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Show .. The straw was shredded and chopped to a "particle size" in the range of 1-4 centimeters. Three different coals were evaluated i.e. a high volatile bituminous, low sulphur coal (Gottelborn), a high volatile bituminous, high sulphur coal from Denmark and a medium volatile bituminous, low sulphur coal (Med Mac). The fuel properties are given in Table 1. The coal fineness was maintained at 75%<75 Jlm during the experiments [11]. The measurements were primarily input-output measurements. The output measurements consisted of flue gas temperature and composition and pollutants (C02, CO, O2, NOx, 502, HCI), heat flux profiles and burnout. The input process variables studied during the experiments were co-firing ratio, swirl level, excess air level, and straw /paper injection mode and velocity. The first part of the experimental campaign was executed in May 1993. The main parameters observed to affect the flue gas compositioI} were the cofiring ratio and the flame type and excess air level. The following ranges of flue gas emissions measured are shown in the table below: Gottelborn/ Danish coal/ MedMac/ Straw Straw Straw NOx(ppm) 150-1000 150- 900 150-950 S02(ppm) 200-850 200-2000 200-575 HO(mg/m3 275-40 " 275-40 300-20 Burnout (0/0) 96-99.9 96-99.9 95-99.4 For all three coals similar NOx trends are observed, as shown in Figure 11. For the high intensity Type 2 flames, which occurred for straw injection through the annulus, a decrease in NOx emissions can be observed for an increasing straw-coal co-firing ratio. For the low NOx penetration flames, created by straw injection through the centre and subsequent penetration of the IRZ, low co-firing ratios (5-200/0) result in marginally higher NOx levels when compared to 100% coal firing. However, further increases in co-firing ratio results in a reduction in NOx emissions. The three coals used in the co-firing experiments had a substantial difference in sulphur content. The straw was relatively low in sulphur (0.160/0). In Figure 12 an overview of the S<h emissions as function of the blending ratio is shown. Similar trends are observed for the high volatile Danish coal (2.10/0 S) and Gottelbom (0.90/0 5). For ,both of the flame types "an increase in co-firing ratio results in a reduction of ~ emissions. " |