Engine choice 2

[dicer]

Why are turbines used in so many applications that reciprocating engines should be used in, as far as electrical generation goes?
Isn't it easier to cogenerate with a recip? And much lower BSFC?

 

[MikeHalloran]

Better salesmen.

Mike Halloran
Pembroke Pines, FL, USA

 

[EdStainless]

Better over all efficiency.
And turbines can ramp power levels much faster.

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Plymouth Tube

 

[ccfowler]

There are many factors involved in the choice of one driver over another. It all depends on the specific application. Reciprocating engines are usually limited to relatively small power requirements (roughly 4000 hp and lower). It is hard to imagine the physical size of a 500 Mw diesel engine, but this is well within the practical size range of steam turbines.

Usually available fuels, space, specific site characteristics, initial cost, continuing costs, available service support, anticipated load profile, expected service life, emission characteristics, staffing requirements, and other power generation resources with which the particular unit will be sharing or supplementing load requirements are the main considerations.

In general, if turbines are not pressed too severely on high metal temperatures or excessively rapid ramping, they can operate continuously for very long times at relatively high loads with excellent reliability (years, not just hundreds or thousands of hours). Depending on cycle temperatures, pressures, and complexity, turbines can deliver efficiencies comparable to the best that reciprocating engines can deliver but at power levels far greater than reciprocating engines can deliver.

Below about 1000 hp, reciprocating engines are likely to be the favored choice.

 

[ScottyUK]

Turbines, particularly steam turbines, are relatively simple machines compared to a recip engine in terms of the small number of moving parts. Most of the auxiliaries, where moving parts are more numerous, can be designed with two or three levels of redundancy to allow maintenance to take place with the machine running. Turbines are very compact for any given power output and have remarkably low vibration levels. They allow use of relatively cheap directly-coupled high-speed turbo-alternators. A diesel machine with an output in the region of one million horsepower, assuming that such a machine could be built, would require a gigantic and stupendously expensive low-speed salient pole generator, again assuming such a machine could be built.

Anyway, who says recips 'should' be used in power generation?



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If we learn from our mistakes I'm getting a great education!

 

[ccfowler]

ScottyUK,

Good point regarding "should!" The only meaningful concept for "should" is that each application should be equipped with whatever makes the most sense for that specific situation.

I've been catching up on micro-turbines a bit lately, and it appears that they may have considerable potential to serve much smaller loads than I had been expecting. I'm sure that these will have the same general characteristics of larger gas turbines in having relatively high fuel consumption rates a reduced power levels. Recips usually do have much better part-load efficiency than gas turbines.

 

[rmw]

Wartsila and Jennbacher for two would say that.

I am a turbine guy all the way, but I thought I should answer Scotty's rhetorical question. Recips should be driving trains but there are plenty out there generating power.

The $$/KWH to install and operate is the determining factor.

rmw

 

[alehman]

Steam turbines are commonly fueled with coal. Not too many recip engines can burn coal.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[dicer]

So then turbines are getting into the .2 ish BSFC range?
Just seems hard to believe, with constant combustion, and the massive amount of heat rejection involved, to make a turbine run it takes massive pumping work because they need alot of airflow, then there is the reduction gearing to put all that speed to work, the recip engine does not need the reduction gearing, I would think that even if the basic engine even came close to a recip's BSFC the killer would be the gear sets required.
There are some very large diesel gen sets world wide, using the same RT 96 Sulzer Wartsila's that the big container ships use, so the generators exist, gosh don't think the generators in Grand Coulee Dam turn any faster than that engine does. I would like to know how much of the available power from a gas turbine is actually used to create power?
They burn close to as much fuel running at speed and no load as they will under load won't they? I am also very surprized that a turbine has such high life expectancy, with the constant heat stress and vibration frequencys imparted to the turbine and compressor blades, the one huge down fall is they are very difficult to filter inlet air too, as we have seen with the jets and volcano dusts lately. And then there is the overhaul costs, high priced exotic metals and complex shapes make the costs very high, along with critical balancing needed to keep it from flying apart at the F1 engine speeds they run at.

 

[EdStainless]

Hydro may be low speed but they don't care about freq. The inter-mountian connection between the large dams is DC (+/-500kv).
So diesels would also need gear boxes, and there are a lot of aux systems on them also. For the same power output they suck the same amount of air as a GT would. Don't forget the very high pressure fuel systems.
From 100's kW through 10's Mw diesels are a great option.
For 100Mw GTs are the better choice.

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Plymouth Tube

 

[rmw]

Dicer,

You need to do some more research on turbines. Some of your statements are blatently off the mark.

rmw

 

[ScottyUK]

dicer,

Have a read of this document:

http://www.berr.gov.uk/files/file18320.pdf

Do you really think the large scale utilties would use turbines if recips were a better solution? Utilities spend a lot of time and money pursuing tenths of one percent improvement in efficiency. I'm sure that recips have been considered.

As RMW says, you really need to do some research. For a start, industrial turbines don't need gearing, they are direct drive to a turbo-generator at either 3000 or 3600 rpm. Steam turbines also typically drive at those speeds although some very large ones in the nuke world are designed for 1500 or 1800 rpm due to the limitations of the materials used in their construction. Aero-derivatives sometimes need gearing, but they are normally used in applications such as peaking stations and large scale emergency power generation where their shortcomings are outweighed by their benefits.

EdStainless,

Hydro turbines might not care about frequency, but they ain't big enough to make the grid dance to their tune so they are constant speed machines once synchronised. The big 'problem' with hydro machines tends to be the low speed which means the generator is a large and expensive salient pole machine reather than a relatively cheap turbo machine. For the benefit of dicer, the same applies to big diesels although I can see I already made that point previously.


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If we learn from our mistakes I'm getting a great education!

 

[dicer]

Scotty, well yeah. Its win win, when someone else foots the bill. What kind of heat recovery are they using? And what is the volume to surface area in the average IC turbine?

 

[ScottyUK]

You're right. It's all a conspiracy by the governments, the utilities, and the turbine manufacturers against the recip engine manufacturers whose product really is a better technical solution.

I wish I had realised earlier what was going on.


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If we learn from our mistakes I'm getting a great education!

 

[MJCronin]

dicey...

Thank goodness for your post, you are again right !!!!

Thank you for pointing out yet another great corporate conspiracy where big corporations and governments try to crush the recips....

Recips have not gotten the respect that they deserve.

Its time that we pass a another new law to re-adjust the playing field in favor of the recips.

 

[ScottyUK]

There's a black helicopter on my lawn! It reads 'Wartsila' on the tail! Help! Help me! They're taking me... they're taking me away.... helllllllpppppppppp...... aaarrrgghhhhh!


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If we learn from our mistakes I'm getting a great education!