Mankind has set itself the challenge to decarbonise its energy system. While progress is being made in the quest for CO2 neutral electricity it is proving more challenging to develop CO2 neutral liquid fuel. The liquid fuel challenge may be addressed in two ways. The first is to simply do away with it all together and to opt for electrification of transport. But that option is not available to air travel leading to the challenge of manufacturing a CO2 neutral jet fuel at a reasonable cost.
[Image from US Navy research test flying a model P-51 Mustang powered by fuel made from seawater derivatives. Image from Smithsonian.]
The US Navy has developed a way of extracting CO2 and H2 from seawater and recombining these raw materials to manufacture alkane polymers in the range C9 – C16 that are useful for conversion to jet fuel. This approach is in general similar to Audi’s e-diesel that I looked into some 18 months ago. So where is the catch? Smithsonian says:
made into fuel at the cost of approximately $3 to $6 per gallon. The low end is equivalent to today’s jet fuel costs, while the high end would be double the price.
Note that at 42 gallons per barrel, $3 works out at $126 per barrel of jet fuel. I suspect this sum was done pre oil price crash (see below).
In my post on Audi’s e diesel I concluded that it would cost 2 to 4 times as much as conventional diesel which is clearly a show stopper. High cost, in general terms, is the cancer running through most Green Tech solutions from solar panels to electric cars and batteries. Given enough money, Man can just about achieve anything. But historically our economies and societies have thrived upon choosing the cheaper and better options – it’s called capitalism. Now we are being mandated to select more expensive and poorer options. This is bound to end in tears.
Given that the motivation for producing syn-fuel is normally to eliminate CO2 emissions the source of electricity used must be CO2 neutral. During WWII the Nazis made synfuel from coal as did the South Africans during the apartheid era proving that the processes are scalable where cost is not the prerogative.
In this post I want to re-examine the cost of manufacturing syn-fuel from a range of carbon neutral sources of electricity including wind, solar and nuclear power. This employs the same methodology as used in my Audi e diesel post. In that post I used Robert Rapier’s energy consumption figures and I have checked with him that these are transferable from diesel to kerosene (jet fuel).
Figure 1 The cost of jet fuel on 14 October 2016 from IATA.
A good starting point is to find out what jet fuel costs today. According to the International Air Transport Association (IATA) the cost was $61.8 / bbl on 14 October. According to the EIA, Brent was trading at $48.87 and WTI $50.35 on that day, the average = $49.61. We can deduce that $12.19 (19.7%) is the refining and transport cost of the jet fuel. Luckily there is no tax on jet fuel and working with tax free barrels makes this analysis cleaner than working with taxed litres as was the case with diesel.
Before going further let us remind ourselves about the processes involved and then to look at the energy balances. The starting point is always to get pure CO2 and H2.
Figure 2 The Audi process uses well established chemical engineering processes.
Audi’s process employs CO2 capture from air and H2 production by high temperature electrolysis of water. The US Navy describes their process as follows:
NRL has made significant advances developing carbon capture technologies in the laboratory. In the summer of 2009 a standard commercially available chlorine dioxide cell and an electro-deionization cell were modified to function as electrochemical acidification cells. Using the novel cells both dissolved and bound CO2 were recovered from seawater by re-equilibrating carbonate and bicarbonate to CO2 gas at a seawater pH below 6. In addition to CO2, the cells produced H2 at the cathode as a by-product.
I don’t have the energy parameters for the Navy process and so will proceed using those used previously for Audi e diesel. It is clearly important to discover which is energetically more efficient. That is a good topic for the comments.
Figure 3 The US Navy apparatus that produces both CO2 and H2 from seawater and combines them to make CnH2n+2 is mounted on a small skid.
Most methods for production of synfuel employ variants of the Fischer – Tropsch reaction:
(2n + 1) H2 + n CO → CnH2n+2 + n H2O
Where n is typically between 10 and 20. For jet fuel the reaction may be summarised thus:
25H2 +12CO→C12H26 +12H2O
Note that the reaction uses CO (carbon monoxide) and not CO2. I speculate that CO is produced from CO2 using the water-gas shift reaction:
CO2 + H2→CO + H2O
Following Robert Rapier’s methodology there are three main components to consider.
