Wood Gasifier
Stages
Burn
Classic build - 55 gallon drum, shaker, starter tube. Need to look at FEMA instructions for relative sizing. Since this is stationary, I could use firebrick and at the outermost layer just seal it to be completely air tight.
I could build with cement instead of metal.
Cyclone Seperator
Good information here: https://www.nrel.gov/docs/legosti/old/3022.pdf (pg 86)
- Maybe make this a spray scrubber.
I want to do a lot of cooling at this stage. The chamber will have water cooling around it. Typically these are built from steel, but I think aluminum will work better to allow greater thermal flow. This will require a pump.
Cooling Tower
Out of the tar vortex I'll have a manifold rising. The bottom will form a slight V so that any condensation will drip back into the tar collector. The tower will have forced air that then passes goes into the burn chamber. This will preheat the air. I think these could be made from aluminum conduit.
Water Scrubber
The gas then enters a tube that also contains a spray of water. I think there will also be plastic medium to increase surface area. The gas exits the tube below the bottom, and there is reserve tank at the bottom. I'll need a pump with pretty decent flow rate for this.
From this I like the 3 tube setup, perhaps 2 would work. Hot(ish) gas enters the bottom of the first tube and rises against a flow of water. Then it goes down a second tube. The first tube will have a very efficient heat transfer because the coolest water will be in contact with the coolest gas.
So this might be really half-baked, but worth investigating. If the incoming air has enough force behind it, it could spin the blades of a turbine. That could drive a centrifugal pump. The whole system would be contained and driven by the airflow. Though the same principle could be used in simpler ways. A turbine in the output shaft could drive a simple one-way pump.
Media Filter
Paper or saw dust. I'd like to get the earlier stages efficient enough to not need this, but it will be better to put it in at first and once I can run it for a long time without changing the filter, then remove it.
Condenser
Not sure if this is necessary. Gas passes through an aluminum heatsink attached to a peltier device. This should cool the air enough to cause any moisture to condense. The heatsink is mounted vertically and the air comes in from the top. The gas then goes down and back up to pass over a second heatsink connected to the other side of the device which then reheats the air. This should allow the peltier to perform very efficiently.
Exit
At this point the gas should be clean enough for the generator. Need a two valve setup to balance the air mixture. I may setup the generator my self. Get an ICE in the correct power range and a separate alternator. I'd like to be able to do 3-phase power.
At this point there also needs to be a flare port that can be used to start the system.
Air Circulation
Air is forced in, first passing over the cooling towers. The air is forced in the top so it runs counter to flow of air in the tubes. It then over a radiator that cools the water used in the tar vortex. The water is flowing counter to the air. This air then passes into the burn chamber. It should already be well above 200F. This should help dry the wood and allow for more efficient combustion.
A simple blower probably won't be enough. Centrifugal may do it, but a supercharger may be better.
Automation
- Shaker
- Low fuel
- Thermal monitoring
- Ash Clean out
If the fuel production can be standardized, I could include a larger hopper and a feeder system. A screw feeder would probably be best. To level sensors could form a Schmitt setup, when it drops below A, fill until it reaches B.
Heat
This could be wired into the heating system.
Fuel Production
I will probably have access to a lot of saw dust. Also no shortage of small branches and brush. Large media needs to get broken down to standard size. Small media will need to be compressed into pellets. Then I need some form of hopper that can feed the system.
I can also experiment with "baking" the fuel at about 250F, probably with a solar kiln to reduce the moisture content. Engine exhaust can be used for this as well.
I should also see if I can find sources of bio-waste. Either free or very low cost, like corn cobs or hulls.
Mechanical Feedback
I will need pumps to move water and air through the system. Rather than having these be electric, it could be more efficient to attach them to the drive shaft of the generator. The only catch is that this will complicate starting the system. I will need some reserve of the gas to run the generator long enough to start the system, then once it's running, pull some of the gas to replenish the starting source.
Start by just using a propane tank. Then figure out how long it takes to get it running. Then figure out how much gas is needed, finally, build a collection tank to hold 2x that.
Collection
I'd like a way to collect the output. Since it takes a while to get this going it would be better if it turned on when the tank was empty and run until it was full. I'm assuming this will be a final backup for electricity, so it could turn on when the batteries and gas tank is low and run until both are full again.