The content of this work deals with natural gas transport within portions of the national grid, focusing on the dynamic simulation of the composition profiles, known as quality tracking. Natural gas is a mixture of different species, therefore its characteristics and properties depend on the fraction of each component, which varies according to the gas field it hails from. Due to the high number of supply sources in the Italian natural gas system, it is important to track and check the movement of the mixture, in order to know the quality of the fuel delivered to each client. Biomethane injection in the grid, already regulated and soon to happen, together with the possible rise in liquefied natural gas (LNG) supplies, could only increase this need. Moreover, the urgent seek for energy solutions that are sustainable from the environmental point of view, in addition to the technical and economical ones, has led to the development of innovative technologies to produce alternative fuels (gas from renewable sources). Their integration with the natural gas grid requires a careful analysis of the subsequent effects, verifying that the quality parameters of the new mixture would not exceed the imposed limits, which assure safety of the system and homogeneity of the flowing natural gas. This work analyses both the current need of dynamic reconstruction of the quality of the gas in the grid (for control and accounting purposes) and the future scenario that includes alternative fuels injection. The first part of the work (Chapters 2 – 5) studies the potentiality of quality tracking within a commercial software (SIMONE), currently used by many European TSOs (Transmission System Operators), in particular Snam Rete Gas, with which part of this Master Thesis has been carried out. SIMONE offers advantages about the dimensions and level of complexity of the simulated grid, in addition to the presence of models to represent all the major components of the real infrastructure. However, there is the disadvantage of a limited control over the simulation parameters, due to the impossibility to access the details of the algorithm. In this part, the study proves the accuracy of the dynamic simulation through comparisons to real data (measurements form instruments located along the grid), which are performed considering multiple combinations of analysis periods and check points. The results show a relative error smaller than 1% in about 80% of the comparisons and higher than 2% only in about 3% of the queries. In addition, the analysis demonstrates the resilience of the algorithm in presence of errors in the volumetric flow and calorific value input data with an order of magnitude similar to the instrumental uncertainty. The second part of the work (Chapters 6 - 7) provides the development of a fluid dynamics model capable of dynamic tracking of composition, to be applied on simple grids, maintaining the maximum control over the parameters, over the correlations to evaluate the physical quantities and over the procedure. First, the model is validated by comparison with real data from a portion of Italian natural gas grid simulated in the first part. Then, it is applied to a relevant case study that considers the injection of hydrogen in a pipeline. Coming from a Power to Gas plant operating to balance a wind farm production, the hydrogen flow profile features significant variations across the time. The analysis performed in this section underlines the need of dynamic modelling to verify the presence of fluctuations in the hydrogen fraction within the mixture along the grid, which are related to the superposition of effects regarding injections and taking loads and which are not shown by the steady state analysis.
In questo lavoro di tesi viene analizzato il trasporto del gas naturale in porzioni di rete nazionale, con interesse alla ricostruzione dell’evoluzione dinamica della composizione, nota come quality tracking. Il gas naturale, infatti, è una miscela e pertanto possiede caratteristiche e proprietà che dipendono dalle frazioni delle specie chimiche che la compongono, variabili secondo il giacimento di provenienza. La molteplicità di fonti di approvvigionamento del sistema italiano rende importante tracciare e controllare lo spostamento della miscela, per conoscere la qualità del gas riconsegnato ai clienti. L’introduzione in rete di biometano, già regolamentata e prossima ad avvenire, insieme al possibile maggiore utilizzo degli approvvigionamenti di gas naturale liquefatto (GNL), non può che accrescere questa esigenza. Inoltre, l’urgente spinta verso soluzioni energetiche sostenibili dal punto di vista ambientale, oltre che tecnico ed economico, ha portato allo sviluppo di tecnologie innovative per la produzione di combustibili alternativi (gas da fonti rinnovabili) e la loro integrazione nella rete di trasporto richiede un attento studio degli effetti dati dall’immissione, in termini di rispetto dei parametri di controllo imposti dal gestore della rete ai fini della sicurezza e dell’omogeneità del gas nelle condutture. Il presente lavoro analizza sia l’aspetto della necessità di ricostruzione della qualità del gas in rete, per esigenze attuali di controllo e contabilizzazione, sia lo scenario futuro di immissione di combustibili alternativi. Nella prima parte (Capitoli da 2 a 5), si analizza la possibilità di quality tracking offerta da un software commerciale (SIMONE) in uso presso molti gestori di rete europei ed in particolare presso Snam Rete Gas, in collaborazione con la quale è stata svolta parte della tesi. Tale software offre vantaggi dal punto di vista dell’estensione e della complessità della porzione di rete che può essere simulata, oltre che per la disponibilità di includere i modelli di tutti i componenti