11 replies to this topic

[bear@apl]

Hi all,

I just posted results from some quick tests of various low pressure ejector configurations here: http://wiki.gekgasif...Ejector-Testing

We were trying driving this with a 600W DC blower, seeing if we could achieve vacuums high enough to be able to start the reactor effectively.

The results weren't particularly attractive.

We're aiming for a few things:
Vacuum and pull rate high enough to start the reactor quickly
Components that will work in an off-grid (battery driven) setup
Low enough motive gas flow that the mixture will be at or below stoichometric (for combustion of the start up gas)

We've seen that we'd like to ideally achieve 10 inH2O at the reactor to bring it up to proper temperatures quickly.

Power consumption should be reasonable. A standard car battery is 12V 52 Ah or (12*52) = 624 Wh. Of this, you really only want to use the top 10-20% to keep the battery in good shape. This would be about 6-10 minutes of run time at 600W. This blower is also 24V, which would require two batteries.

As motive air pressure goes up, you need to use less of it to achieve a reasonable vacuum and flow through the ejector. We can achieve sub-stoichometric mixtures easily with 100 psi shop air, but air consumption at these lower pressures seems to indicate we'd have a very lean mixture out of the ejector.

The blower itself is very nice, and would be great for drawing the gas through, however the aluminum blades with narrow gaps and poor servicability don't make it attractive for a long-lived solution.

Of the various options for an off-grid startup, we're next returning to the 50W blowers while working to eliminate some of the pressure drops and mixture issues that caused problems on the last round of testing.

I know others have been working with blower driven ejectors with some success. I'd be very interested to hear of others results:
Was the resulting mixture combustible?
What were the blower power requirements?
What vacuum could you achieve and did this start your reactor reasonably?

Cheers,
Bear

[bear@apl]

Here are a couple photos of the parts used:

[Driven Energy]

I had an idea that I talked through with one of your guys when I stopped by APL on Friday. What if you started the engine/ gen set with propane. Maybe even a small Coleman bottle and pulled your air thru the gassifier until the readings from the o2 sensor indicated that the reactor was ready. Then switch over.

[fuel spiller]

Lou Gosselin, maker of the 3g-I Gosselin grateless gasifier uses one but only needs 3in water vac (more begins to pull heat from the reactor). He also says he likes the air ejector for simplicity and reliability.

Just a thought... Would it help to 'choke' down the inlet hole for the ss air lines during warm up (less vol more vac)?

[fuel spiller]

Sorry...brainstorm, with a start from Driven Energy's post.
1. start Kubota on bottle gas
2. with a  valve and tee on the exhaust, divert the pressure to a turbo used to aspirate the GEK (flare til 800c)

2b. or, maybe mount an auto ac pump to the Kubota to do the same? (or an ac pump powered ejector?)
Good Luck Bear!

[bear@apl]

Thanks for the input all.
Someone suggested using propane as the ejector motive gas.
As a crude run of the numbers:
If we take the 100 lpm air consumption for a good blasting ejector (propane is denser then air, so would use less for a given ejector performance...)
100 lpm = 6 m3/hr.
propane is 1.882 kg/m3 (http://www.engineeri...sity-d_158.html)
6 m3/hr * 1.882 kg/m3 = 24.9 kg/hr of propane
LPG is 500 kg/m3 *  0.003786 m3/gal = 1.89 kg/gal (http://forum.onlinec...read.php?t=4858)
24.9 kg/hr / 1.89 kg/gal = 13.2 gal/hr
So, a 5 gal tank would last 20 minutes (assuming freezing wasn't an issue at this rate)
I think propane runs in the $2-3/gal range, so this would be around $26-$40/hr.
We'd like to be starting in 1/12 to 1/6th of an hour (5-10 min), so something like $2-7 per start up, possibly more if things aren't going well.

Doesn't seem particularly attractive.

