FLAME IMPINGMENT How docs the furnace provide f or proper combustion? A For fuel to be burned efficiently, the furnace must have adequate combustion space to ensure a thorough mixing of air and fuel. The furnace must also maintain a high enough temperature for complete combustion. The furnace must be tight so that air cannot leak into, or out of, the casing and thus affect the air/fuel ratio. Too high a furnace temperature must also be avoided, as this can le ad to rapid deterioration oflinings (if installed), or possible overheating of vital pressure parts such as tubes or combustion furnaces in scotch marine boilers. Also, the reaction of combustion should be completed before the flue gases leave the combustion chamber so as to avoid flame impingement on tubes and possible overheating List the precautions needed with refractories on oil-fired boiicrs. A Refractories (brickwork) are subject to damage from many causes, such as improperly adjusted fires and vanadium-contaminated oil. Impingement and the resulting carbon buildup arc common. The flame should travel down the furnace on sm boiicrs without touching cither the furnace or the refractory. Long periods of operation on low firing often cause refractor)' damage. The very small flame reduces the combustion chamber temperature and causes poor combustion. Carbon builds up and intense heat is directed at the surface of the refractory, thus causing spalling (facing breaks off). Unless the oil has been specifically treated, there is no relief from the damages caused by vanadium in the oil. Moisture trapped in the refractory may develop steam, which ruptures the surface. Q What checks are made on the fireside of boilers? A Carefully inspect the plate and tube surfaces that are exposed to the fire. Look for places that might become deformed by bulging or blistering during operation. Solids in the waterside of lower generating tubes cause blisters when sludge settles in tubes and water cannot carry away heat. Urheberrechlli ch geschutzlcs Material Maintenance, Impaction, and Repair313 Tiie boiler must be taken out of service until the defective part or parts have been properly repaired. Blistered tubes usually must be cut out and replaced with new. Lap-joint boilers are apt to crack where plates lap in a longitudinal or straight seam. If there is evidence of leakage or trouble at this point, remove the rivets and examine the plate'carefully if cracks exist in the seam. Cracks in shell plates are usually dangerous, except fire cracks that tun from the edge of the plate into the rivet holes of girth seams. Usually,
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