Richard Hill Stick Wood Furnace

[ben]

Steve Unruh just brought this to my attention. Its a pdf report for a stick fueled gasifier furnace. Click on the link below or find it in the future in the reports section.
stick_wood_furnace.pdf

[Clinton Briley]

Hey SteveU, I think the stickwood concept is a viable one. Since it would need to be hand loaded
with stickwood, it will never be completely automated, but it could run unsupervised after loading
for many hours after loading and setting it up. An electronic system to monitor the operation
would be needed for unsupervised operation, but shouldn't be too complex a task.
Thermocouples for the primary and secondary burn chambers and charcoal reduction column. Based on the temperatures in these zones a logic circuit would control primary and secondary air supply. Also a way of determining if there is an oxygen "breakthrough" in the charcoal column would be needed, likely by use of an oxygen sensor. And whatever valves are needed for closing the fuel-gas lines after the gasifier is shut down. I think that covers the basics anyway.
The silage bags I'm considering for gas storage use are made of polyethylene plastic.
The thicknesses vary, but the ones I'm looking at run in the range of 6 to 8 mil.
They don't stop oxygen permeation entirely, but slow it down considerably. I would guess
then that hydrogen would also be able to pass through the plastic as well. But as long
as it does so slowly enough, I see it as a minor concern.
As for the furnace materials, I think castable refractory is the way to go. The upper end
castable temps look to be 3000 degrees F. I would line all of the interior of the furnace
with castable refractory including the charcoal reduction column. A taller hill style water
jacketed steel hopper above the stickwood chamber for longer running time, and a
non-insulated steel hopper for the charcoal above the reduction column.
I believe the temperature in the reduction column can be effectively regulated by controlling the
secondary air supply. If the reduction column is approaching it's temp limit then choke down the
secondary air so there is an excess of fuel to air ratio. Run it that way until the temp of the
reduction column drops to the target range.
Still lots of details to work out.
Talk more later,
Clint

[Steve Unruh]

Hello ClintB.
My thoughts based on last in first out. The charcoal if NOT too cold and gummed up by tars it should have no problem flowing down. The larger problem is charcoal bed particle packing and clogging with ash residue. I do not know how this is managed in a "Brandt" updraft column.
Realize deep bed is a slow, low turbulence high thermal mass process versus a more modern type Imbert which is a fast, very turbulent low mass portable capable process. The old deep beds appear to have had to be mechanically bed agitated or hand pokered to keep the fuel compacted down and knock the ash down thru a grate. With a "Brandt" varient I would try and get the out going gas velocity up high enough to carry the ash out for cyclone or settling tank removal (Kahle did this). No Grate needed then. At charcoal REDUCTION temperature of 650C cast iron and thick plate steels do OK for me. At charcoal OXIDIZATION temperatures of 1600C/2300F everything in contact must be ash insulated or made of a proprietary high nickel alloy or a fragile cast ceramic. The more charcoal that must be oxidized for process heating the less available for thermal-chemical fuel gas Reduction conversion. With only ~20% of the wood fuel possible as carbon/charcoal the challenge is not burning any up unnecessarily. Ha! Ha! Us wood heating people are ingrained charcoal burners. Real hard to unlearn this experience and build/operate something without over airing it too hot and too clean and then burning up (oxidzing) our char and fuel gases.
PRACTICAL, stickwood/cordwood fueling for motor fuel gasification is an ideal that may not prove to be possible. It might be too slow of a reaction process and require too much oxidizing to keep it going.
The deep beds for fossil coal gasification specify 1"-3" chunk break down. I have yet to find any historical wood fuel sizing requirements. All fuels were specified as "dry"? >8% or >15% moisture?,. Fossil coal only reacts on the surface. Woods; especially out of the end grain cuts; are cellular gas permeable and much more reactive. Increasing the end grain surfaces along with interstitial spacing requirements is why in my opinion the light weight portable Imbert types use a chunked/sized sorted wood fuels. Downside: as sponges, woods can more than double their weight in sap and water. It takes a lot of energy to evaporate and vaporize this moisture away. Solar pre-drying is the best - if you have it. With limited solar I still have half the moister to get rid of and this will require sacrificing 1/4 of the wood heat energy to do this. Then the challenge is methods to do this WITHOUT running the vaporized moisture thu the gasifier and having it show up in the out put fuel gas. I think the heat outputs of an IC engines exhaust and cooling system is the key to this. After all they came from the woodgas fuel too. Integrate and recycle these heats to dry and preheat the next fuel load.

