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Coupling a turbine with a pump
5

Coupling a turbine with a pump

Coupling a turbine with a pump

(OP)
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



RE: Coupling a turbine with a pump

2
Have you considered using a Ram Pump ?

These operate on the principle of allowing a column of water to (gravity) flow down a long pipe, and then abruptly shutting off the flow at the discharge end.

The very high inertia of the heavy moving water column will then produce a pressure spike that can push a small volume of water to a surprising height through a non return valve.

The pump pulses by itself and would probably do what you require, but the efficiency will not be terribly high. The advantage is low cost and high reliability.

Well worth thinking about, because these types of systems are frequently lost or destroyed in flash floods. Something more exotic may be damaged beyond repair.  But a simple Ram Pump can often be dug out of the mud and recovered miles down stream and put straight back to work.

RE: Coupling a turbine with a pump

I would need more info on the specific application.  However, look at Gould industrial pumps, Berkely Ag pumps, or American Marsh  to get an idea if this will work for you.

RE: Coupling a turbine with a pump

(OP)
I thank you all.  

Warpspeed: Well, the discharge to be lifted up to the pump position is higher than that hitting the ram pump.  As I said, the water fall has a discharge of about 0.9 m3/s, head of about 6 m.  On the other end, I have a discharge of about 2 m3/s to be lifted up a height of about 3 m.  If I understood about the mechanism of the ram pump, it releases a discharge lower than the discharge entering the pump.  But I need the inverse, i.e. using the power of a lower discharge to lift a higher diacharge.  Will the ramp pump appropraite in this situation ?

thewellguy:  can you give me the links ?

Regards,
Nils

RE: Coupling a turbine with a pump

nilsadams,

I appreciate the problem, that you need to convert a relatively high available pressure head into a much greater flow, rather than just pumping a small proportion of the available flow volume much higher.

Another less elegant idea would be a giant water wheel. Theoretically it could be the most efficient system of all, and would work over a reasonably wide flow range. It should be very tolerant of silt and debris, be self staring and self regulating, and it too has a rather appealing simplicity about it.

See what the turbo pump manufacturers say, but I would expect their turbines and pumps to stop working, or become very inefficient if the available flow rate falls much below the optimum design figure.

   

RE: Coupling a turbine with a pump

Reality check.
Not doubting or dispariging, just putting it in perspective.
The water wheel will require 2 cubic meter buckets passing at the rate of one bucket per second.
A cubic meter weighs a metric ton.
A 50 gal. oil drum holds a little over 400 lbs of water.
That means over 5 oil drums a second.
It's do-able, and a water wheel will probably be quite efficient but BIG.
respectfully

RE: Coupling a turbine with a pump

I did say a GIANT water wheel, and it would probably need to be at least 8 metres diameter, the required buckets would not be completely out of proportion.  

And I totally agree it is not exactly space age technology. I just mentioned it as one possible alternative.

RE: Coupling a turbine with a pump

Turbine driven pumps used to be quite common. The turbine is usually a reverse flow pump and efficiency is low maybe 50%. The usual situation is a large flow dropping through a small head used to lift a small flow through a large head. Common application are at drops on irrigation schemes, rivers etc where the turbine pump is used to supply village water supply.

You have a flow of 0.6 m3/sec dropping 9m and you want to lift 2 m3/sec by 3m. You can’t do it.

The maximum flow with an efficiency of 50% is

Q = 0.6m3/sec x 9m x 50%/3m =  0.9 m3/sec.

You simply need to bolt two suitable pumps together.

RE: Coupling a turbine with a pump

(OP)
I appreciate the contribution of all of you !

As to the waterwheel, I have very complex site that doen't allow me thinking that.  In addition, if I go with that much size, I will face problem with the hydraulic head of the outlet head, which is connected to a big river.

I could go with only a single turbine for the larger flow (2m3/s) and connect the outlet to the river end.  The problem, the construction cost will be huge due to the need for tunnel works and displacement of several electronic installation on the way.  The option I had thaught was to couple the discharge with another pump, in ch the latter can be driven by another fall (with lesser discharge), to discharge it to the existing pipe to the river.

When I calculate the max position of the pump to lift the higher discharge, it won't be more than some centimeters.  Technically as well as financially less attractive.

I am still wondering what kind of options I should think of : ....  

