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Towards Optimization of Radial Multi-Zone Dryer (RMD)
No full textConventional spray dryers are very energy-demanding and occupy a significant amount of floor space. Also, their energy efficiency is quite low. To overcome these issues, a new spray dryer should be developed and optimized. Besides this, conventional dryers always have a vortex separator to segregate the solid phase.This thesis presents details of a novel spray drying technology. Currently, the application is limited to milk drying. However, this technique could be extended to other products suitable for spray drying.In the conventional configuration of milk drying devices, the drying medium and the milk droplets enter the drying chamber from the same direction. This co-current drying technique is practiced along with a relatively low drying medium temperature to prevent the milk particles from overheating. In the spray drying technology, as presented in this work, the milk droplets and the drying medium enter the drying chamber in the counter-current configuration, which increases the slip velocity and thus enhances heat transfer. This also improves the throughput of the dryer; this is known as process intensification.In this case, the drying air temperature is relatively high. To prevent the milk from burning at this high temperature, it is ensured that the residence time of milk droplets in the drying zone is in order of a few milliseconds. After that, the dried product is immediately evacuated to the cold zones. Multiple tangential inlets create a vortex flow to extract the dried milk powder. This dryer configuration is called Radial Multizone Dryer (RMD).To optimize the design of the Radial Multizone Dryer and to achieve optimum quality of the product particles, CFD tools are used. The quality of the products depends upon the final temperature of the product, hence the heat transfer within the reactor has to be optimized that the droplets gain heat just enough for evaporation, and do not overheat. Multi-phase calculations are performed to capture the flow field of the drying medium, the trajectories, and the evaporation of the milk droplets. Simulation results show that the capacity of a pilot-scale model is 108[kg/hr]. Based on the studied conditions, the dryer’s performance is optimized when the Sauter mean diameter of the spray droplets is between 40 to 60 μm. This leads to the drying and evaporation of most of the products
Design of a redimensionable and economic flexure-based 6-DOF manipulator demonstrator
No full textFor their ever increasing operation tolerances in multiple degrees of freedom, collaborating company IMS resorts to industrially available high-end parallel manipulators. These parallel manipulators exhibit several performance benefits over their serial counterparts in terms of overall stiffness, positioning accuracy and payload-to-weight ratio. Parallel manipulators generally outperform their serial counterparts when performing precision based micro-assembly tasks, as the layout enables for higher load carrying capacity and superior stiffness properties. Higher positioning accuracy can be achieved as a result of non-accumulating errors from serial linkages combined with a general stiffer geometry.Over the last years, several performance issues have come to light during continuous operation in industrial environments. Especially regarding fast and short stroke positioning applications, durability and lifetime of the current manipulator seem limited as a result of mechanical wear. Moreover, with ever increasing throughput and tighter processing times, the dynamicperformance aspects of the manipulator are starting to become a holdup in the development of the automation platform.Industrial available manipulators commonly consist of conventional mechanical joints (e.g. universal- or ball-and-socket joint). These joints often rely on the principle of contact mechanics in which wear contributes to loss of accuracy and lifetime. Flexure elements become ever more apparent in the field of precision applications. These elements provide relative motion between two bodies by means of elastic deformation. This operating principle allows for high-accurate and predictable behavior. In comparison to conventional joints, numerous advantages are provided in terms of backlash-, wear- and contamination-free operation, limiting overall hysteresis. However, challenges present itself in the form of limited range of motion resulting from stress limits, decrease in support stiffness for larger deflections and shift of the rotational center (pivot shift).State-of-the-art 6-DOF parallel manipulators in precision positioning applications are presented. This overview mainly focuses on recent developments in combining parallel manipulators and flexure elements. Furthermore, an overview is presented considering the individual components which make up a 6-DOF parallel manipulator and elaborates on the principles, advantages and limitations. Based on the individual components, several concepts are composed, compared and discussed with the stakeholders .This thesis describes the design process of a flexure-based parallel manipulator demonstrator. The demonstrator incorporates a novel principle combining actuation suspension and kinematic joint functionality. The general design focuses on minimized joint rotations for optimal performance of the implemented flexure joints, avoiding the drawbacks presented above.The demonstrator is identified according to system identification procedures to better and effectively control the system. Several tests are performed to observe the performance of the manipulator. Bi-directional repeatability testing is performed using close-range capacitive sensors, resulting in a bi-directional repeatability of 1.3 μm can be achieved without payload,and repeatability of 0.75 μm with 15 N payload on the end-effector.Moreover, general setpoint measurements show an operational velocity >80 mm/s and acceleration of 500 mm/s. The demonstrator possesses a footprint of 295 mm combined with a height of 250 mm. This design demonstrates that the design choices for using limited stroke leaf spring mechanisms in a parallel manipulator can contribute to achieving a cost-effective design with high repeatability
Tar Cracking Reactor Design for Biomass Gasification Processes
No full textIn this thesis, experimental studies on biomass tars thermal cracking, in the temperature range of 1000 – 1200 °C and gas residence time of 4– 10 s, were carried out in three tar cracking reactor configurations, namely continuously stirred tank reactor (CSTR), packed bed reactor and plug flow reactor (PFR), to investigate the feasibility of reducing tar concentration below 150 mg/Nm3 after tar cracking. Tars were sampled with SPA methods and analyzed in GC/MS for quantification and characterization based on the number of aromatic rings in the tar components.It was observed that in CSTR configuration, the high degree of gas axial dispersion was significantly impacting the tar cracking extent, which was observed to be as high as 1100 mg/Nm3 at 1200°C and residence time of 8.3 s. Using alumina packing material with average diameter of 6 mm, lower gas axial dispersion was achieved and tar concentration was measured to be 575 mg/Nm3 at 1200 °C and shorter gas residence time (4.1 s). In PFR configuration from an initial tar concentration of 8500 mg/Nm3, tar concentration was measured to be 100 mg/Nm3 at 1160 °C and gas residence time of 8.1 s. Increasing the initial tar concentration to 20000 mg/Nm3, similar results were obtained at 1150°C. It was also observed that the main products of tar cracking were carbon, hydrogen gas, CO and CO2. Furthermore, the carbon formed after tar cracking significantly decreased at 1160°C, promoting formation of carbon monoxide, carbon dioxide and hydrogen gas. From the experiments, the apparent activation energy for biomass tar cracking was calculated to be 239 kJ/mol. A kinetic model based on the apparent kinetics of the lumped components and degree of axial dispersion based on the dimensionless Bodenstein (Bo) number, was developed to design a tar cracking unit for a 4 ton/h biomass gasification process. <br/
