Subject of the thesis work is the abatement of air emission of the Expander secondary hot rolling mill of Dalmine S.p.A., a Tenaris group company world leader in the production of seamless steel pipes. The hot rolling process consists of the following phases: - Preheating of the pipes up to the process temperature; - Descaling, with high pressure water and salt injection on the surface of the pipe; - Expansion up to the desired diameter; - Reeler rolling mill, for the correction of thickness and internal diameter. The emission of the oven is regulated by the correct functioning of the combustion and the use of dry-low-NOx burners. The emission from the rolling process is instead captured in 3 different treatment phases, descaling, entry and exit Expander, and is collected to a treatment plant consisting of a wet venturi scrubber. The emission presents metallic and saline dusts and due to the use of water not only for the removal of oxides from the surface of the pipe but also for the lubrication of the same, the gaseous flow is characterized by high humidity, making the flow as it is unsuitable for treatment with dry systems, widely used in the field of hot rolling, such as bag filters. The installed treatment plant suffers of corrosion due to the construction material - carbon steel - and allows limited removal efficiencies on the salt fraction of dust, with submicronic dimensions. The first solution envisaged was the installation of a dual-stage pilot washing tower, first equipped with fixed bed stages and then with a floating bed, fed with a portion of the fumes captured by the descaling process. The choice of this solution was based on the high solubility of the salt in water but the results obtained, due to the limited contact times that do not allow to optimize the process, were not satisfactory, allowing only the removal of the coarse metallic fraction of the powders and therefore without obtaining an improvement over the system installed on a large scale. The second solution was the installation of a wet electrofilter precipitator, downstream of the pilot scrubber, due to the low prevalence provided by the fan with which the pilot plant was equipped and the large pressure drops to overcome, in order to capture a significative part of the emission: the results of this treatment system are satisfactory, obtaining a removal efficiency > 95% on salt powders. The thesis work focuses on the characterization of the emission and on a comparison, both from the theoretical point of view and from the experimental point of view, of the abatement technologies applicable to this issue.
Oggetto del lavoro di tesi è l’abbattimento dei fumi derivanti dall’impianto di laminazione secondaria Expander della Dalmine S.p.A., azienda del gruppo Tenaris leader mondiale nella produzione di tubi in acciaio senza saldatura. Il processo di laminazione consta delle seguenti fasi: - Preriscaldo dei tubi fino alla temperatura di processo; - Discagliatura, con iniezione sulla superficie del tubo di acqua e sale ad alta pressione; - Espansione fino al diametro desiderato; - Laminatoio Reeler, per la correzione dello spessore e del diametro interno. L’emissione del forno è regolata dal corretto funzionamento della combustione e dall’utilizzo di bruciatori low-NOx. L’emissione derivante dal processo di laminazione viene invece captata in 3 diverse fasi del trattamento, discagliatura, ingresso ed uscita Expander, e viene convogliata ad un impianto di trattamento costituito da uno scrubber ad umido venturi. L’emissione presenta polveri metalliche e saline e a causa dell’utilizzo di acqua non solo per la rimozione di ossidi dalla superficie del tubo ma anche per la lubrificazione dello stesso, il flusso gassoso è caratterizzato da elevata umidità, rendendo il flusso tal quale inadatto al trattamento con sistemi a secco, di largo utilizzo nel campo della laminazione a caldo, come i filtri a maniche. L’attuale impianto di trattamento soffre molto la corrosione a causa del materiale da costruzione – acciaio al carbonio - e consente di ottenere efficienze di rimozione limitate sulla frazione salina delle polveri, di dimensioni submicroniche. La prima soluzione ipotizzata è stata l’installazione di una torre di lavaggio pilota a doppio stadio, prima dotata di stadi a letto fisso e poi a letto flottante, alimentata con una porzione dei fumi captati dal processo di discagliatura. La scelta di questa soluzione si basava sull’elevata solubilità del sale in acqua ma i risultati ottenuti, a causa dei tempi di contatto limitati che non consentono di ottimizzare il processo, non sono stati soddisfacenti, permettendo la sola rimozione della frazione metallica grossolana delle polveri e senza ottenere dunque un miglioramento rispetto al sistema installato su larga scala. La seconda soluzione è stata l’installazione di un elettrofiltro ad umido, a valle dello scrubber pilota, a causa della bassa prevalenza fornita dal ventilatore di cui era dotato l’impianto pilota e delle grandi perdite di carico da superare per poter captare una parte dell’emissione: i risultati di questo sistema di trattamento sono risultati soddisfacenti, ottenendo un’efficienza di rimozione >95% sulle polveri saline. Il lavoro di tesi si concentra sulla caratterizzazione dell’emissione e su un confronto, sia dal punto di vista teorico sia dal punto di vista sperimentale, delle tecnologie di abbattimento applicabili a tale emissione.
Trattamento dei fumi di un impianto di laminazione secondaria
LABELLA, DAVIDE
2018/2019
Abstract
Subject of the thesis work is the abatement of air emission of the Expander secondary hot rolling mill of Dalmine S.p.A., a Tenaris group company world leader in the production of seamless steel pipes. The hot rolling process consists of the following phases: - Preheating of the pipes up to the process temperature; - Descaling, with high pressure water and salt injection on the surface of the pipe; - Expansion up to the desired diameter; - Reeler rolling mill, for the correction of thickness and internal diameter. The emission of the oven is regulated by the correct functioning of the combustion and the use of dry-low-NOx burners. The emission from the rolling process is instead captured in 3 different treatment phases, descaling, entry and exit Expander, and is collected to a treatment plant consisting of a wet venturi scrubber. The emission presents metallic and saline dusts and due to the use of water not only for the removal of oxides from the surface of the pipe but also for the lubrication of the same, the gaseous flow is characterized by high humidity, making the flow as it is unsuitable for treatment with dry systems, widely used in the field of hot rolling, such as bag filters. The installed treatment plant suffers of corrosion due to the construction material - carbon steel - and allows limited removal efficiencies on the salt fraction of dust, with submicronic dimensions. The first solution envisaged was the installation of a dual-stage pilot washing tower, first equipped with fixed bed stages and then with a floating bed, fed with a portion of the fumes captured by the descaling process. The choice of this solution was based on the high solubility of the salt in water but the results obtained, due to the limited contact times that do not allow to optimize the process, were not satisfactory, allowing only the removal of the coarse metallic fraction of the powders and therefore without obtaining an improvement over the system installed on a large scale. The second solution was the installation of a wet electrofilter precipitator, downstream of the pilot scrubber, due to the low prevalence provided by the fan with which the pilot plant was equipped and the large pressure drops to overcome, in order to capture a significative part of the emission: the results of this treatment system are satisfactory, obtaining a removal efficiency > 95% on salt powders. The thesis work focuses on the characterization of the emission and on a comparison, both from the theoretical point of view and from the experimental point of view, of the abatement technologies applicable to this issue.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/148679