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PROPERTIES OF FUELS

PROPERTIES of
SOLID FUELS
Anthracite Hard Coke Soft Coke Hard
Briquettes
Bituminous
Coal
Lignite
Briquettes
Peat
Briquettes
Wood
Pellets
Wood
Logs
Moisture % 4.5 8.5 8.5 12 7.5 18.5 11.5 11 18.5
Ash % 8.5 9.5 7 8 5 7.5 5 1 1
Volatiles % 8.5 1.5 9 11 32.5 56.5 68 84 84
Hydrogen % 3.5 0.5 2 3 4.5 3.5 5.15 5.6 5.5
Carbon % 85 85 80 80 60 52.5 48.5 45 40
Sulfur % 1 1 1 1 1 2 0.2 0.1 0.1
Heat content kJ/kg 31155 27050 28000 29500 26750 19500 18050 18200 18500
Bulk kg/m³ 879 450 410 830 800 720 750 600 370
Potential heat kW/kg 8.65 7.51 7.78 8.19 7.43 5.42 5.01 5.06 5.14
Bulk Performance kW/m³ 7603 3380 3190 6798 5944 3902 3758 3036 1902

Table averaged from EN13240 and EN14785.

The 'Bulk Performance' figure indicates how much heat is available in each cubic metre of filled firebox. To find the actual heat likely to be given out this will need reducing by the efficiency of the appliance (typically 65 to 75%). However, not all the fuel in the firebox will be burned in an operating cycle, only some 60% to 80% will actually be consumed. To get at a final performance figure we will need to then divide this over the burning cyle in hours, so the whole calculation is:

( Firebox volume in m³ x Bulk performance x efficiency(%/100) x proportion consumed in refuel cycle )
refuel interval in hrs

To simplify matters, table 2 gives the output per cubic metre, already calculated down for typical efficiencies, typical proportions consumed and is given for popular refuelling cycles:

TABLE 2
APPROXIMATE HEAT
OUTPUT PER UNIT
FUEL VOLUME
Refuel interval
Hrs
Rough guide
kW output per m
³
Wood Logs 2 495
Bituminous Coal 4 628
Anthracite 6 577
Anthracite 12 288
Hard Coke 4 385
Peat Briquettes 4 427
Lignite 4 444
Quick Guess   500