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Research article
Development and performance analysis of top lit updraft: natural draft
gasifier stoves with various feed stocks
Arkbom Hailu
a
,
b
,
c
,
*
a
Sustainable Energy Center of Excellence, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia
b
Nuclear Technology Center of Excellence, Addis Ababa Science and Technology University, P.O. Box 16417, Addis Ababa, Ethiopia
c
Department of Environmental Engineering, College of Biological and Chemical Engineering, Addis Ababa Science and Technology University, P.O. Box 16417, Addis
Ababa, Ethiopia
ARTICLE INFO
Keywords:
Performance analysis of gasifier stove
WBT (Water boiling test)
Different feed stock
ABSTRACT
The performance of an Ethiopian-designed and built-in gasifier stove was studied and evaluated. The water
boiling test (WBT) findings are reported. This test was conducted in a controlled setting utilizing eucalyptus,
bamboo, and sawdust-cow dung briquettes as test feedstocks, in accordance with WBT's 4.2.3 standard process
and test manuals. Based on moisture content, the net calorific values of eucalyptus, bamboo, and sawdust-cow
dung briquettes were calculated and determined to be 15.77 MJ/kg, 14.70 MJ/kg, and 15.35 MJ/kg, respec-
tively. The efficiency of this stove was calculated utilizing those three feedstocks. As a result, the gasifier stove's
efficiency having eucalyptus, sawdust-cow dung briquette, and bamboo as feedstock were 32.30 0.3%, 31.5
0.5%, and 26.25 0.25%, respectively. This proportion did not include the ultimate charcoal production, but
when this yield was employed as an energy input for additional charcoal burners, it increased to 53 2%. The
relationship between gasifier stove charcoal production and total efficiency is negatively related, with a linear
equation of Y ¼- 0.7956Xþ22.766 and an R-squared value of 0.92. When compared to local stoves and foreign
gasifier stoves, whose efficiency is in the range of 10 %–39% this efficiency rating was exceptional due to the fact
that space between the internal and external cylinder help the secondary air to preheat before combustion and
also the interior hallow cylinder help the primary air to move evenly in the vertical circular pattern for proper
gasification, it will also help the gases that are produced during gasification process to move to the top part for
combustion, indicating that this study can be fostered for prospective use.
1. Introduction
Biomass fuels are the world's fourth main energy source, accounting
for 13% of the total energy supply (Waldheim and WALDHEIM, 2018),
with a particularly high share in developing nations. In developing na-
tions like Ethiopia, where biomass combustion accounts for 91% of its
primary energy output (Mondal et al., 2018), biomass combustion sup-
plies basic energy requirements for cooking and heating rural families, as
well as processes in a range of traditional industries (Yurnaidi and Kim
2018)(D. Sakthivadivel, P. Ganesh Kumar, G. Praveen Kumar, P. Raman,
Ranko Goic, 2020). In Sub-Saharan Africa, one of the options to satisfy
the household energy demand is to sustainably use fuelwood for cooking
(Hafner et al., 2020). By a ratio of two to three, improved design can
increase the efficiency of biomass utilized for cooking (Bhattacharya
2003).
Improved cooking stoves, such as the gasifier stove, have been shown
to reduce the amount of fuel used in the kitchen while also reducing
pollutants (Adane, Alene, and Mereta 2021). Gasification stoves are also
known as improved stoves since they use less biomass and emit less
pollutants than standard open three-stone stoves. Most governmental and
non-governmental groups in Ethiopia are concentrating their efforts on
improving charcoal and wood injera stoves, rather than developing
gasification stoves.
One of the most significant characteristics of this gasifier stove is that
it collects incomplete combustion volatile gases that would otherwise
escape during the carbonization process or charcoal production and burn
them with primary air that enters through a hole in the middle of the
innermost cylinder's wall from the bottom to the top, the hole being
larger on the top for the combustion of volatile gases, and secondary
preheated air that enters between the outer wall of the combustion
* Corresponding author. ;
E-mail addresses: arkbom.hailu@aastu.edu.et,arkbomh@gmail.com.
