Speight J.G. Natural Gas: A Basic Handbook
Подождите немного. Документ загружается.
5.2
CoalGus
119
Benzene, naphthalene, and other aromatic organics were distilled
from the tar. The remaining viscous liquid was used for road making.
In
the gas holders, the gas was stored till required. This gas consisted
of
hydrogen (48%), methane
(32%),
carbon monoxide
(8%),
ethylene
(ethene)
(2%).
Overall, the goal
of
gas cleaning was tar removal, and there are indi-
cations that the gas manufacturer did
not
check the quality
of
the gas
after the tar had been removed (Davidson,
1913).
The advent
of
electric lighting forced utilities to search for other mar-
kets for manufactured gas. Manufactured gas plants that once pro-
duced gas almost exclusively for lighting shifted their efforts towards
supplying gas primarily for heating and cooking, and even refrigera-
tion and cooling.
Fuel gas for industrial use was made using producer-gas technology.
Producer gas is made by blowing air through an incandescent fuel bed
(commonly coke or coal)
in
a gas producer. The reaction
of
fuel with
insufficient air for total combustion produces CO: this reaction is exo-
thermic and self sustaining. It was discovered that adding steam
to
the input air
of
a producer would increase the CV
of
the fuel gas by
enriching it with
CO
and H, produced by water gas reactions. Pro-
ducer gas has a very low heat
of
combustion
(100
to
150
Btu/ft3;
methane has a heat
of
combustion
of
about
1,030
Btu/ft3), because
the calorific gases CO/H, are diluted with lots
of
inert nitrogen (from
air) and
CO,
(from combustion):
2C(s)
+
0,
+2CO (exothermic: producer gas reaction)
C(s)
+
H,O
40
+
H, (endothermic: water gas reaction)
C
+
2H,O
40,
+
2H, (endothermic)
CO
+
H20
40,
+
H,
(exothermic: water gas shift reaction
120
Chapter
5
History
of
Gas
Processing
The problem of nitrogen dilution was overcome by the blue water gas
(BWG) process, developed
in
the
1850s
by Sir William Siemens. The
incandescent fuel bed would be alternately blasted with air followed
by steam. The air reactions during the blow cycle are exothermic,
heating up the bed, while the steam reactions during the make cycle,
are endothermic and cool down the bed. The products from the air
cycle contain non-caloric nitrogen and are exhausted out the stack
while the products
of
the steam cycle are kept as blue water gas. This
gas is composed almost entirely
of
carbon monoxide and hydrogen
and burns with a pale blue flame similar
to
natural gas.
Because blue water gas lacked illuminants, it would not burn with a
luminous flame in a simple fishtail gas jet as existed prior
to
the dis-
covery
of
the Welsbach mantle in the
1890s.
Various attempts were
made to enrich blue water gas with illuminants from gas oil in the
1860s.
Gas oil was the flammable waste product from kerosene
refining, made from the lightest and most volatile fractions (tops)
of
crude oil.
In
1875,
Thaddeus
S.
C.
Lowe invented the carburetted water gas pro-
cess, which revolutionized the manufactured gas industry and was
the standard technology until the end of manufactured gas era.
A
car-
buretted water gas generating set consisted
of
three elements; a pro-
ducer (generator), carburetor, and a superheater connected
in
series
with gas pipes and valves.
During a make run, steam would be passed through the generator to
make blue water gas. From the generator the hot water gas would pass
into the top
of
the carburetor where light petroleum oils would be
injected into the gas stream. The light oils would be thermocracked as
they came in contact with the white hot checker-work firebricks inside
the carburetor. The hot enriched gas would then flow
into
the super-
heater, where the gas would be further cracked by more hot fire bricks.
The early history of gas production by carbonization starts with the
Flemish scientist Jan Baptista van Helmont
(15 77-1644)
who discov-
ered that a
wild
spirit
escaped from heated wood and coal, and,
thinking that it
direred
little
porn
the
chaos
ofthe
ancients,
he named it
gas
in his
Origins
ofMedicine
(c.
1609).
Among several others who car-
ried out similar experiments, were Johann Becker of Munich
(c.
1681)
and about three years later John Clayton
of
Wigan, England, the
latter amusing his friends
by
lighting, what he called,
Spirit
of
the
Coal.
