HOW the modified power plant would work: The reactor (right) is in a sealed underground silo located in the power plant's coal storage yard. The heat comes from the bed (or pile) of atomic pebbles (the little red dots). The pebbles heat helium gas in the reactor to 1,300°F. The hot helium gas is circulated clockwise to carry the heat from the pebbles to the attached helium-to-water heat exchanger (a "fire-tube" water heater). The heated water (red) that exits through the bottom water pipe of the heat exchanger is supercritically hot (1,150°F), and under about 4,500 pounds per square inch pressure to keep the water from turning into steam. The reactor is rated at about 500 megaWatts thermal so even though the water is carrying almost 1,000°F differential of heat, this will be a large volume of water. In comparison, a conventional PWR reactor's supercritical water undergoes a differential of only about 70°F as it passes through its reactor core - utilizing massive water volume and 6,000 horsepower circulating pumps instead.
NEXT, The heat is carried by the water through new, heavily insulated pipes to a new steam generator located in the power plant. The steam generator is also a type of heat exchanger. This time, the 1,150°F supercritical water is used to make the 1,000°F, 2,400 psi superheated steam needed by the power plant's turbine. The steam generator's steam pipes are connected to the three-stage steam turbine (devices 11, 9, 6) that spins the electricity generator (device 5). The "new" steam is identical to the "old" steam that used to be made by the coal boiler.
Two identical special 200 ton storage vault railroad cars, equipped with with elliptically-keyed wheels, (temporarily removed) would be welded to the ground next to the silo to supply and remove pebbles through pneumatic tubes connected to the car bottoms. The pebbles would be held like machine gun bullets in metal clips on a conveyor belt storage system in the railroad cars. A full load of 450,000 pebbles is about 112 tons containing perhaps 9 tons of uranium.
That's all there is to it folks! What a simple way to end Climate Change. The only new items are the reactor, the two heat exchangers, and a small control and service building located in the now-unneeded coal yard. It should be pointed out that power plant water heaters and steam generators, while not trivial devices, are about 30% the size of conventional nuclear power plant steam equipment so they are much less expensive and can be built in several months almost anywhere.
The heavy black line (also lifted away slightly) shows the now unused coal portion of the power plant. ( Pressure refreshers: Power Plant Steam Path Typical Fossil fuel power plant )
Chapter Two, Part Two: Proposed Demonstration Conversion Projects
A Demonstration Facility will cause a flood of engineering feasibility studies to be made.
If this is a bad idea, it will be caught for sure then.
Michigan: Proposed single reactor demonstration facility at the J. R. Whiting plant near Erie, Michigan. Whiting
Florida: (Left) Full scale demonstration: Add 12 pebble bed conversion boilers to Tampa's huge coal-burning Big Bend power plant. Project outline page: Upgrading Big Bend
According to CARMA, TECO's Big Bend coal-burning power plant makes 30,000 TONs (or 60 million pounds) of CO2 per day. And that 4-unit plant is just one of about 50,000 multi-unit power plants in the world for a total of 138,000 units. Big Bend has about 1 million customers. They own their own coal mine but don't like this either so their additional expansions will be natural gas turbines which are only 2/3s as dirty. Only nuclear can match or exceed all that electricity-generating heat in fossil fuels.
At 1,800 megaWatts, Big Bend is a huge power plant. Areva's biggest and best nuclear plant, the EPR, is only 1,600 megaWatts. It will take about a dozen PBMR 165 megaWatt pebble bed TRISO-fueled reactors to convert Big Bend from coal to nuclear. IMO, Tampa should put in two EPRs next door to Big Bend. There is an excellent transmission line corridor already established along I-75 to feed the entire Florida Gulf coast. Since the ground in that area is already more radioactive than anything Areva's reactors could ever produce (the government won't let Tampons make wallboard out of the area's gypsum due to it's radioactivity), I can't imagine the locals opposing all the money two EPRs would bring in for 50 years.
Climate Change can't possibly be stopped without cleaning up at least the world's 5,000 dirtiest power plants. It's unavoidable. Conversion can be done quickly and should be done first because nothing else will reduce so much CO2 as quickly.
Chapter Two, Part Three: Nothing new needs to be invented. No new technology advances needed!
Buying
the Reactor: PBMR,
Ltd. won't like this, but
I am suggesting we buy only the reactor made by PBMR, as shown at
right, not their entire gas-turbine electricity generation system as shown on their web site.
