| OCR Text |
Show capacity of the boiler (6 MMBTU/hr.) using up to 30% excess air. Atomization of the mixture was achieved using 25-30 psi primary air pressure. Atomization was also demonstrated using steam at 30-34 psig. Preheating of the mixture to 230-250 F was found to be critical in maintaining continuous fuel flow as well as achieving atomization. A supplemental COM heater was provided at the boiler. A steam heater proved to be more effective than an electrical heater since the high temperature of the electrical heating elements cause coking to occur. In addition, a strainer was added to the fuel train to catch debris in the COM which several times plugged the nozzle. The burner nozzle was also redesigned to reduce wear. Ingition of the COM was satisfactory with the existing pilot. However, a minimum of 30 seconds pilot flame duration was found necessary. Flame stability was excellent with these ignition conditions. Carbon burnout efficiency at full firing rate was about 97% and was better at reduced firing rates. However, accumulated ash deposits in the combustion chamber created a severe problem of maintaining a stable flame. Modification of the nozzle diffuser reduced the deposit in the combustion chamber, but resulted in deposits on the rea door. The deposits could not be eliminated. Figures 2, 3 and 4 illustrate the appearance of the deposits. In the furnace tube, it was found that flying ash particles from the flame impinge against the heating surfaces, and a fraction of them stick depending upon angle of impact as well as physical state of the particles. During the first few hours of operation, the furnace tube remains clean, but soon thereafter a build up of deposit is observed. The geometric shape of the deposit depends upon how the droplets impinge against the surface. It was also observed that for some conditions the deposit thickness remains constant, but spreads and covers a greater surface area as operation is continued. This is attributed to the brushing action of the combustion gases flowing over the molten ash adhering to the furnace wall. At the rear door 15-7 |