Bulk production and bag gas fuel storage IS very interesting. Two points though. The fuel gas Hydrogen as H and H2 is very slippery. Look at how fast larger Helium molecule is lost in a latex versus mylar balloon. The fuel gas CO carbon monoxide under certain conditions ( still confusion here) of heating and pressure will convert to incombustible CO2 and a C (soot).

Real important to establish your overall system priorities and goals. Prof. Hills furnace would only work with electrical energy inputs for the fans, pumps and draft controls. Would really benefit from a modern PLC controller. Just like all of the current efficient Pellet, LP, Natural gas and electric stoves and furnaces. My wood heating stove just needs >23% moister wood and me - the experienced operator. I'll do the sizing, loading, poking and decision making. These are my home energy gasification goals too; at the sacrifice of idealistic fuel/energy efficiencies. I am actually designing for a knowledgeable very operator dependent system. Weird? No. Forcing the mind to do something tangible with the hands and body like prepare a meal from scratch; pick and snap green beans for freezing or canning; harvest, dry and store your winter heating fuel - these are all humanistic rewarding things for people to do.
Others are designing to make their gasifier systems to be as easy to operate as any other modern washing machine, clothes dryer or appliance. Decisions. Decisions, eh?
Regards
SteveU.

[Clinton Briley]

Hey SteveU, I've been thinking more about posibilities for the stickwood to engine fuel gasifier
and thought I would run some of them by you. I've been considering the issue of drying
the stickwood suitably for achieving optimal temperature for better pyrolysis and combustion
temperatures. One way of allowing wetter wood to be used would be to run two separate
stickwood burners using one for super-preheating the charge air for the fuel-gas producing
gasifier. Higher combustion temps in the secondary burn chamber would more efficiently
burn and/or crack the tars into noncondensable gases before entering the charcoal reduction
column.
One other issue is whether a practical ash grate could be made for the charcoal column
that wouldn't melt or otherwise break down from the high heat it would be exposed to.
My guess it that a conventional ash grate wouldn't work. You had described your
furnace being setup in an old pre-imbert deep bed style from the old town gas works days.
I've seen illustrations that show the type of setup you describe. Any idea how they delt
with the ash from the process?
Also, would charcoal in the column be likely to need shaking down or will it flow without
the bridging problems associated with raw wood? My assumption is that it would flow
down pretty well by itself but since I've never built one I was hoping some insight could
be offered by you or others.
Thanks,
ClintB

[Clinton Briley]

Hey SteveU, thanks for describing in more detail your stickwood to motor fuel gas experiment.
Your description is much closer to what I thought was a "somewhat" original idea on my part than I
would have guessed it to be. Your goals are very similar to mine. I burn wood for heat also and
like you, want to have a set up that can be used for both heating and creating producer gas.
If succesful in making engine quality gas, I intend to bank it for use as I need it.
I think some of the large silage bags (sometimes called "ag bags" or "bale tubes") used for
storing and ensiling feed for cattle would be ideally suited for storing it without major expense.
I could use the stored gas for running either small or large engines replenishing the supply as
neccesary. Thanks for the reference to the Brandt and the Kalle designs in the charcoal blog.
They should both prove valuable in reaching my goals. The plans Prof. Hill sent me are the
same as those online.... http://stoves.bioenergylists.org/stovesdoc/Hill/stick_wood_furnace.pdf
Likely to have more time this winter to work on the project. In the meantime, I'll try to work out
the details in my head.
Talk more later,
Clint

[Steve Unruh]

Hi ClintB
The rectangular cast iron box hearth I used does have two 30" long preheated primary air inlets on the lower sides. What I did was basically a proof of concept (a stunt) to prove I could too make motor capable fuel gas out of cord fire wood pieces. Box was too wide. Air inlet was too low and big, and only able too flame cut one stick width. I had to preload and bank charcoal against the opposite inlet side and use that as the gas outlet path. Really it worked by pre-ignighting and burning up to red hot heat the whole fuel load and cast iron mass and then closing everything down letting the heated mass create pyrolisis gasses I then let the little engine pull this through the glowing charcoal. Would only last until the endothermic charcoal reduction and surface radiation pulled the temperatures too low to support the processes.

