OCR Text |
Show stream, producing a mixture believed to be similar to the premixed coal burner discussed earlier. This system allows a rapid, cost-effective screening of a wide range of fuels even when the availability is limited to small quantities, such as for many synthetics. ,The system can be run both staged and unstaged for an assessment of the emission formation and control potential. The correlation of N0X emissions with fuel nitrogen content is shown in Figure 10 for fuel lean conditions. The lower curve shows the fuel nitrogen conversion as determined by substituting an argon oxygen mixture for the combustion air. The fuel data for petroleum-, shale-, and coal-derived liquids show the same trend, that is, NO^ increasing with fuel nitrogen content and the fractional conversion decreasing with increasing nitrogen. This is similar to previous data for doped distillate oil and for limited petroleum residual testing. Considering the differences in the fuel sources and properties, it is remarkable that the trend is so consistent. It is also in marked contrast to the previously shown behavior for coals (Figure 7 ). The upper curve representing total N0X, using air as the oxidizer, is drawn through the petroleum-derived fuel data up to 0.8 percent nitrogen and through synthetic fuel data at higher nitrogens. The difference between the two curves represents the thermal N0X. The thermal NOx f°r Pure alternate fuel appears to be consistently higher than that for petroleum oils. (Some of the data shown for the synthetics are blends with petroleum residuals and these approach the petroleum line as the percentage synthetic decreases.) The reasons for this apparent difference have not been determined. This screening data has been used to select a limited number of fuels for testing under staged conditions. An example of the results obtained for a crude shale oil are shown in Figure 11 for two primary zone residence times. The primary air is introduced through the burner and secondary air to complete the combustion is introduced through ports at different downstream locations. In both cases emissions are reduced from about 1900 ppm to less than 200 ppm. The longer residence time gives a somewhat lower minimum over a broader range of primary rates, a characteristic shown in most staged combustion experiments. The minimum achievable N0X emissions for a wide range of fuels is 3-33 33 |