(413a) 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

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