FEMA wood gasifier demonstration and DIY specifications

If you google "fema gasifier" there will be several documents that should pop up. Below is an example:

http://www.soilandhealth.org/03sov/0302hsted/fema.woodgas.pdf

The design itself is proven and safe to say as sustainable. You can use this to generate biochar as an added benefit. There is a surprising duration of energy generation and the model can be scaled to meet higher energy requirements.

I would stop short in calling this particular design as "proven"... unless you wish to emphasize that it is proven to generate a lot of tar and destroy engines. In short, this design (i.e. the "FEMA" gasifier) is well known among gasifier enthusiasts for generating a lot of tar. The problem with this is that an engine powered by such a unit will require a lot of regular maintenance. It's not a bad idea for use as an emergency unit when nothing else is available - more important, this is precisely what the system is designed to accomplish (emergency, and nothing more). Personally, I believe that a FEMA system could be optimized for a very particular fuel and, if run at a more or less constant output, then I believe it could make a reliable and useful unit. However, it's probably best to take the next step and go with what is known as the "Imbert" design.

The single best resource for this technology is the Handbook for Biomass Downdraft Gasifier Engine Systems: http://taylor.ifas.ufl.edu/documents/Handbook_of_Biomass_Downdraft_Gasifier_Engine_Systems.pdf

FEMA design is just that, an EMERGENCY plan. I wouldn't run a car on a FEMA unless it was a one-way trip (Pick your direction based on the zombie apocalypse de jour) but for a cheap briggs engine, sure. You can have multiple engines and rebuild kits for less than the cost difference to get to an Imbert.

Marcos Buenijo wrote:I would stop short in calling this particular design as "proven"... unless you wish to emphasize that it is proven to generate a lot of tar and destroy engines.

Thanks for the added link. I have to disagree with you on one point and that is whether this model is a proven design. Personally, I find the videos rather interesting and chose not to marginalize the author's efforts. More to the point and my intention, I think it is polite to give credit to the person in the video who constructed a polished prototype and in my opinion presented the design very clearly. The FEMA design is generally suited to introduce wood gasification and many variations of this design do power vehicles without destroying them.

Amedean Messan wrote:Thanks for the added link. I have to disagree with you on one point and that is this model is a proven design. Personally, I find the videos rather interesting and chose not to marginalize the author's efforts. More to the point and my intention, I think it is polite to give credit to the person in the video who constructed a polished prototype and in my opinion presented the design very clearly. The FEMA design is generally suited to introduce wood gasification and many variations of this design do power vehicles without destroying them.

The purpose of this design is to get engines running quickly for essential functions when only biomass is available as fuel. It is an emergency unit, and should be used as nothing more. While it can do reasonably well with very dry fuel of a very regular size, it will make a lot more tar than the Imbert under all conditions. Therefore, if one desires to fuel an engine over an extended period with biomass, then moving beyond the FEMA design is the wise decision. I think it's important to provide this kind of disclaimer whenever the FEMA is introduced, especially for those new to the technology.

Marcos Buenijo wrote: It is an emergency unit, and should be used as nothing more.

I am confident you have some insightful knowledge but this sounds a tad bit melodramatic to prove a point. Wayne Keith worked pretty well with a modified FEMA design not that I can attest to any working experience as my knowledge is through literature.

Amedean Messan wrote:

Marcos Buenijo wrote: It is an emergency unit, and should be used as nothing more.

I am confident you have some insightful knowledge but this sounds a tad bit melodramatic to prove a point. Wayne Keith worked pretty well with a modified FEMA design not that I can attest to any working experience as my knowledge is through literature.

I consider the primary purpose of this forum as a resource for education, and I'm trying to encourage the reader to take the claim seriously. So, yeah, I'm being a tad melodramatic. The FEMA is a good unit for learning, so in that sense it can be useful beyond an emergency unit. However, all enthusiasts I know of who use gasification on a regular basis and who started with a FEMA unit have moved on. This includes Wayne Keith whose work I consider to be extraordinary. He got good results using charred wood chunks in a FEMA gasifier to fuel his trucks. This is an important distinction. If one removes most of the volatiles from wood (essentially making charcoal in the process), then gasifier design is not so critical. With good charcoal one can generate a clean fuel gas with a steel can and a couple of tubing connections (see Gary Gilmore's work). The reality is that wood + FEMA = tarry fuel gas.

Actually, I am likely more optimistic about the prospects for using a FEMA than those with more experience than I. If you research other forums frequented by those with experience (such as driveonwood.com, the Yahoo woodgas group, or All Power Labs), then you'll find accounts by those with experience who curse the FEMA with a lot more drama than I've mustered. My experience is very limited, but I remain convinced that a FEMA using a very dry and regularly sized wood fuel can serve in a stationary application reliably for an extended period where the output of the system remains relatively high to keep temperature up. A vehicle application where the output must vary over a wide range is probably the worst use for a FEMA (assuming wood/biomass is used and not charcoal).

