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(October 2009)
Two papers in this series address the application of nuclear energy to Desalination and Hydrogen in transport. This paper covers other applications.
Note that the unit MWt (megawatts thermal) is frequently used, each 3 MWt corresponding to about 1 MWe when electricity is generated.
The potential application of nuclear heat depends mainly on the temperature required. With reactor output temperatures (ROT) of up to 700°C there is a wide range of possibilities, at 900°C there are further possibilities, and at 950°C an important future application to hydrogen production opens up.
Recovery of oil from tar sands
From about 2003 various proposals have been made to use nuclear power to produce steam for extraction of oil from Alberta's northern oilsand (tar sand) deposits and electricity also for the major infrastructure involved. At present a lot of natural gas is used - up to 30 cubic metres per barrel of oil. With projections of three million barrels per day by 2016, a great deal of gas is used and the cost exposure is increasing dramatically. In fact, Canadian natural gas is inadequate to supply the anticipated expansion in oil sands output and its use has major CO2 implications which are creating public concern - about 20% of the energy in the oil is required to produce it and about 80kg of CO2 per barrel is released.
The gas is used as an energy source to make steam to liquefy the bitumen, enabling its separation, and to generate electricity for mining and treatment. The Canadian Energy Research Institute predicts a tripling in gross bitumen production by 2020.
One proposal from Energy Alberta Corp. suggested that a single CANDU 6 reactor (about 1800 MWt) configured to produce 75% steam and 25% electricity would replace 6 million cubic metres per day of natural gas and support production of 175-200,000 barrels per day of oil. It would also save the emission of 3.3 million tonnes of CO2 per year. Other figures from PBMR confirm that each 100 MWt will enable production of 10,000 barrels per day.
The main difference between natural gas and nuclear steam generation is that a fuel-intensive process is replaced by a capital-intensive one.
Oil refining
As well as separating the different components of crude oil by two distillation processes, an oil refinery typically breaks down the residual heavy or long-chain hydrocarbons in a catalytic cracker by adding hydrogen. The hydrogen is produced from natural gas, and it breaks down the long-chain hydrocarbons to yield synthetic crude oil (about 5 kg is used per barrel). This hydrogenation of heavy crude oil is a major use of hydrogen today. Overall, about 15-20% of the energy value of the crude oil is used in producing refined products.
Hydrogen production is by steam reforming of the natural gas, and gives rise to a lot of carbon dioxide. Nuclear power could make steam and electricity and use some of the electricity for high-temperature electrolysis for hydrogen production. (Heavy water and oxygen could be a valuable by-products of electrolysis.)
Coal to liquids
The Fischer-Tropsch process was originally developed in Germany in the 1920s, and provided much of the fuel for Germany during the Second World War. It then became the basis for much oil production in South Africa by Sasol, which now supplies about 30% of that country's gasoline and diesel fuel. However, it is a significant user of hydrogen, catalyzing a reaction with carbon monoxide. The hydrogen is now produced with the CO by coal gasification, part of the gas stream undergoing the water shift reaction. A nuclear source of hydrogen coupled with nuclear process heat would more than double the amount of liquid hydrocarbons from the coal and eliminate most CO2 emissions from the process.Using simply black coal, 14,600 tonnes produces 25,000 barrels of synfuel "oil" (with 25,000 tonnes of CO2).
The hybrid system uses nuclear electricity to electrolyse water for the hydrogen. Some 4400 tonnes of coal is gasified using oxygen from the electrolysis to produce carbon monoxide which is fed to the Fischer-Tropsch plant with the hydrogen to produce 25,000 barrels of synfuel "oil". Very little CO2 results, and this is recycled to the gasifier.
Hydrogen for agricultural fertilisers
Nuclear power has potentially a major role in agriculture.
According to Norman Borlaug, 1970 Nobel laureate and "grandfather of the green revolution", organic nitrogen in the world's soils is only sufficient to feed one third of today's population. The rest must come from inorganic additions. Most of the world's nitrogen fertilizers are made using the Haber process*, combining abundant atmospheric nitrogen with hydrogen. The resulting ammonia is then oxidised to nitrates. But the hydrogen has to be made from fossil fuels, mainly methane, ie natural gas. This is costly and it gives rise to substantial carbon dioxide emissions.
* German scientist Fritz Haber invented the process in 1909 and received the Nobel Prize for chemistry in 1918 for creating "an exceedingly important means of improving the standards of agriculture and the well-being of mankind", which now looks like a considerable understatement.
N2 + 3H2 ⇒ 2NH3
The Haber process produces about 100 million tonnes of nitrogen fertilizer per year and consumes about 3-5% of the world's natural gas production to make the hydrogen for it.