Contents lists available at ScienceDirect
Heliyon
journal homepage: www.cell.com/heliyon
https://doi.org/10.1016/j.heliyon.2022.e10163
Received 2 November 2021; Received in revised form 14 January 2022; Accepted 28 July 2022
2405-8440/©2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-
nc-nd/4.0/).
Heliyon 8 (2022) e10163
chamber and the inner wall of the outer cylinder. This stove has two
advantages: first, it will utilize incomplete gas as a source of energy since
it will totally burn the gas using secondary air, and second, it will prevent
gases from polluting the environment owing to incomplete combustion,
as shown in Figure 1. It will also enable the production of charcoal and
the avoidance of indoor air pollution (Gitau et al., 2019).
Traditional biomass sources such as wood fuel, agricultural residue,
charcoal, and cow dung have been Ethiopia 's primary energy source in
the past and present, and those feed stocks are mostly utilized for injera
baking, thus using this technology for injera baking is important (Adem
et al., 2019). The majority of this energy resource is used inefficiently, so
as a consequence, the biomass resource is used in large quantities. As a
result, natural forest loss has become a significant concern, with forest
cover falling from 40% to less than 12% in less than a century (Babiso
Badesso, Bajigo Madalcho, and Mesene Mena 2020). In addition to this
depletion, collecting wood from the forest takes a long time for most
individuals who engage in this activity, particularly women. As the
percentage of forest cover decreases as a result of population growth,
which is linked to consumption, fuel scarcity will force the use of crop
residues and animal dung as fuel, which would otherwise be used as
animal feed, and for the restoration of soil fertility, It will result in a 7%
fall in agriculture GDP (Zenebe G. 2007). This might result in a signifi-
cant drop in agricultural output at a time when the industry is projected
to produce more, as indicated in the schematic Figure 2 below (United
Nations Environment Programme (UNEP) 2019).
1.1. Stove development in Ethiopia
The primary goal of any energy conversion system's engineering
study is to obtain the needed kinds of energy with the highest possible
efficiency utilizing existing technology. Any energy conversion system
that does not know how much energy can be taken from prospective
sources and how much energy can be saved for the environment is not
economically viable (Geremew et al., 2014)(Mamuye et al. 2018).
Open three stone wood stove is a traditional stove that is extensively
used for cooking and baking across Ethiopia, particularly in rural homes.
The stove's conversion efficiency ranges from 6 to 12 percent, see
(Figure 3 a). It wastes more than 90% of biomass energy; over 95% of the
population relies on biomass for their energy needs, and roughly half of
that energy is consumed for cooking injera, largely on this traditional
three stone fire stove (Tadesse 2020). Millions of tons of biomass fuels are
wasted each year due to its inefficient features and dominance in the
home sector. Aside from that, the smoke produced during its use is
harmful to one's health. Mirt and Gonze can save up to 33% and 20% of
the wood biomass consumed by the typical open three stone stove,
respectively (Amare 2015)(Fekadu et al. 2019). When compared to
Gonze, the Mirt stove can conserve 15% more biomass (Amare 2015), see
(Figure 3 b and c).
These stoves are currently being widely pushed because to their
ability to achieve a fuel economy of up to 31% when compared to an
open fire system. It can also help to enhance the cooking environment by
decreasing indoor air pollution and other issues like burns and over-
heating (Yayeh et al. 2021).
1.2. Benefits of improved stove
The advantages of a better cook stove are divided into two categories:
those that benefit the household and those that benefit the environment.
Internal benefits include lower smoke levels and interior air pollution,
cost and time savings in obtaining fuel, and reduced biomass consump-
tion, as well as the potential to use animal dung as fertilizer instead of
fuel. External benefits include reduced demand on timber and energy
resources, lower GHG emissions, and community skill development and
employment creation during the manufacture of better cook stoves
(Anhalt and Holanda 2009)(Raman et al. 2014).
