Alternative Jet Fuels by swenthomasovelil

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									Alternative Jet Fuels                                                           1



                                 CHAPTER 1

                             INTRODUCTION

       Two primary concerns motivate the consideration of alternatives to
conventional petroleum derived jet fuel in commercial aviation: price and
environmental effects. From 2003 through mid-2008, the rise in world oil
prices led to a commensurate rise in the price of petroleum products,
including jet fuel. In the process, the high price of jet fuel contributed to the
bankruptcy of several airlines and was one factor motivating other airlines to
merge.




            Figure 1.1: OIL PRICES, 1994- MARCH 2008

       Aviation, however, has fewer alternative-energy options to petroleum-
based fuels. In addition to contributing to global climate change, emissions
from aviation degrade air quality. Alternative fuels, if available in sufficient
quantities, could reduce the world demand for petroleum, consequently
reducing the world price of oil and products derived from it and therefore
benefiting commercial aviation. Alternative jet fuels derived from biomass or
renewable oils offer the potential to reduce life -cycle GHG emissions and
therefore reduce aviation’s contribution to global climate change. Several
alternative jet fuels have reduced fuel sulfur content and fuel aromatic
content; using these fuels could result in reduced contributions to ambient
particulate matter, lessening aviation’s impact on air quality.



Department Of Mechanical Engineering                                        AJCE
Alternative Jet Fuels                                                           2




                                CHAPTER 2

                   CONVENTIONAL JET FUEL
       Jet fuel is a type of aviation fuel designed for use in aircraft powered by
gas-turbine engines. The most commonly used fuels for commercial aviation
are Jet A and Jet A-1 which are produced to a standardized international
specification. The only other jet fuel commonly used in civilian turbine-engine
powered aviation is Jet B which is used for its enhanced cold-weather
performance.

       Jet fuel is a mixture of a large number of different hydrocarbons. The
range of their sizes (molecular weights or carbon numbers) is restricted by the
requirements for the product, for example, freezing point or smoke point.
Kerosene-type jet fuel (including Jet A and Jet A-1) has a carbon number
distribution between about 8 and 16 carbon numbers; wide-cut or naphtha-
type jet fuel (including Jet B), between about 5 and 15 carbon numbers.

       Jet A specification fuel has been used in the United States since the
1950s and is only available in the United States, whereas Jet A-1 is the
standard specification fuel used in the rest of the world. Both Jet A and Jet A-
1 have a relatively high flash point of 38 °C (100 °F), with an auto ignition
temperature of 210 °C (410 °F). This means that the fuel is safer to handle
than traditional avgas.

       The primary differences between Jet A and Jet A-1 are the higher
freezing point of Jet A (−40 °C vs −47 °C for Jet A-1), and the mandatory
requirement for the addition of an anti-static additive to Jet A-1.

       Like Jet A-1, Jet A can be identified in trucks and storage facilities by
the UN number 1863 Hazardous Material placards. Jet A trucks, storage
tanks, and pipes that carry Jet A are marked with a black sticker with a white
"Jet A" written over it, next to another black stripe. The annual U.S. usage of
jet fuel was 21 billion gallons (80 billion litres) in 2006.



Department Of Mechanical Engineering                                        AJCE
Alternative Jet Fuels                                                         3



                               CHAP TER 3
            FISCHER-TROPSCH SYNTHETIC FUELS

       This chapter covers jet fuels produced using FT synthesis. The
Fischer–Tropsch process (or Fischer–Tropsch Synthesis) is a set of chemical
reactions that convert a mixture of carbon monoxide and hydrogen into liquid
hydrocarbons. The process, a key component of gas to liquids technology,
produces a petroleum substitute, typically from coal, natural gas, or biomass
for use as synthetic lubrication oil and as synthetic fuel. The F-T process has
received intermittent attention as a source of low-sulfur diesel fuel and to
address the supply or cost of petroleum-derived hydrocarbons Process
chemistry

       The Fischer–Tropsch process involves a variety of chemical reactions,
which lead to a series of both desirable and undesirable byproducts. Useful
reactions give alkanes:

               (2n+1) H2 + n CO → C nH(2n+2) + n H2O

       Where 'n' is a positive integer. The formation of methane (n = 1) is
generally unwanted. Most of the alkanes produced tend to be straight-chain
alkanes, although some branched alkanes are also formed. In addition to
alkane formation, competing reactions result in the formation of alkenes, as
well as alcohols and other oxygenated hydrocarbons. Usually, only relatively
small quantities of these non-alkane products are formed, although catalysts
favoring some of these products have been developed.

