Charcoal Gasification

I've looked into wood gasification during my spare time over the last few years. I had neglected charcoal gasification because most of the energy is lost in the charcoaling process. However, I now consider that if enough of this energy can be harvested for heating applications, then generating charcoal fuel can be preferable. Charcoal gasifiers are smaller, lighter, easier to build, easier to operate, and charcoal has higher energy density than wood fuel. Also, since most of the volatiles are removed during the charcoaling process, it's a lot easier to generate a tar free gas using charcoal. This means a charcoal gasifier is better suited for fueling small engines. However, it can also be used for large engines. In any case, charcoal is a rather amazing fuel source that has distinct benefits over wood.

http://www.youtube.com/watch?v=yL79ci4TH7k (Gary Gilmore)
http://driveonwood.com/forums/charcoal-gasifiers (forum w/Gary Gilmore)
http://www.youtube.com/watch?v=1gmg_Uuz5Ps (example)
http://www.hotel.ymex.net/~s-20222/gengas/kg_eng.html (the Källe gasifier)


I've considered various configurations to harvest the heat from a charcoaling process. However, I won't get into this because it's not the scope of the message here. I wish only to mention the idea and touch on the thermodynamics. The energy remaining in the charcoal represents roughly 1/3 of the energy present in the wood fuel. The remaining energy (the 2/3) is released while burning the volatiles during the charcoaling process. So, the net effect of this process is having only 2/3 of the energy in the wood available for heating. All else equal, this suggests that one who normally burns 2 cords of wood for their heating needs will have to burn 3 cords using this process. This is a simplification of course. Now, each cord of seasoned hard wood processed in this manner will provide about 8 million BTU of charcoal (roughly 800 pounds). This quantity of charcoal is equal to about 70 gallons of gasoline when used to fuel internal combustion engines. What's the best use for this fuel? Well, that depends on the end user. However, I suggest motive power as the best use (such as tractors and automobiles). Powering a genset for battery charging is reasonable. However, there are so many losses here that it would quickly consume the fuel. In my opinion, if used for this purpose it should be limited to providing backup power for power generation systems that do not consume fuel (such as solar panels and wind turbines). The automotive use is particularly interesting to me. My research suggests that a compact car fueled by charcoal will achieve 3 miles per pound of charcoal. So, the charcoal derived from one cord of hard wood will fuel a car well over 2000 miles. My research shows that most homes heated primarily by wood will consume several cords of wood over the winter heating season. So, this process has the potential to provide this heat while also producing an automotive fuel that will take a car a greater distance than most individuals need to travel during a year. So, in theory, this process can provide all heat for the home (both space heating and water heating), generate all the automotive fuel required, and have fuel left over for a small genset to provide back up power generation.

Systems that make charcoal and burn wood as for electricity exist. Search on the wood stove forum.

I wouldn't store the gasses; they are very dangerous.

Dave Turpin wrote:Systems that make charcoal and burn wood as for electricity exist. Search on the wood stove forum.

I wouldn't store the gasses; they are very dangerous.

Yes, systems that make charcoal exist.
Yes, wood can be used for power generation.
Yes, storing the gasses is dangerous, and I don't recommend it.

Perhaps I should clarify the configuration. I do not suggest that gasses be stored. Rather, I suggest that the heat from a regular batch charcoaling process be stored in a thermal mass (such as a large insulated water storage tank) to provide heat over a 24 hour period. Storing a large quantity of heated water for this purpose is nothing new. The process entails loading seasoned wood into the system every day and collecting the charcoal from the previous load. It is the advantages of charcoal gasification over wood gasification that leads me to suggest this configuration.

So all the talk of automotive fuel?

Dave Turpin wrote:So all the talk of automotive fuel?

Yes, charcoal as automotive fuel. See link on the Källe gasifier.

I agree charcoal is an excellent fuel for transport needs but there is an easier way of using it than gasification. If you look up coal slurries you will find that a diesel engine can be run on an approx 50/50 mix of coal and water with modified injectors and fuel pump. The same technology can use charcoal to replace the coal.

renewable john wrote:I agree charcoal is an excellent fuel for transport needs but there is an easier way of using it than gasification. If you look up coal slurries you will find that a diesel engine can be run on an approx 50/50 mix of coal and water with modified injectors and fuel pump. The same technology can use charcoal to replace the coal.

I've heard of this. However, it's also possible to admit the combustible gasses (producer gas) generated by a small charcoal gasifier with the intake air to a Diesel engine, and this improves emissions. In this "dual-fuel" configuration there is a small amount of Diesel admitted for ignition. Wood can also be used in the same configuration with a properly designed gasifier. It makes more sense to use wood vs. charcoal for a few reasons (particularly when considering the energy lost in producing charcoal), but the charcoal gasifier is so much simpler and generates a richer fuel gas. To me, charcoal makes the most sense for the automotive use when used in a "dual-fuel" configuration because the size of the gasifier can be very compact. In fact, it's possible to make a charcoal gasifier so compact that it can be used to fuel a small motorcycle, or even motorize a bicycle. It would be extremely difficult to do this with wood, and if it were done the wood would have to be very highly processed to a small regular size. Dual-fueling a compact car with charcoal could be practical. However, Wayne Keith and others have shown that fueling a full size pickup with wood can not only be done, but that it can work rather well.

I had looked into charcoal gasification while considering a simple gasifier for use in dual-fueling a compact car. I did not consider it a viable means for stationary power generation because so much energy is lost in charring wood. However, Gary Gilmore shows in some of his videos the process of adding particulate biomass to a charcoal gasifier to extend the run times. In principle, it is possible to extend the life of the charcoal dramatically with this process. This configuration is desirable because a wood gasifier cannot normally operate an engine at a very low power (at least not consistently, cleanly, and at optimal efficiency). I've been corresponding with an engineer who is working on this very idea, and he's getting excellent results. Another benefit here is the ability to use less desirable forms of biomass such as shredded pine needles, shredded leaves, grass clippings, etc. (as long as they're dry) that can be added to the charcoal reactor directly thereby saving wood for the occasional charcoaling required. The potential for this system to operate a very low speed engine at low and constant power for battery charging over extended periods is good, and I consider this configuration to be ideal in an off grid setting for minimizing the size and cost of the battery system, limiting discharge on the battery system thereby extending its life, minimizing energy conversion losses (fewer battery losses, and optimizing engine and alternator efficiency), and optimizing waste heat recovery from the system (which is simpler when the power output is low).