1.3. Gasification
The process of transforming solid or liquid feed-stock into an useable
gaseous fuel or chemical feed-stock that may be burned to produce en-
ergy or utilized to manufacture value-added chemicals is known as
gasification (Basu 2010). Even while gasification and combustion are
both thermochemical processes, they differ significantly. Gasification
stores energy in chemical bonds in the resultant gas; combustion releases
that energy by breaking those bonds. Gasification introduces hydrogen
into the feedstock while eliminating carbon, producing gases with a
higher hydrogen-to-carbon (H/C) ratio, whereas combustion oxidizes the
hydrogen and carbon into H
2
O and CO
2
, respectively (Basu 2010)
(Waldheim, IEA and Waldheim Consulting, 2018).
1.4. Gasifier cook stove
1.4.1. Technical features
Gasifier-based cooking systems have numerous enticing features,
including high performance, clean combustion, a uninterrupted and
steady flame, ease of flame management, and perhaps long-term atten-
tion-free operation (Raman et al. 2014).
1.4.2. Working principle
Gasification is the sub-stoichiometric combustion of biomass that
produces a combination of flammable gases such as CO, H
2
, and traces of
CH
4
as well as incombustible gases such as CO
2
and N
2
. A gasifier is made
out of a container into which fuel and a little amount of air are supplied.
The heat required for gasification is produced by partial combustion of
the fuel (Basu 2010).
Pyrolysis of carbonaceous fuels and char gasification are both used in
biomass gasification. During the pyrolysis process, volatile components
Figure 1. (a) Traditional carbonization process (b) Gasifier stove.
A. Hailu Heliyon 8 (2022) e10163
2
from the biomass are released at high temperatures, leaving char behind.
The volatile components and some of the char react with oxygen to
generate carbon dioxide, producing heat (Basu 2010). Gasifiers can be
either natural or forced draft. In the forced draft gasifier, the air needed
for the combustion of fuel is supplied by an external source like a fan or a
blower while in the natural draft gasifier; the draft is created due to the
pressure difference between the heated air near the flame and the cooler
air in the surrounding as illustrated on Figure 4.
1.5. Current trends of gasifier stove
A micro gasifier stove, the ACS IES-15, with a similar design feature to
this one, except the stove did not include an internal hollow cylinder with
a punctured, wall and bottom disk, obtained a thermal efficiency of 36.7
0.4 percent utilizing coconut shell as a feed stock (Sakthivadivel et al.,
2019). Another study indicated that coconut shell has a thermal effi-
ciency of 36.7 1 percent, Prosopis Juliflora has a thermal efficiency of
Figure 2. Schematic diagram of unsustainable biomass utilization.
Figure 3. Cooking stove (a) three stone open fire and injera baking stove (b) mirt (c) gonze in Ethiopia.
Figure 4. Two types of gasifiers (a) forced draft (b) natural draft.
A. Hailu Heliyon 8 (2022) e10163
3
36 1 percent, and wood pellets have a thermal efficiency of 38.5 1
percent (Sakthivadivel and Iniyan 2017). (Osei et al., 2020) achieved a
thermal efficiency of 30.5–38.1 percent by applying WBT version 4.2.3
and using rice husk as fuel.
The efficiency of the stove can be increased by repurposing the heat
lost from the combustion chamber's surface, and in this article, the heat
on the combustion chamber's outer surface is used to heat up the sec-
ondary heat, which is critical to the volatile gas's combustion process.
The heat lost from the combustion chamber's surface can be repur-
posed to increase the stove's efficiency (Kaushik et al. 2016), and in this
article, the heat on the combustion chamber's outer surface is used to
heat up the secondary heat, which is essential to the volatile gas's com-
bustion process effectiveness.
An updraft forced gasifier built and manufactured to produce gas at
an equivalent ratio of 0.5 using a mixed feedstock of rice husk-sawdust
had a thermal efficiency of 17.6 % while using a bluff body B, upper
burner type (Susastriawan et al., 2021). When compared to traditional
stoves, in a paper by (Okino et al., 2021), has obtained a thermal effi-
ciency of 35.5 2.5% using Senna spectabilis as a feed stock, followed by
Eucalyptus grandis 25.7 1.7%, and finally Pinus caribaea 19.0 1.2%.
