Fakultät für Chemische Technologie und Wirtschaft
Refine
Year of publication
Document Type
- Contribution to a Periodical (27)
- Conference Publication (12)
- Article (peer reviewed) (8)
- Part of a Book (6)
- conferenceposter (6)
- Other (3)
- Book (2)
- conferenceslides (2)
- Report (2)
Language
- English (50)
- German (17)
- Multiple languages (1)
Is part of the Bibliography
- no (68)
Keywords
Institute
Carbon Capture is an important technology for the reduction of CO2 emissions in industrial processes. An example is cement production, which produces CO2 as a reaction product. A common separation process is amine absorption, which has a high energy demand during regeneration. The binding of amine on a packed bed would strongly reduce the energy demand.
The formulation of the carrier was tested by extrusion, tableting or granulation leading to longish cylinders, flat cylinders or spheres. The inner surface was determined by N2 adsorption in BET. The formulation step strongly influences the porosity, stability and surface. Stability of tablets showed to have a maximum at a medium compacting pressure. The surface showed to be highest at lower compression, which was to be expected. The surface is highly dependent on the agglomeration mechanism, which is visible in SEM. Different approaches are under investigation to determine diffusion coefficients from BET raw data of CO2 adsorption tests.
To simulate the adsorption process, the packed bed was created using the discrete element method, exported, shrinkwrapped and meshed. The process leads to a geometry, which is smoother than the real packed bed, but creates a realistic, stochastically settled packed bed. The adsorbent zone is represented as a porous gas zone. The flow through the packed bed is simulated by Computational Fluid Dynamics in Ansys Fluent. The diffusion through the pores is modeled based on a diffusion coefficient.
The adsorption is modeled by species adsorption of CO2 in a user defined function managing user defined memory in the cells until reaching a capacity limit. This approach reproduces the capture of CO2 first to the surface and later - limited by diffusion - to the inner region, reproducing breakthrough curves. The size is limited to several g of adsorbent due to the small local mesh size.
Carbon capture ist ein Verfahren zur Abtrennung von CO2 aus Industrieabgasen, wie sie z.B. in der Zementproduktion anfallen. Es gibt verschiedene Ansätze für carbon capture Verfahren, dazu gehören die Amin-Wäsche, Membranverfahren oder „amine-grafted“ Feststoffe. Das binden von Aminen auf einem Feststoff verspricht Energieeinsparungen gegenüber der Amin-Wäsche, die sehr energieintensiv ist. In dieser Arbeit wird näher auf die Formulierung geeigneter Grundkörper, basierend auf pyrogener Kieselsäure, für das „amine-grafting“ eingegangen. Dabei wird zum einen die Bruchstabilität der Grundkörper betrachtet, welche wichtig ist, um eine möglichst hohe Langlebigkeit während wechselnden Adsorptions- und Desorptionszyklen sicherzustellen. Zum anderen wird die Porosität über die BET-Oberfläche bestimmt, von der die Adsorptionskinetik sowie die CO2 Kapazität, die aufgenommen wird, abhängt. Das verwendete Ausgangsmaterial ist pyrogene Kieselsäure im nm Größenbereich. Diese wurde im ersten Schritt mit Wasser in einem Labor-Intensivmischer voragglomeriert, um die Partikelgröße von ca. 2 nm auf ca. 2 µm zu vergrößern. Anschließend wurde dieses Material gesiebt und tablettiert. Die Tabletten wurden danach getrocknet und gesintert um deren Stabilität zu erhöhen. Die Bruchkraft wurde mit einem Texture Analyzer gemessen und die Oberfläche wurde über die Stickstoffadsorption in einem BET-System gemessen.
Der Einfluss verschiedener Parameter auf die Bruchfestigkeit und Oberfläche der Tabletten wurde untersucht. Die verwendeten Tabletten haben einen Durchmesser von 4 mm und eine Dicke von 1,6 mm bis zu 2,6 mm bei einer Fülltiefe der Matrize von 10 mm. Die Kompression wirkt sich bei konstanter Masse auf die Tablettendicke aus. Der Wasseranteil in der Voragglomeration, das Trocknungsverfahren und die Temperatur und Zeit im anschließenden Sintervorgang wurden variiert. Das voragglomerierte Material wurde klassiert und die unterschiedlichen Fraktionen auf Tablettierbarkeit getestet. Große Partikel über 0,8 mm wurden verworfen, da sie die Tablettenpresse verstopfen. Nach dem Trocknen und Sintern hatten die Tabletten ein Gewicht von 12,15 ± 1,06 mg. Der Wassergehalt des voragglomerierten Materials hat ein Minimum bei der Fraktion 0,125 bis 0,25 mm, das im Versuch die Tabletten mit der höchsten Bruchkraft erzeugte. Ein höherer Wassergehalt in den voragglomerierten Partikeln führt zu einer höheren Dichte von den getrockneten und gesinterten Tabletten. Eine weitere Versuchsreihe mit unterschiedlichen Wassermengen zeigte, dass das Tablettengewicht nach dem trocknen und sintern proportional zum Wasseranteil ansteigt, wenn dieser für die Voragglomeration erhöht wird. Dies legt nahe, dass das Wasser einen Einfluss auf die Anordnung der Silica Partikel im Agglomerat hat und ein dichtes packen begünstigt. Nach dem Trocknen der Tabletten hinterlässt dieses Wasser eine Poröse Struktur, die die BET-Oberfläche vergrößert, sich jedoch negativ auf die Tablettenbruchkraft auswirkt.
