Concept 1 / 2
Bioenergy Fundamentals and CHP Efficiency
Heat input from fuel: Q̇_in = ṁ_fuel · H_LHV
Electrical efficiency: η_el = P_el / Q̇_in
CHP total efficiency:
η_tot = (P_el + Q̇_useful) / (ṁ_fuel · H_LHV)
- Typical CHP: 80–90% total efficiency
- Electricity-only: ~30–40%
Steam cycle:
- Boiler: Q̇_in = η_b · ṁ_steam · (h₄ − h₁)
- Turbine: P_el = ṁ_steam · (h₄ − h₅)
Moisture content:
- u = w/(1−w) (moisture from water content)
- Wet wood (50% water) ≈ HALF heating value of dry wood
Typical H_LHV values:
| Fuel | H_LHV |
|---|---|
| Natural gas | ~50 MJ/kg |
| Diesel/oil | ~42 MJ/kg |
| Dry wood | ~18 MJ/kg |
| Wet wood (50%) | ~9 MJ/kg |
| Biogas (55% CH₄) | ~20 MJ/m³ |