buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

30 Daniel Dragomir-Stanciu and Marian Stancu
Fig. 1 shows schematically these regions for downdraft gasifier.
Air
g
g s
Pyrolysis
Combustion
Reduction
Biomass
Fig. 1 – Processes in the downdraft gasifier.
System should contain a cyclone for separating solid particles and a filter
for retaining tar.
2. Design of the Downdraft Gasiefier
2.1. Design Guidelines for Downdraft Gasiefiers
One of the most important parameters for the downdraft gasifiers is so
call “hearth load”.
The hearth load Bg is defined as the amount of producer gas reduced to
normal (p, T) conditions, divided by the surface area of the “throat” at the
smallest circumference and is usually expressed in m³/cm²/h. Alternatively the
hearth load can be expressed as the amount of dry fuel consumed, divided by
the surface area of the narrowest constriction (Bs), in which case hearth load is
expressed in kg/cm²/h.
Because one kilogramme of dry fuel under normal circumstances
produces about 2.5 m³ of producer gas, the relation between Bg and Bs is given
by:
Air
B = 2.5 B .
(1)
In the case of a “single” throat design, hearth diameter at air inlet height
should be 100 mm larger than “throat” diameter. Height of the reduction zone
should be more than 200 mm. Height of the air inlet nozzle plane should be 100
mm above the constriction. Throat inclination should be around 45°…60°.
Gas