principali del sistema di distribuzione. Lo svantaggio consiste però nel limitato controllo sui parametri della simulazione, dato dall’impossibilità di conoscere i dettagli dell’algoritmo interno. Lo studio svolto verifica in questa parte l’accuratezza della ricostruzione a seguito del confronto con i dati reali (misure da strumenti in campo), effettuato per numerose combinazioni di periodi di analisi e punti di verifica, con risultati complessivi di errore relativo contenuto entro l’1% nell’80% circa dei campionamenti e superiore al 2% solo nel 3% circa dei casi. L’analisi dimostra inoltre la robustezza dell’algoritmo in presenza di errori anche sistematici sui dati in ingresso per i valori di portata e potere calorifico di entità corrispondente all’incertezza strumentale. Nella seconda parte (Capitoli 6 e 7), si costruisce un modello fluidodinamico che consenta di tracciare l’evoluzione dinamica della composizione, da applicarsi a reti di complessità ridotta, garantendo il massimo livello di controllo sui parametri introdotti, sulle correlazioni per la stima delle grandezze e sui dettagli del procedimento. In seguito ad una validazione effettuata tramite confronto con i dati della rete di trasporto reale per un tratto simulato nella prima parte, il modello MATLAB® sviluppato viene applicato a un caso studio particolare di immissione di idrogeno proveniente da un impianto Power to Gas, avente funzione di bilanciamento di un parco eolico, caratterizzato da significativa variabilità del profilo di immissione. L’analisi svolta in questa parte dimostra la necessità del modello dinamico nella verifica della presenza di oscillazioni della frazione di idrogeno presente in miscela lungo la rete, legate alla sovrapposizione di effetti delle immissioni e dei carichi di prelievo e non individuabili tramite sole analisi stazionarie.
Analisi e modellizzazione del trasporto del gas naturale nella rete nazionale : quality tracking
COLBERTALDO, PAOLO
2013/2014
Abstract
The content of this work deals with natural gas transport within portions of the national grid, focusing on the dynamic simulation of the composition profiles, known as quality tracking. Natural gas is a mixture of different species, therefore its characteristics and properties depend on the fraction of each component, which varies according to the gas field it hails from. Due to the high number of supply sources in the Italian natural gas system, it is important to track and check the movement of the mixture, in order to know the quality of the fuel delivered to each client. Biomethane injection in the grid, already regulated and soon to happen, together with the possible rise in liquefied natural gas (LNG) supplies, could only increase this need. Moreover, the urgent seek for energy solutions that are sustainable from the environmental point of view, in addition to the technical and economical ones, has led to the development of innovative technologies to produce alternative fuels (gas from renewable sources). Their integration with the natural gas grid requires a careful analysis of the subsequent effects, verifying that the quality parameters of the new mixture would not exceed the imposed limits, which assure safety of the system and homogeneity of the flowing natural gas. This work analyses both the current need of dynamic reconstruction of the quality of the gas in the grid (for control and accounting purposes) and the future scenario that includes alternative fuels injection. The first part of the work (Chapters 2 – 5) studies the potentiality of quality tracking within a commercial software (SIMONE), currently used by many European TSOs (Transmission System Operators), in particular Snam Rete Gas, with which part of this Master Thesis has been carried out. SIMONE offers advantages about the dimensions and level of complexity of the simulated grid, in addition to the presence of models to represent all the major components of the real infrastructure. However, there is the disadvantage of a limited control over the simulation parameters, due to the impossibility to access the details of the algorithm. In this part, the study proves the accuracy of the dynamic simulation through comparisons to real data (measurements form instruments located along the grid), which are performed considering multiple combinations of analysis periods and check points. The results show a relative error smaller than 1% in about 80% of the comparisons and higher than 2% only in about 3% of the queries. In addition, the analysis demonstrates the resilience of the algorithm in presence of errors in the volumetric flow and calorific value input data with an order of magnitude similar to the instrumental uncertainty. The second part of the work (Chapters 6 - 7) provides the development of a fluid dynamics model capable of dynamic tracking of composition, to be applied on simple grids, maintaining the maximum control over the parameters, over the correlations to evaluate the physical quantities and over the procedure. First, the model is validated by comparison with real data from a portion of Italian natural gas grid simulated in the first part. Then, it is applied to a relevant case study that considers the injection of hydrogen in a pipeline. Coming from a Power to Gas plant operating to balance a wind farm production, the hydrogen flow profile features significant variations across the time. The analysis performed in this section underlines the need of dynamic modelling to verify the presence of fluctuations in the hydrogen fraction within the mixture along the grid, which are related to the superposition of effects regarding injections and taking loads and which are not shown by the steady state analysis.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/107893