24 research outputs found

    Effect of long-term high temperature oxidation on the coking behavior of Ni-Cr superalloys

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    The service time of an industrial cracker is strongly dependent on the long-term coking behavior and microstructure stability of the reactor coil alloy. Super alloys are known to withstand temperatures up to even 1400 K. In this work, several commercially available alloys have been first exposed to a long term oxidation at 1423 K for 500 h, so-called metallurgic aging. Subsequently, their coking behavior was evaluated in situ in a thermogravimetric setup under ethane steam cracking conditions (Tgasphase = 1173 K, Ptot = 0.1 MPa, XC2H6 = 70%, continuous addition of 41 ppmw S/HC of DMDS, dilution δ = 0.33 kgH2O/kgHC) and compared with their unaged coking behavior. The tested samples were also examined using scanning electron microscopy and energy diffractive X-ray for surface and cross-section analysis. The alloys characterized by increased Cr-Ni content or the addition of Al showed improved stability against bulk oxidation and anti-coking behavior after application of metallurgic aging due to the formation of more stable oxides on the top surface

    Alumina-based coating for coke reduction in steam crackers

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    Alumina-based coatings have been claimed as being an advantageous modification in industrial ethylene furnaces. In this work, on-line experimentally measured coking rates of a commercial coating (CoatAlloy (TM)) have pointed out its superiority compared to an uncoated reference material in an electrobalance set-up. Additionally, the effects of presulfiding with 500 ppmw DMDS per H2O, continuous addition of 41 ppmw S per HC of DMDS, and a combination thereof were evaluated during ethane steam cracking under industrially relevant conditions (T-gasphase = 1173 K, P-tot = 0.1 MPa, X-C2H6 = 70%, dilution delta = 0.33 kg(H2O)/kg(HC)). The examined samples were further evaluated using online thermogravimetry, scanning electron microscopy and energy diffractive X-ray for surface and cross-section analysis together with X-ray photoelectron spectroscopy and wavelength-dispersive X-ray spectroscopy for surface analysis. The passivating coating illustrated a better performance than the reference Ni-Cr Fe-base alloy after application of an improved pretreatment, followed by piddling changes on the product distribution. Presulfiding of the coating affected negatively the observed coking rates in comparison with the reference alloy, so alternative presulfiding and sulfur addition strategies are recommended when using this barrier coating

    Effect of Long-Term High Temperature Oxidation on the Coking Behavior of Ni-Cr Superalloys

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    The service time of an industrial cracker is strongly dependent on the long-term coking behavior and microstructure stability of the reactor coil alloy. Super alloys are known to withstand temperatures up to even 1400 K. In this work, several commercially available alloys have been first exposed to a long term oxidation at 1423 K for 500 h, so-called metallurgic aging. Subsequently, their coking behavior was evaluated in situ in a thermogravimetric setup under ethane steam cracking conditions (Tgasphase = 1173 K, Ptot = 0.1 MPa, XC2H6 = 70%, continuous addition of 41 ppmw S/HC of DMDS, dilution δ = 0.33 kgH2O/kgHC) and compared with their unaged coking behavior. The tested samples were also examined using scanning electron microscopy and energy diffractive X-ray for surface and cross-section analysis. The alloys characterized by increased Cr-Ni content or the addition of Al showed improved stability against bulk oxidation and anti-coking behavior after application of metallurgic aging due to the formation of more stable oxides on the top surface

    Evaluation of a Ti–Base Alloy as Steam Cracking Reactor Material

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    Low-coking reactor material technologies are key for improving the performance and sustainability of steam crackers. In an attempt to appraise the coking performance of an alternative Ti–base alloy during ethane steam cracking, an experimental study was performed in a jet stirred reactor under industrially relevant conditions using thermogravimetry (Tgasphase = 1173 K, Ptot = 0.1 MPa, XC2H6 = 70%, and dilution δ = 0.33 kgH2O/kgHC). Initially, a typical pretreatment used for Fe–Ni–Cr alloys was utilized and compared with a pretreatment at increased temperature, aiming at better surface oxidation and thus suppressing coke formation. The results revealed a decrease in coking rates upon high temperature pretreatment of the Ti–base alloy, however, its coking performance was significantly worse compared to the typically used Fe–Ni–Cr alloys, and carbon oxides formation increased by a factor of 30 or more. Moreover, the analyzed coupons showed crack propagation after coking/decoking and cooling down to ambient temperature. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy indicated that the prompt and unsystematic oxidation of the surface and bulk caused observable crack initiation and propagation due to alloy brittleness. Hence, the tested Ti–base alloy cannot be considered an industrially noteworthy steam cracking reactor alloy

    Simulation of the Operation of Ixodolysis Unit of the Aspropyrgos Group Hellenic Petroleum Refinery

