Nat gas powered 20kw turbine gen set

[dieselguy86]

Hi guys, been a lurker on here for a long time. Was a member of the yahoo groups back in the early 2000's, I've watched many an engine be put together, from rackets turbine powered bike, rc dons engines, ash powers t3 sized engine, and lastly the most amazing anders turbine.

I built my first turbine in 11th grade (03), powered it with diesel, won some science fair awards, but had to put it away due to having little money available to "r&r". 12 years later I have some machines and tooling, more experience, sometimes more money (depending on the wifes mood) and my own place that I can put shit wherever I want.

Anyways, on a turbo project I started gearing up for but cancelled I had a 71mm billet 6+6 compressor wheel reamed out to fit onto a Garrett gt35r turb wheel. The property I own has 2 large nat gas pipelines going through it and I'm tapped right in. I have an endless amount I can pull (still have to pay!) so I was thinking of building a turbine powered gen set.

I know it would be WAY easier and cheaper to just buy one, but I like a challenge, and I love to build. My eventual goal is to have it fully automatic with FADEC control. I have some friends that own a rather large custom machine shop that live about 3 miles from my house. They have several 5 axis mills, crazy lathes, and a machine I can't think of the name of, passes a current through a really really tiny wire to cut metal. Very precise and the cleanest cuts you'll ever see. They've already made several compressor wheels for diesel performance.

Wrapping this up, would the size wheels I have be eno ugh for say 30hp? I'd like to have a 20kw generator. I know natural gas has a very low power density, but I like knowing I'll never run out of fuel. Thanks for any thoughts/comments!

[racket]

Hi

Could you please provide the compressor and turbine wheel sizes please , inducer , exducer diameters.

Theres no reason why a gas powered GT won't work , but your fuel efficiency will be rather poor unless you use some sort of heat exchanger to recover the exhaust heat from the engine .

For 30 hp you probably need an airflow rate of at least 0.5 lbs/sec ( 30 lbs/min) , so a comp inducer of >50mm .

Do you intend using a freepower turbine to power the gen set or have a single shaft engine setup ?

Cheers
John

[dieselguy86]

Sure thing! Compressor is 53.1mm in, 71mm ex, 56 trim. Turbine is 68.8mm, 84 trim. I want a free power turbine. Ideally I'd like to have an axial turbine, followed by stators and then an axial free power to keep things compact. If I could find a couple chunks of inconel I could have my friend mill out the turbines.
I'm a big fan of K.I.S.S. so I'm all ears for any ideas.

[dieselguy86]

Should also add I'm not too worried about fuel efficiency, this thing won't run very often. A pretty simple water to air exchanger could be setup though if it would produce a significant increase in efficiency.

[racket]

Hi

Yep , she should do the "gas producer" job .

Once you have the gas producer up and running to optimum , we'll talk about freepowers.

Cheers
John

[dieselguy86]

I have kamps book that I'll have to find to get regreshed, but it should work for "roughing in" an axial turbine. Should I go this route, or would it work better using the radial turbo wheel? The turbo wheel won't leave much space for a combustor. Correct me if I'm wrong, but won't I need a "largish" combustor to process the extra amount of natural gas, since the energy density is so low?

The gt35r shaft is for a ball bearing turbo, is that fine or should I use journal bearings? I know journal bearings are alot more forgiving, but it will take more oil and pump to use them. I liked ash powers o-ring dampened bearing cartridge idea

[racket]

Hi

Why not use the radial wheel, they work OK.

As for combustor sizing for you particular fuel , could you post a link to the fuel specs so we have some idea of what its like .

Use the ball bearing cartridge .

Cheers
John

[dieselguy86]

John,

I'll have to email them. Hopefully they don't think I'm a terrorist when I ask for the chemical composition of 2 of the largest transmission lines in eastern US. A quick search on there site says the energy content can vary. The lines are 24" diameter, with thousands of psi of pressure.

I was thinking axial to keep things compact and maybe more efficient? Seems having 2 less 90° turns would be worth a couple extra efficiency points?

