Tulsa Heaters Midstream 2
Fired Heater Efficiency
βWhy is the efficiency of my fired heater important?β
Because inefficient heaters cost you money!
Tulsa Heaters Midstream 3
Measuring Fired Heater EfficiencyThis guide will teach you the process of measuring and calculating your heaterβs efficiency β so you can optimize your plant andsave money.
β’ Based on method outlined in API 560 Annex G
β’ Procedure intended for fired heaters burning liquid or gaseous fuels. Not recommended for solid fuels.
What do we mean by βefficiencyβ?
Tulsa Heaters Midstream 5
Thermal VS Fuel Efficiency
THERMAL EFFICIENCY- total heat absorbed divided by total heat input
FUEL EFFICIENCY- total heat absorbed divided by heat input derived
from the combustion of the fuel only
NOTE: this definition differs from the traditional definition of fired heater efficiency, which generally refers to fuel efficiency
Tulsa Heaters Midstream 6
Equipment Needed
β’ Temperature-measuring devices, such as thermocouples or thermometers, to measure the temperature of:β’ Fuel
β’ Ambient air
β’ Atomizing medium (if applicable)
β’ Flue gas
β’ Thermal fluid
β’ Flue-gas analytical devices to measure oxygen and combustible gases
Tulsa Heaters Midstream 7
Before the Test
Establish and maintain operating conditions
Select and calibrate instrumentation
Perform any re-rating necessary to account for differences between design and test conditions
Ensure fuel is acceptable for the test
Ensure heater is operating properly with respect to the size and shape of flame, excess air & draught
Tulsa Heaters Midstream 8
Testing
Test procedure:
Measurements:
β’ The heater shall be operated at a uniform rate throughout the test
β’ Data shall be taken at the start of the test, and every 2 hours thereafter
β’ The duration of the test shall extend until three consecutive sets of collected data fall within the prescribed limits
β’ Fuel gas quantity and heating value
β’ Flue-gas temperature and composition analysis
Tulsa Heaters Midstream 10
ExampleHot oil heater for gas plant Ambient air temperature: 70Β°F
Relative humidity: 50%Fuel gas composition (vol%):β’ Nitrogen β 1.61β’ Carbon dioxide β 0.15β’ Methane β 98.17β’ Ethane β 0.008
Fuel gas LHVβ’ 20,814 Btu/lb
Fuel gas HHVβ’ 23,115 Btu/lb
Fuel gas temperatureβ’ 100Β°F
Fuel gas pressureβ’ 50 psig
Excess Oxygen: 3% (dry)
Radiation heat loss: 1.5%
Tulsa Heaters Midstream 11
Thermal Efficiency
Where:βπΏ lower heating value of the fuel (Btu/lb)
ββπ heat correction due to air (Btu/lb)
ββπ heat correction due to fuel (Btu/lb)
ββπ heat correction due to atomizing medium (Btu/lb)
βπ assumed radiation heat loss (Btu/lb)
βπ calculated stack heat loss (Btu/lb)
π = ππ³ + βππ + βππ + βππ β (ππ + ππ
ππ³ + βππ + βππ + βππ
Γ πππ
Need to solve for all variables
Step 1:solve for heat loss through the stack (βπ )
Tulsa Heaters Midstream 14
Combustion Worksheet
Fuel Component
Column 1
Volume fraction
%
Nitrogen 1.61
Carbon dioxide
0.15
Methane 98.17
Ethane 0.08
TOTAL -
Total per pound of fuel
-
Insert fuel composition into combustion worksheet
