Nuclear Process Heat for Industry
(Updated August 2015)
- Nuclear energy is an excellent source of process heat for various industrial applications including desalination, synthetic and unconventional oil production, oil refining, biomass-based ethanol production, and in the future: hydrogen production.
- Light water reactors produce heat at relatively low temperatures in relation to many industrial needs, hence the technology focus has been on high-temperature gas-cooled reactors (HTR / HTGR) producing heat at over 700°C.
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 of up to 700°C there is a wide range of possible applications, at 900°C there are further possibilities, and at 950°C an important future application to hydrogen production opens up. About 20% of US energy consumption goes into process heat applications, compared with 35-40% into electricity. In this 20%, replacing fossil fuels with nuclear heat promises much in energy security, price stability and reduced regulatory risks.
The US Department of Energy has been pursuing the Next Generation Nuclear Plant (NGNP) concept since 2005, albeit with diminishing funding. Initially this was focused on eventual hydrogen production, which requires very high temperatures with corresponding technological and cost challenges. The prospect of an operating prototype by 2021 seemed to be receding. Industrial partners in the endeavour, with eleven member companies including reactor vendors Areva and Westinghouse, utility Entergy, and potential end-users of electricity and process heat such as Dow Chemical and ConocoPhillips, have set their sights on a more readily-achievable 750°C outlet temperature for process heat rather than hydrogen production.
A 2011 evaluation by the Idaho National Laboratory (INL) for a typical HTR multi-module plant showed that high-temperature process heat and electric power for use by energy-intensive industries can be produced at an energy price that is equivalent to natural gas in the $6 to $9 /GJ range. Areva's estimates support this.
||Up to 700°C
||Up to 900°C
||Up to 950°C
||Rankine (steam) cycle
||Brayton (direct) cycle
||H2 via steam reforming of methane or high-temperature electrolysis
||Thermochemical H2 production
|Oil and chemical industry
||Tar/oil sands and heavy oil recovery,
Refinery and petrochemical
|Syngas for ammonia and methanol
||Thermochemical H2 production
Process heat applications
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 Pebble Bed Modular Reactor (PBMR) proponents 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.
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 valuable by-products of electrolysis.)
Coal to liquids (CTL)
Various processes are used. Indirect liquefaction accounts for most world production, about 260,000 barrels/41,000 m3 per day. Coal is gasified to syngas and the product synthesized either to diesel and jet fuel, or to gasoline (Mobil or methanol MTG process). Direct liquefaction processes miss the syngas step and are either hydrogenation or pyrolysis and carbonization.
The Fischer-Tropsch (F-T) 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 most of that country's 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.
* Coal gasification produces both CO and H2 feed for F-T, and the water shift reaction turns some CO into CO2 and more H2, both stages using water. In F-T itself hydrogen plus CO converts to alkane hydrocarbons using a catalyst.
At Erdos, Inner Mongolia, China, Shenhua Coal Liquefaction Corp produces 20,000 barrels /3000 tonnes of oil per day from nearly 10,000 tonnes of coal from the Shenfu-Dongsheng coalfield, using US technology. The $2.06 billion Erdos CTL plant was commissioned in 2010 and in 2013 it produced 866,000 tonnes of oil products. It has total design capacity of 1.08 million tonnes, comprising diesel (621,000 t/yr), naptha (321,000 t/yr) and LPG (70,000 t/yr). Water supply is a constraint on operation, and it requires 7-12 tonnes of fresh water to produce one tonne of product, depending on whether direct liquefaction or indirect (based on F-T), along with 9 tonnes of CO2 and 4.8 tonnes of contaminated waste water according to critics. It uses coal hydrogenation at high temperature and pressure with a catalyst.
Shenhua proposes $7 billion plant in Ningdong, Ningxia, China – the Shenhua CTL plant to produce 80,000 barrels/ 13,000 m3/day, using Sasol’s indirect liquefaction technology, based on F-T. Sasol has withdrawn from the venture.
The hydrogenation (Bergius) process requires hydrogen to react directly with coal at high temperature and pressure. Pyrolysis and carbonization processes give less yield, and that usually needs refining. They are not commercial for CTL.
