Hog fuel

Hog fuel is a mixed biomass fuel made from wood residues such as bark, chips, sawdust, screen rejects, slabs, shavings and forest residues. The name comes from hogging equipment that shreds irregular wood waste into a fuel that can be conveyed and burned.

Composition and variability

Unlike wood pellets, hog fuel is not a tightly standardised product. Moisture can range from relatively dry sawmill residues to wet bark and winter storage piles. Ash content rises with bark, dirt, sand and needles. Alkali metals, especially potassium and sodium, vary with species and bark fraction. Particle size can also vary enough to affect conveying and combustion.

Where it burns

Hog fuel is burned in hog-fuel boilers, pulp-mill power boilers, sawmill biomass boilers, district-heating plants and some co-firing applications. It is attractive where residues are local and disposal would otherwise have cost, but it demands robust handling and combustion systems.

Fouling and operating issues

High moisture lowers heating value and can destabilise combustion. Bark and forest residues increase ash, alkalis and chlorine, which can drive slagging, bed agglomeration, superheater fouling, corrosion and air-heater deposits. Oversize pieces can bridge in bins, while fines can create dust and uneven feeding.

Acoustic cleaning relevance

Sonic horns do not improve fuel quality, but they help manage the fouling consequences of variable hog fuel. They are most relevant on convective tube banks, economisers, air heaters and ash hoppers where biomass ash is still friable enough to remove online.

Handling notes

Hog fuel is difficult to store and meter because it can be wet, stringy, frozen, oversized or full of fines. Piles can self-heat, shed water unevenly and segregate by particle size. Conveyors, chutes and bins need generous geometry and tramp-metal protection. Fuel sampling should capture moisture and ash variability rather than a single grab sample. When fouling increases in the boiler, the investigation should start with recent fuel receipts, pile management and bark fraction before focusing only on downstream cleaning.

Handling and combustion context

Hog fuel is variable by nature. It can include bark, chips, fines, knots, sawdust, dirt, sand and occasionally tramp metal. Moisture content, particle size and ash content drive its behaviour in storage, conveying and combustion. Wet, stringy fuel can bridge in bins and feeders. Very dry fines can create dust, fire and explosion concerns. Sand and grit increase erosion in fuel-handling and ash systems.

In boilers, hog fuel affects furnace stability, excess air, carbon monoxide, carry-over, slagging, fouling and bottom-ash quality. Operators need sampling and trend awareness because a fuel pile can change after rain, freezing weather or a new supplier. Acoustic cleaning has no role in making hog fuel uniform, but it can help manage dry ash deposits caused by hog-fuel firing in convective passes, hoppers and air heaters when the ash remains friable.

Measurement and storage notes

Useful hog-fuel measurements include moisture, ash content, particle-size distribution, bulk density and contamination. Storage piles should be managed for drainage, fire risk, freezing, segregation and first-in first-out turnover where practical. Poor storage can turn acceptable fuel into a handling problem before it reaches the boiler.