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Show 2. Calculate the full load axial velocity desired (normally based on minimum velocity at maximum turndown). 3. Calculate the maximum swirl level possible based on swirl generator pressuredrop characteristics, the full load axial velocity and the maximum air pressure available. 4. If necessary, lower the axial velocity to achieve a higher swirl level. 5. Use the isothermal, inviscid model to calculate the burner and quar1 geometry required to generate the desired flow pattern and recirculation rates. BURNOUT Natural Gas 1. Calculate the maximum gas velocity based on the available gas pressure. Compare the inlet gas and air velocity. If the maximum gas velocity is greater than twice the air velocity, then the mixing behavior can be largely controlled by changing the fuel injection behavior. Inject the gas directly into the combustion air for maximum mixing, and along the burner centerline to delay mixing. Calculate the flow field first using the inviscid model, to estimate the optimum angle for the gas injection. 2. If the gas pressure is low and the gas flow cannot be effectively directed then air staging can be used to reduce the fuel and air mixing rate Oil High momentum liquid atomizers also can be used to regulate the mlxlng rate by matching the spray trajectory with the aerodynamic flow pattern established by the burner. The burner flow pattern can first be estimated by using the inviscid model. The atomizer spray angle can be designed to give either quick or delayed mixing between the oil and combustion air. Severa 1 di fferent techni ques can be used to contro 1 the mi xi ng rate between the coa 1 and air stream. The mos t common and eas i 1 y cont ro 11 ed method is air staging. Air can be diverted to outside the quar1, resulting in a fuel rich primary zone and delayed fuel and air mixing. Another method -5- |
