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 Gasifier design considerations....

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tritowns



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PostSubject: Gasifier design considerations....    Fri Jul 17, 2015 11:35 pm

So, I've decided to post some thoughts here on gasifier design in general. While I've been very fortunate to have a few experts in the gasification field mentor me I don't think most people get that lucky and are left stumbling around in the dark or looking to youtube and it's over 95%of bs from those looking to have their 15 minutes of fame. And so you know, this group has inspired more than one part in my systems... so thank you all that post.

So where to begin... If you have a specific question that you'd like covered here in this threads (hopefully) subsequent posts PM me... and I'll then formulate a response to be included here... and no I'm not going to post plans for designs here... this is about inspiring thought and ideas to put into your system should you chose to build one.

So, Gasification for the little guy will typically be batch mode fed for simplicity, as opposed to continuous run 24/7/365. Even some thing that has an auger fed hopper system is batch mode if it needs to be shut down for maintenance. Most people aren't going to build that large so we're not going to consider it here.

The four stages of gasification...

Drying.... It is what it is... heat rises (funny that eh?) this will drive off some of your feedstocks moisture content. where will it go? 40lbs of wood at 20% moisture has a gallon of water in it... do you want that to go through your system? water has been know to put out fires... and other nasty things inside a gasifying unit.

Pyrolyzing.... Heat driving off CO2 and more water vapour as well as wood tars.... oddly enough this can rise up though the feedstock and make it wetter... kinda makes your drying stage important now don't it... This stage is where your wood turns to carbon

Oxidization... Adding oxygen, char made from pyrolyzing glows insanely hot... melt steel hot... turns stainless touching it back into regular steel hot. How much air do you need? just enough... too much and you've made a fantastic heater.

Reduction... This is where all the magic happens. the carbon that is here is super heated and highly reactive... more so that the hydrogen is that is attached to a water molecule. This super heated carbon robs most oxygen atoms from anything passing by... H20 now becomes HH and CO... CO2 becomes 2 x CO. There are some other conversions but those are the two most important. Notice I didn't mention wood Tars... How big of a reduction area do I need? Well, too small and you don't get full reduction of gases. Too Large and you cause un necessary drag on the system overall... Unless you are pushing on your system to feed your engine , your engine has to drag that now combustible wood gas, kicking and screaming out of the system... hence the engine derating while running on wood.

Well, that's it for now... I'll post more to the point type stuff in the near future but atleast we're all on the same page now.. Very Happy
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tritowns



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PostSubject: Re: Gasifier design considerations....    Sat Jul 18, 2015 3:31 am

I have already covered Gasifier math in the gasser math thread in the power generation section of this forum. There you will find the math involved for calculating the restriction sizing to run an engine at a given RPM... normally this is it's work load speed... for most north American small engines it's 3600.

From there we'll go onto building materials, and design considerations for using what you're gonna use.

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T2H
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PostSubject: Re: Gasifier design considerations....    Sat Jul 18, 2015 2:48 pm

Thanks tritowns, I do remember you doing that, much appreciated.
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CVI04



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PostSubject: Re: Gasifier design considerations....    Sun Jul 19, 2015 12:14 pm

Thanks tritowns, I've been considering building a gasifier, but just trying to get things figured out in my head first.
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tritowns



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PostSubject: Re: Gasifier design considerations....    Tue Jul 21, 2015 12:41 am

So materials... I'm a big believer in use what you got... Gasifiers typically aren't square, and for good reason when you're trying to have a certain area hot (but not too hot) it's hard to get into corners.

Cylinders are the preferred shape of choice. Thankfully you can find cylinder shapes in expired propane tanks, water tanks, air tanks... lots of sizes to choose from.

Sch40 steel pipe is easy to be had for reasonable prices... and some times you want a thinker wall on certain parts.

Many people will look for stainless steel thinking that it will yield a superior gasifier. I have only ever built with mild/carbon steel. Stainless expands more than mild steel, and if used as a cooler you need 60% more surface area than mild steel.

