Gasifier musings & questions

In my quest for a multifuel gasifier, I've done a lot of reading and research. At this point I've got questions that I don't see addressed. I'm assuming that is due to no one trying these things out yet or my lack of Google Kung Foo. I'm going to throw some thoughts & questions out here. Some may not work at all, some may not be viable or efficient, and some might lead to something good.

Dirty, tar-laden producer gas is made by heating a container full of gasifyable material in a limited oxygen environment. The material is baked in the same way charcoal makers bake wood. I'm pretty sure this dirty producer gas can be cleaned up by running it through a bed of hot charcoal after it comes out, after which it should be clean enough to go through a filter, cooler, then to the engine.
How much charcoal is required to crack the tar molecules? Can the gas from a large chamber be run through a gallon container of hot charcoal and come out clean, 5 gallon container, 10? What's the minimum?

Producer gas burns differently than gas. The engine needs to be adjusted to run on PG. Would adding HHO (hydrogen) to the fuel intake help the engine's operation on PG in any way? I know it would alter the performance of the engine, but for the better or worse? If for the better, I'd probably power the electrolyzer with a TEG so the engine doesn't have work any harder. (The electrolyzer would not be meant to increase output in any way, just get a more complete burn of the PG and help the engine run. I'm aware the power from the TEG could more efficiently be used to directly charge batteries. This is strictly about engine performance and longevity.)

Storing PG is generally frowned upon because of the volume required for anything useful. However, I'm wondering if routing the PG to a water-seal (upside down barrel inside a water filled, larger barrel) might be useful for refueling the gasifier without shutting down the engine. The engine could continue to run on the PG in the water piston while the gasifier is opened to add more material. It would also help cool the gas, I think. Or maybe the storage container would affect the flow from gasifier to engine in a bad way. Something to consider further, I guess.
Will a few of these water pistons hold enough PG to run an absorption freezer for a day or two, or perhaps a stove for cooking? In theory, PG could run these things, but can enough be stored this way to be practical?

Someone here mentioned storing gas in a bladder set inside a trench with a protective covering over it. Might that store enough PG for useful work? I know earth bags could be used to shore up the walls of a shallow ditch with plastic to help keep water out. Storing PG would allow a person to power something later without having to run the gasifier, or power something over a 24 hour period without running the gasifier the whole time. Also, moisture in the gas tends to condence back to liquid when stored, impurities settle in the liquid, so storing for a day or two may allow for very clean gas even from a less efficient gasifier. If true, perhaps materials other than wood can be gasified, that gas stored until clean, then used. The waste water could be evaporated, the dry stuff Incinerated cleanly later for pollution control.

What constitutes high grade charcoal? I see hardwood mentioned as a prefered material to make charcoal. Is it the material itself that constitutes the quality or the charcoaling process? Can one get high grade charcoal from other materials? Bio briquetting charcoal from grasses and weeds is being done in India right now. Are those charcoal briquettes suitable for a charcoal gasifier, assuming the charcoaling process is done correctly?

I've read that plastic is more energy dense than hardwood by weight. Is this true? I watched someone on YouTube run an engine off gasified plastic. 1 milk jug is supposed to run a small engine on idle for 13 minutes, according to the Walnut Labs outfit that experimented with it. The gas left a parrifin residue in the engine, so the gas needs to be cleaned up so it doesn't do damage. I definitely want to try running that gas up through a bed of charcoal to see if that cleans up the gas. Talk about an abundant, cheap material to gasify.

What would it take to build a DIY fuel cell capable of using producer gas to make electricity? Is this simply beyond our technology level at present?

What about using PG to run a small burner, which heats one side of a TEG? (Thermo Electric Generator) How much PG would need to be stored to accomplish that for 24 hours? I'm thinking of TEG's to charge batteries, here, in a more passive way over time. Also, the producer gas shouldn't have to be quite so pure to run a burner. Efficiency aside, is this possible?

Lots of questions here. Feel free to respond to anything you know about or find interesting. I'm not saying these are good ideas or even possible. If you say something is not a good idea, please explain. If its an efficiency issue or a storage issue or too complicated or flat out impossible, explain why so we can learn something new, please.

