5 replies to this topic

[JayAlchemAPL]

The 10Kw genset that was built over the weekend of the free workshop was equipt with a larger filter made out of a 16 gallon drum. The addition of the larger drum is more forgiving across a wider range of run conditions. The greater surface area allows better cooling of the gasses below the dew point of any residual tars and adds a longer life to the filter because there is a larger cross section that the gasses are able to pass through as the filter media becomes spent over time.

<img src="http://gekgasifier.pbworks.com/f/10kwgensetnight-800.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/wetscrubber_largefilterfabrication.JPG" width="250"/>

The larger filter housing was fabricated over the free workshop weekend with the same design of the filter that Jim built in Costa Rica.

Two 1.5 inch couplings were welded at the bottom, one less than an inch from the bottom for draining fluid, and the other an inch above the first for the gas inlet to the filter. The gas inlet is connected to the gas outlet from the drying bucket.
The manometer for the filter connects to a 1/2 inch coupler welded 5 inches from the top of the drum.

The other option that was added to the larger drum filter, was the addition of a wet scrubber. A third 1/2 inch coupler was welded 5 inches from the top with threads on the inside to add a sparger and a fourth 1/2 inch coupler about 3 inches from the bottom to pull the liquid off the bottom with a small pump.

<img src="http://gekgasifier.pbworks.com/f/wetscrubber_recircsetup.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/wetscrubber_recircpump.jpg" width="250"/>

Circulating a liquid through the bed will pick up some larger chunks that should be kept from entering the recirculating pump. A settling dam was added around the liquid out port at the bottom to protect the pump. I will add a fine screen to fit over the settling dam to catch floating bits.

<img src="http://gekgasifier.pbworks.com/f/wetscrubber_settlingdam.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/wetscrubber_daminstalled.jpg" width="250"/>

The sparger was added to the top 1/2 inch coupler at the top to the threads on the inside of the drum.  The sparger could also be fabricated using four 6 inch long 1/2 inch nipples with small holes drilled through out the pipe and caps on the end to distribute the liquid properly. A small 12v fuel pump was used for the recirculation sparger.

<img src="http://gekgasifier.pbworks.com/f/wetscrubber_spargeroff.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/wetscrubber_spargeron.JPG" width="250"/>

The filter media is suspended from the bottom with a grate that is about 6 inches from the bottom of the drum.
The particle size has a lot to do with the pressure drop across the filter. Bear Kaufmann characterized the relation of filter pressure drop vs. particle diameter of the media which followed closely the theory of the Ergun equation.

Adding a recirculating wet scrubber to the media will in theory increase the pressure drop across the filter, which would suggest that filter media with a larger diameter would be needed.
Two manometers were added on the gas inlet and gas outlet to do some cold testing on various filter medias and recirculation fluids.
<img src="http://gekgasifier.pbworks.com/f/wetscrubber_pressuredroptest.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/wetscrubber_pressuredroptest2.jpg" width="250"/>

Any thoughts on filter media, particle size, liquid composition, or method?

[jimmason]

jay, the set up looks good.  two minor points.

1.  the debris dam in the base should let the liquid fill from the bottom, not over the top with a filter to block the debris.  use a taller piece of c to make the dam go all the way up to the grate at the base of the filter.  (for others, the grate is about 5" off the bottom of the barrel.  thus the liquid tank for the recirc can be in the bottom of the same barrel as the recirc filter bed.

2.  the sparger (where did you figure out such a fancy term?) doesn't need to be so complicated.  i suggest you simply drill a few 1/8 or 3/16 holes in the 1/2 nipple going out across the filter.  4 or 5 holes int that at a spread will give you a better distribution with less hardware.  

i think you should start with the same fuel you are using to run the reactor, which is the pine chips.  or, use the smaller material that is screened out to make the fuel stash.

jim

ps.  here's the drawing of what jay is working on / making.

[JayAlchemAPL]

Thanks Jim,
I had just read your message, after putting together a sparger design I think works better (sparger, its what we called it at my old biodiesel plant, yay). This one does allow a better distribution of the scrubbing agent across the filter. It also uses existing parts we ship with the GEK ;), with the exception of the cross.
<img src="http://gekgasifier.pbworks.com/f/scrubber_drillsparger.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/scrubber_sparger.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/scrubber_spargerinstall.jpg" width="250"/>

A matrix of smaller holes are drilled across a cross of 1/2 pipes. There are a total of 9 holes that are about 1/8th inch. These seem to be a good fit for the small fuel pump set up.

The dam has a grate on the top of it to keep any larger chunks from entering the top- charcoal and wood chips do float. Although bringing it all the way up to the filter media support grate itself would be the same idea, I agree. The dam is just tacked in, there are grooves at the bottom of the barrel that are not flush with the bottom of the dam that do allow a flow of liquid to flow through the bottom to some extent.