William Murdoch (later spelled as Murdock)
(1754-1839)
is
5.1
CoalGus
121
reputed
to
have heated coal
in
his mother’s teapot to produce gas.
From this beginning, he discovered new ways
of
making, purifying,
and storing gas; illuminating his house at Redruth (or his cottage at
Soho)
in
1792, the entrance to the Manchester Police Commissioners
premises
in
1797, the exterior
of
the factory of Boulton and Watt
in
Birmingham, England, and a large cotton mill
in
Salford, Lancashire
in
1805.
In
other examples
of
the use
of
gas in demonstrations, Professor
Jan
Pieter Minckelers lit his lecture room at the University
of
Louvain in
1783 and Lord Dundonald lit his house at Culross, Scotland,
in
1787,
the gas being carried in sealed vessels from the local tar works.
In
France, Phillipe Lebon patented a gas fire
in
1799 and demonstrated
street lighting in 1801. Other demonstrations followed in France and
in the United States, but,
it
is generally recognized that the first com-
mercial gas works was built by the London and Westminster Gas
Light and Coke Company
in
Great Peter Street in 1812, laying
wooden pipes to illuminate Westminster Bridge with gas lights
on
New Year’s Eve
in
1813.
In
1816, Rembrandt Peale and four others
established the Gas Light Company of Baltimore, the first manufac-
tured gas company in America.
In
1821, natural gas was being used
commercially in Fredonia, New York. The first German gas works was
built
in
Hannover in 1825, and by 1870 there were
340
gas works
in
Germany making town gas from coal, wood, peat, and other
materials.
Working conditions in the Gas Light and Coke Company’s Horseferry
Road Works, London,
in
the 1830s were described by a French visitor,
Flora Tristan,
in
her
Promenades Duns Londres.
Thus,
Two rows of furnaces
on
each side were fired up; the effect
was not unlike the description of Vulcan‘s forge, except
that the Cyclops were animated with a divine spark,
whereas the dusky servants of the English furnaces were
joyless, silent and benumbed
....
The
foreman told
me
that
stokers were selected
from
among the strongest, but that
nevertheless they all became consumptive after seven
or
eight years
of
toil and died
of
pulmonary consumption.
That explained the sadness and apathy
in
the faces and
every
movement of the hapless men (Tristan,
1840)
122
Chapter
5
History
of
Gas Processing
The first public piped gas supply was to
13
gas lamps, each with three
glass globes along the length of Pall Mall, London in
1807.
The credit
for this goes to the inventor and entrepreneur Fredrick Winsor and
the plumber Thomas Sugg, who made and laid the pipes. Digging up
streets to lay pipes required legislation and this delayed the develop-
ment
of
street lighting and gas for domestic use. Meanwhile William
Murdock and his pupil Samuel Clegg were installing gas lighting
in
factories and work places, encountering
no
such impediments.
The production
of
commercial amounts of gas coal gasification can be
traced to the
1850s.
Gas producers were invented and the water gas
process was discovered.
In
the
1850s,
the Europeans also discovered
that using coal instead
of
coke in
a
producer results
in
producer gas
that contains ammonia and coal tar.
The year
1875
saw the invention
of
the carburetted water gas process
by Prof. T.S.C. Lowe. The carburetted water gas technology became
the dominant technology from
1880s
until
195Os,
replacing coal gas-
ification.
In
addition, the golden age
of
gas light developed with the
invention and commercial use
of
the Welsbach mantle.
The advent
of
incandescent gas lighting in factories, homes, and
streets, replacing oil lamps and candles with steady clear light, almost
matching daylight in its color, turned night into day for many
making night shift work possible in industries where light was all
important in spinning, weaving, and making up garments. The social
significance
of
this change is difficult
for
generations brought up with
lighting after dark available at the touch
of
a switch
to
appreciate. Not
only was industrial production accelerated, but streets were made
safe, social intercourse facilitated, and reading and writing made
more widespread. Gas works were built in almost every town, main
streets were brightly illuminated, and gas was piped in the streets
to
the majority
of
urban households. The invention
of
the gas meter and
the pre-payment meter in the late
1880s
played an important role
in
selling town gas to domestic and commercial customers.