NOTE: Also, I'm aware of a couple successful attempts to modify a FEMA which took the form of essentially transforming the base FEMA design into an Imbert. One example welded a restriction plate on the end of the fire tube and supplied air to the fire tube via nozzles, and closed off the hopper so all air entered the system through the nozzles. One design also took care to insulate the fire tube. Adding the restriction plate to the base of the fire tube serves a couple functions: (1) ash will accumulate at the base of the firetube between the restriction and inner firetube wall to help insulate, and (2) the combustion gases including tar is force through the restriction where temperatures will be highest. Adding additional insulation can further raise temperatures there which is important for tar reduction. Restricting air supply to a region just above the hearth as opposed to drawing air through the firetube is important as is helps reduce thermal losses that would otherwise be encouraged with combustion taking place over the larger firetube area, and the combustion reaction is isolated at or just below the nozzles which is important for supporting a wide turndown ratio and a variable fuel quality. So, there is some evidence that a few relatively simple modifications to the FEMA can dramatically improve its performance.

Excellent video that covers the shortcomings of the FEMA.

Marcos Buenijo wrote: Personally, I believe that a FEMA system could be optimized for a very particular fuel and, if run at a more or less constant output, then I believe it could make a reliable and useful unit. However, it's probably best to take the next step and go with what is known as the "Imbert" design.

The single best resource for this technology is the Handbook for Biomass Downdraft Gasifier Engine Systems: http://taylor.ifas.ufl.edu/documents/Handbook_of_Biomass_Downdraft_Gasifier_Engine_Systems.pdf

From what i have gleaned form that entire document is that imbert types burn 1% more tar than the FEMA type
The FEMA type burns 99% I do agree it is an improvement , but a lot more engineering/parts to capture that 1% that would be caught in filter medium anyways....
Regular filter changes + liqud collection drains = healthier equipment ... goes without saying

P.S. i'm not saying that 1% isn't important ,if i was drowning 1% more oxygen would be helpful,
I do think home builders could easily create larger inefficiencies modifying designs to capture that 1%

R Scott wrote:FEMA design is just that, an EMERGENCY plan. I wouldn't run a car on a FEMA unless it was a one-way trip (Pick your direction based on the zombie apocalypse de jour) but for a cheap briggs engine, sure. You can have multiple engines and rebuild kits for less than the cost difference to get to an Imbert.

this i 100% agree with

Amedean Messan wrote:I consider the primary purpose of this forum as a resource for education, and I'm trying to encourage the reader to take the claim seriously.

Awesome point glad someone made it , there are going to be a lot of peoples uses and fuel sources that will differ from use to use , and there several types of gasifiers as well...
Once I get a chance i will try to make a table, showing the energy potential compared to bio fuels per acre .... but a second table i will omit is cost against current fuels as it will vary so largely due to regional price and currency differences

In essence i think we can all agree that the FEMA "type" is best for standalone , continuous burn at constant velocity type scenario's...
There are several modifications that can be made to gasifiers in general to make them more efficient (burn hotter/cleaner)
These mods can increase the number fuel types they use , and whether they are variable flow or constant flow for eg...

I don't want the thread to turn "heated" to discourage people in anyway .... it's an awesome , carbon neutral , inexpensive way of power production , whether for electric / automotive or air/water heating and should have more people doing it whom it may be appropriate for .....

David Williams wrote:From what i have gleaned form that entire document is that imbert types burn 1% more tar than the FEMA type
The FEMA type burns 99% I do agree it is an improvement , but a lot more engineering/parts to capture that 1% that would be caught in filter medium anyways....
Regular filter changes + liqud collection drains = healthier equipment ... goes without saying

P.S. i'm not saying that 1% isn't important ,if i was drowning 1% more oxygen would be helpful,
I do think home builders could easily create larger inefficiencies modifying designs to capture that 1%

1% doesn't seem like a lot, but statistics is a funny business. Consider that this 1% may represent a tar load that is orders of magnitude greater than the tar load of a properly tuned Imbert. Also, I express some skepticism that any filtration system will catch all the tar. Therefore, in any case I expect a FEMA design to introduce tar into an engine at a rate many times higher than an Imbert (all else equal). Since the effects of tar on engines is cumulative, then I must recommend that one move away from the FEMA design for anything beyond a genuine emergency or otherwise infrequent/intermittent operations. My line of reasoning is well supported by those with experience, and I encourage all readers to investigate other forums on this topic including driveonwood.com and the yahoo woodgas group. I am not aware of an account where a genuine FEMA design has been used to operate an engine over an extended period without problems (when I write "extended", I mean at least 100 hours of engine operation and preferably 1000).

Let me emphasize again that I believe the base FEMA design can be improved considerably to allow acceptable results in stationary applications. I mentioned in a previous post some modifications that might be done. The goal of any such mod should be to increase temperatures in the hearth reduction zone in order to improve tar cracking. This means that combustion should be isolated to smaller region for higher peak temperatures (i.e. using a nozzle or nozzles), insulation should be provided (using ash build up around restriction ring and/or insulating fire tube), and gas should be forced through the highest temperatures (one purpose of a restriction in the Imbert). Also, the driest possible fuel should be used, and the fuel should be sized properly to minimize bridging or channeling.