Tulsa Heaters Midstream 15
Combustion Worksheet
Fuel Component
Column 1
Volume fraction
%
Column 2
Relativemolecular
mass
Column 3 (1x2)
Total mass
(lb)
Column 4
Net heating value
(Btu/lb)
Column 5 (3x4)
Heatingvalue(Btu)
Nitrogen 1.61 28.0 0.4508 - -
Carbon dioxide
0.15 44.0 0.066 - -
Methane 98.17 16.0 15.70 21,500 337,704.80
Ethane 0.08 30.1 0.02 20,420 491.71
TOTAL - - 16.25 - 338,196.51
Total per pound of fuel
- - - - 20,814.55
(5)
Calculate total mass and heating value of fuel
Tulsa Heaters Midstream 16
Combustion Worksheet
Fuel Component
Column 1
Volume fraction
%
Column 2
Relativemolecular
mass
Column 3 (1x2)
Total mass
(lb)
Column 4
Net heating value
(Btu/lb)
Column 5 (3x4)
Heatingvalue(Btu)
Column 6
Air required(lb air/lb)
Column 7(3x6)
Air required
(lbs)
Column 8
CO2
formed(lbs CO2/lb)
Column 9 (3x8)
CO2
formed (lbs)
Column 10
H2O formed
(lbs H2O/lb)
Column 11 (3x10)
H2Oformed
(lbs)
Column 12
N2
formed (lbs N2/lb)
Column 13 (3x12)
N2
formed (lbs)
Nitrogen 1.61 28.0 0.4508 - - - - - - - - - -
Carbon dioxide
0.15 44.0 0.066 - - - - - - - - - -
Methane 98.17 16.0 15.70 21,500 337,704.80 17.24 270.79 2.74 43.04 2.25 35.34 13.25 208.12
Ethane 0.08 30.1 0.02 20,420 491.71 16.09 0.39 2.93 0.07 1.80 0.04 12.37 0.30
TOTAL - - 16.25 - 338,196.51 - 271.18 - 43.11 - 35.38 - 208.42
Total per pound of fuel
- - - - 20,814.55 - 16.69 - 2.65 - 2.18 - 12.83
(5) (7) (9) (11) (13)
Calculate products of combustion for fuel
Tulsa Heaters Midstream 17
Completed Combustion Worksheet
Fuel Component
Column 1
Volume fraction
%
Column 2
Relativemolecular
mass
Column 3 (1x2)
Total mass
Column 4
Net heating value
(Btu/lb)
Column 5 (3x4)
Heatingvalue(Btu)
Column 6
Air required(lb air/lb)
Column 7(3x6)
Air required
(lbs)
Column 8
CO2
formed(lbs CO2/lb)
Column 9 (3x8)
CO2
formed (lbs)
Column 10
H2O formed
(lbs H2O/lb)
Column 11 (3x10)
H2Oformed
(lbs)
Column 12
N2
formed (lbs N2/lb)
Column 13 (3x12)
N2
formed (lbs)
Nitrogen 1.61 28.0 0.4508 - - - - - - - - - -
Carbon dioxide
0.15 44.0 0.066 - - - - - - - - - -
Methane 98.17 16.0 15.70 21,500 337,704.80 17.24 270.79 2.74 43.04 2.25 35.34 13.25 208.12
Ethane 0.08 30.1 0.02 20,420 491.71 16.09 0.39 2.93 0.07 1.80 0.04 12.37 0.30
TOTAL - - 16.25 - 338,196.51 - 271.18 - 43.11 - 35.38 - 208.42
Total per pound of fuel
- - - - 20,814.55 - 16.69 - 2.65 - 2.18 - 12.83
(5) (7) (9) (11) (13)
Tulsa Heaters Midstream 18
Relative Humidity
Correction for relative humidity:
where:
πvapor vapor pressure of water at ambient temperature
(from steam tables)
πair 14.696 psi
=πvapor
πairΓ
π π»
100Γ
18
28.85moisture in air
Tulsa Heaters Midstream 19
Relative Humidity
Correction for relative humidity:
where:
πvapor vapor pressure of water at ambient temperature
(from steam tables)
πair 14.696 psi
=πvapor
πairΓ
π π»
100Γ
18
28.85moisture in air
=0.364
14.696Γ
50
100Γ
18
28.85
= 0.0077 lbs of moisture per lb of air (a)
Tulsa Heaters Midstream 20
Relative Humidity
Correction for relative humidity:
where:
πvapor vapor pressure of water at ambient temperature
(from steam tables)
