά μελετήθηκαν τρία διαφορετικά συστήματα διαλυτών. Οι διαλύτες που μελετήθηκαν ήταν η μονοαιθανολαμίνη (MEA), η μεθυλ-διαιθανολαμίνη (MDEA) και ένα μείγμα αυτών των δύο σε διαφορετικές συγκεντρώσεις. Η ΜΕΑ αποτελεί τον πιο ευρέως μελετημένο διαλύτη για τη διεργασία χημικής απορρόφησης του CO2 και έτσι τα αποτελέσματα από τη μελέτη της αποτελούν τη βάση σύγκρισης για τους υπόλοιπους διαλύτες. Το βέλτιστο κόστος που υπολογίστηκε για λειτουργία μονάδας απορρόφησης και συμπίεσης διοξειδίου του άνθρακα με χρήση MEA ως διαλύτη είναι τα 45.15 €/τόνο διοξειδίου που δεσμεύεται. Με χρήση διαλύματος MEA-MDEA σε αναλογία 15% wt MEA – 15% wt MDEA το κόστος υπολογίζεται 51.58 €/τόνο διοξειδίου που δεσμεύεται. Το κόστος της διεργασίας αυτή τη στιγμή την καθιστά μη βιώσιμη, καθώς η απελευθέρωση διοξειδίου του άνθρακα στην ατμόσφαιρα από μία βιομηχανία αυτή τη στιγμή κοστίζει 4.6 €/τόνο διοξειδίου, όμως η τιμή αυτή αναμένεται να αυξηθεί ιδιαίτερα τα επόμενα χρόνια. Έτσι, μελλοντικά η διεργασία έχει μεγάλες πιθανότητες να καταστεί οικονομικά βιώσιμη, κυρίως σε συνδυασμό με διεργασίες EOR (Enhanced Oil Recovery).Lately, the climate change caused by the greenhouse effect seems to draw growing attention. As a result, great interest for greenhouse gas mitigation technologies has been manifested. Of all greenhouse gases, the one that is deemed primary responsible for this phenomenon is carbon dioxide whose atmospheric concentration has been steadily rising because of the generalized use of coal for power generation. The most mature technology for the reduction of CO2 emissions is carbon capture from power plant flue gases with the use of alkanolamine solvents as extracting agents that wash the acid the gas out of the total gas mixture. The main problem because of which the specific process does not find general application in a scale appropriate for integration in a power plant is the high end cost that arises because of the high energy consumption to regenerate the solvent. The objective of this thesis was the study, optimization and economic evaluation of the capture and compression process of carbon dioxide, coming from a 500 MW coal fired power plant flue gas. For this purpose, process flow diagrams have been developed using the commercial process simulation software Aspen Plus. With the use of this software, sensitivity analysis have been performed, changing main input design variables. The purpose was to study the effect that each one of these variables has on different output variables that are closely related to the end cost. After the sensitivity analysis have been performed, the equipment that was used every time got sized and economic evaluation of different operation cases of the plant were created. The purpose of the whole procedure was to find the optimal operating conditions, with the use of which the minimization of the end cost would be achieved. The solvent systems that have been studied were monoethanolamine (MEA), methyl-diethanolamine (MDEA) and a MEA-MDEA blend with different concentrations between those two amines. MEA is the most widely studied solvent system for CO2 capture processes and the results obtained from its study are the basis with which the performance of other solvents is evaluated. The optimal cost that has been calculated for the operation of a capture and compression process plant using MEA as solvent is 45.15 €/ton CO2 captured. With the use of a 15% wt MEA - 15% wt MDEA blend the end cost is calculated at 51.58 €/ton CO2 captured. Judging from the end cost, the process is now evaluated as non viable taking into account that releasing carbon dioxide into the atmosphere costs an industry 4.6 €/ton. However, this price is expected to be increased significantly in the near future and the capture process is more likely to become economically viable if it is combined with EOR (Enhanced Oil Recovery) processes.Ηλίας Κ. Νικολαΐδη

Modeling of physical properties and vapor – liquid equilibrium of ethylene and ethylene mixtures with equations of state

