OCR Text |
Show Figure 7 presents reactor maps for the three nitrogen pollutants measured (HCN, MH3 and NO). As with the permanent gas and sulfur pollutant maps, the regions of recirculation and intense reaction are quite evident. The oxidized nitrogen pollutant NO, like C02 and S02 shows the highest levels in the 02-rich core region and decays to lower concentration levels in regions away from the intense reaction zone. The fuel-rich nitrogen pollutants are generally low in the intense reaction zone and show marked increases in the recirculation and downstream zones. However, an exception was noted with the HCN concentration. The concentration level of HCN in a very narrow region along the centerline (0 cm < r ^ 2 cm) rapidly increases from about 150 ppm at an axial location of about 14 cm to 1500 ppm at an axial location of about 21 cm. The level then remains high along the centerline to the reactor exit. This yery rapid increase in HCN suggests that HCN is formed directly as a pyrolysis product of coal rather than being formed in the gas phase as MH3, H2S, COS, etc. appear to do. Carbon, Sulfur, and Nitrogen Conversion. The conversion of the solid fuel to the gas phase is of major interest in any gasification process. In fact, considerable effort has been expended to increase the extent of conversion by many process developers (2). The ultimate analysis of the char samples has permitted the conversion of carbon, sulfur and nitrogen, from the solid fuel to the gas phase to be determined. The following equation, derived from a forced mass balance on ash and either carbon (C), sulfur (S), or nitrogen (N), has been used to determine the local carbon, sulfur, or nitrogen conversion (&) from the char composition data reported in Table 3. ci = 1 " (wash, coal x wi, char>/(wash, char x wi, coal> U) where i is either carbon (C), sulfur (S) or nitrogen (N) and U is the respective weight fraction in the char or raw coal. The equation was based on the assumption that ash is an inert tracer. The coal composition was determined from feeder samples obtained for eacn separate test. 6-19 |