Feasibility Study of Biochar Prepared by Low-temperature Pyrolysis
of Traditional Chinese Medicine Residue
Qian Deng
a
, Aijun Li
b
and Yangwei Wu
c
School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Keywords:
Chinese Medicine Residue, Biochar, Evaluation, Low-temperature Pyrolysis.
Abstract: This study focused on the evaluation of biochar prepared by low-temperature pyrolysis from traditional
Chinese medicine residue, which providing feasibility demonstration for the construction of the industrial
chain in circular economy of Chinese medicinal resources. We found that biochar produced by low-
temperature pyrolysis at 400℃ and 550℃ showed preferable feasibility and fine foreground, and the scheme
of low-temperature pyrolysis at 400℃ is better than that at 550℃. The market of biochar has a relatively large
impact on the evaluation indexes, which can easily lead to the fluctuation of profits or losses.
1 INTRODUCTION
1
With the rapid development of Chinese medicine and
the extension of the related resource based industrial
chains, the yield of Chinese medicinal residue is
increasing year by year. The annual discharge of
Chinese medicinal residue in China is as high as 30
million tons in 2015, among which the production of
Chinese patent medicine takes up the largest part,
accounting for about 70% of the total (Na et al.,
2016). Traditional Chinese medicine residue contains
a certain amount of active ingredients and a large
amount of cellulose, hemicellulose, lignin, protein
and other rich organic ingredients. In recent years, it
has been reported that traditional Chinese medicine
residue is used for edible fungus cultivation, feed
additives, pyrolysis and gasification (Chen, Tan,
Wang, & Wang, 2012; Duan, Su, Sheng, Pei, & Wu,
2013; Wang, Cai, & Zhang, 2020), partly realizing its
resource-oriented utilization. However, due to the
long fermentation cycle, complex composition,
difficult separation, and some may contain toxic and
harmful substances, the utilization of the residue as
feed and fertilizer is still under restriction. Therefore,
how to realize the effective disposal and resource
utilization of Chinese medicinal residue has become
an unavoidable problem in the green development of
a
https://orcid.org/0000-0001-6507-3268
b
https://orcid.org/0000-0003-3738-2308
c
https://orcid.org/0000-0002-0688-3209
Chinese medicinal resource industry and constructing
the industrial chain in circular economy of Chinese
medicinal resource (Duan, 2015; Zhang, Su, Guo, &
Wu, 2015).
Biochar is a substance with high carbon content
formed by pyrolysis and carbonization of biomass
under anoxic conditions at high temperature
(Lehmann, Gaunt, & Rondon, 2006). In recent years,
agricultural straw and garden waste have been widely
used in the preparation of biochar, showing broad
application prospects in soil improvement and
environmental protection (Chen, Zhang, & Meng,
2013; Qian et al., 2016). To a certain extent, Chinese
medicine residue showed high similarity with
agricultural and forestry wastes, which is
characterized by high carbon content and easy to
collect, and also can be used to prepare biochar. Due
to its unique physical and chemical properties such as
high porosity and large specific surface area, biochar
is considered as a potential improver to accelerate the
composting process and improve the final
composting quality (Godlewska, Schmidt, Ok, &
Oleszczuk, 2017). High-temperature composting can
kill pathogenic bacteria, insect eggs and weed seeds
to the maximum extent. What’s more, it can rapidly
degrade easily biodegradable organic substances into
stable humus, and finally transform them into organic
fertilizer. It’s commonly applied in the transformation
316
Deng, Q., Li, A. and Wu, Y.
Feasibility Study of Biochar Prepared by Low-temperature Pyrolysis of Traditional Chinese Medicine Residue.
DOI: 10.5220/0011205000003443
In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 316-320
ISBN: 978-989-758-595-1
Copyright
c
 2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved

