We must not blame poor quality coal for clinker formation and deposition in boilers. Instead we take proper precautions such as poking, flushing by providing more water in the hopper, soot blowing by injecting steam to remove soot deposits on water wall, and making our clinker grinders operational.
Clinker formation is a serious problem in the boilers of thermal power plants which results in forced outage for very long duration and generation loss. The removal of clinkers from the water wall and hopper of boilers is very difficult because clinkers are very hard lumps due to presence of metals in them. Removal of clinkers from boiler is very difficult procedure which takes a long time and the cost involved is also very high. Pneumatic hammering is done manually to dislodge clinkers from boilers, and clinker grinders can be used in grind large pieces of clinkers into small ones.
Causes of Clinker Formation
The causes of clinker formation are low quality coal having low gross calorific value, more ash content, high mineral content, low fusion temperature of ash below 1500 C, and over-firing of the molten slag.
In India the coal used for thermal power plants is often of low quality with low gross calorific value, high ash and minerals content, so the problems of clinker formation and deposition are evident in many plants. The best solution is to avoid the deposition of clinker is precaution.
Blaming poor quality coal may prove harmful for the boiler. Instead of very poor quality coal having high ash and mineral content, clinker formation may be avoided by a sincere attitude of power plant engineers.
Dealing with Clinker Removal
If great care is not taken for poking, then deposition may start, and its sudden collapse may cause injury and burns to workers. A sufficient quantity of water must be provided in the hoppers to flush molten slag and ash so they will not deposit. For flushing of molten ash, water is sprayed into the hopper by the flush pump. Soot blowing must be regularly done to avoid deposition of soot in the water wall by injecting steam at sufficient pressure and temperature to dislodge soot from the water walls tubes.
Clinker grinders are provided in boilers to grind large pieces of clinkers into small ones so that choking of the exhaust hole may be avoided, but it is observed in many thermal power plants that clinker grinders are out of service due to negligence or being considered a redundant feature. Due to this negligence large pieces of clinkers can choke the exhaust hole of the hopper and accumulation of small pieces of clinkers and water starts above it. Clinker grinders must be made operational.
The major cause of clinker formation in a boiler is over-firing due to which ash fuses, hence firing must be properly adjusted by using the right quantity of primary and secondary air ratio in the boiler. Good quality coal having more gross calorific value, less ash content, less mineral content in the coal, and ash fusion temperature above 1500 C must be used to avoid clinker formation. Regular watch must be done on poking. Precautions may avoid clinker formation and its deposition in boilers.
Precaution is the best solution.