The same approach could be used in the automotive setting for a compact gasifier used in dual-fuel mode. In that case it seems quality hard wood pellets should be used. This may require a sophisticated system to control the rate at which the pellets are admitted. It's possible to use reactor temperature as a control input here.

This is a continuation of the previous post. I had mentioned using reactor temperature as a feedback control for admitting particulate biomass to a charcoal gasifier, and that a tight feedback control system might be difficult to achieve in the automotive setting where the conditions are so variable. However, a small stationary system used for battery charging can be optimized for a steady state output. Under these conditions it would be a lot simpler to control the process. I'm convinced that it's possible to use the temperature of the hot fuel gases leaving the gasifier as a control input. An adjustable thermostat (with normally open contacts) can be used to control the auger motor that admits biomass to the reactor. When temperature rises to the set point, then the motor starts. Admitting biomass cools the reactor which will in turn cool the fuel gases. If the auger motor speed is properly selected, then the control can be very tight, and it may be possible to get a clean gas while also extending the life of the charcoal dramatically.

Also, I want to mention a few facts on pine needles that I uncovered. Pine needles have about 5% more energy by dry mass than the best hard woods. On average, there is more than 9000 btu/pound in dry pine needles. Where I'm from (east Texas) it's easy to find very large masses of surprisingly dry pine needles on the forest floor. The ash content of pine needles is about 3%. Anything less than 5% does not normally present a problem of slagging in a gasifier. I know of one successful gasifier system that uses pine needles exclusively, but I have no details on that system. Finally, the bulk density of pine needles is low, but they are easy to shred. The bulk density of shredded pine needles is roughly 10 pounds per cubic foot. I think shredded pine needles may be a good candidate for supplementing a charcoal gasifier.

https://homepower.com/sites/default/files/uploads/webextras/mark8.pdf

This article discusses a small battery charging system assembled with a 4 hp Honda engine driving an automotive alternator at a constant output. This is in general what I have considered, but for use with a charcoal gasifier supplemented with particulate biomass. I was shocked to learn that the engine depicted in the article was put in regular use over a 15 year period for a total run time of 13,000 HOURS!... and that's with no overhaul (i.e. same rings, valves, and bearings). Folks, that's just plain amazing for a small engine like this. Engines are so much more reliable when operated at low speeds and at constant outputs. This durability reinforces my belief that a biomass-fueled off grid power plant can be a practical alternative, and without costing a small fortune as some commercial systems. However, a charcoal based gasification system may be necessary to get sustained low power operation combined with high efficiency. Throw in good waste heat utilization, and you may just have a big winner.

http://driveonwood.com/forum/435

Thread describing a charcoal powered van built during the last year. The power is simply amazing. The van hauls a large trailer that carries the gasifier, fuel, and fuel processing equipment to allow charring on the road! The van achieves highway speeds and can climb steep hills at 55-60 mph. Van has a 300 cubic inch straight 6.

This is not practical by any means, but I bet it's fun! Still, it's clear that a charcoal gasifier can make a rich fuel gas. BTW, they are adding water to the system to moderate the high temperatures and making a lot of hydrogen gas in the process. This is certainly enriching the energy density of the fuel gas.

I'm not affiliated with PlanetGreenSolutions, but to me it sounds like this is the kind of thing you are thinking about:

http://youtu.be/yEMBTnGk5Ws

http://www.PlanetGreenSolutions.com/

$33 grand for the manually-fed version or $55 grand for the computer automated one. Not bad when you consider the cost of a 20kW solar or wind system. If you have access to an unlimited supply of wood, you can be producing 20kW... Or 240kWh per day if it's running half the time. That's enough power for 10 not-particularly-efficient houses or a small farm, including charging your electric cars. electric bikes and electric tractors....

I am not sure how much biomass you need to burn in the thing to make the rated output, but it seems like a small community could be build around one of these, if they have a lot of free biomass and not a lot of solar/wind/hydro options. (They also have a 120kW version but that would probably be suited for a village or a large farm)

Dave Turpin wrote:I'm not affiliated with PlanetGreenSolutions, but to me it sounds like this is the kind of thing you are thinking about:

http://youtu.be/yEMBTnGk5Ws

http://www.PlanetGreenSolutions.com/

$33 grand for the manually-fed version or $55 grand for the computer automated one. Not bad when you consider the cost of a 20kW solar or wind system. If you have access to an unlimited supply of wood, you can be producing 20kW... Or 240kWh per day if it's running half the time. That's enough power for 10 not-particularly-efficient houses or a small farm, including charging your electric cars. electric bikes and electric tractors....

I am not sure how much biomass you need to burn in the thing to make the rated output, but it seems like a small community could be build around one of these, if they have a lot of free biomass and not a lot of solar/wind/hydro options. (They also have a 120kW version but that would probably be suited for a village or a large farm)

The Planet Green System is basically the same as the All Power Labs unit, but the APL system is less expensive and a lot more compact. See their Power Pallets here: http://gekgasifier.com/gasification-store/gasifier-genset-skids/ . Their system is capable of generating one KWh of ac electricity for every 2.65 pounds of bone dry wood consumed. Of course, wood is not "bone dry" when harvested. Also, this efficiency is achieved only when the system is operated at optimal loads which tends to be a very high output relative to the rated power of the system. The efficiency drops to less than half this value at a low part load, but that's characteristic of constant speed internal combustion gensets.

I think these large systems would be ideal for powering a small community. If the waste heat could be efficiently distributed to the homes, then it could be extremely efficient. It would be cool to see an extended family set up something like this to power several homes. However, I am considering a system suitable for a small off grid home.

