SOLIFTEC Factsheet - 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

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 m³
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