Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
1. What is the main component of natural gas?
Methane is the main component of natural gas. Natural gas is
around 85% - 95% methane.
2. What is the chemical formula for methane?
CH4
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2
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
3. How does dry natural gas differ from wet natural gas?
Wet has gas contains heavier hydrocarbons, such as propane,
butane, pentane, hexane and heptanes. Dry gas do not
contain these heavier hydrocarbons.
4. What is the chemical formula for propane?
C3H8
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
5.
What substance is added to natural gas and propane to
give them a distinctive odor?
An odorant known as ethyl mercaptan.
6. Define the term specific gravity.
It is the comparison between the density of any substance to
the density of another, usually water or air.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
7.
What are the specific gravities of natural gas and propane
vapor?
Natural gas’ specific gravity = .55
Propane’s specific gravity = 1.52 or 1.53
8.
What are the ratios of expansion from liquid to gas for
both natural gas and propane?
Natural gas’ ratio of expansion = 1:600
Propane’ ratio of expansion = 1:270
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
9.
What are the boiling temperatures for both natural gas
and propane?
Natural gas boils at -260 degrees F
Propane boils at -44 degrees F
10. Define calorific value.
The energy released when a given volume of fuel is burned.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
What are the accepted calorific values in Btu/ft3 for
natural gas and propane?
Natural gas = 1000 Btu/ft3
Propane = 2520 Btu/f3
11.
12.
What are the limits of flammability for natural gas and
propane?
Natural gas = 4 – 15%
Propane = 2.4 – 9.5%
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
13. Fill in the blanks with the correct word/phrase from the
Choices listed below.
❖
Choices: lowered below, 0.55, heat, boiling
temperature, –44ºF, dry, heat content, 1.52/1.53, vapor,
British Thermal, –258ºF, CH4 , sour, temperature, C3H8,
boiling, raise
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8
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
14. Continued
a)
b)
c)
d)
e)
f)
Wet gas is natural gas containing propane, butane, pentane, and other
heavy hydrocarbons.
Sour gas produced a common ingredient used in rubber products, carbon
black.
Natural gas with all the heavier hydrocarbons removed is also called dry
gas.
The accepted chemical composition for natural gas is CH4. Propane is
C3H8.
Air has specific gravity of 1.0. Vaporized propane’s specific gravity is 1.52
or 1.53
For natural gas it is 0.6.
At atmospheric pressure, propane has a boiling point of –44°F.
For natural gas, the boiling point occurs at –258°F
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
14. Continued
g)
h)
i)
The following statements refer to the vaporization of propane. If the
temperature of a fuel gas is lowered below its boiling point, it will not
vaporize. Propane cylinder pressure always varies with the temperature.
Considering temperature/pressure relationships, in a propane cylinder, an
increase in pressure means that the saturation point or boiling
temperature becomes progressively higher.
Vapour pressure is the term given to the molecular movement of LP
(propane) gas vapours
Calorific value is the heat content of a fuel. It is the energy released when
a given volume of fuel is burned. The common measurement unit used
when gas is burned is the British thermal unit. It is expressed as the
amount of heat required to the raise the temperature of one pound of
water one degree Fahrenheit.
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10
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
15. From the Choices listed, select the word/phrase that
correctly completes each sentence.
❖ Choices: bleach, butyl mercaptan, ethyl mercaptan
Since natural gas is undetectable by smell, the odorant
agent ethyl mercaptan is added for safety purposes.
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11
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
16. From the Choices listed, select the two-word
combination that correctly completes the following
statement.
❖ Choices: dense relativity, specific gravity, relative,
density, saturation point
The comparative weight of a volume of a liquid to an equal
volume of water is its specific
specific gravity or relative density.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
17. Select from the following Choices the number
relationship that correctly completes the following
statement.
❖ Choices: 0.58, 1.54, 0.51, 7.6
The specific gravity of liquid propane is .51
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13
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
18. Select from the following Choices the number ratio that
correctly completes each of the following statements.
Choices: 1:270, 1:300, 1:600, 1:670
At atmospheric pressure, propane gas expands at the ratio
of 270:1 when changing from a liquid to a gas.
The expansion ratio of natural gas from a liquid to a gas is
600:1.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Properties and Safe Handling of Fuel Gases
19. From the following Choices select the number(s)
combination that is appropriate to the fuel designation in
the table.
❖ Choices: 12; 2.4 - 9.5; 920; 3600, 4 -15; 11; 1300; 3600
Combustion Data
Propane
Natural gas
Flame Speed (inches/s)
11
12
Limits of Flammability (%)
Max. Flame Temperature (°F)
2.4 - 9.5
3600
4 - 15
3600
Ignition Temperature (°F)
920
1300
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15
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
20. What is the term used for the chemical process in which
the rapid oxidation of fuel results in the production of
heat?
Combustion
21. Approximately what percentage of air is made up of
oxygen?
Air is 20% oxygen
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
22. What are the approximate ignition temperatures (in °F
and °C) for propane and natural gas?
Natural gas = 1300 degrees F (700 degrees C)
Propane = 920 degrees F (495 degrees C)
23. What are the products of combustion for a hydrocarbon
fuel?
Carbon dioxide (CO2), water vapour (H20) and heat
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17
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
24. State the formula for perfect combustion for natural gas.
CH4 + 2O2 + 8N2 → CO2 + 2H20 + 8N2 + heat
25. What is added to the combustion process to ensure
complete combustion?
