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jackb
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Joined: 14/11/2011
Location: NetherlandsPosts: 5 |
| Posted: 09:30am 15 Nov 2011 |
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Hello
I have a ruined watermill in SW France on the Baise River. I want to rebuild the damm wall to a height of about 1 m and generate some electricity. The original 300 year old turbines in the mill building which sits over a millstream are, I think, unusual as they are vertical shaft turbines. There is a hatch at the bottom of the millpond wall which controls water under 2m of head to enter the bottom of the shaft and turn a propellor.
I would like to do a similar thing in the river but incorporate 3 vertical shafts in the damm wall. I would place the turbines in these shafts with permanent magnet generators on top. I have a very large crane on site so during the wet season i would hoist the turbines out of their shafts for storage. The alternative is to use 500w PowerPals but i would prefer something homegrown. I have seen the Indian "Minihyro Turbine from Scrap"on Youtube. My damm wall would be like that but with vertical shaft turbines not undershot waterwheels. Anyway, I am seeking your comments please.
Jack |
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MacGyver
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Joined: 12/05/2009
Location: United StatesPosts: 1329 |
| Posted: 02:51am 19 Nov 2011 |
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jackb
Welcome to the 4m. It appears you've had several hits, but with no replies. That may be due in part to your not having asked a specific question.
I'm a retired plumber and I can tell you about head height vs static pressure, but there's another factor here, namely your water is already moving (I think) and therefore has an unknown abount of kinetic energy stored within its flow. I should think if you did nothing more than hang an outboard motor boat's propeller on a shaft emersed in the end of that portion of the vertical shafts where the falling water enters calm water again, you'd be able to change its linear movement to rotational and then use a PM alternator or generator, but more specifics are needed for anyone to take a stab at a quality answer.
How much flow do you have and how are you calculating it? What are the 3D dimensions of each shaft? What amount of power are you expecting / needing / hoping for here? Has anyone else done anything like this in your neck of the woods? Are you shooting for a.c or d.c. or mechanilal power as your final product?
These are the kinds of specific questions you should be asking yourself and when you've exhausted your own research, then someone here will surely be able to jump in and lend a hand with a specific question.
Sounds like a great idea for some relatively "free" power; best wishes.
. . . . . MacEdited by MacGyver 2011-11-20
Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
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jackb
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Joined: 14/11/2011
Location: NetherlandsPosts: 5 |
| Posted: 12:53pm 20 Nov 2011 |
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Thanks Mac
Ok, more details:
The Baise River flows at 1 cubic meter per second during the summer. I want to generate 500w 12v DC. So my specif questions are as follows:
1. Can I capture the kinetic energy of the flow by building a spiral weir that funnels the water down the 1m tapered vertical shaft (30cm/12" diameter at to 45cm/18" at bottom. As per PowerPal.
2. What is the difference between collecting the water at the top (as above) and collecting it at the bottom where it is one meter deep? Is the flow normally the same in vertical section? Does the damm wall cause the water to back up and loose its inertia?
In the original mill, the water entered the vertical turbine shafts at the base where it hit vertical vanes that turned the vertical axils. But this was a grist mill where controling the speed was more important than maximising the output. Whilst i would love to restore the original mechanism, I cannot rebuild the damm to wall to its original 3m height necessary for the water to flow through the millstream for local political and environmental reasons. Hense the 1m damm with shafts idea.
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Warpspeed
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Joined: 09/08/2007
Location: AustraliaPosts: 4406 |
| Posted: 10:36pm 20 Nov 2011 |
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Another way to think about this, how much power would be required to RAISE a ton of water each second one metre, which is what you have there ?
Horsepower = pound feet per minute/33,000
Hp = 2,200 Lbs x 3.28 feet x 60 seconds / 33,000
equals 131 horsepower
If you could turn all that to electrical power it would be 98 Kw !!!
There is a huge potential amount of power there.
Even the crudest most ugly inefficient turbine imaginable is going to recover a lot more than 500 watts.
Cheers, Tony. |
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jackb
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Joined: 14/11/2011
Location: NetherlandsPosts: 5 |
| Posted: 08:30am 21 Nov 2011 |
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Thanks Tony, that is very encouraging. If I can get 10kw then it is worth paying EDF for a grid connection. But my design questions still stand because, using your analogy, even a crude vehicle can get us from A to B but we choose to make and ride in a more efficient more durable more comfortable one. PS: I see you work in imperial units. To demonstrate the ease of the metric system the same equation is 1m3/s x 10kn/m3 x 9.8m/s2 = 98kw If G was 10m/s2 instead of 9.8 it would be even easier. |
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Warpspeed
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Joined: 09/08/2007
Location: AustraliaPosts: 4406 |
| Posted: 09:24am 21 Nov 2011 |
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Jack, 10Kw final electrical output should certainly be possible, that sure is a LOT of water.
