Using a turbine in industrial fluid pipelines for power

[dpruit]

I am getting started on a project to replace pressure reducing valves on either natural gas, refined gas, or crude oil pipelines with turbines to recover the lost energy and generate electricity back into the main power grid.
Has anyone heard of this being done before? Any suggestions/obstacles I might run in to that I haven't thought of?

 

[ScottyUK]

Google "turbo-expander"?


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If we learn from our mistakes I'm getting a great education!

 

[zdas04]

Not wasting hp across a regulator is a good thing. My guess is that using it to generate electricity will never pay back the capital cost of the generator selling to the grid, but I've never done the math. Turbines are constant entropy devices so you can expect significant cooling to go with your dP, if there is any chance for condensation or freezing you'll likely get it.

One idea that I've seen work well is to put an ejector or eductor (ejector for gas, eductor for liquid) in the place of a pressure regulator and use it to suck on a part of the system that can use lower pressure.

David

 

[budt]

Does reducing pressure of a GAS with reducing valve (regulator) actually waste energy?

I was led to believe that as a Gas expands to reach the lower pressure it must take heat from its surrounding atmosphere, therefore the possiibility of freezing in some cases.

My understanding of a Gas going from a higher pressure to a lower pressure is: The volume increases at the lower pressure and energy is actually saved on applications that can operate satisfactorily the lower pressure.

I always use an Air Line Reguulator in a Compresed Air Circuit to save Comprsssor HP. This web site shows te annual savings by using a regulator to reduce pressure on the Return Stroke of a Cylinder since that part of the cycle requires little or no work.

http://www.fpweb.com/200/IndZone/Packaging/Article/False/63505/IndZone-Packaging

Needless to say it takes more energy to compress a gas to higher pressures so the energy savings is not 100% but it is well worth the cost of a regulator to operate any sysrem at the lowest pressure that will continuously operate a device as designed. But, initially the air must be compressed to a pressure high enough to meet the requirement of the highest pressure need in the system.

Liquids at pressure are completely different since they are essentially non-compressible and have very little stored energy. That is the reason for the Nitrogen Gas in a Hydraulic Accumulator used to store energy on the oil.

The only way I have found to successfully save energy with liquids is to use a Motor Type Flow Divider with one section being driven by the higher pressure and another section or sections connected to a reservoir and acting as pumps to mix teir flow with the initial higher pressure flow. You can see a Motor Type Flow Divider in a training book I use to teach basics to Maintenance Mechanics and Mechanical Engineers here.

http://www.hydraulicspneumatics.com/200/eBooks/

Go to Chapter 13 and to page 13-10.

In the Advanced book, on the above page, there is a section on Flow Dividers with circuits used to Intensify Flow or Pressure with the Motor Type Dividers. That section has not been presented yet. They are putting up a section every couple of weeks so far.

I use the advanced book to teach how circuits are designed, how they should function and some of their failure modes.

Later on they will be presenting an Industrial Hydraulics Trouble Shooting book I use to teach a class. It uses a method I understand the IRS uses to teach their Agents how to spot Counterfeit Money. I read that the whole class is spent studdying only good bills until they know the real thing so well that a Bogus Bill stands out like the Proverbial "Sore Thumb." To that end over one third of the book is going throug the basic circuits and learning how they work.

That is folowed up with practice circuit schematics with wrong components or other drawing changes. The student is given a Circuit Sequence of Events that was planned, then a desription of what is not working correctly. Then they must diagnose the proble and recommend a fix.

Another section has more practice circuits from systems I have worked on or designed or circuits from the company where the class is presented.

I have only used this one for a local 2,500 employee company so far.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[dpruit]

Thanks for the great input. To clarify, the substance in question is incompressible. An example of this type of technology can be found here:

http://www.gouldspumps.com/download_files/CaseHistories/Summer_2004_GPTurbineRecoversEnergy.pdf

In this case the liquid is cooled water I believe. The device is essentially a pump working in reverse and coupled with a motor that now acts as a generator. All one would need to do is run this through an inveter of sorts and back into the grid right?
At extremely high flows (say 1500gpm) it seems very likely that a good deal of electric generation would occur, especially if we are talking about a pressure drop of somewhere in the range of 100psi or more.
I know many pipelines run over mountain ranges and can result in this scale of back pressure. Say the liquid is gasoline or oil, would there be a problem with significant cooling still? I know phase changes for water are very well defined, is this the case with other incompressible fluids?

 

[budt]

Could you use the same setup as a Hydro-Electric Dam generating facility does?


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[hydtools]

As long as the fluid remains an incompressible liquid there would be no significant cooling. Sounds like a nifty idea to recover otherwise lost energy. Phase change pressure and temperature for other fluids is known, just as they are for water.
You would need more than simply an inverter to feed back into the power grid. You need to prevent backfeed and provide phase match. But that is known art.

Ted

 

[zdas04]

budt,
Your comment on my post about wasting energy by dropping pressure has a completely different set of assumptions than I was using. Neither is wrong, just different applications.

If you are trying to transport gas from one point to another, every ounce of pressure drop below final delivery pressure represents an amount of energy that must be replaced with pumps or compressors. So in an Oil & Gas example, if I have flowing tubing pressure of 1,000 psig and choke the pressure down to 300 psig to keep from damaging the reservoir by flowing to fast; then that 700 psig represents a quantity of energy that is "wasted" and will have to be replaced in a processing plant to get the gas back up to mainline transmission pressure. If I can extract work in that pressure change then replacing that energy is less painful.

In your example you are cutting pressure in a regulator prior to final delivery to reduce the mass flow rate and increase the flow velocity to a device that does work--which saves energy.

David

 

[budt]

David;

I understand what you are saying now. I assumed you were going to use the gas at the lower pressure not have to re-pressurize it after reducing it.

That has to be wasteful as well as expensive.

Now I undestand the reason for driving a generator and retrieving the wasted energy. That way you can come near to breaking even.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[zdas04]

You can't ever get very close to breaking even, but I've seen examples of using a ejector to pull on low pressure lines that helps a lot.

David