Ethylene (C2H4) is one of the most important compounds for the chemical and petrochemical industry, since it has found extensive use in the production of polymers, functionalized hydrocarbons and many other basic and intermediate products. As a result, significant amounts of ethylene are being transported, mainly through pipelines, from the site of production to the relevant industrial areas for exploitation and conversion to products of higher value. Accurate knowledge of the physical properties of the chemical systems involved, as well as the conditions for which two or more phases are formed, is a key aspect to the design and operation of a safe and optimal transportation process. In this work, the capability of three different Equations of State (EoS) in predicting the various physical properties (density, heat capacity, speed of sound, Joule-Thomson coefficient, and isothermal compressibility coefficient) of pure ethylene was assessed. The EoS considered include the Peng-Robinson (PR), the Perturbed Chain – Statistical Association Fluid Theory (PC-SAFT), and the SAFT with the Mie potential of variable range (SAFT-VR Mie) EoS, all of them in their original forms, with respect to the parameterization procedure. Furthermore, the vapor - liquid equilibrium (VLE) of pure ethylene and binary ethylene mixtures with hydrocarbons (CH4, C2H6, C3H6, C3H8, 1-C4H8) and gaseous components (H2, CO2) was calculated and the binary interaction parameters (BIPs) were regressed to optimize the performance of each EoS. Finally, the VLE of ternary mixtures with the components mentioned above and ethylene was predicted using the optimized BIPs. Most of the physical properties of pure C2H4 are predicted with relatively high accuracy by PC-SAFT and SAFT-VR Mie EoS, with none being clearly superior to the other. Both SAFT EoS are more accurate than PR in predicting the pure C2H4 physical properties overall. For phase equilibrium predictions, SAFT-VR Mie is overall the most accurate EoS, but when BIPs are used, the performance of all EoS is of comparable accuracy470149163sem informaçãosem informaçã

Solid–Liquid–Gas Equilibrium of Methane–<i>n</i>‑Alkane Binary Mixtures

In this work, a solid-phase thermodynamic model is coupled with the Soave–Redlich–Kwong (SRK), Peng–Robinson (PR), and Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) equations of state (EoS) to model the solid–liquid–gas equilibrium (SLGE) of binary methane (CH₄) mixtures with normal alkanes (<i>n</i>-alkanes). The mixtures considered include <i>n</i>-alkanes from <i>n</i>-C₆H₁₄ up to <i>n</i>-C₃₆H₇₄. The predictive capabilities of each combined model are validated against available experimental data and vary substantially as the asymmetry of the binary mixture, with respect to the size of the molecules involved, increases. Several aspects of the models, such as the use of binary interaction parameters (BIPs) fitted to experimental vapor (or gas)–liquid equilibrium (VLE/GLE) data and the importance of specific terms of the solid-phase model, are studied to showcase their effect on the accuracy of the calculations. In this way, modifications on the basic combined models are applied. A specific volume translation strategy is adopted for the cubic EoS, in order to describe more accurately the liquid molar volume pressure dependency in the Poynting correction of the solid-phase fugacity. This dependency becomes particularly important for highly asymmetric mixtures, in which SLGE is exhibited at very high pressures. A correlation of the BIPs with the carbon number of <i>n</i>-alkanes is proposed for each fluid-phase EoS, which can be used as a practical alternative to fitting <i>k_ij</i> parameters for other similar mixtures at a relevant range of conditions. Finally, by combining two previously published approaches for calculating the solid-phase fugacity, a new solid-phase model is proposed and calculations are presented in combination with the PR and the PC-SAFT EoS. Every combined model studied in this work retains a predictive nature, except for the newly proposed one, which requires a direct fit to the binary SLGE data. Calculations using the predictive models proposed in this work are in very good agreement with experimental measurements even at high pressures for most mixtures, while the proposed approach for the solid phase shows excellent accuracy in correlating the experimental data. Global phase diagrams are calculated with the adopted and proposed models for specific mixtures to showcase their ability to accurately reproduce the global phase behavior in a wide range of conditions