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 in the Sasol-type plant, 14,600 tonnes produces 25,000 barrels of synfuel "oil" (with 25,000 tonnes of CO2).
A 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 (see box), 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 ( in several steps, but overall: CH4 + O2 ⇒ CO2 + 2H2, so each tonne of hydrogen gives rise to 11 tonnes of CO2).
The Haber process
German scientist Fritz Haber invented the process to combine atmospheric nitrogen with hydrogen 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.
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.
CO2-based methanol production
Avoiding the need to encroach on arable land for biomass such as corn, or clear woody growth elsewhere, methanol production from famously-surplus CO2 can use nuclear heat as well as nuclear-produced hydrogen. See sections below.
Nuclear energy for hydrogen production
Nuclear power already produces electricity as a major energy carrier. It is well placed to produce hydrogen either for converting CO2 into methanol, or if hydrogen itself 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:
- electrolysis of water, using off-peak capacity (needs 286 kJ/mol),
- use of nuclear heat to assist steam reforming of natural gas,
- high-temperature electrolysis (HTE) of steam, using heat and electricity from nuclear reactors, then
- high-temperature thermochemical production using nuclear heat.
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 10 MW 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 for process heat
Three potentially-suitable reactor concepts have been identified, though only the first is sufficiently well developed to move forward with:
- High-temperature gas-cooled reactor (HTR), either the pebble bed or hexagonal fuel block type. Modules of up to 285 MWe will operate at 950°C but can be hotter.
- Advanced high-temperature reactor (AHTR), a modular reactor using a coated-particle graphite-matrix fuel and with molten fluoride salt as primary coolant. This is similar to the HTR but operates at low pressure (less than 1 atmosphere) and higher temperature, and gives better heat transfer. Sizes of 1000 MWe/2000 MWt are envisaged.
- Lead-cooled fast reactor, though these operate at lower temperatures than the HTRs – the best developed is the Russian BREST reactor which runs at only 540°C. A US project is the STAR-H2 which would deliver 780°C for hydrogen production and lower temperatures for desalination.
These are described more fully in the Small Nuclear Power Reactors paper (with coolant characteristics) and the Advanced Reactors paper.
For hydrogen production, high temperature – 750-1000°C, is required, and 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.
For temperatures beyond 750ºC, 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. There remain significant challenges in achieving temperatures for commercial hydrogen production.
High-temperature reactors for process heat
The most advanced HTR project is China's HTR-PM, based on its successful HTR-10 prototype. The demonstration unit being built in Shidaowan links twin 250 MWt units with 750°C outlet temperature to a 210 MWe steam turbine.
In the USA the Department of Energy since 2005 has had a program 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 was to be 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.
Early in 2012 the NGNP Industry Alliance announced that it had selected the 625 MWt Areva HTR design, or 'Gen IV reactor concept', known as Antares, for further development. This will be run with helium as primary coolant at 750°C and a two-loop secondary steam cycle. The NGNP Industry Alliance is collaborating with the European Cogeneration Industrial Initiative (NC2I) in setting targets to build and demonstrate HTR installations in energy-intensive industries over the decade from 2014.
In 2006 the South African PBMR Board formalised the concept of a higher-temperature PBMR Process Heat Plant (PHP) with reactor output temperature of 950°C. The first plants were envisaged for 2016 and the applications would have been oil sands production and petrochemical industry (process steam), steam methane reforming for hydrogen and eventually thermochemical hydrogen production. 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 2011 the program was aborted due to lack of funds.
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. The VHTR is to produce hydrogen on a large scale, with 300 MWt modules each producing 30,000 tonnes of hydrogen per year. KAERI expects engineering design to be done by 2014, construction start 2016 and operation of a demonstration reactor in 2020, with commercialisation about 2025. R&D focus is on development of corrosion-resistant high-temperature materials and components and refractory coated-particle fuel.
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.
Moving forward on hydrogen
A 2004 evaluation by JAEA indicated that by 2010 it expected 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 was to be linked to the HTTR to confirm the performance of an integrated production system, envisaged for 2020s.
