OCR Text |
Show under this deposit remained unmarked. The material was black, kept its shape upon handling, and resisted breaking. This type of deposit was not observed on the other tubes and was not seen in any of the other trials. The metallic heat transfer surfaces made from mild steel were not affected in any tests, showing no oxidation or piting on the exposed areas to the flue gases. Table 7 lists the results of the ash deposition tests. The rate of slag and ash deposition was significantly lower for fine-ground coal firing than for the coarsest coal. During normal firing of the coal, ash had to be removed from the flue, burner block throat, and burner block opening. Ash deposits had to be cleared from the burner block throat every 30 minutes when the finest coal was firing in Trials 1, 5, 6, and 7, every several hours for the middle-size coal, and seldom for the coarsest. After cooling the furnace, black deposits covered all uncooled refractory surfaces, and a deposit buildup surrounded the burner block throat opening (Figure 30). A crusty, light reddish brown deposit covered the water-cooled tubes on the sidewalls near the burner (Figure 31). The ash on the tubes was easily removed by hand, but the black deposits on the walls could not be easily removed from the uncooled surfaces. Samples of the ash and slag deposits have been sent to Sandia National Laboratory for analysis. These results are not yet available. 40 |