C3H8 + 5O2 + 20N2 + excess air → 3CO2 + 4H2O + 20N2 +
excess air + heat
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
26. Name two products of incomplete combustion.
Carbon monoxide and aldehydes
27. How are the three divisions of air supply categorized?
Combustion air, excess air and dilution air
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
28. What is the term used to describe the air that is mixed
with fuel gas before the point of ignition?
Primary air
29. What is the purpose of dilution air?
The purpose of dilution air is to cool the hot vent gases and
to provide a source of air to the draft control device
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
30. What is the air-to-gas ratio that applies to all fuel gases?
The ratio is 10:1
31. What is the normal percentage of combustion air to
excess air requirements for an atmospheric burner?
A volume of excess air equal to 50% of the combustion air
volume
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
32. What are the total air volume supply requirements for an
atmospheric burner?
1000 Btu of input requires 30ft3 of total air supply
33. List four possible causes of incomplete combustion, other
than lack of air.
- Flame temperature drops below 1300 degrees F
- Cracked heat exchanger causing less air and increased CO
- Negative air pressure
- Blocked venting
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
34. What are the three color zones of a stable Bunsen flame?
Inner cone, outer cone, outer mantle
35 -38. In Questions 35 through38, select from the following
the word/phrase that correctly completes each statement.
❖
Choices: secondary, to the total, heat, 5 ft3, excess, total,
920, oxygen, propane, aldehydes, primary, fuel, 1300,
50%, 15 ft3, odor, dilution, CH4, incomplete, oxidation
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
35. The Combustion Triangle’s elements are fuel , heat, and
oxygen .
36. CH4 is the chemical designation for natural gas. Its
ignition temperature is 1300 °F or 700°C.
An ignition temperature of 920 °F or 495°C and a
chemical designation of C3H8 identifies Propane.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
37. Aldehydes : transparent, colorless gases with a
suffocating smell that is toxic and irritating to the eyes.
They are produced by the partial oxidation of fuel
gas(es).
Carbon monoxide : It can cause death if enough is
inhaled; it has no, odor, taste, or smell; it is hard to detect
without proper equipment; and it’s one of the most
harmful products of incomplete combustion.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
38. Combustion air is subdivided into the two classifications of
primary air and secondary air. Total air describes the volume of
air required to allow the appliance to operate
safely and
efficiently.
The volume of excess air required for the efficient operation
of atmospheric burner fired equipment is equal to 50% of the
combustion air requirement or 5 ft3 for each 1000 Btu.
The volume of dilution air required for appliances
equipped with a draft control device should be equal to
the total of the combustion and excess air supplied the burner
or 15 ft3 for each 1000 Btu.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
39. Select from the following Choices the type of combustion
that correctly matches the definition described.
❖ Choices: Complete combustion, Incomplete combustion,
Stoichiometric combustion
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
39. Continued
Definition
The mathematically exact volume of air that
must be mixed with a fuel gas to achieve
perfect combustion.
Complete
combustio
n
All fuel is completely burned and no harmful
products of incomplete combustion are
produced.
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Stoichiome
tric
combustio
n
Unburned fuel will contain carbon, hydrogen Incomplete
carbon monoxide and complex chains of
combustio
alcohol (aldehydes)
n
28
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
40. Match each Definition to one of the following categories
of air.
❖
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
41. From the following Choices, select the correct term that
matches each description.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
42. From the following Choices match the cause the
symptoms described in the Table:
❖ Choices: Cracked Heat Exchanger, Negative Air Pressure,
Blocked Venting, Flame Temperature
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31
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
Description
of Symptoms
23. Continued
Excessive cold air is chilling the flame
front
Excessive air being exhausted from
building
Flame characteristics change as soon as
the blower comes on
Impingement on the cold metal surface
of the heat exchanger
Smoke stick check at draft hood
indicates negative pressure
A change in CO2/O2 levels in flue gases
when the blower starts
Excessive flue gas spilling out of the
draft hood
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Flame Temperature
Negative Air Pressure
Cracked Heat Exchanger
Flame Temperature
Blocked Venting
Cracked Heat Exchanger
Blocked Venting
32
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
43. The amount of gas/air mixture passing through a
burner port is referred to as port loading. It can be
changed by altering either the orifice size or the
manifold pressure. It is important for a stable flame; it
is expressed as Btu/h per sq. in. of port area.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
44. A reduction in gas density occurs at high altitudes,
i.e., for every 2000 ft rise in elevation the barometric
pressure decreases by 1 psia. The volume of natural
gas will thus expand to 1.072 ft3 (Boyles Law).
Describe an effect of this less dense gas on its flow.
The volume of the balloon will increase when there is
atmospheric pressure.
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Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
45. The combustion process must maintain a
temperature of approximately 1300 °F (700°C) for
natural gas.
46. A stable gas flame is a flame that does not waver, lift
off the burner, or flash in the mixing tube.
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35
Gas Trade 3 – Answer Key
Unit: Properties, Characteristics and Safe Handling of
Fuel Gases
Assignment: Combustion
47. From the following Choices, select the correct
amount of air to supply the input stated.
❖ Choices: 100, 3500, 2550, 1000, 255, 350, 10, 2500
100,000 Btu/h requires 1000
ft3 combustion air.
35,000 Btu/h requires 3500 ft3 combustion air.
255,000 Btu/h requires 2550 ft3 combustion air.
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