The design and use of a TLUD gasifier is counter-intuitive;
rather than lighting the bottom of the feedstock pile, the
pile of feedstock must be ignited on top (Figure 1). The
TLUD was made out of 1/8" sheet-iron; it includes a 5'
tall chimney with a 30" diameter, capable of holding up to
24.5 ft
3
of feedstock. A 4"-wheel permanent split capacitor
blower fan was housed in an 18" × 18" square box at the
bottom of the chimney with a hinged door next to the fan
(Figure 2). If the gasification process becomes too hot,
resulting in ashing, or too cool, stalling the process, the
updraft can be regulated using the fan intake vent (Figure
2g). The box is separated from the chimney by a 1" screened
iron mesh, which allows free flow of the draft generated by
the fan and prevents the fan from overheating as the burnline moves from top to bottom. Two custom modifications
were made to the original design of the TLUD (Anderson
2009) which helped produce a uniform burn and provided
a relatively steady control of temperature. The first was a
detachable iron cap with an adjustable snout to control the
smoke, and the second was a clamp fitting for an intake
gas line. The intake gas used for this study was N
2
(99%
commercial grade). Once the burn-line reaches the bottom,
N2
gas is blown through the chimney, displacing any air
(oxygen) and gradually ceasing the gasification. Flushing
the system with an inert gas once the feedstock has been
completely charred prevents combustion, preserves the
char, and increases batch yields.