1. Unit 6 Theory of Gas and Combustion

2. OBJECTIVES Discuss the origins of natural gas and LP gas.
After studying this Unit, the student should be able to:
Discuss the origins of natural gas and LP gas.
Describe how gas is distributed to customers.
Explain the properties of natural , LP, and LP-air gases.
Have a working knowledge of gas combustion and burners.
Describe the condensing by-products of combustion.

3. TYPES OF FUEL Natural gas Manufactured gas Liquefied petroleum (LP)
Propane
Butane

4. Natural Gas About 95% methane and other hydrocarbons
Lighter than air (specific gravity = 0.60)
Colorless and odorless
Odorants are added for detection purposes
Displaces oxygen and can lead to suffocation
Produces about 1,000 btu per cubic foot

5. Manufactured Gas Liquefied Petroleum
Lighter than air (specific gravity = 0.60)
Produces about 540 btu per cubic foot
Liquefied Petroleum
Liquefied propane, butane or a combination of both
Kept in the liquid state until used
Utilizes a tank regulator

6. Propane Butane Produces about 2,500 btu per cubic foot
Heavier than air (specific gravity = 1.52)
Displaces oxygen
Can explode when allowed to accumulate
Butane
Produces about 3,200 btu per cubic foot
Not very popular, difficult to work with

7. GAS COMBUSTION Combustion requires fuel, oxygen and heat
Ignition temperature for natural gas is about 1,100°F
Perfect combustion produces carbon dioxide, water vapor and heat
Imperfect combustion produces carbon monoxide, soot and other products
Flame should be blue with orange tips
Yellow tips indicate that the flame is air-starved and that carbon monoxide is being produced

8. HEAT
OXYGEN
FUEL
COMPLETE COMBUSTION
HEAT
H2O VAPOR
CO2

9. INCOMPLETE COMBUSTION
HEAT
OXYGEN
FUEL
INCOMPLETE COMBUSTION
HEAT
CO2
H2O VAPOR
SOOT CO
TOXINS

10. BURNER FLAMES SHOULD BE BLUE WITH ORANGE TIPS
The orange in the flame is the result of dust particles drawn in with the primary air

11. GAS COMBUSTION
Gas pressure and primary air are the only adjustments that can be made in the field
Gas/air mixture is important
0 to 4% natural gas in the mixture will not burn
4 to 15% natural gas will burn and can explode
16 to 100% natural gas will not burn or explode
Limits of flammability vary for different gases
Excess primary air (about 50%) is supplied for better combustion

12. COMBUSTION EFFICIENCY
Incomplete combustion produces carbon monoxide
Correct air adjustments are essential
CO2 levels aid in secondary air adjustments
CO2 level increases as secondary air decreases
CO2 level for natural gas is 11.7% to 12.2%
CO2 of 14% for butane and 13.7% for propane
Correct flame should be blue with orange tips
Yellow flame indicates the production of carbon monoxide

13. Unit Summary TYPES OF FUEL Natural gas Manufactured gas
Liquefied petroleum (LP)
Propane
Butane
Natural Gas
About 95% methane and other hydrocarbons
Lighter than air (specific gravity = 0.60)
Colorless and odorless

14. Unit Summary Odorants are added for detection purposes
Displaces oxygen and can lead to suffocation
Produces about 1,000 btu per cubic foot
Manufactured Gas
Lighter than air (specific gravity = 0.60)
Produces about 540 btu per cubic foot
Propane
Produces about 2,500 btu per cubic foot
Heavier than air (specific gravity = 1.52)

15. Unit Summary Ignition temperature for natural gas is about 1,100°F
Perfect combustion produces carbon dioxide, water vapor and heat
Incomplete combustion produces carbon monoxide