The purpose of this page is to describe the Steam Generator Module that converts a thorium reactor's molten salt heat energy into superheated steam energy.
coal2thorium.com
The purpose of this page is to describe the
Steam Generator Module that converts a thorium reactor's molten salt heat energy
into superheated steam energy.
The Steam Generator Module: Coal Steam from a
Nuclear Boiler
Steam generator design enables us to create an
efficient and reliable interface between the new thorium reactor and the old
steam turbogenerator.
< Replacing
this. With
this. >
(Right) ORNL-TN-1060 nuclear boiler.
Cost Estimates
Secondary
Cooling Loop Components
The steam generator building
The secondary to tertiary cooling loop clear salt-to-clear salt heat exchanger
The secondary heat exchanger clear salt drain tanks
The secondary cooling loop clear salt circulating pump
The secondary cooling loop overpressure rupture disc
Tertiary Cooling Loop Components
The tertiary cooling loop clear salt drain tanks
The tertiary cooling loop clear salt circulating pump
The 2 tertiary cooling loop overpressure rupture discs
The 4 tertiary cooling loop clear salt flow control valves
Steam Generator Components
The feedwater preheater heat exchanger module
The evaporator-superheater heat exchanger module
The reheater heat exchanger module
The main superheated steam throttle valve
The high pressure turbine superheated steam by-pass valve
Coal Steam from a
Nuclear Boiler
Shown above is the "Classic" superheated -
reheated steam configuration.
By using these types of steam generators, you can configure any single reheat or
double reheat or whatever you encounter.
There is no fossil fuel power plant in the world that can't be repowered this
way.
On the far left are the non-radioactive secondary coolant loop or "Clear Salt" lines connected to the reactor barge's heat exchanger. The small black objects are circulating pumps. The large heat exchanger on the left is the "Clear Salt" to "Steam Generator" salt heat exchanger. Hot clear salt (light yellow) in at top, Cooler clear salt (pink out) at bottom. The fluid Steam Generator salt (yellow) is heated to a temperature of 1,100°F by this heat exchanger. Steam generator salt is a commercially made heat transfer salt called "HITEC."
The 1,100°F Steam Generator salt heats the four different water heat exchangers.
Water Preheater: The blue line depicts the boiler feed water preheater line where the water, already pressurized to the system's operating pressure of 2,500 pounds per square inch (psi), is typically heated to perhaps 500°F before it enters the evaporator. This reduces both the thermal load and thermal stress on the following evaporator stage.
The combination Evaporator - Superheater heats the water to the temperature needed to produce the system's operating pressure - the saturation temperature. For a system running at 2,500 pounds per square inch (psi) this temperature would be 670°F. The saturated steam (pink) is spun (diagonal vanes) as it rises into the superheater tube section to centrifuge any water droplets out of the steam.
By the time the steam rises to the top of the superheater column (red), it has been superheated from its 2,500 psi saturation temperature of 670°F to a temperature of 1,000°F - an additional 330°F which produces a very dry, almost gas-like, turbine blade and bucket-safe steam - and is then either run through the high pressure stage of the turbine (see below) or, via a by-pass line, returned immediately to the reheater stage (pink).
The Reheater stage receives the steam from the high pressure turbine's exhaust at perhaps 500°F and 550 psi. The saturation (turbine-damaging fog) temperature for these conditions is about 475°F so the steam is reheated back to 1,000°F to dry it out again before allowing it to enter the turbine's intermediate pressure stage.
The remainder of the steam path - condensing stage, condenser, feedwater de-aeration - is unchanged from the earlier, original, coal steam system.
Why the author thinks the ORNL-TN-1060 has the "Right Stuff" to replace coal.
The author thinks engineers who have spent their careers around boilers and turbines like these will agree that, while this is not a perfect fit, it is certainly "Good Enough." (If you have candidate boiler and can get the government to expense the engineering costs of an emissions feasibility study, the author knows of a utility engineering firm that's looking for work.)
Replacing coal boilers with nuclear boilers OF THIS TYPE.
(The more advanced high temperature fast-neutron and Molten Salt reactors are far better suited for coal replacement applications than are the older, far less uranium efficient, and cooler common slow neutron reactors. The ORNL-TN-1060 Molten Salt Reactor mentioned here is not a commercial product. Earlier versions go back to 1944.)
