Omni-fueled Gasifier

[ben]

Larry Dobson wanted to share one of his latest gasifier developments with us. Its an omni-fueled gasifier with a unique heat exchange setup. Larry has over 35 years of gasifier experience. You can find his work here.

This is his letter to me:

I’m greatly impressed with the professional work you’ve put in on this webpage, gasification blog/information-center. I have been doing R&D in biomass energy and gasification for 35 years, and have much to share on the subject. However, I am also working on other alternative energy technologies, such as wind and water, and am currently too busy to apply myself fully to the gasification arena. I have been working on the latest plans for a super-gasifier for over a year now, and have decided to make the half-finished design public in order to get others with time and inclination to develop the design further and continue the R&D. The description below and the graphics files attached show the basic concepts, which you may well appreciate, considering your considerable R&D work. I would appreciate it if you would post this info as you see fit, or tell me how best to do so myself.

Warm regards,

Larry Dobson


Any one interested in building a gasifier, do check this one out! http://www.fundamentalform.com/html/biomass_gasifier_breakthrough.html



OMNIFUELED GASIFIER



I have a design for a gasifier that I want to share with the world. It is the culmination of my 35 years of work in the field, and I think it will solve many of the problems that now plague those modeled after the old WWII Imbert gasifiers.

The design is based on the following observations and discoveries:

Fuel in a hopper gasifies best and most evenly, without bridging, when it is vaporized/gasified evenly at the base of a vertical-sided hopper. Whenever there is constriction without size-reduction from burning or gasification, as is often the case in the upper throat of an Imbert gasifier, bridging and uneven gasification occurs.

Whenever there is bridging of the fuel, air supports combustion beneath the bridge, creating hot flames and a spent gas with excess oxygen and little if any energy value. Then the bridge collapses, quenching the flames and heat with cool damp fuel and steam, creating a burst of sooty gas, followed by diminished cool gas production.

Providing the first feed conditions are addressed, preheating the incoming air can almost entirely solve this problem, if it is hot enough (800-1200F), because the endothermic gasification is sustained in a deeper coal bed by the heat of a lesser volume of air. This is quite different from conditions created by a larger volume of cool air, with its oxygen content creating combustion to supply the heat along with lots of diluting nitrogen and CO2.

Of the three fundamental thermodynamic ingredients of Time, Temperature and Turbulence, Time is too often neglected in favor of (old school) Turbulence, as in the jet of speedy air shooting from the tuyers of a downdraft gasifier. I have found it better to let the air slowly permeate the fuel, heating up a large mass of fuel slowly, evenly, creating a large hot coal-bed. letting the gas become saturated with CO and Hydrogen over time and temperature.



Most of my earlier prototype gasifier/combustor systems were based on a rectilinear side-draft gasification flow through a narrow fuel column into a close-coupled combustor surrounded by a ceramic heat exchanger that would preheat the gasification air to at least 800F, even using fuels with up to 2/3 their weight in water. For more details on my previous work, visit http://www.fundamentalform.com/html/energy_from_waste.htm



This new design is superior in several ways:



· The hopper and entire construction is cylindrical, creating more even feed and flow, less thermal stress, simpler construction, more reliable seals.

· A small fraction of the generated gas is burned in a concentric combustion shell, which feeds heat to the incoming air and fuel in the hopper, augmenting the calorific value of the produced gas without diluting it with exhaust, thereby requiring less air for more gasification of a higher quality gas.

· Highly preheated gasification air is introduced to the preheated fuel through large openings between conical slats that create the desired steady-state fuel feed without disruption of the simmering coal bed.

· Any fuel that will fit in the hopper and produce a combustable gas can be gasified ~ logs, chips from the tree trimmers, bark, sawdust, corn cobs, leaves, wood-, straw-, municipal solid waste-pellets, green and wet biomass (up to 2/3 water), household and farm waste, etc.

· A conical grate at the base rotates to dump ashes and break up any bridging.

· Ideally, a microprocessor controller monitors temperature, gas quality, changing conditions at the grate base of fuel column, air preheating, etc. to optimize gas generation quality and quantity, and can also be adjusted to create maximum biochar production instead of CO + H2 if desired.

The technical drawings associated with this design only show the basic concepts, leaving details such as interpenetrating gas and air ducting, lid, seals, dampers, etc. up to the innovation and skills of the fabricator. Initial prototypes may most easily be built of 1/8” 304 stainless interior (cheapest high chromium), including the combustion shell, shown in the drawings as ceramic. There will be areas of thermal deterioration and other preliminary details to be refined down the road, but I hope this gets the show on the road!

