OCR Text |
Show constant of 15 N m /h in most of simulations. Exit t t t The simulation in this study was performed using the F L U E N T code. A P D F model was adopted to simulate the turbulent diffusion combustion using the equilibrium chemistry method for the chemical reactions [8]. Radiation heat transfer was modeled by the discrete transfer method [9]. Since the combustion chamber walls were formed by heat-insulating materials, the heat flux on the walls were assumed to be zero. In fact, the chamber wall was not exactly heat-insulting, therefore the predicted temperature in this study is higher than the measured temperature. The soot formation was also simulated in this study using a two-step Tesner model [10, 11], and the effect of soot particles on radiation was also considered. In the N O x module coupled in F L U E N T code, both thermal- N O x and prompt-NOx were calculated based on the selected reaction models. A rectangle grid system was used for the computational domain, with 47x60x18 grid points in three directions respectively. In the direction of depth, only a half of the chamber was calculated because of the symmetry. r~=====zJ Figure 2 Simulated domain of furnace 3. RESULTS AND DISCUSSION 3.1 Overview on combustion and NOx emission with highly preheated and diluted air In order to have an overview on the combustion characteristics and N O x emission in the regenerative furnace with highly preheated and diluted air, numerical simulations were firstly performed under three cases of operation conditions. The first case simulated the combustion with normal temperature fresh air (323 K, 21 vol% 02), the second with high temperature fresh air (1223 K, 21 vol% 0 2), and the third with high temperature diluted (by nitrogen) air (1223 K, 4 vol% 02). |