Friday, April 23, 2010

coal2nuclear Conversions: Steam turbines or Brayton cycle gas turbines.

Jim Holm has made an important contribution to the discussion of the future of nuclear power in the United States. I believe that Jim was the first person to publicly advocate the recycling of coal fired power plant sites, as nuclear sites. Holm correctly noted advantages for doing so. Practically everyone who is interested in building small reactors, likes Jim's idea, but there is less than total agreement on how best to implement it. First let me note what some of the advantages recycling coal fired power plants sites would give the nuclear power plant constructor. These sites are accessible by railroad. Almost all American coal fired power plants have their coal transported to them by rail. This means that large manufactured parts for a reactor can be transported to the reactor set up site by an existing rail line.

Every one who has looked at the small modular reactor idea has noted that one of their advantage would be the ability to transport major components, for example the reactor core, from the manufacturing factory to the set up site, by truck, rail or barge. The existing rail lines to coal fired steam plants, thus would provide an ideal transportation route, that would require no construction, hence no added expense.

A second advantage would be access to coolant water. Existing coal fired power plants already require access to large amounts of coolant water. Reactors could be simply plugged in to the old plant's existing water coolant system, including the already existing cooling towers. if the new facility is rated at or above the generating capacity of the old plant, more water coolant capacity might have to be argued, but the plant would not start from scratch. In addition it might be possible to simply transfer the water use permit from the old facility to the new facility, eliminating one paper work obstacle to plant construction.

One of the major cost considerations for nuclear plant construction is the overall cost of site development. A coal powered site will already have developed features that can be reused during a conversion to a nuclear power plant in addition to its rail access, and coolant water system One example is its grid access system, which includes a transformer farm, and high tension power lines that connect the plant to the grid. The existing plant grid hookup could cost as much as $100 million to to duplicate.

Other facilities of the old power pant could also be reusable. These would include some of the existing buildings, parking lots, access roads and so on.

Jim Holm has also suggested the reuse of the coal power steam plant's turbines. At one point I floated Jim's turbine reuse suggestion on Nuclear Green and Energy from Thorium. There was a considerable discussion of this idea in the EfT discussion forum. There were a number of critiques. These included questions about cost savings, and the cost of adaptive technologies. Steam turbines have limited lifetimes, and periodically have to be replaced. The operational life of a steam turbine may exceed 50 years, but many coal powered steam plants are over 50 years old. The cost of steam turbine installations can be expected to run from between $400 to $1,500 per MW of generating capacity. Which represents a levelized cost from 2.50 to 6.50 per kWh if operated in a base load (8000 hours per year) plant, or from 4.00 to 12.00 per kWh if operated to meet daytime demand (4000 hours per year). daytime support. To give some idea of the relative cost of the installed steam turbine system, the Energy Information afency estimates that in 2016 the levelized cost of a nuclear power plant will be 119.1. Since all conventional nuclear plants can be expected to operate as base load electrical producers the cost of the installed steam generator would run from 2% to 5% of conventional nuclear plant costs.

Thus even before we examine cost related to the adaption of old steam turbines to new nuclear heat sources, questions about the economic benefits of pairing a new reactor with an old steam turbine should be reviewed.

First if a turbine is near the end of its useful life, it may at the very least need to be refurbished. If the turbine is refurbished, it would also be wise to refurbish the entire system including steam lines and generators as well. But before we do that we would also need to compare the cost of an entirely new turbine system with the cost of the old system.

There might well be other costs of the adaption of old coal pant steam turbines to new small reactors. There are two coal plants located near me in East Tennessee. They are the Kingston Steam plant, and the Bull Run Steam plant. There are considerable differences between the two facilities. The Bull Run plant, completed in 1967 uses a single boiler to heat super critical steam that drives a set of compound turbines that produce a rated 950 MWe. The Kingston plant has 9 separate generation units that use less hot sub critical steam, four unites produce 175 MWe each, while the other five produce 200 MWe each, for a total of 1700 MWe generating capacity. Lets consider using Jim Halm's coal 2 nuclear scheme on the Bull Run plant. Jim at present touts two sodium cooled Generation IV reactors, the Russian B-800 and the GE-Hitatchi S PRISM. The B-800 would be a little small to power the Bull Run turbines to 100% of their rated output. But 3 S PEISMs would do the trick nicely. Furthermore they would be reasonably well matched to the supercritical steam temperature requirements of the Bull Run power plant. But neither the the B-800 nor the S PRISM would be at all well matched to the Kingston steam plant.

Let us now consider the use of the LFTR. The reference concept factory manufactured LFTR is a 100 MWe unit, although unites as large as 400 MWs could probably be factory produced, with cores and other major components being rail transportable. But we would run into major problems matching the LFTRs heating capacity with either the Bull Run or the Kingsport Steam plants. First the heat output from the LFTR would be around 600 C, or perhaps a little less. But we do not need super critical steam heated to 600 C at the Bull Run plant, so some of the potential energy efficiency of the LFTR would be lost. If the LFTRs were run with a Brayton cycle gas turbine they would produce electricity more efficiently using heat from the LFTR to produce super critical steam for a super critical steam turbine would. In time the added value of the extra electricity produced by a Brayton cycle gas turbine system would more than make up for the added cost of replacing the Bull Run supercritical steam turbines, even if those turbines were brand new.

