Effect of temperature and residence time on pyrolysis of rice husk pellet
NLN *156 -6/2021*5
Số: 156 - 6/2021
Trang 5 - 9
EFFECT OF TEMPERATURE AND RESIDENCE
TIME ON PYROLYSIS OF RICE HUSK PELLET
Nguyen Thi Thu Ha1,2, Pham Hoang Luong2, Laurent Van de Steene3,
Nguyen Hong Nam4
1 Energy Technology Faculty, Electric Power University, Vietnam;
2 School of Heat Engineering and Refrigeration, Hanoi University of
Science and Technology, Vietnam; 3Agricultural Research Center for
Development (CIRAD), France; 4 Energy Faculty, University of Science
and Technology of Hanoi, Viet Nam.
E-mail: hantt_ cnnl@epu.edu.vn
Received: December 15, 2020
Accepted: June 29, 2021
Received in revised form: June 28, 2021
Abstract: Biomass, mainly agricultural residues, is found widely available in Vietnam for energy
services. For these ends, it is normally upgraded by thermo-chemical or biological conversions before
being use as clean and efficient fuels. In this work, a pyrolysis of rice husk pellet was performed by mean
of an electrical oven. Three final temperature values were selected i.e 4000C, 6000C, and 8000C. For each
selected value of pyrolysis temperature, three levels of residence time for pyrolysis process were set as
0, 60 and 120 minutes, respectively. Some properties of the final product from the pyrolysis process i.e
volatile, ash content, fixed-carbon and higher heating value (HHV) were measured. The experimental
results have shown that in the current range of experimental work, charcoal products could get the highest
fixed-carbon content at the pyrolysis temperature of 6000C and with the residence time of 120 minutes.
Key words: Pyrolysis, rice husk pellet, biomass, charcoal.
NOMENCLATURE:
A - ash content, %
M – moisture content, %
FC – fix carbon content, %
V – volatile mater content, %
HHV – higher heating value, MJ/kg
Tf – final temperature of pyrolysis, oC
t – resident time, minute
carbon dioxide emission, gasification is
a
I. INTRODUCTION
promising route for agricultural residue treatment.
To enhance energy conversion efficiency, biomass
is usually upgraded to a more advanced energy
form before being gasified. Biomass pyrolysis to
produce charcoal is one of the most popular
options.
Vietnam is a long-standing agricultural country
with approximately 175 million tons of raw materials
for the production of biomass energy. It will be
equivalent to nearly 70 million tons of oil, twice the
total oil and gas exploitation volume of the Vietnam
Oil and Gas Group in 2016 [1]. The agricultural
residues, especially rice husk- one importance
biomass source, can be converted to useful energy
by several methods, i.e. thermo-chemical or
biological conversions. Among these methods, due
to a high energy conversion efficiency and low
Biomass pyrolysis to produce charcoal is one of
the most effective energy upgrading methods. In
the agricultural countries as Vietnam, the
capacities of rice products are very large,
especially rice husk. Although biomass can be
NLN *156 -6/2021*6
used directly as a primary energy resource,
pyrolysis will help to create a more advanced form
of energy. Charcoal, a product of pyrolysis, can be
converted into a gas fuel by gasification. This
enables biomass to be better applied in the
industrial electric generation where fossil fuels
have normally been used [2,3]. There are several
works to apply such technology to provide thermal
and / or electric energy [4,5]. In addition, the
application of rice husk pellet appears attractive in
Vietnam. This paper will present an experimental
study on pyrolysis of the rice husk pellet to
investigate the effect of the final temperature and
the residence time on the quality of char products.
a)
b)
II. EXPERIMENTAL METHODOLOGY
Materials selected for pyrolysis was rice husk
pellet with the properties presented in Table 1.1:
Table 1: Rice husk pellet properties.
M
(%)
V (%)
FC
(%)
A (%) HHV, MJ/kg
7.8
60.5
17.7
14.0 16.08
The rice husk pellets with 10 mm of diameter
and 20 mm of length were placed in the steel box
as shown in Fig. 1a. Total mass of these pellets for
each experiment was 200 grams. Sand was used
to fill the space between the cover and body of the
steel box. The box was then put in an electrical
furnace (see Fig. 1b) to start the pyrolysis process.
