In recent years, Renewable Power to Fuels technology is becoming a vitally important pathway from the value-added products point of view. This electricity-to-fuel transformation is regarded as an efficient way not only to preserve renewable energy (i.e. wind and solar) and to offset the fluctuating nature of these sources but also to generate synthesis fuels with respect to the demand for, the capacity limitation and the existing infrastructure of the targeted products. In this sense, many E.U. countries are transforming CO2 into clean and the carbon-free products to achieve the targets of greenhouse gas (GHG) emissions. With regards to the renewable energy action plan, each E.U. country has a contribution target to reach by 2020: Italy’s overall target is to reach 17% of contribution, and it has already surpassed this (it reached 17.5% by the end of 2015). Germany is aiming for 35%, whereas Austria has a targeted of 34% . In this study, two main scenarios through Power to Fuels conversion are considered: 1) Power to Gas (PtG) technology (methanation process); 2) Power to Liquid (PtL) technology based on Dimethyl ether (DME), a direct one-step process, and Low Temperature Fischer Tropsch (LTFT) process. Therefore, the conceptual design of all three processes based on a Solid Oxide Electrolysis Cell (SOEC) is analyzed. In the optimized configuration of methanation, a methane fraction of 95% at the outlet is achieved, which is compatible with the existing pipeline network. The main challenge of this technology is the lack of accurate and explicit kinetic data for its catalyst. Also, the heat released from methantion and its utilization for providing the heat required for electrolysis is another issue in the latest configuration of methanation. In DME synthesis, four explicit Langmuir Hinshelwood Hougen Watson (LHHW) kinetics were implemented in Software Aspen plus. The main challenge in one-step direct DME synthesis (based on renewable energy) is the low value of yield and selectivity of the DME product (15% and 78% in the once-through process, respectively). However, the separation process and recycling of unreacted syngas in order to achieve high purity of the DME product is quite complex due to the presence of the unreacted syngas and the CO2 produced in the one-step synthesis process. Above all, it leads to higher operational costs. In the optimized configuration of LTFT based on renewable energy, a comprehensive simulation was conducted. To model an FT reactor, an external subroutine within an Excel spreadsheet through USER2 MODEL on the simulator was implemented. It was found that total efficiency of the system was achieved at 76.6 %. However, the main challenge of this configuration is the low value of liquid products due to the low capacity of the SOEC. Having considered the challenges and limitations of each process, it is concluded that FT synthesis is more interesting to model due to the complexity of the products and the more highly developed catalyst and reactor used. As a consequence, this dissertation mainly focuses on the dynamic modeling of a Fischer-Tropsch Slurry Bubble Column Reactor (FT-SBCR), which is considered as the best candidate for Fischer-Tropsch synthesis. In the dynamic modeling of FT-SBCR, a comprehensive computer model was developed to investigate flexible reactor operation. This flexibility was performed by a step-change of syngas flow rate load (3.5, 5, 7.5 m3/h) in a low-temperature Fischer–Tropsch synthesis. It was found that the dynamic simulation is not only able to predict all Fischer–Tropsch components over the reactor bed but can also describe the behavior of superficial gas velocity as a sub-model using the overall gas mass balance. The effects of a step-change volumetric syngas flow on the performance of the FT slurry reactor, CO conversion and α-value, as well as information about the inside of reactor were investigated. The results show that the temperature distribution of the slurry reactor remains constant under base load and change load conditions. It is concluded that load change conditions do not have a negative influence on the temperature distribution inside the reactor and the dynamic model of the slurry reactor presented responds quite well to the load change conditions.
Renewable Power to Fuels: Dynamic Modeling of Slurry Bubble Column Reactor in Lab-scale for Fischer-Tropsch Synthesis under variable loads of synthesis gas / Seyednejadian, Siavash. - (2018 Sep 11).
|Titolo:||Renewable Power to Fuels: Dynamic Modeling of Slurry Bubble Column Reactor in Lab-scale for Fischer-Tropsch Synthesis under variable loads of synthesis gas|
|Data di pubblicazione:||11-set-2018|
|Appare nelle tipologie:||8.1 Doctoral thesis Polito|
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|Thesis-to upload.pdf||Power to Fuels: Dynamic Modeling of a Slurry Bubble Column Reactor in Lab-Scale for Fischer Tropsch Synthesis under Variable Load of Synthesis Gas||Tesi di dottorato||PUBBLICO - Tutti i diritti riservati||Embargo: 18/09/2021 Richiedi una copia|