Mini steam turbines -- convert a turbocharger?

[swyves]

I am involved in a project taking place among small communities in rural Peru, mainly in rainforest areas. Population density is low, there is no road infrastructure, and development levels range from third world towns to uncontacted tribes. Power is a major problem. Solar is expensive and not well suited to a rainforest; there's no wind, no hills for hydroelectricity, etc etc etc. Fuel is hard to obtain and expensive. Biofuel infrastructure is not operational.

What I'm wondering is whether we can make low cost steam turbines, perhaps by cannibalising turbochargers (using the exhaust turbine) or superchargers (running them backwards) from vehicle salvage, and get the shaft to do some useful work, for electricity or rotary power in smaller communities. Efficiency is not really an issue; there's no shortage of dead wood we can burn to generate steam. However, the system does have to rugged and field maintainable, preferably with minimal training. If we can get 50W, we can at least get a radio running for each community. With a kilowatt or two, we can really make a difference, maybe with lighting, water purification, even local light industry. As a pipe dream, if we could get a system weighing in the lowish hundreds of kilos (or less) to generate 10kW or more, then this can be used to power boats, which are the only means of transport in the region.

The aim is that with steam, anything can be used as fuel. Even installing basic ethanol distillation in this region is difficult and expensive, and the number of people who could benefit from any fixed installation is small as the population is so spread out.

So, is it feasible, or are we (a) not going to get anything, (b) going to get so little power that it's pointless, or (c) going to kill our turbines in seconds and have systems that won't keep working or chew through parts too fast. Low cost is the main concern; anything technical is going to be expensive here, but raw materials are not too bad and we can easily hire skilled welders and metalworkers (though don't expect much in the way of CNC out here). I'm hoping we could get truckloads of old turbos from broken vehicles to import from the USA.

Any thoughts, or indeed suggestions for totally different systems, much appreciated.

 

[MikeHalloran]

First problem: Turbos need a steady flow of clean lube oil to keep their bearings alive.



Mike Halloran
Pembroke Pines, FL, USA

 

[rmw]

There are so many problems with this where do I start....????

rmw

 

[swyves]

Putting an oil pump and filter into the system doesn't seem like a deal breaker, and getting a supply of oil to the system has got to be easier than oil plus fuel for an ICE; but an unstartable list of other problems is more worrying.

 

[GregLocock]

Well, it seems like a reasonably trivial problem to hook a turbo up to a steam boiler and see if the idea has any legs at all. My guess is that it'll work, but you'll have problems with the gearing - the turbo is running at 80000 rpm, you probably want 3000 rpm. Impeller erosion would also be a big deal.

I dispute that efficiency is unimportant, mankind has a long history of laziness and expediency.

Given that you always have a river around I'd have thunk a turbine generator in the river would be a better bet.

Cheers

Greg Locock


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[swyves]

You're right, I should just get my hands dirty and rig one together, see whether it's got legs. We're using small hydro to great effect in a similar project in the highlands, but these jungle rivers are very very slow -- centimeters drop per linear kilometer, flow speed maybe 1kph. It's really a very tough environment to get alternative energy systems to work. And yeah, the turbine gearing is indeed going to be a problem. Thanks a lot for the answer!

 

[JStephen]

I'm not that familiar with turbochargers, but is there even an outlet shaft? I thought it was just two turbines coupled right together.

Generating and using steam very efficiently involves high pressure and high temperature, and thus relatively high tech. Generating and using steam in a primitive and inefficient mannter involves generating a LOT of steam, so you're looking at a fairly large boiler to power it.

While you might get old turbochargers for cheap, you're not going to find boilers that easy to locate or move.

For 50 watts, a pedal-powered generator would work, and be a lot cheaper and more convenient than anything steam-powered you could come up with.

 

[rmw]

Cummins toyed with an engine that had two turbo's in the exhaust stream. One turbocharger that drove an output shaft that geared into the engine so as to recover waste exhaust heat back into usable shaft power. It was the second turbo in the string, the first did what a normal turbo does which is compressing combustion air for the engine. I doubt that there were many built or many available for cannibalizing.

I do on the other hand know about steam power plants, especially wood fired power plants and I do know about engine turbochargers, and the two aren't compatible. One is designed for hot low pressure engine exhaust and the other hot higher pressure steam vapor. About the only thing that they have in common is that they spin, and typically not even in the same speed range as noted in an earlier post.

