Coupling a turbine with a pump 5

[nilsadams]

Hello,

I would like to combine a turbine with a pump in order to lift water up to the pump position. I am considering two options:

Either (1) using a turbine pump
Or (2) using a turbine and then connect it to a pump

From financial and technical point of view, which one is a better option ?

I want to lift water up to the pump (turbine) position, which is 3 meters (bellow the pump position) using a discharge of 2 m3/s. Just beside to the pump position, there is a cannal where the pumped water needs to be discharged. The idea of using a turbine is because I have a water fall of about 6 meters to the pump (turbine) position with a flow rate of discharge of 0.9 m3/s.

Thanking in advance,
Nils

 

[waross]

Hi Nils
The turbine would be at "D".
The pipe from "D" to "E" would be able to withstand negative pressure. To get the full effect of the suction of the pipe from "D" to "E" it must be completely full of water. To that end, you would fit a tee on the discharge of the turbine. This would have a dead end pipe and serve as a high point to collect any air in the system. The air could be removed by a small water sealed vacuum pump.
respectfully

 

[Warpspeed]

That definitely sounds like the best option, and my calculations agree with your 200 Kw potential power level.

Only difficulty could be purging the pipe to begin with, especially if the run from D to E is not a steady continuous down hill fall. I believe getting a downward slope the whole way after the turbine may be fairly important.

 

[nilsadams]

waross, warpspeed, thanks a lot !

I have now a better picture of this option. As to purging of the pipe from D to E, in case of low flow, how about increasing the water velocity of the discharge from the turbine so as to keep the pipe at relatively high pressure ? And then somewhere before discharging to the point E, I expand the pipe so as not to cause erosion in the receiving river.

Again, thank you guys !

With regards,
Nils

 

[waross]

Hi Nils
Actually, increaasing the velocity will Decrease the pressure rather than increase it. To get the full effect of the "D" to "E" suction head the air must be removed. A vacuum pump at the discharge of the turbine is probably the more dependable and efficient for the turbine operation, compared to reducing the tubing size.
A couple of comments;
I am past the point of direct experience and my comments are based on basic principles, and a lot of past research on small energy systems.
I imagine when you do the numbers on the relatively small return on investment the project will be dropped, but I understand that if the boss wants to know, your job is to find out.
I'm on the road and my I-net access is limited so if I don't respond right away i'm probably out of touch for a day or so.
respectfully

 

[BRIS]

The closed system is what I proposed above (i.e a closed system to suck the water out of the turbine). I am not sure that you need a vacuum pump. I would provide a crest in the pipe downstream of the turbine and provide an air relief valve with non-return flap (let air out but not in)at the crest. When you prime the system the pressure at the crest will be positive and air will be evacuated. During operation the pressure at thecrest will be negative any air in the system will be entrained and evacuated at the outlet - I have designed many self priming air regulated siphons using this system.

The outlet at E needs to be submerged to prevent the siphon breaking.

It is probably not a problem for the low head system but you may need to consider lowering the level of the turbine to get adequate NPSH.

If you are using a reverse flow pump as a turbine you may find 100 kw a little optimistic.

 

[waross]

Hello BRIS
You are probably right. If the volume and velocity of the turbine is adequate to flush out any air, the vacuum pump would not be needed.
respectfully

 

[nilsadams]

BRIS, waross, thanks!

I assumed that the outlet of the turbibe should be closed (linked to a closed pipe) upto E. And the point E is submerged. What is the effect of the submerged depth on the suction pressure at the turbine ? I thought to consider a cross-flow turbine. Will this type of turbine usable under such condition with suction pressure ?

Regards,
Nils

 

[waross]

The depth of submergence will make no difference to the head.
As for the type of turbine and the effect of suction head, we will have to start googleing manufacturers of small turbines. I'm out of time right now, but i will look when I have time.
respectfully