Energy-Process Integration of the Gas-Cooled/Water-Cooled Fixed-Bed Reactor Network for Methanol Synthesis

The paper deals with the techno-economical assessment of the gas-cooled/water-cooled fixed-bed reactor network for methanol synthesis. The study is the extension of the first-principles model for the watercooled reactor already proposed in our prior work (Manenti et al., 2013). Here, the optimization is extended to the steam generation and the reactor length ratio. As a result, basing on the integrated optimization of energy and process yield, we propose to significantly revise the common design. The traditional water/gas cooling reactor length ratio could be significantly reduced with consequent simultaneous increase in methanol production and steam generation as well, however preserving safety and operational ranges. The economic benefit deriving from the proposed design for a medium-scale process is estimated in more than 1.7 M€/y

Process development for fine chemicals (Acetaldehyde Dimethylacetal) synthesis

Tese de doutoramento. Engenharia Química. Faculdade de Engenharia. Universidade do Porto. 200

Renewable Power to Fuels: Dynamic Modeling of Slurry Bubble Column Reactor in Lab-scale for Fischer-Tropsch Synthesis under variable loads of synthesis gas

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% [1]. 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

Dynamic Operation of Power-to-X Processes Demonstrated by Methanol Synthesis

Chemische Energiespeicher hergestellt im Rahmen von sogenannten Power-to-X (PtX) Prozessen werden in Zukunft aufgrund des fortschreitenden Ausbaus der Strompoduktion aus regenerativen Energiequellen und der notwendigen Defossilisierung von Industrie- und Verkehrssektor eine zunehmend wichtige Rolle spielen. Hierbei wird der Methanolsynthese aus Kohlendioxid (CO2) und nachhaltig produziertem Wasserstoff (H2) im Energiesystem eine Schlüsselposition zugeschrieben, da Methanol bereits heute ein wichtiger Baustein im globalen Treibstoff- und Chemiemarkt ist. Im Vergleich zur konventionellen Methanolsynthese basierend auf fossilen Energieträgern birgt die Methanolsynthese aus CO2-reichen Gasen, welche aus industriellen Prozessen, der Biomasseverwertung oder der Luft gewonnen werden, die Problematik schlechterer Gleichgewichtsumsätze, einer veränderten Reaktionskinetik und der beschleunigten Katalysatordesaktivierung. Zudem unterliegen die Herstellung von H2 aus der Wasserelektrolyse mit erneuerbarem Strom und ggf. die CO2-Versorgung aus dem gekoppelten Industrieprozess einer Dynamik, die für die Methanolsynthese eine große Abweichung vom aktuellen Stand der Technik darstellt. Für diese geänderten Rahmenbedingungen existieren in der wissenschaftlichen Gemeinschaft insbesondere zur Simulation des Synthesereaktors keine validierten Modelle. Eine detaillierte reaktionskinetische Beschreibung des Reaktionsnetzwerkes in technischen Reaktoren ist daher notwendig, um die Methanolsynthese aus nachhaltigen Rohstoffen in Zukunft zu ermöglichen. Um dieses Defizit zu adressieren, wurde in dieser Arbeit mithilfe einer skalenübertragbaren Simulationsplattform eine Miniplantanlage dimensioniert, deren Reaktor das thermochemische Verhalten eines industriellen dampfgekühlten Rohrbündelreaktors mit hoher Übereinstimmung abbildet. Ein neuartiges Messkonzept bestehend aus einer hochaufgelösten faseroptischen Temperaturmessung zur Erfassung des axialen Temperaturprofils im Reaktor sowie einer FTIR-Produktanalyse wurde implementiert, um ein Kinetikmodell für das Reaktor- und Prozessdesign abzuleiten, welches über den gesamten für Power-to-Methanol (PtM) Prozesse relevanten Parameterbereich validiert wurde. Der Vergleich zu Kinetikmodellen aus der Literatur demonstrierte deren Limitierungen und zeigte den Mehrwert des in dieser Arbeit implementierten methodischen Ansatzes sowie die Relevanz des neuen Kinetikmodells zur praktischen Umsetzung von PtM Verfahren. Darüber hinaus zeigte die Validierung des im Rahmen dieser Arbeit aufgestellten dynamischen Modells anhand eines exemplarischen Lastwechsels an der Miniplant eine hohe Übereinstimmung zwischen experimentellen Daten und Simulationsergebnissen. Somit konnte die hohe wissenschaftliche Relevanz des vorgestellten Miniplant-Validierungsansatzes für die Untersuchung des stationären und dynamischen Reaktorverhaltens von PtX Synthesen gezeigt werden

A Comprehensive Study Of Esterification Of Free Fatty Acid To Biodiesel In a Simulated Moving Bed System

Simulated Moving Bed (SMB) systems are used for separations that are difficult using traditional separation techniques. Due to the advantage of adsorption-based chromatographic separation, SMB has shown promising application in petrochemical and sugar industries, and of late, for chiral drug separations. In recent years, the concept of integration of reaction and in-situ separation in a single unit has achieved considerable attention. The simulated moving bed reactor (SMBR) couples both these unit operations bringing down the operation costs while improving the process performance, particularly for products that require mild operating conditions. However, its application has been limited due to complexity of the SMBR process. Hence, to successfully implement a reaction in SMB, a detailed understanding of the design and operating conditions of the SMBR corresponding to that particular reaction process is necessary. Biodiesel has emerged has a viable alternative to petroleum-based diesel as a renewable energy source in recent years. Biodiesel can be produced by esterification of free fatty acids (present in large amounts in waste oil) with alcohol. The reaction is equilibrium-limited, and hence, to achieve high purity, additional purification steps increases the production cost. Therefore, combining reaction and separation in SMBR to produce high purity biodiesel is quite promising in terms of bringing down the production cost. In this work, the reversible esterification reaction of oleic acid with methanol catalyzed by Amberlyst 15 resin to form methyl oleate (biodiesel) in SMBR has been investigated both theoretically and experimentally. First, the adsorption and kinetic constants were determined for the biodiesel synthesis reaction by performing experiments in a single column packed with Amberlyst 15, which acts as both adsorbent and catalyst. Thereafter, a rigorous model was used to describe the dynamic behaviour of multi-column SMBR followed by experimental verification of the mathematical model. Sensitivity analysis is done to determine robustness of the model. Finally, a few simple multi-objective optimization problems were solved that included both existing and design-stage SMBRs using non-dominated sorting genetic algorithm (NSGA). Pareto-optimal solutions were obtained in both cases, and moreover, it was found that the performance of the SMBR could be improved significantly under optimal operating conditions

Enthalpy as internal energy in plug flow reactor models: A long-lasting assumption defeated and its effects on models predictions in dynamic regime

In this paper, a general dynamic model of a pseudo-homogeneous catalytic plug flow reactor (PFR) is developed, which does not apply the traditional assumption of negligible difference between enthalpy and internal energy inside its energy balance. Such a model is then compared to a second dynamic PFR model, whose energy conservation equation identifies internal energy with enthalpy. The aim is that of quantitatively investigating the real suitability of the identification of these two thermodynamic quantities (internal energy and enthalpy) in PFR modeling problems. The Claus process is selected as a meaningful case study for the aforementioned purposes