Efficiency Calculation
Known Data - Fuel Qgr = Gross Calorific Value (kJ/kg)
Qnet = Net Calorific Value (kJ/kg)
K1 = Constant based on Gross or Net Calorific Va l u e
K1g = (255 x %Carbon in fuel)/Qgr
K1n = (255 x %Carbon in fuel)/Qnet
K2 = % max theoretical CO2(dry basis)
K3 = % Wet Loss
H2= % Hydrogen
H2O = % Water
Measured Data: Tf = Flue Temperature
Ti = Inlet Temperature
O2m = % Oxygen in flue gas
O2r = Oxygen reference %
Calculated Data: Tnet = Net Temperature
% CO2 content in flue gas
% Dry Flue Gas losses
% Wet losses
% Unburned carbon loss
% Efficiency
Tnet = Flue Temperature - Inlet Temperature
Dry flue gas loss % = 20.9 x K1 x (Tnet)/K2 x (20.9 - O2m)
Wet loss % = 9 x H2+ H2O/Qgr x [2488 + 2.1Tf - 4.2 Ti]
Simplified = [(9 x H2+ H2O)/Qgr] x 24 25 x [1 + 0.001 Tnet]
Wet loss % = K3(1 + 0.001 x Te n t )
Where K3 = [(9 x H2+ H2O)/Qgr] x 24 25
Net Efficiency % = 100 - dry flue gas losses
= 100 - 20.9 x K1n x (Tnet)/K2 x (20.9 - O2m )
Gross Efficiency % = 100 - {dry flue gas losses + wet losses}
= 100 -{[20 . 9 % / ( 2 0.9 x K1g x (Tnet)/K2 x
( 2 0.9 - O2m)]+[K3 x (1 + 0.001 x Tnet)]}
Excess Air = [(20 . 9 % / ( 2 0.9% - O2m%)) - 1] x 10 0 %
CO2% = [(20.9 - O2m) x K2/20 . 9 ]
Unburned fuel loss% = K4 x CO / ( C O + CO2)
NOTE: CO scaled in %
Where K4 = 70 for coke
= 65 for anthra c i t e
= 63 for Bituminous coal
= 62 for coal tar fuel
= 48 for liquid petroleum fuel
= 32 for natural gas
The formula for K4 is based on the gross calorific value Qgr. To obtain the
loss based on net calorific value multiply by Qgr/Qnet. Since this loss is
usually small this conversion has been ignored. This loss is subtra c t e d
from the efficiency.
Oxygen Reference CO(n) = CO x (20.9 - O2r )
( 2 0.9 - O2m )
XAIR %: Excess air calculated from the measured oxygen and type of
( ) fuel used. During a combustion test “O2>20%” will be dis
played while in clean ambient air.
Prs: Flue draft pressure reading. Displayed when pressure
sensor fitted. See “UNITS MENU” for scales.
NO: Nitric Oxide reading in ppm or mg/m3. Displayed when
Nitric Oxide sensor fitted. Also displayed as “NO (n)” when
referenced to oxygen. The display will read “O2>20%” if
referenced values selected and instrument is in clean
ambient air.
NOx: Calculated total Nitric Oxides displayed in ppm or mg/m3.
Where NOx = NO + P%NO, note P can be set from 0-9%,
default = 5%. See “SELECT MENU”. Also displayed as
“NOx (n)” referenced to oxygen. The display will read
“O2>20%” if referenced values are selected and instrument
is sampling clean ambient air.
SO2: Sulphur Dioxide reading in ppm or mg/m3. Displayed when
Sulphur Dioxide sensor fitted. Also displayed as “SO2 (n)”
referenced to oxygen. The display will read “O2>20%” if
referenced values selected and instrument is in clean
ambient air.
O2 ref%: Toxic gas measurements can be referenced to defined
(O2r) oxygen levels. See “SELECT MENU” for details.
Combustion Efficiency Calculation
The efficiency calculation is based upon British Standard BS845.
This identifies three sources of loss associated with fuel burning:
Losses due to flue gasses: Dry Flue gas loss
Moisture and hydrogen
Sensible heat of water vapor
Unburned gas
Losses due to refuse: Combustible in ash
Combustible in riddling
Combustible in dust
Other losses: Radiation
Convection
Conduction
Other unmeasured losses
Net efficiency calculations assume that the energy contained in the
water vapor (formed as a product of combustion and from wet fuel) is
recovered and the wet loss term is zero. Gross efficiency calculations
assume that the energy contained in the water vapor is not recovered.
Since the fuel to combustible matter in ashes, riddling, dust and grit,
radiation, convection and conduction are not included.
KM900CO/P-MAN P. 9