NOTE: See the specs on the APL 10 KW unit. The power output is listed at 3-10 KW. Why not 2 KW or 1 KW? Well, it turns out that these systems have to draw air at a sufficient rate to maintain high temperatures in the reactor. Otherwise there is a high liklihood of generating tar gases that can overwhelm the filter train and engine. A charcoal gasifier can solve this problem. Therefore, it can be better suited for a very low power system that serves a small off grid home. Of course, one could operate a large system during winter days by using a lot of electricity for space heating applications, charging batteries, and while using engine exhaust to heat a thermal mass. This higher capacity could also be used to power an air conditioning system during the summer months. Still, it's a very expensive unit that really should be downsized and made more affordable. Designing a small, low power system optimized for battery charging and waste heat recovery has a place.

Just sharing one of my wacky ideas. I like the idea of using a modernized piston steam engine with good thermal efficiency and fueled by biomass as an off grid power plant. One of the main benefits of a piston steam engine in this setting is the ability to operate at very low power for extended periods while providing heat in a convenient package. Steam is an excellent heat transfer medium. Unfortunately, these systems are not available. So, I considered, why not a biomass fueled steam generator for heating applications? Furthermore, since my recent research shows that charcoal gasifiers can power very small engines cleanly and with impressive energy density, then how about a system that chars wood chips at a controlled rate while generating steam on demand? The charcoal produced from the system can then be stored for use as required in fueling small engines.

I'll describe a basic configuration to get the reader thinking on the topic. Particulate biomass like wood chips is gravity fed through a vertical pipe section. A hopper is connected to the top. A lower section of the pipe is surrounded by a combustion chamber fueled by pyrolysis gases generated from the heated wood chips. A key point to consider is that pyrolysis occurs at a rate directly proportional to the rate at which the biomass feeds through the system (within limits). So, it's possible to govern the steam rate with a motorized auger tha removes charcoal from the base of the system. A steam generator tubing coil is placed above the combustion chamber in the annular space between the pipe and exterior shroud used to form the combustion chamber. The draft draws air into the base of the system to cool the lower pipe (and charcoal within) and combust the pyrolysis gases escaping from a ring of holes in the inner pipe at the base of the combustion chamber. These hot combustion gases pass over the steam generator coil before heating the hopper that contains the fuel (thereby drying and/or preheating the fuel before it enters the pipe).

The steam generated is sent through an insulated line to a high point in the system, then distributed to various heating applications. This is controlled in two ways. First, each load has a valve to control flow. Second, the final pass of the steam/condensate is through an insulated water storage tank. The temperature of the water in this tank is used as a control for the auger motor.

This is a continuation of the previous post. The system I described there is rather sophisticated, but I do not believe it would be inherently difficult to build after the prototyping were completed. Building a biomass fueled steam generator for heating applications (w/o the charcoaling system) would be a lot simpler. In that case, it's possible to use small pieces of rough cut firewood stacked onto a grate. The system burns at a low rate in updraft fashion to generate smoke continually that is combusted separately for heating a steam generator. The smoke is pulled out of the side of the unit by the draft generated by a flue placed next to the unit (I've seen such a system, and it works well). NOTE: The fuel hopper is closed at the top, air enters at the base of the fuel hopper via a grate, and exhaust gases leave at the top of the flue. The output is controlled by positioning a damper on the flue.

I've considered a simple mechanical thermostat by allowing the flue to be actuated by connecting a cable to an automatic window opener (see one example here: http://www.amazon.com/RIGA-Auto-Open...+Window+Opener). The idea here is that the window opener can be placed in a central location in the home to monitor temperature, and position the damper accordingly. Using a solid steam radiator with some size and thermal mass seems like a good idea. NOTE: Something like this might be devised to generate a lot of charcoal if the grate were configured to allow large pieces of charred wood to fall down into a collection chamber. The benefit of this approach is that the wood does not have to be chipped, and no auger is required.

Just sharing more of the research on charcoal gasification that I've uncovered. Again, the benefits of charcoal gasification over wood gasification is the ability to operate a very small engine cleanly and efficiently. Unfortunately, half or more of the energy in the wood is lost in converting it to charcoal. What I've considered is a means to operate a very small wood gas engine system by essentially charring the wood in place. So, technically it's sort of a hybrid wood/charcoal gasifier that tries to get the best of both worlds. This may be possible by using the heat in the engine exhaust, but it may be difficult to transfer enough heat to the fuel to make this conversion. Forcing wood chips with an auger through a tube that is aggressively heated with engine exhaust might do it. It seems the pyrolysis gases given off could overwhelm the charcoal reaction and drop temperatures. Therefore, I suggest that the gases given off be directed down into the air supply tube (see diagrams of Kalle gasifier to see how air is directed down into the charcoal with a tube). These gases would be combusted to add heat directly to the reaction and moderate temperature drops that would otherwise occur. The charred wood would be augered directly into the charcoal hopper. Any volatiles that remain in the wood would be driven off within the hopper as the fuel approaches the high temperature at the reaction zone, and these volatiles can be cracked in the reduction zone as long as the temperatures are high enough. It seems that if the wood can be charred sufficiently with the engine exhaust heat, then this process would work.

Burning wood to heat a barrel full of more wood does not strike me as the best solution to home power or transportation fuel because wood is an actual resource that has uses other than burning and because wood is not all that fast to replace itself; takes years to grow a tree. The air pollution issue with making charcoal can be overcome, so I'm not opposed to using wood for that reason.

That said, if we add a different technology to charcoal production, we can do this without burning ANY wood at all. Matter of fact, we can use municipal and agricultural waste exclusively. Now, if waste becomes the source of charcoal, and if we can produce charcoal in a clean fashion, we're looking at solving two problems with one system; making energy and reducing the material going into landfills.

Charcoal gasification looks good to me for reasons already listed, so I don't really need to cover it. Suffice it to say, charcoal gasification is viable.

Bio-briquettes are the technology that can be added to charcoal gasification to eliminate wood from the equation. Bio-briquettes are made by compressing loose waste materials into blocks. Just about any organic material can be used to make these briquettes; pine needles, waste paper, cardboard, leaves, sawdust, weeds, manure, ect... They can also be pressed into any shape or size you want.

Bio-briquettes can be turned into charcoal. This is already being done, so it's not really a theory at this point. Bio-briquettes can also be burned straight for heat, so we have a charcoal base and the necessary heat in one waste product.

