October 13, 2004
Hgher Temperature Superconducting Wire Continues To Advance
An article in the Christian Science Monitor reports that Sumitomo Electric Industries and American Superconductor Corp. (AMSC) are heading to market with next generation high temperature superconducting ceramic wire.
The wire, produced in Osaka, Japan, is narrower than the width of a pencil.
To develop the market, Sumitomo - Japan's biggest electric cablemaker - will offer the cable at competitive prices - about two to five times the price of conventional copper, Mr. Saeki says.
But Sumitomo will soon have competition. American Superconductor Corp. of Westborough, Mass., is working with the Oak Ridge National Laboratory [NIST] on a more advanced version of the wire, which could be used as transmission lines for electric utilities.
This type of wire still needs to be cooled by liquid nitrogen to a range of -452 to -320 degrees Fahrenheit. So this stuff isn't going to be used as building wiring. But it could still be used for power lines and in motors for ships, trains, and other large pieces of equipment.
The article gives the impression that Sumitomo's next generation wire is coming to market right now. While AMSC is still 3 or 4 years from hitting the market with their next gen wires but they are already shipping existing designs and claim to be the world leader in higher temperature superconducting wire sales.
AMSC is the world’s leading developer and manufacturer of High Temperature Superconductor (HTS) wire. AMSC's first generation HTS wire, based on a multi-filamentary composite architecture, is capable of carrying over 140 times the power of copper wires of the same dimensions. It is the industry leader in both price and performance and is the product of choice in a variety of applications including power cables, motors, generators, and specialty magnets.
AMSC announced break-through results in September of 2002 of its second generation HTS wire beating the Department of Energy's benchmark for performance by 15 months. Second generation wire, when available in commercial quantities in the next three to four years, is expected to cost two to five times lower than first generation HTS wire and will significantly broaden the market for HTS-based products and applications. As a form-fit-function replacement for first generation wire, second generation will require no re-engineering of applications developed and commercialized using first generation wire.
What sort of future will higher temperature superconducting materials make possible? Jesse H. Ausubel, director of the Program for the Human Environment at The Rockefeller University in New York, has an article in The Industrial Physicist one one potential future application of higher temperature supercondutors: the zero-emission power plant (ZEPP) and the Continental SuperGrid.
The ZEPP is a supercompact, superfast, superpowerful turbine putting out electricity and carbon dioxide (CO2) that can be sequestered. Investments by energy producers will make methane (natural gas) overtake coal globally as the lead fuel for making electricity over the next two to three decades. Methane tops the hydrocarbon fuels in heat value, measured in joules per kilogram, and thus lends itself to scaling up. Free of sulfur, mercury, and other contaminants of coals and oils, methane is the best hydrocarbon feedstock.
Ausubel quotes a source that expects ZEPP plants to boost methane-to-electric conversion efficiency from 55% to 70% and imagines a future of methane fueled 5000 MW and 10,000 MW electric power plants fuels by oxygen which has been purified from the atmosphere using croygenic separation. He envisions power plants operating under such enormous pressures that the carbon dioxide by-product of combustion comes out in liquid form for easy capture to send to sequestration facilities. The whole article is pretty interesting. Though a competing argument can be made for the continued spread of smaller electric power generators for local generation and use of electricity. That is the future that KnowlegeProblem blogger Lynne Kiesling thinks distributed energy generation systems are a real possibility, especially if the regulatory environment can be changed to be more accommodating to them. As I've previously pointed out, this might ultimately lead all the way down to cars as distributed electric power generators.
It makes little sense to adopt a steam-cycle powerplant just because you have a newly compact and efficient alternator; you'd still have all the inefficiencies of the Rankine cycle and the bulk of the turbine itself. It would make much more sense to use fuel cells as a topping cycle and gas turbines as the second stage before worrying about tertiary recovery (acknowledging that gas turbines are also candidates for superconducting alternators).
The USA is not going to use powerplants as Ausubel thinks, for one simple reason: natural gas is increasingly rare and expensive in the USA, and converters limited by the Carnot efficiency are just not going to make good enough use of the costly resource. However, coal is already being gasified in oxygen-blown retorts, and fuel cells will run as well if not better on scrubbed coal syngas as they do on methane. As a bonus, fuel cells can run at pressures high enough to liquefy the effluent CO2 once cooled; you'd be unable to do this with a gas turbine, and even a steam boiler might be problematic.