We are supposed to be totally metric down here in Oz, but I am old enough to remember imperial units from the dim ancient past.
I just find some mental processes and problems make more sense in imperial, but regardless, the answer should still come out the same.
There are companies that supply small commercial packaged hydro plants, but at horrific cost.
If you were sneaky devious and cunning, you may be able to get them interested enough to quote on a suitable turbine/generator combination and supply some engineering drawings and specifications of their product.
That should at least give you some ideas about what is required, how to go about it, and even provide a starting point for a do it yourself completely home built turbine. Edited by Warpspeed 2011-11-22
Cheers, Tony. |
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jackb
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Joined: 14/11/2011
Location: NetherlandsPosts: 5 |
| Posted: 02:58pm 21 Nov 2011 |
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Good thinking.
PowerPal has some pretty detailed drawings on the spiral penstok and the draft tube that i want to use.
Let me ask you this: PMG seems to be preferred but i like the idea of the alternator becuase you can remotely control the field to suit the waterflow. Then it wouldnt matter if you oversized the alternator. Or would it?
BTW, whilst I live in Rotterdam and France now, I am also AUS. I started RMIT in 1972 using Imperial and finished in Metric. Whitworth still has its fans in Euroland especially with pipes. Formula 1 prefers BSP over metric or NPT.
Jack |
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Warpspeed
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Joined: 09/08/2007
Location: AustraliaPosts: 4406 |
| Posted: 07:57pm 21 Nov 2011 |
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The way most larger alternators work, is there is a PM "exciter" to generate some initial dc power, and that is then used to energise the field windings of the main machine though some kind of magic voltage regulator box.
From what little I know about this subject, radial inflow turbines are generally low rpm very high torque devices, and the alternator of correspondingly large diameter and a very large number of poles, they don't seem to normally run gearboxes.
For a do it yourself project, the gears from a decent sized truck differential should easily handle the torque, and provide a speed step up of about x4 to x5
This also allows some scope for changing the ratio once it is up and running.
The wheel bearing on a vertically mounted truck diff should also be robust enough to carry the turbine mechanical load, and a "tailshaft" made long enough to reach a convenient mounting place for a conventional horizontal shaft alternator.
You may be able to salvage a low rpm alternator off an ancient diesel gen set.
Some of those real oldies were built to chug away at quite low rpm, unlike modern high speed diesels. The alternator may have six or even eight poles if you are lucky.
If you can resurrect an old diesel alternator, exciter, and control box, that is all you really need.
A bit of careful restoration and repair, and it should work a treat.
Cheers, Tony. |
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jackb
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Joined: 14/11/2011
Location: NetherlandsPosts: 5 |
| Posted: 02:44pm 22 Nov 2011 |
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I guess thats why Fisher and Paykel motors are often used. They can be rewired to change the number of phases, poles in series and poles in parallel. If the turbine can cope with more load then an extra stator can be used. But this is not as attractive as being able to turn a knob and increase the magnetic field of an alternator and control the speed to some extent. I am picking up two F&P direct drive motors when i visit Melbourne in December.
Have you heard anything about a controlbox for multi pole generators that automatically selects the best combination of phases and poles to suit what its getting from the turbine?
Speaking of turbines, what do you think of a ships propellor (30 cm) at the top end of the draft tube as the mechanism to win energy from my swirling falling water?
The other design criteria is that the generators must be easily removed from the dyke after the summer. The river is a torrent in spring. PowerPals would be suitable but they are 5000 each and a bit inflexible ie automatically cut out if the flow is too high or too low.
jack |
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Warpspeed
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Joined: 09/08/2007
Location: AustraliaPosts: 4406 |
| Posted: 08:10pm 22 Nov 2011 |
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I suppose it depends on your final power goal.
There is enormous potential energy to tap into, but if your desire is only for a few hundred watts, almost anything is going to work.
There is massive total mass flow, but the flow velocity may not be all that high, and that is going to set a practical limit to turbine tip speed and operating rpm.
Compared to a wind turbine, a low pressure head water turbine is going to be a slow machine.
Not being familiar with the location, it is not really possible to imagine ways to begin tackling this problem in a practical way.
Switching the windings of an FP around has it's limitations, because you can only really switch (combine) windings that are in phase with each other.
A better way may be to rectify the various phases into bulk dc, and then convert that to the required output voltage with a switching power supply.Edited by Warpspeed 2011-11-24
Cheers, Tony. |
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