Another aspect is what to do with all that extra steam power that will be available on sites that have coal units smaller than 1,000 MWe? A second turbine gallery with new small low-cost coal steam turbine-generators comes to mind. The second gallery could also be located in another unneeded portion of the coal yard. Dual set of heat exchanger-steam generators. The fact that the reactor has a common liquid coolant for both sets means the control rod system doesn't need to be any different.
Come to think of it, you could bus the secondary coolant into multiple steam generators and run an entire older coal plant with a half-dozen turbines, perhaps adding a couple of new ones, off a single ORNL-TN-1060.
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About coal and nuclear boilers
W
Hot Water Boilers, Steam Boilers
There are over 1 billion boilers in the world. Why do we use boilers?
Ancient Romans used boilers to provide heated water for their bath houses. Most of the world's boilers are used to provide heated water rather than steam.
Why use a liquid to transport heat?
A cubic foot of water will carry about 3,000 times as much heat as a cubic foot of air.
Why use steam boilers?
Modern Man has been using steam boilers for about 300 years to convert heat energy into mechanical energy. The first use of a steam boiler for mechanical power was the engine devised in 1710 by
Thomas_Newcomen for pumping water out of mines.Water is a wonderful way to turn heat energy into mechanical energy because when you turn water into steam it changes state, expanding its volume 1,600 times. If the steam is not allowed to expand freely in volume, its pressure will go up drastically. That's where all that piston-pushing power in a steam locomotive comes from.
A steam explosion is one of the deadliest forms of explosion known to Man. Boilers have to be competently built, installed, maintained, and operated.
When the steam is turned back into water by cooling, it changes state again, this time contracting in volume 1,600 times, creating a powerful vacuum. This is extremely helpful when discharging steam from the final stage of a steam turbine.
How does the author know there are more than 10 million boilers in the world?
"The world commercial boiler market rose to $ 1.7 billion and 587,000 units in 2001, growing at 3% per annum. The fastest growing markets are Russia at 9% per annum, followed by China, Turkey and the UK." -- American Boiler Manufacturers Association Magazine
If the boiler replacement market is about 587,000 units per year and, if a typical boiler's life is 25 years, that means there are 587,000 times 25 or about 15 million commercial boilers out there.
BOILERS can be as powerful as a million horsepower, but, as can be seen below, are more often about 600,000 or so horsepower.. Unlike a vehicle, they operate constantly, spewing out Global Warming CO2 into the environment for years at a time. Over time, this really adds up. Its quite understandable they account for about 70% of Global Warming.
Its difficult to understand why the environmentalists haven't made any moves to replace fossil fuel combustion boilers with nuclear fission boilers/steam generators. There are many replacement nuclear boilers coming on the world's markets - some 50 different units from 15 different countries.
This site is advocating replacing fossil fuel boilers with high temperature nuclear boilers to end Global Warming.
Why use high temperature - instead of conventional - nuclear reactors to replace coal boilers?
A 550°F conventional nuclear reactor can't power a 1,000°F coal plant . . . It simply isn't hot enough. Coal can produce heat over 2,000°F. Coal power plants use 1,000°F steam for higher efficiency. Conventional nuclear reactors cannot produce steam hotter than 550°F, so conventional nuclear reactors cannot be used to produce coal's 1,000°F steam. High-temperature nuclear reactors will work just fine.
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T
Most of
the world's nuclear reactors cannot replace a coal boiler.
Going with what we've got today.
This may be the major reason no one else (to
the author's knowledge) has a web site like this.
A Tale of Three Steams
Most of the world's nuclear reactors are slow-neutron,
water cooled, running at perhaps 550
Zeroing in
on a reactor with the "Right Stuff"
for making the right kinds of steam.
(Most of below from several different
Wikipedia URLs.)
Coal boilers make much more sophisticated types of steam than a nuclear boiler's crude "Teakettle" steam.
In addition to the basic saturated steam made by both nuclear and coal boilers, coal boilers also make "superheated" steam and "reheated" steam. This is what gives coal burning power plants their greater thermal efficiency.
(Below) The Pressurized Water Reactor or PWR. 2/3 of the world's conventional water cooled reactors are of this type.
(Below) The Boiling Water Reactor or BWR. 1/3 of the
world's conventional water cooled reactors are of this type.
