Concept Diagram - Mobile Woodgas System - 1.0.3

Hi Everyone,

Here is the latest version of the diagram; gas recirculation and producer insulation have been removed.

Thank you to Dutch John, David Orrell, and Steve Unruh for their excellent input. Additional revisions will be made, I’m sure.

Matt from Vancouver, B.C., Canada

Hello and welcome Matt,

You cannot collect all condensate in one tank, because of different pressure drops in the system. This would cause gas to bypass. If I were pyrolysisgas in top of the gasifier, I would travel by the condensate lines and the fine filter to the engine, because that is the easiest way. Besides that, you want to observe the condensate you drain. Especially condensate from a cooler after filtration tells you a lot about gasquality.

A wood dryer can work on stationary systems. For mobile use it is too heavy. I would take exhaust heat, because it has a higher temperature.

Cyclone after the gasfier is good, takes out a lot of dust. Doesn’t need a condensate drain, because it must stay way above dew point. Dust in the collector can be a bit damp, but not wet. Collector should be large. The fluffy part of the dust does not pack.

Blower can be pushing. It stays clean from dust, condensate and tar, but lighting of the gasifier can only be done electric, since it is pressurized. A sucking blower allows you several ways of lighting, but it has to be after filtration to keep it somewhat clean.


hello matt, welcome to drive on wood, i like your diagram, pre-heating / and drying the chips before putting them in the chip hopper has been one thing i want to try sometime . i have not mounted my gasifier on my truck yet so i have a lot of the same questions as you do ., dutch john,s advice and info is great, DAVID-O

DJ: Thank you for your excellent input. I have altered the diagram. Regarding the wood dryer, I will be putting the system into the back of a large truck so the additional weight of the dryer will not be a problem for my application; you do make a good point, perhaps those who do have weight restrictions could consider a combination cooler/dryer to greatly reduce the total weight. Cheers, Matt.

DAVID-O: Thank you for your input, I have altered the diagram to show the name as Wood dryer/pre-heater; I am sure the wood pre-heating will be an efficiency improvement so thank you for that input. By the way, I have already benefitted from all of your other posts on this site, even before I became I member I was reading your great input. Cheers, Matt.

Hello and Welcome BCMatt
No offense intended with the “BC”. Something necessary because there are now 7-8 Matts in the membership rolls here.
DJ’s advice is good. Pressurized system starting with electricity IS difficult for early work/fabrication!

You have not declared whether this is for stationary or mobile. Important details to this decision affecting grate operation, system component air flow cooling and fuel hopper fuel flowing downs as a minimum to this declaration.

Your fuel conditioning/drying bin is possible; but . . . . I have hand touched and operated two of these and seen pictures of several more built. Then helped scrap out a couple of these. Problems are using ready made gas heat is that part of the gasifer system is under from positive, neutral to negative pressure cycling variations a lot. Flat sides “tin can” pop in and out a lot with variable engine loading and internal producer hearth changes, and even just the whole system heating up and cooling down. The reduced gas flow velocity and the corner forced turing causes a lot of difficult to remove internal soot building up in the gas heating chamber walls and you end up with a condensate slurry goop in the bottom of the gas chambers. You are loosing over 1/2 your drying heat out the outside wall so then really should externally insulate. Gets expensive, complicated and difficult to maintain fast. Too many downsides in real world usage. Produced gas heat is much better close coupled, utilized back into the internal gasifier producer in any way possible. The dry warmed air blown through the downstream cooler condenser is fair game for fuel drying/conditioning on a stationary system.
AND since you ARE showing IC engine running the 70% wastes heats in surface, coolant and exhaust from the engine are all fair game too. High quality exhaust heat is best into the gasifier/producer. This WILL heat and cause open air fuel wood to smoke and burn unless first cool air tempered tempered down - a waste. The other lower quality dry engine heats are great as is for fuel stock pre-conditioning.
All of these should be used as is possible. As DJ says this is hard on a mobile with space and weight restrictions. Much easier when planned in on a stationary system.

Steve Unruh

Hi again BCMatt
Ok, I read fast but type very slowly.
If I seem to obsess about fuel wood drying and warming excessivly it’s 'cause been a long, long time since you and I have seen a 90F/32C day, eh? We’d be happy with just a string of more than two days not raining with wood drying sunshine wouldn’t we?
Anyhow there are enough waste heats in the gasifier/filtering/cooling system and a woodfueled internal combustion engine to take picked up winter wet 60% moister Douglas Fir and spruce woods down to an internal gasifier hearth needed 10-15% moisture.

The Great Frozen North people have to design and fuss and worry about frozen condensate blockages. SW NA and the dry hot climates have none of these worries - but very little, very slow growing wood and dependent on Urban waste fuels. SE NA and equatorial tropic climates have the wood fuels and can afford to be casual and just throw away heats as a waste. Ach! But the terrible bugs and snakes there.

Usage matters. Climate matters. Available fuel wood matters. Heck. After a while you learn change One thing at all, and it will matter somehow in a working woodgas system.
Why it is impossible to say any one system layout can ever be universal.

Big truck? OK. Concept only. Imagine a multiple cell flat bed aprrox 150mm thick. Engine coolant into one. Engine exhaust into another. I once even postulated ready fuel wood gas into a 3rd cell. One too many stored woodgas “BOOMs!” nixes that idea out of my head. Sacked or bin stored fuel wood being heated by the warm bed surface. Opps. Yes, our 250 days of rain. Need a bed rain cover too.

A better heat recover concept is instead of horizontally spreading out the heat sources stack them vertically. This is done internally in the best of gasifier hearth/hopper designs. Now expand this idea to the external heats. Cyclone on the bottom -> cooler above -> then fuel wood dryer on top. Open topped dried fuel wood bin then rake chuted directly fed into the gasifier hopper.
Stationary you can add the engine heats and forced air flow into this vertical rising heat fuel drying stack.

Temperate rain forest like you and I live in best to “Never Let a (generated) BTU Escape FREE Unused!”

Steve Unruh

Steve Unruh: Thank you for your excellent points; I have revised the diagram.

Matt from Vancouver, B.C., Canada

Hey BCMatt,
On your revised block diagram . . .
You never want to be putting the ready made woodgas back into or around the reactor. To much combustible gas taken to any kind of potential ignition source is very B-A-D. One of the reasons for the system “Whooshes”, “Booms”, “Sneezes”. Also, the now somwhat cooled gas from the piping and cyclone would then rob needed heat from the producer hearth core areas.
Good hearth/hopper design recirculates made gas heat internally back inti the incoming hearth core air and sometimes into the fuel hopper before the gas is removed.
Insulating the producer hearth core is fine and even beneficial for small kW/BTU systems especially stationary. Externally insulating the producer for BIG supply systems such as needed for an F-series loaded 460 CID engine will potentially overheat to metal destruction under many circumstances variable road driving use will force on you. External insulate later if able or seasonally needed like in the winter.

Unfortunately system sizing changes many variables including temperature control.

Regards S.U.

Steve Unruh: I revised the diagram; the gas recirculation and producer insulation have been removed. Thank you for the great input; that is why I am a member of this site, to get great help from members like you.

Matt from Vancouver, B.C., Canada