Simplified versions can be built initially. The interior fuel/air-feed configuration would also work well with a simple heat-exchanger preheating the incoming air with heat from the producer gas instead of the more complex concentric combustor/preheater.

I’m trying out a more direct approach to materialize my inventions. Rather than involve corporations, grants, entrepreneurs, banks, taxes, patents, and protection in all the ways sanctioned accountability reaps its share and retards the process, I am going as direct as possible. which is to fully share my gift wherever I dare give up security, in this case these drawings. Can the people manifest directly, as a government of the people, in a new creative spontaneity, in a far more satisfying directness? Ah.....life is such a discovery these days!

This is no longer a patentable design, as I hereby release it to the public domain, in the hopes that others will implement these new design features and do the R&D work necessary to bring biomass gasification to a new level of practicality, offering a greater contribution to decentralized alternative energy technologies.

[Larry Dobson]

I like it! I'm throwin a party now for my son, a steel drum band leader extraordinaire ~ here he comes now!

[ben]

I will set up an omni-fuel group and we can chat over there.

[Steve Unruh]

It would be easier for me to bring up what stuff I have to either of your locations. I am way off the beaten path and once you've seen one mountain valley. . .well. Take a look: google map Yacolt WA 98675, satellite view, zoom in and our old 1904 farm house in just under the most eastward "R" in E. Yacolt Rd., our trees are aretangular block to the SE just north of the Verizon satellite dishes.
In addition to a too small 10"x19", I have the 12"x20", 14"x21.5" SS shells and a 3/16" by 14" round base plate set up for a 1 1/4" rotating hollow pipe rotating grate mounting.
And I would be willing to buy a sheet of 304 stainless - I will need some panels for my highmass hearth charger bin.
No secrets here Larry - just a brute force "Russian" style fuel wasteful 'get 'r done build. I would bring up this hearth too so you could see the double cast iron primary air heating channels. Good for 400-650F preheating. I will read your paper.
Ben before we roll off this front page - how do you want us to proceed with communication exchange? Your personal blog here? As a group? Emails?
Regards
SteveU.
I will read

[ben]

I'm in Toledo near I-5 exit 57. 2.5 hours + a ferry ride south. Steve is an hour south and east of me. Maybe we can hit everyones shop starting with yours and working south.

[Larry Dobson]

Steve & Ben ~ I'm stoked! As a team, it looks like we have a productive diversity.
To more fully grasp some of the concepts, have you read my DOE report, "Biomass Energy - State of the Technology, Present Obstacles & Future Potential"? It's at http://www.stiltman.com/html/doe_report.html
Sounds like we're all busy this summer, but a person-to-person meeting with anyone in the region who is interested would be good. Where are you located? I'm on Whidbey Island in Puget Sound. We could have a gathering here.

[ben]

Steve,

Its funny you mention Kalle. My next Woody has a better ability to break down the biomass into charcoal and then gasifiy the charcoal. Jonathan Spreadborough has had some great ideas that I am trying to improve upon in my quest for two stage gasification for the creation of natural gas and liquid fuels. Next years big project.

Even if cordwood had to be cut in half it would still be a very viable solution. Most wood around here is a good species for gasifying too.

It sounds like you like to turn wrenches which is good because that is my least favorite part. Ive owned too many volkswagons!

[Steve Unruh]

Yes Mr Dobson, very serious.
As you have noticed Ben is a very quick, good fabricator. I've seen his welding - excellent. And his modern communication skills are self evident too.
Me: I can barely type and am even camera shy. But as a slow, methodical grind away rock type I could be chained to a table and do the slow inch by inch TIG welding hearth area stainless would require.
As a recently retired master auto tech I am accustomed to thinking about moving heat around with liquids, gas/liquid phase changing and even with just air movements.
Ben as horrified as I was with your liquid jacketing idea (I had visions of smoky out door wood furnaces and every gooy, sticky tarry overcooled stovepipe/chimney I've had to clean with an air to air heat recovery unit in it) I think now you are correct. Maybe with a thin half hight water filled cooling jacket we could then cool the output fuel gasses below 212F (100C) to condense the water vapor out of it for IC useage. The cooling water would be warmed perfectly to be a domestic hot water source. The European gas engine men are then even slightly reheating the fuel gas above moister dew point before feeding it into an engine.

