Waste-to-energy and biomass
Hog fuel
Also known as hogged fuel, mill residues, bark fuel.
Hog fuel is the coarse, mixed wood-residue stream — bark, chips, sawdust, screen rejects, urban-arisings green waste — burned in pulp-mill bark boilers and biomass side boilers. The name comes from the "hog" mill that shreds raw wood waste into a burnable consistency.
Composition and variability
Hog fuel composition is even more variable than wood pellets because no densification or sorting standardises it. Moisture content swings from 30% (kiln-dried sawmill residues) to 60% (fresh winter bark). Ash content and alkali loading vary with bark fraction (high alkali) versus wood fraction (lower).
Where it burns
- Hog-fuel boilers / bark boilers at pulp mills
- Standalone biomass boilers at sawmills and forest-products operations
- Smaller WtE / biomass cogeneration plants
- Co-fired with coal or wood pellets
Fouling
Hog-fuel ash slags moderately on the radiant section and fouls the convective pass. Sonic horns on the convective pass and air-heater cold end are standard cleaning equipment.
Related terms
Related terms
- Hog-fuel boiler and bark boilerA hog-fuel or bark boiler burns wood residues, bark and screened biomass to provide auxiliary steam at pulp mills, complementing the kraft recovery boiler.
- Recovery boilerA recovery boiler burns kraft black liquor to generate steam, electrical power and recovered pulping chemicals. Iconic application for sonic horns on superheater cleaning.
- 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.