OCR Text |
Show 5 The radiant furnace is designed to operate in the 2200°F to 2400° F range. The bed will operate at lower temperatures, closer to 1800° F. These temperatures are higher than those commonly used in larger installations, and is due primarily to the requirement of obtaining 1600° to 1650° F temperatures on the pressurized air side back to the gas turbine. The bed material is a refractory sand, capable of withstanding high temperatures without fusing . Also it should be noted that this is approximately a 2: 1 scale up from a previous experimental fluid bed/furnace/gas turbine cycle. Actual operating data on this design is not yet available, as the unit is now scheduled to begin operation in the spring of 1995. It should be noted that operating temperatures chosen for wood fuel are not conducive for sulfur capture by limestone (1550° F process), and are not recommended for fuels containing silica, such as rice hulls. For these fuels, reduced bed temperatures, and furnace temperatures are required, which can be obtained by heat absorbing elements within the bed, changes in excess air, and possible changes in the turbine peak operating temperature. NOx Control Nitrogen oxides are formed by both of two mechanisms. One is the direct conversion of gaseous nitrogen at high temperatures to nitrogen oxide, and the other is the conversion of organic nitrogen to nitrogen oxide. Although in this design it is expected that all of the nitrogen oxides may come from the fuel nitrogen, it is still worthwhile to review the thermal NOx formation. Figure 2 shows the nominal lower heating value of the candidate wood fuel versus moisture content. Typical ranges for moisture content are from 30% to 70% water on a dry fuel basis. At 50% moisture the LHV is approximately 5000 Btu/lb of fuel (dry fuel plus water). The fuel analysis is presented as Table 1, and represents both a specific wood and a "typical" wood. |