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    148 σ.Η παρούσα διπλωματική αποτελεί μία απόπειρα προσομοίωσης της μονάδας ιξωδόλυσης του Διυλιστηρίου Ασπροπύργου του ομίλου ΕΛ.ΠΕ. Η προσομοίωση βασίσθηκε σε δεδομένα λειτουργίας περίπου 20 χρονικών περιόδων, σε διάστημα 12 ετών (περίπου). Τα δεδομένα ήταν βιομηχανικής ακριβείας. Αρχικά, έγινε μία εκτενής διερεύνηση της βιβλιογραφίας για την προσέγγιση του κινητικού μοντέλου και για τις απαραίτητες παραδοχές της προσομοίωσης. Επιλέχθηκε κινητική ψευδοπρώτης τάξης για τα 5 ψευδοπροϊόντα που παράγονται από την μονάδα ιξωδόλυσης (ένα ψευδοσυστατικό και τέσσερα πετρελαϊκά κλάσματα). Εξ΄ αιτίας του γεγονότος ότι τα δεδομένα ήταν βιομηχανικά και όχι εργαστηριακά, περιείχαν σφάλματα και δεν ήταν τακτοποιημένα και οργανωμένα όπως αυτά μίας εργαστηριακής διάταξης. Έτσι, απαιτήθηκε μεγάλο χρονικό διάστημα για την επεξεργασία των δεδομένων, τη διόρθωσή τους και τον ‘καθαρισμό’ τους. Η ανάπτυξη κώδικα σε SQL προς επεξεργασία αυτής της τεράστιας βάσης δεδομένων που μας δόθηκε ήταν μία από τις επιλογές που έγιναν σε αυτήν την διπλωματική. Στην πράξη, φάνηκε ιδιαίτερα ορθή επιλογή καθώς με ταχύτητα μπόρεσε να γίνει επεξεργασία πολλών δεδομένων και προσθήκη όταν αυτό χρειάζεται κι άλλων δεδομένων (π.χ στον χαρακτηρισμό τροφοδοσίας). Τα βήματα της μοντελοποίησης ήταν συνοπτικά τα παρακάτω: 1. Απλοποίηση της μονάδας και επιλογή των σωστών παραδοχών μέσω ιδιαίτερα εκτενούς διερεύνησης της βιβλιογραφίας 2. Κατάστρωση του μοντέλου και των ισοζυγίων ενέργειας και μάζας του αντιδραστήρα. 3. Επιλογή των δεδομένων. Τα βασικά λειτουργικά δεδομένα αντιστοιχούσαν σε 3500 ημέρες οι οποίες μετά τη διαδικασία επιλογής μειώθηκαν στις 980. 4. Διερεύνηση της εξάρτησης της κινητικής από τους διαθέσιμους χαρακτηρισμούς της τροφοδοσίας. 5. Πρόβλεψη των συνθηκών εξόδου του αντιδραστήρα με το κινητικό μοντέλο που επιλέχθηκε και των εκτιμήσεων που έγιναν στις παραμέτρους των ισοζυγίων. Το μοντέλο προσομοίωσης που αναπτύχθηκε προβλέπει αρκετά ικανοποιητικά τα κλάσματα μάζας τριών εκ των πέντε προϊόντων στην έξοδο του αντιδραστήρα καθώς και τις θερμοκρασίες εξόδου. Από τα διαθέσιμα δεδομένα χαρακτηρισμού της τροφοδοσίας της μονάδας δεν κατέστη δυνατός ο προσδιορισμός της εξάρτησης της συμπεριφοράς του αντιδραστήρα από την ποιότητα της τροφοδοσίας.This thesis is an attempt to simulate the Visbreaking unit of Aspropyrgos Refinery Of Hellenic Petroleum Group. The simulation was based on 20 run’s data, or 12 years’ data approximately. These data were of industrial precision. Initially , an extensive investigation of the references has taken place on the approximation of the kinetic model and to lead to the necessary assumptions of the simulation. A model of 5 pseudocomponets of pseudo-first order reaction was assumed to describe the pyrolysis happening in the reactor. As mentioned above, because the data was industrial it contained errors and was not organized. So, a long period consumed in data processing to correct and “clean” that. The development code into SQL for processing that large database , that given by the industry, was one of the choices made in this thesis. In retrospect, it seems to be an appropriate choice for the quick processing and modifying of the database. The basic steps of the modeling are summarized below: 1. Simplification of the unit and selecting the right assumptions through an extensive investigation of the references 2. Design of the model and creation of the energy and mass balances of the reactor. 3. Data selection. The key operational data corresponding to 3500 days ,after the selection process were reduced to 980). 4. Investigation of the dependence of the kinetics of the available feed characterizations. 5. Forecast the reactor output, based on the proposed kinetic model by using the Runge Kutta method and the assessments were made on the parameters of the mass and energy balances. The developed model can predict satisfactorily three of the five pseudocomponents on the top of the reactor, as well as the outlet temperature . Judging by the available characterization data of the unit, it was not possible to determine the dependence of the behavior of the reactor by the feed quality.Σταμάτης Α. Σαρρή

    Coking tendency of 25Cr-35Ni alloys : influence of temperature, sulfur addition, and cyclic aging

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    25Cr-35Ni base alloys are the most frequently used materials for steam cracking reactors. The influence of cyclic aging, reactor temperature, and adding sulfur containing compounds before or during cracking on the rate of coke deposition on a classical 25Cr-35Ni alloy is evaluated using a jet stirred reactor equipped with an electrobalance. As expected, the initial and asymptotic coking rate increased with increasing reactor temperature. Scanning electron microscopy coupled with energy dispersive X-ray (SEMEDX) analysis indicated that more Ni and Fe is present on the surface at higher cracking temperatures. Presulfidation led to increased coke deposition and decreased CO yields compared to the reference. When a sulfur containing compound was added continuously, coke deposition increased significantly but carbon oxide formation was suppressed. A pronounced amount of coke was measured in the reactor, followed by suppressed generated amounts of carbon oxides downstream. When combined with the continuous addition of sulfur containing compounds, presulfidation has little effect. Depending on the conditions, the effect of aging of the material is different: during the reference run and when only presulfidation was applied, coking rates increased as the material aged. When sulfur containing compounds were added continuously, with our without presulfidation, coking rates decreased as the material aged. This can be related with increased amounts of MnCr2O4 and Cr2O3 observed by SEM and EDX analysis
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