Bill Bianchi : Let me take a few nibbles here, and allowing for me to be wrong -here goes, Yes I think that you will always have enough charcoal to filter your Producer
Gas P.G. ! In fact I think that you can then run your Burn products of dirty charcoal thru a second batch of charcoal when gasifying charcoal ! In this case think of a
set of inner-conected 'bells' !

H.H.O. gas may or may not be a null-sum game, but in this case it might make a statuary engine running at a fixed speed run more efficiently, and smoother, I get
what you are saying here ! For longevity of your engine, an older diesel unit with a big Fly wheel running at 800 R.P.M. should last forever !

With careful filtering through charcoal and water, you should have precipitated out a liquid component, which should itself further split into a bio-gasoline, a bio-diesel,
and something we can call creosote for further cracking !#

Without the liquid components, that P. G. would be a high grade of Methane, and could be added directly to your households Bio-gas Reactor/Storage vessel*,and used
for cooking and running a 'gas' refrigerator! O. K., I WAS WRONG, Much of what is left after the liquid components of wood gasification are cooled and captured, are
Hydrogen, methane, butane and their 'ols. methanol, butanol, some forms of propane and some CO2!

When Charcoal is gasified, most of the flammable gas produced is Carbon Monoxide ! In both cases while these flammable gases Could be stored in exactly the same
manner as the methane in a Bio-Gas reactor, I think that they could not safely be stored in a Bio-gas reactor ! With daily production leading to storage, the near constant
presence of these gases would result in Some adsorption of them into the water component of your Bio-Gas reactor !

The Bio-gas Reactor corrects for one of the few problems of layer composting ! With the compost pile running aerobically we lose CO2 and Methane - CH4 to the Air !
A well running Bio-gas reactor not only traps and saves the methane, the bacteria makes more of it ( I Think ) and less CO2, Plus dealing with fats that would 'kill' a
regular compost pile !Plus producing a Compost 'Tea' in equal amount to the slops added automatically every time ! plus the sediment at the bottom of the tank being
generally its compost equivalent !

* If we had our Bio-gas reactor co-located in a Greenhouse we would add months of P.G. creation due to warm, happy bacteria. Plus the Large Thermal Mass of the
Bio-Gas Reactor would moderate the Temperature swings and add time to our Greenhouses growing season. Plus it could still function as our P.G. Storage device past
the end of our growing season !

# with a side operation to crack plastic back down to petroleum, It would definitely be worth the effort to clean up our Producer Gas P.G. stream to create the already
mentioned co-products especially as the creosote could be run back thru ether process ( I Think )

Generally I have a low opinion of You Tube videos, but there is one showing very crude equipment to Crack out the Liquid components and shows use of the clean-ish
P.G., I will have to find it and make a second Post ! In the meantime there are the Gary Gilmore Charcoal gasifying videos!

There still is a multiplication factor here, even allowing for my faulty memory and a need for Co- co- location(s), this needs more thought !

For the Future/Good of the Crafts ! Be safe, keep Warm ! As always, your comments and questions are solicited, and Welcome ! PYRO-LOGICALLY Big AL

Bill Bianchi wrote:Dirty, tar-laden producer gas is made by heating a container full of gasifyable material in a limited oxygen environment. The material is baked in the same way charcoal makers bake wood. I'm pretty sure this dirty producer gas can be cleaned up by running it through a bed of hot charcoal after it comes out, after which it should be clean enough to go through a filter, cooler, then to the engine.
How much charcoal is required to crack the tar molecules? Can the gas from a large chamber be run through a gallon container of hot charcoal and come out clean, 5 gallon container, 10? What's the minimum?

Tar cracking is highly endothermic... how to keep the charcoal hot? Also, tar cracking consumes the charcoal as does the reactions of CO2 and H20 with the hot carbon. It seems you're describing charcoal filtration here. If so, then charcoal will quickly be overwhelmed by the high tar load in raw pyrolysis gas. The only way to get rid of most of the tar in raw pyrolysis gas is through combustion. You have to burn the tar. The combustion products (CO2 and H20) can then be reacted with hot charcoal along with what tar remains. Since these reactions are endothermic, then the combustion process must add heat to the charcoal. This is exactly what a conventional gasifier does while also supplying heat to drive pyrolysis. If you provide an outside source of heat for pyrolysis, then in principle there would be more heat left over for gas processing. If you recall I once suggested using the engine exhaust heat in a wood gas engine system to drive pyrolysis. Also, if you recall, there is research suggesting that the tars generated at lower temperature such as those available from engine exhaust are simpler and more easily cracked. If you intend to use gasification for the purposes of powering an internal combustion engine, then consider this approach.