       Generally, the Fischer–Tropsch process is operated in the temperature
range of 150–300 °C (302–572 °F). Higher temperatures lead to faster
reactions and higher conversion rates but also tend to favor methane
production. As a result, the temperature is usually maintained at the low to
middle part of the range. Increasing the pressure leads to higher conversion
rates and also favors formation of long-chained alkanes both of which are
desirable. Typical pressures range from one to several tens of atmospheres.



Department Of Mechanical Engineering                                      AJCE
Alternative Jet Fuels                                                             4


Even higher pressures would be favorable, but the benefits may not justify the
additional costs of high-pressure equipment. A variety of catalysts can be
used for the Fischer–Tropsch process, but the most common are the
transition metals cobalt, iron, and ruthenium. Nickel can also be used, but
tends to favor Carbon dioxide reuse

        All jet fuels produced using FT synthesis has similar characteristics,
regardless of which feedstock is used. The small variations in FT jet-fuel
properties that might occur are primarily associated with the operating
conditions (e.g., catalyst, temperature, and pressure) within the synthesis
reactors and how the direct products of the synthesis are treated and
processed. Since feedstock choice does not drive fuel properties, FT jet fuels
share common characteristics with regard to compatibility with existing
infrastructure and aircraft, aircraft emissions, and their relative merit for use in
aviation.



COMPATIBILITY IN CURRENT SYSTEMS
       FT jet-fuel blends are considered to be drop-in fuels. At concentrations
up to a 50-50 blend, they meet the performance specifications of Jet A. The
use of a neat FT fuel (i.e., unblended, 100-percent FT fuel), would have
implications for aircraft fuel systems because of the reduced aromatic content.
Certain types of elastomers used as seals in aircraft fuel systems expand in
the presence of aromatic compounds found in conventional petroleum–
derived jet fuel. If an FT fuel were used, the elastomers would contract,
possibly causing fuel leaks. The susceptible elastomers are nitrile-rubber
based, and fuel additives are being developed to improve seal performance.
Additionally, a pure FT fuel would ha ve reduced lubricity that may promote
wear on engine components.

       Because of their paraffinic composition and low aromatic content, neat
FT fuels have a specific energy that is approximately 2 percent higher and an
energy density that is approximately 3 percent lower than that of typical Jet A.
The increased specific energy means that less fuel weight would be required
to fly a given distance. Considering the worldwide fleet of aircraft, commercial


Department Of Mechanical Engineering                                          AJCE
Alternative Jet Fuels                                                          5


aircraft using neat FT jet fuel would, on average, consume about 0.3 percent
less energy.

        Since the weight required to fly a given distance would drop, the use of
FT jet fuel could allow an aircraft to take off with a slightly larger payload
without exceeding the maximum takeoff weight, with the result being less
energy consumed per unit of payload carried. The reduced energy density of
neat FT jet fuel will shorten the maximum range of an aircraft. Though
compatibility issues associated with FT jet fuel have been identified, they are
in the process of resolution. When used as a blend with Jet A, all compatibility
issues appear to be resolved, and FT jet receives a neutral rating. If used
unblended, lubricity issues and seal integrity may require that FT jet fuels
have an enhanced fuel-additive package or be limited to use in aircraft without
nitrile-rubber seals.

ENVIRONMENTAL EFFECTS
       FT fuels have low aromatic content and are nearly sulfur free. For
these reasons, they have the potential to reduce emissions that degrade air
quality near airports. Recent tests show that large reductions in primary PM
are possible using FT fuels. Recent tests have investigated the emission
characteristics of a CFM56, a modern, high–bypass ratio        turbofan engine,
when operating on synthetic fuels. The data from these tests demo nstrate the
primary-PM reductions that may be achieved with the use of low-sulfur, low-
aromatic alternative fuels, such as those created from FT synthesis. Efforts to
characterize the emissions of other fuels in in-service engines are continuing,
being coordinated by CAAFI.The emissions of both primary PM and
secondary PM from SOX in FT fuel would be reduced by more than 10
percent as compared to the baseline fuel, Jet A.

       Furthermore, the improved thermal stability of FT fuels may allow for
fuel-system and engine design improvements to increase operating efficiency.
All of the testing conducted to date, which includes a variety of engine designs
and vintages, suggests that the ultra low levels of sulfur and aromatic




Department Of Mechanical Engineering                                       AJCE
Alternative Jet Fuels                                                           6


compounds of an FT fuel would lead to a substantial reduction in aviation’s
PM emissions.

