Notes from Windward: #68
Our TLUD Produces Char for the GEK
Opalyn updates our gasification work
Windward has been experimenting with gasification units for several years. For example, we've built a top-lit up draft gasifier--called "TLUD" for short to differentiate that design from downdraft gasifiers such as the GEK. When complete, we're looking forward to using this TLUD to fire our traditional masonary baking oven with wood chips. Our TLUD gasifier has been standing by pending an improved burner design and a more efficient air supply.
Our initial work on the TLUD was done using our shop air compressor. That allowed us to test and confirm the design, but it's not a cost-effective way to generate the volume of compressed air needed. Two more common ways to generate low pressure air are squirrel-cage and paddle-wheel blowers. A check through the "Depot," our cache of used equipment and materials, turned up a 1/2 hp paddle-wheel unit that looked about the right size, so we hooked that up in order to run the TLUD enough to provide the char needed to start up the GEK.
A TLUD operates as a fluidized bed, a design which enables it to burn anything from large chunks of wood down to sawdust. Compressed air enters at the bottom of the unit and rises up through the biomass until it encounters the flame-front working its way down. The burning charcoal heats the wood just below the flame-front generating pyrolosys gas that is then converted to H2 and CO as it passes through the glowing charcoal layer. By stoping the TLUD prematurely, we were able to recover a few gallons of charcoal that's the same size and shape as the wood chips that we'll be fueling the GEK with.
lighting the TLUD
Here is our TLUD. The unit in the above photo is open to facilitate igniting the surface of the wood chips. Soon after the above pic was taken the lid and burner were put in place and secured with chain to prevent the lid from flying off in the event of a gas build up within the unit. With the new paddle fan running we had gas burning in just a few minutes, and were pleasantly surprised to note that the 1/2 hp was considerably stronger than needed.
testing out a 1/2 hp paddle fan
With the air supply question resolved, the next challenge involved coming up with a better burner design--we can't finish building the traditional oven until we have a reliable burner to build into the masonry. One of the nifty things we picked up on our trip to visit Jim at the ShipLab facility in Berkeley was an improvided burner based on a swirl design. Gas burners have to mix air with gas in order to create a combustible mixture, and that's usually accomplished using an inspirator which operates via the venturi effect. Essentially, a gas flowing past an opening will suck air in through that opening; the gas and air then combine to create a burnable mixture.
The problem with using a burner designed to work with either propane or natura gas is that those gases have a higher propagation rate than wood gas does. When the gas is flowing fast enough for the ispirator to work, it enters a linear burner at a rate faster than the flame front burns back toward the burner--in effect, the gas keeps blowing the flame out.
Opalyn relighting the TLUD's linear burner
Jim at Shipyard Labs in Berkeley came up with a design that gets around that problem--a swirl burner. We were delighted at how effectively Jim's design dealt with the problem of blow out, and are looking forward to mounting one on our TLUD.
One of our guiding philosophies is the Japanese concept of Kaizen, meaning continuous incremental improvement throughout all aspects of life. This means that we get a system up and running early on knowing that there will be large areas for improvement. We learn more by getting a small version of a system going, than by waiting until all the problems "appear" to be solved. No design survives contact with the real world, and the sooner we can ferret out design flaws, the better.
the GEK gets an initial load of charcoal
The next day when the TLUD had cooled down, we opened it up and transferred the needed charcoal to the GEK. Gasification is a dynamic process, and charcoal generation is a key part of that process, so the GEK will generate its own charcoal from here on--but it was very nice to have the TLUD standing by to give the GEK a "jump start."
Notes From Windward - Index - Vol. 68