Bjorn’s Corner: Why e in ePlane shall stand for environment, Part 15. Carbon-neutral fuels.

March 27, 2020, ©. Leeham News: In this week’s Corner, we analyze the use of carbon-neutral fuels for airliner use.

Almost all variants of carbon-neutral fuels have the “drop-in” advantage, they can replace our regular jet fuel in a mixed capacity or entirely with none or minimal changes to our present aircraft and their engines.

It’s a big subject, and I will use the next Corners to explain the key alternatives, their production process, and what benefits and problems they bring.

Figure 1. airbp is distributing bio-jet fuel produced by Neste. Source: BP

The fundamental advantage of carbon-neutral fuels

The majority of carbon-neutral fuels are chemically similar enough to our airliner Jet A-1 fuel that they can be approved as a “drop-in” alternative. This means a recognized authority creates a fuel specification that is qualified for use in airliners by the aircraft OEMs and as long as fuel producers adhere to the specification the fuel can be used in the approved aircraft’s fuel systems.

The alternative fuel is approved either in a mix with a ratio of alternative fuel to Jet-A1 of up to typically 50% or as an outright replacement for Jet-A1.

The alternative fuels that are approved for use in our airliners today are bio-based fuels. Bio-based fuels are produced from biomass, bio fats and oils or other waste products. They are the alternative to fossil fuels in the short term for air transport. They been in development over the last decades and are in active use today with a handful of airports offering them as an alternative to the fossil Jet A-1 fuel for business aircraft and airliners.

We will discuss their production, cost, and adoption more in-depth in a subsequent Corner.

The alternative to bio-based fuels is synthetic fuels. A production process synthesizes the fuel’s hydrocarbons from CO or CO2 sources with gaseous hydrogen to form the jet fuel’s hydrocarbons.

The synthetic fuel process is energy-intensive and seems unattractive at first. If we could store produced energy efficiently, synthetic fuels would not be an alternative. But we can’t.

We have analyzed the problems of storing energy in a chemical process in our battery discussions. For large energy levels and long time storage, battery storage is unpractical.

The world’s renewable energy production, like hydroelectricity, wind, or solar energy, is often produced at places and at times when there is no local energy need. Synthetic fuel can then be seen as long time storage of energy from sources where there is no immediate local consumption.

Examples are remote geothermal, waterelectricity, wind, or sun energy production. The windiest parts of the planet are the open seas where no energy consumption takes place, the sunniest places the deserts where no people concentrations are. And so forth.

Seen in this perspective, synthetic fuel production can be a rational way to use the natural sources of renewable energy the globe offers. By nature of a more complex total solution, synthetic fuels are a longer-term carbon-neutral fuel alternative.

Airliner approved bio-fuels exist and are used today. We will look deeper into these in the next Corner.


18 Comments on “Bjorn’s Corner: Why e in ePlane shall stand for environment, Part 15. Carbon-neutral fuels.

  1. I think possibly the most important issue surrounding alternative fuels is their particulate emissions (PM) levels. I haven’t seen mention of much research about this but last year an AAAS journal referred to a 2011 study that indicated aviation particulate emissions create significantly more warming than aviation CO2.

    The importance of this is that by virtue of more consistent chemical make up synthetic fuels can burn more cleanly, reducing PM. The reductions reported in are very large. That paper is old but certainly current road vehicle GTL (I think the only available is Shell GTL diesel) is demonstrating significantly reduced PM.

    As an asude, my recollection (not sure if correct) is that a significant part of the reason for synthetic fuel development was to make use of the gas that was otherwise flared off (ie completely wasted) from oil rigs.

    • I suspect the particulate study will eventually be disproven as inconsequential like most such things are. They are easy allegations/theories to make but require real science to disprove. hence please be careful about what a person with an obvious scientific understanding kike you says, some people take it as gospel. Pine forest die back that was blamed on sulphur from coal power stations turns out to have been caused by agricultural changes. The nitrous oxide in California’s air that is causing photochemical smog and is detectable in Antarctica comes from nitrate fertilisers NOT diesel engines.