JAEA has developed the conceptual design for a 600 MWt GTHTR300C unit for hydrogen cogeneration using direct cycle gas turbine for electricity and IS process for hydrogen, with helium outlet temperature of 950°C and secondary helium at 900°C, deploying the first units after 2020. The thermal power provided for the hydrogen system can be increased from 170 to 370 MW if required – at the lower level 202 MWe of electricity is produced, with gas turbine inlet temperature of 850°C. This could produce hydrogen at 24,000 m3/hr. The IS hydrogen system beyond the intermediate heat exchanger would be non-nuclear grade, in line with other hydrogen production facilities. A total of 30 GTHTR300C units could produce hydrogen to operate 5.9 million fuel cell vehicles (at 170 MW) or up to 12.6 million at 370 MWt.
The economics of thermochemical hydrogen production look good. General Atomics earlier projected US$ 1.53/kg based on a 2400 MWt HTR 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.
In 2013 an IAEA report said that “nuclear generated hydrogen has important potential advantages over other sources that will be considered for a growing hydrogen share in a future world energy economy. Still, there are technical uncertainties in nuclear hydrogen processes that need to be addressed through a vigorous research and development effort. Safety issues as well as hydrogen storage and distribution are important areas of research to be undertaken to support a successful hydrogen economy in the future.”
Production of methanol using hydrogen, DME
Following on from thermochemical hydrogen production, and considering the storage and portability challenges of hydrogen itself, as well as the radical change to fuel cell cars, attention has turned to methanol. As noted above: portable hydrogen storage is difficult, especially for automotive use. Any future fuel for cars needs to compete with petrol at 32 MJ/L or diesel fuel at 39 MJ/L and be no more difficult to store and refuel than LPG.
LNG has similar problem to hydrogen, ethanol comes from biomass, but methanol can be made from CO2 and hydrogen. If the hydrogen is nuclear-produced, and CO2 is a problem due to its abundance, automotive fuel can be provided forever, using present engine technology. For diesel engines, dimethyl ether (CH3-O-CH3) is better, and this is made by dehydrating a couple of methanol molecules. It is a gas but can be stored under low pressure as liquid, like LPG. These two have energy density of 18-19 MJ/L, so less than oil-based fuels, but usable and easily stored. The post-oil future may be methanol-based.
Also, methanol can be used in fuel cells, if these are preferred over internal combustion engines.
Methanol, and dimethyl ether (DME) derived from it, are good energy carriers, and DME in particular can substitute for diesel fuel. Methanol today is produced in a variety of ways, but ideally it will be produced from abundant atmospheric CO2 regenerated with hydrogen produced by nuclear energy using more nuclear energy in the conversion process.
CO2 + 3H2 ⇒ CH3OH + H2O ∆H - 49.5 kJ/mol at 25°C, - 58 at 225°C, exothermic
(the endothermic reverse water shift reaction CO2 + H2 ⇒ CO + H2O will occur at same time, along with: CO + 2H2 ⇒ CH3OH ∆H - 91 to - 98 kJ/mol - exothermic)
Dimethyl ether is made in a dehydration reaction:
2CH3OH ⇒ CH3OCH3 + H2O ∆H - 23 kJ/mol
In Iceland, methanol production is already occurring using CO2 captured from flue gas and hydrogen from electrolysis using renewable energy. The company Carbon Recycling International was set up in 2006 to produce Renewable Methanol for automotive use and also biodiesel.RM.
DME is already used as propane replacement, and world production capacity is over 10 million tonnes per year. China alone is aiming for 20 million tonnes per year DME capacity by 2020. Sweden is producing BioDME from black liquor.
Methanol, together with derived dimethyl ether (DME), can be used as: (i) a convenient energy storage medium; (ii) a readily transportable and dispensable fuel for internal combustion engines and compression ignition (Diesel) engines with little engineering change; (iii) for fuel cells; and (iv) as a feedstock for synthetic hydrocarbons and their products, including fuels, polymers and even single-cell proteins (for animal feed and/or human consumption).
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