Boiler Operating Costs with #6 Oil and Natural Gas

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Boiler Operating Costs with Natural Gas and #6 Oil Dr. Herbert Eckerlin Center for Boiler Studies Raleigh, NC March 27, 2002

Transcript of Boiler Operating Costs with #6 Oil and Natural Gas

Page 1: Boiler Operating Costs with #6 Oil and Natural Gas

Boiler Operating Costs with Natural Gas and #6 Oil

Dr. Herbert EckerlinCenter for Boiler Studies

Raleigh, NC

March 27, 2002

Page 2: Boiler Operating Costs with #6 Oil and Natural Gas

Why Measure Parasitic Losses?

• Cost comparison based on “stack loss” only ignores parasitic losses and costs associated with oil-firing

• Important to quantify thermal losses and parasitic losses to determine the “true bottom line” efficiency and steam cost

• Bottom line efficiency helps in choosing the most economic fuel

Page 3: Boiler Operating Costs with #6 Oil and Natural Gas

Fuel

Stack Loss

Tg

% O2

Fire Tube Boiler

Page 4: Boiler Operating Costs with #6 Oil and Natural Gas

Effects of Excess Air on Flue Gas Composition

15

10

5

0-50 0 50 100 150 200

Excess Air

CO

CO2

CO2

O2

CO

2, C

O, o

r O

2(%

)

IncompleteCombustion

Excess Air (%)

Page 5: Boiler Operating Costs with #6 Oil and Natural Gas

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Typical Oil Firing SetTypical Oil Firing Set--upup

Page 6: Boiler Operating Costs with #6 Oil and Natural Gas

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Q StackThermal Losses Common forThermal Losses Common forNatural Gas and #6 Oil Natural Gas and #6 Oil –– stack lossstack loss

Page 7: Boiler Operating Costs with #6 Oil and Natural Gas

Thermal Losses Common for Natural Gas and #6 Oil

• Stack Loss– Largest single loss– Depends on flue gas temperature, ambient air

temperature, excess air and type of fuel– To determine stack loss, measure all above

parameters

Page 8: Boiler Operating Costs with #6 Oil and Natural Gas

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Q Stack

Q CO

Q CH

Thermal Losses Common for Natural Thermal Losses Common for Natural Gas and #6 Oil Gas and #6 Oil –– CO and UnCO and Un--burnt CH burnt CH

Page 9: Boiler Operating Costs with #6 Oil and Natural Gas

Thermal Losses Common for Natural Gas and #6 Oil

• CO and un-burnt CH – Caused by incomplete combustion– Lack of air to support complete combustion– Poor mixing of fuel and air– Poor atomization of fuel oil

Page 10: Boiler Operating Costs with #6 Oil and Natural Gas

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Q Oil Storage Tank

Q Stack

Q CO

Q CH

Parasitic Losses for #6 OilParasitic Losses for #6 OilTank HeatingTank Heating

Page 11: Boiler Operating Costs with #6 Oil and Natural Gas

Parasitic Losses for #6 Oil

• Oil Tank Heating– Fuel oil is viscous and requires heating to

facilitate pumping– Generally heated to 140 F– Heat loss can be quite high for single wall un-

insulated oil storage tanks

Page 12: Boiler Operating Costs with #6 Oil and Natural Gas

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+Q Oil Heater

Q Oil Storage Tank

Q Stack

Q CO

Q CH

Q Oil Pumping

Parasitic Losses for #6 OilParasitic Losses for #6 OilPumping & PreheatingPumping & Preheating

Page 13: Boiler Operating Costs with #6 Oil and Natural Gas

Parasitic Losses for #6 Oil

• Oil Pumping– Pumps are required to circulate oil from storage

tank to the burner• Oil Preheating

– To ensure proper atomization, oil must be heated 200 – 220 oF

– Generally heated by steam or hot water– In some fire tube boiler application, steam/hot