CONCLUSION

       Because of their high cetane number (a measure of the fuel’s ability to
resist preignition) and near-zero sulfur content, FT fuels are attractive for
automotive diesel applications. Cetane number is not a relevant fuel
parameter for turbine engines, and aircraft engines are not equipped with
catalytic converters that require the use of CAAFI fuels. Consequently, it is
likely that FT diesel will carry a price premium over FT jet fuel in nations with
stringent fuel-quality standards for automotive fuels. This finding assumes that
current regulations associated with air quality at airports are continued and
that there are no mandated reductions of GHG emissions specifically targeted
at commercial aviation

       In summary, we have some evidence that use of FT fuel in automotive
applications is likely to provide greater societal benefits and demand a price
premium over commercial aircraft operations. These include the extent to
which FT fuels will reduce engine maintenance and increase reliability, and
whether and how commercial aviation will be required to improve airport air
quality or to control GHG emissions. The following chapters deals with FT
fuels from Natural gas, Coal and Biomass




Department Of Mechanical Engineering                                        AJCE
Alternative Jet Fuels                                                          7


                                CHAPTER 4
    FISCHER-TROPSCH FUELS FROM NATURAL GAS

       This chapter deals with Natural gas which can be used as a FT fuel.
Natural gas is a gas consisting primarily of methane. It is found associated
with other fossil fuels, in coal beds, as methane clathrates, and is created by
methanogenic organisms in marshes, bogs, and landfills. It is an important
fuel source, a major feedstock for fertilizers, and a potent greenhouse gas.

       Before natural gas can be used as a fuel, it must undergo extensive
processing to remove almost all materials other than methane. The by-
products of that processing include ethane, propane, butanes, pentanes, and
higher molecular weight hydrocarbons, elemental sulfur, carbon dioxide, water
vapor, and sometimes helium and nitrogen.

       The image below is a schematic block flow diagram of a typical natural
gas processing plant. It shows the various unit processes used to convert raw
natural gas into sales gas pipelined to the end user markets.

       The block flow diagram also shows how processing of the raw natural
gas yields byproduct sulfur, byproduct ethane, and natural gas liquids (NGL)
propane, butanes and natural gasoline (denoted as pentanes +).




Department Of Mechanical Engineering                                       AJCE
Alternative Jet Fuels                                                         8




Figure 4.1SCHEMATIC FLOW DIA GRAM OF A TYPICA L NATURA L GAS PROCESSING
PLANT



PRODUCTION POTENTIAL
        As the world price of oil rose early in the decade, considerable
commercial attention was directed at the potential of GTL facilities. A number
of factors have led to proposed projects being scaled back. Based on current
planned production in Malaysia, Qatar, and South Africa, we estimate that
global production of GTL in 2017 will be between 200,000 and 300,000 bpd,
of which up to one quarter, 50,000 to 75,000 bpd, could be economically
dedicated to jet-fuel production. The actual jet-fuel production fraction could
be significantly lower. Because of the high value of, and growing demand for,
natural gas in North America, production of GTL-derived jet fuel in commercial
quantities there is highly unlikely.




Department Of Mechanical Engineering                                      AJCE
Alternative Jet Fuels                                                           9


PRODUCTION COST
       A number of factors complicate estimating the production cost of GTL.
These include proprietary information on capital costs and performance and
the cost of the natural-gas feedstock. Based on an assessment of stated
commercial interest in GTL, and the option of compressing and shipping the
natural gas as LNG, we estimate production costs for GTL-based jet fuel to
range from $1.40 to $2.50 per gallon.

ENVIRONMENTAL EFFECTS
       Natural gas is often described as the cleanest fossil fuel, producing
less carbon dioxide per joule delivered than either coal or oil, and far fewer
pollutants than other fossil fuels. However, in absolute terms it does contribute
substantially to global carbon emissions, and this contribution is projected to
grow. According to the IPCC Fourth Assessment Report in 2004 natural gas
produced about 5,300 Mt/yr of CO2 emissions, while coal and oil produced
10,600 and 10,200 respectively but by 2030, according to an updated version
of the SRES B2 emissions scenario, natural gas would be the source of
11,000 Mt/yr, with coal and oil now 8,400 and 17,200 respectively.

       In addition, natural gas itself is a greenhouse gas (methane) far more
potent than carbon dioxide when released into the atmosphere, although
released in much smaller quantities. Natural gas is mainly composed of
methane, which has a radiative forcing twenty times greater than carbon
dioxide. This means a ton of methane in the atmosphere traps in as much
radiation as 20 tons of carbon dioxide. Carbon dioxide still receives the
attention over greenhouse gases because it is released in much larger
amounts. Still, it is inevitable in using natural gas on a large scale that some
of it will leak into the atmosphere. Current USEPA estimates place global
emissions of methane at 3 trillion cubic feet annually, or 3.2% of global
production direct emissions of methane represented 14.3% of all global
anthropogenic greenhouse gas emissions in 2004




Department Of Mechanical Engineering                                        AJCE
Alternative Jet Fuels                                                           10


CONCLUSION
       As discussed above, GTL fuels have been in commercial production
since 1993 in Malaysia, and there are additional plants in both the start-up
and construction phases in Qatar.