As far as other exotics go, while they can work and do work, you can typically get by with regular steel if you design around it's short comings. It's biggest being it starts to degrade at temperatures over 500 degrees F.


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tritowns



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PostSubject: Re: Gasifier design considerations....    Tue Jul 21, 2015 11:42 pm

So you have an engine you want to run on woodgas,done the math for sizing your system, have gathered up some metal to do a build with... What type of feed stock are you going to use?

Your choice of fuel will determine a lot about how you build your reactor. There is no such thing as a one unit does it all... I wish there was, but there isn't.

I have found though running engines (and this is very close) that 1Kw needs 2Hp and 4lbs of wood and hour.

So an engine actually making 10 Hp on wood gas is gonna use 20 lbs of wood an hour. That's dried wood not green. Species aren't all created equal, some woods are more dense than others. Some also have a lot more mineral ash you will have to contend with. Oak is an awesome wood, but has a lot of tannic acid which can lead to hopper erosion.

Oh, so I remember, typically condensate from the hopper will be acidic... any condensate after the hearth should be base... just the way it is.

Do you have access to the amounts of dried feed stock that you will need to run your unit as much as you're going to want to run it? Do you have to go get that feedstock yourself out of the forest? Do you have a means to process it and dry it? All these questions are as important as the actual design of the final system you build... Always more to ponder...

Stay tuned more to come.
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T2H
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PostSubject: Re: Gasifier design considerations....    Wed Jul 22, 2015 6:39 am

tritowns I appreciate your experience and as well giving points to consider in diving into this realm.

My thoughts are when someone says there is no such thing as a one unit does it all.......
Now there is a challenge to be taken up.

A system that can burn different fuels and obtain good gas production.

So now I want to develop a unit that does it all, well within in reason:>) lol

I never let anyone convince me a thing cannot be done.

Problem with that line of thinking is the creation of a box that many researchers choose to reside in based upon their own experience and experimentation.

Just because their experience and experimentation says they have not achieved such a thing does not mean it is not possible.

It may not be worth it in the long run, but I do not believe it is not possible.
No such word in my vocabulary, I think Edison and the wright brothers would agree.

I do not live in boxes created by others and when I am told that is the way it is and this is how it is done and it cannot be done any other way................. I think ok you can stay in that box I am not.

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tritowns



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PostSubject: Re: Gasifier design considerations....    Wed Jul 22, 2015 7:20 am

My system that I sell is set up to be swappable. I know I have had it fuel everything from 8 HP to 25 HP.

LOL... I do get it, hence why I'm building the unit I'm currently working on.

I do wish anyone good luck on any of their endeavors.

Sizing is everything, trying to get a 10HP engine to run on a gasifier that is designed to run fist sized chunks for a 350 Chev is gonna be more than a little hard... it may run for a short period of time if it's already very hot to start with, but it won't run well long as the gasifier wouldn't pulled on hard enough to keep making good gas. And you wouldn't fill the hopper with rice hulls and expect it to make good gas for that 350 engine with a system set up for chunks. Always so much to consider.

I suggest writing out what your real world requirements are and then build to meet those needs. I'd rather build two complete systems that work perfectly for the engines they are to fuel than one system that kinda does it, but not well.


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PostSubject: Re: Gasifier design considerations....    Wed Jul 22, 2015 7:26 am

I do know and have considered all that you have shared.
Even in my response to you was in a light hearted manner, already seeing ways in my mind as to how to achieve it which you eluded to in your response.

I realize you would need to have modules that could be added or changed out to meet different fuel needs, thus why I said may not even be worth the effort.

Now in an apocalyptic world scenario we know the answer would be yes it would be worth it:>)

Thanks for all your suggestions and advice, all great primer for those of us ready to dive in.