water heating is augmented by electric heating

Page 14: Boiler Operating Costs with #6 Oil and Natural Gas

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+Q Oil Heater

Q Oil Storage Tank

Q Atom

Q Stack

Q CO

Q CH

Q Oil Pumping

Parasitic Losses for #6 OilParasitic Losses for #6 OilAtomizationAtomization

Page 15: Boiler Operating Costs with #6 Oil and Natural Gas

Parasitic Losses for #6 Oil

• Oil Atomization– For proper combustion, oil must be broken up

into small particles– Done by injecting steam or compressed air into

small oil supply at the burner

Page 16: Boiler Operating Costs with #6 Oil and Natural Gas

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+Q Oil Heater

Q Oil Storage Tank

Q Atom

Q Stack

Q SootBlowers

Q CO

Q CH

Q Oil Pumping

Parasitic Losses for #6 OilParasitic Losses for #6 OilSoot BlowingSoot Blowing

Page 17: Boiler Operating Costs with #6 Oil and Natural Gas

Parasitic Losses for #6 Oil

• Soot Blowing– Soot is created by oil burning– Soot leaves deposits on boiler tubes– Reduces heat transfer to boiler fluid– Generally cleaned by steam or compressed air– Fire tube boiler generally do not use soot blowers– Soot removal must be done by punching the tubes when

stack temperature gets too high– Should be done at least quarterly to prevent high stack

temperature resulting in high stack loss– Boiler must be shut down when tubes are punched

Page 18: Boiler Operating Costs with #6 Oil and Natural Gas

Flue Gas Temperature Over Time

200

250

300

350

400

450

0 5 10 15 20 25 30Days

Deg

F

#6 Oil High Fire

Gas High Fire

Gas Low Fire#6 Oil Low Fire

Page 19: Boiler Operating Costs with #6 Oil and Natural Gas

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+Q Oil Heater

Q Oil Storage Tank

Q Atom

Q Stack

$ Water$ Chemical $ Preheating

$ Maintenance$ Fuel Oil Additives

$ Oil Inventory

$ Corrosion

Additional Makeup Water

Q SootBlowers

Q CO

Q CH

Q Oil Pumping

Parasitic Losses and Cost for #6 OilParasitic Losses and Cost for #6 OilInventory, Additives, Maintenance etc.Inventory, Additives, Maintenance etc.

Page 20: Boiler Operating Costs with #6 Oil and Natural Gas

Parasitic Losses and Cost for #6 Oil

• Oil Storage Inventory– Storing oil on site ties up capital– This investment yields no return

• Oil Additives– Purposes

• Reduce sludge in oil storage tank• Improve combustion• Reduce soot deposits• reduce cold end corrosion

Page 21: Boiler Operating Costs with #6 Oil and Natural Gas

Parasitic Losses and Cost for #6 Oil

• Corrosion and Maintenance– Sulphur in oil causes cold end corrosion– Adds to maintenance costs– Reduces boiler life

Page 22: Boiler Operating Costs with #6 Oil and Natural Gas

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Q Oil Heater0.35%

Q Oil Storage Tank8.40%

Q Atom0.93%

Q Stack 12.4%

Q SootBlowers

Q CO

Q CH

Q Oil Pumping1.15%

220oF

Radiation 1.0%

$ Water$ Chemical $ Preheating

$ Maintenance3.41%

$ Fuel Oil Additives

$ Oil Inventory0.30%

$ Corrosion

Additional Makeup Water

140oF

Summary of Thermal and Summary of Thermal and Parasitic LossesParasitic Losses

Page 23: Boiler Operating Costs with #6 Oil and Natural Gas

Bottom Line Efficiency forOil Firing

100

Stack Loss 12.4

Radiation 1.0Oil Pumping 1.15

Oil Atomization 0.93

Corrosion & Maintenance 3.41Oil Inventory 0.3

Oil Heating 0.35

Oil Tank Heating 8.4Bottom Line Efficiency 72%

Page 24: Boiler Operating Costs with #6 Oil and Natural Gas

Bottom Line Boiler Efficiency Comparison

82.590

72

0102030405060708090

100

N.G. StandardBoiler

N.G. HighEfficiency Boiler

#6 Fuel Oil

Page 25: Boiler Operating Costs with #6 Oil and Natural Gas

Effect of Parasitic Losses on Cost of Delivered Steam

$7.3230.6

$/GJcents/litre

Cost of Delivered Steam(considering stack and parasitic losses)

$1.238.6

$/GJcents/litre

Incremental Cost Increase(due to parasitic losses)

$6.09$/GJCost of Delivered Steam(considering stack and radiation losses)

22.0$5.27

cents/litre$/GJ

Average Fuel Cost

Page 26: Boiler Operating Costs with #6 Oil and Natural Gas

Conclusions

• On average, parasitic losses can add about 9 cents per litre to #6 fuel oil price

• Take into account all parasitic losses and costs associated with #6 fuel oil firing while comparing costs with natural gas

• Keep boilers properly tuned for maximum efficiency