conventional energy sources

1. CHAPTER 9 - Natural Gas
Introduction
Natural gas is a nonrenewable fossil fuel, because most scientists and
engineers believe that natural gas (as with oil) was formed from the remains of
tiny sea animals and plants that died 300 to 400 million years ago. As noted
earlier, when these sea animals and plants died, they sank to the bottom of the
oceans where they were buried by layers of sediment that turned into rock.
Over the years, these layers increased in height to several thousands of feet,
subjecting the remains to high pressure, which, when combined with the high
temperature of the Earth, converted this matter into not only oil, but also
natural gas. Over time, high concentrations of natural gas became trapped in
the layers of rock.
As with other fossil fuels, natural gas was formed in the Earth’s crust,
possessing the ability of rising toward the Earth’s surface.

2. Introduction
Natural gas is often found with oil. The oil fields of the Middle East once
contained about one-fifth of the world’s natural gas reserves. In the past, large
quantities of natural gas recovered along with oil were burned because there
was no use for the energy locally.
Natural gas consists of a mixture of different gases. The main component is
methane (CH4), which is odorless, colorless, and tasteless. Companies add a
chemical odorant called mercaptan (with an odor like rotten eggs) so that any
escaping gas can be detected. This process is employed as a safety measure.
Natural gas ranks second, after oil, in energy consumption in the United States
and approximately 25 percent of the energy consumed is supplied by this fossil
fuel.

3. Early History
Before natural gas was commercialized, the protocol to manufacture gas from
coal was developed in Europe in the seventeenth century. However, it was not
until the 1800s that gas was commercialized along with the manufacturing of
gas from coal. Natural gas was first used in the United States in 1816 to
illuminate the streets of Baltimore with gas lamps.
An important invention was made in 1855 by a German scientist, R. V. von
Bunsen. The burner, named for him, is known to every student of science and
engineering. The burner subsequently led to its use as a fuel in a variety of
industrial applications.
The full commercialization and application of natural gas required the
development of a safe, economic method of piping. This occurred with the
development of seamless steel pipes in the 1920s. Thus, the combination of
(1) improved drilling techniques, (2) pipelines to deliver the gas, and (3)
machines and appliances that run on gas resulted in a new viable fossil fuel for
use in industries and other applications.

4. availability/Distribution
U.S. forecasters had predicted only a 50-year supply of natural gas remained
from known reservoirs during the 40-year period of 1950–1990. However,
approximately 20 trillion ft3 of natural gas was annually consumed during the
1980–2000 period.
The reason for the additional availability has resulted from improved
exploration, drilling, and recovery techniques.
Production, consumption, and international trade in natural gas should
progressively increase in proportion to available reserves.
The United States produces about one-fifth of the world’s natural gas demand
each year.

5. availability/Distribution
One of the new sources of natural gas being explored is shale gas, which is
natural gas that is trapped in shale formations. Shale is essentially a common
form of sedimentary rock.
The use of fracking techniques to extract natural gas from shale deposits has
expanded rapidly in recent years in the U.S. However, there are several
negative environmental impacts being raised by various groups.
Natural gas is moved in the United States via an extensive network of pipe-
lines taking the gas from the well head to feeder pipelines to major lines
connected to major users.
The distribution of natural gas from one location to another is accomplished
with the use of compressor stations. As noted earlier, a compressor increases
the pressure of the gas, providing the driving force to move the gas along the
pipelines. Compressor stations are spaced approximately 50 to 100 miles
apart, moving the gas along the pipelines at about 15 miles per hour.

6. availability/Distribution
Some natural gas is stored in huge underground reservoirs. These are typically
filled in the summer so that there will be enough natural gas during the winter
heating season. Other systems for storing gas, e.g., expansion tanks, are also
available. The roof of the expansion tank is movable, rising and falling to
maintain a constant pressure. Pressurized tanks can also be used to store gas
near end users to assure that an adequate supply is available to meet a
fluctuating demand.