During the First World War, the gas industry’s by-products, phenol,
toluene, ammonia, and sulfurous compounds were valuable ingredi-
ents for explosives. Much coal for the gas works was shipped by sea
and was vulnerable to enemy attack. The gas industry was a large
employer
of
clerks, mainly male before the war. But the advent
of
the
typewriter and the female typist made another important social
5.1
Coal
Gas
123
change that was, unlike the employment of women in war-time
industry, to have long-lasting effects.
The inter-war years were marked by the development
of
the contin-
uous vertical retort, which replaced many of the batch-fed horizontal
retorts. There were improvements in storage, especially the waterless
gas holder, and distribution with the advent of
two-
to four-inch steel
pipes to convey gas at up to
50
psi as feeder mains to the traditional
cast-iron pipes working at an average
of two-
to
three-inch
water
gauge. Benzole as a vehicle fuel and coal tar as the main feedstock for
the emerging organic chemical industry provided the gas industry
with substantial revenues. Petroleum supplanted coal tar as the pri-
mary feedstock of the organic chemical industry after World War
Two, and the loss of this market contributed to the economic prob-
lems
of
the gas industry after the war.
By the
1960s,
manufactured gas, compared with its main rival
in
the
energy market, electricity, was considered “nasty, smelly, dirty, and
dangerous” (to quote market research of the time) and seemed
doomed to lose market share still further, except for cooking where its
controllability gave it marked advantages over both electricity and
solid fuel. The development
of
more efficient gas fires assisted gas to
resist competition
in
the market for room heating. Concurrently, a
new market
for
whole house central heating by hot water was being
developed by the oil industry, and the gas industry followed suit. Gas
air heating found a market niche
in
new local authority housing
where low installation costs gave it an advantage. These develop-
ments, the realignment of managerial thinking away from commer-
cial management (selling what the industry produced) to marketing
management (meeting the needs, wants, and desires
of
customers)
and the lifting of an early moratorium preventing nationalized indus-
tries from using television advertising, saved the gas industry for long
enough to provide a viable market for what was to come.
The slow death of the town gas industry was signaled, even hastened,
by the repeated discoveries of natural gas and the advantage was
taken
of
this new indigenous energy source.
As
a result there was a
“rush to gas”
for
use in peak load electricity generation and
in
low-
grade uses in industry. The effects on the coal industry were very sig-
nificant;
not
only
did coal
lose
its
market
for
town
gas
production, it
came to be displaced from much
of
the bulk energy market also.
124
Chapter
5
History
of
Gas Processing
In the earliest days
of
the town gas industry, coal tar was the major
waste from which the gas had
to
be cleaned. The tar considered a
waste and often disposed into the environment in and around the
plant locations. While uses for coal tar developed by the late-l800s,
the market for tar varied, and plants that could not sell tar at a given
time could either store tar for future use, attempt
to
burn it as fuel for
the boilers,
or
dump the tar as waste. Waste tars were often disposed
of
in old gas holders, adits, or even mine shafts (if present). Over time,
the waste tars degrade with phenols and benzene (and other
mono-
aromatics-toluene and xylene), and polycyclic aromatic hydrocar-
bons escape as pollutant plumes into the surrounding environment.
The shift
to
the carburetted water gas process initially resulted
in
a
reduced output
of
water gas tar as compared to the volume
of
coal
tars. The advent
of
automobiles reduced the availability
of
naphtha
for carburetion oil, as that fraction was desirable as motor fuel. Gas
manufacturing plants that shifted to heavier grades
of
oil often expe-
rienced problems with the production
of
tar-water emulsions, which
were difficult, time consuming, and costly
to
break. The production
of
large volumes
of
tar-water emulsions quickly filled up available
storage capacity at manufactured gas plants, and the waste was often
dumped in pits, from which they may or may not have been later
reclaimed. Even
if
the tar was reclaimed, the environmental damage
from placing tars
in
unlined pits remained.
The increased use
of
natural gas removed the necessity
of
dealing
with the tar by-products that are a product
of
coal gasification. How-
ever, as was soon discovered, natural gas usually contains substances
that can have a detrimental effect
on
distribution systems, such as
water and sulfurous substances that can cause corrosion.