of organic solid waste into fertilizer at home and
abroad. Biochar plays a role in increasing the organic
matter content of fertilizers, so it lays a foundation for
the development of high-temperature aerobic
fermentation for organic fertilizer preparation
technology based on the synergistic enhancement of
"bacteria / mud/ carbon". Therefore, the techno-
economic evaluation of biochar production from
Chinese medicinal residue is of great significance to
produce organic fertilizer.
In this study, the material flow and energy flow of
Chinese medicine residue pyrolysis system were
accounted by regarding Chinese medicine residue as
conventional biomass. We analyzed the economic
performance of the pyrolysis system of traditional
Chinese medicine residue to prepare biochar by
techno-economic analysis method. The detailed
techno-economic evaluation of the project was
carried out from the perspectives of production cost,
profitability, sensitivity analysis and so on.
2 MATERIALS AND METHODS
2.1 Materials
The Chinese medicine residue analyzed in this article
is based on the research of Guo(Guo, 2013) from
Henan Wanxi Pharmaceutical Co., Ltd. The wet base
industrial analysis, dry base elemental analysis and
low heating value (LHV) are shown in table 1.
Table 1: Industrial analysis, elemental analysis and LHV of Chinese medicine residue (Guo, 2013).
Industrial analysis (wt% wet basis) Elemental analysis (wt% dry basis)
LHV
(MJ/kg)
M FC V A C H O N S
12.5 12.41 72.62 2.47 42.4 6.2 47.39 1.06 0.15 14.90
The pyrolysis system of Chinese medicinal
residue was divided into four units: raw material
pretreatment, pyrolysis, separation and cooling. The
heat of the pyrolysis system was released by the
combustion of pyrolysis gas. The three-state yield
was estimated according to formulas (1)(2)(3) (Guo,
2013). In order to obtain stable quality biochar, the
high-temperature solid products from pyrolysis were
cooled by cooling air and water. The input of cooling
air was mainly reflected in the power consumption.
The power consumption in the pyrolysis system was
mainly used in blower and water pump, and the most
important consumption is the blower. The cooling
water and power consumption during pyrolysis can
be calculated according to formula (4) (5)(Wei,
2018).
Y

= 0.09T − 27.9(400℃ ≤ 𝑇 ≤ 900℃)
(1)
Y

= −1.5 × 10

T

+ 0.13T +
7.58(400℃ ≤ 𝑇 ≤ 900℃ )
(2)
Y

=4.8×10

T

− 0.09T +
67.6(400℃ ≤ 𝑇 ≤ 900℃）
(3)
Power
(
T
)
=1.25×10

T

−1.96×
10

T

+ 1.03T − 140
(4)
Cooling water
(
T
)
= −4.2 × 10

T

+
6.2 × 10

T

− 29T + 4742
(5)
2.2 Methods
To assess the economic values of preparing biochar
by low-temperature pyrolysis, profitability of the
project was analyzed based on estimation of total
investment and cost. The sensitivity analysis was
carried out by considering two key factors of selling
price and operating cost. The economic benefit and
anti-risk ability of the project were reasonably
evaluated, which provides a theoretical basis for its
industrialization.
The total investment of this project is composed
of fixed capital investment (FCI), interest during
construction and working capital. The equipment
purchase and installation cost of pyrolysis system
were estimated by the production scale index method,
which can be formulated as below.
𝐼

=𝐼

(
𝑃

𝑃

)

×𝐶

(6)
𝐶

=𝐸𝑅×𝜎 (7)
in which, 𝐼

,𝑃

are the investment amount and
production scale of similar projects or production
facilities that have been completed, 𝐼

, 𝑃

are the
investment amount and production scale of proposed
projects or production facilities, n represents the
production scale index, and 𝐶

illustrates price
adjustment index. 𝐸𝑅 and 𝜎 mean the exchange rate
between US dollar and RMB in reference year and
price index of fixed assets investment in reference
year compared with that in 2019. 𝜎 is based on the
data published in China Statistical Yearbook. The
equipment involved in this study was designed
according to the current technical state, and the
production scale index, purchase cost and installation
coefficient of the equipment can be found from the
actual equipment data(Dutta, Sahir, & Tan, 2015;
Feasibility Study of Biochar Prepared by Low-temperature Pyrolysis of Traditional Chinese Medicine Residue
317

