The Study on the Operation Characteristics of a Rotary Kiln Incinerator and Its Application to Industrial Wastes Treatment
Date Issued
2004
Date
2004
Author(s)
Lee, Chih-Ping
DOI
zh-TW
Abstract
This study simulated the combustion field of a rotary kiln incinerator using the computational fluid dynamics code FLUENT. Rice hulls, oil sludge and waste tires represent three different kinds of industrial wastes in this study. The lower heating values of rice hulls, oil sludge and waste tires are 2767kcal/kg, 5888kcal/kg and 8318kcal/kg respectively. If the lower heating value is less than 2778kcal/kg (5000BTU/lb), then auxiliary fuel is required to keep combusting. Therefore, the amount of the auxiliary fuel should to be estimated in the case of treating rice hulls.
In this study, the combustion field was regarded as a three-dimensional flow field and the flow was supposed to be a steady state and incompressible. The finite volume method and SIMPLE (Semi-Implicit Method for Pressure Linked Equation) algorithm, which ensures correct linkage between pressure and velocity, were adopted to solve the governing equations. The standard k-ε turbulence model and the P-1 radiation model were included in the simulation of this study. Two modeling approaches, EDM and PDF, were employed for the combustion reactions respectively. The dimensions and operating conditions were determined according to an industrial rotary kiln incinerator. In situ temperature measurement form the rotary kiln incinerator had been finished and was compared with the numerical results.
The revolutionary speed of the rotary kiln incinerator was controlled at 0.2 or 0.5 or 0.8rpm. The excess air was supplied with 0 or 50 or 100 or 150% and the excess air ratio of the rotary kiln to the secondary chamber was 1 to 4. In the case of treating rice hulls, the combustion efficiency reached to 99.3% while the revolutionary speed was set at 0.5rpm and excess air was supplied with 100 or 150%. In the case of treating oil sludge, the combustion efficiency reached to 99.7% while the revolutionary speed was set at 0.5rpm but wasn’t obviously affected by changing the amount of excess air. In the case of treating waste tires, this study predicted that the reasonable range of temperature is 1088~1142K while solid wastes with higher heating value are treated in the rotary kiln incinerator under the designed operating conditions.
The difference between a premixed flame and a diffusion flame was also discussed in this study. In the simulation of the premixed flame, the average temperature dropped as the supply of excess air increased. In the simulation of the diffusion flame, the average temperature rose as the supply of excess air increased. The reason is that the excess air absorbed the heat energy in the premixed flame but helped for the mixture of the fuel and oxidant in the diffusion flame.
In the comparison between the EDM and the PDF combustion model, the PDF combustion model is more proper than the EDM combustion model in the description of a flame. In the EDM modeling, the top temperature didn’t happen in the position which had the most reaction rate; hence the simulation results don’t coincide with physical phenomenon. In the PDF modeling, the top temperature happened near the position which had the stoichiometric mixture fraction ; hence the simulation results coincide with physical phenomenon.
Subjects
機率密度函數燃燒模式
旋轉窯焚化爐
廢輪胎
渦流消散燃燒模式
計算流體力學
油污泥
稻殼
waste tires
Eddy Dissipation Model (EDM)
Probability Density Function model (PDF model)
rice hulls
Computational Fluid Dynamics (CFD)
Rotary kiln incinerator
oil sludge
Type
thesis
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