If an efficient stove is used to heat the charcoal chamber, like a rocket stove, and the dirty producer gas is piped out from the charcoal chamber and into the stove so the stove burns it cleanly, then the pollution issue is handled and a portion of the heat required to make charcoal comes from the material in the charcoal chamber itself.

From there, if we can use the waste heat of the process for home heating and hot water heating, the charcoal making operation would become a clean, useful process that does more than make charcoal for motor fuel from waste material.

Thoughts?

Bill, sound reasoning on paper.

One can make charcoal with minimal additional inputs using a retort. You only need additional heat to dry the material and start the gasification, the gasification drives the rest of the process. And figure out a way to use the waste heat.

Warning: Once people have this figured out, the waste stream will gain value and price the DIYer out of the market--just like waste veggie oil.

Good points, Scott. I think you're right about making charcoal with minimal resources.

As for waste gaining value, I think that would be a good thing over all, though a pain in the keister for those using this for home power.

If more waste material is ever needed to serve demand, there are a few options to increase the "fuel" available. Cudzu (sp?) is a plant that grows out of control in the south, up to a foot a day, apparently. That's one possible source. Some species of bamboo grow quite quickly, so maybe that's another. The household waste would eventually be used for this by the family living there, so each household would require a bit less from outside sources. Then, we have grass clippings, leaves, and other weeds that can come from the yard.

If that's still not enough, we have vast grasslands that could be harvested in a sustainable way and plenty of waste materials in the forests.

I don't know exactly how this would work on a large scale, but all the technology necessary is already established and for now, at least, the material is cost free. I imagine that if this caught on, businesses would spring up to supply the charcoal and fabricate the charcoal gasifiers and efficient charcoal makers.

I have a system in mind to heat the home and hot water that should mesh with this pretty well. It involves heating thermatic oil, then circulating the oil to where you need to heat something. It's a closed loop system and it also will use solar energy in addition to a furnace.

This gasification technique alone could go a long way to decentralizing the production of energy in a sustainable way, if I'm not overlooking some obvious hurtle.

First, let me emphasize that this idea of mine is only one of many. I do not necessarily consider it ideal. I outlined it mainly because I've not yet seen it described elsewhere. Consider it only as a controlled charcoaling process to provide heating applications no different than a wood furnace, but with the added benefit of producing charcoal that can be put to use in fueling small engines. The main purpose is prevent wasting so much energy in the charcoaling process. As far as using biomass sources other than wood, I'm all for that. Finally, I'm not terribly concerned about sustainability problems with this approach. My primary concern is energy independence for individuals. Most people simply will never consider this kind of technology because breaking a nail and/or straining a muscle is likely.

I desired to operate a wood gas engine system at outputs that are generally too low for wood gasifiers, and charcoal solved this problem. However, I now take the position that a more powerful wood gas engine system can be used efficiently in the residential setting by putting the mechanical energy to use in driving an a/c compressor directly (for space cooling - use an automotive a/c compressor and store a partially frozen mass of water that can be used in a mini chilled water system). Also, during winter months additional mechanical energy can be applied toward electricity generation that can be used in space heaters to prevent excessive charge rates on a battery system (and avoiding a large battery)... heat from the system can be stored in a thermal mass to be tapped in the same "chilled" water system for air heating as required. Ken Boak's system (google Ken Boak Lister powercubes) is fundamentally identical here, but he lives in a cold climate with little need for the chilled water system. As far as automotive fuel goes, if one can acquire a cost effective feed stock for ethanol production, then using the additional electricity generated from the system during the winter months can be used to conveniently power a simple reflux still with the heat from the still retained in the home for space heating.

There really are innumerable possible configurations, and I've considered many more that involve other systems. For example, a reasonably efficient piston steam engine can show impressive overall efficiency if the heat it put to full use, and that system can use a much wider range of biomass fuel sources. There are various ways to construct chilled water systems powered by heat, and the steam exhausted from a steam engine is ideal for many such systems... a few prospects are promising. Even more practical is to minimize electricity consumption such that a heat engine is unnecessary. That way, one can stick to PV and wind for electricity, then provide all other energy requirements with a simple biomass-fueled furnace and/or steam generator and perhaps some solar thermal applications also. Since heat is more easily accessed by individuals, then it seems reasonably to seek ways to optimize its use. Certainly it seems clear that trying to power an off grid home as a grid tied home (i.e. primarily with electricity) is not practical.

I think more people than you realize will be interested in implementing this technology, both in the developed countries and undeveloped. Especially people in poverty stricken nations.

We need passive energy production systems to go with this, but charcoal gasification and the waste heat applications from making it would be a nice base technology to start with.

Marcos, if you were making charcoal and you had a separate charcoal gasifier running, could the dirty producer gas from making charcoal be directed into the bottom of the charcoal gasifier to clean it up?
Would the charcoal in the gasifier crack the tar in the gas from the charcoal maker, which is directed into the bottom of the charcoal gasifier?
Just wondering if there is enough heat in the charcoal gasifier to not only gasify charcoal, but clean up dirty producer gas as well?
Engine exhaust was pumped into the charcoal gasifier I saw on youtube to cool the reaction down in the gasifier. Would wood gas do the same if pumped into the charcoal gasifier instead of engine exhaust? Would that cool the reaction inside too much for the lit charcoal to crack the tar in the dirty gas being put in at the bottom?
Thanks

Bill Bianchi wrote:Marcos, if you were making charcoal and you had a separate charcoal gasifier running, could the dirty producer gas from making charcoal be directed into the bottom of the charcoal gasifier to clean it up?
Would the charcoal in the gasifier crack the tar in the gas from the charcoal maker, which is directed into the bottom of the charcoal gasifier?
Just wondering if there is enough heat in the charcoal gasifier to not only gasify charcoal, but clean up dirty producer gas as well?
Engine exhaust was pumped into the charcoal gasifier I saw on youtube to cool the reaction down in the gasifier. Would wood gas do the same if pumped into the charcoal gasifier instead of engine exhaust? Would that cool the reaction inside too much for the lit charcoal to crack the tar in the dirty gas being put in at the bottom?
Thanks