      Fisher-Tropsch aviation fuels and diesels tend to form far less particulates because they are consistently long linear chains (instead of closed up cyclic isomers) which burns smoothly, consistently and completely so few, if any, particles will leave a jet engine.

      It turns out that the diesel particulate problem is about to be completely eliminated. Oddly it was simply a matter of adding a Bunsen burner like shroud over the injectors. With the particulate problem gone combustion engineers can focus entirely on the problem that isn’t really a problem NOX.

      Maybe something similar for jet engines?

      There is also DME “Di Methyl Ether” and OME or monooxymethylene ether (OME1). (OME1 is made from methanol on a commercial scale and has a cetane number of 38; it can be mixed with additives to produce OME1a diesel fuel (CN 48).) It is a drop in replacement apart from materials compatibility issues, It is particulate free and if blended with conventional diesel eliminates the particulate/NOX quandary. OME should make a good jet fuel though it is less dense, so maybe a blend.

  2. On TV in New Zealand recently was a Kiwi man living in L.A. who had developed a way of using bacteria to convert CO2 to hydrocarbons. Virgin recently view issuing the fuel. It may be a smart way forward?

    • sunlight plus algae plus CO2 gives you more algae i.e. protein biomass creation. biomass to fuels is established.
      Research from the 90ties actually.
      Center for renewables in Denmark was rather busy in that domain.

    • These bacterias are normally known as plants – fir, oak, pine, birch and other, also – all kind of vegetations, crops, grass and so. They all convert CO2 into hydrocarbons since the time of Creation.

  3. Some countries require bio fuel mix into diesel and gasoline besides requiring very low sulfur content. One side effect from these “pure” fuels is a slightly lower energy content as sulfur and coal residues takes part in the combustion process and thus lower the fuel consumption/liter a bit. The “mix in rations” and purity of the fuel varies in the EU from country to country. Some of the synthetic fuels when enough condensation water is added can allow bacteria growth “diesel pest” and for Aircrafts that is very much unwanted effect forcing adding pestecides into the fuel.
    Still you add engineers, competition and government specified testing to solve the problems popping up. Often it takes a tragic accident to push safety and development forward.

    • I purposely avoid biofuels because I don’t want to encourage land use for biofuels. The tragic nature of the problem became apparent when EU subsidies caused clearing of rainforest in asia an the death of many Orangutan. There is a place for it, maybe, if they are 100% waste based. 3rd generation biofuels are more promising as they can run on waste crops. Lubricating and Hydraulic oils made from crops like rape are far less polluting when spilled by equipment used in sensitive areas. Bio lubricants are actually better than minerals oils and as good as synthetics and would likely save 1% on our roads. That would be a better use for them. The water problems is over stated. Normal oil accumulates water. You can get on line monitors to provide a warning. The standard filter can be replaced with a polymeric one which will absorb moisture (up to a limit)

      • The water in sythetic fuel is not a big problem until bacteria/algea starts to grow in the tanks, those producing HVO brag that their pure fuel stops those bacteria/alge growth.
        One problem around the world is that goverments slls off tropical forests cutting to the highest bidder that cleans the area and some burn/plant sugar cane/Palm oil etc on huge areas. Often is the ground after the first harvests not that nutrient and large amounts of fertilisers and pestisides are needed while most wild life is gone. I support the Orangutangs every month with some $ still the UN should calculate where the jungle should stay and dedicate some very good areas for food growing and push goverments to restore ruined farmlands to farming or replanted forests of a good mix for the animals.
        Airlines can help by “growing their own fuel” in a eco friendly way (like algea in desert salt water ponds) and goverments enforce them to do it step by step and like during the railway boom get to own the land where they grown algea and other crops and + 1 mile around it.
        The high tech engine manufacturers could help with needed equipment and maintenece programs making them grow the correct mix of algea (that easily get polluted by other algea ruin their business.)

