Modelling of mercury adsorption in natural gas pipelines

Grammenou, Eleni; Γραμμένου, Ελένη

dc.contributor.author	Grammenou, Eleni	en
dc.contributor.author	Γραμμένου, Ελένη	el
dc.date.accessioned	2020-04-15T13:14:30Z
dc.date.available	2020-04-15T13:14:30Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/50196
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.17894
dc.rights	Αναφορά Δημιουργού-Όχι Παράγωγα Έργα 3.0 Ελλάδα	*
dc.rights.uri	http://creativecommons.org/licenses/by-nd/3.0/gr/	*
dc.subject	Mercury	en
dc.subject	Natural gas	en
dc.subject	Adsorption	en
dc.subject	Simulation	en
dc.subject	Steel pipelines	en
dc.subject	Υδράργυρος	el
dc.subject	Φυσικό αέριο	el
dc.subject	Προσρόφηση	el
dc.subject	Προσομοίωση	el
dc.subject	Χαλύβδινοι αγωγοί	el
dc.title	Modelling of mercury adsorption in natural gas pipelines	en
dc.title	Μοντελοποίηση της προσρόφησης υδραργύρου σε αγωγούς μεταφοράς φυσικού αερίου	el
heal.type	bachelorThesis
heal.classification	Engineering	en
heal.classification	Modelling	en
heal.language	en
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2019-07-08
heal.abstract	Mercury (Hg) and its compounds are inherently traceable in fossil fuels, including natural gas, crude oil and coal. When reservoirs are exploited, elemental mercury and the other forms that may be present in the reservoir, partition to separated phases (oil, gas and water) and travel throughout production and processing systems. Even if present in minor concentration (a few ppb), different forms of mercury can provoke severe implications during gas and oil processing. Besides its toxic nature, mercury might be responsible for catalyst deactivation and it is highly corrosive when interacting with materials of processing equipment, as it amalgamates. In the past, the detrimental interactions of mercury with downstream aluminum heat exchangers, such as those used in cryogenic hydrocarbon recovery natural gas plants and in natural gas liquefaction plants, have been reported to result in major industrial accidents, due to mechanical failure and gas leakage. Mercury, as a trace component of natural gas, can be transported through pipelines, from the well to the reception facility. However, mercury is detected in the inlet facilities after an extended period of operating time, due to its slow accumulation, via adsorption mechanisms, inside the flowlines. This is known as “mercury lag effect”. Once the pipe walls become saturated, mercury will “breakthrough”. The time, prior to mercury concentration reaching a critical point which ordains the installation of mercury treatment units, is called time to breakthrough. Although the interaction of mercury with steel and stainless steel is known, there is a lack of extensive research on the primary mechanisms of mercury uptake in pipelines and on the conditions which favour the adsorption and desorption kinetics. Considerable scientific work is currently under way. Aside from the above-mentioned difficulties, the confidential character of the gas and oil industry impedes the publication of valid field and experimental data. The scope of this Diploma Thesis is the development of a model for mercury adsorption/desorption in natural gas transport pipelines, able to estimate the time taken for mercury breakthrough based on first principles. Moreover, it provides the time-dependent adsorption profiles of mercury for several inlet concentrations (100-5000 ng/Sm3) and pipe’s adsorption capacities (0.0038-10 g/m2). The model was built and run in MATLAB. To this end, a literature review was conducted regarding possible methods of mercury accumulation onto metal surfaces and already existing adsorption models. Hereupon, the variables of the model are defined, the main assumptions are stated, and the mathematical formulation permits a rigorous description of mercury physical adsorption, limited to the formation of a monolayer. The reverse process of desorption is, also, studied. Since segmentation is a popular approach to fluid dynamics, the examined pipeline was effectively discretised to ensure model results’ accuracy and reduce the computational intensity associated with solving the model. Using the thermodynamic model UMR-PRU, which has been successfully applied to natural gas mixtures, physical properties, such as gas density and mercury fugacity coefficient, were calculated, and the rest of the parameters were defined by appropriate methods. Furthermore, the effect of main model assumptions and parameters, on mercury adsorption profile and breakthrough time, was investigated. Afterwards, the model was developed in Aspen Plus Custom Modeler. Initially, the simulation was run in dynamic and steady state mode, to validate MATLAB model results, with fixed parameters. At a later stage, it was extended to serve a user-interactive environment, enabling the study of the adsorption phenomenon in any pipeline, provided that the user defines of stream inlet conditions and pipe characteristics. The simulation produces the mercury concentration profile at the exit of the pipeline over time, as well as the adsorption front along the pipe, allowing the user to closely observe the adsorption phenomenon in real time. The successful implementation of the mercury adsorption model from MATLAB Aspen Custom Modeler, renders it an easy-to-use pipeline simulation tool. It shall not be neglected that the ACM mercury adsorption model holds, also, great potential to be integrated, with minor modifications, into the Aspen Plus/Hysys units’ palette. This work presents a model for estimating the time for mercury breakthrough in natural gas transport pipelines, based on the simplified approach of mercury accumulation due to physical adsorption onto the steel surface of the pipe wall. A systematic and thorough approach is attempted regarding the calculation of the model parameters, and a sensitivity analysis is employed to examine the effect of parameters’ uncertainty. The model reveals that an increase in the mercury inlet concentration decreases breakthrough time at the reception facilities, whereas increasing adsorption capacity of the pipe increases the time for mercury breakthrough, as it is expected by the theoretical background of adsorption process. An empirical equation for the prediction of the breakthrough time as a function of the mercury concentration in the pipeline inlet and the pipeline adsorption capacity, expressed in Specific Surface area terms, has been developed. The parametric analysis reports the sensitivity of the model to the mass transfer coefficient, which participates in the mercury mass transfer term to the pipe walls and vice-versa, the compressibility factor of the gas, as well as parameters related to desorption kinetics, such as the activation energy and pre-exponential factor. The model of mercury adsorption is a useful tool for the natural gas industry, as it points out the time limit before the installation of mercury treatment facilities becomes imperative for personnel safety and equipment maintenance. For this reason, its implementation in Aspen Custom Modeler allows its use by a broader audience.	en
heal.advisorName	Voutsas, Epaminondas	en
heal.advisorName	Βουτσάς, Επαμεινώνδας	el
heal.committeeMemberName	Βουτσάς, Επαμεινώνδας	el
heal.committeeMemberName	Μπουντουβής, Ανδρέας	el
heal.committeeMemberName	Ταούκης, Πέτρος	el
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Χημικών Μηχανικών. Τομέας Ανάλυσης, Σχεδιασμού και Ανάπτυξης Διεργασιών και Συστημάτων (ΙΙ). Εργαστήριο Θερμοδυναμικής και Φαινομένων Μεταφοράς	el
heal.academicPublisherID	ntua
heal.numberOfPages	81 σ.
heal.fullTextAvailability	true