Completely different bearing systems, completely different seal systems, and as JStephen has pointed out, turbo's typically don't have an output shaft.

I keep thinking about if this challenge was mine to solve, how would I go about meeting the need. Turbo's isn't it. But, unfortunately, I don't have anything to offer on that small of a scale as an alternative. I am also familiar with remote sparsely populated villages light years away from anywhere as well. So cannibalizing a small wood fired power plant isn't the answer either, the smallest that I know of would be way too big for a village or even a few nearby villages. And way too technically challenging.

Most of what you want to do is done with small engine generators, but obviously I understand why that isn't feasible. I still own and use a small Honda 2500 kw gen set that was originally used for bringing power to remote third world villages when we needed power for medical instruments.

I wish you luck. I wish I had something to offer. I'll keep thinking....

rmw

 

[swyves]

Great answers, guys, thanks a lot. Quite apart from the technical problems, you also highlight a serious extra issue: enough steam with enough pressure to make decent power is also apt to be extremely dangerous, so any system of this kind is probably just too risky to install for unsupervised operation by people with absolutely no technical training. Back to the drawing board, I guess.

One other "tried and failed": a similar project to ours tried installing a pilot small scale bioethanol plant a couple of years ago. The village was able to grow a few hectares of sugar cane with no problem, the fermentation and distillation (to azeotrope) worked, and then it all ended up getting drunk. One village with a severe alcoholism problem, plus an epidemic of methanol poisoning, and still no power. Oh, and pilot biodiesel programs in the region (larger scale than we're looking at here, mind) are causing incredible levels of environmental degradation.

 

[IRstuff]

The fundamental problem isn't the what turns the generator, per se; it's the amount of useable mechanical power required to generate the electricity. For every kilowatt-hour produced by a mechanical generator, you need at least a kilowatt-hour of some sort of mechanical energy.

Steam, by itself, has very little mechanical energy. Only when pressurized steam is released is there sufficient mechanical energy to do the work of turning the generator. High pressure boilers require significant amounts of high strength metals, in addition to the safety aspects of the system.

While river water is obviously a reasonable choice, most locations have insufficient flow rates to generate much electricity, and allowing only natural flow runs the risk of seasonal fluctuations that may be unacceptable for reliable generator. This is why dams are almost invariably associated with hydroelectric power, since the height of dam concentrates the mechanical potential energy into a seasonally consistent source. But, damming a river is a non-trivial exercise, particularly in a region where torrential rains may result in flash flood conditions.

TTFN

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[EngineerTex]

You might have a better time converting old lawnmower engines. Here's a link of a page I had seen a week or so back while I was thinking about dumping the power copmany out at my farm. Ultimately, I decided against it, because it wouldn't run an air conditioner. And if it won't do that, then I'm not going to bother.

http://www.lynxsteamengines.com/converting.cfm

Additionally, if actually do you try that route, you can find loads of places on the net to show how to re-wire a common alternator to turn out 120V 3-phase power, by simply bypasing the voltage regulator and wiring the field coils to a rheostat. Then, it's just a matter of a v-belt and a couple of pulleys.

As for the boiler, this lawnmower system is only appropriate for up to about 40 psi, which is still lethal, but not in the way that a 550 psi, 500 degree boiler is. If you said that you have welders and such, I would think that a re-tasked welding gas bottle (O2 or CO2 - not acetylene) normally used for 3000 psi should be able to handle the task, simply connected with some Swagelock fittings. NOTE: I AM NOT ENDORSING THAT AS A GOOD IDEA. IN FACT, THE TERM "HARE-BRAINED" COMES TO MIND. However, if anyone fancies himself as McGyver, he might try it and then stand inside a bunker.

I think that you should be able to get used lawnmower engines by the boatload for around the same amount you would pay for a used turbo (around 5 bucks).

Be careful.

Engineering is not the science behind building. It is the science behind not building.

 

[racookpe1978]

OK. Then back up and plan on using low-tech, low-pressure steam.

We ran many years of railroad steam engines on coal and wood (fire-tube boiler, the exhausted steam from the two pistons vents up into the front of the boiler to induce draft from the firebox in the rear through the tubes and out up the stack.

