4
et al. 2018), roller presses, piston presses, cubers, briquette presses, screw extruders, tabletizers, and agglomerators (Satlewal et al. 2017).
When used for bioenergy, rice straw’s bulk density influences the combustion
process as it affects the time required in the reactor (Zhang et al. 2012). Rozainee
et al. (2008), as cited by Zhang et al. (2012), reported that a low bulk density causes
poor mixing and nonuniform temperature distribution (unfavorable operating conditions), which decreases energy efficiency.
The moisture content of rice straw is an important consideration when determining how to process it and what it will be used for. For example, moisture content
affects the heating value of the straw, which is important when the byproduct is
intended for use as bioenergy. In addition, if rice straw volume is to be reduced, the
moisture content before compression should be between 12 and 17% (Kargbo et al.
2010). Unfortunately, the moisture content can fluctuate greatly due to the method
and duration of the straw’s storage (Topno 2015).
1.2.2 Thermal Properties
The calorific value is an essential parameter that shows the energy value of rice
straw, if to be used for bioenergy. Rice straw’s energy efficiency can be calculated
by dividing its energy output by its calorific value, which may be expressed as the
higher-heating value (HHV), wherein latent heat of the water is included, or lowerheating value (LHV). In terms of calorific value, rice straw has an HHV that ranges
from 14.08 to 15.09 MJ kg
−1
, as determined by different studies as shown in
Table 1.1 and is comparable to rice husks with a calorific value of around
14.2 MJ kg
−1
. However, the calorific value of rice straw is just one-third of that of
kerosene, which has a calorific value of 46.2 MJ kg
−1
.
In the proximate analysis, volatiles refer to the volatile carbon, combined water,
net hydrogen, nitrogen, and sulfur, which are first driven off in combustion. Rice
straw is characterized by high volatiles or volatile matter (VOM) (60.55–69.70%),
which is comparable to the biomass of other byproducts, such as sugar cane bagasse,
corn straw, wheat straw, etc. In bioenergy applications, specifically in combustion,
a high VOM has advantages, such as easier ignition and burning; but it also leads to
a rapid, more difficult-to-control combustion (Liu et al. 2011). Fixed carbon refers
to the carbon left after the volatiles are driven off. Rice straw has a fixed carbon
ranging from 11.10% to 16.75%, which is also comparable to other biomass.
The ultimate analysis reveals the elemental carbon, hydrogen, oxygen, nitrogen,
and sulfur composition of rice straw. Compared to fossil fuels, the carbon content of
rice straw biomass is less, while the oxygen and hydrogen contents are higher. As
shown in Fig. 1.3, the van Krevelen diagram shows the hydrogen-to-carbon (H:C)
and oxygen-to-carbon (O:C) ratios of various fuels. The ranges of H:C and O:C in
rice straw are 1.1–1.36 and 0.94–1.06, respectively, which place it in the biomass
region of the van Krevelen diagram, specifically in the cellulose region.
Rice straw ash content, which includes noncombustible residues, is around
18.67–29.1%. The high silica content of rice straw (Table 1.2) causes erosion probN. V. Hung et al.
et al. 2018), roller presses, piston presses, cubers, briquette presses, screw extruders, tabletizers, and agglomerators (Satlewal et al. 2017).
When used for bioenergy, rice straw’s bulk density influences the combustion
process as it affects the time required in the reactor (Zhang et al. 2012). Rozainee
et al. (2008), as cited by Zhang et al. (2012), reported that a low bulk density causes
poor mixing and nonuniform temperature distribution (unfavorable operating conditions), which decreases energy efficiency.
The moisture content of rice straw is an important consideration when determining how to process it and what it will be used for. For example, moisture content
affects the heating value of the straw, which is important when the byproduct is
intended for use as bioenergy. In addition, if rice straw volume is to be reduced, the
moisture content before compression should be between 12 and 17% (Kargbo et al.
2010). Unfortunately, the moisture content can fluctuate greatly due to the method
and duration of the straw’s storage (Topno 2015).
1.2.2 Thermal Properties
The calorific value is an essential parameter that shows the energy value of rice
straw, if to be used for bioenergy. Rice straw’s energy efficiency can be calculated
by dividing its energy output by its calorific value, which may be expressed as the
higher-heating value (HHV), wherein latent heat of the water is included, or lowerheating value (LHV). In terms of calorific value, rice straw has an HHV that ranges
from 14.08 to 15.09 MJ kg
−1
, as determined by different studies as shown in
Table 1.1 and is comparable to rice husks with a calorific value of around
14.2 MJ kg
−1
. However, the calorific value of rice straw is just one-third of that of
kerosene, which has a calorific value of 46.2 MJ kg
−1
.
In the proximate analysis, volatiles refer to the volatile carbon, combined water,
net hydrogen, nitrogen, and sulfur, which are first driven off in combustion. Rice
straw is characterized by high volatiles or volatile matter (VOM) (60.55–69.70%),
which is comparable to the biomass of other byproducts, such as sugar cane bagasse,
corn straw, wheat straw, etc. In bioenergy applications, specifically in combustion,
a high VOM has advantages, such as easier ignition and burning; but it also leads to
a rapid, more difficult-to-control combustion (Liu et al. 2011). Fixed carbon refers
to the carbon left after the volatiles are driven off. Rice straw has a fixed carbon
ranging from 11.10% to 16.75%, which is also comparable to other biomass.
The ultimate analysis reveals the elemental carbon, hydrogen, oxygen, nitrogen,
and sulfur composition of rice straw. Compared to fossil fuels, the carbon content of
rice straw biomass is less, while the oxygen and hydrogen contents are higher. As
shown in Fig. 1.3, the van Krevelen diagram shows the hydrogen-to-carbon (H:C)
and oxygen-to-carbon (O:C) ratios of various fuels. The ranges of H:C and O:C in
rice straw are 1.1–1.36 and 0.94–1.06, respectively, which place it in the biomass
region of the van Krevelen diagram, specifically in the cellulose region.
Rice straw ash content, which includes noncombustible residues, is around
18.67–29.1%. The high silica content of rice straw (Table 1.2) causes erosion probN. V. Hung et al.