OCR Text |
Show 6 4-4 Characteristics of CO As shown in the results of the elementary experiment, when firing rate was reduced in a fixed amount of gas turbine exhaust, CO was generated at T.D.R. of 1:3 to 1:4. In order to analyze the CO generating mechanism and to evaluate the burner, we performed simulation of heat transfer in the furnace. The three-dimensional steady state hot model calculation shown in Table 3 was applied. Fig. 17 shows the results of simulation conducted to get the distribution of CH4 concentration, temperature, and 02 concentration at the burner load of 100%, the firing rate of 2,800 kW and the burner load of 25%. The Y-Z coordinates in Fig. 17-1) correspond to the burner tile surface, and the length is considered to be the test furnace inside diameter, 1100 mm. The burner is installed in the center. Natural gas is spouted from the center, and gas turbine exhaust for firing is spouted from the periphery of the center. The X coordinate axis represents the lengthwise direction of test furnace, i. e. the flowing direction of firing exhaust gas. The figure shows the distribution of CH4 concentration in the horizontal direction and the flow velocity in the vertical direction. Fig. 17-1) and -2) show the distribution of CH4 concentration. Generally, the visible flame length is the part having a CH4 concentration of 1% or more. The length of the part having a CH4 concentration of 1% or more in the simulation is 2.6 m at the burner load of 100% and 0.25 m at the burner load of 25%. These values agree sell with the actually measured flame length 2.1 m and 0.4 m. Therefore, it is considered that the firing mechanism can be analyzed by this simulation. Fig. 17-3) and - 4) show the distribution of temperature, and Fig. 17-5) and -6) show the distribution of O? concentration. Fig. 19-7) and -8) show the sectional O? distribution of flow. In the area of 1 m the burner the flow is faster and 0 2 is consumed more quickly at the burner load of 100% than at the burner load of 25%. The distribution of temperature is found more than 1500 K for the whole furnace. This means that complete firing is performed. On the other hand, at the burner load of 25%, 02 is consumed in the area of 0.5 m from the burner surface, and the area of temperature exceeding 2000 K is narrow, and the area near 1500 K is large. As the flow of exhaust gas at 500°C is faster near the flame, it is considered that the flame is cooled dawn at its outside by the turbine exhaust gas, and CO is generated at a low load. Its considered that method of this solution is to reduce the gas turbine exhaust gas flow velocity, and to make the flame diameter small by reducing gas nozzle angle. 5. CONCLUSION We succeeded in the development of supplementary firing burner for gas turbine repowing system. The features of this burner are shown below. 1) It can be applied to both the existing and newly installed boilersteam turbine system. 2) The exhaust gas port of the burner is devided into two stages and the burner can be fired both with gas turbine exhaust gas, and with fresh air at the regular inspection of the gas turbine. |