       The advantages of liquid methane as a jet engine fuel are that it has
more specific energy than the standard kerosene mixes do and that its low
temperature can help cool the air which the engine compresses for greater
volumetric efficiency, in effect replacing an intercooler. Alternatively, it can be
used to lower the temperature of the exhaust.




Department Of Mechanical Engineering                                          AJCE
Alternative Jet Fuels                                                          11


                                   CHAPTER 5
          F ISCHER-TROPSCH FUELS FROM COAL

       This chapter deals with Coal that can be used as a FT fuel. Coal is a
readily combustible black or brownish-black sedimentary rock normally
occurring in rock strata in layers or veins called coal beds. Coal is composed
primarily of carbon along with variable quantities of other elements, chiefly
sulfur, hydrogen, oxygen and nitrogen.

       Coal begins as layers of plant matter accumulate at the bottom of a
body of water. For the process to continue the plant matter must be protected
from biodegradation and oxidization, usually by mud or acidic water. The wide
shallow seas of the Carboniferous period provided such conditions. This
trapped atmospheric carbon in the ground in immense peat bogs that
eventually were covered over and deeply buried by sediments under which
they metamorphosed into coal. Over time, the chemical and physical
properties of the plant remains were changed by geological action to create a
solid material.

       Refined coal is the product of a coal-upgrading technology that
removes moisture and certain pollutants from lower-rank coals such as sub-
bituminous and lignite (brown) coals. It is one form of several pre-combustion
treatments and processes for coal that alter coal's characteristics before it is
burned. The goals of pre-combustion coal technologies are to increase
efficiency and reduce emissions when the coal is burned. Depending on the
situation, pre-combustion technology can be used in place of or as a
supplement to post-combustion technologies to control emissions from coal-
fueled boilers.

PRODUCTION POTENTIAL

       Taking     into   account    coincident   demonstrations   of   CCS   and
opportunities for cost reduction through experience -based learning, Bartis,
Camm, and Ortiz (2008) estimate that a maximum production capacity of
200,000 bpd of coal-derived liquids in 2015, growing to 500,000 bpd in 2020,


Department Of Mechanical Engineering                                         AJCE
Alternative Jet Fuels                                                            12


could be available in the United States, approximately one -quarter of which
could be jet fuel. Assuming that 300,000 bpd of CTL production exists i n
2017, approximately 75,000 bpd of FT jet fuel from coal could be available.

PRODUCTION COST
       Based on the analysis by Bartis, Camm, and Ortiz (2008), summarized
in Appendix A, the estimated costs of production range is $1.60 to $1.92 per
gallon (in 2005 dollars) of synthetic diesel fuel, on an energy-equivalent basis
to Jet A.

ENVIRONMENTAL EFFECTS

       There are a number of adverse environmental effects of coal mining
and burning, specially in power stations including:

               1)       Generation of hundreds of millions of tons of waste
       products, including fly ash, bottom ash, flue gas desulphurization
       sludge, that contain mercury, uranium, thorium, arsenic, and other
       heavy metals

               2)       Acid rain from high sulfur coal

               3)       Interference with groundwater and water table levels

               4)       Contamination of land and waterways and destruction of
       homes from fly ash spills.

               5)       Impact of water use on flows of rivers and consequential
       impact on other land-uses

               6)       Dust nuisance

               7)       Subsidence      above   tunnels,   sometimes   damaging
       infrastructure

               8)       Coal-fired power plants without effective fly ash capture
       are one of the largest sources of human-caused background radiation
       exposure


Department Of Mechanical Engineering                                           AJCE
Alternative Jet Fuels                                                          13


                 9)     Coal-fired power plants shorten nearly 24,000 lives a year
       in the United States, including 2,800 from lung cancer

                 10)    Coal-fired power plants emit mercury, selenium, and
       arsenic which are harmful to human health and the environment

                 11)    Release of carbon dioxide, a greenhouse gas, which
       causes climate change and global warming according to the IPCC.
       Coal is the largest contributor to the human-made increase of CO2 in
       the air

       Based on analysis conducted by MIT as part of this study and prior
research by the RAND Corporation and others, we report a fairly broad range
for the mine-to-wake GHG emissions for jet fuel derived from coal. Without
CCS, life-cycle GHG emissions for CTL jet fuel are estimated to be between
2.0 and 2.4 times greater than those of conventional jet fuel. More than half of
these emissions are associated with fuel production.

       Variation in the emissions from coal extraction adds another layer of
complexity. For example, bituminous coal production from some underground
mines involves emissions of CH4 that can add appreciably to the overall
WTW GHG emissions.