We should also note that our performance numbers/desires come from working with finer fuels. Starting up a gasifier run on pellets would take more energy/air/propane than something with less flow resistance.

Driven Energy: I had an idea that I talked through with one of your guys when I stopped by APL on Friday. What if you started the engine/ gen set with propane. Maybe even a small Coleman bottle and pulled your air thru the gassifier until the readings from the o2 sensor indicated that the reactor was ready. Then switch over.

Well, when compared to using propane for the ejector, something like this looks better. The Kubota gas fuel consumption is around 0.3 kg/kWh, so, if you ran a compressor at 3 kW, you'd be close to 1 kg/hr of propane consumption. If startup was 10 minutes, that would be 0.05 kg of propane, or about $0.10-$0.20 of propane. This would require a propane regulator and compressor as part of the system.
You'd gain the benefit of nearly instantaneous power (less compressor usage) until the reactor came up to temperature.

Note that you wouldn't want to be running the gas through the engine and out to the O2 sensor via exhaust during startup, due to the quality of the gas. But there are other ways to know the gasifier is working well - primarily the internal temperatures, but possibly instrumentation of the flare if needed.

fuel spiller: Lou Gosselin, maker of the 3g-I Gosselin grateless gasifier uses one but only needs 3in water vac (more begins to pull heat from the reactor). He also says he likes the air ejector for simplicity and reliability.
Just a thought... Would it help to 'choke' down the inlet hole for the ss air lines during warm up (less vol more vac)?

What fuel size does Lou use/recommend? We tend towards using finer materials that have additional suction requirements. Chunks and cubes are a lot less demanding. Also agreed on the ejector for simplicity/reliability (they just require a good deal more energy, which becomes an issue when trying to design around battery based operation).

Bringing the reactor up to temperature is more a function of air flow into the reactor, not the suction on it. Suction is a proxy measure for gas/air flow. So, the goal would be to reduce any pressure losses in the system to get more air into the reactor at lower pressures.

Towards this end, bypassing the packed bed filter during startup will help. Going to larger fuels would help, but we want to maintain the ability to work with finer fuels. Adjusting the air nozzle size would help a little, but the air lines and nozzles only contribute an inch or two of pressure drop at the desired flows, and you need smaller nozzle sizes for an effective jet into the combustion zone.

Cheers,
Bear

[fuel spiller]

Lou's unit runs on small wood pellets, but it has a rotating cone over the straight hearth. It runs 5- 10 horse i.c.e.s, with a very small amount of hopper.
His last posted email address
elevatorman@shaw.ca
BTW... a power pallet with an automotive a.c. pump hooked to a 'spare air tank' (with a pressure switch run to the clutch) would be a handy option for rebuilding a comunity. If the tank was large enough (or ganged together), could it start the gek on stored air?

[Driven Energy]

What if instead of starting on propane, you started on stored wood gas?

[fuel spiller]

Way back in highschool, I recall students burning 'biomass' in a homemade vac pump made from a plastic milk jug (bottom cut off) being pulled up from a sink or bucket full of water (aka grav. bong).
Scaled up to a 55 gal drum and a secondary containment tank, one could draw and store 200 liters of woodgas. (A small hand winch used to raise and hold). This device could also provide suction to draw air thru the gek for start ups.

[Driven Energy]

I have seen old pictures or compressed (high/ med pressure) wood gas circa 1940's on vehicles. I have heard that it degrades quickly back to H20. Anyone have more background on why high pressure storage is a bad idea?

[fuel spiller]

Bear always has a way of putting it best...
http://www.gekgasifi...hread.php?t=246

such a common question, This should be part of the FAQs

[fuel spiller]

While looking at old photos, I see that every blower/ fan used seems to have a gear reduction (the motor is offset from the center of the blower housing) most look like this was "done in shop".
Perhaps a clothes dryer blower box with a jack shaft (for reduction) run by a 12 vdc motor (less than continuous duty but longer duty cycle than a starter motor has).

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