I believe it could, and this is essentially the configuration I have described in several other posts. CONSIDER THE TRADITIONAL IMBERT design as a charcoal gasifier, and things will become clear. Here, the air enters the reactor through the nozzles. This air immediately combusts the pyrolysis gases to generate intense heat. Since the heat is concentrated at the hearth, the temperatures are high. This high temperature causes the fuel mass above the nozzles to pyrolyse (to become charcoaled). This the source of the pyrolysis gases that are combusted at the nozzles. The goal is to release and combust as much of the pyroysis gases as possible so that only charcoal exists at and below the nozzles. Unfotunately, there is NOT enough air to do this because the volatile content of wood is TOO HIGH. So, what tars are not combusted must pass through the extremely hot charcoal bed to be cracked. Now, the combustion gases (CO2 and H20) are ALSO passing through the hot charcoal bed to be reduced to CO and H2, and this is ENDOTHERMIC (which means it drives down the temperature). When the hot charcoal cracks (i.e. reduces) the tars, then that is also endothermic. So, it's a CATCH 22 because you need high charcoal temps to crack tars, and everything you throw at the charcoal wants to drop its temperature. The solution to minimize what the charcoal has to process while highly insulating against heat loss. One of the most important things to do is (1) insulate the hearth, and (2) use fuel that is as dry as possible. The size of the fuel is also important (see below).

The configuration I described in other posts uses the exhaust gases directly from the engine to heat an insulated auger tube through which biomass is forced with an auger. This charcoals the biomass. The charcoal that forms drops down into the charcoal reactor. The pyrolysis gases that form in the tube are split: some go with the air supply into the charcoal reactor (these are combusted and this both destroys these tars and adds heat to the reactor) and the others are taken into the charcoal hopper which is fairly small and highly insulated - these pyrolysis gases have to pass through the high temperature charcoal reduction lobe where they are cracked. The engine exhaust gases pass finally to the fuel hopper along with the hot air from the engine cooling fan to dry the biomass fuel in the hopper, and the high temperature fuel gases might also be used to transfer some heat to the hopper if necessary. So, the fuel is completely dried before entering the auger and being exposed to the highest temperatures from the engine exhaust gases, and this is very important otherwise heat will be wasted in drying the fuel in the tube and this will also admit water vapor to the reactor and drive down temperatures. You want to get the free water out of the fuel before it enters the auger tube.

This basic configuration attempts to reduce the heat load on a typical wood gasifier by using the high temperature heat from the engine exhaust to perform the drying and more important MOST of the pyrolysis function that is normally done at the hearth of the Imbert design. It also allows for much better thermal insulation. The combined effect is higher temperatures in the reactor that can process all tars reliably and more important is that most of the tars are admitted to the reactor alongside the air supply so that most of the tars are incinerated. Understand that a problem with the traditional Imbert design is that many of the tar vapors generated are not exposed to air because the fuel particles themselves will shield the tar vapors and allow tar to "channel" past the hearth and avoid oxygen and high temperatures thereby resulting in a fuel gas with a lot of tar vapors. This problem is avoided by admitting most of the tars vapors in the air supply tube and mixing them with the air supply. So, burning as much tar as possible in the air supply tube takes care of most tars through incineration while simultaneously adding a lot of heat to the reactor to raise temperatures for cracking whatever tars remain (mostly those admitted with the fuel when the auger drops the charred biomass into the hopper). These tars HAVE to pass through the reduction lobe to get out (see link on the Kalle gasifier). As long as the temperature at the reduction lobe is high enough, then things should work out. Note that the All Power Labs system does essentially that same thing, but it is not optimized for low power operation. I'm convinced that the approach here will regenerate a lot more heat into the system while also reducing thermal losses at the reactor for better results, especially at low power. I considered it as a way to use smaller engines efficiently with gasification. It's a hybrid charcoal/wood gasifier that tries to get the best of both worlds: (1) generating a clean gas at low outputs, and (2) not having to generate charcoal separately (i.e. using biomass fuel directly). Using a highly insulated auger tube with as small a diameter as practical, making sure only dry fuel gets into the auger, and highly insulating against thermal losses in the reactor should be done.

NOTE: With respect to the approach you described, you should be able to direct some pyrolysis gas from a charcoaling process to two locations: (1) a furnace that drives the charcoaling process (i.e. heats the wood for charcoaling), and (2) into the charcoal reactor WITH THE INTAKE AIR such that the pyrolysis gases are incinerated and pulled into the reactor as combustion gases (CO2 and H2O). Again, this is what the Imbert does, just in a different configuration. In the Imbert, some heat from the hearth supplied by pyrolysis gas combustion at the nozzles drives pyrolysis. In this set up some pyrolysis gases are pulled off the charcoal retort to drive pyrolysis by burning separately in a furnace under the retort. If this set up could split the flow of pyrolysis gases precisely while also protecting against heat loss with excellent thermal insulation, then it should work. However, without a good build you would find that the charcoal is consumed in the charcoal gasifier faster than you can make it in the retort. To prevent this you would need good insulation and you would need to make sure the wood used in the retort is very dry, so make use of the heat from the system to dry the wood before you place it in the retort. In fact, this is one of the first configurations I considered, but finally went with the previous described approach to prevent having to charcoal separately. Also, using the engine exhaust gases to drive pyrolysis of dry biomass provides a natural feedback control since the heat rate provided for this pyrolysis is directly proportional to the output of the system... so no need to fret over how the flow of pyrolysis gases from the charcoal retort is split. Turns out there is enough heat in the exhaust gas from the engine for charcoaling as long as the fuel is dry and enough heat is transferred to the fuel in the auger tube.

NOTE: I can't help but note again that using a small biomass furnace for direct heating applications, and also to power a chiller (with additional heating applications at the condenser) is a more efficient way to use biomass than power generation. I've come to the realization that the most practical way to power an off grid home is to minimize electricity usage to the point where a modest PV array can provide all electricity. A small biomass furnace can do the rest by using heat efficiently, and a small genset can be used for electricity generation (battery charging) when solar (or wind) isn't sufficient. Also note the post I made earlier in this thread where a small biomass furnace can be devised to generate charcoal while also generating steam on demand for heating applications. This approach allows a store of charcoal to be maintained for use in powering engines as required while making full use of the energy in the biomass fuel.