The thermal efficiency of a forced-up draft gasifier with a feed stock
holding capacity of 1.5 kg of rice husk, a complete cooking time of 1 h,
and dimensions of 60 cm high and a diameter of 16cm was evaluated to
find out its thermal efficiency. A thermal efficiency of 34 % for RHGS
(Rice Husk Gas Stove), with fuel consumption rate of 1.5 kg h
1
, com-
bustion zone velocity of 1.46 cm/min, time to boil 3 L of water, 19 min,
and 32.41% char was produced (Punin 2020). When analyzing the Rice
Husk Gasifier stove with different five parameters, the correlation of
charcoal output vs thermal efficiency is inversely connected in this paper,
which is similar to this article finding on (see Fig 20)(Punin 2020).
An article with thermal performance evaluation of an improved
biomass cookstove for domestic application obtained an average thermal
efficiency of approximately 33% while boiling 7.5L of water (Barpa-
tragohain et al. 2021). A natural draft gasifier with rock type of pyrolysis
stove, has obtained over all thermal efficiency of 45.6% and a bio char
produced from this stove was used for amendment of soil and it was burnt
at very high temperature (Hailu 2020). A natural up draft gasifier with
height of 34 com and 16cm diameter and 2m chimney height obtained an
overall efficiency of 38.6 (Shaisundaram et al., 2021).
Based on the above findings, this study aims to build a natural up
draft gasifier stove that can achieve an overall efficiency of more than 45
percent without the use of a fan or blower for the primary and secondary
air. The size of the stove, which is the most important factor, will be
determined by the quantity of biomass holding capacity and the distance
between the feed stock and the stove bottom component, which will be
determined by the amount of heat lost. An internal hallow cylinder that
is perforated is included to maximize the effectiveness of the combustion
process as well as the gasification process. The hole on the bottom of the
cylinder is small, but it grows larger as it progresses to the top, which
will perfectly facilitate the internal gasification as well as combustion
process. Additionally, secondary air will enter the gasifier stove through
the space between the external cylinder and the internal gasifier
chamber. The heat that escapes from the surface of the gasifier chamber
via convection and conduction heats the secondary air, resulting in a
good combustion process on the gasifier chamber's outer top part. All of
this thinking will provide a solid foundation for enhancing the stove's
overall efficiency.
2. Materials and methods
2.1. Stove specification
The gasifier stoves are made of sheet metals using simple mechanical
works and consist of fuel chamber to fill the biomass residue for burning,
air inlets for partial combustion and pot stand for supporting the cooking
utensils.
The gasifier stove is a natural one that did not require any form of
energy to drive the air into the gasifier stove, unlike the other type of
gasifier stoves that depend on electricity that is used to drive the air into
the gasifier stove. This gasifier was made out of mild steel sheet metal
and has a bulk fuel capacity of about 0.0005 m
3
(500gm) for a good
gasification process. In this performance test, we used feed stocks in this
range but this does not mean the internal fuel cylinder capacity is 0.0005
m
3
. The fuel cylinder is twice the size of this value, which means the fuel
to be gasified was filled to half the height of the fuel cylinder for a good
gasification process. The stove was made up of two concentric tubes of
different sizes, known as the outer cylinder and fuel cylinder (as shown in
Figure 5. The fuel cylinder is sealed at the bottom, and inside it, there is a
hollow cylinder with a perforated wall and bottom disk with dispersed
hole to allow primary air and support fuel, and finally there is a top
support that will be placed on top of the outer cylinder to hold the pot.
All of the stove's components are self-contained and is built without
the use of temporary or permanent connectors. The gasifier stove has an
overall height of 32 cm and a diameter of 19 cm. The presence of a central
column for air in this stove distinguishes it from previously produced Top
Lit- Updraft Natural Draft (TLUD-ND) gasifier stoves. The air column is
drilled on the surface, as shown in the right-hand side of the left bottom
Figure 5 (a), to allow more primary air radially into the fuel at different
stages to compensate for air clotting that might occur while running with
tiny sized fuel as we travel up the fuel column. This prevents the flame
gasification from becoming air-starved owing to fuel particle inter-
locking. Furthermore, near the top of the central air column, closely
spaced comparatively bigger holes were bored to transmit additional hot
post-gasification secondary air. The inclusion of two hot secondary air
entrance ports is intended to provide sufficient air while keeping the
stove short and minimizing heat loss (see Figure 5).