CONCLUSION
       The two key components of the technology base have been
demonstrated at commercial scale: coal gasification in the production of
electricity at IGCC power plants and gas cleanup and FT synthesis at GTL
facilities. Additionally, methods used to separate CO2 from process streams,
such as those at CTL facilities, have been in widespread commercial use for
decades. Pipeline transportation of CO2 is practiced today.




Department Of Mechanical Engineering                                         AJCE
Alternative Jet Fuels                                                        14


                                 CHAPTER 6
      FISCHER-TROPSCH FUELS FROM BIOMASS

       This chapter deals with Biomass which can be used as a FT fuel.
Biomass, a renewable energy source, is biological material derived from
living, or recently living organisms, such as wood, waste, (hydrogen) gas, and
alcohol fuels. The most conventional way on how biomass is used however,
still relies on direct incineration. Forest residues for example (such as dead
trees, branches and tree stumps), yard clippings, wood chips and garbage are
often used for this. However, biomass also includes plant or animal matter
used for production of fibers or c hemicals. Biomass may also include
biodegradable wastes that can be burnt as fuel. It excludes organic materials
such as fossil fuels which have been transformed by geological processes
into substances such as coal or petroleum.

       Biomass is carbon based and is composed of a mixture of organic
molecules containing hydrogen, usually including atoms of oxygen, often
nitrogen and also small quantities of other atoms, including alkali, alkaline
earth and heavy metals. These metals are often found in functional mo lecules
such as the porphyrins which include chlorophyll which contains magnesium.

       Biomass can be converted to liquid fuels via gasification and FT
synthesis to produce a fuel that we call a biomass-to-liquid (BTL) fuel. This
technology is currently in the demonstration phase. A German firm, CHOREN,
is now constructing a small commercial BTL plant with a capacity of almost
300 bpd of liquid product that began start-up operations in 2008
(Kiener,2008). Solena Group, in partnership with Rentech, has announced
plans to develop and build a BTL facility that would produce 1,800 bpd of fuel
(70 percent of which is JP-8 intended for the U.S. Air Force) from agricultural,
forestry, and municipal waste from northern and central California; the facility
is scheduled to begin construction in Gilroy, California, in 2009.

       There are a number of technological options available to make use of a
wide variety of biomass types as a renewable energy source. Conversion



Department Of Mechanical Engineering                                       AJCE
Alternative Jet Fuels                                                          15


technologies may release the energy directly, in the form of heat or electricity,
or may convert it to another form, such as liquid biofuel or combustible biogas.
While for some classes of biomass resource there may be a number of usage
options, for others there may be only one appropriate technology.

THERMAL CONVERSION
       These are processes in which heat is the dominant mechanism to
convert the biomass into another chemical form. The basic alternatives are
separated principally by the extent to which the chemical reactions involved
are allowed to proceed (mainly controlled by the availability of oxygen and
conversion      temperature)   Combustion,      Torrefaction,   Pyrolysis,   and
Gasification.

CHEMICAL CONVERSION
       A range of chemical processes may be used to convert biomass into
other forms, such as to produce a fuel that is more conveniently used,
transported or stored, or to exploit some property of the process itself.

BIOCHEMICAL CONVERSION
       A microbial electrolysis cell can be used to directly make hydrogen gas
from plant matter. As biomass is a natural material, many highly efficient
biochemical processes have developed in nature to break down the
molecules of which biomass is composed, and many of these biochemical
conversion processes can be harnessed.

       Biochemical conversion makes use of the enzymes of bacteria and
other micro-organisms to break down biomass. In most cases micro-
organisms are used to perform the conversion process: anaerobic digestion,
fermentation and composting. Other chemical processes such as converting
straight and waste vegetable oils into biodiesel are transesterification. Another
way of breaking down biomass is by breaking down the carbohydrates and
simple sugars to make alcohol. However, this process has not been perfected
yet. Scientists are still researching the effects of converting biomass.




Department Of Mechanical Engineering                                         AJCE
Alternative Jet Fuels                                                           16


PRODUCTION POTENTIAL
       The existing biomass power generating industry in the United States,
which consists of approximately 11,000 MW of summer operating capacity
actively supplying power to the grid, produces about 1.4 percent of the U.S.
electricity supply.

       Because there are technical risks, albeit small, associated with
designing commercial CBTLplants, only a fraction of the near-term production
potential of CTL can be diverted to CBTL.NETL (2007d) estimates that the
production potential of CBTL could reach 45,000 barrels (middle distillates
and naphtha) per day by 2017 under an accelerated schedule; as in the case
of CTL, the majority of this output would be FT diesel fuel.

