The removal of acid gases, such as CO2 and H2S, from natural gas is an important step in natural gas purification to meet pipeline quality standard specifications as a consumer fuel, to enhance the heating value and to avoid pipeline and equipment corrosion. An interesting idea is to purify the gas within the extraction well through a “downhole purification” by means of water scrubbing. The aim of this work has been to perform a feasibility analysis aimed at designing this process. The hydrodynamics of the system has been analyzed at atmospheric conditions by investigating the two-phase flow which establishes in a circular column of 240 mm inner diameter. Experiments have been performed to measure the gas holdup and the collected data have been used to fit the parameters of a correlation which allows to estimate the gas holdup for different systems at different gas flow rates. The obtained correlation has been compared with some of the numerous correlations proposed in the literature. Then, in order to have a sample of statistical significance, some data reported in the literature for systems similar to the ones considered in the present work have been used to produce a correlation for the gas holdup which allows to better describe the systems of interest. A literature review on the volumetric mass transfer coefficient has been performed to select an appropriate correlation for it. Furthermore, pressure-temperature-composition experimental data for the two binaries CO2-H2O and H2S-H2O at typical downhole conditions have been collected from the literature and have been compared with the results provided by the PSRK Equation of State as implemented in Aspen Plus® V8.0 to assess the reliability of this thermodynamic model. These data have been used to estimate the K-factor which is another fundamental parameter required to design the investigated absorption bubble column. In the end, the height of the column which is necessary to reach a given purity specification in the outlet gas stream has been calculated, also forecasting the performance of the process at high pressure conditions, which are typical of downhole processes.
La rimozione dei gas acidi (CO2 e H2S) dal gas naturale è un importante processo atto ad ottenere le specifiche di purezza richieste per poter trasportare ed utilizzare tale gas. Un’idea innovativa consiste nel condurre tale processo di purificazione, denominato downhole, direttamente nel pozzo di estrazione attraverso un assorbimento fisico della CO2 e del H2S in H2O. Lo scopo di questo lavoro è stato quello di analizzare la fattibilità di tale processo, focalizzando l’attenzione sull’altezza della colonna necessaria per ottenere le specifiche di purezza richieste. La fluidodinamica del sistema è stata analizzata a pressione atmosferica, studiando il moto bifase che si sviluppa in una colonna avente diametro interno pari a 240 mm. Sono state condotte prove sperimentali per misurare i valori di gas holdup, utilizzati successivamente per determinare i parametri di una correlazione, ottenuta tramite analisi dimensionale, che permette di stimare tale grandezza per diversi sistemi. La correlazione proposta è stata in seguito confrontata con alcune correlazioni riportate in letteratura. Successivamente, dati di gas holdup per sistemi simili a quelli analizzati nella campagna sperimentale sono stati utilizzati per stimare i parametri della correlazione per meglio descrivere il sistema di interesse. In seguito, sono stati ricercati in letteratura una correlazione che permettesse di stimare il coefficiente volumetrico di scambio materiale e le composizioni di equilibrio per i sistemi binari CO2-H2O e H2S-H2O alle condizioni tipiche di un processo downhole. Tali valori d’equilibrio sono stati poi confrontati con i risultati ottenuti implementando l’Equazione di Stato PSRK in Aspen Plus® V8.0 per verificare l’affidabilità del modello termodinamico. Successivamente, i dati d’equilibrio sono stati utilizzati per determinare la costante di ripartizione dei sistemi considerati. Infine, è stata determinata l’altezza della colonna d’assorbimento necessaria per raggiungere una data specifica di purezza della corrente gassosa, considerando anche pressioni elevate, tipiche dei processi downhole.
Purificazione di gas naturale da composti acidi mediante assorbimento fisico downhole
SANTUS, DANIELE;SALVAGNO, NICOLA
2013/2014
Abstract
The removal of acid gases, such as CO2 and H2S, from natural gas is an important step in natural gas purification to meet pipeline quality standard specifications as a consumer fuel, to enhance the heating value and to avoid pipeline and equipment corrosion. An interesting idea is to purify the gas within the extraction well through a “downhole purification” by means of water scrubbing. The aim of this work has been to perform a feasibility analysis aimed at designing this process. The hydrodynamics of the system has been analyzed at atmospheric conditions by investigating the two-phase flow which establishes in a circular column of 240 mm inner diameter. Experiments have been performed to measure the gas holdup and the collected data have been used to fit the parameters of a correlation which allows to estimate the gas holdup for different systems at different gas flow rates. The obtained correlation has been compared with some of the numerous correlations proposed in the literature. Then, in order to have a sample of statistical significance, some data reported in the literature for systems similar to the ones considered in the present work have been used to produce a correlation for the gas holdup which allows to better describe the systems of interest. A literature review on the volumetric mass transfer coefficient has been performed to select an appropriate correlation for it. Furthermore, pressure-temperature-composition experimental data for the two binaries CO2-H2O and H2S-H2O at typical downhole conditions have been collected from the literature and have been compared with the results provided by the PSRK Equation of State as implemented in Aspen Plus® V8.0 to assess the reliability of this thermodynamic model. These data have been used to estimate the K-factor which is another fundamental parameter required to design the investigated absorption bubble column. In the end, the height of the column which is necessary to reach a given purity specification in the outlet gas stream has been calculated, also forecasting the performance of the process at high pressure conditions, which are typical of downhole processes.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/102365