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Biomass Pyr olysis and Bio-Oil Refineries 223

Perhaps the most advanced slow pyrolysis reactors developed so
far were those built and operated by the wood-distillation industry
(Klar and Rule 1925). Advanced batch and semicontinuous reactors
such as the American, Schwartz, Ljungberg, Ottelinska, Reichenbach,
Leschhorn, Swedich, Bosnian Meiler, and Meyer kilns were used by
this industry.
Brazil is currently, the world largest charcoal producer with an
annual production output of around 10 million tons of charcoal most
of which is used in the iron and steel industry (Peláez-Samaniego
et al. 2008). In spite of the size and importance of this industry, car-
bonization reactors in operation are basically traditional low-efficiency
processes with very low recovery of volatile factions. The yields of
charcoal obtained are around 25 mass%. The main pyrolysis reactors
in operation in Brazil are (1) internally heated by controlled combus-
tion of the raw material (autothermal systems) and (2) externally
heated by combustion of firewood, fuel oil, or natural gas (Peláez-
Samaniego et al. 2008).
Internally heated kilns sacrifice up to 20 percent of the biomass in
an initial heating step in which air is supplied to heat up the kiln. The
yields of gases and vapors are as high as 60 percent. Some of the most
common configurations of this type of kilns are alvenaria kilns and
metallic kilns (Rosillo-Calle et al. 1996; Pinheiro 2001; Kammen and
Lew 2005; de Meira et al. 2005).
Externally heated kilns are commonly used to produce large vol-
umes of charcoal. Heat is provided by hot combustion gases pro-
duced by an external combustion chamber where an auxiliary fuel is
burned. Although the control of the process is better and the resulting
charcoal has better quality, these systems are more expensive to build
and operate (Peláez-Samaniego et al. 2008).

7.5.2 Fast Pyrolysis
Although fast pyrolysis is related to the traditional carbonization
industry, polycondensation reactions leading to the formation of
charcoal are greatly mitigated, and the selectivity toward fragmenta-
tion and depolymerization reactions favored by heating the biomass
particles at rates between 10 and 10,000°C/s. Thus, these reactors are
able to convert up to 80 mass% of the biomass into a single oily phase
(Bridgwater et al. 1999). Fast pyrolysis was developed in the 1970s
and 1980s as a response to some of the challenges created by the first
and second petroleum crises.
Low yields of gases (around 15 mass%) are obtained when the
residence time of pyrolysis vapors is below 2 s (Graham et al. 1984).
An exhaustive analysis of the present status of biomass pyrolysis
technologies is not possible within the scope of this chapter. Excellent
reviews on biomass fast pyrolysis technologies can be found elsewhere