Excessive moisture can result in clogged pipelines, because water and
methane form solid hydrates under certain pressures and tempera-
tures. In addition, extracted natural gas contains dust that can cause
defects
in
compressor or regulation stations. After extraction, natural
gas undergoes a process during which it is dried and solid particles
(dust) are removed.
If
necessary, the process includes the removal
of
higher hydrocarbons and any sulfurous substances that may be
present. The refining technology depends on composition.
Natural gas processing begins at
the wellhead. The
composition
of
the
raw natural gas extracted from producing wells depends
on
the depth,
5.2
NaturalGus
125
and location of the reservoir, the geology of the area, and whether or
not the gas is
associated
or
non-associated
(Chapter
3).
5.2
Natural
Gas
Gas processing (Mokhatab et al.,
2006)
consists of separating all of the
various hydrocarbons and fluids from the pure natural gas
(Figure
5-1).
Major transportation pipelines usually impose restric-
tions
on
the make-up of the natural gas that is allowed into the pipe-
line. That means that before the natural gas can be transported it
must be purified. While the ethane, propane, butane, and pentanes
must be removed from natural gas, this does not mean that they are
all waste products. Gas processing is necessary to ensure that the nat-
ural gas intended for use is as clean and pure as possible, making
it
the clean burning and environmentally sound energy choice. Thus,
natural gas, as it is used by consumers, is much different from the nat-
ural gas that is brought from underground up to the wellhead.
Although the processing of natural gas is in many respects less com-
plicated than the processing and refining of crude oil, it is equally as
necessary before its use by end users. The natural gas used by con-
sumers
is
composed almost entirely of methane. However, natural gas
found at the wellhead, although still composed primarily of methane,
is by
no
means as pure.
Raw natural gas comes from three types of wells: oil wells, gas wells,
and condensate wells. Natural gas that comes from oil wells is typi-
cally termed
associated gas.
This gas can exist separate from oil in the
formation (free gas), or dissolved in the crude oil (dissolved gas). Nat-
ural gas from gas and condensate wells, in which there is little or
no
crude oil, is termed
non-associated gas.
Gas wells typically produce raw
natural gas by itself, while condensate wells produce free natural gas
along with a semi-liquid hydrocarbon condensate. Whatever the
source of the natural gas, once separated from crude oil (if present),
it
commonly exists in mixtures with other hydrocarbons; principally
ethane, propane, butane, and pentanes.
In
addition, raw natural gas
contains water vapor, hydrogen sulfide (H,S), carbon dioxide, helium,
nitrogen, and other compounds.
In
fact, associated hydrocarbons,
known as
natural gas liquids
(NGLs) can be very valuable by-products
of natural gas processing. Natural gas liquids include ethane, pro-
pane, butane, iso-butane, and natural gasoline that are sold separately
and have a variety of different uses, including enhancing oil recovery
in
oil
wells,
providing raw materials
for
oil
refineries or petrochemical
plants, and as sources of energy.
126
Chapter
5
History
of
Gas Processing
Most natural gas production contains,
to
varying degrees, small (two
to eight carbons) hydrocarbon molecules in addition to methane.
Although they exist
in
a gaseous state at underground pressures, these
molecules will become liquid (condense) at normal atmospheric pres-
sure. Collectively, they are called condensates or natural gas liquids
(NGLs).
The natural gas extracted from coal reservoirs and mines
(coal-bed methane) is the primary exception, being essentially a mix
of mostly methane and carbon dioxide (about
10%).
Various types
of
processing plants have been used since the mid-
1850s
to extract liquids, such as natural gasoline, from produced
crude oil. However,
for
many years, natural gas was
not
a desirable
fuel. Prior to the early
20th
century, most
of
it was flared or simply
vented into the atmosphere, primarily because the available pipeline
technology permitted only very short-distance transmission.
It was not until the early
1920s,
when reliable pipe welding tech-
niques were developed, that a need for natural gas processing arose.
Yet, while a rudimentary network
of
relatively long-distance natural
gas pipelines was
in
place by
1932,
and some natural gas processing
plants were installed upstream in major production areas, the depres-
sion
of
the
1930s
and the duration
of
World War I1 slowed the growth
of
natural gas demand and the need for more processing plants.