I have all the materials right now, I am in the middle of finishing up a slip roll built from free treadmills I picked up off of craigslist that I need to get done before my gasifier build.

I have found that the Chinese are now selling a system on ebay for about 2,500 US dollars.

Anyone who have and will be purchasing them will find in a year or two a failed system due to corrosion and temp limitations in the burn chamber and yet people are lining up to buy the dog gone things from them.
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tritowns



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PostSubject: Re: Gasifier design considerations....    Wed Jul 22, 2015 8:31 am

Most of the people I know of that bought the stak variant have tried imbertizing it... with and without success... I have lots to post here... and I'll slowly continue too as I have time at my desk at the shop.

I really do want every one to succeed with gasification.

I will post some stuff here that will be more than worth the wait.
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tritowns



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PostSubject: Re: Gasifier design considerations....    Thu Jul 23, 2015 1:37 am

Safety,

This is from a owners manual I made for the last gasifier I shipped out....

"This system uses heat to produce combustible gas. It could cause serious harm or
death to those around it if not respected.
Be cautious, the gasifier can be hot!
This unit generates colorless, odorless, tasteless, poisonous carbon monoxide gas. Always use the
gasifier outdoors. If you should begin to feel faint, nauseous, or have pin point vision seek fresh
air immediately. This is NOT campfire smoke, even though it may smell similar. Even though
the gasifier system may be turned off, the gases will still be inside the system.
Never park a gasified vehicle or generator in a garage the same day it is run. There may still be
toxic fuel gas in the system.
Please take note that when you are doing maintenance (especially opening the hopper or the
gas filter) that the system still contains large amounts of gas.
Always have a carbon monoxide meter in the area where you are working. Carbon monoxide
meters are available at hardware stores in the smoke detector section."

Where will you house or keep your system when not in use? As always lots to think about...

So you built a system, have you made provisions for the ignition of flammable gas inside the unit when it's hot and running? Most builders will incorporate some form of puffer or puff lid. To be honest puffs (gas igniting in the hopper) aren't really that worrisome... when designed for it there is just a gentle wooof kinda sound and the lid raises and lowers letting out excess gas.

A back fire (gas igniting below the grate) can be a little different can of worms... typically happens when your feed stock gets lower than your nozzles and can send everything left in your hearth area into the heavens.... a shower of sparks and hot coals ensue... not really that fun to deal with and tends to scare the living heck outta ya... I've only had that happen once and it was my fault.
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tritowns



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PostSubject: Re: Gasifier design considerations....    Fri Jul 24, 2015 12:18 am

Ok so the things I consider most important when looking at designing a system (gasifier)

It's all about conservation of energy.

Hopper condensate. Anything I can get out at the top of the system doesn't have to go through the hot area and cool it. Every time you cool the reaction down you pose the threat of making tar... not a good thing.

Insulate your hearth from the inside. Max Gasman was always telling me to "stop heating the crows..." Use every bit of your naturally occurring heats to drive the system to make gas. Any time you pull heat from an area that needs it you have to consume more feed stock to reheat it... instead of making wood gas. It may be hard to believe but the ash and char that is naturally made in the system is wonderful insulation. So take advantage of it in your designing.

Incinerate tar inside your system to drive the reaction... You can't easily filter tar out of wood gas. I've watch many people just keep adding another filter to no avail. It is far easier to just not make it in the first place.

Do not pull heat from the reduction zone to preheat your incoming air. The reduction zone needs that heat to make co and hh. People will try to overcome this stealing of heat by increasing the reduction zone char bed size... it still needs the heat to convert to co and hh and you now have added unnecessary drag to your gasifier.

Any heats after the grate are fair game for your air preheat, and the faster you cool the gas (by air preheating) the less actual system cooling you're need over all.
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tritowns



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PostSubject: Re: Gasifier design considerations....    Fri Jul 24, 2015 11:22 pm

So where to start... after trying a fema system I decided I needed something better. I didn't just want to build what everyone else was.

