When smoking food, the fuel (whether it's wood or
charcoal) is first heated to produce smoke, and what's left
over is burnt for heat. The smoke of course provides the
flavor in a barbecue, but the hot gas which results from
burning is flavorless.
This means that a conventional smoker has
a mix of yummy
smoke and flavorless hot air.
This idea is to separate, as much as possible, the
production of smoke, from the production of hot air, and
only expose our food to the smoke.
Here's how I expect it to work:
Wood pellets start in a hopper with a close fitting lid.
When the smoker is operating, the lid should only be lifted
to add more fuel.
The pellets are moved out of the bottom of the hopper into
a screw conveyor -- the variant where the screw is rigidly
attached to the tube, and the tube and screw rotate
together.
Part of the conveyor tube is heated externally, by a fire.
This of course heats the wood pellets within, causing
pyrolysis. Smoke and charcoal emerge from end of the
conveyer opposite the hopper.
The smoke is directed into the food cooking chamber,
which is as close to airtight as possible.
After flavoring the food, the smoke is mixed with air and
fuel gas (propane at first), and burnt. This fire is then
used to heat the conveyor tube. Finally, the waste gas is
pulled up the chimney by an electric exhaust fan.
The charcoal which falls out of the screw conveyor falls
into a second hopper, which feeds into a charcoal gasifier.
In the gasifier, air is pulled through the charcoal,
producing carbon monoxide, a gaseous fuel. This carbon
monoxide (as soon as production of it begins) replaces the
propane fuel.
To distribute heat more evenly in the food cooking
chamber, a convection fan might be added (fan blades
inside, motor outside of course).
To improve fuel efficiency, an economizer might be added
-- a heat exchanger between the air about to be sucked out
through the fan, and the air being used for combustion.
For temperature control, a computer regulates the exhaust
fan speed, the rotation rate of the screw conveyor, how
much air is allowed to flow through the gasifier, and the
amount of propane supplied.
Users should be cautioned that concentrated wood smoke is
flammable, so whenever the cooker is operating, they
should be very cautious when opening the cooking chamber
to add, remove, or turn food.