Waste-to-energy and biomass
Straw and agricultural-residue firing
Also known as straw firing, agricultural residue boiler, ag-residue firing.
Straw and agricultural-residue firing — wheat straw, rice straw, corn stover, palm fronds — is a regionally important biomass-energy practice, dominant in Denmark, parts of Germany, China, India and Spain. Crops are baled or pelletised and burned in dedicated boilers, typically BFB or CFB designs that tolerate the difficult ash chemistry.
Why straw is hard to burn
- Very high potassium content — K₂O often 10–25% of ash; far above wood
- High chlorine content — particularly rice and wheat straw; drives chloride corrosion
- Low ash-melting temperature — KCl-rich ash melts at 700–800 °C and bonds to tubes as low-melt sticky ash
- Silica content — abrasive on grates and bed materials
The combination defeats steady-state operation on conventional designs and accelerates tube wastage faster than any fossil-fuel-only boiler would experience.
Cleaning
Straw-fired boilers are challenging acoustic-cleaning targets but also where the technology earns the most operational value. Sonic horns on the superheater, generating bank and economiser keep deposits from consolidating into the unrecoverable bonded slag that would otherwise force frequent water-washing.
Related terms
Related terms
- Alkali metals in ashAlkali metals (Na, K) in biomass and waste-fuel ash form low-melting compounds that bond to boiler tubes as sticky deposits and poison SCR catalysts.
- Chloride-induced corrosionChloride-induced corrosion is the accelerated tube-wall thinning caused by chlorine-rich deposits on WtE and biomass boilers. The dominant tube-failure mechanism in WtE.
- Low-melt sticky ashLow-melt sticky ash forms when alkali-rich ash particles soften at typical convective-pass temperatures and bond to tube surfaces. Defeats steam sootblowers; primary target for sonic horns.
- BoilerA boiler is a vessel that converts fuel chemical energy into steam by heating water. Coal-fired, biomass, oil, gas and recovery boilers all foul; sonic horns clean heat-transfer surfaces.