Page 280 - Pipeline Rules of Thumb Handbook

Gas—General 267

The rate or speed at which the turbine wheel revolves is a reforming the process of thermal or catalytic cracking of
measure of the velocity of the gas. natural gas, liquefied petroleum gas, refinery gas or gas
Venturi Meter a meter in which the flow is determined from oil, resulting in the production of a gas having a dif-
by measuring the pressure drop caused by the flow through ferent chemical composition.
a Venturi throat. The flow rate is proportional to the square refinery gas a gas resulting from oil refinery operations
root of the pressure drop across the throat. consisting mainly of hydrogen, methane, ethylene, propy-
minimum charge a clause which provides that the charge lene and the butylenes. Other gases such as nitrogen and
for a prescribed period shall not be less than a specified carbon dioxide may also be present. The composition can
amount. be highly variable and the heat content can range from
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natural gasoline those liquid hydrocarbon mixtures con- 1,000 to 2,000Btu/ft .
taining essentially pentanes and heavier hydrocarbons reserves see preceding section.
which have been extracted from natural gas. send-out the quantity of gas delivered by a plant or system
natural gas liquids a term used for those mixtures of hydro- during a specified period of time.
carbon fractions that can be extracted in liquid form from specific gravity of gas the ratio of the density of gas to the
natural gas. In the widest sense, they can comprise any density of dry air at the same temperature and pressure.
combination of the following: ethane, propylene, propane, standard metering base standard conditions, plus agreed
butylene, isobutane, n-butane, pentanes, hexanes, hep- corrections, to which all gas volumes are corrected for
tanes, and octanes. purposes of comparison and payment.
net calorific (heating) value the net calorific value at con- summer valley the decrease which occurs in the summer
stant pressure of a gaseous fuel is the number of heat units months in the volume of the daily load of a gas distribution
produced when unit volume of the fuel, measured under system.
standard conditions, is burned in excess air in such a way therm 100,000Btus.
that the materials after combustion consist of the gases thermie the heat required to raise the temperature of one
carbon dioxide, sulfur dioxide, oxygen, nitrogen and water metric ton of water 1°C (centigrade).
vapor, and that the pressure and temperature of the town gas gas piped to consumers from a gas plant. The gas
gaseous fuel, the air and the materials after combustion are can comprise both manufactured gas (secondary energy)
one standard atmosphere and 25°C. This value is derived and natural gas (primary energy) used for enrichment.
from the measured gross figure. transmission company a company which operates a natural
non-associated gas see preceding section on “reserves gas transmission system and which either operates no retail
terminology.” distribution system, or, as defined by the American Gas
off-peak the period during a day, week, month or year when Association (AGA) receives less than 5% of its gas operat-
the load being delivered by a gas system is not at or near ing revenues from such retail distribution system (see also
the maximum volume delivered by that system. distribution company or gas utility).
peak or peak load the maximum load consumed or pro- unaccounted for gas the difference between the total gas
duced by a unit or group of units in a stated period of time. available from all sources and the total gas accounted for
peak shaving the practice of augmenting the normal supply as sales, net interchange and company use. The difference
of gas during peak or emergency periods from another includes leakage or other actual losses, discrepancies due
source where gas may have either been stored during to meter inaccuracies, variations of temperature, and
periods of low demand, or manufactured specifically to pressure and other variants.
meet the peak demand. unassociated gas see preceding section.
pressure maintenance (repressing) a process in which utilization factor the ratio of the maximum demand on a
natural gas is injected into a formation capable of produc- system or part of a system to the rated capacity of the
ing crude petroleum to aid in maintaining pressure in an system or part of the system under consideration.
underground reservoir for the purpose of assisting in the water gas see blue water gas.
recovery of crude. watt the meter-kilogram-second unit of power, equivalent to
producer gas a gas manufactured by burning coal or coke one joule per second and equal to the power in a circuit
with a regulated deficiency of air, normally saturated with in which a current on one ampere flows across a potential
steam. The principal combustible component is carbon difference on one volt.
monoxide (about 30%) and the gross heat content is wobbe index the gross calorific value of the gas divided by
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between 120 and 160Btu/ft . the square root of the density of the gas as compared with
recycling see cycling. air.