Nitrogen flow with flow rate of 1.5 l/min was used
during pyrolysis and char cooling periods.
Experiment mode settings were consisted of final
temperature and residence time. The heating rate
was remained unchange of 30C/min for all
experimental runs. The oven was first turned on so
that the furnace temperature increased gradually
until the pyrolysis temperature was reached. This
value was kept for a certain period of time (i.e
residence time) before the oven was turned off.
The product of pyrolysis process is shown in Fig.
1c.
c)
Figure 1: a) Box of rice husk pellet; b) Electrical
furnace c) Char product.
Pyrolysis conditions: Final temperatures were
o
o
400, 600, 800 C, heating rate was 3 C/mins,
residence time: 0, 60, 120 mins. The pyrolysis
system is shown in Fig.2.
Figure 2: Pyrolysis system
NLN *156 -6/2021*7
III. EXPERIMENTALRESULTS
The char properties are presented in table 2.
Table 2: Char properties
HHV,
Tf
t
FC
A
Yiel,
%
V (%)
MJ/k
g
oC
min
(%)
(%)
0
60
120
0
60
120
0
22.8 47.6 29.6 20.41 42.6
19.7 50.2 30.1 20.61 42.0
17.3 52.2 30.5 20.97 40.3
400
600
800
6.8
6.2
4.4
4.9
3.9
3.1
57.9 35.3 20.95 36.7
58.4 35.4 21.33 36.6
58.8 36.8 21.49 35.7
a)
58
37.1 20.85 35.2
60
120
57.9 38.2 20.62 34.4
57.6 39.3 20.50 34.2
b)
Figure 4: Effect of final temperature and residence
time on FC content (a) and HHV (b).
a)
Table 2 and Fig 3, 4 show that: when the final
o
o
temperature rises from 400 C to 800 C and the
residence time rises from 0 mins to 120 mins., FC
content of char grows up very significantly. At 400
oC, if the residencs time increases from 0 to 120
mins, it makes FC content of char increases 9.7%,
from 47.6% to 52.2%, meanwhile in the
temperature range of 600 – 800 oC, the increase is
slight and almost evenly. It can be explained as
following: The volatile meter releases strongest
o
around 400 C in pyrolysis process [6], therefore
the residences time is the important factor for both
yiel and quality of char (FC content). Besides, due
to the high volatile meter content of rice husk
pellets (17.3 – 22.8%), the increase in residences
time is an advantage point for volatile meter
release strongly continuously. In contrast, in the
b)
Figure 3: Effect of final temperature and
residence time on the volatile meter (a) and
ash (b) in char
o
range of 600 -800 C, the rate of volatile meter
NLN *156 -6/2021*8
escape decreased [6]. Furthermore, when the less
volatile content in the pellet (6.8 – 0.8 %), the less
effect of residences time on yiel and FC content.
The experimental data also shows that the char
reaches the highest FC content and HHV in the
conditions: Tf = 600 oC and residence time of 120
will be more uniform and higher than rice husk
pellets temperature due to the smaller particles and
bulk density.
o
mins, 5.8% and 21.49 MJ respectively. In 400 C,
when the residence time increases from 0 to 120
mins, FC content of char grows 47.6% to 52.2%,
therefore the HHV of char goes up slightly.
Meanwhile, by the pyrolysis temperature is 800 oC,
the FC content tends to decrease slightly when the
residence time extended. It also goes down
compare to char of 600 oC, the most reduction with
120 mins residence time condition, reached 5%.
This trend also mentioned in [7]: With high
temperature pyrolysis, a small part of FC in
biomass is converted into gas fuel. According to
Anca Couce et al [8], the secondary reactions that
Figure 5. FC of rice husk char and rice husk
pellets char. (Heating rate 30C/min, residence
time 120 mins.)
o
occur during the formation of char above 750 C
can lead to the phenomenon that a part of FC is
oxidized by the gases produced by previous
primary pyrolysis reactions. Chen et al [9] and Fu
et al [11] also confirmed that the char production of
900 oC pyrolysis can be decreased in the pore size
and surface square, therefore it is not advantage
for both gasification and combustion.
V. CONCLUSION
Temperature is the significant factor which effects
on the rice husk pellet pyrolysis for char production.
