OCR Text |
Show is 56W/m2R. The ratio of the time that the slab is on the skid beams to the time that the slab is on the walking beam is 9 to 1. The walking period is 300 seconds. So, the slab is on the skid beams for 270 seconds first, and then the slab is on the walking beam for 30 seconds. The radiative absorption coefficient is assumed to be 0.12, 0.16 and 0.20m1. The range between 0.12 to 0.20 m 1 is reasonable for the practical furnace at LNG, L P G and C O G as the fuel. Emissivity of the surfaces is assumed to be 0.8. no-firing preheating reheating soaking zone zone zone zone C JI Tw=Tg[K] Tg=1273[K] 1523[K] 1573[K] 1523[K] } 180 [min] 303[K] IE h=56[W/m2K] Ts^Tg-150[K] ^ 10000 * 10000 i>*e 10000 ><r 10000 -M 1473[K] Figure 3 Computational conditions 3.3 The temperature profile of gas in x-direction The temperature profile of gas in the lower zone is assumed in three configurations type A, B and C shown in figure 4. The horizontal axis shows the distance from left side walking beam, x. The vertical axis shows the local temperature of gas at the position x normalized with mean gas temperature of each control zone. Type A is uniform. Others are linear functions of x. The deviation to the mean temperature is ± 2.5% for type B and ± 5 % for type C. Type A is assumed in upper zone in all cases to reduce the influence of the temperature profile of gas in the upper zone to the "skid mark". 2 1.05 3 1.04 The influence of the skid position and the temperature profile of gas to the "skid mark" are investigated using the numerical procedure and the conditions. At first, the READ and the self absorption ratio are calculated. The calculation domain is divided into 8 x 50 grids for lower zone and into 3 x 50 grids E 1.03 ID Q. 1.02 % 101 * 1 <D 0.99 4 0.98 E 0.97 O 0.96 Z 0.95 Type Aflat TypeB:±2.5% ' TypeC:±5.0% 0 0.5 1 1.5 Distance [m] Figure 4 Temperature profile of gas |