πair 14.696 psi
=πvapor
πairΓ
π π»
100Γ
18
28.85moisture in air
=0.364
14.696Γ
50
100Γ
18
28.85
= 0.0077 lbs of moisture per lb of air (a)
=air required
1 β moisture in air (a)
(7)
= 16.82 lbs of wet air per lb of fuel
=16.69
1 β 0.0077
(b)
Tulsa Heaters Midstream 21
Relative Humidity
Correction for relative humidity:
where:
πvapor vapor pressure of water at ambient temperature
(from steam tables)
πair 14.696 psi
=πvapor
πairΓ
π π»
100Γ
18
28.85moisture in air
=0.364
14.696Γ
50
100Γ
18
28.85
= 0.0077 lbs of moisture per lb of air (a)
=air required
1 β moisture in air (a)
(7)
= 16.82 lbs of wet air per lb of fuel
=16.69
1 β 0.0077
(b)
= lbs wet air per lb of fuel(b) β air required(7)
= 0.1295 lbs of moisture per lb of fuel (c)
= 16.82 β 16.69
Tulsa Heaters Midstream 22
Relative Humidity
Correction for relative humidity:
where:
πvapor vapor pressure of water at ambient temperature
(from steam tables)
πair 14.696 psi
=πvapor
πairΓ
π π»
100Γ
18
28.85moisture in air
=0.364
14.696Γ
50
100Γ
18
28.85
= 0.0077 lbs of moisture per lb of air (a)
=air required
1 β moisture in air (a)
(7)
= 16.82 lbs of wet air per lb of fuel
=16.69
1 β 0.0077
(b)
= lbs wet air per lb of fuel(b) β air required(7)
= 0.1295 lbs of moisture per lb of fuel (c)
= H2O formed(11) + lbs of moisture per lb of fuel(c) + atomizing steam
= 2.31 lbs of H2O per lb of fuel (d)
= 2.17 + 0.1295 + 0
= 16.82 β 16.69
Tulsa Heaters Midstream 23
Excess Air
Correction for excess air:
=(28.85 Γ%O2)(
N2 formed28
+CO2 formed
44+
H2O formed18
)
20.95 β%O2[ 1.6028 Γlbs H2O
lbs air required+ 1]
lb excess air per lb of fuel
NOTE: If oxygen samples are extracted on a dry basis, a value of zero shall be inserted for line (e) where a value is required from lines (c) and (d). If oxygen samples are extracted on a wet basis, the appropriate calculated value shall be inserted.
Tulsa Heaters Midstream 24
Excess Air
Correction for excess air:
=(28.85 Γ%O2)(
N2 formed28
+CO2 formed
44+
H2O formed18
)
20.95 β%O2[ 1.6028 Γlbs H2O
lbs air required+ 1]
lb excess air per lb of fuel
NOTE: If oxygen samples are extracted on a dry basis, a value of zero shall be inserted for line (e) where a value is required from lines (c) and (d). If oxygen samples are extracted on a wet basis, the appropriate calculated value shall be inserted.
=(28.85 Γ%O2)(
N2 formed28
+CO2 formed
44+
H2O formed18
)
20.95 β%O2[ 1.6028 Γlbs H2O
lbs air required+ 1]
(13) (9) (d)
(c)
(7)
=(28.85 Γ 3)(
12.8328
+2.6544
+018
)
20.95 β 3[ 1.6028 Γ0
16.69+ 1]
= 2.50 lbs of excess air per lb of fuel (e)
Tulsa Heaters Midstream 25
=lb of excess air per lb of fuel
air requiredΓ 100
Excess Air
Correction for excess air:
=(28.85 Γ%O2)(
N2 formed28
+CO2 formed
44+
H2O formed18
)
20.95 β%O2[ 1.6028 Γlbs H2O
lbs air required+ 1]
lb excess air per lb of fuel
NOTE: If oxygen samples are extracted on a dry basis, a value of zero shall be inserted for line (e) where a value is required from lines (c) and (d). If oxygen samples are extracted on a wet basis, the appropriate calculated value shall be inserted.
