A schematic of the on-farm updraft gasification system is presented
in Fig. 1. The fixed bed reactor was cylindrical in shape with
an average feed rate of 40 kg h1. The feedstock was transferred
from a hopper to the top of the reactor by means of a motorised
screw feeder. The reactor was filled to the top with PL, which
was continuously rotated downwards at approximately 5 rpm
using steel impellers. Two induced draft fans located downstream
from the gasifier pulled the gasification medium air from the bottom
of the reactor through the gasification system generating the
updraft, which also resulted in a slight pressure drop. The speed
of the fans controlled the air flow rate and air intake to maintain
a bed temperature between 580 and 680 C. Two thermocouples
were placed inside the reaction zone of the reactor to measure
the temperature. The gasifier was preheated with propane gas
which was initially maintained as the feedstock was added until
auto-thermal conditions were achieved. Tar and water condensed
on the cold surfaces of metal packing in two water cooled scrubber
units and were collected in a storage tank. The gas entered the first
scrubber at around 85 C and exited it around 50 C; the gas exited
the second scrubber at around 32 C. The product gas passed
through an additional air cooled heat exchanger with the aim of
lowering the moisture content in the gas before flaring in a gas
burner. A Testo 350 XL was used to measure the flow rate of the
cooled product gas, being 28.8 Nm3 h1 at 12.3 C. The residual
unconverted solid char passed through a grate at the base of the
gasifier and was augered into a sealed collection drum. The flow
rates of the char and the tar/water emulsion were determined several
times by measuring the mass output during a time period of
30 min. A more detailed description of the gasifier and the process
can be found in Joseph et al. (2012). The gasifier operated for 14 h
on each of three consecutive days and >560 kg of litter was
gasified.