Battery electric trains or Hydrogen Trains?

[randyrippley]

Recuperated gas turbines have now got much better in efficiency terms than they were the last time they were seriously considered however.

Just checking some figures.........
a 12-cylinder EMD645 weighs around 12-13 tonnes for around 2100kW
A Rolls Royce T406 (the turboshaft from the V-22 Osprey) weighs around 450kg for around 4500kW
OK you'd have to beef up the turbine in rail use to allow extended servicing and maybe derate it, but you've got space for 10-11 tonnes of traction batteries in a gas turbine / battery hybrid

 

[HSTEd]

Just checking some figures.........
a 12-cylinder EMD645 weighs around 12-13 tonnes for around 2100kW
A Rolls Royce T406 (the turboshaft from the V-22 Osprey) weighs around 450kg for around 4500kW
OK you'd have to beef up the turbine in rail use to allow extended servicing and maybe derate it, but you've got space for 10-11 tonnes of traction batteries in a gas turbine / battery hybrid

You can also use a high speed turbine optimised alternator that will be much lighter. Since you are not transmitting the power beyond the vehicle anyway it doesn't matter if it's generated at 400Hz.

Having a big battery pack would also help with the low partial-load efficiency of gas turbine engines.

 

[Domh245]

Would you not need a larger volume of fuel tank to achieve an equivalent range to a Diesel, and that would eat up the room for batteries?

 

[randyrippley]

Would you not need a larger volume of fuel tank to achieve an equivalent range to a Diesel, and that would eat up the room for batteries?

A turboshaft driving an alternator charging a battery bank can be run at constant speed / constant load / constant power output and would be far more fuel efficient than historic turbine attempts. It should be possible to achieve an efficiency similar to that of a diesel

 

[HSTEd]

Would you not need a larger volume of fuel tank to achieve an equivalent range to a Diesel, and that would eat up the room for batteries?

The marinised T406 (for use on hovercraft etc), the MT7, has a specific fuel consumption of 243.2g/kW/hr.

Figures for the CAT C175-16 used on the Class 68 are hard to find, but figures derived from the generator set fuel consumption suggest a 100% load figure (assuming a diesel specific gravity of 0.83) of approximately ~223g/kW/hr, or about 220g/kW/hr if we knock off a bit for the losses in the permanent magnet alternator, which are extremely efficient.

So the fuel consumption of the Liberty turboshaft is higher, but not by an enormous amount.
Something on order of 10%.

And as this is a hybrid we will often operate in a higher efficiency regime since the turbine can switch on and off and allow the battery to move the train at low power demands.

 

[Domh245]

So just to add to that, a bit of googling reveals that the energy densities and specific energies of the 2 fuels are similar (although diesel does have the advantage in both cases - ~3MJ/kg and 5MJ/l) so you should be able to keep a similar fuel tank, replace the diesel engine with a gas turbine and batteries, and achieve a similar range. The only problem I can see is that a gas turbine running at a continuous level isn't going to be particularly pleasant for passengers in terms of noise unless there is a lot of insulation.

 

[najaB]

The only problem I can see is that a gas turbine running at a continuous level isn't going to be particularly pleasant for passengers in terms of noise unless there is a lot of insulation.

I don't see why there is a problem, gas turbines aren't loud. Jet engines are but that's because you're using the exhaust stream for direct propulsion. In power generation a applications you can slow the exhaust right down so that there's no shear layer and so very little noise.

Running at a constant level also means that you can tune the insulation so that it's even more effective.

 

[randyrippley]

.................The only problem I can see is that a gas turbine running at a continuous level isn't going to be particularly pleasant for passengers in terms of noise unless there is a lot of insulation.

Noise won't be as big a problem as you suggest. This would be a turboshaft application, not a jet so you won't get the high velocity exhaust which is the source of most of the sound. The energy goes into the shaft, not the jet

 

[gingertom]

The marinised T406 (for use on hovercraft etc), the MT7, has a specific fuel consumption of 243.2g/kW/hr.

Figures for the CAT C175-16 used on the Class 68 are hard to find, but figures derived from the generator set fuel consumption suggest a 100% load figure (assuming a diesel specific gravity of 0.83) of approximately ~223g/kW/hr, or about 220g/kW/hr if we knock off a bit for the losses in the permanent magnet alternator, which are extremely efficient.

So the fuel consumption of the Liberty turboshaft is higher, but not by an enormous amount.
Something on order of 10%.

And as this is a hybrid we will often operate in a higher efficiency regime since the turbine can switch on and off and allow the battery to move the train at low power demands.

on the basis of these rough calculations there would be merit in a trial. Only problem would be funding: who's prepared to put hand in pocket?

 

[randyrippley]

on the basis of these rough calculations there would be merit in a trial. Only problem would be funding: who's prepared to put hand in pocket?

The people with the turbine technology would be Rolls Royce (who purchased Allison) or GE. Both have turboshafts in the right size. Best for the power integration would be GE Power Conversion (what was Converteam in France). Not sure who the best source of batteries would be.
As to who builds the loco, do GE still own an assembly plant?

edit
These people seem to have the batteries
http://corvusenergy.com/

 

[James James]

I hate to rain on the turbine party, but is anyone in the real world planning to use turbines for hydrogen? There's a reason why existing projects are using fuel cells - and noise is certainly one - but there's also a significant difference in efficiency.

 

[gingertom]

I hate to rain on the turbine party, but is anyone in the real world planning to use turbines for hydrogen? There's a reason why existing projects are using fuel cells - and noise is certainly one - but there's also a significant difference in efficiency.

don't think there was any suggestion here of using hydrogen as a fuel for a turbine.