RE: Coupling a turbine with a pump

I think I have lost the plot!. 1) you cannot get out more energy than you put in:  you can't lift 2m3/sec by 3.0m. from an input of 0.6m3/sec dropping 9.0m and 2) you need to consider the economics: construction of tunnels etc. to recover 30kw of electricity may not be cost effective.

RE: Coupling a turbine with a pump

(OP)
BRIS:

The plot goes like that:

There are two water fall sources. one for bigger discharge (2 m3/s) with a fall of about 3 meters and a second with smaller discharge (0.9 m3/s) with a fall of about 6 meters.  with this setup there is an existing combined discharge to a river at about 2.9 m3/s.

Now, for me, the 2m3/s scheme seems attractive if I find some technical solution to increase the head from 3 m to possibly 5 or 6 meters.  If I do that it means I have to dig down, thus I will be below the level of the combined chanel.  

Ok, then le me think of this but then I have to lift the water back to the level of the combined channel.  To lift water to the combined channel, I then took the option of using a pump.  But a pump will consume energy to run and eventually my solution may not be feasible.  I then thought how about a turbine pump that uses the 0.9 m3/s scheme (6 m fall) as energy source so that it may help me lift the water from the turbine of the 2m3/s scheme.  

Unfortunately, the energy source with the 0.9m3/s scheme turbine-pump cannot help me lift water at (2m3/s)more than some centimeters (<1m).  It means, with the current set up, I can increase the head of the 2m/s scheme only by a few centimeters (i.e, head=3.xx m).  The other option I left is to go deep up to 6 m but then think of all the heavey construction work (tunnels, displacemnt of some existing installations and utility lines, .. with lots of messy stuff).  Honestly, it doens't sound feasible but the client want to see the turbine installed through some technical solution.  So, am wondering and wondering and wondering what kind of technical solution to bring to my client.... :)  I hope you got it.  True, a picture worth a thausand times of words..



  

 

RE: Coupling a turbine with a pump

Gentlemen, I have used pumps called turbine pumps, but from some of the responses I am wondering if we are talking about a reaction turbine close coupled to a pump, or if there is a special arrangement of pump and turbine combined in one case that is able to divert some of its flow at a higher pressure than inlet pressure?
Have I misunderstood or am I about to learn something new?
Thanks

RE: Coupling a turbine with a pump

It is difficult to visualise the complex topography of your project without the aid of a map or a photograph.

But you mention that an expensive tunnel on the outlet side may be a solution.

Rather than tunnel through obstructing high ground, would it be possible to go over the top with a siphon ?

A small volume turbine pump could then be used to fill the pipe and displace the air up to the high point.  A natural siphon would then begin, resulting in a massive flow increase for free, and away it would go all by itself.

The required drive turbine and pump could be fairly small, and overall efficiency would not be an issue, it would only need to generate the necessary very high head pressure to fill the ascending pipe and get the siphon started.

RE: Coupling a turbine with a pump

A much less violent way to start the siphon might be to first slowly fill the ascending pipe, that was sealed against draining back, by a submerged swinging check valve at the intake.

The discharge end could be sealed off with a large gate valve. Once water reached the high point, it would then begin to fill the descending pipe. An open air vent at the highest point allowing all the air to be purged.

When the entire pipe is completely filled, close the air vent.  If the gate valve at the discharge end is then slowly opened, flow can be allowed to very gently build up to any desired level.  Flow could be automatically modulated to pump almost the entire river volume without pumping the suction intake dry.

The turbine machinery is only required to initially fill and start the system. It could be comparatively small in size, and should last forever because of the low usage.    

 

RE: Coupling a turbine with a pump

For low head low costs turbines the solution is a reverse flow pump but they have relatively low efficiency. I still don't understand the objective of increasing the drop in the 2m3/sec stream if you then have to pump it back up into the tail race. This must be less efficient than generating power from the available head and flow of the two streams.
 For such schemes the most feasible solution will be achieved with minimum capital costs which will preclude solutions using tunnels and siphons. Your most cost effective solution would likely to be to provide turbines on the two falls with minimum civil works.  I suggest however that a basic cost estimate comparison of capital and o&M costs against the value of producing +/- 30kwhr will demonstrate the project not to be feasible. It doesn't sound feasible to me.

