30
Pelletized rice straw can be used as fuel, animal feedstock, or material for anaerobic digestion. The pelletizer die hole size is known to have an important effect on
the moisture content of the pellet, while the temperature reached during pelletization can also influence pellet quality.
Straw densification through pelletizing can increase bulk density from 600 to
800 kg m
−3
(Kaliyan and Morey 2009; Kargbo et al. 2009). The average specific
mass of a straw pellet may also reach 1244 kg m
−3
, which is higher by 1000% compared with loose straw. Said et al. (2015) reported that the ideal value for highquality pellets is 1200 kg m
−3
. Pelletized rice straw has an advantage of preventing
straw materials from floating in water when using the straw for other processes such
as anaerobic digestion. The use of enriched pellets as feed for cows results in minimal waste and leftovers during feeding.
The production costs of rice straw pellets are computed based on the estimated
cost of equipment and assumed cost of straw and labor at the locality (including
depreciation, material, and labor costs). In one case study in Vietnam (Nguyen-VanHieu et al. 2018), materials (straw and cattle feed additives) cost US$ 280 t
−1
; straw
prices ranged from US$ 90 to 100 t
−1
; and depreciation, labor, and electricity costs
were estimated based on the existing rice husk pelletizing system. Given a pelletizing cost of US$ 22.6 t
−1
, straw pellets cost approximately US$ 125 t
−1
. Pelletizing
can significantly reduce transportation costs. In the same case study, a cubic bale
was sold at a price of US$ 110 t
−1
excluding transportation cost, which was about
US$ 35.5 t
−1
for a distance of 1000 km by truck. The cost of grinding straw was
estimated at US$ 100 t
−1
. Transporting pelletized straw was found to be more economical and practical compared to bales.
2.6 Conclusions and Recommendations
Alongside the spread of combine harvesters, government regulations against open
field burning of rice straw, and increasing use of straw, mechanized collection is
gaining ground in Asia. Small balers with a capacity of 1–2 t h
−1
, which are easy to
maneuver in small fields, have been found suitable in Cambodia, the Philippines,
and Vietnam. The self-propelled baler—a successful innovation in Vietnam—is
being adapted in Southeast Asian countries, such as Cambodia and the Philippines,
because it reduces labor requirements in hauling baled straw from the field to the
bund. Another advantage is the machine’s rubber chain-wheel mechanism, which
makes it suitable for use in wet fields, particularly in areas where field drainage is a
problem.
A case study in Vietnam showed that mechanized collection can reduce costs by
about 68% compared to manual collection. As labor scarcity rises, machines become
a more sustainable option for Asian rice fields where farmers have traditionally
resorted burning straw after harvest, which is easier and cheaper.
As Asian countries move towards field consolidation and upgrading of contractual arrangements among farmers, mechanized collection is likely to become more
C. Balingbing et al.
Pelletized rice straw can be used as fuel, animal feedstock, or material for anaerobic digestion. The pelletizer die hole size is known to have an important effect on
the moisture content of the pellet, while the temperature reached during pelletization can also influence pellet quality.
Straw densification through pelletizing can increase bulk density from 600 to
800 kg m
−3
(Kaliyan and Morey 2009; Kargbo et al. 2009). The average specific
mass of a straw pellet may also reach 1244 kg m
−3
, which is higher by 1000% compared with loose straw. Said et al. (2015) reported that the ideal value for highquality pellets is 1200 kg m
−3
. Pelletized rice straw has an advantage of preventing
straw materials from floating in water when using the straw for other processes such
as anaerobic digestion. The use of enriched pellets as feed for cows results in minimal waste and leftovers during feeding.
The production costs of rice straw pellets are computed based on the estimated
cost of equipment and assumed cost of straw and labor at the locality (including
depreciation, material, and labor costs). In one case study in Vietnam (Nguyen-VanHieu et al. 2018), materials (straw and cattle feed additives) cost US$ 280 t
−1
; straw
prices ranged from US$ 90 to 100 t
−1
; and depreciation, labor, and electricity costs
were estimated based on the existing rice husk pelletizing system. Given a pelletizing cost of US$ 22.6 t
−1
, straw pellets cost approximately US$ 125 t
−1
. Pelletizing
can significantly reduce transportation costs. In the same case study, a cubic bale
was sold at a price of US$ 110 t
−1
excluding transportation cost, which was about
US$ 35.5 t
−1
for a distance of 1000 km by truck. The cost of grinding straw was
estimated at US$ 100 t
−1
. Transporting pelletized straw was found to be more economical and practical compared to bales.
2.6 Conclusions and Recommendations
Alongside the spread of combine harvesters, government regulations against open
field burning of rice straw, and increasing use of straw, mechanized collection is
gaining ground in Asia. Small balers with a capacity of 1–2 t h
−1
, which are easy to
maneuver in small fields, have been found suitable in Cambodia, the Philippines,
and Vietnam. The self-propelled baler—a successful innovation in Vietnam—is
being adapted in Southeast Asian countries, such as Cambodia and the Philippines,
because it reduces labor requirements in hauling baled straw from the field to the
bund. Another advantage is the machine’s rubber chain-wheel mechanism, which
makes it suitable for use in wet fields, particularly in areas where field drainage is a
problem.
A case study in Vietnam showed that mechanized collection can reduce costs by
about 68% compared to manual collection. As labor scarcity rises, machines become
a more sustainable option for Asian rice fields where farmers have traditionally
resorted burning straw after harvest, which is easier and cheaper.
As Asian countries move towards field consolidation and upgrading of contractual arrangements among farmers, mechanized collection is likely to become more
C. Balingbing et al.