Huang, 2015; Jones, Valkenburg, Walton, Elliott, &
Czernik, 2009).
Working capital represents cash kept on hand for
day-to-day plant operations like accounts receivable,
cash on hand, raw material and product inventory,
which is recouped in the last year of the analysis(Du,
2012). In this study, working capital is assumed to
equal a fixed percent of FCI, which is taken as
5%(Bond et al., 2014).
The interest during the construction period was
calculated according to formula (8).
𝑞

=(𝑃

+


𝐴

)𝑖
(8)
in which, 𝑞

is interest accrued in year j of the
construction period, 𝑃

means the sum of
accumulated loan amount and interest amount in year
(j-1), 𝐴

represents the loan amount in year j of
construction period, and i illustrates annual interest
rate.
According to the capital cost method developed
by Peters et al.(Peters & Timmerhaus, 1958), the total
capital investment can be estimated by the total cost
of the purchased equipment. The accuracy of the
estimation based on this method is usually less than
30%.
Cost estimation was analyzed from three aspects:
variable operating costs, fixed operating costs and
cost analysis. Profitability was carried out from three
aspects of time-based evaluation index, value-based
evaluation index and ratio-based evaluation index.
The static investment payback period, net present
value (NPV) and internal rate of return (IRR) were
selected to evaluate the profitability. The calculation
formula is as follows.
𝑃

= (Year of positive cumulative cash
flow)-1+ (The absolute value of cumulative
net cash flow last year/ Net cash flow of the
y
ear)
(9)
𝑁𝑃𝑉 =
∑
(𝐶𝐼 − 𝐶𝑂)

(1 + 𝑖

)



(10)
𝑁𝑃𝑉 =
∑
(𝐶𝐼 − 𝐶𝑂)

(1 + 𝐼𝑅𝑅)

=0


(11)
In this study, the project investment cash flow
table was used to evaluate the project from the
perspective of pre-financing. The total investment of
the project was used as calculation basis to reflect the
cash flow and outflow during operation, so as to
calculate the economic indicators of the project.
3 RESULTS & DISCUSSION
When the design capacity of disposal amount of
Chinese medicine residue for low-temperature
pyrolysis in this study is 10 ton per hour, the three-
state yield and energy consumption at different
temperatures were calculated as table 2. Biochar was
the main product of pyrolysis system, and the by-
product were bio-oil and bio-gas. Bio-oil was sold
while bio-gas were burned for heating.
Table 2: Three-state yield and energy consumption at different temperatures.
Temperatur
e (℃)
Output Input
Bio-
g
as
(
wt%
)
Bio-oil
(
wt%
)
Biocha
r
(
wt%
)
Power
(
kWh
)
Coolin
g
water
(
k
g
)
400 8.1 35.58 39.28 384 3740
550 21.6 33.71 32.62 416 5592
3.1 Investment Estimation
According to the above estimation methods of FCI
and working capital, their values can be obtained
respectively, as shown in table3.
Table 3: Estimation of total investment and production cost.
—
TDC
a
TIC
b
FCI Working Capital Loan interest TCI
c
Cost (10
4
¥) 8758.51 5255.11 14013.62 700.68 367.25 15081.55
a
TDC = Total direct capital.
b
TIC = Total indirect capital.
c
TCI = Total capital investment.
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
318

