Module 11 · Emissions and Environment3 min read
Boiler Ash Handling and Disposal
A solid-fuel boiler is also an ash plant. Indian coals and many biomass fuels carry a lot of ash, and every kilogram has to be removed, conveyed, stored and sent somewhere — without dust, fire or spills.
You'll learn
- Distinguish bottom ash from fly ash
- Estimate ash quantity from fuel and ash content
- Describe dry, wet and pneumatic handling
- Know the routes for storage, use and disposal
Before this: Coal and lignite, Particulate Control and Stack Height
BeginnerThe idea in plain words, and where you meet it. No maths.
Two kinds of ash
- Bottom ash: falls through or off the grate, or drains from a fluidized bed. Coarse, sometimes clinkered, and hot.
- Fly ash: carried with the flue gas and caught in the economizer and air heater hoppers and the dust collector. Fine and dusty.
The split depends on the firing method: a grate keeps more as bottom ash, a fluidized bed sends more out as fly ash.
IntermediateThe formula, its units, and a worked example on real plant numbers.
How much ash
Worked example
Ash from a 5 TPH coal-fired boiler
Given
- 5,000 kg/h at 10.54 kg/cm²(g), feedwater 80 °C; coal at 4,000 kcal/kg, 82% efficiency; ash 35% as fired (illustrative — use your fuel analysis); 20 h/day.
- Coal burnt: 891 kg/h.
- Ash: 891 × 0.35 = 312 kg/h.
- Per day: 312 × 20 ÷ 1,000 = 6.2 t.
Answer: About 6.2 tonnes of ash a day to remove, store and dispatch.
- Dry mechanical: screw or drag-chain conveyors from hoppers to a silo or bunker. Simple; needs dust control at transfer points.
- Wet: ash quenched and sluiced or carried as slurry. Cools and suppresses dust, but makes a water and settling problem.
- Pneumatic (dense or lean phase): fly ash blown in pipes to a silo. Enclosed and clean, good for dry fly ash that will be sold.
ExpertThe fine print: where the simple model breaks, and what it costs.
Storage, use and disposal
- Store enclosed or covered and dispatch in covered vehicles; open ash heaps are a common consent violation.
- Dry fly ash has buyers: cement, bricks and blocks. Rice husk ash is a sought-after silica source. Keep it dry and separate to keep it saleable.
- Fly ash utilization notifications from MoEFCC target coal and lignite thermal power plants; for a process boiler, the SPCB consent sets how ash is stored and where it may go.
Key takeaways
- Bottom ash comes off the grate or bed; fly ash leaves with the flue gas.
- Ash quantity = fuel burnt × ash fraction; with high-ash fuels it is tonnes per day.
- Dry mechanical, wet and pneumatic handling each trade cost, dust and water.
- Store covered, keep sellable ash dry, and follow the consent for disposal.