My speculation is that the USA is first going to go to IGCC to achieve greater efficiency and pollution reduction, and then replace the gas turbine/steam turbine system with a fuel cell topping cycle. The waste gas will go through a combined-cycle if CO2 is not being sequestered, or used to make steam and then cooled to the liquefaction point if it is to be injected underground or piped away. Sequestering systems will run their fuel cells at several hundred PSI to minimize the work required to compress waste gas. Total efficiency? Figure 76% cold-gas efficiency for the gasifier, 60% efficiency for the fuel cells and 25% conversion of the waste heat from both: call it (.76 * .6) + (.24 + .4 * .76) * .25 = 59%.
I may have spoken a bit too soon. However, the ZEPP could certainly be improved with the use of a fuel-cell topping cycle. If the CO2-expansion cycle starts at a temperature of 800 C (a not-atypical SOFC operating temperature) and 400 bar, the graph in the AIP article could be projected to yield a thermal efficiency of about 50%. The gasifier may be able to supply heat at a similar temperature, allowing the waste heat of the gasifier to be converted to work at the same efficiency. This would yield (.76 * .60 + (.24 + .76 * .40) * .5 ) = 72.8% before the air-separation plant overhead is considered. I note that the Tampa Bay IGCC plant has approximately 20% overhead for its ASU, while only producing about 25% of its total thermal output from the gasifier. That 20% accounts for 8% of the total heat value of the fuel, assuming an overall efficiency of 40%.
If we assume that 4x the amount of oxygen will be required in either type of ZEPP (to burn all the fuel), the total overhead rises to 32% and the net output falls to... 40.8%. Unless I missed something, it hardly seems worth doing.
It looks to me that even a fuel-cell-powered unit dies by the power consumption of the ASU; the only benefit you get is the ability to liquefy the CO2 effluent. So what does Ausubel know that I don't?
As someone involved in the superconductivity business, I love to see such positive statements but unrealistic expectations are not helpful at all.
The original Christian Science Monitor article by John K. Borchard (and published by USA Today yesterday (http://www.usatoday.com/tech/news/techinnovations/2004-10-14-superwires_x.htm ) says that superconducting motors are twice as efficient as ordinary electric motors. This is wrong of course: typically a superconducting motor wastes half the energy which is not quite the same thing, i.e. it would waste 1.5% instead of 3%, so it would be 98.5% efficient as opposed to 97% efficient.
In superconducting electric cable applications, even if the superconducting material were free, there are expenses and losses. For a start, installing an underground cable costs 20x that of an overhead cable I understand (in a green field site). For an AC cable, the losses are about 1/3 dielectric losses, 1/3 superconducting hysteresis losses and 1/3 thermal leakage. [A DC cable doesn't have either of the first two but solid-state AC/DC converters have their own capital cost and inefficiences.] These heat losses in the cable appear as heat load on the cryogenic coolers. The cryogenics appear as a capital cost (the cryogenic refrigerators are not cheap) and as a running cost (the electricity used to run the coolers). What you save is the ohmic losses in the copper conductor so the running costs can be less than for copper cables (depending on cryogenics maintenance costs). In principle you can reduce the thermal leakage by using thicker insulaton. However, you can also reduce ohmic losses in a copper conductor simply by using thicker cables with more copper. So the competition between copper and superconducting cables can be expressed purely in terms of capital cost and the volume of cable where that is a limitation.
The result is that superconducting cables are probably very competitive for power transfer now in inner cities which need more power using existing ducts. However there are a couple of orders of magnitiude of cost/benefit between that and medium distance (a few hundred km) applications.
Much more important is that superconductive cables and machines can create low impedance links, can adjust power factors and support voltage, and can provide fault current limitation independently of impedance - all of which which can increase the efficiency and reduce the capital cost of extending the conventional grid and distribution systems. This is where the primary benefit appears so far as energy policy is concerned. The timescales are much shorter than for cables: I would reckon major production takeoff in 8-15 years.
PS Sumitomo and AMSC both had stands last week at the Applications of Superconductivity biannual conference and they have a reciprocal-license deal covering IPR. The "second generation" tape is much further away as a cost-effective solution than the announcements suggest. The announcements generally relate to technical capability, not to low-cost production, which will take yet more years and years. AMSC also has produced some nice reports on the USA grid problems and where superconducting machines and cables can help.
thanks for a nice information