gravity fluid feed to an underground mine down a vertical mineshaft. 1

[ECD40]

I'm looking for some hydraulic flowrate help with a problem that I'm trying to solve.

The problem is that a fluid of 1.24 specific gravity, has to be delivered down a mine shaft which is 3,300 feet deep, but I don't want to build any static head in the pipe. Therefore, it needs to be designed as a free flowing 'drain-pipe', with the top open to the atmosphere. The flowrate is 1,250 USgpm. This is well beyond any plumbing formula for rainwater down-comers.

Does anyone have any idea what formula would apply to such a massive 'free-fall' of liquid, so that the pipe can be sized. Also, what would the terminal velocity of the fluid be inside of the pipe. I might put a turbine in the pipeline after some later thought, but that is not the current issue.

Any help will be appreciated.

thanks,
ECD40

 

[ECD40]

Great comments and help from all - thank you.
I have a big problem with no easy solution.
Maybe I had better have another look at the turbine option, with the 3,300 feet of head at 1.24 SG and 1,250 USgpm continuous flowrate. A Pelton turbine may do the job. Any thoughts on this?
Thanks,
ECD40
(I'll be off-line until mid next week.)

 

[miningman]

And once again , without asking for confidential details, unless your SG of 1.24 is derived such that the fluid is 100% aqueous, as opposed to suspended solids, do you think your Pelton wheel can withstand the abrasive nature of these solids.??

 

[ECD40]

Dear miningman,
The fluid is clear with zero solids and still has an SG of 1.24. No abrasion on any rotating machinery.
regards,
ECD40

 

[LittleInch]

Have I missed something. What turbine option??

For a turbine to do any useful work to generate electricity you need the biggest pipe you can get and have a high pressure at the bottom of your pipe which you said you didn't want...

A great way of getting free electricity, but needs more capex.

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

 

[MikeHalloran]

... and the pipe ahead of the nozzle in front of the turbine still needs to withstand the full static head of the shaft's drop, so you need fairly thick pipe, or maybe stepped thickness as the pipe goes down, and a fairly substantial structure to support the pipe and the turbine, and you need to do something with whatever energy you extract from the turbine.

Is there a complementary flow of 'spent' fluid that has to go up the shaft? That might make a bucket/chain conveyor, or a pump driven by the turbine, attractive.



Mike Halloran
Pembroke Pines, FL, USA

 

[cvg]

well, no you do not have to withstand the full hydraulic head. Pressure relief valves are typically used to mitigate high transient pressures (in case of fast shutdown for instance). A penstock would be designed to flow full though without air.

 

[ECD40]

Hello All
The turbine option was mentioned in my opening statement on June 8. It is an option to the 'drainpipe'.
Yes, the fluid would now have to run as a full pipe, and the familiar hydraulic formulae apply. The pipe wall at shaft top would be schedule 80 increasing to schedule 160 by the time the pipe reached the shaft bottom. We anchor these pipes to the shaft wall at every 20 feet or so. The turbine would be located at a mine level off the shaft, so no problem there.
The static pressure in the pipe would be about 2,500 psi. Quite different to the 'drainpipe' alternative and schedule 40 pipe.
Preliminary calculations indicate that there could be about 8 MW of power available, so it's nothing to sneeze at, but it will take a lot more Capex, but with a credit towards the Opex.
The spent fluid does indeed have to be disposed of, but that is also true in the case with the drainpipe. The disposal is a different problem that I may ask for your comments at a later date.
Talk to you next week.
Thanks again,
ECD40

 

[katmar]

Check the potential power your turbine could generate. The 8 MW seems very optimistic to me.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[LittleInch]

I sense a unit issue there somewhere. I get at best 1.3MW and it could be a LOT lower depending on how much frictional resistance you take out ( I only assumed 100m of friction losses) based on 1250 USPGM (285 m3/hr)

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

 

[miningman]

Well while we're checking units, each 100 feet of head provides 41psi ( clear water ) , so in this instance we have
33 x 41 x 1.24 or 1680psi, not 2500psi. But the thing that really puzzles me , is how do we then dispose of the fluid at the bottom of the shaft?? Unless it is a volatile liquid that could go out in the ventilation air ( and thats totally ignoring safety issues) I hope no one is going to suggest it gets pumped back to surface!!

 

[LittleInch]

I thought the whole point of the exercise was that the OP wants to get this mysterious fluid to the bottom of the shaft to do something with it....

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

 

[katmar]

OK, so we have got 1600 psi or so down there and we need to lose this across the nozzle into the turbine. Is there anyone who knows how to calculate the size of that nozzle and the velocity of the liquid hitting the turbine blades?

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[miningman]

Once again, I know some of my old text books have chapters devoted to hydroelectricity etc, but I am not going to encourage that discussion. With all due respect to the OP, this discussion has so many loose ends, I cant see it ever developing into anything usefull. We dont know what this mysterious fluid is, we dont know if we are looking at a 4 inch or 18 inch pipe , we dont know what the prime purpose of the exercise is ( the turbine seems to be an afterthought).

I look forward to the OP providing these details because working in shafts is my bread and butter, and I might just learn something here if the OP is onto something totally new.

 

[ECD40]

Hello All,
I've been off-line for a while, but still working on the problems.

If the fluid, which I can advise you now is saturated brine with an SG of 1.24, goes underground in a 'drainpipe or rain-leader' type flow, we will need a 10" diameter pipe. This is in accordance with the Uniform Plumbing Code, that considers that the pipe is only using 7/24th. of the total cross section. There will be no static head build up at the shaft bottom, as the fluid would discharge through the open ended pipe. The terminal velocity of the fluid in the pipe will be about 10 feet/sec., but running along the pipe wall.
However, this does not give us any benefit of energy recovery from the 3,300 feet elevation change. If we add a Pelton wheel turbine at the shaft bottom, we can take advantage of the full potential static head by running the pipe full. Of course, the pipe wall thickness required for each option will be different, due to the great differences in static head. The economics of each will need to be calculated before a final selection can be made.

So to go back to my original request for help/information, the Uniform Plumbing Code adequately addresses the 'free fall flow' of water in a vertical pipe, which in this case indicates a 10" diameter pipe. I checked with some hard rock mines with deep shafts, that use a lot of water for drilling, and they use the 'drainpipe' type flow for transferring water to the underground.

The Pelton wheel turbine option still needs some investigation, but the power generated may be a lot less than I had hoped for, so it may go nowhere.

Regarding what will we do with the saturated brine that we sent down the shaft - well that's a different part of the project.

Thanks for all of your help and good comments along the way. I don't know how long this thread remains active, but I'll try to give you an update when the engineering has progressed further and the project confidentiality can be relaxed a little.

Regards to all,
ECD40

 

[LittleInch]

Thanks for the update.

Terminal velocity of 3m/sec looks a little low to me, but if it's discharging into an air gap above a tank, maybe doesn't matter so much.

To get something useful for your energy recovery, I guess you want to restrict your friction losses in your pipe to about 10% max of the total head loss, so in your case 300ft of friction losses to calculate the required pipe size.



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

 

[lilliput1]

Why not just design it so overflow would flow back to the source reservoir? Use 8" pipe for both the riser and the vent at top. Loop the vent pipe back to discharge with air gap over the reservoir. Just like underground oil tanks with fill and vent pipe with the vent pipe outlet located above the fill port.

 

[lilliput1]

Also put manual valve at the bottom for operator to control flow and outlet pressure.

 

[lilliput1]

The valve at the bottom should be cracked open to vent air the bottom of the pipe as the riser is being filled. Fill the riser with only the amount of fluid required.