I stumbled upon work by Stephen Abbadess who was using wood gas to test a small steam turbine he was developing. He hadn't ran an engine with his design so I asked him if would mind me trying. His opinions were very positive. Needless to say we have been sharing and collaborating on ideas ever since.

This is what I started with...



I had to figure out on my own nozzles spacing and sizes but I can honestly say it worked pretty good. Good enough that is the basis for most of what I do gasification wise.

Stephen has on more that one occasion posted to the web tecn drawings of his complete gasifier. You can check out his systems and other work at http://northernselfreliance.com/
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tritowns



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PostSubject: Re: Gasifier design considerations....    Fri Jul 24, 2015 11:35 pm

I'm a big believer in using the KISS method of design.... every piece of steel you add to a system makes it that much heavier and is one more place that can fail.

A fellow in Sweden asked me to look at a drawing he was thinking on building... simple as simple can be. His hearth was to be made of 8" sch 40 pipe some flat plate and a short piece of 3 1/2 sch 40 tube to be used as a restriction ring.

His ideas were solid in that a natural occurring char cone would insulate the inside of the oxidization zone. He forgot though that your reduction area is as important so I suggested he add a piece of 6" sch 40 hanging below to act as insulation... Something like this



Done this way the whole hearth is self insulating.... all heat after the grate can be used for what ever you like with out disrupting the reactor process itself.
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PostSubject: Re: Gasifier design considerations....    Sun Jul 26, 2015 12:01 pm

So is this self insulating due to the char cone section?

Makes sense, also thanks for going into detail about tar and how to avoid it, all conclusions I had come to before reading it.

Also the thoughts on insulating and using heat off the system to pre heat the main air injection.
Thanks for sharing your thoughts.
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tritowns



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PostSubject: Re: Gasifier design considerations....    Sun Jul 26, 2015 11:32 pm

Yes, it is self insulating because of the naturally occurring ash/char cone. Ash inside a gasifier should never appear as white/gray. If you find white coloured ash it probably means excessive oxygen or an air leak.
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PostSubject: Re: Gasifier design considerations....    Sun Jul 26, 2015 11:36 pm

Ok, thanks for the tip on what to look for on excessive oxygen.
It will be fun paying around with different ideas and ratios.

It has really been nice of you to cover the essentials which I think many of us do not consider since most of the gassers out there posting videos really do not cover the details.

Thanks so much, really.
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PostSubject: Re: Gasifier design considerations....    Mon Jul 27, 2015 4:53 am

also thanks here as well tritowns
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tritowns



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PostSubject: Re: Gasifier design considerations....    Mon Jul 27, 2015 11:17 pm

Nozzles... or limiting the oxygen into the system.

Short of having an open top you'll need to get air into the reactor in the proper location for it to do it's magic.

There are lots of tables to be found on line that will get you in the ball park. It's funny that what most people call the Imbert tables are really tables developed by the Swedes in the 70's and don't have anything to do with Imbert at all.

How many nozzles and how big? Well common practice is to have a nozzle for every 4" of circumference of your nozzle ring. incoming air can only spread out so much because your feed stock is in the way.

How big of hole do you put in the end? After a whole lot of math that I did myself I discovered that most past nozzled units had a total combined cross sectional area of between 5% to 9% of the cross sectional area of the restriction. Myself I usually start at 5% and work my way up from there.

How do you tell when your nozzles are too big? This was something I was told by one of my mentors and later seen first hand it's effects... start off with a size you know will make gas and then slowly enlarge them, testing by running the engine you wish to fuel every time you do so. When the gasifier starts puffing when the engine load is removed go back a couple of sizes and you should be good for that application. Very scientific...

I personally tend to run a lot smaller nozzles than most people out there because of the feed stock I use. I feel smaller nozzles give better penetration into the feed stock that what a larger nozzle would.
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tritowns



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PostSubject: Re: Gasifier design considerations....    Mon Jul 27, 2015 11:27 pm

Just a pet peeve of mine... when is an Imbert not an Imbert... or are all gasifiers that have nozzles Imberts?