South Africa's Pebble Bed Modular Reactors, (Pty) Ltd. (PBMR)
make a 1,700°F gas-cooled reactor filled with helium. And, I think
they also have a process heat version designed. Inert and a good
carrier of heat, the helium in the reactor is pressurized to 1,300 psi to further
improve heat transfer. This kind of gas pressurization will make a
non-shockwave gas escape like a punctured tire, but, since there is no
liquid-to-gas phase-state change, there isn't a violent
explosion hazard of
the type steam can produce. Both pebble bed and prismatic reactors use
helium at about this pressure. I believe no one knows more about how to
make a commercially successful circulating pebble reactor than PBMR.
Partner Westinghouse is calling it the first of the Generation-IV reactors.
Gen-III+ is probably most accurate with the VHTR/NGNP being tomorrow's Gen-IV
Pebble Bed.
About 2,000 people are currently working on construction of the demonstration reactor and it's facilities. It is on schedule to start up in 2014. Also, at this time, PBMR has only a pilot pebble plant said to be making about 270,000 TRISO pebbles a year. Contrary to folklore, TRISO particles can be cracked and the uranium inside recycled. For sure, there are plenty of downsides and difficulties associated with pebble bed reactors, many due to the nature of the TRISO pebble itself. The world doesn't realize it yet, but it is in desperate need of billions of pebbles every year. France, China, Germany, and the United States have made TRISO pebbles in the past. Britain, Japan, Russia, and the United States have also made TRISO prisms in the past.
(It should be pointed out that Westinghouse already has a small NRC-certified 650 megaWatt conventional reactor, the IRIS - International Reactor Innovative and Secure, that would be an excellent mass-produced choice for providing the electricity needed to power Shell's clean shale oil recovery system.)
Conversion is that simple. Illustrating the Coal Yard Nuke idea, the above is an anatomically correct simplified coal burning power station schematic diagram from Wikipedia. This sketch shows what I hope PBMR, Ltd. would accept as an alternate application of their reactor. Their design: http://www.iaea.or.at/programmes/inis/aws/htgr/fulltext/29026679.pdf Original image: http://en.wikipedia.org/wiki/Fossil_fuel_power_plant GNU Free Documentation License
Key technical items in addition to the PBMR reactor:
(A) Already in common use in conventional PWR reactors, an excellent way to interface a gas-cooled high temperature pebble bed reactor with an existing coal-fired steam plant turbine is to use "SUPERCRITICAL" HOT WATER - water under more than 3210 psi. Supercritical water is a gas with the density of the liquid having a very high volumetric heat capacity (right, olive colored area). Its a way to manage and transport heat energy when using several reactors in parallel to drive a single very large power turbine or a single reactor to drive several older small power turbines with different steam requirements. http://en.wikipedia.org/wiki/Supercritical_fluid
(B) If steam is above 700°F, and at it's natural pressure, it is usually called SUPERHEATED STEAM.
(C) The supercritical water heater is built as a dual-tube calandria (a drumless fire-tube & water-tube boiler that does not require expensive heavy forgings) in a tub filled with unpressurized liquid lead (green outline in power plant sketch above) to carry the heat between the helium pipes and the water pipes. This design is a work-around that might be a new invention. Because the helium in the reactor is under comparatively low pressure, the liquid lead heat conductor under atmospheric pressure will make water ingress into the reactor impossible in the event of a supercritical hot water leak, a key safety issue in a design that mixes HTGRs and supercritical water.
Since the supercritical water is twice as hot as is used in a conventional PWR nuclear plant, a very experienced company such as Babcock & Wilcox should be called upon to make the first few water heaters and steam generators.
Supercritical water, 1,000°F superheated steam, and calandrias have been in common use in power plants for more than 50 years. Nothing new here.
Two identical special 200 ton storage vault railroad cars, equipped with with elliptically-keyed wheels, (temporarily removed) would be temporarily welded to the rails next to the silo to supply and remove pebbles through pneumatic tubes connected to the car bottoms. The Germans used automated pneumatic transport systems on their pebble bed reactors, the U.S. MIT pebble bed reactor design is even more sophisticated. The pebbles would be held in metal clips on a conveyor belt storage system in the railroad cars. A full load of 450,000 pebbles is about 112 tons containing perhaps 9 tons of uranium.
