Carbon dioxide is an acid gas and one of the most undesirable greenhouse gases that contributes to anthropogenic climate change. The largest amount of CO2 released into the atmosphere is produced by combustion of fossil fuels in power plants to produce electricity. The absorption of CO2 with aqueous amine solutions is the most mature technology suitable for post-combustion capture. However, it is energy-intensive because of the reboiler duty required in the regeneration column. In the last years, new solutions for CO2 capture have been proposed. One of the possibilities is the Chemical Looping Combustion (CLC) technology. In CLC oxygen is transferred from the combustion air to the fuel by means of an oxygen carrier. The fuel and the combustion air are never mixed, and the gases from the oxidation of the fuel, CO2 and H2O, leave the system as a separate stream. Water can be removed by condensation so pure CO2 is obtained without any loss of energy for separation. This makes CLC an interesting alternative to other CO2 capture schemes. This thesis work has been focused on the design and cost analysis of the two possible CO2 capture technologies, namely chemical absorption into a MonoEthanolAmine (MEA) aqueous solution and CLC, considering the same gaseous fuel in order to make a proper comparison. Furthermore, the compression system used to bring the captured CO2 to the desired final conditions has been considered. Firstly, the absorption of CO2 with a 30 wt% MEA aqueous solution has been analyzed, varying the CO2 capture rate between 80% and 95%. Simulations of the MEA plant have been performed with ASPEN Plus® integrated with an external Fortran subroutine developed by the GASP group of Politecnico di Milano. Then, the design of the CLC scheme, consisting of two interconnected fluidized beds has been carried out, considering NiO as oxygen carrier, and the scheme of a combined cycle for energy production has been also considered and designed. An economic evaluation of the two systems, also taking the influence of the carbon tax into account, has been performed aimed at determining which is the most convenient one.
L’anidride carbonica è un gas acido ed è tra i più indesiderati tra quelli che contribuiscono all’effetto serra. La maggior parte della CO2 emessa in atmosfera è prodotta dalla combustione di combustibili fossili nelle centrali elettriche per la produzione di energia. L'assorbimento di CO2 mediante soluzioni amminiche è la tecnologia attualmente più matura tra quelle di cattura post-combustione. Tuttavia, l’energia richiesta per la cattura di CO2 è elevata, a causa della quantità di calore da fornire al ribollitore della colonna di rigenerazione del solvente. Di recente sono state proposte nuove soluzioni per la cattura di CO2. Tra queste c’è la Chemical Looping Combustion (CLC). L'ossigeno viene trasferito dall'aria di combustione al combustibile tramite un oxygen carrier, così da evitare il contatto diretto tra combustibile ed aria. I gas prodotti dalla combustione, CO2 ed acqua, sono praticamente puri. L’acqua può essere rimossa per condensazione, ottenendo così CO2 pura senza spreco di energia. Questo rende la CLC un’interessante alternativa ad altri sistemi di cattura di CO2. Questo lavoro di tesi è incentrato sul design e sull'analisi dei costi delle due tecnologie di cattura della CO2 (assorbimento chimico con soluzioni amminiche e la CLC), considerando lo stesso combustibile utilizzato in un impianto di potenza di una raffineria, per avere un confronto più realistico tra le due. E’ stato considerato, inoltre, anche il sistema di compressione per portare la CO2 catturata alle condizioni finali desiderate. In primo luogo, si è analizzato l'assorbimento di CO2 con una soluzione di MonoEtanolAmmina (MEA, al 30% in peso), variando la percentuale di CO2 catturata tra l'80% ed il 95%. Successivamente si è analizzato il design dei reattori per lo schema relativo alla CLC, che è composto da due letti fluidi: come oxygen carrier è stato selezionato NiO ed è stato, inoltre, considerato ed analizzato anche il ciclo combinato per la produzione di energia. Un’analisi economica delle due tecnologie è stata, inoltre, condotta, prendendo anche in considerazione l’influenza della carbon tax, allo scopo di determinare quale tra le due possa essere la più conveniente.
Post-combustion and chemical looping combustion technologies for CCS : techno-economic analysis
SOLDINI, ALICE
2016/2017
Abstract
Carbon dioxide is an acid gas and one of the most undesirable greenhouse gases that contributes to anthropogenic climate change. The largest amount of CO2 released into the atmosphere is produced by combustion of fossil fuels in power plants to produce electricity. The absorption of CO2 with aqueous amine solutions is the most mature technology suitable for post-combustion capture. However, it is energy-intensive because of the reboiler duty required in the regeneration column. In the last years, new solutions for CO2 capture have been proposed. One of the possibilities is the Chemical Looping Combustion (CLC) technology. In CLC oxygen is transferred from the combustion air to the fuel by means of an oxygen carrier. The fuel and the combustion air are never mixed, and the gases from the oxidation of the fuel, CO2 and H2O, leave the system as a separate stream. Water can be removed by condensation so pure CO2 is obtained without any loss of energy for separation. This makes CLC an interesting alternative to other CO2 capture schemes. This thesis work has been focused on the design and cost analysis of the two possible CO2 capture technologies, namely chemical absorption into a MonoEthanolAmine (MEA) aqueous solution and CLC, considering the same gaseous fuel in order to make a proper comparison. Furthermore, the compression system used to bring the captured CO2 to the desired final conditions has been considered. Firstly, the absorption of CO2 with a 30 wt% MEA aqueous solution has been analyzed, varying the CO2 capture rate between 80% and 95%. Simulations of the MEA plant have been performed with ASPEN Plus® integrated with an external Fortran subroutine developed by the GASP group of Politecnico di Milano. Then, the design of the CLC scheme, consisting of two interconnected fluidized beds has been carried out, considering NiO as oxygen carrier, and the scheme of a combined cycle for energy production has been also considered and designed. An economic evaluation of the two systems, also taking the influence of the carbon tax into account, has been performed aimed at determining which is the most convenient one.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/136157