Larry the appeal to me, and sounds like Ben is the possiblity to have somthing that will fuel with commonly availabe and understood cord/stick wood form. The used base is hugh. Look on every corner to the out of work fellows with a pick-up and a chainsaw and a load of wood for sale. I know of a few thousand off-gridder in the US/Canada alone. Think of all of the (yuck!) outdoor wood furnace manufacturers and users. Many would like a system using their wood to make a little electricity in addition to heat. Having to mechanically reduce this wood down to a uniformly sized, 15% moister dryed chip or chunk is where "everyman" master of his own heat and power is stalled at now. Too much machinery, too much dino-fuels and too much man-hours to honestly call a sustainable solution yet.
With practical construction considerations you would have to keep us on track not to compromise out the essential element of your design proposal as I understand them: unrestricted fuel flow; intake air counterflow prewarming, then then heating with output fuel gases, then a final oxidization level superheating before introduction; slow non-turbulent fully enveloping pyrolization?,partial oxidization and reduction? of the fuel charge; and active mechanical manipulation (viva Kalle!) of the char.
Regards
SteveU.

[Larry Dobson]

Steve,
You are correct for the most part in your analysis of the process. Unless you have a very large efficient final heat exchanger, you may not get condensation just heating the gasification and sacrificial combustion air, simply because the flow is so low. It can be done, and would be worth developing for applications like a mobile IC engine where cogenerated heat is usually wasted and condensing H2O out of the gas is necessary. If you have a use for the waste heat, like heating a building, higher flow volumes of air can cool the gas more efficiently. I would begin with a simpler version, eliminating the air-preheat combustion shell, incorporating instead a concentric heat exchanger heating the incoming gasification air with the outflowing woodgas. This will not give optimum gas-energy content nor handle green cordwood as well, but will be simpler to construct and test. I would not use mild steel sheet for the inner lining or hearth, since it will probably burn up too fast. Use thin 304, which isn't that expensive. Remember, the more you preheat and insulate the incoming air, the less chance there will be of super-hot oxidation at the hearth, and the resulting destruction of metals. It sounds like you and Ben are serious about trying it out, and I will help with details. Congratulations on your woodgas furnace running an ICE! I am curious about the details of construction.
LAD

[ben]

Steve,

I may have a window in early August to throw one of these together with you. I would definitely like to see the cordwood burner too. Obviously that would blow the market wide open. Cordwood by weight is cheap. Keep your shells. We will build the first one or two in 12 or 14 ga. mild steel to work out the bugs. Then we can step up to 1/8" 304.

I think it needs a big water jacket around the outside for CHP. We'll see. Whose bringing the forklift?

[Steve Unruh]

Hi Guys
Larry Dobson after looking over you previous gasifer/combustor designs I can see you too have become a believer in primary air preheating, process insulation, and excessive moister condensing and removal. This is good. Too many designers ignore or disbelieve these factors.
In defense of stovers: if successful they have learned anumber of things.
How very hot and how much time it does take to cleanly, completly final dry, heat, pyrolize, oxidize/reduce/combust wood fuels. At these temperatures and times you learn very fast how quickly cast iron, sheet and plate steels and even stainless can be destroyed with too much oxidization Turbulence. I have an 8 stove collection as proof. Once learned I now use 40% less
wood and haven't had to clean my 23 foot chimney in 14 years. And wood stovers learn just how much bloody hard work it is to collect, process, dry, cover store, and handle a 5000 hour useage in a years supply of wood fuel.

Larry if I may restate, correct please:
The heat source to drive all the processes is from controlled sacrificially oxidizing some of the wood fuel as I and probably Ben hope the volatiles portion.
Then we "barrow" some of this heat to vaporize the excessive air in humidity, fuel moister, and even keep vaporized the normal oxidization H2O bi-product.
The super heated water vapor is then used to transfer this "borrowed" heat into the reduction process and other than the small amount reduced there continues on through as a hot vapor out with the fuel gases and give back the last remaining useable "borrowed" heat to pre-warm the incoming air stream as it is condensed out as a collectable fluid out of the out going fuel gas stream.
Heat is not lost or thrown away out side the process.

Ben, I will call you. This design will require 5-6 shells. I have some stainless shells I will not be using now in pursuing my own stationary high mass design. We are close enough I could contribute to a collaborative build up to test just how Omni - fuel this design can be. (Sh-h-h, I have now been able to get a 1 1/2 hour run time on a an IC engine in a 300 pound cast iron hearth - on 16" firewood.)
I'd like to see if this low flow, low mass design could do the same on vertical stick wood and produce the 45 CFM fuel gas needed for my India woodgas engine conversion.
Yes I know, time on our farms. Really is none until October/November slow down.
Regards
SteveU.