Unit 6 Theory of Gas and Combustion

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.

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 Odorants are added for detection purposes Displaces oxygen and can lead to suffocation Produces about 1,000 btu per cubic foot

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

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

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

HEAT OXYGEN FUEL COMPLETE COMBUSTION HEAT H2O VAPOR CO2

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

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

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

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

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

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)

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