  4. Despite best efforts at plastic recycling much, although sorted when collected, still goes into landfill – black food trays etc. With techniques available for converting it back to diesel/avtur like fuels this is a scandalous waste and it should all be processed and used

    • Plastic reuse are popping up besides the PET bottle recycling, many are going the way of syngas + filtration and F-T conversion to liquid fuel. Robotic waste sorting is also helping out making the raw material mix better for the processes.

  5. In regards to the synthetic fuels. Courtesy of the USAF and US DOE Fischer-Tropsch jet fuel has a specification and has been certified. From the point of view of the fuel produced it doesn’t matter whether the syngas going to the FT catalytic reactor comes from coal, natural gas or CO2/H2 extracted from the air or sea water.

    Broadly there are two routes. One is to take the CO2 and H2 and convert them to syngas C0/H2 over a catalyst (‘reverse combustion’) and then react to produce jet fuel directly or to convert to methanol. Methanol can easily be converted by Mobils ZSM5 zeolite catalyst to gasoline and jet fuel, unfortunately this jet fuel is not yet certified (though there is no reason it cant be). One can also also make DME and OME efficiently (90% or more) with OME being replacement or blend for diesel and likely jet fuel.

    There are a couple of nice short cuts. CO2 and H2 can be directly reacted to produce methanol (being done in Iceland) and CO2 and Steam can be electrolysed together to produce syngas in one operation.

    CO2 can be extracted efficiently from the air (by amines and hydroxides) and from concentrated sources such as cement kilns.

    Surprisingly one of the easiest way to extract CO2 is from sea water. You pass current through it and extract the carbonic acid and remove that via the membrane separator. US Navy did a lot of work on making their own jet fuel on their nuclear aircraft carriers.

    There are also routes where the CO2/H2o is heated over catalysts (cerium oxide) directly to make syn gas without electrolysis and thermo chemical reactions that would work with solar heat or best of all nuclear.

    If you listen to scientists working on China’s thorium thermal neutron molten salt breeder reactor project they envisage using the CO2 take from the atmosphere to make carbon fibres and plastics not just fuels. The Chinese mean to control this nuclear technology.

    • A YouTube video by a scientist from the US NRL “National Research Laboratory” doing a presentation on the topic about how to extract CO2 from sea water and river water as a feed stock for making Jet Fuel.

      The US Navy is interested because it wants to make Jet Fuel on its nuclear aircraft carriers. I suppose you could use tidal or wind power from drone kites out to sea.

    • I downloaded and read this report (skimmed for 60 minutes).

      The questions I have about this scheme is
      1 What will happen to aviation when jet fuel costs EUR 0.7-1.4. the report says fuel is 20%-25% of an airlines operating costs. Jet fuel is currently EUR 0.18 (a bit lower than normal due to Saudi Oil Price War). Will airfares double?
      2 The report costs renewable electricity but seems to assume renewable electricity as available in sufficient quantities.
      3 Also I cant see utilisation factors in the report, how often will plant be shutdown due to no wind to power the electrolysers.

      The report suggests that by 2030 the majority of Nordic jet fuel can come from these sources.

      The basic idea is to anaerobically ferment agricultural waste to produce methane which is injected into the gas network. Some of this methane will be used to produce jet fuel. Because 25%-50% of Bio Gas is CO2 this CO2 has to be removed anyway, rather than venting it to atmosphere the long term intention is to use it to produce electro-methane or e-fuels (also called PtL or PtG Power to Liquids/Gas).

      The potential for biogas, using waste only, in the Nordic countries is about 200 pentajoules (as methane) which roughly matches the 200 pentajoules needed by aviation (as jet fuel). This does not count the potential electro-fuel nor the potential use of wood as a fuel.

      The suggestion is to then start production of jet fuel via fischer-tropsch using the methane, taken out of the gas network.