The gray rods sticking into the ground provide a passive conductive, rather than radiative, thermal path into the environment in the event reactor goes into Doppler thermal limiting mode. Also, the standard PBMR reactor has a 1 meter layer of graphite insulation located between the toroidial vertical pebble chamber and the reactor wall to stop both neutrons and heat. This feature makes the Doppler mode efficient.
The sheet metal loop to the right of the reactor is a passive chimney-type heat exchanger to keep heat from building up in the silo without allowing silo air to escape.
Installing and connecting the new steam generator heat exchanger and adding new controls are all that will change in the power plant. There will be a new small, separate, reactor operations building for the pebble bed reactor(s) located nearby in the coal yard. The remotely controlled reactor(s) will provide hot water for making steam as needed by the power plant. The power plant's original steam temperatures and pressures remain unchanged. Much simpler than the full PBMR system as presented in this document: http://www.iaea.or.at/programmes/inis/aws/htgr/fulltext/29026679.pdf
PAY CLOSE ATTENTION TO THIS: According to PBMR, their reactor is capable of producing 180 megaWatts electrical. The magic of the Coal Yard nuke system is the concept of using them as central supercritical hot water heaters to produce enough heat to power one or more steam generators. Say you have several old, small turbines whose power does not add up to more than 180 mWe. As an example: an old plant with single 25, 50 and 75 mWe units could be powered by one reactor with its hot water output split into 25, 50, and 75 mWe steam generators. If different temperatures are needed, that can be done also. If you have a fairly new big 500 megaWatt electrical unit, three PBMRs running in tandem driving a single 500 mWe steam generator would be needed to max out that puppy. Using supercritical hot water gives us incredible flexibility in matching all those old steam plant turbine combinations.
Plants already running on supercritical steam could have several reactors arranged in a ring around a central boiler.
Nuclear reactors are extremely reliable. Nuclear submarines have only one. Also, since this is a pebble bed, it doesn't have to take a month vacation every year for refueling.
Unlike conventional nuclear, upgrading a coal burning power plant to pebble nuclear does not increase the amount of cooling water needed. Notice in the drawing above, the turbine steam condensation system remains untouched so the amount of cooling water needed is unchanged. This is due to the fact that pebble reactors duplicate fire, conventional reactors cannot. Also, the stack losses are gone, and since a coal fired plant uses three-stage 1,000°F turbines as compared to conventional nuclear power plant's 550°F two-stage turbines, the efficiency has got to be higher than either of them. Might cover the cost of those expensive pebbles.
Coal Plants have plenty of life left in them.
An excellent investment in our future. Over half the U.S. fossil fuel power plant generating capacity was built after 1980. Since power plant life is considered to be as long as 60 years, we have 40, 50 or even more years of life left in our most recent (and largest) fossil fuel plants. Well worth the cost of conversion. Projecting 1980 through 2006 EIA values (growth = new power plants) to the vertical ordinate, we find about 0.3 + 1.0 = 1.3 T kWh, which, at 2 lb of CO2 per kWh, (Table 4) is about 1.3 BILLION tons of U.S., or 6.5 world, CO2 every year.
The IPCC has identified 5,000 multi-unit fossil fuel power plants worldwide that are the really big CO2 polluters. If they are big, they are fairly new. It is critical we concentrate on them first. They should be converted rather than shut down. We can't put our energy-starved mega-cities on an energy diet at a time when we need more electricity for water desalination, plug-in hybrid cars, and summer air conditioning to fight ever-worsening Climate Change.
Chapter Two, Part Four:
Power plant coal yards provide
plenty of room for TRISO pebble bed reactors.
(Right, below, Looking North) Big Bend plant,
located on Tampa Bay's big southeast bend, showing it's enormous black coal
yard. Plenty of room for some small PBMR reactors to
be buried underground there. The white warm discharge water seen
just below the stacks is where manatees hang out in the winter to keep warm.
The small light colored building located at the upper right is the water
desalination facility that supplies
25% of Tampa's
drinking water. Desalination facilities consume extremely large amounts of
electricity.
(Left, above, looking southwest) Underground and underwater pump/generators at the 1,800 megaWatt Ludington, Michigan, pumped energy storage facility on Lake Michigan's coast. Enough electrical energy to keep Detroit going for about 8 hours.
End of