Bill Bianchi wrote:Producer gas burns differently than gas. The engine needs to be adjusted to run on PG. Would adding HHO (hydrogen) to the fuel intake help the engine's operation on PG in any way? I know it would alter the performance of the engine, but for the better or worse? If for the better, I'd probably power the electrolyzer with a TEG so the engine doesn't have work any harder. (The electrolyzer would not be meant to increase output in any way, just get a more complete burn of the PG and help the engine run. I'm aware the power from the TEG could more efficiently be used to directly charge batteries. This is strictly about engine performance and longevity.)

I believe adding H2 to the fuel gas can help engine performance at higher engine speeds. If the system is devised for stationary power generation, then I see little net benefit to this. An engine tuned for producer gas does quite well at modest speeds that are optimal for stationary power generation. There is no need to enhance the fuel gas. I disagree strongly that TEG's can charge a battery system more efficiently than a wood gas engine system (unless you're considering some cutting edge TEG system or a theoretical argument). Note that the high efficiency often cited for TEG's consider energy conversion of the heat that actually moves through the unit and not the heat that is available to be converted. It's one thing to convert heat to electricity at 15% efficiency, and quite another to convert 15% of the total heat energy available from biomass combustion to electricity (which is what a good wood gas engine system can do - and ac electricity at that).

Bill Bianchi wrote:Storing PG is generally frowned upon because of the volume required for anything useful. However, I'm wondering if routing the PG to a water-seal (upside down barrel inside a water filled, larger barrel) might be useful for refueling the gasifier without shutting down the engine. The engine could continue to run on the PG in the water piston while the gasifier is opened to add more material. It would also help cool the gas, I think. Or maybe the storage container would affect the flow from gasifier to engine in a bad way. Something to consider further, I guess.
Will a few of these water pistons hold enough PG to run an absorption freezer for a day or two, or perhaps a stove for cooking? In theory, PG could run these things, but can enough be stored this way to be practical?

Do the math. One c.f. of producer gas at STP has roughly 135 btu.

Bill Bianchi wrote:Someone here mentioned storing gas in a bladder set inside a trench with a protective covering over it. Might that store enough PG for useful work? I know earth bags could be used to shore up the walls of a shallow ditch with plastic to help keep water out. Storing PG would allow a person to power something later without having to run the gasifier, or power something over a 24 hour period without running the gasifier the whole time. Also, moisture in the gas tends to condence back to liquid when stored, impurities settle in the liquid, so storing for a day or two may allow for very clean gas even from a less efficient gasifier. If true, perhaps materials other than wood can be gasified, that gas stored until clean, then used. The waste water could be evaporated, the dry stuff Incinerated cleanly later for pollution control.

In principle, I think this is true. Storing gas will settle impurities. However, raw pyrolysis gas has extremely high tar content. So, this might be useful for cleaning gas from a gasifier if it's a good unit. I've considered everything you have considered in gasification over the years (perhaps not the exact form, but the same principles) and I came back to the conclusion that the best solution is to just design a good gasifier that makes gas with low tar and try to filter what little tar survives.

Bill Bianchi wrote:What constitutes high grade charcoal? I see hardwood mentioned as a prefered material to make charcoal. Is it the material itself that constitutes the quality or the charcoaling process? Can one get high grade charcoal from other materials? Bio briquetting charcoal from grasses and weeds is being done in India right now. Are those charcoal briquettes suitable for a charcoal gasifier, assuming the charcoaling process is done correctly?

Hard wood makes the best charcoal mainly because it has less volatile content (so less tar and easier to get rid of tars) and the material is a lot more dense thereby generating a charcoal that is more dense which is easier to handle and store without breaking up. Soft woods make good charcoal in a properly designed and operated charcoaling system, but it's just not as dense and it's more fragile than charcoal from hard wood.