2.2. Feed stocks
The initial step of the experiment was to gather different feedstocks for
the water boiling tests in orderto complete the tasks in a consistent manner.
According to this, eucalyptus logs that had been utilized for building but
were no longerneeded, residual bamboo left over fromlocal chair and table
builders, and manually produced briquette from eucalyptus sawdust and
cow dung were all cut into appropriate sizes, see (Figure 6,Figure 7 and
Figure 8). Following the collection of the materials, a precise digital
weighing scale was utilized to weigh the water and feedstock, see (Figure 9
b and c). The waste or by products were chosen to examine how well this
gasifier performs with a low-cost feed stock while also assisting us in
removinga waste or by product in a sustainable energy usage way.The feed
stock supplies used in the study were readily available in the nearby area.
A mixture of saw dust with cow dung (MSCD) was in the proportion of
72.28% and 27.72% respectively.
2.3. Test protocol
There are three sorts of tests that may be used to assess a stove's
performance. These tests are classified as follows, depending on the na-
ture of the tests:
1) Water boiling Test (WBT)
2) Control Cooking Test (CCT) and
3) Kitchen Performance Test (KPT)
In the current experiment however, only WBT is conducted, since the
main objective of this experiment is determining the performance of the
stove using different feedstocks and comparing it with other stoves.
1) Water boiling test (WBT):
It is a laboratory-based test thatis carried out by a qualified technician in
a controlled setting toassess the stove's performance and many parameters
A. Hailu Heliyon 8 (2022) e10163
4
that influence it. It is a valuable tool for fine-tuning the stove design to the
needs of the user (PCIA &Global Alliance 2013). The only things neededfor
this experiment are a gasifier, feed stocks with itsheating value, firestarting
material, water, a pot, and a temperature monitoring equipment. We may
determine the stove'sthermal efficiencyusing the data from those materials
and the relevant thermodynamics principles and formulas.
2.4. Testing equipment
The data gathering technology used to evaluate the gasifier stove was
extremely sensitive, with digital weight balances being utilized to ensure
accuracy, see (Figure 9 b and c). For the various data acquisition tasks,
the following equipment was required:
➢Digital stopwatch, used to record the time of each different activities
(i.e., boiling) during the tests.
➢Digital thermometer indicator (VICTOR 70 Digital Multi-meter)
range: 0 C–800 C as shown in Figure 9 (a) below with 1/10 C
accuracy with model of K thermocouple wire for measuring the
ambient temperature, boiling water temperature and the external
body surface temperature of the gasifier stove.
➢Electronic balance, with accuracy of 1gram, and capacity of 620 gm
and 4000gm as show in Figure 9 b and c. These devices were used to
Figure 5. Fabricated gasifier (a) disassembled part, top and side view (b) assembled part (c) sectional view.
Figure 6. Eucalyptus feed stock (a) used eucapyptus log from construction (b) wood shop (c) sliced eucalyptus log.
Figure 7. Left over bamboo, (a) bamboo chair (b) bamboo leftover (c) chopped bamboo.
A. Hailu Heliyon 8 (2022) e10163
5
Figure 8. Preparation for MSCD (a) eucalyptus sawdust from wood shop (b) mixing cow dung with water (c) mixing saw dust with cow dung.
Figure 9. Equipment's for the water boiling tests (a) victor 70 digital multi-Meter (b) 620 max digital weight balance (c) 4000gm max weight balance.
Figure 10. Work flow chart.
A. Hailu Heliyon 8 (2022) e10163
6
measure the weight of those different feed stocks and the weight of
water in the pot respectively.
➢Aluminum pots, plastic bottle to carry the water from the water tap to
the pot.
➢Thick heat resistance glove made from Cattle skin, kerosene and
match, fire starter.
➢Furnace to measure the moisture content; help to find the calorific
value of feed stock.
➢Closed cane, to extinguish the charcoal produced in the gasifier using
air starvation techniques. And plastic bag to hold charcoal for
weighing.