PRODUCTION COST

       For a CBTL facility accepting 15 percent as -received biomass on a
mass basis and producing 10,000 bpd of FT products, we estimate production
costs ranging from $1.99 to $2.34 per gallon of jet fuel. However, it is
important to note that the production costs of CBTL could span the entire
range of costs for CTL and BTL: One option for CBTL is to cofire
opportunistically in CTL facilities as biomass feedstocks become available, in
which case the amount of biomass feed may be very low on average. It is
likely that, in practice, the amount of biomass available to a facility would vary,
from perhaps 10 to 30 percent by mass.


ENVIRONMENTAL EMPACT

       On combustion the carbon from biomass is released into the
atmosphere as carbon dioxide (CO2). The amount of carbon stored in dry
wood is approximately 50% by weight. When from agricultural sources, plant
matter used as a fuel can be replaced by planting for new growth. When the
biomass is from forests, the time to recapture the carbon stored is generally
longer, and the carbon storage capacity of the forest may be reduced overall if
destructive forestry techniques are employed.




Department Of Mechanical Engineering                                         AJCE
Alternative Jet Fuels                                                      17


       The biomass feedstocks investigated in the BTL pathway include waste
biomass (e.g., forest residue, agricultural residue) and nonfood energy crops
(e.g., herbaceous biomass) assumed to be grown on land that did not
contribute to emissions of CO2 due to land-use change. The life-cycle GHG
emissions of BTL are estimated to range from 0.08 to 0.17 times those of
baseline conventional jet fuel. The low end of this range represents BTL
produced from crop residues and the high end represents BTL produced from
dedicated biomass crops.



CONCLUSION
       Concurrent with technical issues with respect to production, there is a
need to develop a biomass-supply industry capable of supplying the
significant quantities of biomass needed to support a full-scale CBTL or BTL
industry.




Department Of Mechanical Engineering                                     AJCE
Alternative Jet Fuels                                                           18


                                CHAPTER 7
                   FUELS FROM RENEWABLE OILS

BIODIESEL AND BIOKEROSENE

       This chapter deals with jet fuels from renewable oils. Biodiesel refers to
a vegetable oil- or animal fat-based diesel fuel consisting of long -chain alkyl
(methyl, propyl or ethyl) esters. Biodiesel is typically made by chemically
reacting lipids (e.g., vegetable oil, animal fat (tallow)) with an alcohol.

       There are two principal chemical differences between biodiesel and
petroleum-derived diesel fuel: First, biodiesel contains oxygen, and second,
the length of the carbon chains in biodiesel is inherited from the feedstock.
These differences in chemical composition affect the fuel properties of
biodiesel; some of these are critical to aviation—namely, freeze point, thermal
stability, specific energy, and energy density.

       A variety of oils can be used to produce biodiesel. These include:

               1)       Virgin oil feedstock; rapeseed and soybean oils are most
       commonly used, soybean oil alone accounting for about ninety percent
       of all fuel stocks in the US.

               2)       Waste vegetable oil (WVO);

               3)       Animal fats including tallow, lard, yellow grease, chicken
       fat, and the by-products of the production of Omega-3 fatty acids from
       fish oil.

               4)       Algae, which can be grown using waste materials such as
       sewage and without displacing land currently used for food production.

               5)       Oil from halophytes such as salicornia bigelovii, which
       can be grown using saltwater in coastal areas where conventional
       crops cannot be grown, with yields equal to the yields of soybeans and
       other oilseeds grown using freshwater irrigation.



Department Of Mechanical Engineering                                          AJCE
Alternative Jet Fuels                                                          19


       Today, multi-feedstock biodiesel facilities are producing high quality
animal-fat based biodiesel. Currently, a 5-million dollar plant is being built in
the USA, with the intent of producing 11.4 million litres (3 million gallons)
biodiesel from some of the estimated 1 billion kg (2.2 billion pounds) of
chicken fat produced annually at the local Tyson poultry plant. Similarly, some
small-scale biodiesel factories use waste fish oil as feedstock.

       Biokerosene is kerosene derived from biomass. Kerosene is a
flammable, hydrocarbon liquid that is used in aviation to power jet engines.
However, biokerosene has not become widely used in aviation because it has
been unable to meet the technical requirements of aviation fuel, such as high
energy content per volume and a low freezing point. Until very recently,
biokerosene for aviation fuel was not viewed as a realistic alternative to
traditional fossil fuels. Possible sources for biokerosene include synthetic
biofuels made by gasifying biomass liquefied by the Fischer-Tropsch process,
and green diesel based on a hydrogenation process of vegetable oils.

       Biodiesel has better lubricating properties and much higher cetane
ratings than today's lower sulfur diesel fuels. Biodiesel addition reduces fuel
system wear, and in low levels in high pressure systems increases the life of
the fuel injection equipment that relies on the fuel for its lubrication.
Depending on the engine, this might include high pressure injection pumps,
pump injectors.