I can say quite positively that not all nozzled gasifiers are Imberts. The system i build has nothing to do with Imbert math or design and only shares it's similarities in the respect that it has nozzles... nothing else about it is Imbert.

It kinda drives me a little crazy when someone says they built an Imbert gasifier... really? Your gasifier looks like this?



Notice no method to remove excess moisture from the hopper, not self insulating.... why would you build that limited machine?

Again, just one of my pet peeves. Take credit for your own work... you deserve it.
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PostSubject: Re: Gasifier design considerations....    Fri Jul 31, 2015 2:12 pm

Great stuff triwowns, will be regurgitating this:>)
So by size of hole in the end of the injectors, do you mean what diameter of tube or really do you mean size of hole, or is it both diameter of tube and size of hole?

Really great stuff, I love it gives me some good reading to digest and mull over.

Now as far as removing excessive moisture, it would appear to me that the moisture would rise deflect off the top of the lid, would most of it drop back to the bottom of the outer housing between the two walls where the gas is ejected?

If so, it would basically now be recirculating water back into the system.

With having a conical top would you think it would be productive to add a third outer chamber in where the condensation would be deflected into it like say some water distiller systems I have looked at.

Or straight forward what you tritowns do?

Thank you very much for taking the time and effort to provide information and as well to get us to think the process over, love it.
Now your starting to sound like a professor.
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tritowns



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PostSubject: Re: Gasifier design considerations....    Fri Jul 31, 2015 10:07 pm

I'm going to answer this with several posts from the shop once I get there... for now here is another drawing pulled off the net for y'all to ponder

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tritowns



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PostSubject: Re: Gasifier design considerations....    Fri Jul 31, 2015 10:23 pm

In the imbert system pic I posted the inner hopper is sealed off and surrounded by hot exiting wood gas.

I don't build that way. While I can't show you exactly what I do as that is part of our systems magic... lol... I will say this.

System heat comes from the hearth and rises up the center of the hopper. Hot gasses hit the lid and flow outwards to the hopper vessel body. It does this in any system that doesn't have the feedstock hopper surrounded with hot gas like an imbert. If the top and sides of the hopper are cool, condensates will from and can be collected before they get too close to the hearth to re vaporize or get sucked through the system. Why not work to encourage those natural gas flows so that they help dry out your feedstock.

Everything I do in the systems I build is done with a purpose and has been tested for hours to make sure it works for the benifit of the whole system.

I can't stress enough having goals written down for the system you want to build... keep them in front of you, it makes it easier in the designing in the long run. I can't begin to say how many mistakes I could have eavoided had I done this... lol...


Last edited by tritowns on Sun Aug 02, 2015 1:49 am; edited 1 time in total
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tritowns



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PostSubject: Re: Gasifier design considerations....    Sat Aug 01, 2015 12:59 am

Nozzles....

a nozzle is a nozzle is a nozzle... lol

I have seen where the a pipe is used as a nozzle or a pipe is threaded inside and acts as a carrier for a plug that is drilled with the right sized hole for a nozzle... I tend to use that later.

I find that 1/2 sch 40 pipe can be threaded for 3/8 pipe plugs and they work well for nozzles up to 1/4"

I am now with using 1/8 sch pipe as a nozzle as well... it is welded closed, that welded end flattened and then drilled with the right sized hole. Here is a pic of what i'm trying, and so you know, I haven't shared this anywhere else yet.





I think you can figure it out from here.

as always the total combined CSA of the nozzle holes should start out between 5% to 9% of the restrictions CSA
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PostSubject: Re: Gasifier design considerations....    Sat Aug 01, 2015 2:28 am

Here is an excellent article on getting the wet out...

http://www.allpowerlabs.org/gasification/resources/papers/monorator.html

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