Two (cheap loose pistons will work OK, and you get better efficiency with better machineing when you want to pay higher prices) pistons driving a slow speed dc generator at 12 volts. Picture an old steam engine with generator on the "axle"

1) Battery power bank gets charged for use when steam plant is down, solar cells as alternate power. Use an inverter to get the ac needed, run as much dc appliances as you can to avoid transfer inefficiencies. 12volt power gives you compatibility with lots of car and aftermarket radios and service gear.

2) Later, when your steam gets to more than 100 - 150 psi (the old standard of 150 lb flanges and fittings still holds true! -

3) Steam engines used multiple driven wheels from two pistons getting routinely more than 100 mph in the later years. 60 mph was done many times before and during the Civil War. You will get enough power to run as many small generators as you want to burn fuel.
4) Or go the other way_ Run 4, 6, or 8 pistons like they did in ships at the turn of the century. USS Texas (1910 technology) used multiple-expanding pistons to improve efficiency.

 

[benta]

The gearing is not necessarily a problem.
Capstone's gas turbine generators drive a PM synchronous generator directly and uses an inverter to convert to 50/60 Hz.

http://www.capstoneturbine.com/_docs/datasheets/C30 NatGas_331031D_lowres.pdf

Benta.

 

[BrianPetersen]

What is it proposed that the power is going to be used for?

If it's for small power demands, re-think solar cells and a battery. No moving parts, no high pressures or temperatures. If it's for lighting, LED lighting cuts power demand to a minimum compared to traditional types of lighting.

If it's for larger power demands the first option is to try to cut power demand so that you can re-think it as a small power demand.

If that's not possible then you need to re-think the thermal efficiency equation and in this day and age, re-think emissions, too. The old locomotive piston engine steam plants were only around 6% efficient and, from the modern perspective, emissions of all types were beyond extreme.

A central power plant of even a moderate size will allow things to be done (regarding both efficiency and emissions) that are not possible via simple backyard fixes.

Air conditioning and refrigeration are possible using thermal absorption cycles so that there is no electricity demand for the compressor; circulating pumps and fans associated with these systems can be low power demand devices. Google "ammonia absorption cycle".

 

[drawoh]

swyves,

I was investigating small steam turbines quite a few years ago. It looked like an interesting hobby project.

You have steam at some temperature and pressure. You will pass it through some number of stages until it reaches room pressure. Your steam turbine must be designed around these pressure drops. Your turbocharger is single stage, right? Even steam piston engines use multiple stages, hence the triple expansion engines you read about on old steamships.

You have two efficiency problems. Your turbocharger almost certainly is not adapted to your pressure conditions. Small turbines have proportionally more blade clearance than large turbines.

JHG

 

[JStephen]

"You will pass it through some number of stages until it reaches room pressure....Even steam piston engines use multiple stages, hence the triple expansion engines you read about on old steamships."

If you have cooling water available, you condense the steam so outlet pressure is less than atmospheric; also lets you re-use the water, which is fairly essential on an oceangoing ship.

 

[CH5OH]

external heat (burning wood), small power requirement
smells like a stirling engine to me

 

[berkshire]

Why not run a gasoline engine on wood gas, there are plenty of plans out there for simple wood gas generators ?
You say you have plenty of dead wood available.
B.E.

 

[KENAT]

I have to second racookpe1978 & berkshires suggestions.

Fundamentally, what you're saying is the best available fuel/energy source you have is wood. For some of your applications you need to generate electricity, however for water pumping at least, and potentially boat propulsion, there is no need for the intermediate electricity step.

Long before anyone had heard of the turbinia steam engines were being used for both stationary power needs (including water pumps) and for vehicles - including the boats you mentioned.

Given the technology infrastructure in your region I suggest you at least consider more primitive steam engine designs than turbines. A quick internet search should turn up something - for instance this steam powered generator.

Alternatively, if it's easier to ship in small existing IC engines and just adapt them to wood fuel then Berkshire's wood gas proposal has serious merit.

http://www.green-trust.org/woodgas.htm

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[KENAT]

On the Wikipedia entry, one of the references is a 2 stroke engine (on a scooter) converted to be steam powered. Maybe worth a look.

I still have problems imagining a system designed to run on a gasoline/oil mixture wont have issues running on steam but maybe it's a start. Perhaps it doesn't matter if the engine life runs out a bit quick if you can replace it.

There are plenty of steam enthusiasts that home build scale steam engines. Maybe you can find enough information to piece together a design for a gen set using moderate technology.

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