It was looking over the Imbert that made me ask. Looks like there are several configurations to accomplish home power with heat and gasification. Our present approach harnesses the heat for home heating and water heating. Charcoaling at the same time should allow the producer gasses to be piped back into the furnace for added heat and a reduction of fuel usage. The charcoal byproduct can be used later to actively back up passive electric generation every few days via a generator to top off a home battery bank.

What you laid out is more than a little interesting, and complicated for a regular user to operate. For now, we are going to stick to using the heat more directly for home and water heating and save the charcoal for use later to power a generator.

We'll be tackling passive generation after we get this active portion up and running.

Let me know if you've found a way to replace the battery bank yet. LOL.

Thank you for all the time you've taken replying to my posts. I learn something new every time.

Bill Bianchi wrote:It was looking over the Imbert that made me ask. Looks like there are several configurations to accomplish home power with heat and gasification. Our present approach harnesses the heat for home heating and water heating. Charcoaling at the same time should allow the producer gasses to be piped back into the furnace for added heat and a reduction of fuel usage. The charcoal byproduct can be used later to actively back up passive electric generation every few days via a generator to top off a home battery bank.

What you laid out is more than a little interesting, and complicated for a regular user to operate. For now, we are going to stick to using the heat more directly for home and water heating and save the charcoal for use later to power a generator.

We'll be tackling passive generation after we get this active portion up and running.

Let me know if you've found a way to replace the battery bank yet. LOL.

Thank you for all the time you've taken replying to my posts. I learn something new every time.

As far as the battery goes, I've concluded that maintaining a battery in the off grid setting is the most practical thing to do as long as electricity is used. Strategies to minimize the size and discharge on the battery will greatly reduce the long term costs. Getting electricity usage down is the single most important thing to do.

About generating charcoal from wood, the retort method seems to work very well. I've seen large drums take 100 pounds of wood down to high quality charcoal, and without particularly good insulation. This led me to believe that gravity feeding wood chips through a vertical duct/pipe section might be used to devise a controlled charcoaling process to see good results. I mentioned this in a previous post. The idea here is that pyrolysis gases can be combusted in a combustion chamber that surrounds the duct thereby heating the wood chips within to drive pyrolysis for charcoaling. The pyrolysis gases are taken from the heated section and directed into the combustion chamber for air mixing and combustion. A coil of tubing can be placed above the combustion chamber for steam generation by directing all combustion gases over this coil, and the combustion air can be taken from the bottom of the unit to preheat the duct and cool the charcoal somewhat, and what heat is not captured by the steam generator coil is used to preheat the wood in the hopper (by heat transfer as the hopper must be sealed). In principle, it's a very elegant design. Of course, there are always devils in the details. I considered placing an auger in the base of the unit that pulls charcoal out which would also drop the level of wood in the duct down closer to the combustion chamber and this would control the rate at which pyrolysis gases are generated, and this would be used to control the rate of steam generated and used in heating applications.

I just wanted to make sure you saw that post as I think that basic idea has merit. Another interesting configuration is setting up something like this to generate charcoal while also providing heat for an ethanol still. I mention this basic configuration in another thread where the heat from an ethanol still is used for heating applications (such as space heating during winter). If someone has a source of cheap fermentable sugars, then this seems reasonable. So, one can make charcoal for a stationary back up generator, ethanol for a vehicle, and use the heat from the still to heat the home (essentially powering the still for free). Steam would be a very convenient heat transfer medium for an ethanol still.

You're welcome... it's not often I get to field good questions.

NOTE: Another configuration that I believe has merit is using a small biomass furnace to power a small piston steam engine designed specifically for longevity by operating a low speeds for extended periods. If the thermal efficiency is reasonably high (for a steam engine this means 6-8% or better) and the engine extremely durable, then this approach has merit. The steam exhausted from the engine can then be used in all heating applications discussed before, and there is no need to generate charcoal here - and a much wider range of biomass fuel sources can be used. Also, such a system would be particularly useful in minimizing discharge on a battery system allowing it to last a lot longer. I've actually done more research on small scale steam power than anything else (and I used to be a steam plant operator), so if you want to go there just say the word. Unfortunately, the lack of hardware makes this problematic (like most of my ideas). The reason I considered charcoal gasification and wood gasification was the lack of hardware for small scale steam systems, but I remain convinced that small scale steam can be superior in the off grid residential setting.

I agree that a steam engine is the best solution, when considering durability, efficiency, and effectiveness.

I've researched steam engines for this purpose. The biggest critism seems to be the danger involved for someone not very familiar with boilers and steam engines. Someone like you would have zero trouble running one. Someone like me would get very good at it very quickly because I have a strong desire to learn and because I would be in contact with you before I ran one, to get advice and precautions. Most folks, though, would find it to be either too much work, not pay enough attention to the things that require attention in order to operate safely and reliably, or do something monumentally stupid that causes an accident.

Not saying gasification is without risk, but it seems a little more user friendly for the average person and the folks who sell steam engines seem to recommend gasification over steam for those only looking to go off the grid.

Me, I definitely want to operate a steam engine for home power at some point, mainly because I am fascinated by steam engines. Once you have one, or two or three, and know how to safely operate and maintain it/them, you're darn near bullet proof.

On a more positive note about steam engines, I've noticed there are people (Mike Brown? Green Steam) trying to make them available for home power. Maybe the day will come when people get back to using them. I do believe they could be made safer to operate if used strictly for battery bank charging, as you suggested.

You can make your charcoal out of a number of materials besides wood. Just google around and you will find grasses, sugar cane, etc. packed into containers and turned into char.
There are also a number of outdoor heating systems that you could modify to produce the heat needed for char and retain the waste heat for greenhouse, home heating, etc.
You may wish to look at the many different systems that are now used to create biochar.
If you really want the steam engine then look at http://home.earthlink.net/~dlaw70/12stmng.htm get the books on the boiler operation first.

Bill Bianchi wrote:I agree that a steam engine is the best solution, when considering durability, efficiency, and effectiveness.

I've researched steam engines for this purpose. The biggest critism seems to be the danger involved for someone not very familiar with boilers and steam engines. Someone like you would have zero trouble running one. Someone like me would get very good at it very quickly because I have a strong desire to learn and because I would be in contact with you before I ran one, to get advice and precautions. Most folks, though, would find it to be either too much work, not pay enough attention to the things that require attention in order to operate safely and reliably, or do something monumentally stupid that causes an accident.

