50
configurations can be used for biomass pyrolysis such as rotary kilns, fluidized bed,
fixed bed, entrained flow, and tubular reactors. Pyrolysis systems can also be combined with other thermal conversion technologies (Chen et al. 2015).
Data and experience on rice straw pyrolysis are mostly from laboratory-scale
experiments. There are limited studies reported on bio-oil production in a bench- or
pilot-scale process with capacities ranging from 1 to 3 kg h
−1
(Park et al. 2004;
Tewfik et al. 2011; Yang et al. 2011). Various studies on rice straw pyrolysis show
promising results. In the investigation of Nam et al. (2015) using bench scale auger,
batch, and fluidized bed reactors, a 43% bio-oil yield from rice straw was obtained
using a fluidized bed reactor and 48% bio-char yield was obtained using a batch
reactor. The bio-oil and bio-char heating value from the study were 31 and
19 MJ kg
−1
, respectively, and the energy conversion efficiencies of the different
reactors tested ranged from 50 to 64%. In another study (Park et al. 2014) using
slow pyrolysis process, the combined energy yields from bio-oil and syngas reached
60% at pyrolysis temperatures over 500 °C. Biochar served as the main product
capturing 40% energy and 45% of rice straw carbon. Rice straw was also compared
with other lignocellulosic biomass (i.e., corn cob, wheat straw, rice husks) in a study
conducted by Biswas et al. (2017). Maximum bio-oil production from rice straw of
about 28.4% was observed at 400 °C.
Similar to other lignocellulosic biomass, rice straw, which contains about 38.3%
cellulose, 22.2% hemicellulose, and 14.23% by weight lignin (Ukaew et al. 2018)
exhibits maximum decomposition at temperatures ranging from 300–450 °C
(Biswas et al. 2017). Bio-oil produced using an entrained flow type pyrolyzer at
550 °C contains high carbon content (54.12% wt) and H/C molecular ratio contributing to high energy content of about 29 MJ kg
−1
(Tewfik et al. 2011). Rice straw
bio-oil, however, was found to be slightly acidic (Yang et al. 2011; Park et al. 2004).
This can be improved by pretreating the biomass by torrefaction prior to pyrolysis
(Ukaew et al. 2018). The removal of minerals via dilute acid washing can also
increase bio-oil production, particularly levoglucosan. Baloch et al. (2016) also suggested that leaching rice straw with water can improve the pyrolysis process. Higher
bio-oil yields at temperatures greater than 500 °C were also obtained from acidwashed rice straw compared to untreated rice straw using a fixed bed reactor operated at 300 to 700 °C (Li et al. 2012). Some drawbacks on rice straw pyrolysis
include the need for biomass drying and grinding, which requires additional energy
input to the process.
4.3.2 Gasification
Gasification is the thermal conversion of carbonaceous biomass in an oxygendeficient environment to produce synthesis gas (or syngas) through a series of
chemical reactions. The basic reactions involved in gasification are the following
(Agarwal 2014; Young 2010):
M. C. Maguyon-Detras et al.
configurations can be used for biomass pyrolysis such as rotary kilns, fluidized bed,
fixed bed, entrained flow, and tubular reactors. Pyrolysis systems can also be combined with other thermal conversion technologies (Chen et al. 2015).
Data and experience on rice straw pyrolysis are mostly from laboratory-scale
experiments. There are limited studies reported on bio-oil production in a bench- or
pilot-scale process with capacities ranging from 1 to 3 kg h
−1
(Park et al. 2004;
Tewfik et al. 2011; Yang et al. 2011). Various studies on rice straw pyrolysis show
promising results. In the investigation of Nam et al. (2015) using bench scale auger,
batch, and fluidized bed reactors, a 43% bio-oil yield from rice straw was obtained
using a fluidized bed reactor and 48% bio-char yield was obtained using a batch
reactor. The bio-oil and bio-char heating value from the study were 31 and
19 MJ kg
−1
, respectively, and the energy conversion efficiencies of the different
reactors tested ranged from 50 to 64%. In another study (Park et al. 2014) using
slow pyrolysis process, the combined energy yields from bio-oil and syngas reached
60% at pyrolysis temperatures over 500 °C. Biochar served as the main product
capturing 40% energy and 45% of rice straw carbon. Rice straw was also compared
with other lignocellulosic biomass (i.e., corn cob, wheat straw, rice husks) in a study
conducted by Biswas et al. (2017). Maximum bio-oil production from rice straw of
about 28.4% was observed at 400 °C.
Similar to other lignocellulosic biomass, rice straw, which contains about 38.3%
cellulose, 22.2% hemicellulose, and 14.23% by weight lignin (Ukaew et al. 2018)
exhibits maximum decomposition at temperatures ranging from 300–450 °C
(Biswas et al. 2017). Bio-oil produced using an entrained flow type pyrolyzer at
550 °C contains high carbon content (54.12% wt) and H/C molecular ratio contributing to high energy content of about 29 MJ kg
−1
(Tewfik et al. 2011). Rice straw
bio-oil, however, was found to be slightly acidic (Yang et al. 2011; Park et al. 2004).
This can be improved by pretreating the biomass by torrefaction prior to pyrolysis
(Ukaew et al. 2018). The removal of minerals via dilute acid washing can also
increase bio-oil production, particularly levoglucosan. Baloch et al. (2016) also suggested that leaching rice straw with water can improve the pyrolysis process. Higher
bio-oil yields at temperatures greater than 500 °C were also obtained from acidwashed rice straw compared to untreated rice straw using a fixed bed reactor operated at 300 to 700 °C (Li et al. 2012). Some drawbacks on rice straw pyrolysis
include the need for biomass drying and grinding, which requires additional energy
input to the process.
4.3.2 Gasification
Gasification is the thermal conversion of carbonaceous biomass in an oxygendeficient environment to produce synthesis gas (or syngas) through a series of
chemical reactions. The basic reactions involved in gasification are the following
(Agarwal 2014; Young 2010):
M. C. Maguyon-Detras et al.