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This research investigated the combustion behavior of pulverized biomass under different degrees of severity during a torrefaction processes. The fuel studied in this work was natural rubber trees and the torrefaction process varied from 0.4 to 1 solid yield. The fuel was ground using a cutting mill with a 1 mm sieve. Torrefied biomass from the grinding process had average particle sizes of 216 to 394 µm. The combustion behavior was studied using Computational Fluid Dynamics (CFD) through numerical modeling and simulation of an industrial pulverized biomass furnace with a thermal capacity of 1 MW. Heat transfer, fluid flow, reaction kinetics, species transport and discrete phase particle movement were done using commercial CFD software, Ansys Fluent, to study the conversion of chemical energy into thermal energy and emissions released by combustion. Simulation results showed that torrefied biomass provided a higher temperature than raw biomass (25.9%) because of better hydrophobic properties and lower composition of hydrogen and oxygen. Combustion of torrefied biomass tends to have lower carbon monoxide emissions, whereas nitrogen dioxide and carbon dioxide emissions tend to increase due to more intense combustion compared to raw biomass. Carbon monoxide emissions decreased by up to 86.5%. Nitrogen dioxide and carbon dioxide emissions increased by a maximum of 74.8% and 34.7%, respectively. Sulfur dioxide emissions decreased by up to 26.5% since the sulfur components in the fuel were released during the torrefaction process. [ABSTRACT FROM AUTHOR]

Inertial Electrostatic Confinement (IEC) fusion reactors are fusion-powered devices that produce energy and radioactivity using electric fields to confine ions and induce particle collisions. The primary objective of this research is to simulate a multi-grid IEC device to evaluate the neutron production rate (NPR) using XOOPIC software and to study the variables affecting neutron production within the IEC, including the voltage supplied to grid, the ion currents supplied to the system, and the radius of the innermost cathode grid. The scope of this study includes simulation of an IEC device with 1 mm grid diameter, 25 cm exterior grid radius as anode, a continuous injection of deuterium ions into the system, and a high vacuum of the background gas. From the simulation results, it was found that supplying highly negative voltage to the cathode grid affected the depth of potential well and ion confinement. The neutron production rate tended to increase linearly as more negative potential was applied to the grid. The IEC device was able to increase the neutron production rate from 1.73 x 104 n/s to 1.41 x 105 n/s when the supply voltage to the cathode grid was reduced from -200 kV to -500 kV. Increasing the depth of the potential well results in greater ion confinement in the core region of the IEC device, where neutrons are the most generated because the kinetic energy of the ions is at their highest, thus maximizing the probability of fusion reactions. By modifying the radius of the cathode grid, the neutron production rate was increased from 1.21 x 105 n/s to 2.19 x 105 n/s when the cathode radius was increased from 50 mm to 80 mm. The effect of increasing fusion reactions in the core region is the same as adding a more negative potential to the cathode grid. However, the difference is that it does not increase the ion density of the core. Rather, it increases the extent to which the reaction can take place. Increasing ion current affected the ion density within the system. The IEC device was able to increase the neutron production rate from 1.38 x 105 n/s to 1.96 x 105 n/s when the ion current was increased from 0.1 A to 2 A. This is due to increased ion density in the system, which increases the possibility of ions colliding and causing fusion reactions. [ABSTRACT FROM AUTHOR]

In this study, a magnetohydrodynamics simulation of a plasma propulsion system for small satellites was studied and modelled using COMSOL Multiphysics and SOLIDWORKS software. This research aimed to study the operating process of a plasma propulsion system for small satellites. A PPS-1350 Hall Thruster with a xenon propellant was used as the prototype model. The propulsion system injects electrically neutral xenon gas through the propellant feeder (anode) into the discharge chamber to form positively charged xenon plasma and generate thrust. In this study, a plasma propulsion system model was simulated. This study contained 4 modules consisting of electrostatics, magnetic fields, fluid flow and plasma modules. The results were validated by comparing them with PPS-1350 experimental data. The study found that the simulation results tend to be lower than those obtained in the experiments. With a xenon mass flow rate of 2.31-3.7 mg/s, the thrust was found to be around 41-66 mN. When compared to the experimental results at the same mass flow rate, thrust was found to be around 46-80 mN. Overall, the deviation between the simulation and actual operating data were found to be within 20% despite some model simplifications and limited access to actual operating data and internal dimensions. Given that the prediction is on the conservative side, it can still be said that the simulation model of the PPS-1350 Hall Thruster is reasonably accurate and acceptable. The results of this study will be used as knowledge for further analysis of plasma propulsion systems. [ABSTRACT FROM AUTHOR]

Nowadays, the utilization of pulverized coal is limited only in large-scale enterprises in Thailand as the knowledge of pulverized coal burner technology in small-scale burners is not widely known and studied. Therefore, it is important to keep on research and development efforts in order to further propel the pulverized coal technology into widespread use because it has many attractive features such as lower fuel cost, reduced pollution, and better combustion efficiency. The objective of this research is to numerically model and analyze the combustion characteristics of pulverized coal in an axisymmetric 2-D combustion chamber model by using CFD. For experimental validation, this work focuses on the following simulation conditions: coal particle diameter smaller than 74 µm, primary air mass fraction of 25%, secondary air mass fraction of 65%, and tertiary air mass fraction of 10%. The pulverized coal is sprayed into the burner along with the primary air and mixed with the secondary and the tertiary air in the burner due to the effect of the secondary air vortex flow. The governing equations for the turbulent flow analysis in the combustion chamber is the Turbulence Model Standard K-E. For particle motion analysis, including devolatilization and heterogeneous combustion is analyzed by Discrete Particle Model (DPM). Homogeneous combustion is analyzed by using Eddy-Dissipation model. It is assumed that the concentration of the chemical reaction is fast kinetics, thus, the reaction rate is therefore dominated by the turbulent flow concentration. In addition, the Discrete Ordinates method is used to model thermal radiation phenomena. The flow behavior of fuel, air, and the combustion gases as well as the combustion reaction are modeled and analyzed the ANSYS FLUENT program. In this study, the experimental results of internal burner temperature at 300 kW were used to validate the simulation results from CFD. The simulation results showed that the flames in the burner are spiraled out before converging into the flame lines in the main combustion chamber. The maximum temperature inside the main combustion chamber was 1637 °C and the maximum temperature at the burner inside the pre-combustion chamber was 1370 °C, which was slightly higher than the results from experiment at 1325 °C. The first-law combustion efficiency of this burner was found to be 80% primarily due to incomplete combustion, energy loss from excess air, and unburned coal particles leaving the combustion chamber. The results of this study will be used as a body of knowledge for further analysis of combustion characteristics of pulverized coal and for the improvement of pulverized coal burners in the future. [ABSTRACT FROM AUTHOR]