Water Maker - Turbine

[jroberts]

After doing quite a bit of research on CF and the web I have a question for all the WM gurus out there:

Would it be efficient to put a 12v turbine generator downstream of the brine outlet of the pressure vessel to capture some of the energy?

My thought is something like a turbo on an ICE and rather than a more complicated setup like on a Spectra WM and simply converting pressure to electricity.

[Lepke]

Do you have a turbine that will work with the brine flow rate? I've used turbines on creeks for house power, but the smallest used a 4" pipe.

[Adelie]

Originally Posted by jroberts

After doing quite a bit of research on CF and the web I have a question for all the WM gurus out there:

Would it be efficient to put a 12v turbine generator downstream of the brine outlet of the pressure vessel to capture some of the energy?

My thought is something like a turbo on an ICE and rather than a more complicated setup like on a Spectra WM and simply converting pressure to electricity.

Flow rate is probably not enough to be worthwhile. If it was the turbine would cause back pressure issues that would decrease production.

I know the early Pur's claimed some sort of pressure recovery system that decreased energy use.

Turbo on an ICE recovers energy that would otherwise be wasted. Generally that power wasted power was recovered to increase horse power for the same size engine by pressurizing the air for the intake and using more fuel. Fuel use for a given horse power is about constant.

Diesels like to use turbos because it widens the power band so fewer gears need to be used in a vehicle transmission as well as increasing horsepower for a given size.

Compound-turbos were used late in the era of piston engined commercial airliners to add power to the output shaft directly rather than increasing intake pressure at the pistons which also increases fuel use. Thus there was some increase power and engine weight but no extra fuel was used so fuel economy was much improved. Nightmare to maintain but only recently have jets approached the same fuel economy.

[jroberts]

I believe the water pressure on the brine output from the pressure vessel should be approx 800 psi. I don't know what the pressure should be after the pressure regulator/valve (that controls the pressure in the vessel). Does anyone have any figures?

There are 10W micro turbines on Amazon that run on low pressure. What about stringing enough in series to gain some efficiencies in the system?

What about putting a micro turbine between the pressure vessel and the regulator to take advantage of the high pressure?

[dougweibel]

Why would you want to use a turbine here, unless you already have a water maker and and are trying to retrofit something? If so I think if you could size a turbine for the flow rate it is possible. How much energy you could get??? Maybe worthwhile, maybe not.

If you are just looking for a more efficient water maker arrangement then Spectra and others have energy recovery devices (Clark Pumps) that will be much more efficient than a turbine would be for this applications. They recover energy from the water pressure at the brine outlet of the membrane and use it to boost the pressure of the water going in to the membrane.

[jroberts]

Thanks Doug. I do not currently have a WM but am considering it. I'm thinking through the design of a DIY and comparing it to a complete kit.

I'm putting out my questions for brainstorming purposes (theoretical and practical).

The clark pump that Spectra uses is a complicated pump system. The way I see it, the more complicated the more potential for malfunction or repair. I may be mistaken but I believe that a clark pump gains approx 10% in efficiency.

For a 12V DC motor/pump that uses approx 800W, a 100W turbine providing approx 80W after line losses would equal a clark pump. The benefit of this would be that I could use a basic motor/pump and if the turbine malfunctioned it could be eliminated or bypassed.

[Paul L]

Originally Posted by jroberts

Thanks Doug. I do not currently have a WM but am considering it. I'm thinking through the design of a DIY and comparing it to a complete kit.

I'm putting out my questions for brainstorming purposes (theoretical and practical).

The clark pump that Spectra uses is a complicated pump system. The way I see it, the more complicated the more potential for malfunction or repair. I may be mistaken but I believe that a clark pump gains approx 10% in efficiency.

For a 12V DC motor/pump that uses approx 800W, a 100W turbine providing approx 80W after line losses would equal a clark pump. The benefit of this would be that I could use a basic motor/pump and if the turbine malfunctioned it could be eliminated or bypassed.

Take a look at the specs for 12v DC watermakers at around the 7gph size. Compare a Spectra with clark pump to say a Rainman. The power usage difference is far higher than 10%.

[dougweibel]

Originally Posted by Paul L

Take a look at the specs for 12v DC watermakers at around the 7gph size. Compare a Spectra with clark pump to say a Rainman. The power usage difference is far higher than 10%.

I think Paul is correct. Watermakers with an energy recovery device are quite a bit more efficient. The correct way to compare is Watt-Hours per gallon produced (energy per gallon).

Clark pumps can be a failure point. I have one and am not crazy about it. On the other hand they are a fairly simple mechanical device. Many owners I have spoken with feel the Clark pump is more reliable than the boost pump. Brand also makes a difference. I have a SeaRecovey, and I'll stay away from SeaRecovery units with an "energy recovery device" in the future. Spectra has a great reputation and great service AFAIK.

[Sailmonkey]

Originally Posted by jroberts

I believe the water pressure on the brine output from the pressure vessel should be approx 800 psi. I don't know what the pressure should be after the pressure regulator/valve (that controls the pressure in the vessel). Does anyone have any figures?

There are 10W micro turbines on Amazon that run on low pressure. What about stringing enough in series to gain some efficiencies in the system?

What about putting a micro turbine between the pressure vessel and the regulator to take advantage of the high pressure?

Turbines work on flow volume more so than pressure.

After the regulating valve the pressure should be near zero as there is no restriction in the flow to the overboard discharge.

What is the fluid flow rate required to operate these 10 watt micro turbines?

FYI, at 12.6-13.2 volts 10 watts is .79-.83 amps. You’d be better off with a small solar panel.

[zstine]

using a pump driven by the 800psi brine to drive a second pump to supply water to the pressure pump is a valid way to recapture energy. similar concept to a turbo, but A tubine would not be the type of pump needed since we have high pressure with low flow. you would want a positive displacement pump, like an axial piston pump. the driven pump would reduce or perhaps eliminate the need for the pressure reduction needle valve. the driven side would need a slightly bigger displacement since more salt water goes into the WM than comes out in brine... certainly sounds doable and viable BUT expensive. stainless steel pump heads run near $1000. you need 2 for this recovery system. could experiment with cheap pressure washer pumps for a few hundred $. wont last long in salt though.
edit.. I see you want to drive a generator head.. so that's only 1 pump head needed plus the generatorand some control/ electrical equipment. still viable.

[PirateGuy]

Originally Posted by Sailmonkey

Turbines work on flow volume more so than pressure.

After the regulating valve the pressure should be near zero as there is no restriction in the flow to the overboard discharge.

What is the fluid flow rate required to operate these 10 watt micro turbines?

FYI, at 12.6-13.2 volts 10 watts is .79-.83 amps. You’d be better off with a small solar panel.

This👍🏼

[mitiempo]

I have a Spectra 380C. It produces about 14 gallons of fresh water per hour. It has a 10% Clark pump. That means it rejects 90% of the input as brine. So 126 gallons per hour brine flow. That should give you an idea of what kind of flow you have to deal with.

By the way the 14 gallons of fresh water production consumes 18.5 amps @ 12 volts.

[Mike Banks]

No. There is no free lunch.

[Adelie]

There is no free lunch, but you can spend money to minimize waste.

I've reconsidered my earlier statement about not enough flow rate. I still wonder how much pressure differential there will be and whether back pressure will cause problems at the membrane.

But for $10 it's worth trying it just for the experiment. My kind of thing.