Properties of Fuel Gases Flashcards
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A gas technician is investigating a reported gas odor in the basement of a residence. Which property of propane (LPG) is most critical to consider in this scenario?
Answer: Its specific gravity is greater than air, causing it to accumulate in low areas.
Propane has a specific gravity of approximately 1.52, making it heavier than air (specific gravity of 1.0). This means that if a leak occurs, the propane gas will sink and collect in low-lying areas like basements, creating a significant safety hazard. Natural gas, with a specific gravity of about 0.6, is lighter than air and would dissipate upwards.
Which of the following statements accurately compares the heating value of natural gas and propane?
Answer: Propane has a significantly higher heating value per cubic foot than natural gas.
Propane has a much higher energy content by volume compared to natural gas. A cubic foot of propane yields approximately 2,500 BTUs, whereas a cubic foot of natural gas yields about 1,000-1,030 BTUs. This difference is crucial for appliance orifice sizing and system design.
Incomplete combustion of a hydrocarbon fuel, such as natural gas or propane, occurs due to insufficient oxygen. What is the primary toxic gas produced as a result?
Answer: Carbon Monoxide (CO)
When there is not enough oxygen for complete combustion, the burning process is incomplete and produces carbon monoxide (CO), a colorless, odorless, and highly toxic gas. Complete combustion ideally produces carbon dioxide (CO2) and water vapor.
The 'flammable range' or 'explosive limits' of a fuel gas refers to the concentration of gas in a gas-air mixture that will support combustion. What defines the Lower Explosive Limit (LEL)?
Answer: The minimum concentration of gas in air that will burn.
The Lower Explosive Limit (LEL), also known as the Lower Flammability Limit (LFL), is the lowest concentration (percentage) of a gas or vapor in the air that is capable of producing a flash of fire when an ignition source is present. A mixture below the LEL is considered 'too lean' to burn.
A technician is converting a furnace from natural gas to propane. What fundamental property difference requires the technician to change the orifices?
Answer: Propane has a higher heating value and requires a different air-to-gas ratio.
Propane has a higher heating value (approx. 2,500 BTU/ft³) than natural gas (approx. 1,000 BTU/ft³). To deliver the correct amount of energy and ensure complete combustion, a smaller orifice is needed for propane to restrict the higher-energy fuel flow. Propane also requires a different air-to-gas ratio for combustion (approx. 24:1) compared to natural gas (approx. 10:1).
What is the specific gravity (or relative density) of a gas a measure of?
Answer: The ratio of the gas's density to the density of air.
Specific gravity, also known as relative density, for a gas is a dimensionless quantity that compares the density of that gas to the density of a reference material, which for gases is typically air. Air is assigned a specific gravity of 1.0. Gases with a specific gravity less than 1.0 are lighter than air, and those with a value greater than 1.0 are heavier than air.