Bill Bianchi wrote:I've read that plastic is more energy dense than hardwood by weight. Is this true? I watched someone on YouTube run an engine off gasified plastic. 1 milk jug is supposed to run a small engine on idle for 13 minutes, according to the Walnut Labs outfit that experimented with it. The gas left a parrifin residue in the engine, so the gas needs to be cleaned up so it doesn't do damage. I definitely want to try running that gas up through a bed of charcoal to see if that cleans up the gas. Talk about an abundant, cheap material to gasify.

Gary Gilmore has experimented with admitting particulate plastic into a charcoal reactor with good results. Note that this was not a "bed of charcoal", but a charcoal reactor. The plastic had to be admitted at a controlled rate to prevent dropping the reactor temps too low. Charcoal gasifiers run so hot that they generally require a source of cooling. Often this is provided by admitting engine exhaust gases to the reactor or admitting steam. In both cases these products react with the charcoal to reduce temperatures via endothermic reactions while increasing gas production (H20 and CO2 converted to H2 and/or CO). In the case of plastic admitted to a charcoal reactor, the plastic is vaporized and the vapors are cracked in the high temperature carbon environment (both high temps and free carbon drive these reactions). This is similar to the process of cracking tars in pyrolysis gas. The principle to keep in mind is, again, that the plastic is admitted at a controlled rate (not too fast). The problem with biomass is that the volatile (read: tar) content is too high to make this a simple process. A biomass gasifier is kinda like admitting plastic to a charcoal reactor so quickly that the endothermic cracking reactions drive the temperatures down to the point where the organic vapors just pass through. A solution can be had by thoroughly drying and partially charcoaling wood to remove the water and some of the volatiles, then run a more or less conventional Imbert. Again, this is very similar to what the All Power Labs Hot ToTTi is doing, but they send everything through the system. They can get away with it because they tap the engine exhaust heat. However, their system by no means optimizes the process. It's possible in principle to heat the biomass a lot more aggressively with the engine exhaust effectively regenerating a lot more heat into the biomass and lightening the load on the gasifier. As I described before, this leaves a lot more high temperature heat at the hearth for gas processing.

Bill Bianchi wrote:What would it take to build a DIY fuel cell capable of using producer gas to make electricity? Is this simply beyond our technology level at present?

More than I'm willing to spend. I would look into plasma to clean the gas sufficiently for a fuel cell. There is a small company in Florida experimenting with this, and they have multiple patents on their process.

Bill Bianchi wrote:What about using PG to run a small burner, which heats one side of a TEG? (Thermo Electric Generator) How much PG would need to be stored to accomplish that for 24 hours? I'm thinking of TEG's to charge batteries, here, in a more passive way over time. Also, the producer gas shouldn't have to be quite so pure to run a burner. Efficiency aside, is this possible?

Do the math. However, I emphasize that you have to get very high temperature differential in a TEG for high efficiency, and high temps on the hot side can't catch all the heat in a burner. So, let's say you want 600F on the hot side and you have a burner at 1500F. Depending on the rate you would be lucky to get half the heat into the TEG. So, if the TEG is 20% "efficient" and you can only get half the heat through it, then it should be considered as only 10% efficient (numbers for illustrative purposes only). Now, you also have to cool the cold side, and you have to get very low temps for high temperature difference. In practice this generally means water cooling which consumes energy and if the cold side is to be as cool as possible, then you can't let the water get too hot... this means a high flow rate which consumes more energy. Also, if the water is too cold then the quest for higher efficiency in the TEG also reduces the water temperature such that it can't be used for many useful heating applications. There are lots of catch 22's.

Bill, this is really a segue from the previous post. In another discussion I had suggested a model where biomass is not used for electric power generation. If you recall, I suggested a better use for biomass resources in heating applications and space cooling with absorption (in the off grid setting at least). In general, I believe this is the more efficient model. However, in regions where solar insolation is low and average temperatures are low, then I can defend a configuration like Ken Boak's system (discussed elsewhere: google "ken boak lister powercubes"). Ken lives in the UK, so that configuration seems ideal.

