3
ability based on global rice production data (IRRI 2019) and the straw:grain ratios
of 0.5 and 0.7 from the experiment.
Annual rice straw production is in the ranges of 100–140, 330–470, and 370–520
million t/year in Southeast Asia (SEA), the whole of Asia, and over the world,
respectively (Fig. 1.2).
1.2 Rice Straw Properties and Composition
Utilization of rice straw is dependent on its characteristics, which can be divided into
three major categories: (1) physical properties, (2) thermal properties, and (3) chemical composition. Physical properties include bulk density, heat capacity, and thermal conductivity. Density is the most relevant to the handling and storage of rice
straw. Thermal properties, and heating value; these properties are relevant when biomass is converted to energy. Chemical composition, such as lignin, cellulose, hemicellulose/carbohydrates, and nutrient contents, are relevant to applications, such as
for livestock feed and soil fertility. Characterizing rice straw is helpful for life cycle
analysis and efficiency calculations. The most common methods used in the characterization of rice straw can be referenced from the National Renewable Energy
Laboratory (NREL) and the American Society for Testing and Materials (ASTM).
1.2.1 Physical Properties
Based on various studies, the bulk density of rice straw can vary depending on the
different forms it may take. Loose rice straw, collected directly from the field, can
range in density from 13 to 18 kg m
−3
in dry matter (dm) (Migo 2019). Chopped
straw, ranging in length from 2 to 10 mm (Chou et al. 2009), can have a density
range of from 50 to 120 kg m
−3
(Liu et al. 2011), depending on the equipment used.
Depending on the baler equipment used, baled straw size and the compression ratio,
and thus bulk density, will vary. A round rice straw bale with a 70-cm length and
50-cm diameter has a bulk density ranging from 60 to 90 kg m
−3
dm (Nguyen-VanHung et al. 2016b). The density of rice straw briquettes with a 90-mm diameter and
7- to 15-mm thickness is 350–450 kg m
−3
dm (Munder 2013). The density of rice
straw pellets with an 8-mm diameter and from 30 to 50 mm in height is 600–
700 kg m
−3
dm (Nguyen-Van-Hieu et al. 2018).
As compared to rice husks, which have a density of between 86 and 114 kg m
−3
(Mansarav and Ghaly 1997), unprocessed, loose rice straw has a low density. This
means a higher volume per kilogram, implying higher shipping and handling costs
as well as more complications in processing, transportation, storage, and burning
(Duan et al. 2015, Liu et al. 2011). Rice straw volume can be reduced through processing but this will require additional energy inputs. Various size-reduction methods can increase density of the straw including using of pellet mills (Nguyen-V-Hieu
1 Rice Straw Overview: Availability, Properties, and Management Practices
ability based on global rice production data (IRRI 2019) and the straw:grain ratios
of 0.5 and 0.7 from the experiment.
Annual rice straw production is in the ranges of 100–140, 330–470, and 370–520
million t/year in Southeast Asia (SEA), the whole of Asia, and over the world,
respectively (Fig. 1.2).
1.2 Rice Straw Properties and Composition
Utilization of rice straw is dependent on its characteristics, which can be divided into
three major categories: (1) physical properties, (2) thermal properties, and (3) chemical composition. Physical properties include bulk density, heat capacity, and thermal conductivity. Density is the most relevant to the handling and storage of rice
straw. Thermal properties, and heating value; these properties are relevant when biomass is converted to energy. Chemical composition, such as lignin, cellulose, hemicellulose/carbohydrates, and nutrient contents, are relevant to applications, such as
for livestock feed and soil fertility. Characterizing rice straw is helpful for life cycle
analysis and efficiency calculations. The most common methods used in the characterization of rice straw can be referenced from the National Renewable Energy
Laboratory (NREL) and the American Society for Testing and Materials (ASTM).
1.2.1 Physical Properties
Based on various studies, the bulk density of rice straw can vary depending on the
different forms it may take. Loose rice straw, collected directly from the field, can
range in density from 13 to 18 kg m
−3
in dry matter (dm) (Migo 2019). Chopped
straw, ranging in length from 2 to 10 mm (Chou et al. 2009), can have a density
range of from 50 to 120 kg m
−3
(Liu et al. 2011), depending on the equipment used.
Depending on the baler equipment used, baled straw size and the compression ratio,
and thus bulk density, will vary. A round rice straw bale with a 70-cm length and
50-cm diameter has a bulk density ranging from 60 to 90 kg m
−3
dm (Nguyen-VanHung et al. 2016b). The density of rice straw briquettes with a 90-mm diameter and
7- to 15-mm thickness is 350–450 kg m
−3
dm (Munder 2013). The density of rice
straw pellets with an 8-mm diameter and from 30 to 50 mm in height is 600–
700 kg m
−3
dm (Nguyen-Van-Hieu et al. 2018).
As compared to rice husks, which have a density of between 86 and 114 kg m
−3
(Mansarav and Ghaly 1997), unprocessed, loose rice straw has a low density. This
means a higher volume per kilogram, implying higher shipping and handling costs
as well as more complications in processing, transportation, storage, and burning
(Duan et al. 2015, Liu et al. 2011). Rice straw volume can be reduced through processing but this will require additional energy inputs. Various size-reduction methods can increase density of the straw including using of pellet mills (Nguyen-V-Hieu
1 Rice Straw Overview: Availability, Properties, and Management Practices