Not saying gasification is without risk, but it seems a little more user friendly for the average person and the folks who sell steam engines seem to recommend gasification over steam for those only looking to go off the grid.

Me, I definitely want to operate a steam engine for home power at some point, mainly because I am fascinated by steam engines. Once you have one, or two or three, and know how to safely operate and maintain it/them, you're darn near bullet proof.

On a more positive note about steam engines, I've noticed there are people (Mike Brown? Green Steam) trying to make them available for home power. Maybe the day will come when people get back to using them. I do believe they could be made safer to operate if used strictly for battery bank charging, as you suggested.

I know, and it's a real shame that we don't have biomass fueled small steam engines available that are cost effective and efficient. It's a shame because it absolutely can be done, but it seems nobody wants to risk resources on its development. The same applies to the chillers I discussed before. We don't have the biomass fueled small steam engines because liquid petroleum distillates are widely available and internal combustion engines are cheap, and we don't have the chillers because inexpensive grid electricity is widely available.

Seriously, when confined to a sustainable energy model, think about what's possible with a micro steam engine that is durable, efficient, and designed to operate for extended periods at a low output, AND a system that puts the heat in the steam exhaust to full use for such applications as space heating, water heating, air conditioning, etc. A local system of biomass processing and delivery could be done for some regions where all kinds of biomass is pelletized and delivered directly to residences in storage vessels (in fact, this is done in some regions where the pellets are used in space heating - well, might as well go the extra mile and use these pellets for power generation, water heating, and air conditioning). The numbers look quite good for a steam engine with relatively low thermal efficiency, but it has to get higher than the 4-5% seen in engines such as the Mike Brown engine (and even lower for the Green steam engine). BTW, the Mike Brown engine is well built, but primitive and inefficient. The Green steam engine is just plain junk. However, a solid small engine capable of no more than 1 KW electrical, designed for continual operation, and a net thermal efficiency of only 10% would be ideal for just about any region that has suitable biomass fuel available. The best prospect I've seen here is a small version of the "waste heat engine" being developed by Cyclone Power Technologies (www.cyclonepower.com). Unfortunately, it seems those guys can't get anything to market.

Until something truly modern and mass produced becomes available, the best option (assuming someone is dead set on the steam engine option) is to devise a simple single cylinder bash valve uniflow piston steam engine for no more than one hp to operate at a constant output for battery charging and extensive waste heat recovery. The furnace should be devised to use biomass with as little processing as possible, and the steam generator should be a monotube design. Things get so much simpler when the power is low and continuous, and such a system would be quite safe. Still, without exceeding a certain efficiency threshold that is very difficult to achieve in practice, then it's more practical to just use photovoltaics and wind for electricity, then make efficient use of the heat from a biomass furnace.

ADDENDUM: Another prospect that I am enthusiastic about is thermo electric generators (TEG's). I haven't seen anything available yet that meets my criteria. I would be very excited about a unit capable of providing 8% NET thermal efficiency from a biomass furnace (meaning 8% of the energy actually released by burning the fuel in the furnace is converted to electricity and not merely the heat that moves through the unit) while also generating steam at atmospheric pressure on the cold side. If the price were reasonable and the unit highly durable, and capable of providing electricity at a rate of 500 watts or more at the ratings given, then this would be hard to beat.

I'm completely with you on the TEG's, especially during the winter when cooling the other plate could be done with a cold water/antifreeze mix from outside. The excess heat can heat the home and hot water as well, so there's a lot of benefit to running the furnace.
Not so sure about summer operation, when home heating is not desired and water sitting outside doesn't get so cold. Seems a waste of burnable material to make only electricity and hot water from the heat. On the other hand, if solar heat could be configured for convenience and ease of use during the summer, we'd have a winner. There has to be a way to use a solar oven for the heat source. For cooling the other side, I'm not sure what would work. Well water at my place is cold enough, but I don't want the well pump running all the time.

I wouldn't use TEG's exclusively, but they should compliment an integrated system nicely, I think. Hope the price comes down on them or someone comes up with a DIY design for one that puts out a usable amount of power.

All right, I'm done rambling.

Bill Bianchi wrote:I'm completely with you on the TEG's, especially during the winter when cooling the other plate could be done with a cold water/antifreeze mix from outside. The excess heat can heat the home and hot water as well, so there's a lot of benefit to running the furnace.
Not so sure about summer operation, when home heating is not desired and water sitting outside doesn't get so cold. Seems a waste of burnable material to make only electricity and hot water from the heat. On the other hand, if solar heat could be configured for convenience and ease of use during the summer, we'd have a winner. There has to be a way to use a solar oven for the heat source. For cooling the other side, I'm not sure what would work. Well water at my place is cold enough, but I don't want the well pump running all the time.

I wouldn't use TEG's exclusively, but they should compliment an integrated system nicely, I think. Hope the price comes down on them or someone comes up with a DIY design for one that puts out a usable amount of power.

All right, I'm done rambling.

On the TEG's, note that I mentioned (1) steam generated on the cold side, and (2) high thermal efficiency (net). This would provide the benefits of a good small steam system - but with no moving parts. So far I've seen nothing that can approach this, and my being "enthusiastic" about the prospect was perhaps an overstatement. Note again that steam can be used to power a chiller very effectively. I'm not interested in a TEG if it requires cooling water pumped at a high rate, nor if it requires a high temperature heat transfer fluid for the hot side. If a system can be devised for direct firing with water maintained on the cold side to be vaporized (and with the steam contained for continual reuse and with full heat recovery of the latent heat), then this would interest me.

R Scott wrote:Bill, sound reasoning on paper.

One can make charcoal with minimal additional inputs using a retort. You only need additional heat to dry the material and start the gasification, the gasification drives the rest of the process. And figure out a way to use the waste heat.

Warning: Once people have this figured out, the waste stream will gain value and price the DIYer out of the market--just like waste veggie oil.

