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In grills, propane or butane (bottled) gas will usually produce more BTU's
than natural (methane) gas in grills because propane is delivered at a
higher pressure, and therefore more gas is available for burning at any
given time. It also produces more BTU's per cubic foot of gas. Propane gas
pressure is adjustable by a pressure regulator which normally provides gas
at 6.3 ounces per square inch (11 inches of water column). Natural gas is
normally delivered to households at 4 ounces per square inches (7 inches of
water column) past the regulator --- corrected for elevation.
GAS FACTS
Because liquid is more dense than gas, butane and propane are bottled
under pressure in their liquid state. Their low boiling points causes them
to make a phase change to gas when the bottle valves are opened. For
heating/cooking purposes, methane is delivered by pipe because methane gas
requires tremendous pressure and cooling to change into liquid.
Propane's ( C3H8) boiling point, at atmospheric pressure, is -44° F. while
butane's (C4H10) boiling point is 310° F. Natural (methane, CH4) gas boils
at -260° F. Higher boiling point is why propane is more widely used as
bottled gas than butane.
Without getting too deeply into physics, boiling points rise with
pressure. Bottled gasses are under varying pressures, depending upon the
quantity of gas in the tank and temperature. Therefore, while propane boils
at -44° at atmospheric pressure, 14.7 pounds per square inch (psi), the
boiling point of the liquid under 100 pounds of pressure per square inch
will be much higher.
Thus, when the propane bottle is left outdoors and the ambient temperature
gets down below the 30os, propane does not vaporize as well and your grill
may not be able to produce as much heat. To remedy this, store the bottle
in a heated area overnight, wrap it in a blanket to take it outdoors, and
the gas will vaporize much better. An option is to wrap the gas bottle in a
small electric blanket.
Propane gas is 1.5 times heavier than air, while natural gas is only 60%
as heavy as air. Butane is 2 times as heavy as air. This means that propane
or butane gas will flow to the lowest point available and, when it
accumulates, presents an explosion hazard. Natural gas will dissipate in
air, and can still be ignited, but it presents less of a hazard than
propane or butane because it would be less concentrated.
Propane produces 2488 BTU's per cubic foot of vapor (gas) while methane
produces 1000 BTU per cubic foot. The ideal air-to-gas ratio for combustion
is 24 to 1 for propane and 10 to 1 for methane.
Gas fired stoves have been used in homes for more than a century. During
that time, there has been little change in the technology. The entire
operating system consists of a gas valve, an orifice (read small hole), a
venturi ( a tube having a variable slotted section to draw in air) and a
burner (a tube or other shape which has holes in it for the gas/air mixture
to exit).
Continued on Page 3
Smoky's 5th basic position for really great barbecue'n.
'According to Smoky' is © by C. Clark Hale
who is solely responsible for its content. Comments
should be addresses to cchale@bellsouth.net |
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