Steam Powered Eductor Energy System

Steam powered eductors are a simple, though less efficient way to pump water http://en.wikipedia.org/wiki/Injector . They were first used as a boiler feed pump on a steam locomotive. Their disadvantage over mechanical modes of pumping is low efficiency.

I am curious though as to whether they could be used effectively in an integrated micro pumped storage energy system. The specific application i had in mind is an aquaponic system where exhausted hydroponic water is needed to circulate to a clean upper level reservoir. This reservoir could be oversized and placed at a higher head elevation and used as both a clean water reservoir for aquaculture make-up and also as a small micro-hydro storage system. Steam to power the eductor could be generated through one or a combination of bio-gas, solar and biomass resources. The system could be designed with nearly no moving mechanical parts (use an eductor for the boiler feepump).

I haven't got a good handle on what the efficiency would end up being, but know for the electrical generation component it would be low. However the mechanical simplicity and potential to integrate the wasted energy into other functions could make it an attractive overall system for certain off grid applications, particularly for northern climates where alot of heat is going to have to go into the operation to keep it running during the winter months. There the eductor would basically serve a dual purpose of pumping and warming the water as well as providing a small amount of electricity for other system operations. Any thoughts or feedback on the idea ?

Here's how it works. http://www.venturipumps.com/eductor.htm

Jet pumps are eductors. I suppose that in a greenhouse situation where heat is being produced, a steam pump could raise the water and it could be aerated on it's descent. I don't have a clue to efficiency, but since all of the heat remains inside, I'm going with 100%. Similar to those little fans that stick onto a wood stove or grow lights in an electrically heated house. No net energy loss.

See description at wikipedia: http://en.wikipedia.org/wiki/Steam_jet_ejector#Feedwater_injectors

I have considered this before. Perhaps small venturi vacuum pumps can work for this purpose (see example here: http://www.2linc.com/venturi_vacuum.htm). I speculate, but I think this might work well with low pressure flow requirements. There are also available steam ejectors at McMaster.

Thanks for the links Marcos and Dale, I did some digging and found a helpful reference catalog.

For the system flows i have in mind a 1/2" eductor http://www.clarkreliance.com/site/applications/DocumentLibraryManager/upload/e-200-1.pdf should work. Having a more difficult time determining efficiency though. According to the linked document I found eductor efficiencies as high as 8% (calculated using 150psig saturate steam as motive force while exhuasting against 30 ft of head). With a carnot limit efficiency at that temp of 36%, that is 22% of carnot efficiency. Not good but not terrible.

What i really wonder is if that efficiency ratio holds while going to higher temps and motive steam pressures, the manufacturers don't make eductors for higher temps and pressures, presumably because waste steam is most often used and no one wastes high quality steam on eductors, however if it held you could conceivably exceed conventional steam engine efficiencies with a far simpler system. Say 1010 deg F (or higher since fatigue and failure are of little concern in this application) @ 22% carnot efficiency you'd be around 14% eductor efficiency, @ 80% micro turbine that would be 11% electrical efficiency. That is all speculation though as i really can't find anything on eductor efficiency other than manufacturers stated performance numbers at those low temps. My hunch is that the efficiency ratio declines though as temp and pressures increase. Still i'd like to figure out how to properly model the situation. For small scale systems this might be a pretty workeable route to go.



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A steam powered jet pump could be used to move water from the lower floor of my cottage to an upstairs tub. I don't think I'll do that, but good to know that the RMH could do something like that with the addition of a pressure vessel (with 2 relief valves, safer than a pressure cooker with one). No heat would be lost, so inefficiency would not be a problem.

Nick Raaum wrote:What i really wonder is if that efficiency ratio holds while going to higher temps and motive steam pressures...

The most informative reference I've found from the old days, 1898, on venturi steam jet injectors, as they called them, is:
Strickland L. Kneass (1894). Practice and Theory of the Injector. John Wiley & Sons: 3rd edition 1910
https://archive.org/download/practicetheoryof00knearich/practicetheoryof00knearich.pdf

At that time it was common for commercial injectors to have an operating ratio of one pound of steam to 8 to 13 pounds of water injected into boilers pressurized from 120 psi up to 150 psi. So it is very clear that early injectors were designed to operated against substantial pressure. The efficiency of course depends on the energy requirements for the specific boiler system to obtain the steam. Kneass made it very clear that Giffard got all the basic designs for his first venturi steam injector correct, and that the significant improvements seen since then were the products of attention to detail and improved manufacturing techniques. I'm not sure but about 30 years or so ago a lot of research was put into improving jet injector designs, whether steam or non-steam, with the result that today it is common to see industrial compressed air jets used for mundane purposes such as drying or blowing off dust on conveyor lines, or more exotic jobs such as gas field burn off Tulip devices, with entrainment volumetric motive fluid to suction fluid ratios of 1:20; more specialized applications where they specifically adapt the physical dimensions of the injector to the specific motive and suction fluids can range upward to 1:50 or even higher which is simply phenomenal. That might be one of the reasons you won't see much information about venturi jet injector efficiencies - it might make folks start thinking a little too much. If you have an efficient boiler setup and can get a well made venturi steam jet injector suited to your specific needs, I think you'll be pleasantly surprised at how well it works.