HYDRO PROCESSED RENEWABLE JET FUEL
       Plant oils, animal fats, or waste grease (renewable oils) may be
processed to yield a fuel that has properties suitable for commercial aviation
use. These fuels are created using a process that first uses hydro treatment to
deoxygenate the oil and then use hydroisomerization to create normal and
isoparaffinic hydrocarbons that fill the distillation range of Jet A. Because they
are paraffinic, these fuels have properties similar to those of FT fuels. Several
companies either have developed or are developing hydro processing
techniques to create paraffinic fuels that can substitute for conventional
middle-distillate products:



Department Of Mechanical Engineering                                        AJCE
Alternative Jet Fuels                                                           20




       In February 2008, Virgin Atlantic, in collaboration with Boeing, General
Electric, and Imperium Renewables (a biodiesel producer from Washington
state), conducted a flight test of a Boeing 747 with one engine operating on a
20-percent blend of a biodiesel made from babassu and coconut oils. The
analysis presented in this section is primarily based on an assumed 5-percent
blend of biodiesel with Jet A. Where appropriate, analysis of a 20-percent
biokerosene blend, similar to that used in the Virgin Atlantic flight test, is also
presented. The relatively low blending concentrations were chosen such that
the fuels could potentially meet the freeze-point requirements of Jet A.


HALOPHYTES AS JET FUEL

       Threatened by new limits on carbon emissions, two major firms in the
aviation industry have turned to Masdar, the Abu Dhabi Government-owned
clean technology firm, to help find a replacement for jet fuel made from
saltwater plants.

       Boeing, the US aerospace giant, and Honeywell UOP, a fuels
producer, announced yesterday they had commissioned the Masdar Institute
of Science and Technology to study the potential for producing commercial
quantities of fuel from two types of plants that grow in saltwater.

       The aviation industry hopes biofuels can provide a low-carbon
alternative to petroleum, but biofuels producers have come under fire for
displacing food production on arable land. Both algae and saltwater plants,
known as halophytes, could be the answer, the industry hopes, since they do
not need fresh water or valuable land.

       A halophyte is a plant that naturally grows where it is affected by
salinity in the root area or by salt spray, such as in saline semi -deserts,
mangrove swamps, marshes and sloughs, and seashores. An example of a
halophyte is the salt marsh grass Spartina alterniflora (smooth cord grass).




Department Of Mechanical Engineering                                          AJCE
Alternative Jet Fuels                                                        21


        Halophytes are said to be highly productive sources of biomass
energy, thrive in arid land and can be irrigated with sea water, making them
suitable for biofuel. According to Boeing, with improved plant science and
agronomy, early testing results indicate that halophytes have the potential to
deliver very high yields per unit of land.

        The halophyte study will evaluate aquaculture management and
practices, land use and energy requirements and identify any potential
adverse ecological or social impacts associated with using halophytes for
energy development, specifically for aviation biofuel development. To verify
data gathered during the analysis, the study will be peer-reviewed by third
parties and measured against practices and principles developed by the
Roundtable for Sustainable Biofuels. The results are expected to be available
in late 2010.

       The Sustainable Aviation Fuel Users Group said it was currently
working on research into using algae and jatropha curcas -based biofuels,
both of which are believed to have a significantly lower environmental and
carbon impact than fuels made from corn or other food crops. It added that it
was also about to launch a new project to assess the viability of halophytes, a
class of plants that thrive in saltwater habitats, which it is hoped can be
produced in large quantities without eating into agricultural land.

        Major arid or semi-arid halophyte agriculture problems include
pumping and draining the required high volumes of irrigation water from sea
or ocean sources.

       Also, not all arid or semi-arid lands are suitable for crops. Benefits of
halophyte agriculture include freeing up arable land and freshwater resources,
cleansing the environment, decontaminating soils, desalinating brackish
waters, and carbon sequestration. Furthering the case for halophyte
production, as these plants are grown in the desert, they will produce a cooler,
wetter land surface, which could lead to rainfall in areas of the world where
rainwater is in short supply.




Department Of Mechanical Engineering                                       AJCE
Alternative Jet Fuels                                                               22



COMPATIBILITY IN CURRENT SYSTEMS
       There have been concerns with respect to the compatibility of straight
biodiesel with diesel engines, including decomposition during storage and
freezing at low temperatures. The relatively high freeze point of biodiesel
requires that it be used in a blend when used for jet aircraft. A more serious
issue is the potential for FAME to break down during engine operation.

