Bio Aviation Fuels

8/7/2019 Bio Aviation Fuels

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Bio Aviation Fuels

Introduction

The Dramatic increase in fuel prices in recent years has caused concern inaviation industry. The current aviation fuel is produced from crude oil. Thediscovery of new crude oil resources has become a rarity; however, the globaldemand for aviation fuel is increasing at a faster rate. This has awakened theaviation industry and supply and prices of aviation fuel has become a topic ofdebate involving ATAG, stakeholders, Governments, industry and ResearchInstitutions.

Due to low prices, availability and technical advantages, long life time and highcapital investment in aircrafts, kerosene derived from crude oil is considered tobe the preferred aviation fuel. This trend is likely to continue for another 2-3

decades. Among the technical advantages kerosene has good flowcharacteristics viscosity and freeze point, clear combustion, low luminosity,good energy density and good thermal stability.

The concerns about rising prices, energy security, and aviation emissions haveled to look into alternative fuels. The potential of alternative fuel in aviation is nota new concept. Early jet engines were developed using hydrogen as fuel. Due tothe requirements for aircraft to use a fuel with high energy content per weight andper volume, kerosene has become a standard aviation fuel in 1970s syntheticaviation fuels based on shale oil, tar sands, and coal liquids were investigated,but their prohibitive cost became the main hurdle in their commercialization. In

1980s biofuels such as ethanol, esters of fatty acids were also mooted for use asaviation fuels, but could not be pursued due to their high cost and low energydensity.

The main challenges that an alternative aviation fuel must address include:

1. Reducing environment impact. Aviation industry consumes 2% of all fossilfuels burnt i.e. about 12% of total fuel consumption of entire transportsector. CO2 emission is only about 3% of total CO2 generated by thetransport sector, but its environment impact is under spot light.

2. Reducing operating costs.

3. Improving availability and diverse supply options.4. Meeting specifications/need of the aircraft industry.5. Safety norms which are becoming more and more stringent with the rise of

aviation industry.


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The alternative fuels for aviation industry may also face several obstacles/problems, which include:

1. Lead time for fuel and additive development are long ~ 10 years.

2. Airlines do not like aircraft that needs special fuel.3. Little incentive to develop aircraft/engines running on special high

performance or alternative fuel.4. Local alternative fuel potion common on ground transportation fuels only

applicable to general aviation.5. Hydrogen, the cleanest fuel, would require completely new aircraft and

infrastructure.Intergovernmental Panel on Climate Change (IPPC) in its Report Aviation andGlobal Atmosphere 1999 have reported the impact of emissions from civilaviation. This Report has also commented Alternative fuels may appear

environmentally friendly but technical problems occur in adapting the fuel tocurrent aircraft design and aviation infrastructure.

This report deals with the alternative aviation fuel options, biofuels in particular,and their role in future aviation industry and outline the R &D needs for thedevelopment of bio aviation fuels.

Alternative Aviation fuel options:

There are number of alternative fuel potions for aviation, these can be classified

as follows:

1. Synthetic liquid fuels derived from coal, natural gas, or biomass. Itsometimes also refer to fuels derived from other solids such as shaleoil, tar sand, waste plastics etc.

2. Bio aviation fuels Fatty acid esters (biodiesel) derived fromagricultural or wild oil crops like soya, palm, jatropha, algae etc.

3. Other oxygenates methanol, ethanol

4.Hydrogen obtained from fossil fuels such as petroleum, natural gasand coal, biomass, and water etc.


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5. Biomethane methane from agricultural waste, forest waste andMunicipal solid waste (MSW) etc.

6. Nuclear

Renewable Aviation Fuels:

Biofuels (Biodiesel):

Biodiesel (mono-alkyl esters of fatty acids) can be produced by transesterificationof glycerides obtained from vegetable oils, waste oil products and algae oresterification of fatty acids with methanol. Biodiesel is a partial substitute forkerosene. It is expected to reduce fuel cycle carbon emissions and is readilybiodegradable.

There several disadvantages with the use of biodiesel as aviation fuel. Theseinclude poor low temperature properties (high cloud and pour points), oxidationstability, and water penetration. Biodiesel has potential for use in blends withkerosene as aviation fuel. The cost is however high as compared to currentcrude oil based jet fuels.

Methanol:

Methanol is not a suitable jet fuel. Its energy density is too low in either mass orvolume terms. There is also an emissions problem with methanol as it produces

formaldehyde at idle or low power, thus creating health hazards to the groundstaff at airports. Due to its low flash point (18oC) it is not safe. For JP-8 theminimum requirement of flash point is 38oC.