** in several steps, but overall: CH4 + O2 ⇒ CO2 + 2H2
If the hydrogen can be made simply from water, the CO2 is avoided and a valuable organic chemistry feedstock is conserved. Nuclear power can produce hydrogen by electrolysis, particularly high-temperature electrolysis, and in the future it may be made thermochemically as described above. An abundant supply of low-cost hydrogen would greatly boost world agricultural productivity through increased availability of nitrogen fertilizers.
Biomass-based ethanol production
Commercial-scale ethanol production from cellulose in a biorefinery requires energy input. Two processes can be used: biochemical fermentation, or thermochemical conversion. Either way, the energy input needed to produce ethanol from cellulose materials (such as wood) is equivalent to 25 to 38% of the output, mostly as steam (though the thermochemical process also requires high temperatures).
As well as burning the lignin content of feedstock, some energy can readily be supplied by nuclear plants as cogeneration, on a carbon-free basis. In future, the lignin may be converted to liquid fuels, probably by hydrogenation. In this case, the yield of liquid fuels from biomass can be increased by about half, per unit of input. Much of the nuclear energy input is as low-temperature steam, essentially a by-product of electricity generation, and hence low-cost.
Nuclear energy for hydrogen production
Nuclear power already produces electricity as a major energy carrier. It is well placed to produce hydrogen if this becomes a major energy carrier also, in addition to its roles in oil refining and fertiliser production.
The evolution of nuclear energy's role in hydrogen production over perhaps three decades is seen to be:
Steam reforming of methane requires temperatures of over 800°C to combine methane and steam to produce hydrogen and carbon monoxide. A nuclear heat source would reduce natural gas consumption by about 30% (ie that portion of feed which would simply be for heat), and eliminate flue gas CO2 emissions.Apart from this, the efficiency of the whole process (primary heat to hydrogen) moves from from about 25% with today's reactors driving electrolysis (33% for reactor x 75% for cell) to 36% with more efficient reactors doing so, to 45% for high-temperature electrolysis of steam, to about 50% or more with direct thermochemical production.*
* Due to the need to compress hydrogen, plus the inefficiency of the fuel cell, from hydrogen to electric drive is only 30-40% efficient at this stage, giving 15-20% overall primary heat to wheels, compared with 25-30% for PHEV.
Low-temperature electrolysis using nuclear electricity is undertaken on a fairly small scale today, requiring about 50 kWh per kilogram produced. However, the cost of hydrogen from it is higher (one source says: $4-6 per kg, compared with $1.00-1.50 from natural gas, but another source says cost will be same as electricity @ 4c/kWh when natural gas is US$ 9.50/GJ - cf $7 in July 2005).
High-temperature electrolysis (at 800°C or more) has been demonstrated, and shows considerable promise. It requires about one third less energy that low-temperature electrolysis. US research is at Idaho National Laboratory in conjunction with Ceramatec.
Hydrogen from nuclear heat
Several direct thermochemical processes are being developed for producing hydrogen from water. For economic production, high temperatures are required to ensure rapid throughput and high conversion efficiencies.
In each of the leading thermochemical processes the high-temperature (800-1000°C), low-pressure endothermic (heat absorbing) decomposition of sulfuric acid produces oxygen and sulfur dioxide:
H2SO4 ==> H2O + SO2 + 1/2O2
There are then several possibilities. In the iodine-sulfur (IS) process iodine combines with the SO2 and water to produce hydrogen iodide which then dissociates to hydrogen and iodine. This is the Bunsen reaction and is exothermic, occurring at low temperature (120°C):
I2 + SO2 + 2H2O ==> 2HI + H2SO4
The HI then dissociates to hydrogen and iodine at about 350°C, endothermically:
2HI ==> H2 + I2
This can deliver hydrogen at high pressure.
Combining all this, the net reaction is then:
H2O ==> H2 + 1/2O2
All the reagents other than water are recycled, there are no effluents.
The Japan Atomic Energy Authority (JAEA) has demonstrated laboratory-scale and bench-scale hydrogen production with the IS process, up to 30 litres/hr.
The Sandia National Laboratory in the USA and the French CEA are also developing the IS process with a view to using high-temperature reactors for it.
General Atomics' preliminary laboratory work on thermochemical production was to be be complete by 2006. A 10MW pilot hydrogen plant using fossil heat was then to be built, followed by nuclear thermochemical production by 2015.
The economics of hydrogen production depend on the efficiency of the method used. The IS cycle coupled to a modular high temperature reactor is expected to produce hydrogen at $1.50 to $2.00 per kg. The oxygen by-product also has value.
For thermochemical processes an overall efficiency of greater than 50% is projected. Combined cycle plants producing both H2 and electricity may reach efficiencies of 60%.
