calculating maximum Hydropower Turbine output with a given water tank

[yon1000]

Hello,

I'm calculating feasibility of using grey water in high rise buildings to generate hydroelectricity.
let's assume a given water volume of 100 cubic meters a day and a water head of 100 meter.
what should be the diameter of the pipe and thus what should be the flow rate in order to maximise the total power generated through the turbine?
lets assume emptying the tank will be done once ( or more ) a day.

 

[TugboatEng]

Actually, I have an idea that could work. Mount a tank on a lever that is situated under the drain pipe. When the tank fills and reaches a certain level, a brake is released and the tank falls. As it falls the lever spins a generator or operates a pump that can inject fresh water back in to the system. Once at the bottom the tank is dumped and the arm raises back in to position. This eliminates all of the special piping and flow questions.

 

[rb1957]

"Grey water has a pretty clear definition- it's any waste water from a stream that does not include fecal matter.

So it's likely to have food waste, trash, etc in it."

ok ... you did discern my main thought, but "food waste, trash" will still have "objects" in them. Even if it's just the drain from a wash basin or kitchen sink, even if there's a filter to catch the largest lumps ('cause I's expect at least 1/2 the people would remove these filters).

Yes, there's some energy in this waste water, but the energy density is so low that it makes it Very inefficient to collect. Of course the building may want to say "look, we're being so energy conscious that we're generating power from waste water" ... ie marketing hype (as opposed to sensible/practical).



another day in paradise, or is paradise one day closer ?

 

[yon1000]

Is there a certain equation to decide the needed pipe diameter to maximise total energy generated without pressure loss?. or just to try mulitple pipe diameters to find out maximum energy generated.
also you have suggestion( calculation wise) how to tackle the storage problem, in order to utilize as much floors as possible.
given let's say 100 floors. whould you reccommend certain algorithm or equations to determine the location, size and amount of storage tanks for maxumium utlization of floors in a minimum cost.

 

[LittleInch]

Just try different pipe diameters. Your issue here is that you can make it what you want, depending on how long you want the turbine to run for and how many times a day, which then impacts on your options for the number and size of tanks. but realistically you don't want to be smaller than 50mm. You need to assume something and set some arbitary but reasonable limits.

You just need to run a few options to try and bookmark the issue.

Once you add cost in then you're adding a further variable.

SO for 100 floors, my best minimum is one tank every 10 floors, with a 50mm pipe emptying as needed once the tank fills up. Make the tank able to take one hour of max flow. That's the smallest you will get away with.

Then max is probably one tank at say 1/3 of the way up and one at 2/3 the way up. To save space make it an 80-mm pipe and again size the tank for min one hour of max flow (usually morning when everyone's having a shower and setting the washing machine going). If you don't have it assume peak hourly flow is 25% of the daily flow and you will be on the right side of the curve.

And when you do all of that you'll have spent about 100 or 1000 times more money than any energy you will harvest, but maybe it's not about that??

Have fun.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[rb1957]

isn't the idea trying to take advantage of the potential energy of the tall building ?

so a collector tank every floor, then plumbed to the turbine. How to join all these pipes together efficiently ? Maybe have a small turbine in each line (one for each tank) ?

What happens when the turbine doesn't work/turn ? and escape duct around the turbine ?

I think it'd be more beneficial to use the grey water to irrigate a roof top garden ... green rooves are all the rage, and visibly "green".

another day in paradise, or is paradise one day closer ?

 

[LittleInch]

rb 1957 - the whole idea is bonkers, but we're just seeing what is even vaguely feasible. You won't get any joy from one floor - not enough water.

To irrigate the roof you need a pump - even more energy... And it will smell of washing machine....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TheTick]

Run the water through a solar still so it can be used for non-potable applications like washing.

 

[yon1000]

Hello everyone,

I've had some issues with formula,
goal is to have the highest output per day with the minimal size turbine to save on the turbine cost.
up until now I have few equations such as Potential Energy in a Tank or Reservoir
and output of hydro-power turbine.
I am missing a few equations and contents.
formula of Time to empty a water tank( does the height of the water tank from the floor effects it),I've some online but none of them were direct and straightforward.
does the water velocity formula exiting the tank of (2gh)^0.5 is based on the h of the tank or the ground?
In the formula of hydro-power output(Pth = ρ*q*g*h), I'm very focused on the Q. I calculate it based on v*a(velocity and cross section of pipe) but I don't understand how the flow rate(Q in litter/sec) in the pipe at the has nothing to do with the falling height(water head above ground).

I've has some problems with finding proper costs and specfications.
with the turbine, I've found turbine by PowerSpout, a Pelton turbine of 1.2kw with flow rate of 0.05-8 litter/sec, but how will I know the out If its not in max flow( 8 l/s).
with 50 mm pipe I've calculated 1.9l/s( 66 floors of water*2.5 cubic meter per floor) daily but since water must accumulate in the tanks I'll be able to operate the turbine probably no more than 12 hours or even less .
Also If you know other companies of small Pelton turbine generators with quatations that would be awesome.

thank you very much for the help.

 

[Artisi]

How do you get all the waste water to the roof, or does it just appear there by magic, the costs of pumping it to the roof will probably be a greater expense than any recovery you get from power generation, if it actually works.
But lots of luck and enjoy your hobby.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Oh man,

Forget the water velocity formula - irrelevant for your purpose

I don't understand your second point. Hydro power has an h term in it. This is the head across the turbine which is your hydrostatic head minus any frictional losses in the pipe. The trick with hydro power is to minimise the frictional losses in the pipe (penstock in hydro power terminology, but "pipe" to most of the rest of the world) so that the turbine sees as much of the hydrostatic head that it can.

Power spout has an online calculator. I would advise you to use it.

https://www.powerspout.com/

Really quite neat units.

But watch out for the maximum size of particle as these types of turbines use jets inside and the nozzle size for a small unit will be quite small.

So if you're collecting 66 floors of water, this means that you won't have a large head? So you've traded higher flow for a much lower head?

Be clear what your design now is, but you won't find much better than the company you found by the look of it.

It still won't make sense to do this, but it is fun trying.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

By a little bit of trial and error, to get 1.2kW ( not a lot) with 8 l/sec you need appro 30m of static head.

So with a 25% of the flow, to get 1.2kW you need approx 120m head

.
But then you have a jet with a diameter of 5.6mm. Not very big for "grey" water

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.