Ash Handling System
What is Ash?
- Ash is the residue remaining after the coal is incinerated.
Composition of ash handling system?
- SiO2, Al2O3, Fe2O3, CaO , MgO.
Why Ash Handling System is required?
- In Thermal Power Plant’s coal is generally used as fuel and hence the ash is produced as the byproduct of Combustion. Ash generated in power plant is about 30-40% of total coal consumption and hence the system is required to handle Ash for its proper utilization or disposal.
Ash terminology in power plants?
- Fly Ash ( Around 80% is the value of fly ash generated)
- Bottom ash (Bottom ash is 20% of the ash generated in coal based power stations.
What is fly ash?
- Ash generated in the ESP which got carried out with the flue gas is generally called Fly ash. It also consists of Air pre heater ash & Economiser ash (it is about 2 % of the total ash content).
What is bottom ash?
- Ash generated below furnace of the steam generator is called the bottom ash.
Volume of ash and properties
The ash handling system handles the ash by bottom ash handling system, coarse ash handling system, fly ash handling system, ash disposal system up to the ash disposal area and water recovery system from ash pond and Bottom ash overflow. Description is as follows:
- A. Bottom Ash Handling System
Bottom ash resulting from the combustion of coal in the boiler shall fall into the over ground, refractory lined, water impounded, maintained level, double V-Section type/ W type steel- fabricated bottom ash hopper having a hold up volume to store bottom ash and economizer ash of maximum allowable condition with the rate specified. The slurry formed shall be transported to slurry sump through pipes.
- B. Coarse Ash (Economizer Ash) handling System
Ash generated in Economizer hoppers shall be evacuated continuously through flushing boxes. Continuous generated Economizer slurry shall be fed by gravity into respective bottom ash hopper pipes with necessary slope.
- C. Air Pre Heater ash handling system
Ash generated from APH hoppers shall be evacuated once in a shift by vacuum conveying system connected with the ESP hopper vacuum conveying system.
- D. Fly Ash Handling System
Fly ash is considered to be collected in ESP Hoppers. Fly ash from ESP hoppers extracted by Vacuum Pumps up to Intermediate Surge Hopper cum Bag Filter for further Dry Conveying to fly ash silo.
Under each surge hopper ash vessels shall be connected with Oil free screw compressor for conveying the fly ash from Intermediate Surge Hopper to silo. Total fly ash generated from each unit will be conveyed through streams operating simultaneously and in parallel.
- E. Ash Slurry Disposal System
Bottom Ash slurry, Fly ash slurry and the Coarse Ash slurry shall be pumped from the common ash slurry sump up to the dyke area which is located at a distance from Slurry pump house.