Biomass Power Plant
Agri-residue and wood-chip fired boilers producing green steam & power.
Biomass plants burn agricultural residues, wood chips or briquettes in traveling-grate or fluidized-bed boilers to raise steam that drives a turbine or supplies process heat.
How it works
- 1
Biomass fed via conveyor onto grate or into FBC bed.
Fuel — briquettes, rice husk, bagasse, wood chips or agri-residue — is weighed, screened for stones and metal, and stored under cover. Moisture below 15–20 % matters more than anything else: wet fuel steals furnace heat, drops bed temperature and cuts efficiency point for point. Drag chain or belt conveyors feed a day silo, then rotary/screw feeders meter it into the furnace.
- 2
Combustion releases heat, raising steam in water walls & superheater.
On a travelling grate the fuel bed burns as it moves; in an AFBC the fuel burns inside a fluidised bed of hot sand held at 850–900 °C by primary air through the distributor nozzles. Secondary/over-fire air completes combustion in the freeboard. Radiant heat is absorbed by the water walls, and the saturated steam from the drum is then dried and heated further in the superheater to 440–510 °C.
- 3
Flue gas passes through economizer, air preheater and ESP/bag filter.
Downstream of the superheater the gas gives up more heat in the economizer (feedwater preheat) and air preheater (combustion air preheat), then the ESP or bag filter takes particulate down below 30–50 mg/Nm³ before the ID fan pushes it up the stack. This back-end train is where most of the recoverable efficiency lives — every 20 K of extra stack temperature is roughly 1 % of boiler efficiency lost.
- 4
Steam drives a back-pressure or condensing turbine for power.
Superheated steam expands through the turbine. A back-pressure machine exhausts at process pressure (3–10 bar) for a factory, giving very high overall fuel utilisation in cogeneration; a condensing machine expands to vacuum against a surface condenser and cooling tower for maximum electrical output. Extraction-cum-condensing sets do both.
- 5
Ash removed via bottom ash system and pneumatic fly ash line.
Bottom ash is quenched and removed by submerged scraper conveyor; fly ash is collected from economizer, APH and ESP hoppers and moved pneumatically to a silo. Biomass ash is high in potassium and silica — it is valuable as a soil amendment or brick additive, but is also the reason for bed agglomeration and superheater fouling.
Key components
Weighbridge, storage yard/shed, drag chain and belt conveyors, magnetic separator, screen, day silo with level sensors and rotary/screw feeders with VFD. Dust suppression and strict housekeeping are mandatory — accumulated biomass dust is explosive.
AFBC: air distributor with bubble caps, bed material (silica sand), bed coils and in-bed thermocouples; excellent for mixed and low-grade fuels. Travelling grate: chain grate with adjustable speed and air compartments; simpler, better for uniform sized fuel. Both feed water walls, drum, superheater and desuperheater.
ESP charges particles with high-voltage discharge electrodes and collects them on grounded plates, rapped periodically into hoppers. Bag filters use pulse-jet cleaned fabric bags. Monitor emission, hopper level, rapping and (for bags) ΔP and inlet temperature — a wet or over-temperature bag house fails fast.
Multistage impulse/reaction turbine with governor valves, lube-oil system, gland sealing, barring gear and vibration/axial-shift protection. Coupled through a gearbox to the alternator. Steam purity matters: silica or sodium carryover deposits on blades and quietly destroys output.
Rejects condenser heat for the condensing set. Its performance directly sets the condenser vacuum — a 10 mbar loss of vacuum costs roughly 1 % of turbine output, so tower cleanliness is an electricity-generation issue, not a housekeeping one.
Typical operating parameters
Problem solving videos
Safety notes
- •Fuel yard dust explosion risk — housekeeping critical.
- •CO monitoring in silos.
- •Hot ash burns — cool before disposal.
Maintenance schedule
- •Daily: bed material top-up, ash system, fuel quality.
- •Weekly: soot blower, ID/FD/PA fan checks.
- •Annual overhaul: tube thickness, refractory, turbine inspection.
Problem solving matrix
| Issue | Likely cause | Fix |
|---|---|---|
| Bed defluidization | Agglomeration, high alkali fuel | Blend fuel, drain & refill |
| High flue gas temp | Fouled economizer | Soot blowing, offline clean |
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