Effect of temperature and residence time on pyrolysis of rice husk pellet

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 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 Received in revised form: June 28, 2021 
Accepted: June 29, 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: HHV – higher heating value, MJ/kg 
 o
A - ash content, % Tf – final temperature of pyrolysis, C 
M – moisture content, % t – resident time, minute 
FC – fix carbon content, % 
V – volatile mater content, % 
I. INTRODUCTION carbon dioxide emission, gasification is a 
 promising route for agricultural residue treatment. 
 Vietnam is a long-standing agricultural country To enhance energy conversion efficiency, biomass 
with approximately 175 million tons of raw materials is usually upgraded to a more advanced energy 
for the production of biomass energy. It will be form before being gasified. Biomass pyrolysis to 
equivalent to nearly 70 million tons of oil, twice the produce charcoal is one of the most popular 
total oil and gas exploitation volume of the Vietnam options. 
Oil and Gas Group in 2016 [1]. The agricultural 
residues, especially rice husk- one importance Biomass pyrolysis to produce charcoal is one of 
biomass source, can be converted to useful energy the most effective energy upgrading methods. In 
by several methods, i.e. thermo-chemical or the agricultural countries as Vietnam, the 
biological conversions. Among these methods, due capacities of rice products are very large, 
to a high energy conversion efficiency and low especially rice husk. Although biomass can be 
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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 a) b) 
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. 
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 c) 
as shown in Fig. 1a. Total mass of these pellets for Figure 1: a) Box of rice husk pellet; b) Electrical 
each experiment was 200 grams. Sand was used furnace c) Char product. 
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. 
 Pyrolysis conditions: Final temperatures were 
400, 600, 800 oC, heating rate was 3 oC/mins, 
residence time: 0, 60, 120 mins. The pyrolysis 
system is shown in Fig.2. 
 Figure 2: Pyrolysis system 
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 III. EXPERIMENTAL RESULTS 
The char properties are presented in table 2. 
 Table 2: Char properties 
 HHV, 
 T t FC A Yiel, 
 f V (%) MJ/k
 oC min (%) (%) % 
 g 
 0 22.8 47.6 29.6 20.41 42.6 
 400 60 19.7 50.2 30.1 20.61 42.0 
 120 17.3 52.2 30.5 20.97 40.3 
 0 6.8 57.9 35.3 20.95 36.7 
 600 60 6.2 58.4 35.4 21.33 36.6 
 120 4.4 58.8 36.8 21.49 35.7 
 a) 
 0 4.9 58 37.1 20.85 35.2 
 800 60 3.9 57.9 38.2 20.62 34.4 
 120 3.1 57.6 39.3 20.50 34.2 
 b) 
 Figure 4: Effect of final temperature and residence 
 a) 
 time on FC content (a) and HHV (b). 
 Table 2 and Fig 3, 4 show that: when the final 
 temperature rises from 400 oC to 800 oC 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 
 around 400 oC in pyrolysis process [6], therefore 
 the residences time is the important factor for both 
 yiel and quality of char (FC content). Besides, due 
 b) 
 to the high volatile meter content of rice husk 
 Figure 3: Effect of final temperature and pellets (17.3 – 22.8%), the increase in residences 
 residence time on the volatile meter (a) and time is an advantage point for volatile meter 
 ash (b) in char release strongly continuously. In contrast, in the 
 range of 600 -800 oC, the rate of volatile meter 
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escape decreased [6]. Furthermore, when the less will be more uniform and higher than rice husk 
volatile content in the pellet (6.8 – 0.8 %), the less pellets temperature due to the smaller particles and 
effect of residences time on yiel and FC content. bulk density. 