And of course it would be extremely inefficient to use heat from LFTRs to produce steam for the Kingston Power plants, although it would be easily possible to match each steam unit's output to a LFTR's output. Thus for the Kingston Steam plant the LFTR replacement would clearly offer significant efficiency advantages if Brayton cycle gas turbines were included with the replacement units. The Bull Run plant could be powered by sodium cooled reactors, but it has not been established that three S Prism reactors producing super critical steam for the existing turbines would offer levelized cost advantages offer over four 250 MW LFTRs powering Brayton turbines.

Jim has argued that the existing turbine systems of coal fired steam plants, would offer the greatest value for the coal to nuclear conversion. I disagree. Far from rejecting Jim's suggestion, LFTR advocates have elaborated on it, while offering substantial efficiency improvements by the suggested replacement of old and worn out steam units, with advanced Brayton cycle gas turbine technology.


Anonymous said...

Charles, thanks for addressing this topic. Refitting coal plants will have to come.

I am not knowledgeable about the state of readiness of the Brayton gas cycle turbine. I seem to recall that the South Africans were developing a helium gas turbine, but have given up on the concept. Is there a working prototype of a Brayton gas cycle suitable for operation with high temperature nuclear power anywhere in the world? What gas is likely to be used? It seems to me that developing the gas turbine might be the most expensive part of bringing LFTR technology to implementation status. The airline industry certainly has the experience base to start from, but certainly changing the application must involve significant design modification. John Tjostem

Charles Barton said...

John, The South Africans simply bit off more than they could chew. There are as of yet no developmental programs for Brayton cycle helium turbines, that still has to come, but clearly the added efficiency would more than justify the developmental costs.

Anonymous said...

Hmmm... That's interesting. Where did you first hear about this? Do you have other blog posts I can take a look at?

Justin Davis
MK Partners
Workplace Efficiency Experts

DV8 2XL said...

One of the reasons I am not big on trying to salvage the turbine side of coal plant conversions, is that it would become a nightmare from a regulatory stand-point, as well as added complexity to the engineering. Retrofitting is a drag from design to application, with all sorts of 'Oh God, no' moments when you open something up and things aren't what you were expecting.

Most everyone that has done similar in industry hates retrofits, and everyone that has also knows that most if not all of the projected savings will most likely be sucked up by delay, and necessary changes. These things only look good in the boardroom and in the imagination of the designers.

Brownfielding the old coal plant and starting from there, is the only wise path to take.

DW said...

His site is an 'idea' site. To poise the problems and possible solutions. He even used my "build'em in shipyards' proposal as a way transporting large and small nukes to coal plants.

Yes, turbines on nukes are built to different specs than turbines on gas or coal. There are a variety of there issues as well, most notably steam flow specs and reheat temp and flow. All these would have to be engineered correctly but the *idea* is excellent because it addresses the MW-per-MW superstition issue that solar and wind would just get car sick trying to implement and the large space most coal plants take up with regard to their coal yard, human resources such as trained operators and maintenance; existing grid access; existing transportation access and cooling water and hazardous waste licensing.

John's site presents a whole order of magnitude making the case for coal2nucelar that needs to be pursued from the principal of replacing coal with nuclear.

A "plan" given to, say, the state of Wisconsin, with 6000MWs of coal power, and calls for the replacement of their 13 or so coal plants with, say, 4 to 6 nuclear plants. The idea here is a "si se puede" moment for those that want to phase out coal altogether and THIS is the point.

Anonymous said...

I don't see the importance of reusing the steam turbine. Even NPP's replace their steam turbines periodically. You can still use the existing synchronous generator, the control system, the fire suppression system, the protective relaying & switchgear and power distribution system. You can still use the existing foundation and base. That is a huge savings in time of construction and expense. Replacing the steam turbine is a minor issue.

The biggest issue is likely all the flak you would get from regulatory authorities for placing a NPP at the site, which may be close to a populated area. OK to dump all that Coal Waste on the ground, in the water and into the atmosphere. But, God forbid a NPP that terrorists will be lining up in droves for an opportunity to Chernobyl it. Probably you would need a buried NPP to appease the paranoid & delusional.

I agree with DV8 that retrofits are usually more trouble than they're worth, but if you are talking about a well planned, nationally or internationally mobilized effort to rapidly replace CO2 belching Coal Power plants, I would say it could be done very efficiently and cost effectively.

Friakel Wippans said...

I mostly agree with the general sentiment. The value of a former coal plant to site a nuclear plant is mostly in its "external" infrastructure : physical access by rail and road, grid connection and switchyard, existing water rights and access for cooling, etc.

But the plant itself ? No. It's pretty much worthless. The characteristics of a coal-fired plant are just too different from a nuclear plant, whether a LWR, LMFR or a MSR. Different steam conditions, different controls, different utilities and balance of plant and so on and so forth.

Also, the maintenance in coal-fired plants is generally not that great. Burning coal is a bottom feeder business. Not the highly-stable, long-term thinking, squeaky clean world of NPPs. God knows in which shape the equipments will be when the operator tries to retrofit them for a nuclear conversion...

Just level down the coal-fed dinosaur and build a clean nuclea power plant in its place.


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