RE: Coupling a turbine with a pump

I think you need to explain a little clearer what you are trying to do and what the installation will look like. 2m3/sec at low head is not a problem - many of the larger pump companies could do this with axial flow or mixed flow vertical pumps.also check round the pump companies that are involved in flood irrigation etc.

can you put a sketch / drawing onto a website somewhere so we can look at it.
 

Naresuan University
Phitsanulok
Thailand

RE: Coupling a turbine with a pump

(OP)
I thank you all again.

I will be glad to show a sketch but don't know how where to present it.  

Ok, let me try a bit with some thing visual.  Look at the following points.  Join ACDE.  Then Join AD.  AC is with 2m3/s, 3m scheme.  BD is 0.9m3/s, 6m scheme.  DE is combined drainage to a river which is about 4 meters below D.  On top of DE, there are several constraints : roads, pipelines, other electro mechanical installations serving the industrial site.  Between D and E, there is also property line limitation.  It means I cannot install F beyand some boundary.

I plan a turbine at C.  But I still have a head of more than 3 m between C and E.  So, I want to lower C to F to get a total head of 6 meters.  But if I go to discharge through FE, I will be forced to use a tunnel.  To avoid the tunnel works, I had taken the option of using BD as a hydropower source to install a turbine (or turbine pump ?) at D in order to lift the discharge from F to D and then use the existing drainage pipe DE.  

It sounds that using BD doesn't seem sufficient to lift the 2m3/s discharge from F to D.  So, I am now thinking either to connect FE with a tunnel or I don't know if a siphon option can work with this confugration without losing some head.  

               *B

*A              
\
 \
  \
   \*C    *D         
             
             
                
    
      *F
                                   *E (River)
       

RE: Coupling a turbine with a pump

(OP)
I mean "Join BD"

RE: Coupling a turbine with a pump

Ok got it.

There is little point in your original proposal of using the head B to D to pump back from F to D. Even if there was sufficient energy, which there is not, it would be more effecient to use  a turbine generator on each fall.

Why do you not simply pipe from A to C to E and from B to D to E and place your turbines at E ?.

Using a siphon on the downstream side of the turbine(s) is possible but it is simpler to locate the turbines at the lowest point (E).

Are A to C, B to D, C to D and D to E all pressure pipes?

RE: Coupling a turbine with a pump

(OP)
BRIS,

Thanks.  

"Why do you not simply pipe from A to C to E and from B to D to E and place your turbines at E ?. "

Well, that could be a good option if I had no any constraint.

Do you mean two penstocks ?

The problem is that, just immediately after D, there is an electromecanical equipment designed to control and record the flow from both ACD and BD.  The two discharges must combine together at the point of the equipment. The point where there is this equipment is on atm pressure.  Afterwards, the pipe is under pressure upto the point E (River).  Again, the area around E is not the property of my client.  It means, it needs another legal procedure if we take the option to install the powerhouse at E.  The other risk to the turbine is, point is closer to a big river with significant flooding in case of a 20 to 30 years return period. Thus we may need to invest a good structure for the power house.

There is a sort of siphon between A and C.  As the rest, the way up to A as well as that of B is through Chanel (open).

That would create a lot of disorder if we remove the flow control equipment beside D. Again, on the surface between C and D there is a private road (for cars).  

But let me assume that it may be possible to displace those equipment and can get permission for installation at E.  Now my question : is it possible to use a sort of forked penstock ?  I mean, just thinking to join a pipe AD and BD at point D and then use a single pipe EF as it is.  As I said earlier, point A and Point B are not at the same level.  How can you view the impact of using such penstock on the overall head at E.  

Am working at a complicated cite sad but it is also interesting to encounter such challenges

RE: Coupling a turbine with a pump

As I understand your situation you want to move water from F to the river by the most economical means.
Siphons should work well. I would suggest multiple smaller siphons. You will need flow control to throttle or disable some siphons at periods of low flow. You will need a small pump and valves to start the siphons. An alternate is to use large pumps to start the siphon action and then let the pumps spin free in the siphon induced flow. This has the advantage that you can increase flow by starting the pumps during times of exceptionally high flow.
Basically design a conventional pumping scheme while keeping in mind that the layout should be conducive to siphon flow when the pumps are stopped.
respectfully

RE: Coupling a turbine with a pump

(OP)

You mean to make hydraulic connection through FDE using siphon from F to D ?

