Environmental Engineering Reference
In-Depth Information
Different shares of constituent compounds result in
specific densities, mostly between 0.78 and 0.89, but this
attribute is commonly measured in
API (American Pe-
troleum Institute) gravity, where
API
ΒΌ
(141.5/specific
density)
131
:
5 (oil with specific gravity 1.0 has
API
10). Oils with gravities above 31.1
are classified as light,
heavy oils have
API below 22.3. Many of the world's
important crude oils are medium or only moderately
light (Platt's 2005). Saudi crudes rate only
API 28-33,
other Persian Gulf export streams range mostly between
30 and 35, and crude from Alaska's North Slope has
API 29. In contrast, some North African (Libyan and
Algerian) and Nigerian oils are very light, with
API 37-
44 and with very low pour points (
21
Cto
36
C).
Natural gases are largely mixtures of the three simplest
alkanes: methane (CH
4
), ethane (C
2
H
6
), and propane
(C
3
H
8
). Data available for distribution systems in the
United States show CH
4
ranging from 73% to 95%,
C
2
H
6
from 3%-13%, and C
3
H
8
from 0.1% to 1.3%.
Butane, pentane, and sometimes a few higher homo-
logues are also present in the extracted gas and are sepa-
rated as natural gas liquids. CO
2
,H
2
S, N, He, and water
vapor are found in many gases. The heat content of nat-
ural gases obviously declines with the presence of these
impurities and rises with the share of higher alkanes. Ex-
treme values for raw natural gases are approximately 30-
45 MJ/m
3
, with pure CH
4
at 35.5 MJ/m
3
. They are
the least-polluting fossil fuels, but because their energy
density under normal pressure is only 1/1000 that of
crude oil, their use as portable fuel is limited. Natural
gases are commonly associated with or dissolved in crude
oils, but they also exist as free (dry) gas that is not in any
contact with crude oil in a reservoir or that occurs in en-
tirely separate formations. A share of reservoir gas that is
liquefied once it reaches the surface is known as natural
gas liquid.
Use of hydrocarbons as fuels is of very recent origin.
Because of seepages of oils ''burning pillars'' of natural
gas, and bitumen pools, hydrocarbons were known from
antiquity but were used only infrequently in building
materials or as protective coatings (Forbes 1964). Nota-
ble exceptions include the burning of bitumens in Con-
stantinople's thermae during the late Roman Empire and
the Chinese use of natural gas in Sichuan, mainly to
evaporate brines (Adshead 1992). This extraction began
during the Han dynasty (200
B
.
C
.
E
.), and it was made
possible by the invention of percussion drilling, with
teams of laborers raising and letting fall (by jumping on
a lever) heavy iron bits attached to long bamboo cables
from bamboo derricks (Needham 1964). In 1835 the
deepest well reached the depth of 1 km (Vogel 1993).
The place with the longest tradition (since the early
Middle Ages) of local crude oil use is the Absheron pen-
insula of the Baku region on the Caspian Sea in Azerbai-
jan. By the late eighteenth century there were scores of
shallow wells from which oil was extracted for the pro-
duction of kerosene (by primitive thermal distillation)
for local lighting as well as for export (in skins) by camels
and ships. In 1837 Russians set up the first commercial
oil-distilling factory in Balakhani, and in 1846 the
world's first exploratory oil well was drilled to the depth
of 21 m in Bibi-Heybat. During the 1850s the higher
cost of whale oil used for illumination led a number of
entrepreneurs toward the small-scale beginnings of alter-
native oil-based industries.
In 1853 Abraham Gesner from Nova Scotia started
producing kerosene from coal in his North American
Kerosene Gas and Lighting Company on Long Island.