I think bill is well on the way to sorting this by his thoughts on using thermal oil. All he needs now is a thermal oil steam evaporator and a Kobelco Steamstar generator and he will be able to power the local neighborhood.

Bill Bianchi wrote:I'm completely with you on the TEG's, especially during the winter when cooling the other plate could be done with a cold water/antifreeze mix from outside. The excess heat can heat the home and hot water as well, so there's a lot of benefit to running the furnace.
Not so sure about summer operation, when home heating is not desired and water sitting outside doesn't get so cold. Seems a waste of burnable material to make only electricity and hot water from the heat. On the other hand, if solar heat could be configured for convenience and ease of use during the summer, we'd have a winner. There has to be a way to use a solar oven for the heat source. For cooling the other side, I'm not sure what would work. Well water at my place is cold enough, but I don't want the well pump running all the time.

I wouldn't use TEG's exclusively, but they should compliment an integrated system nicely, I think. Hope the price comes down on them or someone comes up with a DIY design for one that puts out a usable amount of power.

All right, I'm done rambling.

Problem with Tegs there not very efficient maybe 8% max electrical efficiency. Whereas steam can be in excess of 50% electrical efficiency and 90% overall efficiency.

r john wrote:Problem with Tegs there not very efficient maybe 8% max electrical efficiency. Whereas steam can be in excess of 50% electrical efficiency and 90% overall efficiency.

I agree on the TEG's. These are not a viable solution for efficient power generation. However, your figures on steam are suspect. The best modern large steam power plant can approach 50% net thermal efficiency. With generator and power transmission losses the electrical efficiency can be in excess of 40%. A modern combined cycle power plant can reach the figures you offer, but I wouldn't call that steam power.

More important, while I don't know, I also don't imagine that Bill is considering a scale that could make use of modern power generation equipment in a cost effective way. When one is restricted to the small scale (less than 100 hp, and preferably less than 10 hp), then efficient steam power is not an option. The hardware is not available. Personally, I believe it's within reason for one to develop a reasonably efficient low power steam power plant for combined and heat and power of a home, but anything beyond this scale would be far too expensive for most to consider. Also, getting more than 20% thermal efficiency from such a small steam power plant would be very unlikely. In fact, anything more than 10% would be difficult.

Marcos Buenijo wrote:

r john wrote:Problem with Tegs there not very efficient maybe 8% max electrical efficiency. Whereas steam can be in excess of 50% electrical efficiency and 90% overall efficiency.

I agree on the TEG's. These are not a viable solution for efficient power generation. However, your figures on steam are suspect. The best modern large steam power plant can approach 50% net thermal efficiency. With generator and power transmission losses the electrical efficiency can be in excess of 40%. A modern combined cycle power plant can reach the figures you offer, but I wouldn't call that steam power.

More important, while I don't know, I also don't imagine that Bill is considering a scale that could make use of modern power generation equipment in a cost effective way. When one is restricted to the small scale (less than 100 hp, and preferably less than 10 hp), then efficient steam power is not an option. The hardware is not available. Personally, I believe it's within reason for one to develop a reasonably efficient low power steam power plant for combined and heat and power of a home, but anything beyond this scale would be far too expensive for most to consider. Also, getting more than 20% thermal efficiency from such a small steam power plant would be very unlikely. In fact, anything more than 10% would be difficult.

Marcos

Steam efficiency has moved on with twin screw compressor technology not quite down to 10 kw level but the two steamstar models are 160kw and 132kw well within the bounds of community generating schemes.

http://www.kobelco.co.jp/english/ktr/pdf/ktr_29/016-022.pdf

R john, I referenced the link. There is no direct mention of the thermal efficiency of these screw expanders. However, the output of 157 kw provided with a steam consumption rate of 3000 kg per hour implies a net thermal efficiency well under 10%.

Marcos Buenijo wrote:R john, I referenced the link. There is no direct mention of the thermal efficiency of these screw expanders. However, the output of 157 kw provided with a steam consumption rate of 3000 kg per hour implies a net thermal efficiency well under 10%.

If you look at Fig 14 that gives the efficiency curve for each turbine topping out at over 50% and 60%. Even my old 1937 Bellis & Morcom engines do well over 10% efficiency.

R john, the paper discusses the "efficiency" of the engine in many places (and graphs). However, it is vague in that it does not specify what kind of "efficiency". It might be mechanical eff., carnot eff., rankine eff., etc. The paper does not discuss THERMAL efficiency. It does note that the expander requires 3000 kg of steam per hour to deliver 157 kw (doesn't specify mechanical or electrical power). One kw is about 3412 btu, and one kg of steam requires around 2500 btu of heat to generate. Do the math. The thermal efficiency is well under 10%. The paper suggests steam normally wasted is used to power this engine, so it seems designed to use low pressure saturated steam. If so, then this efficiency is very good for such low quality steam.

Marcos

If your talking thermal efficiency thats a total different ball game. Most CHP plants run at 80 to 90 per cent efficiency its just how you split between electric and heat that is the difference.

http://www.bios-bioenergy.at/en/electricity-from-biomass/screw-type-engine.html

r john wrote:Marcos

If your talking thermal efficiency thats a total different ball game. Most CHP plants run at 80 to 90 per cent efficiency its just how you split between electric and heat that is the difference.

http://www.bios-bioenergy.at/en/electricity-from-biomass/screw-type-engine.html

OK, so we've cleared things up - these engines do not (indeed, cannot) have the extremely high thermal efficiency suggested in your previous posts. Thermal efficiency is what fundamentally distinguishes/differentiates one heat engine from another. When people consider the "efficiency" of a heat engine, then it is thermal efficiency that is generally considered. Hence, you can understand my consternation at your claim of "50% electrical efficiency" (BTW, the only way I know to interpret this claim is that 50% of the heat provided to the system is converted to electricity, and this implies a thermal efficiency so high as to be unbelievable).

The engine in the link you provided lists "Electric efficiency at nominal load operation of 12,6 %" using steam at 500F and about 360 psig. This is very good efficiency for a once through expander at these parameters, especially with the fairly high exhaust pressure. In particular, the high condenser pressure/temperature makes for excellent use of the heat in cogeneration applications. I agree that these seem to be great for combined heat and power purposes. However, they really should be made much smaller for real impact.