2.5. Data gathering procedures
The following schematic diagram depicts the overall working flow of
this research, Fig 10. The tests are repeated a number of times in the
fourth phase using various feed supplies. To accomplish so, the data
collecting technique and equipment were both identical, allowing the
experiments to be compared.
The research was fully experimental, as demonstrated by the work
flow charts in Fig 10. Therefore, the techniques employed in this study
were mostly focused on data gathering during the tests. The data ob-
tained for performance calculations may be divided into three categories.
3. Lower heating value of the feed stocks
The moisture content (MC) on dry basis of biomass is the quantity of
water in the material dry weight, expressed as the percentage of the
materials dry weight (Reeb 1999)(PCIA &Global Alliance 2013). MC of
the fuel sample is established using the oven-drying method, one of the
methods covered in ASTM D4442. After weighing, the item is put in an
oven set to 103 þ2C (214F–221F) and held there until no weight
change is detected after 4 h of weighing. In 12–48 h, a 25 mm (1in)
diameter timber piece will attain a consistent weight (Reeb 1999)
(Simpson 1997).
The moisture content of each feed stock was measured using a con-
ventional technique. The samples were placed in an oven set at 102 Cat
2:00 a.m. the next morning, after 24 h, the weight was measured again
after it had completely dried, and the weight difference between these
two measurements was the number of moisture content on those feed
stocks, as shown in Table 1.
The lower heating value for thermal efficiency calculation can be
determined using the aforementioned moisture content value of those
feed stock and their higher heating value (HHV) from literature (Parikh
et al. 2005).
3.1. Weight of water, biomass and charcoal
The weight of water, biomass (as a feed stock), and ultimately the
charcoal generated after full gasification are all required parameters for
calculating Overall efficiency. The digital weight balances were used for
this measuring assignment, as illustrated on Figure 9 (b and c).
3.2. Temperature data of the water
Temperature data was gathered every 5 min for each of the different
testes. These temperature readings were taken in order to determine the
water's highest and lowest temperatures. Apart from that, a temperature
profile is drawn as illustrated in Fig 13.
3.3. Test setup for WBT
The first condition for a water boiling test is that it must be conducted
in a controlled setting with constant sun intensity and wind speed over a
period of time (PCIA &Global Alliance 2013). Aside from that, the
temperature in the region must remain consistent.
The experiment was carried out in front of a material lab where no
combustible materials were present. And, the location was a controlled
setting with no variations in wind speed, ambient temperature, or sun
intensity. After the materials have been measured (weight of water and
feed stock, water, and air temperature), the wood can be fired using
kerosene and match, fire starter, as indicated in Fig 11 (a) below.
By doing so, the test was proceeded after placing the pot on top of the
gasifier burner at various times on different feed stocks. The tests were
repeated fifteen times in this performance evaluation, Fig 11 (b) depicts
the general test setup for the water boiling test. The temperature of water
was measured at 5-minute intervals using a Victor 70C digital multi-
meter with a combined K-type thermocouple thermometer.
In this test, the thermocouple must be placed in the middle of the pot
with its tip 50 mm above the bottom of the pot. As a result, we shall
measure the temperature of the water rather than the temperature of the
pot bottom (PCIA &Global Alliance 2013). When performing this test,
take all necessary precautions, such as wearing thick heat-resistant gloves
and avoiding combustible materials near the stove.
3.4. Technical calculations
The ratio of the energy used in the boiling process to the caloric
content in the fuel used is described as stove performance by using water
boiling test (WBT). The thermodynamic consideration underpins the idea
of efficiency. The efficiency of advice for a given operation is the ratio of
the energy output to the input energy, according with second rule of
thermodynamics (PCIA &Global Alliance 2013)(Mohammadreza
Rasoulkhani and Mohammad Hossein Abbaspour-Fard 2018)(Abasiryu
et al. 2015). Heat is created in a biomass-fired cook stove by partial
combustion of the biomass. Some of the heat created is transmitted to the
vessel by radiation and convection from the fire bed and exhaust gasses
which is used to boil water (D-Lab 2017). The remaining heat is lost to
the environment through evaporation, distance from fuel to pot,
convective loss from wind, unburned volatile gases, and radiation from
pot, cool combustion air or fuel, radiation from stove, conduction
through stove, wet wood stove, and pot contents (Zube 2010).
