Atilla Biyikoglu

A Two-Dimensional Mathematical Modeling of Combustion Chambers of Coal-Fired Boilers with a Fixed Bed

Steady-state combustion has been investigated for both the simulation of reactive turbulent flow within the combustion chamber and a fixed bed of a small-scale coalfired boiler. For this purpose, the one-dimensional code, CLAYER (Biyiko < lu 1998), developed for determining the thermo-chemical field of coal combustion in a fixed bed, the zero-dimensional code, CREK (Pratt and Wormek, 1976), used in determining the thermo-chemical field of reactive turbulent flows, and the twodimensional code, TEACH (Durst and Loy, 1984), used in determining the hydro-dynamical flow field in the combustion chamber, were combined and modified. The unreacted shrinking core model (Ishida and Wen, 1971) was used for coal combustion. The turbulent reactive flow in the combustion chamber is analyzed using k– k turbulence, four-flux radiation, and combustion models, including chemical equilibrium and kinetics calculations. The temperature and gas emission distributions in the fixed bed and combustion chamber are predicted for coal feeding rates 14, 18, and 21 kg/h and for coal types Imported, Soma, and Tunçbilek lignites. The comparison of the existing experimental data with the emission calculations at the exit of the combustion chamber has resulted in an agreement with an acceptable degree.

A parametric study on coal gasification for the production of syngas

In this parametric study, the effects of coal and oxidiser type, air-to-fuel ratio, steam-to-fuel ratio, reactor temperature, and pressure on H2 and CO amounts at the gasifier output, H2/CO, and higher heating value of the syngas produced have been calculated using a coal gasification model. Model simulations have been performed to identify the optimum values which are assumed to be 100 % for both cold gas efficiency and carbon conversion efficiency in the gasification process. From this study, it may be observed that the moisture content of the coal type is of crucial importance for the air gasification process; the O2 content of similar coals (taking into consideration the moisture and H2 content) is of significant importance for the air gasification process. When compared with air gasification, air-steam gasification becomes a more effective coal gasification method. The optimum working condition for air-steam gasification is to carry out the process at one atmosphere. High gasifier temperatures are not needed for the air-steam gasification of coal.

Design and Optimization of a Low Temperature Organic Rankine Cycle and Turbine

In this study, low temperature Organic Rankine Cycle (ORC) systems with single and two-stage turbine are proposed for the production of electricity. The refrigerant R-134a is selected as working fluid based on peak temperature of the cycle for solar and geothermal applications. The design criteria of ORC system is introduced and explained in detail. The radial inflow turbine is selected to satisfy the design requirements. The cycle performance is taken as a key point in the design criteria. The system performance map is constructed based on both velocity triangles and approximate efficiency of turbine. The procedures for turbine and cycle design are introduced in detail. The components of cycle and turbine are modeled using baseline correlations via real gas tables and macros created on Excel for the refrigerant, R134a. Finally, the turbine geometry is optimized to attain maximum turbine efficiency via MATLAB optimization toolbox.Copyright

Optimization of a sensible heat cascade energy storage by lumped model

Abstract In this study, the concept of exergy is used to analyze and optimize a sensible heat cascade thermal energy storage system which is developed for storing exergy and later using it efficiently. The system is composed of a liquid–gas heat exchanger, an electrical heater, an insulated vessel, a large water bath as a storage liquid and air as the system gas. The units that should be improved are determined by evaluating the irreversibilities caused by viscous losses in the heat exchanger, heat transfer occurring in the storage, electrical heating, removal processes and mixing of the hot gases at the exit of the storage process with ambient air. First and second law efficiencies and irreversibility sources of the system are compared with the thermal energy storage systems having a unique energy resource. Removing time, optimum storage time and the number of transfer units of the heat exchanger are also determined for different operating conditions by minimizing the irreversibilities in the system.

Design of a Nozzle for the Production of Metal Powder via Gas Atomization

In this study, a nozzle has been designed in order to produce metal powder via the method of gas atomization. The design has been performed in two stages. At the first stage of design, the size and geometry of the nozzle have been determined using empirical relations as a pre-design. At the second stage, a parametrical analysis has been done using a CFD code. As a parametrical study, the effects of nozzle exit angle, throat distance and protrusion length on pressure and flow velocity at the nozzle exit are investigated with the numerical model. Appropriate values for the investigated parameters have been determined to get maximum pressure in vacuum condition at the tip of the melt. The nozzle has been designed based on the determined parameters.Copyright

Development of a Swirl Nozzle for Powder Technology

In this study, a gas atomization nozzle for metal powder production has been designed and modeled numerically. The design has been performed in two stages. At the first stage of the design, the size and geometry of the nozzle have been developed to obtain circulated flow through the nozzle as a pre-design. At the second stage, a parametrical analysis has been done using a CFD code. The geometry of the nozzle has been changed and the effect of geometric parameters was determined to find out the more efficient nozzle design parameters. Gas behavior at the nozzle exit and effect of the gas on the melt delivery tube tip has been investigated. Appropriate values for the investigated parameters have been determined to get maximum pressure in vacuum condition at the tip of the melt. The pressure observed at the melt delivery tube was compared with the experimental melt tip pressure data. These results suggest that the CFD solutions can be used in the design of the nozzle. Thus, the lower cost and shorter time would be possible to develop highly efficient nozzle geometry.Copyright

Simulation of Combustion in a Coal-Fired Boiler with a Fixed Bed

In this study, steady-state combustion in boilers with a fixed bed has been investigated. The solution method and the discretization of the governing equations of two-dimensional turbulent reactive flow in the combustion chamber and one-dimensional coal combustion in the fixed bed are explained. Control volume and finite difference methods are used in the discretization of the equations in the combustion chamber and in the fixed bed, respectively. Kinetic calculations are employed in the solution of turbulent reactive flow equations in the combustion chamber. The combustion of coal particles in the fixed bed is ruled by the reaction-controlled mechanism. The distributions of temperature and some of the chemical species through the combustion chamber and the fixed bed are presented. Also, the variation of coal particle size with the fixed bed height is given.