The experimental data also shows that the char 
reaches the highest FC content and HHV in the 
 o
conditions: Tf = 600 C and residence time of 120 
mins, 5.8% and 21.49 MJ respectively. In 400 oC, 
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 
occur during the formation of char above 750 oC pellets char. (Heating rate 30C/min, residence 
can lead to the phenomenon that a part of FC is time 120 mins.) 
oxidized by the gases produced by previous 
primary pyrolysis reactions. Chen et al [9] and Fu V. CONCLUSION 
et al [11] also confirmed that the char production of 
 Temperature is the significant factor which effects 
900 oC pyrolysis can be decreased in the pore size 
 on the rice husk pellet pyrolysis for char production. 
and surface square, therefore it is not advantage 
for both gasification and combustion. The result of pyrolysis study shows that in the 
 range of expriment, the quality of char from the rice 
The previous research with rice husk in the same husk pellet reached the maximum value with 
conditions [10] also dedicates that FC content pyrolysis conditions: the final temperature is 600 
tends to decrease when pyrolysis temperature is 
 oC, the heating rate is 3 oC/mins, the residence 
above 7500C. Figure 5 reveals that FC rate in rice 
husk pellet char is slightly higher than in rice husk time is 120 mins. Besides, for char production, the 
 o
when final temperature is below 6000C. It can be pyrolysis process should not go beyond 800 C as 
explained that the rice husks temperature profile its FC content would be decreased.
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[5] C.T.Chang, M. Costa, M. Lavilletta, A. Macaluso, D. Piazzullo, L. Vanoli. Thermo-economic analyses 
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[7] Hoang-Luong Pham. Wood Energy Basics: A Technical Document, Regional Wood Energy 
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[8] Anca-Couce Andrés, Alba Dieguez- Alonso, Nico Zobel, Anka Berger, Norbert Kienzl and Frank 
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[9] Dengyu Chen, Yanjun Li, Kehui Cen, Min Luo, Hongyan Li and Bin Lu. Pyrolysis poly generation of 
 poplar wood: Effect of heating rate and pyrolysis temperaturE. Bio resource Technology. (2016) 
[10] Nguyen Thi Thu Ha, Pham Hoang Luong. Effect of temperature and heating rate in rice husk pyrolysis 
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ẢNH HƯỞNG CỦA NHIỆT ĐỘ VÀ THỜI GIAN NHIỆT 
PHÂN ĐẾN CHẤT LƯỢNG NHIỆT PHÂN CỦA VIÊN NÉN 
TRẤU 
Nguyễn Thị Thu Hà1,2, Phạm Hoàng Lương2, Laurent Van de Steene3, 
Nguyễn Hồng Nam4 
1 Khoa Công nghệ năng lượng, Đại học điện lực, Việt Nam 
2 Viện Khoa học và Công nghệ Nhiệt-Lạnh, Đại học Bách Khoa Hà Nội 
3Trung tâm nghiên cứu quốc tế về nông nghiệp (CIRAD), Cộng hòa Pháp 
4 Khoa Năng lượng, Đại học Khoa học và Công nghệ Hà Nội, Việt Nam 
E-mail: hantt_ cnnl@epu.edu.vn 
 TÓM TẮT 
 Sinh khối, chủ yếu là phụ phẩm nông nghiệp, được sử dụng rộng rãi ở Việt Nam như một nguồn năng 
lượng năng lượng. Đối với mục tiêu cấp nhiệt, sinh khối thường được nâng cấp bằng cách chuyển đổi nhiệt 
hóa học hoặc sinh học trước khi được sử dụng làm nhiên liệu sạch và hiệu quả. Trong công trình này, quá 
trình nhiệt phân viên trấu 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 nhất 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 tính của sản phẩm cuối cùng từ các quá trình nhiệt phân này, tức là 
chất bốc, hàm lượng tro, cacbon cố định và giá trị gia nhiệt cao (HHV) đã được xác định. Kết quả thí nghiệm 
cho thấy trong phạm vi thí nghiệm, sản phẩm than hoa đạt hàm lượng cacbon cố định cao nhất ở nhiệt độ 
6000C với thời gian nhiệt phân là 120 phút.