[rollei_list] Re: OT - Turbines generating electricity
- From: Ardeshir Mehta <ardeshir@xxxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Thu, 27 Jan 2005 21:21:21 -0500
David,
Thanks for your input.
The greatest attraction of the gas turbine, and that from which all its
peripheral attractions derive, is its utter simplicity and directness
in getting power from burning gas.
In the internal-combustion piston engine there are pistons stopping and
starting, spark plugs firing, valves opening and closing, camshafts
camming, breaker points breaking, connecting rods rocking back and
forth on piston pins, perhaps even fuel injection squirting
intermittently. It's a wonder that all this can go on 60-70 times per
second in a car as one cruises on the freeway without disturbing the
stereo. That it does is testimony to the efficacy of year-in year-out
incremental development of its details.
In the gas turbine, by contrast, motion is simple and continuous. All
the parts that are in motion are just rotating.
The turbine is quiet too, assuming full silencing of intake and
exhaust: its only characteristic sound need be the whine of the
turbines.
You are right that cargo is still shipped today by diesel-powered
ships, but I get the distinct feeling that that's largely the case
because turbines are still frightfully expensive compared with diesel
engines. Any gas turbine developed as of now requires a fair quantity
of very expensive metal, mostly nickel and cobalt, in the areas of high
temperature (such as turbine blades). The cost of processing the metals
is a much greater factor than that of the raw materials. Chrysler's gas
turbine department estimates that we would be using up 15-16% of the
free world's annual nickel if just 10 million turbines per year were
produced, and that's a big chunk of the metal! Shares of INCO would go
through the roof, and Sudbury, Ontario would become a boom town.
But that's all because we're still using essentially the same basic
design for gas turbines which was developed during and just after
WW-II. Metals are the wrong kind of material for turbines. They get
weak at high temperatures. To overcome this drawback, hard-to-machine
metals are needed. Modern ceramics, capable of withstanding much higher
temperatures, combined with the ability to cast them into complex
shapes, are clearly the way to go in the future. They would enable much
simpler gas turbines to be designed. This ought to bring down the cost
of gas turbines in the future. Besides, ceramics are made out of dirt,
quite literally. They won't exhaust the supply of the raw material out
of which they are made!
Multi-fuel capability is another turbine trump card. You don't actually
NEED special fuels to run a gas turbine - it will run on almost any
hydrocarbon fuel: kerosene, diesel fuel, furnace oil, LNG, LPG,
151-proof rum, etc.
As you say, turbines are considerably more space-efficient than
reciprocating engines. That's a clear advantage of turbines over
reciprocating engines. And so is low weight for any given power (that's
why the best helicopters are also turbine-powered).
Now low weight is an advantage that DOES apply to cars (and trucks). So
does space-saving. So, of course, does the elimination of mechanical
complexity (pistons, crankshaft, gears, transmissions, etc.) For
comparable power it comes out 50% lighter and about 30% smaller, and
this is with regeneration. These figures are for the heavy truck units
Ford Motor expects to have in production soon: they are in the 335- to
450-bhp range. Also, in a truck the turbine's quietness and smoothness
advantages really do mean something: compared to a big diesel the
difference is huge.
Just ask yourself why turbine-engined and hybrid cars have been banned
since 1969 by the rules from Formula 1! A turbine-engined hybrid F-1
car would lap Michael Schumacher many times over before the end of the
race.
Cold starting is another credit for the turbine. The resistance of a
gas turbine to spinning up to starting speed does not change much with
cold ambient temperature. The greatest advantage of the turbine here is
in contrast to the diesel, which depends heavily upon cranking speed to
get up combustion temperature. Gas turbine proponents say that the cold
starting advantage could alone mean a substantial reduction in urban
air pollution on extremely cold days by eliminating aborted starts.
Besides, there is the reliability factor. Of their truck turbine, the
Ford people say "better than the diesel", and that means, better than
500,000 miles to the first major overhaul! Moreover, there is no such
thing as a tune-up for a gas turbine. No timing to adjust, no spark
plugs to replace (a single sparkplug-like device is used to get
combustion during starting, but it is self sustaining once started),
and what fuel injection there is is simple compared to that used in
cars. As for mechanical wear, it does not affect turbine emissions in
any significant way since the combustion process is not affected by
bearing or turbine wear. Deterioration in the accuracy of the fuel
delivery system and high-temperature erosion of the combustion chamber
(which would be obviated with the use of ceramics) seem to be the only
sources of emission deterioration, and even then, these cannot possibly
be as significant as valve, piston-ring and cylinder, carburetor or
mechanical fuel-injection wear in a piston engine. (It must be said,
however, that Ford's engineers are only working on turbines for trucks,
not for cars. I wonder why.)
Moreover, the high temperatures of combustion possible in a gas turbine
reduces pollution considerably, and maybe even eliminates it
altogether. This is a HUGE advantage for cars, simply because of their
large number. One well-known turbine expert, George Huebner of
Chrysler, even says that the unburned hydrocarbons in polluted air
ingested by the engine can be burned in the turbine! (See for example
http://www.turbinecar.com/mags/R-T1972.htm). IOW, the turbine engined
car even CLEANS UP the air as it drives along. Wow.
As for lots of hot gases in the turbine's exhaust, as long as one has
large amounts of high-temperature gas available, one can utilise it, in
many different ways. The higher the temperature difference between the
exhaust air and atmospheric air, the better the heat in the exhaust
gases can be utilised. That, after all, is what thermodynamics is all
about, innit?
Cheers.
+++++
On Thursday, January 27, 2005, at 01:11 PM, David Seifert wrote:
> Ardeshir,
>
> I certainly wouldn't characterize this as a "trend" in shipbuilding.
> The vast majority of tonnage is being built with really conventional
> low or medium speed diesel engines driving shafts via gearing. While
> gas turbines are, indeed, quite efficient in the weight/power ratio,
> weight is seldom much of an issue for a large vessel. There are a
> couple of issues, first is the cost of fuel. Jet A costs a lot more
> than bunker fuel and the prices are much more volatile too! Second is
> a highly inefficient conversion of heat to electricity. None of the
> heat in the exhaust gasses are converted to electricity and are thus
> wasted unless you go to a very fancy system like GE created for
> Chantier and Celebrity. In this system the hot exhaust gasses are used
> to heat water which, in turn, runs a steam turbine which generates yet
> more electricity. This goes a long way to solve the heat recapture
> problem without messing with the efficiency of the gas turbine. Again,
> a very elaborate (and fairly large) system to improve on the
> fundamentally weak fuel efficiency problem of gas turbines.
>
> I have sailed on both diesel (both geared and diesel-electric) and
> turbine (both steam and gas) powered commercial vessels and I can tell
> you there is a distinct difference. The turbine powered ships are much
> smoother and vibration free. Other than the cachet Celebrity was
> convinced to go gas turbine not for the fuel efficiency reasons (there
> are none) but for space efficiency. The power plant is much smaller
> than an equivalent diesel system and thus provides more revenue space.
> Completely different economics.
>
> Needless to say, none of this applies to cars!
>
> Best,
> David
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