Lacks one level of containment.
"Teakettle" or basic saturated steam [evaporator steam] is the only kind of steam produced by conventional nuclear reactors running at about 550°F (300°C). This produces a pressure of about 1,050 pounds per square inch. Saturated steam contains droplets of water that will erode the blades of the turbine, so the steam is run through a "dryer" - a series of baffles - that cause the water droplets to separate and drain down to the bottom of the dryer and then be returned to the feedwater inlet system. The dried steam is then sent into first an intermediate pressure turbine and then a low pressure condensing turbine. As you can see from the efficiency curve (below), running at these temperatures produce only mediocre efficiencies, but if this is all the hotter the reactor can go, its what's accepted.
(Below) The core of a typical fossil fuel power station.
Note the steam lines going back and forth between turbine and boiler.
Note the by-pass (10) on the high pressure turbine stage (11) and where it goes.
Coal, natural gas, and oil burning fossil fuel boilers begin with the firebox jacket [evaporator] (1) making a hotter 670°F (300°C) saturated steam which produces about 2,500 psi, but since a fossil fuel fire boiler can easily heat twice that temperature, the wet saturated steam is taken off ABOVE the water at the TOP of the "steam drum" (device 17, above) and then (2) run through the boiler again and superheated an additional 350°F or so. Since the steam is at 2,500 pounds per square inch (its basic saturated pressure) but 350 degrees hotter than needed to make the basic pressure, the steam becomes very dry and has the characteristics of a gas rather than a fog-like vapor. This very hot and dry steam is used to drive the high pressure stage of the three-stage turbine. Notice from the efficiency chart these temperature conditions may produce a 5% more efficient power plant.
Going into the high pressure turbine stage (11) [note the bypass valve, 10] at 2,500 psi and 1,000°F, the steam expands, transferring its energy into mechanical energy, loosing both pressure and temperature in the process, and may come out at 500 psi and 500°F. Steam saturation temperature at 500 psi is 467°F, so the steam coming out is almost fog-like with droplets - potentially very damaging to turbine blades if the temperature were any lower. No problem with a fossil fuel boiler - just (3) reheat it back to 1,000°F [but still at 500psi] with yet another pass through the boiler before sending it, still at 500 psi, into the intermediate (9) and condensing (6) turbine stages. Nice and dry so fog-like water droplets won't damage the turbine blades and buckets, this adds a fair slug of thermal energy too, pushing efficiency even higher.
You may want to trace out the steam path in the fossil fuel power plant drawing above, paying attention to the evaporator steam drum (device 17). Devices 11, 9, and 6 are the high, intermediate, and low pressure turbines. Boiler tubes 19 are the superheat, boiler tubes 21 are the reheat. Water in a drum this hot and under this much pressure can make a terrible explosion so, by mounting the drum next to a roof 15 or more stories high, a steam drum explosion won't take the power plant and everyone in it with it.
(Below) Making coal steam with a high temperature nuclear reactor.
Coal steam from a nuclear
boiler
(Click on image for larger image, then click on that
image again for further detail.)
When the uranium and thorium dissolved in the melted salt is flowing between the black nuclear graphite rods in the reactor, atom-splitting or "fission" occurs, releasing heat, making the melted salt hotter. The circulation pump moves this hotter fluid to the "Primary Heat Exchanger" where the heat is transferred to a secondary heat transfer loop made of clean, unradioactive melted salt of the same type as the fuel salt. This is salt that can enter the outside world beyond the slightly radioactive confines of the reactor containment (blue walls).
The secondary heat transfer loop then heats the secondary heat exchanger, heating in turn, the tertiary heat transfer loop. The salt in the tertiary loop is a commercial heat transfer salt called "HITEC." The tertiary salt loop protects the reactor in the event one of the three salt-to-water heat exchangers leak. Recall the reactor and salts are always unpressurized but the water and steams can be under as much as 2,500 pounds per square inch pressure. If a leak occurs, it will be a violent entry into the salt loop - ruining the tertiary loop salt. Notice also there is no coal boiler steam drum so the threat of a steam drum explosion is now ended.
Notice there are valves controlling the amount of heat available to each of the salt-to-water heat exchangers and the exchanger bypass line. This enables fine-tuning of the steam's qualities far beyond what you can do with a coal boiler. This aspect tends to mitigate somewhat the inefficiencies introduced by having three salt loops.