After World War 11, particularly during the
1950s,
the development
of
plastics and other new products that required natural gas and petro-
leum as a production component coincided with improvements
in
pipeline welding and pipeline manufacturing techniques. The
increased demand for natural gas as an industrial feedstock and
industrial fuel supported the growth
of
major natural gas transporta-
tion systems, which
in
turn improved the marketability and avail-
ability of natural gas for residential and commercial use. But also, the
requirement for clean gas became more stringent and the evolution
of gas cleaning became a necessity.
Commercial production of natural gas and transportation
in
the
United States dates back to
1859
when Edwin Drake struck oil near
Titusville, Pennsylvania. Natural gas that accompanied the produc-
tion of crude oil was an undesirable by-product of petroleum produc-
tion efforts and was often simply vented or flared.
Soon
however,
small volumes
of
natural gas began to be piped to local municipalities
to
displace manufactured
gas
volumes, which
were
used in early dis-
tribution systems for lighting and fuel.
5.2
Natural
Gas
127
The first recorded instance of natural gas transmission dates to
1872
when a two-inch iron pipeline about five miles long was constructed
between Titusville and Newton, Pennsylvania, and operated at a pres-
sure of
80
psi. The first natural gas pipeline that spanned a distance of
more than one hundred miles was constructed in
1891
and connected
gas fields in central Indiana to Chicago.
Soon,
larger lines developed
in Pennsylvania, New York, Kentucky, West Virginia, and Ohio.
Many of these gas pipelines
soon
began to experience operational
problems with plugging from a mixture of hydrocarbon liquids that
was referred to as
drip
gasoline.
These hydrocarbon liquids posed par-
ticular problems in colder conditions and stream crossings where
lower temperatures were prevalent. The natural gas stream began to
be treated for removal
of
drip
gasoline,
or as often referred to as casing-
head gasoline, which provided the origins of the modern gas pro-
cessing industry (Figure
5-2).
While initially there was very little
demand for gasoline, the advent of the automobile in the early
1900s
forever changed this landscape. Automobiles were
soon
being built
faster than the supply of natural gasoline could keep up with. Motor
vehicles numbered around
2
million in
1915
and roughly doubled in
the next
two
years. Demand and prices for gasoline soared.
As the natural gas market developed and pipeline technology
advanced, producers began to explore for non-associated gas fields
and together with associated gas began to “condition” production for
transportation and merchantability purposes. Natural gas contains
mostly methane and ethane, but as produced will often contain such
heavier hydrocarbon components as propane, butanes, and pentanes
along with water, carbon dioxide, hydrogen sulfide, helium nitrogen,
and other trace elements (Chapter
3).
Conditioning generally con-
sisted
of
removing water and any free liquids, partial or full dehydra-
tion of the gas stream, and
sweetening
of
the
gas
with chemical agents
to offset carbon dioxide and hydrogen sulfide concentrations where
required to make the gas merchantable and suitable for pipeline
transportation.
The development of the natural gas processing industry was now
maturing from the era of simple collection of casinghead natural gas-
oline. Beginning in the
1920s
to about
1940
natural gasoline produc-
tion was accomplished through early absorption plant technology.
As
this technology advanced in the
1940s,
new, lighter end extraction
products emerged, most notably liquefied petroleum or
LP
gas,
made
up of a combination of butanes and propane, which were removed
128
Chapter
5
History
of
Gas Processing
Figure
5-2
A
modern gas-cleaningplant.
through more advanced lean oil absorption technology. Subse-
quently, propane emerged as the dominant natural gas liquid
product, which by the mid
1950s
exceeded production of natural gas-
oline. Again, technological progress coupled with economics allowed
further advances in the industry, which began to focus on the pro-
duction of ethane
in
the late
1950s
and early
1960s.
Ethane produc-
tion continued to grow and exceeded propane production by the
early
1990s.
It
is interesting to note that the early economic drivers
for ethane production included controlled wellhead natural gas prices
and volumetric based pricing, i.e., per Mcf, which largely ignored the
heating content value of the residual gas stream. Most of the market
demand for these products evolved as the refining and petrochemical
industries developed.
Prior to regulation in the United States, commercial natural gas
quality characteristics evolved over time and reflected generally-
accepted operating practices, the state of processing technology, and
market conditions. With the advancement and standardization of gas
processing technology in large-capacity “straddle” plants along major
trunk lines, the conditioning and processing of the natural gas