Biomasses - Energy Content when Used as Fuel
Approximately energy content in different biomasses, used as fuels (not prosessed material):
See also Heat of combustion
| Bio Fuel | Energy content (MJ/kg) |
|---|---|
| Alfalfa straw | 18.5 |
| Charcoal | 30 |
| Coal | 28 |
| Coconut husks | 10 |
| Coconut shells | 18 |
| Coffee husks | 16 |
| Commercial wastes | 16 |
| Cotton hulls | 19.5 |
| Cotton stalks | 17.5 |
| Domestic refuse | 9 |
| Dung, dried | 16 |
| Grass, fresh | 4 |
| Groundnut shells | 20 |
| Maize cobs | 19 |
| Maize stalks | 18 |
| Methane from biogas | 55 |
| Paper, newspaper | 17 |
| Peat | 14.5 |
| Petroleum Oil | 42 |
| Rice hulls | 15.5 |
| Rice straw | 15 |
| Soybean stalks | 19 |
| Straw, harvested, baled | 15 |
| Sorghum bagasse | 19 |
| Sugar cane residues | 17 |
| Wheat straw | 19 |
| Wood, green with 60% moisture | 6 |
| Wood, air-dried to 20% moisture | 15 |
| Wood, oven-dried to 0% moisture | 18 |
- 1 MJ/kg = 0.28 kWh/kg = 430 Btu/lbm
Wood required to Boil a Litre of Water
The energy to heat one litre of water ( 1 kg) with specific heat 4.2 kJ/kg oC from 20 oC to boiling 100 oC can be calculated with the heating equation
q = m cp dt (1)
where
q = heat (J, Btu)
m = mass of water (kg, lb)cp = specific heat of water (J/kg oC, Btu/lb oF)
dt = temperature change ( oC, o F )
Inserting the values
q = (1 kg) (4.2 kJ/kg oC ) (1000 J/kJ) (( 100 oC ) - (20 oC ))
= 336000 J
= 336 kJ (kW/s)
= (336 kW/s) / (3600 s/h)
= 0.093 kWh
With energy content of air dryed wood 15 MJ/kg (15000 kJ/kg) and combustion efficiency 0.25 (25%) - the amount of wood to heat the water can be calculated as
m w = q / μ h w (2)
where
m w = mass of wood (kg)
μ = combustion efficiency
h w = energy content wood (kJ/kg)
Inserting the values
m w = (336 kJ) / 0.25 ( 15000 kJ/kg )
= 0.09 kg
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