Production reactor requirements
High temperature - 750-1000°C, is required, though at 1000°C the conversion efficiency is three times that at 750°C. The chemical plant needs to be isolated from the nearby reactor, for safety reasons, possibly using an intermediate helium or molten fluoride loop.
Three potentially-suitable reactor concepts have been identified, though only the first is sufficiently well developed to move forward with:
These are described more fully in the Small Nuclear Power Reactors paper (with coolant characteristics) and the Advanced Reactors paper.
The long-delayed South African Pebble-Bed Modular Reactor (PBMR) Demonstration Power Plant is now expected to start construction at Koeberg in 2009 and achieve criticality in 2013 - possibly a few years behind the Chinese version. It will be for electricity production.
However, In 2006 the PBMR Board formalised the concept of a higher-temperature PBMR Process Heat Plant (PHP) with reactor output temperature of 950°C. The first plants are envisaged for 2016 and the applications will be oil sands production and petrochemical industry (process steam), steam methane reforming for hydrogen and eventually thermochemical hydrogen production. This design is being submitted to US Department of Energy as a candidate Next-Generation Nuclear Plant.
Each 600 MWt module would produce about 200 tonnes of hydrogen per day, which is well matched to the scale of current industrial demand for hydrogen.
In South Korea the Nuclear Hydrogen Development & Demonstration (NHDD) project is focused on HTR technology for both hydrogen production and liquid hydrocarbons. It was launched in 2006 as a key program supported by MOST.
The Korean Atomic Energy Research Institute (KAERI) earlier submitted a Very High Temperature Reactor (VHTR) design to the Generation IV International Forum with a view to hydrogen production from it. This envisaged 300 MWt modules each producing 30,000 tonnes of hydrogen per year. KAERI expects the design concept to be ready in 2008, engineering design in 2014, construction start 2016 and operation in 2020.
KAERI also has a research partnership with China's Tsinghua University focused on hydrogen production, based on China's HTR-10 reactor. A South Korea-US Nuclear Hydrogen Joint Development Center involving General Atomics was set up in 2005.
In the USA the Department of Energy is seeking bids to develop a Next-Generation Nuclear Plant (NGNP) which is to be an HTR capable of producing hydrogen, electricity or process heat. The NGNP is to be licensed by the NRC and built in Idaho with substantial cost share intended from industry. The focus is on process heat applications, thereby broadening the end-user base for nuclear energy.
Molten fluoride salts are a preferred interface fluid between the nuclear heat source and the chemical plant. The aluminium smelting industry provides substantial experience in managing them safely. The hot molten salt can also be used with secondary helium coolant generating power via the Brayton cycle, with thermal efficiencies of 48% at 750°C to 59% at 1000°C.
Moving forward
A 2004 evaluation by JAEA has indicated that by 2010 it expects to confirm the safety of high-temperature reactors and establish operational technology for an IS plant to make hydrogen thermochemically. In April 2004 a coolant outlet temperature of 950°C was achieved in its High-Temperature Engineering Test Reactor (HTTR) - a world first, and opening the way for direct thermochemical hydrogen production.
Meanwhile a pilot plant test project producing hydrogen at 30 m3/hr from helium heated with 400 kW is under way to test the engineering feasibility of the IS process. After 2010 an IS plant producing 1000 m3/hr (90 kg/hr, 2t/day) of hydrogen should be linked to the HTTR to confirm the performance of an integrated production system, envisaged for 2020s.
JAEA plans a 600 MW GTHTR300C unit for hydrogen cogeneration using direct cycle gas turbine for electricity and IS process for hydrogen, deploying the first units after 2020. This could produce hydrogen at 60,000 m3/hr (130 t/day) - "enough for about a million fuel cell vehicles" (@ 1 t/day for 7700 cars).
The economics of thermochemical hydrogen production look good. General Atomics projects US$ 1.53/kg based on a 2400 MWt HTGR operating at 850°C.with 42% ovrall efficiency, and $1.42/kg at 950°C and 52% efficiency (both 10.5% discount rate). At 2003 prices, steam reforming of natural gas yields hydrogen at US$ 1.40/kg, and sequestration of the CO2 would push this to $1.60/kg. Such a plant could produce 800 tonnes of hydrogen per day, "enough for 1.5 million fuel cell cars" (@1 t/day for 1800 cars).
In the meantime, hydrogen can be produced by electrolysis of water, using electricity from any source. Non-fossil sources, including intermittent ones such as wind and solar, are important possibilities (thereby solving a problem of not being able to store the electricity from those sources). However, the greater efficiency of electrolysis at high temperatures favours a nuclear source for both heat and electricity.
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