- Some of the major Challenges in Boilers are :-
- To minimize size and weight.
- To meet required life.
- To be resistant to fouling and corrosion.
- To minimize cost.
- Poor Maintenance
Statistics indicates that about two-thirds of all boiler failures and nearly all unscheduled shutdowns are caused by poor maintenance and operation.
Scale formations in boilers are responsible for lost efficiency, increased maintenance and operating costs not to mention lost revenue due to outages and downtime. Most scale formations in boilers occur due to the presence of hardness in the make-up water. This hardness reacts in the high temperatures environment within the boiler to form and insoluble scale. This insoluble scale coats the heat transfer surfaces, acting as an insulator to impede heat transfer.
Hardness isn’t the only cause of scale formation in boilers, other impurities such as iron, silica, copper, oil, etc. are often found in samples of boiler scale. In fact, it is rare to find scale which isn’t the result of several of these impurities.
Slagging and Fouling
Slagging occurs in boiler furnaces where ash deposits are exposed to the radiant heat of the coal flames, while fouling occurs in the boiler’s convective passes. Slagging & fouling are mainly observed in coal- fired boilers.
Excessive ash deposits on a coal fired boiler’s heat transfer surfaces will reduce its efficiency, and in extreme cases a boiler can be shut down by ash related problems. It has been estimated that slagging incidents cost the global utility industry several billion dollars annually in reduced power generation and equipment maintenance.
Corrosion occurs in boilers due to two major reasons. The most common cause is dissolved oxygen entering the system via the feed-water. Another common cause of corrosion in boiler systems is low pH within the boiler. This reduced pH may result from carbon dioxide infiltration or form contamination by other chemicals. The oxygen causes very localized corrosion to occur in the form of pitting. The pits are small but deep pinpoint holes which eventually can penetrate tube walls and cause their failure.
Oxygen corrosion is normally controlled by driving the oxygen from the feed-water in a deaerating heater/deaerator or by chemically removing it with an oxygen scavenger such as sodium sulfite. There are many contaminates which can infiltrate a boiler system and cause low pH levels to develop.