Ethanol:

Ethanol due to its similar properties as methanol is also unsuitable for use asaviation fuel. Its flash point is even lower than methanol.

Synthetic liquid fuels:

Synthetic liquid fuels, known as Fischer-Tropsch Kerosene (FT-fuel) is producedfrom various carboniferous including biomass via syn gas. To date most researchon FT-Fuels has been done by the South African Company SASOL.


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FT-Fuels derived from biomass would provide fuel cycle CO2 benefits comparedto mineral kerosene. FT- Fuels are virtually sulfur free and low in aromaticcontent, which leads to poor lubricity. These disadvantages can be overcome byuse of additives.

Hydrogen:

Use of liquefied hydrogen as a jet fuel offers potential environmental advantages,if H2 is derived from the gasification of biomass or by electrolysis of water usingrenewably generated electricity. It would provide advantage due to its higherenergy density than mineral kerosene. H2 however, presents significant technicalchallenges and would require changes to the airframe design and developmentand modification of jet engines.

Liquefied Bio-methane:

There has been some research and interest in developing LNG fueled jets informer Soviet Union. ADTKs Tupolev 154 with its one engine modified has flowntest flights on LNG. As the aircraft can be operated on LNG, there is a possibilitythat they can be operated with Bio-methane produced from renewable sources.With Bio-methane the fuel cycle CO2 benefits would be much greater, but therewould be some emissions of methane, which is a green house gas.

Among the various options mentioned above, the following four renewable fueloptions seem suitable for detailed research:

1. Biodiesel as kerosene extender2. FT-kerosene derived from biomass3. Liquid H2 produced from renewable sources such as biomass or water.4. Bio-methane

Besides these, hydrotreated lipids from vegetable oils and algae may alsoprovide suitable alternative as aviation fuel. The major problem cost associatedwith biodiesel can be overcome if lipids are produced from cheaper raw materialssuch as biomass.


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Conclusions and Issues:

1.Kerosene based fuels would continue to be the principal fuel forcommercial aircraft for the next2-3 decades. Alternatives equivalent arehowever, open for further study and research to make them widelyacceptable aircraft fuel in the future. Emphasis is likely on the fuelsderived from renewable sources such as biomass.

2. Oxygenates such as methanol and ethanol are not viable options becauseof their low energy densities and likelihood of aldehyde emissions at idleand low power operation.

3. Liquid bio-methane (synthetic natural gas, SNG) can be used as aircraft

fuel but is not likely available in large quantities for used as substitute tokerosene based fuels.

4. Biodiesel, Biomass derived FT-Fuels and Hydrogen offer eco-friendlyalternatives to kerosene based aviation fuels, but warrant further researchand development particularly to reduce cost and specific propertiesmandatory for aviation fuels.

5. Biodiesel and FT-Fuels are better suited as blended fuels with kerosenebased fuels.

6.

Biodiesel requires further research to improve its cold flow properties,thermal stability, and cost. Cold flow properties and thermal stability canbe improved by use of additives and improvements in productionprocesses. About 75-80% component of cost of biodiesel is raw materialcost. Low cost raw materials like lipids from algae, non-edible oil andbiomass derived lipids are potential options for production of biodiesel.Research is however needed to efficiently extract lipid from algae,improving lipid content its lipids content and finding value addition to theassociated biomass.

7. Biomass can be converted to lipids by bio-processing using suitablebacteria. Biomass is available in abundant quantities at very low price.

8. FT-Kerosene could be used in current aircrafts with few, if anymodifications. Due to negligible sulphur and aromatics its lubricity is lowand needs to be improved.


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9. In South Africa Sasol has already certified a jet fuel blend containing 50%coal derived FT-Fuel and 50% conventional kerosene.

10. H2 is a clean burning fuel and has a vast potential for use as aviation fuel.

Use of hydrogen requires new design of aircraft and engine. Further thereis a need to install sufficient capacity to produce hydrogen from biomassat relatively cheaper cost. Currently Hydrogen from biomass is not aneconomical option as compared to hydrogen from non renewables suchas natural gas or other fossil based sources. Research in this area isneeded.

11. To reduce cost of production of hydrogen from biomass co-production ofFT-Fuels with hydrogen is a potential option. Another option can be to useCO produced with H2 to produce value added products based on CO andCO2 such as Fertilizers and chemicals.

12. Co-production of methanol with FT-Fuels from biomass may also reducecost of aviation fuels.

13. Among the other options for renewable aviation fuels hydrotreatment oflipids, obtained from vegetable oils and algae, to produce hydrocarbonsequivalent to conventional kerosene seems to have potential for furtherstudy for its use as aviation fuel.

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Bio Aviation Fuels