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Show with the furnace size were selected. Application of the FDI to actual furnaces Since 1992, we have continued to introduce a combination of the FDI and the regenerative system to actual furnaces. In the basic construction as shown in Fig. 8, FDI gas nomes are set on both sides of the regenerative burner. The regenerative burner has a gas nozzle inside for holding the flame when the temperature is low. When the temperature inside the furnace rises above the ignition point, and enters a sufficiently safe range, gas will be injected from the FDI gas nozzles[2]. To date, there are more than ten of these systems, including those under construction in Japan. The use of this system in particular is increasing greatly overseas, mainly in the United States. The representative uses are for batch type forge fmnaces, reheating furnaces and aluminum melting furnaces . Tables 1 and 2 show actual results of FDI in Japan and overseas, respectively. Almost all of the furnaces have attained a NOx ratio of less than 150 ppm (02 = 0%). Generally, in most cases, the NOx emission at furnaces in normal use is smaller than that at the experimental furnace. The main reason for this is that in the actual furnace the output of the burner is held down lower than the maximum and so the calorific capacity of combustion chamber is small. In order to further widen the range of possible uses for the FDI, we have been continuously developing FDI regenerative systems using different methods. New generation of FDI systems will next be explained. 3. FDI New Generations 3.1 FFR (full-time FDI Regenerative Burner) Even though FDI has excellent results is energy savings and low NOx emissions, relatively high initial costs and complex control systems sometimes cause difficulties to expand its applications. Also conventional FDI system can be used only in the upper 9(XtC for range self-ignition, so an additional bwner system to heat up furnaces is needed. In order to overcome these problems, the FFR was developed. The construction is as shown in Fig. 9 Features of FFR Differing from the method mentioned earlier, air nozzles are arranged aroUD9 the gas nomes. Actually at Tokyo Gas, there is the history that when development of the FDI was first taken in hand a start was made with this type. The characteristics of this burner are as follows: 1) as regenerators are embedded in the inside walls of the furnace, the exterior area of the furnace is smaller, 2) as cooling air is used for holding the flame when the temperature is low, the burner can be used without any additional nozzles from the low temperature range, 3) as a direct ignition method is used and no additional nomes are used, the number of pipes is not much different from that of ordinary burners. Comparison between FFR and conventional FDI burners is shown Fig. 10. Since coolino air volume is less than 1/10 of all combustion air volume, the small flame does not increase NOx /::I emissions. In fact, the higher speed of air velocity speed provided by several nomes surrounding a gas nozzle reduces NOx emission due to more self-induced recirculation. Characteristics of FFR Two types of FFR exist. FFR-700 for 700kW and FFR-350 for 350kW combustion rates, have been developed and tested. Fig. 11 shows FFR-700's NOx characteristics with furnace temperature. Low NOx perfonnance is comparable or even better to a conventional FDI system. Fig. 12 shows characteristics of pre-heated air temperature and exhaust gas temperature. Even under 1350°C for a furnace temperature, exhaust gas temperature can be kept |