I'm still muddling through a project to build an absorption chiller, but it's only been less than a month since I started. This stuff is very time consuming and expensive. I'm convinced that a chiller designed for no more than one ton cooling capacity and fueled by biomass would prove to be among the most useful off grid energy devices ever devised. The system I am working on is designed to provide a cooling rate between 1/2 and 1 ton while also providing heat at its condenser at a temperature of 140-150F for heating applications. The system is designed to be powered by DC electricity produced by photovoltaics. The idea is to power the system at full capacity when the solar array is producing, but drop to a lower cooling rate at most other times in order to minimize battery discharge. This will provide enough cooling for a properly designed modest off grid home while providing enough heat for all heating applications including biomass fuel drying, water pasteurization (water for washing), water distillation (potable water only), and water heating. The system can also be configured for space heating. So far, this is the most efficient and versatile system I've considered for making use of biomass fuel in the off grid setting. In fact, I consider the potential for such a system to be so promising as to justify on purely economic grounds the use of commercial biomass pellets due to the leverage presented by the extensive heat regeneration. Pellets are not necessary, of course, but they are very convenient and highly energy dense.

A word on TEG's... I am somewhat optimistic about TEG's, but I would consider a different configuration. As long as a large proportion of the heat from a furnace can be sent through the TEG while also rejecting this heat at a high enough temperature to drive a chiller, then that would be an interesting configuration. This would allow for generating a lot of the electricity required of the chiller while not consuming any additional fuel. For heating applications using a biomass furnace a TEG could generate the electricity required to power a circulating pump and fan coil unit for a hydronic heating system. A TEG can be useful to minimize battery discharge and the size of a solar array used in an off grid setting (assuming biomass is used as a fuel source). I do not see TEG's as a good model for primary electricity generation... but maybe one day.

Bill, if you're still experimenting with biomass gasification, then consider the following.

A FEMA gasifier will generate a clean gas if fueled by charcoal. This was demonstrated by Wayne Keith who fueled his trucks for a while with a FEMA gasifier using charred wood chunks. I propose a system where dry particulate biomass such as wood chips is fed through a long insulated auger tube that is heated with engine exhaust gases. The auger dumps the fuel directly into the top of a highly insulated fire tube. Air is admitted also to the top of this fire tube, and this air is highly preheated with the hot fuel gases leaving the base of the gasifier. This configuration seems fairly simple to construct. If enough heat can be regenerated into the system via both air and fuel preheating, then it seems that the pyrolysis function normally required of a downdraft wood gasifier can be eliminated or reduced to the point where the temperatures in the system remain high enough to ensure reliable tar cracking. There are all sorts of ways to play around with this basic configuration. For example, might admit air into the system via the auger tube itself which would induce a flaming pyrolysis front at the end of the auger tube. This should ensure that all biomass is fully pyrolysed (i.e. charcoaled) before it enters the fire tube. The insulated fire tube should be packed with charcoal that would provide both the raw carbon and high temperatures required for gas processing. I think this is worth a try... although expect seriously high temperatures. This approach might allow (or even require) the use of wetter biomass.

NOTE: I mentioned this elsewhere, but I'll emphasize it again. Regenerating heat into a gasifier is a tricky business. For example, let's say you only preheat air supplied to a gasifier by using the exiting fuel gases. This certainly adds heat to the process. However, it does not add more air. The result of this process can be higher tar production in the fuel gas because the higher air temperature adds to the temperature in the reactor which can increase the rate of pyrolysis... however, without adding additional air to burn this higher tar load, the results can be more tar getting past the hearth. Generally, regenerating heat only by preheating the air supply works well only with a very well insulated system that also uses very dry fuel. Fuel size is also important as I've emphasized elsewhere because too small a fuel size can insulate sections from high temperature or air and allow tar gases to channel past the hearth. If the heat in the engine exhaust is tapped to take care of a good part of the pyrolysis function, then the heat introduced in the air supply through preheating is not used up in pyrolysis. So, even though there is no more air provided, not having to supply energy to drive pyrolysis makes for much higher hearth temperatures that can crack tars that are not combusted. The ideal state in my mind would be for a system like this to regenerate so much heat that the fuel is fully charcoaled at the end of the auger tube with only combustion gases, charcoal, and whatever tar vapors cannot be combusted leaving the auger tube. The volatile content of wood is too high for all the tars to be combusted. However, with so much heat supplied to the system via regeneration, it seems with good insulation that these tar vapors could not survive past the fire tube.

double post