Hydropower from water mains.. 7

[wizeguy]

Given that water is pumped from the reservoir to the town,
is it feasible/practical to use the kinetic energy produced in the pipeline to drive turbines installed along the mains waters, for electricty generation??

how would one calculate the potential generation ??

With standard hydro calculations they use flow rate and head... but in this case head wouldn't apply??


cheers
vin

 

[davidbeach]

If the water is pumped, any energy you extract with your generation would have to be supplied by the pumps. Add in the inevitable losses and the additional energy into the pumps will exceed the energy out of the generation.

Where the water flow is entirely gravity powered there are already locations that use turbines for pressure reduction and generate power in the process.

 

[dpc]

Any energy in this system is provided by the pumps, unless there is a net elevation difference between the reservoir and the town. So any electric energy generated would come from the electric energy used to run the pumps. Add in the losses, and you will be using more energy than is being produced.

I once worked on a project to install a small hydro turbine on the outfall of a sewage treatment plant. In that case, the elevation difference between the plant and the ocean provided the necessary head to run the turbine.

 

[vpl]

Wizeguy

Both davidbeach and dpc are correct, the arrangement you're discussing uses more energy than it produces. However, having a reservoir run a turbine under peak power conditions and then refilling the reservoir under low power conditions can be economically viable.

Look up "pumped storage" in Wikipedia. You might also want to do a search on TVA's Raccoon Mountain pumped storage unit.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[wizeguy]

Thanks for the replies....

I understand that energy is used to run the pumps, and that any energy extracted would be less than what is used to run the pump etc.

However this is how I was looking at the concept....

Water is being pumped to my house right now, through the local councils water mains pipeline, it has been for the past 30 odd years and will be for another 30 + years. If that water is fed through a series of turbines before reaching my taps, it could generate some electricity to feed into the grid.

The idea was to have a number of turbines along the pipeline. If pumps are needed after each turbine to maintain pressure, then yes the system would be worthless.

The idea was to use the kinetic energy that exists in the water mains system to generate some more electricity.

vin

 

[davidbeach]

That would reduce the pressure being delivered. If you don't need the pressure it probably wouldn't be being provided. There are exceptions; I have to have a pressure reducing valve on my water service since the houses 150-200 feet higher up the hill need some water and the mains are pressurized sufficiently to supply those customers. In theory I could generate power while producing that pressure drop. Not enough volume, nor nearly continuous enough to make it worth while.

 

[wizeguy]

The turbines would have to be between the pump and the township.... it wouldn't work on a per house or per street basis, as you've said not enough volume or continuous supply.

The pressure drop was the only concern....

cheers, thanks for your input....

vin

 

[cranky108]

Actually there might be a good reason to use a hydrogeneration following a pump station, and that would be if the pump was needed to pump the water over a high pass and on the other side a pressure reduction was required. The hydrogeneration could be used to recover some of the pumps energy. (Stranger things have happened).

I expect this would not be a common occurance.

 

[wizeguy]

Ok then.... so the major flaw in this system would be the reduced pressure after passing the turbine?

If the issue of loss of pressure was "resolved" then this system maybe worthwhile?? (a big if I know!)

I suppose it would depend on how much pressure was lost after passing through the turbine/s, and how much energy is required to return the pressure back to "normal"?

(obviously the energy produced from the turbines collectively would have to be significantly more than what would be required input to bring the water pressure back to normal)

How would you calculate the water pressure lost through the turbine?

Which brings me back to my other question of.... how would you calculate the potential energy generation from the water pressure in a pipeline?

vin

 

[dcasto]

You can do the math wizeguy, delta p time mass rate = energy. You'll see tha you either need lots of delt p or a lot of water.

 

[wizeguy]

is this where the Tesla turbine or Tesla pump might be employed? or the Wolfhart Willimczik pumps?

vin

 

[davidbeach]

Energy is energy.

Cranky, in a sealed pipe the water going down the other side will tend to reduce the work necessary to lift the water up the hill. The water system will also have probably tunneled to avoid the need for the lift in the first place.

 

[cranky108]

You are correct. The example I was thinking of has a lake between the pump station and the hydrogeneration.
Also apperently the lift isen't as great as the fall.

 

[MJCronin]

"wizeguy"

I believe that you are persuing a device of the "second kind".

http://en.wikipedia.org/wiki/Perpetual_motion

Additionally, the comments stated above are good advice.

Also, please remember that, in any municipal water distribution system some energy must be "left on the table" because there is a minimum system pressure required for the "folks that live on the hill" that is not required by the "folks that live in the valley"

Wize, do you have an engineering background ????

-MJC

 

[btrueblood]

"Cranky, in a sealed pipe the water going down the other side will tend to reduce the work necessary to lift the water up the hill."

Yes, that is called a syphon. Only works to 32 feet or so, then the water column on the downhill side cavitates.

But, a tunnel under the pass avoids the issue altogether.

 

[cranky108]

I'm sure someone else did a complete evaluation some years ago.

 

[waross]

With standard hydro calculations they use flow rate and head... but in this case head wouldn't apply??

I am afraid that you have to leave "head" in the equation.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rmw]

I have to think that the OP doesn't have an engineering background.

However, the answers by some good engineers were very good in this case.

rmw

 

[Apakrat]

Will admit to being old and stupid but still interested in how things work!

Has this old coot followed accepted practices to calculate the waterwheel thingy?

Any help or comment would be much appreciated

http://en.wikipedia.org/wiki/Newton

http://www.ajdesigner.com/phphorsepower/horsepower_equation_rotating_horsepower.php

This is also posted at

http://www.apakrat.com/American/Question1.html

where the numerals can be highlighted and copied.
Thank Ya'll

 

[dcasto]

my comment is that the more work you take out, the higher the water will rise behind the wheel, is there a place to allow the water to rise?