[racket]

Hi

What will be the fuel supply pressure to your engine control ??

There won't be a lot of difference with turb efficiency between your radial inflow and a small homemade axial , the radial one should be cast in Inconel, so unless you do a very good job of the axial using a similar material so that your max T I Ts will be similar , any reduction in temps with the axial will mean lower power output potential .

You could probably get away with using a suitably sized commercially produced axial wheel from one of the RC micro turbine jet engines.

Cheers
John

[smithy1]

I've got a couple of ~66mm axial turbine wheels if it helps, but I fear they may be too small for this project....also have a few even smaller 54mm items....and a couple of the tiny 32mm jobbies....all of them inconel.

Cheers,
Smithy.

[dieselguy86]

I'm interested in one of the 66mm ones. I found my kamps book, once I get refreshed I'll see how close that is to what I need. Sure would save alot of time and hassle.

*Edit* Did some searching, remembering the GTBA site had a list of places to get parts for home builds. Found a site that has turbine wheels, www.jetmax.ch/en/turbine_wheels.htm 66mm,70mm, and 85mm, also have matching ngv available. Time for some number crunching which I'll admit isn't my greatest skill...

John, I don't know what the pressure is for a house. When this place was a functioning farm they had some grain dryers that used massive amounts of fuel and they were tied into the same line. So I should have plenty of volume, I'm guessing pressure is around 100psi? I'll see what I can find.

[racket]

Hi

Yep , you'll be needing good fuel pressure to overcome the air pressure within the engine before it can flow into the flametube.

Generally a turbine wheel ~90 - 100% of the comp exducer diameter is required , any bigger and things get "unbalanced" with regards flows etc ..............a 70mm axial turb wheel would be OK .

Cheers
John

[dieselguy86]

Thought I would share the link to the guys that live right around the corner from me, here. I talked to one of them (there's 3 owners) about machining a compressor out of some titanium that I have, seemed interested as he could use what he learns to make titanium versions of there wheels. I will probably have them machine the freepower turbine when I get to that point, I forgot to ask if they've ever machined inco 718.

Kamps recommends a grade 12.9 bolt to use as a shaft. has anyone used anything else with success?

I also found out that household natural gas pressure is only 2-3 psi, ill have to call/email to see if pressure above that is available, or if ill have to upgrade everything to use say 100psi pressure. I know here in the states homes are powered by single phase power, to go to 3 phase they consider you "commercial" and charge you a $200 per month service fee, instead of $50 a month. if natural gas isn't possible I may have a propane tank installed, liquid fuel as a last resort.

[smithy1]

Your combustion chamber pressure will be ~35psi+ (P2) at full noise, so you need at least that just to overcome the P2 pressure, then quite a bit more to have any decent throttle control.

Using liquid fuel such as diesel or kerosene will enable the use of a automotive fuel injection pump...it's less forgiving but easier in the long run.

Cheers,
Smithy.

[dieselguy86]

I actually keep about 1,000 gallons of diesel handy for my business. during busy season ill burn this in about week and a half to 2 weeks, so my supply stays pretty fresh, which solves the headache of always keeping fresh fuel around. but I was hoping to use gas to keep things simple, no fuel pump/filter, easier and faster starts, cleaner running, a lot cleaner and less smellier teardowns etc. figured I could have a 1,000lb propane tank hauled in and filled, and use an evap cc to run the liquid propane.

I was hoping to design a "pto" or auxiliary drive in my gearbox to drive the oil pump and fuel pump if I have to go diesel/kero. would like a 24v electric oil pump only for startup and shutdowns, once running the mechanically driven oil pump can takeover, this will keep electrical consumption to a minimum, for some reason I don't like having large loads on an electrical system.

im torn between 2 starting methods, electric motor start, or forced air. the easiest would be forced air using a hobby grade EDF (electric ducted fan) unit. these move an unbelievable amount of air, especially running on 24v, I just don't know if it would be enough to spin this size of a gt over? I like the electric motor start for compactness and a lot less clutter, but im not real familiar with them, don't know where to even start to build/buy one.