| OCR Text |
Show excess O2 was held constant up to and including 12.5% level of gas heat input. At the 37.5% gas heat input level, the excess O2 level increased slightly. U p to the 12.5% gas heat input, the ratio of under grate air to burner air could be kept the same as full coal firing. At the 2 5 % gas heat input level when this was maintained the excess O2 level increased and along with it the opacity and particulate level. This ratio was readjusted for the 37.5% gas heat input level and the opacity and particulate came down with the excess 02. This was the only tuning that was done on the boiler. When only 7 % gas was introduced, the best opacity reduction occurred; a 3 2 % reduction in opacity is achieved. As the gas heat input is increased, the opacity reduction increases but the largest reduction in opacity is when a small amount of gas is introduced at the same excess 02. Steam Temperatures Steam temperatures remained stable over the whole range of gas heat input. This can be seen in Figure 5. In fact, at the highest level of gas heat input, the steam temperature dropped a few degrees. Particulate, NOx and S02 Reduction The reduction in particulate, N O x and S 0 2 achieved by the cofiring each provide benefits differently. SUPERHEATER STEAM TEMPERATURES 0 10 20 30 40 GAS HEAT INPUT, % Figure 5 The reduction in particulate has two benefits: the reduction in unburned carbon (which increases efficiency) and the reduction in particulate that is emitted. Figure 6 shows the reduction in particulate; very little reduction is achieved at the 12.5% gas heat input, but at the 37.5% gas heat input, the reduction in particulate is greater than 4 0 % . The primary benefit to most users of this technology is a means to meet a particulate requirement if the current ash capture system is not meeting the regulations. A NOx emission reduction credit can be traded either internally within the plant, in a bubble, or in many states it can be sold on the open market as a commodity. N O x credits are currently trading for $3,000 a ton. At the N O x reduction shown on Figure 6 the approximate savings per month are $17,000.00. This opportunity does not exist in all areas of the country. Figure 7 shows the particular reductions for each level of gas heat input. At 12.5% gas heat input, the N O x reduction is 17%. At 2 5 % gas heat input, the reduction is 3 0 % and at IWH AJFRC SYMPOSIM MAI 1 6 |
