Biomass Gasification for Fueling Internal Combustion Engines

[buenijo]

I did a search of the forums here and was surprised to see virtually no mention of wood gasification technology. So, I'm providing an introduction to the technology. Those who have read my other posts know that I'm particularly interested in small scale steam power with biomass fuel and extensive waste heat recovery. However, if suitable biomass fuel is available, you don't mind the fuel processing required, and electrical power delivered at a high rate is the primary goal, then wood gasification might be ideal.

These videos provide a good demo:

http://www.youtube.com/watch?v=mnjDq...eature=related
http://www.youtube.com/watch?v=FL7vj...eature=related

These videos provide more thorough explanation:

http://www.youtube.com/watch?v=qlq3_CCVniU (series of videos)

Some good publications:

http://www.tpub.com/content/altfuels01/0276/index.htm (probably the best single resource)
http://www.fao.org/docrep/t0512e/T0512e00.htm
http://www.woodgas.net/files/FEMA_em...y_gassifer.pdf (good for introduction only, as this design is known to produce a lot of tar)

Forums that discuss the technology:

http://driveonwood.com/forum
http://tech.groups.yahoo.com/group/WoodGas/

Some units available for purchase:

www.allpowerlabs.com
www.vulcangasifier.com
www.victorygasworks.com
www.garringergasifier.com

[Acala]

Yes. It seems that hundreds of thousands of vehicles in Europe were converted to run on wood gas during WWII.

I don't think it is very efficient, compared to using the same biomass to run a steam engine. But if you already have a gasoline engine and you have no gasoline, wood gas seems like a serious alternative.

[buenijo]

Yes. It seems that hundreds of thousands of vehicles in Europe were converted to run on wood gas during WWII.

I don't think it is very efficient, compared to using the same biomass to run a steam engine. But if you already have a gasoline engine and you have no gasoline, wood gas seems like a serious alternative.

The efficiency of these systems can be a complicated topic, particularly when so many definitions of "efficiency" exist. A gas engine fueled by wood will see a net thermal efficiency of 15%, and 20% is possible. This assumes the system is operated at or near its optimal efficiency, which tends to be a high output relative to its rated power. By contrast, a typical small steam system sees 5 - 8%. A small steam system can be a lot more efficient, but not without some really complicated and expensive engineering. So, if wood is the desired fuel, and high power levels are desired, then the gas engine is the more efficient option. Things get a lot more complicated under real world conditions. In the end, it all depends on the application.

[buenijo]

(I copied this from the victorygasifier.com site. I think the "Hotwatt" system that Ben Peterson developed is very nice. In particular, I applaud his emphasis on waste heat recovery. I like the technology, and I love Mr. Peterson's design. However, it seems clear to me that very few people have access to enough suitable biomass fuel to power this system as a primary home power plant. There's a niche for this technology, but photovoltaics and wind power should provide a core renewable power base for electricity - at least where it's cost effective. One thing's for sure... no "lazy man" would be interested in this system. Although, as far as renewable off grid power goes, this technology might be the most cost effective solution currently available.)

http://victorygasifier.com/24-hour-power/
The Lazy Man’s Approach to 24 Hour Heat & Power
By Ben Peterson

"Lot’s of folks think that to get 24 hour heat and power you need to run 24 hours a day. Not only is this impractical, time consuming and just plain “no fun.” It’s not necessary. The Hotwatt philosophy to 24 hour heat and power is to convert a small amount of your wood waste into usable fuel gas to power engines, then store that heat and electricity for use through the day. Did you know that most of the energy we make is just wasted as lost heat or line transmission losses? Wood, even waste wood is a resource. Why use more than you have to. We would like to see our customers using around 2 acres of their land to provide all of their heat and power needs for the entire year. Alder is a good crop if you are starting from scratch.



Pictured above is the Hotwatt coupled to a genset for power and a water heat storage tank to store waste heat. Behind the Hotwatt is a mobile battery pack for this demonstration.



So back to our lazy man approach.

One day a month you gather your branches, pallets, or other feedstock and get it prepared for the gasifier by sizing and drying it to spec. Bag it up and set it to the side. If you aren’t prepared to invest one day a month prepping your feedstock, then this technology might not be for you.
When you wake up in the morning you simply fill the Hotwatt with a load of wood, then press start. Pour yourself a cup of coffee and come back to start up the genset and go back to your day.
The Hotwatt powered genset will recharge your battery pack while the forced hot air heats your home. Perform your most load intensive tasks while the engine is running so that you don’t drain your batteries. The residual stored heat and power will be used throughout the day to maintain your comfort. After a few hours the system will shut off based on the timer settings.
In the evening you walk over to the unit and repeat step 2.(coffee optional) The house is then brought up to temperature again for the night and the batteries are again recharged.
By harvesting every scrap of energy stored in the wood you can use much less than you think. By running the engine around 4 hours per day you can greatly extend its life and lower your service costs and any noise.

With very little effort you are now in charge of your own grid. It’s operating at just above the cost of your time and it’s in balance with nature. Simple.

Please note that we sell only the Hotwatt and genset at this time. Batteries are easily purchased locally from an off-grid supplier and hot water storage tanks are available on the internet. Set-up costs should include a plumber and an electrician.

Thanks for reading!"