 

RE: Coupling a turbine with a pump

I have been thinking a bit more about siphons. The maximum theoretical suction lift of any system is limited to 10.3 metres, and the practical maximum is probably a bit less than that.

That is not likely be a problem here, but it is something to keep in mind.

If you do decide to use a siphon between F and E, no additional pump will be required to initially charge the siphon pipework. A high pressure water source is already available directly from either A or B.

Another advantage of a siphon between F and E is that there would be no machinery located at E except for a motorised gate valve, which could be remotely operated from F  

RE: Coupling a turbine with a pump

Yes. Is this feasible? The lower the discharge elevation, the better the siphons will work.
Of course there will be a lot of compromises before you decide on a scheme but compromise is often a big part of design.
You will need some controls but the power used in the controls and occasional pumping to start the siphons will be a small part of the power required to pump everything.
Are you trying to get run-off water to the river. Is the flow steady or dependant on rainfall or some other factor?
Tell us a little about the overall picture, please.
respectfully

RE: Coupling a turbine with a pump

(OP)
I thank you guys !

The variation of the flow is not much.  The flow what I described above are almost represents the 80 to 90 % flow time in my FDC.  It means I have relatively constant flow sources.

As to using a siphon, the discharge elevation (D) is higher than the saction elevation (F).  Most siphons I see go up from the suction elevation but the descharge elevation goes down below the discharge elevation.  I would be glad if you make me clear a siphon with higher discharge elevation than the saction elevation can be operational.  If I connect the discharge end to the pipe leading E, perhaps the link FDE can give me a discharge elevation lower than the saction elevation.

Regards,
Nils

RE: Coupling a turbine with a pump

Sorry I have not read through all the replies so I may be stating something that has already been considered.  I w agree that given your constraints a siphon could provide the best solution. Place your turbine at F and provide a closed pressure conduit from the outlet of the turbine from F to D to E. The siphon will prime. You may need to provide an air valve with a non return flap at D (a valve that lets air out but not in).

Clearly you will have to abandon/remodel the electo mecahnical arrangement at D. You can provide a flow meter and regulated valve at the turbine to control flows.

RE: Coupling a turbine with a pump

(OP)
Warpspeed, waross , BRIS,

Thanks. How do you dimension the siphon in terms of height and performance.  Do you know commercially available siphons of the kind BRIS mentioned ?

RE: Coupling a turbine with a pump

The discharge end of a siphon is below the inlet end. The water flows from the end with the higher elevation to the lower elevation.
You must arrange your discharge so that the discharge is lower.
A basic siphon is just a pipe from point "A" to point "B" at a lower elevation. You can use the difference in head between the inlet and the discharge as the pressure drop and work backwards from the pressure drop tables to determine the flow rate with different sizes of pipe.
Starting the siphon. The pipe must be completely full of fluid.
Method #1 is to close the discharge end with a valve and fill the pipe with a small pump. The inlet must be closed. A check valve may work. The air has to be vented at the high point. When the pipe is full of fluid and the air has been removed, the valve at the discharge is opened and the flow starts.
Method #2 Is to use a pump with a great enough volume to flush the air out of the pipe ahead of the fluid. Once the flow of fluid has purged the air the pump may be stopped and the flow will continue.
yours

RE: Coupling a turbine with a pump

My understanding of sizing a siphon is that the difference in elevation from inlet to outlet is the driving pressure. Flow stabilises at a point where total pressure drop down the length of pipe equals the driving pressure.

Possibly the most trouble free way to do this would be to dig a pit or a well at F down to at least the same depth as the river bed at E.

Build your siphon so that both ends are completely submerged down to the same level. In other words have no deliberate built in fall. Prime your siphon, and open both ends.  The water in the well will then exactly equal the level in the river. Flow could be in either direction, but the water levels will always end up exactly equal.

As turbine discharge water flows into the well, the level will rise, and the siphon will begin to flow. Flow rate will be proportional to the difference in water level at each end.

That difference in level could be kept fairly small by having a large enough siphon pipe flow area. In fact the pipe could never be made too large.

Just design the siphon pipe so that it might flow for example 3 cubic metres per second at a one metre pressure head, for whatever total pipe length is required. Or choose any figures you like.

