Jet Fuel From Air, Water, and Uranium

Jet Fuel from Air, Water, and Uranium

Charles Forsberg and John Michael Galle-Bishop

Massachusetts Institute of Technology

Liquid fuels can be produced from air and water. We developed flowsheets for production of 6400 barrels per day of JP5, a jet fuel that is useable as diesel fuel. Carbon dioxide is extracted from air. Water is obtained from the ocean. Heat and electricity is provided by either a light-water reactor (LWR) or a high-temperature reactor (HTR). LWRs are the existing commercial nuclear power technology. The thermal heat to liquid fuel efficiency is ~22% versus the typical heat to electricity efficiency of 33%. HTRs are an advanced reactor. The heat to liquid fuel efficiency is ~31% versus a heat to electricity efficiency of 45%.

The design goal was a nuclear tanker for the U.S. Navy that could manufacture on-board at-sea all the liquid fuel as needed for a carrier task force. This included fuel for both the carrier aircraft and all escort vessels. Such a tanker would free the U.S. Navy from most of its logistical burdens. JP5 is a refined jet fuel for navy applications that is compatible for use in diesel engines and thus could meet all U.S. Navy at-sea liquid-fuel requirements. The flowsheets are identical to those required to manufacture unlimited liquid fuels from air and water. The plant size is ~1% of a global-scale oil refinery. Consequently, the work provides an estimate of what is required to produce liquid fuels with no net release of carbon dioxide to the atmosphere. The analysis indicates that the upper limit on the cost of liquid fuels is between 2 and 3 times the cost of electricity on a per unit heat basis. On a per unit energy basis, liquid fuel prices today in the U.S. are about equal to the price of electricity.

Figure 1: Top-Level Flowsheet for Air and Water to Jet Fuel/Diesel

The flowsheet is show in figure 1. The major process steps include.

• Carbon dioxide feedstock. Carbon dioxide is extracted from air by absorption. This technology is being tested in pilot plants.

• Water feedstock. Water is purified and converted to steam—a commercial technology.

• Syngas production. Water in the form of steam and CO₂ are fed to high-temperature coelectrolysis cells to produce syngas (H₂, CO) and oxygen. Added hydrogen is made by high-temperature steam electrolysis. High temperature electrolysis operates at temperatures near 800°C, is at the pilot plant stage of development, and is based on solid-oxide electrolytic fuel cells operated in reverse. This process uses about 75% of the energy of traditional alkaline-cell electrolysis.
• Liquid fuels production. The syngas is fed to a Fischer-Tropsch (FT) system to convert syngas to liquid fuels. Micro-channel chemical reactors are assumed. The FT process is a commercial process whereas micro-channel chemical reactors are in the pilot plant stage of testing.
• Refining. Standard refining technology is used to produce the final JP5 liquid fuel
• Auto thermal reforming. The FT process produces a relatively wide distribution of hydrocarbons. Refining operations can convert many of these products to JP5 but there are significant light and heavy products that are not convertible. All of these are recycled back to an auto-thermal converter and burnt with oxygen to produce a syngas for recycle to FT.

The process requires heat at different temperatures. The LWR peak temperature is 285°C whereas the HTR peak temperature is 700°C. Resistance heating is used where required to obtain high temperatures. The process produces a single product (JP5). If a broader product slate is desired, the refining and auto thermal reactor capacities and inefficiencies would be reduced. The energy savings with a broader product slate would be small.

The technologies were chosen based on efficiency and space requirements. Space is a major constraint aboard a ship but would not be a constraint for a land-based facility. Each of the non-commercial technologies is at a point where a reasonable case for future commercial deployment can be made. For each non-commercial technology there is a backup commercial technology. For hydrogen production, it is conventional electrolysis, a technology that has been commercial for over a century.

As would be expected, most of the energy input is for electrolysis that requires 590 MWe. The heat balances for the system are shown in Table 1. The capture of carbon dioxide from the atmosphere is not a major energy consumer.  

The production of liquid fuels from air and water using nuclear energy could be commercialized if (1) there were strict limits on greenhouse gas releases, (2) there was a decision not to depend up foreign liquid fuels, or (3) the prices of fossil fuels rise significantly. In the mid-term, there are two potential markets. The first market is the military where the cost of fuel includes the security requirements under hostile conditions (ships, aircraft) to assure delivery. The second market may be in countries such as Iceland with very low cost electricity and very high liquid fuel prices. In a broader context, this liquid fuels option provides an upper limit on the cost of liquid fuels. In the context of policy, including R&D investments, it places an upper limit on what long-term transport energy options (hydrogen, biofuels, batteries, etc.) could become economically viable.

Table 1. Heat and Energy Balances for Producing 6400 Barrels of JP5 Jet Fuel Per Day Using a Light-Water Reactor or High-Temperature Reactor

System	LWR	HTR
Reactor Power
Total Thermal Power (MWth)	2082	1456
Thermal Power to Power Cycle (MWth)	1973	1285
Electrical power from Power Cycle (MWe)	658	650
Thermal Power for Process Heat (MWth)	109	171
CO2 Capture and Desalination (MWe)	21.7	21.7
High Temperature Coelectrolysis
Temperature of heat input (°C)	27-285	27-655
CO2 Feed Heating (MWth)	7.80	21.1
H2O Feed Heating (MWth)	69.3	102
HTCE Heat Total (MWth)	77.1	123
HTCE Electricity (MWe)	534	534
High-Temperature Electrolysis
H20 Feed Heating (MWth)	12.0	17.6
HTE Total (MWth)	12.0	17.6
HTE Electricity (MWe)	55.9	55.9
HTE Electric Resistance Heating (MWe)	0.771	0.0
Auto thermal Reforming
H2O heating (MWth)	10.3	13.4
Hydrocarbon Heating (MWth)	2.96	7.86
ATR Heat Total (MWth)	13.2	21.2
ATR Electric Resistance Heat (MWe)	5.380	0.481
Product Upgrade
Temperature of heat input (°C)	7-285	7-350
Product Upgrade (MWth)	6.24	8.59
Electric Resistance Heating (MWe)	2.49	0.0
Compression (MWe)	4.85	4.85
Compression Non-Refining (MWe)	34.3	34.3
Overall Cycle Performance
Power cycle efficiency	33.1	44.6
Heat JP5 Combustion/Reactor Heat Input	21.8	31.1

J. M. Galle-Bishop, Nuclear Tanker Producing Liquid Fuels from Air and Water, Thesis, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 2011