Combustion fuels and biomass: Approximately what is the carbon content by weight (mass %) in air-dried wood commonly used as a solid biofuel?

Introduction / Context:
Understanding the elemental composition of common fuels helps in estimating heating value, carbon emissions, and combustion stoichiometry. Air-dried wood is a widely used biomass fuel in boilers and gasifiers. Knowing its typical carbon percentage allows quick back-of-the-envelope calculations for energy and CO2 output.

Given Data / Assumptions:

• Air-dried wood (not oven-dry), with moisture still present.
• Typical proximate/ultimate analyses are assumed for mixed hardwood/softwood.
• We seek a representative mass-percent of carbon, not an exact species-specific value.

Concept / Approach:
Biomass contains carbon, hydrogen, oxygen, small amounts of nitrogen, ash, and moisture. For air-dried wood, ultimate analyses commonly report carbon near one-half of the dry mass. Moisture lowers the apparent fraction slightly versus oven-dry, but the round-number estimate widely used for calculations remains about 50% carbon by mass.

Step-by-Step Solution:
Start from typical ultimate analysis (air-dried): C ~ 48–52%, H ~ 5–7%, O ~ 40–45%, minor N/S/ash.Round to the standard engineering estimate used in preliminary designs.Thus select 50% as the closest representative value.

Verification / Alternative check:
Handbooks and biomass databases consistently list wood near 50% carbon by mass on an air-dried basis, confirming the rule-of-thumb.

Why Other Options Are Wrong:
10% and 25% underestimate carbon severely for lignocellulosic solids. 80% carbon corresponds to high-rank coal or char, not fresh air-dried wood.

Common Pitfalls:

• Confusing oven-dry and air-dry bases; moisture content changes values.
• Using bark or char data for fresh wood fuel; those differ markedly.

Final Answer:
50%