=(28.85 Γ%O2)(
N2 formed28
+CO2 formed
44+
H2O formed18
)
20.95 β%O2[ 1.6028 Γlbs H2O
lbs air required+ 1]
(13) (9) (d)
(c)
(7)
=(28.85 Γ 3)(
12.8328
+2.6544
+018
)
20.95 β 3[ 1.6028 Γ0
16.69+ 1]
= 2.50 lbs of excess air per lb of fuel (e)
(7)
(e)
=2.50
16.69Γ 100
= 14.98 lbs excess air (f)
Tulsa Heaters Midstream 26
=lb of excess air per lb of fuel
air requiredΓ 100
Excess Air
Correction for excess air:
=(28.85 Γ%O2)(
N2 formed28
+CO2 formed
44+
H2O formed18
)
20.95 β%O2[ 1.6028 Γlbs H2O
lbs air required+ 1]
lb excess air per lb of fuel
NOTE: If oxygen samples are extracted on a dry basis, a value of zero shall be inserted for line (e) where a value is required from lines (c) and (d). If oxygen samples are extracted on a wet basis, the appropriate calculated value shall be inserted.
=(28.85 Γ%O2)(
N2 formed28
+CO2 formed
44+
H2O formed18
)
20.95 β%O2[ 1.6028 Γlbs H2O
lbs air required+ 1]
(13) (9) (d)
(c)
(7)
=(28.85 Γ 3)(
12.8328
+2.6544
+018
)
20.95 β 3[ 1.6028 Γ0
16.69+ 1]
= 2.50 lbs of excess air per lb of fuel (e)
=percent excess air
100Γ lbs moisture per lb fuel + lb H2O per lb fuel
(7)
(e)
=2.50
16.69Γ 100
= 14.98 lbs excess air (f)
(f)(c) (d)
=14.98
100Γ 0.1295 + 2.31
= 2.33 total lbs H2O per lb of fuel (corrected for excess air) (g)
Tulsa Heaters Midstream 27
Stack Loss
ComponentColumn 1
Component formed(lb per lb of fuel)
Carbon dioxide 2.65
Water vapor 2.33
Nitrogen 12.83
Air 2.50
Total 20.31
(9) from combustion worksheet
(13) from combustion worksheet
(g) from excess air worksheet
(e) from excess air worksheet
Tulsa Heaters Midstream 28
Stack Loss
ComponentColumn 1
Component formed(lb per lb of fuel)
Column 2
Enthalpy at T(Btu/lb formed)
Carbon dioxide 2.65 100
Water vapor 2.33 192
Nitrogen 12.83 120
Air 2.50 110
Total 20.31 -
Exit flue-gas temperature, ππ: 500Β°F
Values taken from enthalpy tables in API 560, Figures G.6 and G.7 for each flue-gas component
Tulsa Heaters Midstream 29
Stack Loss
ComponentColumn 1
Component formed(lb per lb of fuel)
Column 2
Enthalpy at T(Btu/lb formed)
Column 3
Heat content(Btu/lb of fuel)
Carbon dioxide 2.65 100 265.31
Water vapor 2.33 192 446.72
Nitrogen 12.83 120 1,539.27
Air 2.50 110 274.98
Total 20.31 - 2,526.28
Exit flue-gas temperature, ππ: 500Β°F
βπ = heat content at ππ = 2,526.28 Btu/lb of fuel
Step 2:solve for additional heat losses
Tulsa Heaters Midstream 31
Thermal Efficiency
Where:βπΏ lower heating value of the fuel (Btu/lb)
ββπ heat correction due to air (Btu/lb)
ββπ heat correction due to fuel (Btu/lb)
ββπ heat correction due to atomizing medium (Btu/lb)
βπ assumed radiation heat loss (Btu/lb)
βπ calculated stack heat loss (Btu/lb)
π = ππ³ + βππ + βππ + βππ β (ππ + ππ
ππ³ + βππ + βππ + βππ
Γ πππ
Tulsa Heaters Midstream 32
Heat Losses
Heat loss due to air:
ββπ = ππa Γ (ππ β ππ) Γ ( ππ ππ)
where:
ππa specific heat of air
ππ temperature of air (Β°F)
ππ temperature of design air (Β°F)
ππ ππ the sum of ππ and ππ, expressed as
pounds of air per pound of fuel (from lines (b) and (e) on the excess air and relative humidity work sheet)
= ππa Γ (ππ β ππ) Γ ( ππ ππ)
= 0.24 Γ (70 β 60) Γ (16.81 + 2.50)
ββπ = 46.37 Btu/lb
Tulsa Heaters Midstream 33
Heat Losses
Heat loss due to fuel gas:
ββπ = ππfuel Γ (ππ β ππ)
where:
ππfuel specific heat of fuel gas
ππ temperature of fuel gas (Β°F)
ππ temperature of design fuel gas (Β°F)
= ππfuel Γ (ππ β ππ)
= 0.587 Γ (100 β 60)
ββπ = 23.47 Btu/lb
Tulsa Heaters Midstream 34
Heat Losses
Heat loss due to atomization medium:
ββπ = βπΈ Γ ( ππ π‘ ππ)
where:
βπΈ enthalpy difference
ππ π‘ mass of steam (lb)
No atomization steam in this case.
