OCR Text |
Show Initially, a slag and ash deposition test was performed for 9.5 hours with the finest coal (Trial 6). After 9-1/2 hours of operation the probe was pulled from the flue and found to have large deposits of dark brown slag in between the tubes. The large deposits were removed by hand from the tubes and then a soft brush was used to clean the remaining surface of the probe of the light brownish gray powdered ash. Some small amounts of deposition were lost in removal of the probe from the flue so the real deposition was slightly greater than the quantity measured. These small losses were observed in all tests. Based on the amount of material collected it was decided to reduce the duration of the subsequent tests to about 2 hours (Trials 7 through 10). A photograph of the probe after 2 hours of operation for Trial 7 (finest coal) is shown in Figure 26. For this trial the probe had no large deposits between the tubes, with most of the light brownish-gray color ash on the insulated side plates. The deposits were soft and easily removed with a soft brush. It appeared that this ash would be very amenable for removal by soot blowing. Trial 8 (middle-size coal particles) was run for 1.42 hours, but had greater deposits that are similar to the deposits in Trial 7. The coarsest coal was used in Trial 9, and after 2 hours of operation large deposits of slag and ash were found on the probe tubes. Figure 27 is a photograph of the front view of the slag and ash deposition probe (facing the furnace interior) after Trial 9, and Figure 28 is a top view of the same probe. The spaces in between the tube were blocked with dark brown slag that could be removed by hand and light brownish gray ash on the remaining surfaces, which was removed by a brush. Removal by soot blowing might have been difficult and would have required more frequent blowing. In Trial 10 a coal with a bimodal particle distribution was fired during the slag and ash deposition tests. For this test the amount of slag and ash was not unusually high or low, but the type of deposition was interesting. On the rear probe tubes a deposit of very hard material adhered to the upstream surface. This is the surface that viewed the furnace interior and is shown in Figure 29. A hammer was needed to remove this deposit on the rear tube, and metallic surfaces }7 |