3.2 Cost Estimation
Due to the different operating parameters, the quality
of biochar will change. It is necessary to set the
corresponding selling price according to the heating
value of the product. The selling price of biochar is
1200 ¥/t at 400°C and 1500 ¥/t at 550°C(Du, 2012).
A summary of operating costs is given in Table 4, the
cost of biochar per ton at 400°C is 857.37 yuan, and
the cost of biochar per ton at 550°C is 1079.27 yuan.
As temperature rising, the power and cooling water
required in the pyrolysis process are increased.
Meanwhile, the yield of biochar is reduced, resulting
in an increase in unit operation cost.
Table 4: Summary of operating costs.
Project
—
Cost (10
4
¥)
400℃ 550℃
Production cost
Operation cost
36114.59 38528.01
Depreciation expense 14013.62 14013.62
Financial cost —
3055.52 3055.52
Unit cost —
857.37 ¥/t 1079.27 ¥/t
According to the detailed cost analysis, we found
that the financial cost only accounts for 5.75% of the
total cost, and the production cost accounts for
94.25% in the low-temperature pyrolysis. The largest
proportion of
production
costs is raw material costs,
accounting for 29.97% of the total cost, followed by
depreciation and maintenance costs, accounting for
26.35% and 15.81%, respectively. Reducing costs
can be achieved by reducing raw material costs or
increasing production. In the low-temperature
pyrolysis at 550°C, the financial cost accounts for
5.5% of the total cost, and the production cost
accounts for 94.5%. The largest proportion of
production costs is still raw material costs, followed
by depreciation and maintenance costs, which is
similar to the result at 400°C.
3.3 Profitability Analysis
According to the analysis of cash flow, the NPV of
low-temperature pyrolysis at 400℃ and 550℃ are
respectively 15.65 million yuan and 15.04 million
yuan, both of which showed high economic benefits.
The IRR is greater than the benchmark rate of return
8%, and the two values are the same. The payback
periods are 6.78 and 6.88 years, respectively, that is,
6.78 and 6.88 years after putting into production can
be profitable, which are less than the benchmark
payback period of eight years. The results indicate
that the low-temperature pyrolysis at 400°C is better
than that at 550°C.
3.4 Sensitivity Analysis
Sensitivity analyses were conducted to evaluate the
sensitivity of financial performance (i.e., NPV, IRR
and payback period) of the pyrolysis operation to
biochar selling price and operating cost. The range of
each variable from -20 to +20 percent of the baseline
value was used in the sensitivity analyses while the
other variables remained constant. According to the
sensitivity analysis results of the selling price and
operating cost, the impact of price change on the three
indicators is greater than the operating cost,
indicating that the selling price of biochar is the most
influential variable for the financial performance.
4 CONCLUSIONS
In this study, the economic benefits and production
cost of low-temperature pyrolysis of Chinese
medicine residue to produce biochar were
comprehensively studied, and the sensitivity analysis
of some typical variables was carried out. The main
conclusions are as following:
(1) Through technical and economic analysis, the
total capital investment of the biochar preparation
project was calculated to be 150.82 million yuan, and
the production costs of biochar at 400℃ and 550℃
were 857.37 ¥/t and 1079.27 ¥/t, respectively. The
production costs were increased with temperature. In
addition, raw material cost, depreciation cost and
maintenance cost were the top three cost components.
(2) Through the analysis of project cash flow, it is
found that the production projects of biochar at 400°C
and 550°C showed fair profitability and economic
benefit, and the economic benefit at 400°C was
higher. However, the payback period in the two cases
was 6.78 and 6.88 years, respectively, showing the
relatively poor anti-risk ability.
(3) Through the sensitivity analysis of operating
costs and selling price, the selling price of biochar has
a relatively large impact on economic benefit, which
can easily lead to high profits and losses.
In this article, the by-product of pyrolysis bio-oil
Feasibility Study of Biochar Prepared by Low-temperature Pyrolysis of Traditional Chinese Medicine Residue
319

was sold and bio-gas were used for combustion
heating. The utilization method is simple and we
ignored the influence of bio-oil price. In addition to
direct sale, bio-oil can also improve economy through
quality rectification. To this end, the market for bio-
oil is deserving of more attention in future studies.
ACKNOWLEDGMENTS
This work was supported by “National Key R&D
Program of China (2019UFC1906600)”.
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