A REVIEW OF THE COMMON CAUSES OF BOILER FAILURE IN THE SUGAR INDUSTRY
Unscheduled boiler outages in process industries are a major problem resulting not only in expensive emergency repairs, but also loss of production. This paper draws on the experience of the author's company relating to common failures of pressure parts of boilers. The paper identifies the most common types of pressure part failure and the metallurgical mechanism involved. With a knowledge of the underlying failure mechanism a number of basic causes can be identified. The paper suggests solutions that, if implemented, can reduce the incidence of unscheduled outages and thereby improve profitability.
The NALCO Guide to Boiler Failure Analysis
Water-Formed and Steam-Formed Deposits. Long-Term Overheating. Short-Term Overheating. Caustic Corrosion. Chelate Corrosion. Low pH Corrosion During Service. Low pH Corrosion During Acid Cleaning. Oxygen Corrosion. Fire-Side Corrosion. Oil Ash Corrosion. Coal Ash Corrosion. Waterfall Corrosion. Cold End Corrosion. Dewpoint Corrosion. Hydrogen Damage. Corrosion Fatigue Cracking. Stress Corrosion Cracking. Erosion. Cavitation. Forming Defects. Welding Defects. Material Deficiency. Graphitic Corrosion. Dealloying.
OPERATING EXPERIENCE ON SINGLE AND THREE PASS BOILERS IN THE CANE SUGAR INDUSTRY WITH PARTICULAR REFERENCE TO EROSION AND DRUM WATER LEVEL STABILITY
Two boiler designs have recently emerged to suit the present requirements of the cane sugar industry, viz the single pass panel wall unit and the three pass, bottom supported boiler with an open pitch furnace tube construction. The former is less susceptible to erosion compared with the original concept of the three pass boiler. It is believed that the three pass unit in its present form as installed at Tongaat will be effective in reducing erosion in the tube bank. The effect of fuel properties on the performance of boiler plant is considered and it is shown that efficient operation, in addition to improving the utilisation of bagasse, can result in a significant reduction in tube erosion. A relationship is presented for determining dust loadings as a function of the grate heat release rate and the fuel ash content at the furnace and main bank exits. Circulation studies undertaken on both boiler types are presented indicating very similar circulation rates. Shrink and swell characteristics and hence the drum level stability can be related to the volume of water contained in the system and the water plan area in the drum at the steam - water interface. Finally the mechanical design features of the two boiler designs are compared to provide an insight into the design philosophies relating to the two units.