[Acala]

The efficiency of these systems can be a complicated topic, particularly when so many definitions of "efficiency" exist. A gas engine fueled by wood will see a net thermal efficiency of about 15%, and 20% is possible. This assumes the system is operated at its optimal efficiency, which tends to be a high output relative to its rated power. By contrast, a typical small steam system sees 5-8%. A small steam system can be a lot more efficient, but not without some really complicated and expensive engineering. So, if wood is the desired fuel, and high power levels are desired, then the gas engine is the more efficient option. Things get a lot more complicated under real world conditions. In the end, it all depends on the application.

I have not done any study of the subject, but where the loss of energy seems to be in a wood gas system is in all the heat used to produce the hot, bare carbon. In other words, when you put wood in your gasifier, much of the heat generated by the burning of the cellulose, which happens entirely in the gasifier, is lost. I think some is recovered in the breaking of the h-o bonds, but my understanding is that the gasifiers run HOT!. A good steam boiler would capture most of that. But then lots of heat escapes a steam engine with the exhaust.

So I guess I don't know.

[danda]

I looked into wood gasification briefly because I would like to use it to power our tractors and such. However, I wanted to generate the gas, store it, and use it later.... and it seems that wood gasification is not good for that, though I forget why exactly. They all strongly recommend running the engine directly off the gasifier, which means it must be physically on board the vehicle. ick.

Now for a home genset, i can see where wood-gas could be more practical. The pics and article above are pretty cool.

Has anyone heard of storing the gas and using it later on demand? Or can you explain why that is a bad idea?

[Dr.3D]

I looked into wood gasification briefly because I would like to use it to power our tractors and such. However, I wanted to generate the gas, store it, and use it later.... and it seems that wood gasification is not good for that, though I forget why exactly. They all strongly recommend running the engine directly off the gasifier, which means it must be physically on board the vehicle. ick.

Now for a home genset, i can see where wood-gas could be more practical. The pics and article above are pretty cool.

Has anyone heard of storing the gas and using it later on demand? Or can you explain why that is a bad idea?

If wood gas is anything like coal gas, it can be stored in an inverted barrel, submerged in water. The biggest problem with this is having to anchor a cylindrical basket around the floating drum to keep it from falling over. The more gas you want to store, the bigger or more drums you need. When I was a kid, they had some that were 100 feet in diameter and 7 stories high. They had a rather expensive cage built around them to keep the drum from falling over.

Here is a picture of one of the smaller ones. Might be a little big for one home.

[Deborah K]

Biomass Gasification?? Sounds like what my poor husband goes through every time he eats chili.

sorry

[Dr.3D]

Biomass Gasification?? Sounds like what my poor husband goes through every time he eats chili.

sorry

LOL, that's azz gaz.... I understand it is similar to wood and coal gas though, in that is contains some methane.
BTW.... it's usually harder on those around the person suffering from azz gaz than it is on the sufferer.

[buenijo]

I have not done any study of the subject, but where the loss of energy seems to be in a wood gas system is in all the heat used to produce the hot, bare carbon. In other words, when you put wood in your gasifier, much of the heat generated by the burning of the cellulose, which happens entirely in the gasifier, is lost. I think some is recovered in the breaking of the h-o bonds, but my understanding is that the gasifiers run HOT!. A good steam boiler would capture most of that. But then lots of heat escapes a steam engine with the exhaust.

So I guess I don't know.

Hi Acala. I edited the orginal post to add some publications available online. The first one I added ("Handbook of Biomass Gasifier Engine Systems") is probably the single best resource there is.

The thermal losses from a good gasifier are about the same as those from a good steam boiler (about 20%)... that is, a good steam boiler will be 80% efficient. The very high temperatures in a gasifier are achieved through limited combustion in a very small volume, and a good gasifier will have excellent insulation to maintain high temperature there. It's important to understand that most of the biomass is not combusted in the gasifier. Rather, the high temperature converts the solid structure of the fuel to a vapor (mostly CO, H2, CO2, H2O vapor, and tar vapors). Furthermore, some endothermic reactions take place where much of the heat of combustion used to maintain the high temperature is converted to chemical energy(*). The primary fuel gases produced include carbon monoxide, hydrogen, and small amounts of hydrocarbons. The thermal losses that do occur are mostly those associated from cooling the gas before it moves into the engine.

The primary reason for the higher thermal efficiency of a gasifier engine system is the higher temperature and higher expansion ratio in the gas engine vs. the conventional steam engine. Still, I believe a good small steam system has advantages over biomass gasification in a home power setting for its ability to use a much wider range of biomass fuels with less processing, superior waste heat recovery, relative simplicity, and its ability to operate quietly at very low power levels for many tens of thousands of hours. Unfortunately, while it's possible for steam to do this, it's going to take some clever engineering combined with a lot of money to make a system competitive with a good wood gas engine system.

(*) The endothermic reactions include the formation of CO and H2 from C and H2O, the formation of CO from C and CO2, and the cracking of tars. So, while a lot of the volatiles are combusted in the system, very little of the charcoal (i.e. carbon) is combusted (the free oxygen is consumed in the combustion of volatiles). Rather, the hot char that remains reacts with combustion products of the volatiles (CO2 and H2O) to generate more fuel gas. In other words, the system converts a lot of the combustion heat to chemical energy.