      The suggestion is, somewhat latter, via production of hydrogen via electrolysis of water to also convert the CO2 into electro-methane and also pump that into the gas network. The location chosen for this is in the district heating stations Nordic countries have to pump warm water around districts. The methanation reaction and fischer tropsch reaction is exothermic so will produce useful waste heat.

      This is where things get a little paradoxical. It would be better to convert the CO2 directly into jet fuel rather than via the intermediate step of CH4. The authors are probably concerned by the viability since methanation can likely more easily be carried out at a local area near the agricultural source in the heating district and want to transmit the gas from dispersed locations.

      Living in Australia I don’t understand district heating in Nordic countries. I believe modern 5th generation system pump water at about 20C around a district (to minimise heat loss) and then heat pumps increase the heat for use in heating offices and dwellings.

      There are a couple of little side lines such as burning garbage and wood waste to collect CO2. I do not think that burning wood is a good idea. It should be mechanically shredded and fermented to alcohols via 3rd generation biofuel technology so as not to produce insoluble ashes that are of no use in maintaining forest fertility.

      The report does not deal with other boil fuels such as genetically engineered sugar beet which can produce a 2nd/3rd crop just before winter and have a positive energy balance.

  6. Good topic and good answers.Thx Stan for the link above very interesting.I agree with those that worry about deforestation and palm oil tree replacement.Its devastated huge swaths of virgin forest.However using animal waste and associated straw is very different.
    One question.There are 7.5 billion humans producing waste on a truely industrial scale.Furthermore we know ( in general) exactly where it goes – flushed down a toilet.As far as I understand it this goes to treatment plants which then flush it into the sea ( generalisation).No pun intended but that’s a terrible waste.It is neither fertiliser ( it could be – see Martian) nor converted into gas products re this discussion.
    Surely there must be a better route to produce hydrocarbon energy than just ‘treating’ it and then shoving into our overpolluted oceans?

    • I have a story for you about human waste and its potential for methane production. A while back (Im in Australia its the late 80s) the father of a girl I was dating was an ethnic German from pre war Romania. Prior to the 2nd world war, as a civil engineering student, he was sent on a study tour to Frankfurt Germany. There he said the city took human sewage and alternately put it into 1 of 5 large tanks. At a certain point a crane moved a lid onto the tank and the methane it collected was burned to produce electricity while the output was fertiliser and clean water that was put into the Rhine.

      Also I recall Chinese Engineers came up with a system for collecting family sewage waste in the 1980s that produced enough fuel to cook for a family of 3 and provide them their hot water. My father who worked for the local water authority said they had internal combustion engines that ran of the sewage gas but they were replaced due to the maintenance costs. The are of course large numbers of “self sufficiency” enthusiasts doing this. I believe an average human conservatively produces 1100KL/day biogas which is about 0.3KW.Hr. A cow will produced 0.4 cubic meters or about 2.4KW.Hr. If food waste was utilised in these digestors it would supplant as much as 18% of natural gas use.

      Cheap energy has made our lives beautiful, healthy and much better. If we go back to renewables our standard of living will go backwards quite a bit. Hopefully not too much.

    • They used to “refine the shit” and put it back on farmland, but as it contains many other chemicals like medical residues and metals the Eco-farmes don’t want it.
      There are sites popping up making “bio gas” from waste water before sending it on. Linde-AGA are big on this. Especially new wastewater plants in Western Europe get these “Bio-gas” fermenters. Natural gas is still much cheaper but they develop bio gas with new bacteria mixes producing more and better bio gas slowly closing the gap.

      • Apart from manure the “biogas potential” of waste food (domestic, restaurant, food processing, waste crop) that in many countries like my own, mostly goes to landfill (where it’s biog gas production is very poorly utilised) rather than proper anaerobic digesters is apparently astonishing. It seems to be around 0.6 cubic meters CH4 per capita which is around the same as a litre of jet fuel. Unlike most biofuel crops the cost of processing and collecting it is a fraction of the energy return. There is some “low hanging fruit” around and we certainly need to get organised. I’ve long seen it as a soil fertility issue.

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