ββπ = 0
Tulsa Heaters Midstream 35
Radiation Losses
Heat loss due to radiation:
βπ = βπΏ Γ%radiation loss βπ = 20,814 Γ 0.015
βπ = 312.24 Btu/lb
Step 3:solve for thermal and fuel efficiencies
Tulsa Heaters Midstream 37
Thermal Efficiency
Where:βπΏ 20,814 Btu/lb
ββπ 46.37 Btu/lb
ββπ 23.47 Btu/lb
ββπ 0 Btu/lb
βπ 312.24 Btu/lb
βπ 2,526.28 Btu/lb
π = ππ³ + βππ + βππ + βππ β (ππ + ππ
ππ³ + βππ + βππ + βππ
Γ πππ
Tulsa Heaters Midstream 38
Thermal Efficiency
Where:βπΏ 20,814 Btu/lb
ββπ 46.37 Btu/lb
ββπ 23.47 Btu/lb
ββπ 0 Btu/lb
βπ 312.24 Btu/lb
βπ 2,526.28 Btu/lb
π = ππ³ + βππ + βππ + βππ β (ππ + ππ
ππ³ + βππ + βππ + βππ
Γ πππ
π = ππ³ + βππ + βππ + βππ β (ππ + ππ
ππ³ + βππ + βππ + βππ
Γ πππ
π =)ππ, πππ + ππ. ππ + ππ. ππ + π β (πππ. ππ + π, πππ. ππ
ππ, πππ + ππ. ππ + ππ. ππ + πΓ πππ
π = 86.4%
Tulsa Heaters Midstream 39
Fuel Efficiency
Where:βπΏ 20,814 Btu/lb
ββπ 46.37 Btu/lb
ββπ 23.47 Btu/lb
ββπ 0 Btu/lb
βπ 312.24 Btu/lb
βπ 2,526.28 Btu/lb
ππ = ππ³ + βππ + βππ + βππ β (ππ + ππ
ππ³Γ πππ
Tulsa Heaters Midstream 40
Fuel Efficiency
Where:βπΏ 20,814 Btu/lb
ββπ 46.37 Btu/lb
ββπ 23.47 Btu/lb
ββπ 0 Btu/lb
βπ 312.24 Btu/lb
βπ 2,526.28 Btu/lb
ππ = ππ³ + βππ + βππ + βππ β (ππ + ππ
ππ³Γ πππ
ππ = ππ³ + βππ + βππ + βππ β (ππ + ππ
ππ³Γ πππ
ππ =)ππ, πππ + ππ. ππ + ππ. ππ + π β (πππ. ππ + π, πππ. ππ
ππ, πππΓ πππ
ππ = 86.7%
* Based on $2.75/MMBtu gas price
Tulsa Heaters Midstream 42
Conclusion
Knowing how to check your heaterβs efficiency gives you the
knowledge and power to improve your facility and optimize
your heater. As we have seen, improving efficiency can help
save your facility a lot of money.
What are you waiting for? Go check and start saving now!
Tulsa Heaters Midstream 43
Want to learn more? Check out our other resources
RESOURCES
Follow us:
www.tulsaheatersmidstream.com