Doing it that way requires no flow control on the siphon. You can shut down your turbine and the siphon will just stop flowing too. Or if turbine flow increases beyond the design flow, the well just runs a little higher.

I think I would run more than one siphon pipe for reliability and ease of starting. I might also build a well at both E and F to ensure neither end of the siphon could ever become exposed and admit air, even if the river runs very low.  There should easily be enough flow through both wells to constantly sweep them clean, and keep them completely free of mud and silt.

These wells do not need to be large, just deep, with the pipe ends running well below the minimum possible river water level. The only way the siphon can ever fail is if air enters the system somehow. A couple of suitably deep wells would certainly make that much more unlikely.

 

RE: Coupling a turbine with a pump

I like that Warpspeed. You can extract the air at the high point with a small water sealed rotary vacuum pump and the siphon will start by itself. That way you do not need any valves to start the siphon. Simple cheap and reliable.
I hope nilsadams can use the concept.
Respectfully

RE: Coupling a turbine with a pump

I had not thought of that, but you are quite right. The siphon pipe could remain completely open at both ends, and all the air extracted from the high point. It might be a fairly lengthy process to fill the entire siphon starting from a completely dry pipe. But it should only need doing once. If there were multiple siphon pipes it may still be a fairly economical way to do it, as only one vacuum pump would be required.

If both the siphon pipe ends can be sealed, the whole thing could then just be filled with water, and fairly quickly, which may be faster and cheaper.

I suppose it depends on the relative cost of a suitable vacuum pump, versus multiple large gate valves.

RE: Coupling a turbine with a pump

You don't need to consider it as a siphon if you connect a pressure pipe to the delivery side of your turbine and pipe it to point E. You then have a closed system from pint A to E with your turbine somewhere along it. The head across the system is elevation A-E and the head across your turbine is elevation A-E - friction and other losses. You will need air relief valves on the crest(s) and these need to let air out not in. (not vacuum breakers). The size of the siphon pipe is determined from economics, smaller the diameter greater the head loss and lower the head across the turbine. I would suggest size for a velocity of o.75 to 1.0 m/sec.

You need to consider NPSH and lower the turbine to achieve adequate positive pressure. (this may be higher or lower than point F depending on losses)

If you adopt the open well solution at F as suggested by others a simple method of priming your siphon would be to provide a bypass around your turbine which tees into your siphon pipe. You will need a foot valve on the bottom of your siphon pipe in the well at point F. To start run the flow through the by pass to flush out the air. Close the by pass and the siphon will start to suck from your wet well at F. Open your turbine and the system is operating. (you will need the by pass in any case for maintenance).



RE: Coupling a turbine with a pump

(OP)

I thank and appreciate your devotion here to figure out and suggest options to this problem.  Using siphon is taking the momentum.  Just to give you one more figure, the aerial distance between A to E is about 100 m.  Using a siphon from A to E (or F to E) will not be convenient due to some private property structures that will not allow to pass the siphon up to the river.  

If am going to use s siphon (s), it would rather be from F to D.  The problem that I couldn't figure out yet is the elevation of the siphon outlet at D is higher than the Elevation at the turbine (F).  From your comments, the siphon requires driving pressure to be operational.  But from F to D, the pressure head would be negative.  If I were to assume to connect the siphon from F to E, it would be possible to create pressure head  or maintain similar water level in two wells as warpspeed suggested.  But from F to E, I cannot go on the surface or make some earth works to pass the siphon.  That option may then take me back to the use of a tunnel.

Now, from your comments,am trying to figure out how to use a siphon from F to D using a valve to remove air at the siphon crest Or if I can use a vacum pump ? I would be glad if you put your further comments on this.  All your comments have been very helpful to figure out a solution to such a real challenge.