        Further complications arise because of the reduced energy density of
biodiesel, as compared to Jet A. Assuming that the freeze point scales linearly
within this range of blending percentages, then a 5-percent biodiesel blend
would have a freeze point of approximately –41 degrees Celsius and may
meet the Jet A freeze-point specification of –40 degrees Celsius. However,
other measurements indicate that blends containing only 1 percent biodiesel
may not meet freeze-point requirements

       Testing indicates that some biodiesel blends, even when blended at
just 1 percent, could lead to unacceptable thermal-stability degradation
Because of concerns about the thermal stability of jet fuel, biodiesel is
currently not being transported in U.S. petroleum pipelines. The concern is
that trace quantities of biodiesel will trail back to jet fuel that is traveling in the
same pipeline and that this contamination will lead to an unacceptable
degradation in the jet-fuel thermal stability. In Europe, biodiesel is currently
being transported via pipeline as a blend with conventional diesel fuel, but
there is ongoing research to determine the effect on jet-fuel quality and an
acceptable level of biodiesel contamination of jet fuel.

CONCLUSION
        However, there are continuing concerns regarding the freeze point,
thermal stability, and specific energy of these fuels, especially in formulations
that can be economically produced. It appears that biodiesel and biokerosene
are better suited for ground-transportation applications, for which specific
energy and freezepoint concerns are not as critical.




Department Of Mechanical Engineering                                             AJCE
Alternative Jet Fuels                                                          23


                               CHAPTER 8

                             CONCLUSIONS

       Alternative sources of fuel for aviation could be used to expand and
diversify supplies of jet fuels. To the extent that such alternative fuel supplies
reduce world demand for crude oil, world oil prices would be reduced, to the
benefit of commercial aviation as well as all other users of petroleum. The
same economic benefits to aviation occur through energy conser vation (a
barrel saved has the same effect as a barrel displaced by alternative fuels)
and by expanding use of alternative fuels in ground transportation (a barrel
displaced in ground transportation has the same effect as a barrel displaced
in aviation). Even though some alternative fuels can be produced at costs that
are well below current world oil prices, the prevailing prices will be those
associated with petroleum-derived fuels.

       If the goal of the commercial aviation community is to moderate the
long-term trend of      increasing petroleum prices, the preferred strategy
consists of promoting efficiency in the use of petroleum in all end -use sectors
(including aviation, of course) and promoting alternative-fuel production and
use    in   all   end-use   sectors    that   are   dependent    on    petroleum
.

       Efforts are ongoing to certify these fuels for aviation use. Should low-
cost feedstock become available, there would be a ready market for the fuels.
If these feedstocks do not require the use of arable land that would otherwise
be used for food production, GHG emission reductions could be significant. A
substantial reduction in the environmental impacts of aviation on air qualit y
could be achieved by removing sulfur from the existing fuel supply. This
approach could be fully implemented within five to ten years.




Department Of Mechanical Engineering                                        AJCE
Alternative Jet Fuels                                                          24


                                  REFERENCES
   i.   James I. Hileman, MIT ; David S. Ortiz, RAND ;James T. Bartis, RAND;
        Hsin Min Wong, MIT; Pearl E. Donohoo, MIT ; Malcolm A. Weiss, MIT;
        Ian A. Waitz, MIT, Near-Term Feasibility of Alternative Jet Fuels,
        Technical Report(PDF File),2009

  ii.   Bilal M. McDowell Boman; Dan L. Bulzan; Diana I.; Centeno -Gomez;
        and Robert C. Hendricks, Glenn Research Center, Cleveland, Ohio,
        Biofuels as an Alternative Energy Source for Aviation—A Survey,
        NASA/TM—2009-215587(PDF File),2009

 iii.   R.C. Hendricks; D.M. Bushnell, Halophytes Energy Feedstocks: Back
        to Our Roots, The 12th International Symposium on Transport
        Phenomena and Dynamics of Rotating Machinery Honolulu, Hawaii,
        2008

 iv.    McCormick, Biodiesel Handling and Use Guide,Third Edition(PDF
        File),2009

  v.    http://www.nrel.gov/vehiclesandfuels/npbf/pdfs/40555.pdf. Retrieved
        2006-12-18.

 vi.    http://www.pseez.ir/gas-en.html. Retrieved 2007-07-17.

vii.    http://www.energy.gov.ab.ca/OilSands/1106.asp. Retrieved 2008-02-
        02.

viii.   http://www.greenaironline.com/news.php?viewStory=621

 ix.    http://www.greenbang.com/study-eyes-potential-for-jet-fuel-from-
        saltwater-mangroves_12021.html

  x.    http://memagazine.asme.org/web/Green_Energy_Leader_Job.cfm

 xi.    http://www.greencar.com/articles/5-things-need-fischer-tropsch-
        process.php




Department Of Mechanical Engineering                                         AJCE

								
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