PACIA Carbon
Solutions Forum 3 29 September 20
Boiler and Steam Efficiency
What does it mean?
Andrew Hook - Area Manager, Nalco
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Purpose, Process, Payoff
Purpose:
• To explain boiler and steam efficiencies
through case studies, and impact on carbon
Process:
• Initial definitions
• Walk through “real-life” examples, discussing
impacts on carbon
Payoff:
• Awareness of ways to impact on efficiency
• Routes to getting more information
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Boiler Anatomy
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Boiler efficiencies and
Carbon?
• Steam is generated through combustion of fuel
– Fuel : CxHy+(X+[Y/4])*O2 -> XCO2+Y/2*(H2O)
– Want to maximize the energy obtained from this
combustion
• Hence, any losses from the boiler box and stack losses
reduces efficiency
• Efficiencies of boilers (and steam systems) are a
function of the losses:
– Overall Efficiency (“Heat loss method”) can be
defined as:
• (TAFT – TSTACK)/(TAFT – TAMBIENT) *100
Where AFT=Adiabatic Flame Temperature
Stack = Flue Gas Temperature
Ambient = Ambient Dry Bulb
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For the test later on…
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Boiler efficiencies and
Carbon?
• This method of efficiencies is the “input - output”
method:
– Net Energy contained in steam / (Total energy
obtained from combustion) *100
http://www.abma.com
• Rules of thumb:
– CO2 generation per tonne of fuel burnt (normal
efficiencies)
• Natural Gas
• Oil
• Black Coal
:
:
:
2.8 tCO2/t fuel
3.0 tCO2/t fuel
2.3 tCO2/t fuel
Note that NG has a higher energy content
http://www.eia.doe.gov/oiaf/1605/coefficients.html
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What are “normal efficiencies”?
• Boiler Efficiency will never be 100%
• Losses:
– Insulation
– Stack
• Air is 79% Nitrogen, 21% Oxygen, so most air is along
for the ride!
• Water generated in combustion carries latent heat out
the stack too!
• “Typical” boiler efficiencies:
– Natural Gas:
– Oil:
– Black Coal:
80-85%
75-80%
75-78%
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Case Study 1:
Economizer Failure
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Case Study 1:
Economizer Failure
• Failure of economizers led to 40°C reduction in
feedwater temperature
– What is the loss in efficiency?
– What is the CO2 impact? Cost?
– Why did they fail?
• Loss of efficiency:
– Loss of each 6°C = 1% efficiency (roughly)
– Therefore, lost around 6% efficiency (from 80%)
• CO2 impact and Cost:
– Prior to failure, used around 10,000 m3/day of natural gas,
after 12,000m3, running around 7500 hr/yr, $3.41/GJ
– Extra 1750 t/year CO2, $99,100/yr cost increase ($57/t..)
• Failure? Poor deaeration of feedwater
– Remedy – on-line monitoring of feedwater and
control of oxygen scavenger
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Case Study 2:
Tube Scaling
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Case Study 2:
Boiler Scaling
• Deposition of scale led to approx 2% increase in fuel
and increase in stack temp of around 45°C
– What is the loss in efficiency?
– What is the CO2 impact? Cost?
– Why did this happen?
• Loss of efficiency:
– Increase of each 22°C in stack temp = 1% efficiency (roughly)
– Therefore, lost around 2% efficiency (from 80%)
• CO2 impact and Cost:
– Current: 473, 000 GJ/yr fuel, 8000 hr/yr at around 2% fuel
increase, around 3.41 $/GJ as natural gas
– Extra 570 t/year CO2, $32,250/yr cost increase
• Failure? Use of “dirty” precipitating phosphate
program on poorly softener water
– Remedy – monitor hardness breakthrough from
boilers, use solubilizing chemical program, watch cycles
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Case Study 3:
Cycles of Concentration
• Boiler in Case Study 1 running at 20 cycles of
concentration (expect 50 cycles)
– What is the loss in efficiency?
– What is the CO2 impact? Cost?
– Why is this happening?
• Loss of efficiency:
– Approximately 1%
• CO2 impact and Cost:
– Using around 10,000 m3/day of natural gas, running around
7500 hr/yr, $3.41/GJ, water around $1/kL
– Extra 993 t/year CO2, $65,960/yr fuel cost increase , $14,100
water increase
• Why is this happening? Habit and focus on cycles
– Remedy – monitor cycles, push to limits, but no more
than 50 in low pressure boilers (HP 50-100)
– Technologies available for tight control
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Case Study 4:
Cycles of Concentration
• Boiler in Case Study 1 running at 30% condensate
return (expect 50%)
– What is the loss in efficiency?
– What is the CO2 impact? Cost?
– Why is this happening?
• Loss of efficiency:
– Approximately ZERO (as boiler efficiency!)
• CO2 impact and Cost:
– Using around 10,000 m3/day of natural gas, running around
7500 hr/yr, $3.41/GJ, water around $1/kL
– Extra 2656.2 t/year CO2, $176463/yr fuel cost increase,
$92211 water increase
• Why is this happening? Leaks habit, and focus on
condensate return%
– Remedy – monitor return and condensate % return
and elevate priority
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Reference Sites
• US Department of Energy (DOE)
– Great site, many, many worked examples
• EREP website:
www.epa.vic.gov.au/bus/erep/default.asp
• The internet is a great resource for many tips
• Nalco Water Handbook (plug for our
company!)
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