Regards,
Nils






RE: Coupling a turbine with a pump

A siphon transfers fluid from the high point to the low point. If "D" is higher than "F" the siphon will work but unfortunately in the wrong direction.
I understand that you have a tunnel now between "D" and "E".
Is it of sufficient size that you can install a pipe inside it to provide the needed fall for "F" "D" "E"?
What is the source of the water? If "F" is process waste water, is there anything that can be done to increase the elevation at which it is collected?
If you do go with a turbine at "D" there are some types that do not have to be installed at the absolute lowest part of the flow. If the discharge from a suitable turbine at "D" was closed and able to withstand negative pressure the efficiency would benefit from the additional 4 meters head from the drop to the river.
It looks like you can get a combined drop of 7 meters.
You mention measurement and control at point "D". Measurement is cheap and easy. Control is difficult to understand. It would seem to be very difficult to control the flow of a waterfall from the bottom.
Suggestion #1 Use a siphon with a siphon pipe installed inside the existing tunnel from "D" to "E".
Suggestion #2 Install a turbine at "D" and close the discharge from "D" to "E" so that it will withstand negative pressure. Instal a pump to pump from "F" to "C". Add this flow to the total flow. The pump can be direct coupled to the turbine or belt driven from the turbine.

Suggestion  #3 Close the piping from "C" to "E". Install a venturi at "D" to suck water from "F".
If this is physically feasible it will be passive, relatively cheap, and automatic. As long as there was flow from "C" to "E" the venturi will be drawing from "F". It should handle a mixed air and water flow as well as a solid water flow.
respectfully

RE: Coupling a turbine with a pump

(OP)
waross:

Yes, I am using process water with fairly constant discharge.  The current discharge line is through ACDE. There is no flow down to F.  I just wanted to install a turbine at F to increase pressure head from A to F if I find economical option to lift water back to D.  The reason to go back to D is simply to use the existing discharge pipe from D to E. In your 3rd suggestion, the venturi stuff can also be interesting.  I have to look at the capacity and pricing.


sed2developer:

"Hyrdam", is it like a ram pump ? Do you have experiences in it ? I will look at in detail. For me it could be interesting if the output discharge is almost the same as the input discharge in order to either (1) generate higher power by directly connecting the penstock from the lifted water tank or (2) lift equivalent dicharge from F to D  so that there will not be storage at F do discharge differences by using "hyrdam".

With regards,
Nils





RE: Coupling a turbine with a pump

(OP)
sed2developer:

I checked the hydram site. looking at the performance chart, I don't think it has a capacity that match my flow-in and flow-out requirement. The daily discharge I am considering in this problem is much higher than the max values listed in the chart.

RE: Coupling a turbine with a pump

Hello nilsadams;
I think that I may have misunderstood something. Is there a source of water at "F"?
If the only water sources are "A" and "B" and you have an existing tunnel or pipe from "D" to "E", things change a little. Then run the flow "A" "C" "D" through a turbine at "D" and enclose the discharge so that the the drop from "D" to "E" adds to the total head. You may have to add a small water sealed vacuum pump to keep the discharge free of air and the final discharge should be below water level if possible. If you can divert the water from "B" to the inlet at "C" you will have a total of 2.9 cubic meters per second.
The head from "C" to "D" to "E" will be 3M + 4M = 7 M.
I make that to be about 200 kw at 100% efficiency.
Dropping the water to "F" to get more head and then returning it will take more energy than you will gain.
The best you will be able to do is use a turbine that can use the head of the discharge as well as the head of the inlet and close the pipe from the turbine to the river.
at the end you will get 200 kw less efficiency losses. In the real world, I would expect anything ovewr about 125 kw to be a bonus and wouldn't be surprised to see 100 kw or less.
respectfully

RE: Coupling a turbine with a pump

(OP)
waross,

thanks a lot.  Yes you got the point.  I don't have water source at F.  The use of vacuum pump at D and pressure pipe from DE was not in my mind.

If I understood well your suggestion, Everything from A to E (if I pass through ACDE) should be a closed system.  Thus, I will have my penstock up to D (turbine + vacuum pump ?) + pressure pipe upto E, right ?  How do you couple the vacuum pump with the turbine at D or where do you put it ? Or it can be anywhere between D and E ? If you can elaborate me what you said "You may have to add a small water sealed vacuum pump to keep the discharge free of air and the final discharge should be below water level if possible. "
It sounds good to me to go ahead with this option as the others would be complicated and costly.  

Regards,
Nils

RE: Coupling a turbine with a pump

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

RE: Coupling a turbine with a pump

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.

RE: Coupling a turbine with a pump

(OP)
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  

RE: Coupling a turbine with a pump

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

RE: Coupling a turbine with a pump

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.

RE: Coupling a turbine with a pump

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

RE: Coupling a turbine with a pump

(OP)
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

RE: Coupling a turbine with a pump

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

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