Wood Biomass Combustion Heat

Overview

Engineering reference data for Wood Biomass Combustion Heat in combustion engineering.

Key Formulas

Heat Release

$Q = \dot{m} \cdot HV$

Fuel energy release rate.

Air-Fuel Ratio

$AF = \frac{m_{air}}{m_{fuel}}$

Mass of air per mass of fuel.

Excess Air

$EA = \frac{O_2}{21 - O_2} \times 100\%$

From flue gas oxygen measurement.

Variables

Symbol	Description	Unit
$Q$	Heat release rate	W
$\dot{m}$	Mass flow rate	kg/s
$HV$	Heating value	J/kg
$AF$	Air-fuel ratio	—

Practical Combustion Principles

The theoretical high heat value (HHV) of 8660 Btu/lb (20.14 MJ/kg) is derived from perfectly dry wood in a pure oxygen atmosphere and is not representative of real-world combustion. Practical combustion values depend heavily on moisture content, which reduces usable energy.

A key engineering rule of thumb is that one weight unit of wood has enough energy to evaporate approximately six weight units of water. This relationship is critical for understanding the energy penalty of using wet fuel.

Combustion Heat by Wood Condition

This table provides approximate combustion values for wood in different states.

Moisture Content vs. Usable Energy

Moisture content impacts both volumetric and gravimetric energy density. The following table quantifies this effect.

Key Observations:

• By volume, wet wood retains about 85% of the energy of oven-dry wood.
• By weight, wet wood contains less than half (42%) of the energy of oven-dry wood.

Boiler Horsepower Equivalents

These are common industry conversion factors for wood-fired boiler systems.

• 6.3 lbs of dry wood = 1 Boiler Horse Power
• 11.6 lbs of wet wood = 1 Boiler Horse Power

(1 Boiler Horse Power = 33,475 Btu/hr = 9.809 kW)

Interactive Charts

References

• Original Source