Coating is an important process in the chemical, food and pharmaceutical industry for applying flow agents, adding colorants, applying a protective layer against humidity, for the selective release of the contents or applying a flavor layer to goods. This is usually done in a fluidized bed (Wurster coater) or a
coating drum. Pneumatic conveying systems are usually already installed for conveying particulate media, for example between process steps or the filling. In pneumatic conveying, the fluidized state of the Wurster Coater is already present. The basic idea of the current project is to implement the coating step directly in the pneumatic conveying system.
Experimental approach:
The coating tests were carried out using a vacuum system. For this purpose, various coating chambers with different nozzle arrangements were printed using a rapid prototyper. The nozzles used were also printed in-house and adapted to the requirements.
Particles with a diameter of 3 mm were used for the tests and sprayed with a common protective coating as well as blue dye. The particles were heated to 120°C in order to supply the necessary heat to evaporate the solvent.
Images of the coated particles were taken and evaluated with ImageJ to analyze the coating result. The amount of coating delivered changes the coating layer linearly as expected. The tests showed that it is possible to coat particles during pneumatic conveying. A comparison with coating in a Wurster coater showed that the amount of overspray is higher than in a Wurster coater, leading a lower efficiency in the coating step in pneumatic conveying though.
A novel multi-purpose mixer was set up, which allows the change of the blade angle during the process and provides aflow field with respect to the needs of the mixing task. It features as well as a coaxial stirrer for highly viscous liquids andhence has three degrees of freedom. The stirrer considers the integration and validation of an optimization strategy forthe autonomous identification of an optimum operating point based on automated tests. The validation was conducted ina mixing process with several process input parameters, which is commonly used in industrial applications. The powerdraw of the main stirrer was used as a optimization parameter, representing the power used for dispersing. The speedand direction of the main and secondary stirrers, respectively, as well as the angle of the stirrer blades, were used as inputprocesses. The proposed control scheme automatically identifies and corrects drops in energy dissipation rates.
In this study, a novel hydrocyclone design was developed featuring a variable inlet geometry, which enables adjustment of the inlet area during operation. This allows control over the flow velocity within the cyclone, thereby maintaining a constant tangential velocity despite changes in volumetric flow rate. The prototype demonstrated a constant separation efficiency across a volumetric flow range spanning a factor of two between its minimum and maximum capacities. Two control strategies were investigated: operation at constant pressure drop and operation at constant inlet velocity, both under varying flow rates and inlet geometries. To initially examine the influence of key parameters, hydrocyclones with fixed geometries were fabricated using rapid prototyping and employed in experimental trials. These findings informed the subsequent development and construction of a dynamically adaptive steel prototype capable of dynamic geometrically adjustment.
Mixing plays a crucial role in industry, for e.g., fine and petrochemicals, food, pharmaceuticals, and mineral processing. The selection of the stirrer is based on the desired flow pattern and the rheological properties of the material being processed. A change in the mixing task or a significant shift in material properties during the process can lead to decreased efficiency, longer mixing times, or poorer mixing quality. To address the need for handling various tasks across a wide range of applications with the same mixer, a multi-purpose mixer with adjustable tools was developed. It consists of a coaxial stirrer with an inner and an outer stirrer. The blades of the inner stirrer can be changed in inclination during the process. This allows different tasks, such as dispersion, aeration, and suspension, to be performed efficiently in succession without the need for tool changes. Additionally, the process parameters can be dynamically changed to compensate for changes in the process. Energy input into the fluid serves as a key parameter to quantify the quality of a dispersion process. The three independent actuators can be used to achieve the best energy input. To identify the optimal settings, a control algorithm called the "automated design of experience" was developed. This algorithm adjusts the speed of the main and coaxial stirrers and the blade angle in a sequential manner, evaluating whether these changes lead to improved or worsened energy input. It is hence possible to determine optimum mixing parameters in an automated way.
Motivation:
Hydrocyclones are designed for a specific operating point but react badly to a change in operating conditions. Reducing the flow rate results in lower centrifugal forces and hence separation efficiency. Increasing the flow rate increases the pressure loss, while the separation efficiency suffers from increased turbulence. It is also not possible to react to modifications of the material or liquid phase to be separated. The aim of the present development is to create a cyclone that can react to variable operating parameters to keep the separation efficiency at a high level.
Material & Methodology:
Good separation in cyclones requires a stable formation of the secondary vortex, which can be characterized by high tangential flow velocity (Schubert 2003). By implementing a variable cross-section in the inlet channel, the feeding velocity into the cyclone can be kept constant at changing flow rates to maintain the secondary vortex and keep comparable separation efficiency and pressure loss. An inline turbidity measurement at the upstream outlet can be used to monitor dynamically the separation efficiency. The variable cross-section area can be controlled depending on the fluctuating volume flow or on a specific outlet concentration based on the measured turbidity. Experiments showed that operating the system at a constant pressure loss improves the separation efficiency despite a reduction of the volume flow. Efficient separation at different or even fluctuating volume flow is hence possible.
Wasserstoff aus erneuerbaren Quellen ist ein zentraler Baustein zur Erreichung der Klimaziele, wobei die Wasserelektrolyse eine Schlüsseltechnologie darstellt. Dabei entsteht Sauerstoff als Koppelprodukt, das bereits in verschiedenen Anwendungen genutzt wird. Diese Studie bewertet das techno-ökonomische Potenzial der Nutzung von Elektrolysesauerstoff für die Synthese von Ethylenoxid (EO) und Vinylacetatmonomer (VAM). Abhängig vom Strompreis können die Produktionskosten für Wasserstoff um6–12 % gesenkt werden, wenn Sauerstoff zu Marktpreisen verkauft wird. Die Herstellungskosten von EO und VAM können um bis zu 4,5 % reduziert werden, sofern Sauerstoff kostenfrei bereitgestellt wird. Die Integration in industrielle Cluster ermöglicht Synergien für die Nutzung von Wasserstoff und Sauerstoff.
