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# Biomasses - Energy Content when Used as Fuel

Approximately energy content in different biomasses, used as fuels (not prosessed material):

Biomasses - Energy Content when Used as Fuel
Bio FuelEnergy 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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