| OCR Text |
Show concentration distribution and are backed with numerical results. From the above mentioned, absolute value of NO has many uncertain points, but tendency of NO value agrees with measured results,then we can use calculation results to understand tendency and predict NOx value. TECHNIQUE FOR MAKING THE FURNACE TEMPERATURE UNIFORM As related to technique for making the furnace temperature uniform we have many datas which contain in-furnace fuel distributed combustion, etc. We show the representative example in Fig. 15 tested in 1mX1mX3.8m testing furnace, fuel : 13A city gas, combustion capacity : 30X104 Kcal/hr (348.9KW), air ratio : 1.2, preheated air temperature : 1,000'C. We tested in three types of fuel and air injection method, namely center gun type, eccentric gun type and counter flow type which is called the extreme distributed combustion. It shows three dimensional time averaged temperature distributions in which smaller temperature difference has been observed compared with conventional combustion. (C) shows uniform temperature limit in future and has ±20'C temperature difference. From the large scale experimental datas temperature difference is ±25c in the center of two burners or in the center between burner and furnace wall, and is ±50'C in all furnace on the burner axis, and near by furnace wall. TECHNIQUE FOR RAISING THE FURNACE TEMPERATURE WHICH MEANS HIGH EXERGY HEAT TRANSFER A small test furnace, 1m length, 1m width and 1m height for testing basic heat transfer characteristics was made. Six test pieces, 100mmx642mmX6mm/piece separated by 10mm from each other were placed in the furnace bed. The results are shown in Fig.16. This shows the comparison of conventional combustion and high temperature air combustion on the average heat flux under the condition in which the average temperature of the heated plates was held a constant 35c. As the value of 0CQ we get 0.75-0.85 in high temperature air combustion compared with 0.7-0.8 in conventional combustion shown in Fig.17.1, Fig.17.2, and these datas were not changed by fuel variety, COG and LPG, and burner types. It is not cleared yet how much the increase of 0 C G value is influenced by gaseous emissivity £ and convection heat transfer. From these datas it is recognized that high temperature air combustion improved raising the average furnace temperature and promoted homogeneity of in-furnace temperature distribution. PRACTICAL PLANT DESIGN We have already designed practical plants which have main specification included high efficient techniques for reheating furnace, heat treatment furnace and aluminum melting furnace. Here we show the example of reheating furnace trial design results. We set the general design conditions in slab reheating furnace and billet reheating furnace shown in Table 4. At first, supposing that we adopt regenerative combustion system we aim at simultaneous achievement of saving energy, downsizing and low NOx by use of project development results. Fig.18 shows designing flow for high performance reheating furnace. There is no difference from conventional designing method, however, we utilize many variety of data bases which contain furnace height, 0co, combustion property in high temperature air combustion and furnace control, etc. These datas are so different from conventional datas of reheating furnace that we can design and produce different new image. Fig.19 shows technological key points in high performance industrial furnace design. - 7 - |