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(Below) Why hotter is more profitable. Why your father's reactor won't cut it.
Conventional nuclear power plants in the United
States run at 300°C (550
Superheated steam and liquid water cannot coexist under thermodynamic equilibrium, as any additional heat simply evaporates more water and the steam will become saturated steam at some higher pressure. However, under dynamic conditions some degree of superheating is often possible.
To produce superheated steam in a power plant or for processes (such as drying paper) the saturated steam, from the steam drum, is passed through a super heater. The superheater may be radiant, convection or separately fired.
Superheated steam is not useful for building heating. Saturated steam has a much higher useful heat content
(Below) Locomotive "Firetube" boiler layout showing how superheated steam is obtained.
Beyond superheated steam: Reheated steam: Steam is also reheated between the high pressure and intermediate pressure turbine stages in power plants. Note: Superheated steam is NOT reheated steam. See reheat description below.
An excellent description of why we
need to reheat multi-stage turbine steam:
http://www.qrg.northwestern.edu/thermo/design-library/reheat/reheat.html
As a captured pdf:
Reheat - Using Reheat Cycles .pdf
A reactor configured to emulate a coal burning boiler will need to produce both superheated and reheated steam in addition to basic wet steam. This is why sodium-cooled reactors with multiple heat exchangers have the "Right Stuff" to be candidates for coal boiler emulators. With several heat exchangers - they don't have to be the same size - we can make both superheated and reheated steam in addition to basic wet steam.
(Left)
Basic Rankine Cycle with single turbine stage.
(Right) Two stages of turbine with reheat
(HTR2).
A typical coal burning power plant has three stages of turbine on a generator.
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(Above) ORNL-TN-1060. Click on it for larger view.
Overpower Repowering: Double repowering two existing units or an additional turbine-generator.
Repowering
a supersized coal burner to nuclear. The new equipment: A ORNL-TN-1060
reactor mounted on a Reactor Barge and a
new low-cost "Generic" turbine-generator (located in a new building in the
now-unneeded coal yard nest to the
original coal burning power plant). The addition of a
second turbine-generator almost doubles the electricity output of the power plant for
very little additional cost - $300 million installed
(turbine-generator-cooling-transformer-building) cost gives us 1.3 billion
dollars of new electrical generating capacity at perhaps
This approach ends the Global Warming CO2 this plant was producing while almost doubling its electrical output. What's not to like from a deal like that?
How
a supersized coal burning power plant can be repowered with a mobile modularized
nuclear reactor: A typical coal burning power plant (above) has 
Mass production is important
to cash-strapped Global Warming mitigation. Never underestimate the
power mass production has over price. The Model T sold for
$850 in 1909, by 1920, mass production brought the price of a higher quality
Model T down to $290, or 1/3 the 1909 price. Mass production is the
way to dramatically bring unit costs down and quality up. To date,
there have been no mass produced basic nuclear boilers. The author has
found several references to such in the literature and has added David
Walter's version to the "Building
Reactor Barges" page.
Westinghouse actually began to mass produce nuclear power plants in shipyards in 1970.
"Westinghouse leaders recognized that they would need a partner with extensive shipbuilding experience, and attracted the participation of Newport News Shipbuilding and Drydock Company. The two companies created a 50/50 partnership company that became known as Offshore Power Systems. Public Service did not simply make design suggestions; they signed contracts for two plants [each a dual 1,200 MWe barge] designated Atlantic 1 and 2. These contracts provided most of the funding required to complete the detailed engineering drawings, produce the license application, and to build the manufacturing facility." - Rod Adams
Check out those Russian
construction photos.
They are building a BN-800 by hand in snow. It
could be built a lot quicker, more accurately, and cheaper if it were being
Installation: The reactor's concrete barge (with stainless steel reinforcing rods) could be towed anywhere in the world by an ocean-going tug to wherever the supersized power plant is located. The barge would then be floated next to the power plant via a temporary access channel dredged into the power plant's coal yard. At high tide, the barge's pre-cast bottom piling sockets are set on the pre-driven foundation pilings. The access channel would then be filled in. Eventually, the barge would be buried, the barge becoming the upper part of the reactor's foundation.
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Multiple loads can be placed on the same nuclear boiler.
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