The result of pyrolysis study shows that in the
range of expriment, the quality of char from the rice
husk pellet reached the maximum value with
pyrolysis conditions: the final temperature is 600
The previous research with rice husk in the same
conditions [10] also dedicates that FC content
tends to decrease when pyrolysis temperature is
above 7500C. Figure 5 reveals that FC rate in rice
husk pellet char is slightly higher than in rice husk
when final temperature is below 6000C. It can be
explained that the rice husks temperature profile
o
oC, the heating rate is 3 C/mins, the residence
time is 120 mins. Besides, for char production, the
pyrolysis process should not go beyond 800oC as
its FC content would be decreased.
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heating industrial combustion chambers. Hanoi University of Science and Technology. (2018)
[2] Adams P.W.R and Manus M.C. Small-scale biomass gasification CHP utilization in industry: Energy
and environmental evaluation. Sustainable Energy technologies and Assessments 6. (2014)
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the current Status of the Technology. Energies. (2009).
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haracteristics of rice husk and rice husk pellet using a downdraft fixed-bed gasifier. Renewable Energy.
(2011)
[5] C.T.Chang, M. Costa, M. Lavilletta, A. Macaluso, D. Piazzullo, L. Vanoli. Thermo-economic analyses
of a Taiwanese combined CHP system fuel with syngas from rice husk gasification. Energy. (2018)
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NLN *156 -6/2021*9
[7] Hoang-Luong Pham. Wood Energy Basics: A Technical Document, Regional Wood Energy
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(1999)
[8] Anca-Couce Andrꢀs, Alba Dieguez- Alonso, Nico Zobel, Anka Berger, Norbert Kienzl and Frank
Behrendt. Influence of heterogerous secondary reactions during slow pyrolysis on char oxidation
reactivity of woody biomass. Energy&Fuel. (2017)
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process for char coal production. Thermal Energy review. (2018)
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ꢀNH HƯꢁNG CꢂA NHIꢃT Đꢄ VÀ THỜI GIAN NHIꢃT
PHÂ N ĐꢅN CHẤT LƯỢNG NHIꢃT PHÂ N CꢂA VIÊN NꢆN
TRẤU
Nguyễn Thị Thu Hà1,2, Phạm Hoàng Lương2, Laurent Van de Steene3,
Nguyễn Hồng Nam4
1 Khoa Cô ng nghệ năng lượng, Đại học điện lực, Việt Nam
2 Viện Khoa học và Cô ng nghệ Nhiệt-Lạnh, Đại học Bá ch Khoa Hà Nội
3Trung tâ m nghiên cứu quốc tế về nô ng nghiệp (CIRAD), Cộng hò a Phá p
4 Khoa Năng lượng, Đại học Khoa học và Cô ng nghệ Hà Nội, Việt Nam
E-mail: hantt_ cnnl@epu.edu.vn
TꢀM TꢁT
Sinh khối, chủ yếu là phụ phẩm nô ng nghiệp, được sꢀ dụng rộng rã i ở Việt Nam như một nguꢁn năng
lượng năng lượng. Đối với mục tiêu cꢂp nhiệt, sinh khối thường được nâ ng cꢂp bằng cá ch chuyển đổi nhiệt
hó a học hoặc sinh học trước khi được sꢀ dụng làm nhiên liệu sạch và hiệu quả. Trong cô ng trì nh này, quá
trì nh nhiệt phâ n viên trꢂu được thực hiện bằng lò điện. Ba giá trị nhiệt độ cuối cùng được chọn là 4000C, 6000C
và 8000C. Đối với mỗi giá trị của nhiệt độ nhꢂt định, 3 mức thời gian lưu trú cho quá trình nhiệt phân được đặt
lần lượt là 0, 60 và 120 phút. Một số đặc tí nh của sản phẩm cuối cùng từ cá c quá trì nh nhiệt phâ n này, tức là
chꢂt bốc, hàm lượng tro, cacbon cố định và giá trị gia nhiệt cao (HHV) đꢃ được xác định. Kết quả thí nghiệm
cho thꢂy trong phạm vi thí nghiệm, sản phẩm than hoa đạt hàm lượng cacbon cố định cao nhꢂt ở nhiệt độ
6000C với thời gian nhiệt phâ n là 120 phút.
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