Does show proof of concept though. Really what I did was more a pre-Imbert deep bed gasification technique from the town gas works days.
I've been more successful with this hearth piece horizontally stacking the wood I intend to do some serious development on this this winter. This puts out a lot of surface heat I will use to heat my shop. I an not willing yet to photo anything until I could make it self feeding with at least a 5 hour useable gas production time and be able to be made out of common plate steel and poured refractory ( not an old obsolete made in Yugoslavia cast iron recognizable as a wood stove). Gonna end up being a 1000+ pound 90% heat, only 10% fuel gas stationary small engine fueling system.

How does the plans you have from Dr Hill compare to the down load on this site?

I like you ideas in concept. Use the trunk and major limb wood as the raw fuel. Charcoal convert the lumps, stubs, crotches and twigs into the reduction charcoal.
When you gonna start building and develop this?

Regards
SteveU.

[Clinton Briley]

Hey Steve, I've been aware of Professor Hill's wood gasifier for a number of years. I first read
about it in "The solid fuels Handbook". I even managed to contact the good professor (must
have been 8 or 10 years ago) and he was gracious enough to not only send me a copy of the
plans which are now available on the internet, but also to answer my questions regarding the
construction and operation of the furnace after I had a chance to read the plans. At that time however, I was not aware that wood could be and was succesfully used decades ago to fuel internal combustion engines. I've only become aware of the process just recently and find it an irresistably interesting subject. In theorizing different configurations of the gasification theory,
I have considered using various hybrid designs utilizing aspects of the Hill furnace and of the various gasifier designs. Your testimonial that a Hill furnace variation has powered an engine
(however marginally) is validation to at least some of my theories. One of the hybrid designs
I've been considering is coupling a Hill furnace with a charcoal packed updraft gasifier-reduction column. The firetube water jacketed heat exchanger would be replaced with what is essentially
a standard updraft gasifier fueled with charcoal. Orienting the two designs in this way
would accomplish several things. One is that combustion of the wood gases resulting
from burning the stick wood would be complete (or very nearly complete) before the
hot combusted gases pass through the charcoal gasifier. The problems commonly
associated with wood tars are now all but gone. The updraft gasifier variation need not run at
the higher temps typically associated with charcoal fueled gasifiers since we can control
the temp by varying the amount of secondary air provided for complete combustion of
the stickwood gases(any additional oxygen would create more heat in the charcoal bed).
This means that the charcoal can be utilized primarily for reduction of our gases rather
than being additionally burned at a high rate to provide all of the heat for the chemical
process of reduction as well. What little tars that might remain now have a chance
of being cracked when passing through the gassifier. Preparation of the main fuel charge is
made easier....stickwood instead of chips. It is however still neccesary that the stickwood be
of low moisture content. Some might consider the need to make significant amounts of high quality charcoal a drawback to this design, but I think it is worthy of prototyping.

Please share your thoughts on the proposed device.
ClintB

[andre vachon]

Richard hill's pioneering work in wood gasification goes unheralded for the most part, in my opinion.

[Steve Unruh]

Yes I did recommend this as an example how how the air jet at #1 was being used to flame cut the vertical sticks wood #4 so the would drop down. Not shown but explained in the text is that the upper fuel jacket #9 was found to have to be used as a water per-heater to keep the fuel sticks cool enough so they would not combust full length from the rising heat. So what's this got to do with motorfuel gasification? Well if you shut down the #2 secondary combustion air after the concrete thermal mass #3 is hot out of the combustion zone throat #5 you get uncombusted woodgas. Cyclone it, cool it, filter it, run it in an engine. Not speculation. Not theory. I have now done this in a 300 pound cast iron hearth for up to 1 1/2 hours. Crude. Very fuel inefficient. But it is capable of gasifing on length split 16" long cord wood sticks. Longer wood would be better.
Regards
SteveU.