OCR Text |
Show Pulverizer Air/Fuel Ratio The B&W MPS-89 pulverizers have been calibrated to an airflow curve which results in an air to fuel ratio of 2.5:1. This is believed to be high. Frequent when the throats are worn, the operators will run these pulverizers with the air biased even higher, over 3:1. The adverse effects can be seen in more smoke and rolling fire in the bottom of the furnace, slag build-up and higher CO concentrations in the burner zone. If the air/fuel ratio was to be reduced to the 2:1 range, it is felt that overall flame quality would be improved. However, this requires modification of the throat design and has not yet been done. Furnace Bottom CO Gas sample ports were installed at six locations along both the front and rear walls just below the bottom row of burners (see Figure No. 15). This permitted sampling the furnace gas for CO and O2 in the region directly below the burners and an area prone to tube wastage in the past. There was a wide range io CO values obtained. The early testing with the Avon 9 burner with the counter spin impeller looked extensively at increased O2 levels and different pulverizer combinations in attempting to lower CO levels that were frequently in the range of 5,000 to 10,000 ppm. This provided little improvement. Also, high CO levels existed with the B&W cell burner on Eastlake 5 at lower loads and fewer burners in service. Tests conducted on Avon 9 with a 50/50 mix of parallel spin and counter spin impellers showed improvement, particularly when firing mostly the parallel spin burners. Preliminary data obtained at Eastlake 5 with the parallel spin shows much improved (lower) CO levels. The lines graphed on Figure No. 19 indicate the general trends and range of CO values for the various burner combinations. It is apparent for the CO data, however, that the parallel spin impeller is providing a better quality of combustion and that CO is adversely affected by increasing the firing rate of the pulverizer. In general, it has been found that CO levels correspond closely with the visual appearance of the lower furnace region. When the furnace appears bright and clear with little or no side wall slag, CO levels are usually in the range of 500 to 1,000 ppm. When the furnace has a redish tinge, rolling smoke hitting in the corners and slag on the side walls, CO is usually over 2,000 ppm. Future Work Plans for additional testing include post start-up testing of Eastlake 5 with the new air register and parallel spin impellers. This has been temporarily delayed due to precipitator problems which appear to be partly due to a finer ash partical generated by these burners. Investigation of this problem is currently in progress which has delayed the burner work. |