1) The energy required to separate CO2 from air. 3.2 tonnes of CO2 are required to make a tonne of e diesel and an energy cost of 250kWh per tonne is identified giving a total of 800 kWh.
2) The energy required to make H2 from water. 294 kgs of hydrogen are required to make 1 tonne of fuel. At this point RR does not give the energy used but simply quotes the cost $4 / kg. Converting that to electricity at 6.9c per kWh (US price) works out as 4 / .069 *294 = 17,044 kWh to make 294 kgs of H2.
3) The thermal energy used in the conversion process is 1750kWh per tonne of CO2 (3.2 tonnes) = 5600 kWh.
CO2 separation = 800 kWh
Hydrogen production = 17,044 kWh
Thermal energy for conversion = 5,600 kWh
Total = 23.444 MWh per tonne
Total = 3.279 MWh / barrel
Note that by far the largest energy cost is the electrolysis of water consuming 73% of the total energy budget. Anyone who can substantially reduce that energetic cost will surely win a Nobel Prize.
The final stage of this analysis is to work out the cost. Here we need the cost of various low carbon sources of electricity where I use the levelised cost of electricity (LCOE) as published by the EIA. Calculating LCOE is a bit of a black art since it involves assumptions about the future cost of fuel for fossil based systems and assumptions about future manufacturing cost, life span and capacity factors for renewable based systems. But the arithmetic is simple. We simply multiply the $/MWh by 3.3 to get $ / bbl of jet fuel.
Figure 4 Summary of LCOE for common forms of carbon neutral electricity from the EIA. HAWP estimates from KiteGen (internal documentation) and Makani (video interview with Corwin Hardman). Beyond what is discussed in the text, just look at these numbers for offshore wind and solar thermal. The public are more accustomed to knowing the price of oil. But not the production cost of electricity. Try selling Joe Public a cheap holiday where the cost of jet fuel is $500 / bbl. But this is UK, Scottish and EU government policy. Stick that on your manifesto and get elected!
Cynical readers will no doubt be critical of my using unaudited KiteGen numbers for high altitude wind power (HAWP) (see disclaimer at end). These numbers are based on IEA and NREL methodologies and will of course be subject to verification following actual deployment. The figures 20 to 7 are based on mid maturity of the technology with between 50 ($20) and 5000 ($7) machines deployed. The numbers may seem unbelievable but bear in mind the enormous mass advantage that HAWP has over ground turbines (20 versus 1300 tonnes) and the higher capacity factor of HAWP both of which feed directly into a lower LCOE. Other HAWP players make similar claims:
Much lower Levelised Cost of Energy (LCoE) than conventional wind and other renewables.
While the late Corwin Hardman of Google Makani claims $30 / MWh for their system that may be less efficient than KiteGen’s.
Abundant energy at low cost for everyone, everywhere. Without CO2 emissions, at low cost and without subsidies. This is how we see the future.
The technology to make liquid fuel from CO2 and H2 has existed for nigh on 100 years. The main barrier to wide-spread deployment is the uncompetitive cost of fuel that is produced. The main cost centre is the electricity consumed where, for example using onshore wind as the source would lead to Jet A1 costing over $200 / bbl compared with $62 / bbl today. This is a show stopper.
The cost of synfuel can be attacked from two directions. The first is to make the process more efficient to reduce the amount of energy consumed. But this will inevitably at some point meet a thermodynamic barrier that cannot be crossed. The other approach is to tackle the cost of the electricity consumed. < $20 / MWh is the magic number that would make Audi’s e diesel and Extra Virgin Jet Fuel competitive with fossil fuels. High altitude wind power is the only show in town that holds any promise.
I am currently engaged by KiteGen as a consultant on a commission basis during their third round capital raising exercise. I am delighted to announce that KiteGen have been selected to present at the Techtour CleanTech investor summit in Rotterdam next month.