 

[najaB]

I hate to rain on the turbine party, but is anyone in the real world planning to use turbines for hydrogen?

There's no reason it couldn't be done - LOX/LH2 turbines have been in use for decades in the aerospace sector. But, more realistically, you would feed your turbine on methane rather than hydrogen. It's just as easy to make and a lot easier to store.

 

[HSTEd]

Well given the huge weight of the diesel plant, you could build a diesel-battery-electric locomotive.
Since a megawatt hour battery, a gas turbine plant and a five tonne transformer would still weigh less than the diesel.

(And whilst a five tonne transformer will struggle to get much more than 1.5MVA - that doesn't really matter since the locomotive can use the battery and run the transformer flat out whenever on 25kV)

 

[gingertom]

one of the big manufacturers needs to take it on to see if there's a viable product at the tend of it.

 

[randyrippley]

don't think there was any suggestion here of using hydrogen as a fuel for a turbine.

Yes there was - that was my starting idea. However methane would be a lot safer to use/store.
Whats interesting is that one of the spec sheets I saw on the use of the MT7 in ships was that using methane or LPG as fuel enabled you to push out turbine inspections to 23,000+ hours. Would really cut inspection/service costs

 

[gingertom]

Yes there was - that was my starting idea. However methane would be a lot safer to use/store.
Whats interesting is that one of the spec sheets I saw on the use of the MT7 in ships was that using methane or LPG as fuel enabled you to push out turbine inspections to 23,000+ hours. Would really cut inspection/service costs

The energy density of hydrogen is pretty poor. I'd go with LPG.
There are other ways of making turbines more efficient. A number of years ago I think it was the Canadians who developed a system of turning a turbine with a small but efficient diesel engine to avoid having to run the turbine inefficiently at part throttle. When high power was needed the turbine was already turning, only needing to be fuelled & fired up and the diesel de-clutched. A combination of this together with hybrid battery technology might be viable. But being able to generate ~5000hp with hydrogen and power a long distance train is going to be a massive undertaking, requiring large amounts of tank space. I can;t see it happening.

 

[najaB]

The energy density of hydrogen is pretty poor. I'd go with LPG.

If we're talking about zero-carbon then methane is the way to go. It can be captured from existing industrial processes (e.g. sewage treatment) and also made by direct reduction of carbon dioxide.

 

[HSTEd]

Or dimethyl ether, manufactured from dehydration of methanol produced by reduction of carbon dioxide.

It has the advantage of not being a cryogenic fuel.

 

[gingertom]

If we're talking about zero-carbon then methane is the way to go. It can be captured from existing industrial processes (e.g. sewage treatment) and also made by direct reduction of carbon dioxide.

methane is not zero carbon.

 

[ac6000cw]

How bad are gas turbines for pollution emissions compared to diesel engines?

Do they require exhaust after-treatment to get them down to Euro 3b levels (and tighter standards in the future)?

 

[The Ham]

If we're talking about zero-carbon then methane is the way to go. It can be captured from existing industrial processes (e.g. sewage treatment) and also made by direct reduction of carbon dioxide.

methane is not zero carbon.

Methane may not be zero carbon, however by burning it rather than releasing it significantly reduces the CO2e as methane it's worse (about 25 times worse gram for gram released) for global warning than CO2.

 

[HSTEd]

methane is not zero carbon.

it is if produced by reduction of atmospheric carbon dioxide.
It is simply a more efficient way of holding hydrogen.

 

[najaB]

methane is not zero carbon.

It is if captured from existing processes (zero additional carbon - and don't forget that methane is ten times worse than CO2). It's also zero carbon if produced from atmospheric CO2 by the Sebatiare (sp?) process.

 

[randyrippley]

How bad are gas turbines for pollution emissions compared to diesel engines?

Do they require exhaust after-treatment to get them down to Euro 3b levels (and tighter standards in the future)?

A gas turbine burning a gaseous fuel can achieve much higher combustion efficiency than anything burning a liquid fuel. You could achieve something close to 100% efficiency ( I mean combustion efficiency, not thermal efficiency)

 

[randyrippley]

Or dimethyl ether, manufactured from dehydration of methanol produced by reduction of carbon dioxide.

It has the advantage of not being a cryogenic fuel.

Awkward stuff to handle though due to its flammability and ability to dissolve just about everything organic.......storage would be a pain, very hard to stop it leaking. I'd feel safer with hydrogen on board

Flash point is -41 deg C

 

[najaB]

I'd feel safer with hydrogen on board

That's why I prefer methane. Very energy efficient, non-toxic and that carbon atom makes it a lot less leaky than hydrogen.

 

[HSTEd]

Awkward stuff to handle though due to its flammability and ability to dissolve just about everything organic.......storage would be a pain, very hard to stop it leaking. I'd feel safer with hydrogen on board

Flash point is -41 deg C

Meanwhile hydrogen can literally diffuse through metals.

 

[randyrippley]

Meanwhile hydrogen can literally diffuse through metals.

Small quantities of venting hydrogen would simply diffuse away at a concentration which would not be liable to spark.
Dimethyl ether leaking would face you with a ball of floating flaming gas. Ether fires are very difficult to control - I know, I've had to do it in the past. Still have nightmares of chasing a fireball down a building with a powder extinguisher, trying to knock the fire down. We couldn't stop it.

 

[najaB]

Small quantities of venting hydrogen would simply diffuse away at a concentration which would not be liable to spark.

But why not add a carbon atom to the mix and get the benefits of a gas without the risk of toxic exposure?