7. Characterization
Natural gas consists mostly of methane and other hydrocarbons including
ethane, propane, butane, and pentane. Other gases include carbon dioxide,
nitrogen, and helium, all of which detract from the heating value. The density of
natural gas at ambient conditions is approximately 0.60 lb/ft3, compared to that
of air at 0.75 lb/ft3. The heating value is about 1000 Btu/scf.
Natural gas is sold in unit volumes, usually in cubic feet. The energy contained
in a cubic foot of natural gas is usually expressed in British thermal units, or
Btu. 1 Btu is the amount of energy required to raise the temperature of 1 pound
of water 1°F. One cubic foot of natural gas has about 1,100 Btu. Natural gas is
usually sold to pipeline companies in standard measurements of thousands of
cubic feet (Mcf). Most customers are billed by the number of therms of natural
gas consumed. One therm is equal to nearly 100 ft3 of a typical natural gas.

8. Extraction
Natural gas is extracted from the Earth by drilling a well to a natural gas pocket
that is under a high pressure. Location and drilling techniques used for oil are
also used for natural gas. Natural gas has some minor impurities, which are
easily removed. Impurities include moisture, hydrogen sulfide, and carbon
dioxide. Acid impurities are removed by a scrubber
Gas is also now being commercially extracted domestically from coal beds,
shales, and tar sands.
Some might suppose natural gas can be hard to locate since it is usually
trapped in porous rocks deep underground. Scientists and engineers have
used many methods to find natural gas deposits. They may examine surface
rocks to determine clues about these underground formations. They
occasionally detonate small explosions or drop heavy weights on the Earth’s
sur- face and record the sound waves as they rebound from the sedimentary
rock layers underground. They have also measured the gravitational pull of
rock masses deep within the Earth.

9. Processing
After natural gas comes out of the ground; it goes to a processing plant where
it is cleaned of impurities and separated into its various components.
Approximately 90 percent of natural gas is composed of methane, but it also
contains other gases such as ethane, propane, and butane.
Propane and butane, after being recovered from natural gas, are bottled as
liquids under slight pressure. The same is true of ethane. Approximately 50
percent of the natural gas liquids presently are sold to the consumer as bottled
gas; the remainder is sent to refineries. These other gases are further refined
and can be blended with gasoline to increase its volatility and its octane rating.

10. Transportation/Transmission
The most efficient, least costly means of transporting natural gas is by pipe-
line.
Gas can also be transported in pressurized tanks. Liquefied natural gas (LNG)
must be kept under very high pressures and at very low temperatures during
transport.
LNG is obtained by cooling natural gas to a temperature of –260°F. At this
temperature, natural gas becomes a liquid, and its volume is reduced by a
factor of approximately 600.

11. Environmental Issues
All the fossil fuels—coal, petroleum, and natural gas—release pollutants into
the atmosphere when burned. However, of these primary fuels, natural gas is
the most environmentally friendly fossil fuel. Combusting natural gas produces
less oxides of sulfur, carbon, and nitrogen than other fossil fuels. Natural gas
also emits little to no ash (particulate) into the environment.
The main sources of environmental concern related to natural gas may be
placed in these four categories:
1. Pipeline leakage
2. Liquefied natural gas transport risks
3. Combustion: carbon emissions, SOX, NOX
4. Health and safety

12. Environmental Issues
To summarize, the five major environmental pollutants of concern in using
primary fossil fuels are the following:
1. Carbon monoxide, CO
2. Particulates, PM
3. Oxides of nitrogen, NOX
4. Unburned hydrocarbons, HC
5. Oxides of sulfur, SOX

13. Future Prospects and Concerns
To recap, there are benefits to natural gas development. When combusted, it is
cleaner than coal or oil and releases fewer emissions.
Currently, interstate pipeline companies are reassessing their markets and
positioning themselves for the future.
Other challenges in the future include the outcome of electric utility
deregulation, and the market for electric vehicles. As noted in the Introduction,
less than 5 percent of the natural gas is currently employed in “electric” cars.
Also, many major cities are converting buses, garbage trucks, mail trucks, and
other vehicles to natural gas. Electric utilities are installing natural gas-fueled
power plants to comply with air regulations. Thus, natural gas usage is likely to
increase.

14. Future Prospects and Concerns
Finally, engineers and scientists are also researching new ways to obtain
natural gas in the form of methane from biomass—a fuel source derived from
plant and animal wastes. There are several ways to convert biomass into
natural gas. Another method to recover the methane gas converts aquatic
plants such as sea kelp into methane gas. Kelp farms could be a new source
for methane in the future.
Methane gas is naturally produced whenever organic matter decays.
There are other small-scale projects that are being designed to convert animal
waste to methane locally and to use the gas locally. As energy prices rise,
invention and innovation will help forge new advances in meeting the energy
needs of the future.