Ash Handling System

What is ash handling and why is it required?

Thermal power plants that generate electricity by burning coal also produce a lot of residue ash as a waste material, which needs to be properly disposed-off from the Plant.

Since almost 40% of coal is converted to ash, a large amount of ash is continuously being generated and is present in various forms in the power plant, due to which an efficient ash handling process is required for optimal performance of the power plant.

Ash handling system is a set of methods by which ash can be cooled down to manageable temperature, transferred to a disposal areas or storage container and further utilized in other industries.

As the operating conditions of power plants are extremely harsh and corrosive, Ash handling systems must be designed and developed in such a manner that they are able to withstand heavy wear and tear, occasional system failures and high-volume transportation and storage.

Two types of Ash are generated in thermal power plants during the conversion of coal to electricity:

  • Fly ash
  • Bottom ash

Almost 80% of ash generated in power plant is Fly ash and generally is in form of very fine particles. It is collected via apparatus such as economizer hoppers, air pre-heater hoppers, electrostatic precipitators and dust collectors positioned in the flue gas processing system.

Bottom Ash is generated below the furnace of steam generator and accounts for around 20% of total ash generated in a power plant. Bottom ash is mostly coarse in nature hence it needs to be further crushed in grinders and crushers before being transported to ash handling systems.

What types of Ash handling systems are available and in use worldwide?

Ash handling systems deploy several types of pneumatic conveyors or mechanical conveyors or slurryfication depending on type of ash being handled. Ash handling systems are generally divided into following types:

  • Bottom ash handling system
  • Fly ash handling system
  • Ash slurry disposal system

Bottom ash handling system comprises of following stages:

  • Bottom ash is collected in bottom hopper located under the furnace boiler
  • This ash is treated through clinkers and grinders to normalize the bottom ash size
  • It is then transported to bottom ash silos for temporary storage or to ash ponds in slurry form.

Fly ash handling system comprises of following stages:

  • Coarse ash is continuously captured via economizer hopper situated after the boiler exhaust
  • Fly Ash is collected in air-preheater hoppers is batch wise evacuated using pneumatic conveying system
  • Fine fly ash is captured via electrostatic precipitators / fabric bag filters and / or combination of ESP & Bag filter in fly ash hoppers.

This combination of economizer, air-preheater and electrostatic precipitators are used to capture and transfer fly ash into fly ash silos

Ash slurry disposal system comprises of following types:

    A. HIGH CONCENTRATION ASH SLURRY DISPOSAL SYSTEM -

  • Fly ash silos and bottom ash silos dump the ash onto conveyor belts.
  • These conveyor belts are used to transport ash to slurry mixing tank where it is mixed with water to create ash slurry
  • Slurry pumps are used to transport ash slurry to ash dyke area via ash slurry transportation pipes
  • High concentration slurry disposal system (HCSD) are used to homogenously mix ash slurry and transport it to ash disposal sites using carbon steel pipelines.

  • B. LEAN ASH SLURRY DISPOSAL SYSTEM -

  • Bottom ash collected from bottom of the furnace through jet pumping system or SSCC to a slurry sump
  • Slurry pumps are used to transport ash slurry to ash dyke area via ash slurry transportation pipes