<img src="http://gekgasifier.pbworks.com/f/sctubber_damscreen.jpg" width="250"/>

I also sieved and washed some of the charcoal for starts, to get some of the smaller/finer particulates out. Washing to get the finer particulates will prolong the life of the liquid phase for any tars to be scrubbed. A range of 1/2 to 2.5 inch chunks will be used as the filter media at first to see the pressure difference between dry and wet scrubbing options across the new drum filter.

<img src="http://gekgasifier.pbworks.com/f/scrubber_particlesize.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/scrubber_washcharcoal.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/scrubber_draincharcoal.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/scrubber_drycharcoal.jpg" width="250"/>

The sparger should go between the filter media and the finer filter (steel wool), this is a typical practice to keep the liquid phase from entering the outgoing gas stream.
<img src="http://gekgasifier.pbworks.com/f/scrubber_ste.jpg" width="250"/> <img src="http://gekgasifier.pbworks.com/f/scrubber_topgrate.jpg" width="250"/>

I'll be sure to try the wood chips next for the filter media. For now I'll circulate water, but wood chips will be better suited for biodiesel, for they could mold and turn to compost faster with water than the expected life of the media to be able to stand filtering tars.

[JayAlchemAPL]

These charcoal chunks were too large to do any significant filtering even with water running through it. The pressure drop was almost negligible and a tar test before and after the filter during a run showed that not much of the filter was working with chunks this large, I over shot it!

Now I'm sifting out smaller bits of wood chips through 1/2in, 1/8th in, and 16th inch screens. I'll do two cold tests with the 1/2-1/8th and 1/8th-1/16th wood bits, to see how adding water will shift the Ergun equation. The Ergun equation describes the relationship of particle diameter vs. pressure drop across a filter. Bear did some work with the Ergun equation that he posted here.

Recirculating a liquid through the packed filter media will likely change the void space variable in the equation.

<img src="http://gekgasifier.pbworks.com/f/sifting.JPG" width="250"/> <img src="http://gekgasifier.pbworks.com/f/16thinscreen.JPG" width="250"/>

Another note,
There was a question about the two bungs at the bottom of the filter drum, the top one is for the gas in, and the bottom one is to drain any liquid that has collected at the bottom.
<img src="http://gekgasifier.pbworks.com/f/lowerbung.JPG" width="250"/>

[jimmason]

that is helpful info jay.  can you clarify over what range you found the largish charcoal with water to have negligible pressure drop?  i think you said you ran it all the way to the max of the ejector potential, yes?

remember that on the dry charcoal chunks, the previous tour of this question determined that about 1/8" grains are ideal.  such size gives an acceptable pressure drop (a couple inches in the beginning at high flow rates), and does good work for filtering.  remember that filtering performance with impact or centrifugal methods like this is nearly linearly related to the pressure drop through it.  you have to see a pressure drop if you are making any progress.   scrubbing will start to change this rule.  electro static methods change it greatly.  but we are in simple impaction here.

it seems you are missing an important 1/4" screen size in your test.  it is likely that the grain size relevant once water is added is a little bigger than the previous 1/8".  1/2" is a major change.  you might want to use everything that will pass through 1/4", with the fines removed by 1/8".  

on a related note, we had to go to lowe's in jasper, tennessee yesterday to get screen to make charcoal for the filter at grant miller's place.  here is a photo of the power hut where we're setting up his gek.   (grant is the one in the middle with his arm on the gek, protecting it from inquisitive neighbors.  why do all the neighbors always show up when someone gets/builds/acquires a gasifier?).





j

[JayAlchemAPL]

With the charcoal above, I actually ran the GEK and took tar samples by pulling it through a fiberglass strip with an air pump. This was a quick comparison to see if I was out of range with the size of the filter media, of which I was. Samples taken before and after the filter looked very much the same with and without the water recirculation scrubber.

In other news, I have sieved out 1/4-1/8th in wood chips and 1/8-1/16th inch wood chips for cold testing.
<img src="http://gekgasifier.pbworks.com/f/1_4thscreensieve.JPG" width="250"/> <img src="http://gekgasifier.pbworks.com/f/1_8thscreensieve.JPG" width="250"/> <img src="http://gekgasifier.pbworks.com/f/16thinscreen.JPG" width="250"/>

The graph below represents the 1/4-1/8th diameter wood chips in the large drum filter filling an area of 1.3 cubic feet. The red points denote dry filter media, and the blue points refer to the pressure drop vs. flow rate while the wet scrubber is circulating water.
<img src="http://gekgasifier.pbworks.com/f/wetscrubber4th_8th.JPG" width="350"/>

I have only tested dry and wet scrubbing with the 1/4-1/8th inch wood chips so far. The 1/8-1/16th I will be sieving out today.