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

 

[Apakrat]

Thanks for the comment dcasco. Still showing my ignorance, I suppose this build up would be in the Gulf of Mexico, when considering the little thingy, about the size of 1/3 of a 55 gallon barrel, and supported by a raft anchored in the Mississippi River some where about Vicksburg.

 

[dcasto]

apakat kinetic energy = 1/2 mv^2, not force. You'll need to know the width of the paddles

The torque will be the force acting on the paddle across the area. The unit will slip and turn a lot slower than the 74 rpm's.

 

[Apakrat]

Appreciate the recommendations dcasto! Been looking for a good reason for throwing in a 50% efficiency factor until further data from testing is available. Just didn’t know where or why to apply the reduction.

Again, Thank You

 

[sow]

I don’t think the idea is totally out of the question. Although fundamentally different I have seen these on raw water systems from reservoirs where the head is otherwise throttled to control the flow.

If the system is at the start of a long high pressure main then you may step down the pressure to branches, include pressure control strategies, design in back pressure in order to clear hills or maintain pressures in certain branches of the main.

It might just be feasible to replace these controllers with micro turbines that can control the pressure / flow.

However there are lots of whats and ifs surrounding the implementation of such ideas.

 

[cranky108]

Sort of like a turbo charger, where the bypass can be partually opened to increase the total flow rate, or pressure. (I know the bypass in a turbo charger is to control the speed).
But by blending the rates of the turban, and the bypass, you can control the total flow rate.

 

[danberry]

Hydropower from water mains ???

Come-on guys. this can't be serious. Its candid-forum. They are going to post this thread on some campus billboard so the engineering students can get a good laugh to relax after a hydraulics 101 quiz.

 

[davefitz]

there apparently are a few applications where a pelton wheel was used as a power generator- and I understand in some chemical refineries they have configured pumps to operate in reverse, to recover power as opposed to simply throttling across a pressure reducing valve. Noweadays one can automatically synchronize the small generator to the grid using teh same solid state technology as per Capstone turbine or small wind turbines.

 

[cranky108]

The eazy way to synchronize a small Pelton wheel is to use an induction generator.
Pelton wheel power generation can be used to reduce the water pressure, and works well with drops greater than 1000 ft.
The issue as I've seen it is you have to drop the pressure before entering a treatment plant, where it is repressurized after treatment.

 

[waross]

From the original post:

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??

No. In a well designed pumping system only enough energy is imparted to the flow to to give good service to all the consumers. If you were successful in extracting energy from the flowing water in a well designed system then the pressure and/or flow to the consumers would suffer.

Had you asked;
We have a mountain reservoir at an elevation of X feet above the highest user. We presently use a pressure reducing valve to maintain a lower pressure in the town. Can we use a turbine to extract energy from the water as we drop the pressure?
The answer would be a qualified yes. Even though you can easily calculate the expected energy, you may have controlability issues in smaller systems.
Mechanically feasible. Yes, with qualifications.
Electrically feasible. Yes
Financially feasible. Unknown. As the head increases and the flow increases the financial feasibility generally will improve.

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

 

[cranky108]

Financial Feasibility, Questionable. The issue as I understand it is the cost of operation of the pressure reducing valve. And the valve would be required even if the water were flowing into a pond.
But with green power, the electricity can be sold for a higher cost that other generation.

 

[waross]

The pressure reducing valve would be replaced by the turbine. There is quite a bit of energy developed by a pressure reducing valve with a large differential pressure and a large flow.
The lost energy heats the water, but with a high flow and the relatively high specific heat of water the temperature increase is not often noticed.
Hint, multiply the flow times the pressure difference to get an idea of the amount of energy lost in a pressure reducing valve.
I remember an assignment from my school days.
A water fall is 100 feet high. What is the temperature difference between the top and bottom of the fall.

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

 

[dcasto]

all BS give it up.

 

[cranky108]

dcasto, I agree power from water provider is BS. However power from run of pipe isen't. The difference is magnitude and CL2