The energy utilized in the boiling process, or the energy that enters
the pot, has two observable effects: increasing the water's temperature
to its boiling point, and evaporating the water. The boiling efficiency
could be calculated by calculating the total energy required in raising
the water temperature from its beginning temperature to boiling point,
and also in evaporating a known amount of water (PCIA &Global
Alliance 2013). In the efficiency calculation, the lower calorific value
of the fuel is utilized. The total energy provided can be calculated by
Table 1. Moisture contents of the samples.
Sample
type
Weight
differences
(Moisture
content)
(gm)
Percentage
of Moisture,
M
cwb
2
(%)
Average
moisture
percentage
M
cwb
(%)
Moisture
content
on dry
basis,
M
cdb
3
(%)
Average
M
cdb
(%)
Eucalyptus 1.3 8.44 7.84 9.22 8.51
1.2 7.64 8.28
0.9 7.44 8.04
Bamboo 0.3 7.32 8.74 7.89 9.59
0.3 10.00 11.11
0.4 8.89 9.76
Mixture of
Sawdust
with Cow
dung
1.2 7.69 7.60 8.33 8.23
1.4 7.87 8.54
1.4 7.25 7.82
A. Hailu Heliyon 8 (2022) e10163
7
measuring the total amount of fuel used during the test period (see Fig
14) and utilizing the net calorific value or LHV (lower heating value)
(see Table 2).
The following calculation, similar to cooking efficiency, is used to
determine the thermal efficiency of the gasifier stove. The total input
power to the water, as shown in the calculation, is the sum of the energy
used to increase the water temperature to its ultimate temperature and
the energy used to evaporated water. This value is divided to the lower
heating value of an equivalent dry fuel burned (Berrueta et al. 2008)
(Abasiryu et al. 2015)(PCIA &Global Alliance 2013)(Kaushik et al.
2016).
η
th ¼mwi*Cpw *ðTeTiÞþmwevp*L
fcdLHVf
(1)
η
¼mwi*Cpw *ðTeTiÞþmwevp*L
fac (2)
η
¼mwi*Cpw *ðTeTiÞþmwevp*L
fcd:LHVf Emoist mchar *LHVchar
The dry fuel (f
cd
) and E
moist
can be calculated using Equation (3) and
Equation (4) respectively
fcd ¼fuel mass wet ð1MCÞ(3)
Emoist ¼fuel mass wet:MC ð4:186ðTe TiÞþ2260Þ(4)
where:
η
th
¼Thermal Efficiency (PCIA &Global Alliance 2013)(Abasiryu
et al. 2015),
η
¼Overall Efficiency (Mohammadreza Rasoulkhani and Mohammad
Hossein Abbaspour-Fard 2018).
f
ac
¼energy value in the wood excluding energy in char (Shai-
sundaram et al., 2021).
m
w, i
¼mass of water initially in cooking vessel, gm
m
char
¼mass of charcoal (gm).
C
pw
¼specific heat of water (4.186 kJ/kg
o
C).
m
w, evap
¼mass of water evaporated, gm
f
cd
(W
dry
)¼mass of equivalent dry fuel consumed, gm.
T
e
¼temperature of boiling water,
o
C
T
i
¼initial temperature of water in pot,
o
C
MC ¼Moisture content of a fuel percentage (Wet fuel –dry fuel)/100.
L¼latent heat of evaporation at 100 C and 105 Pa, 2260 kJ/kg
(PCIA &Global Alliance 2013),
LHV
f
¼Lower heating value (net calorific value) of the fuel, MJ/kg)
see Table 2.
LHV
char
¼Lower heating value of charcoal, 28 MJ/kg (Berrueta et al.
2008)(Abasiryu et al. 2015).
Using the moisture content on the dry basis and higher heating value
(HHV) of those feed stocks from literature, the lower heating value can be
calculated for thermal efficiency as well as overall efficiency calculation
(Parikh et al. 2005)(Gebreegziabher et al. 2013). Three samples were
used for each of the three feed stocks in a moisture content test, as shown
in Fig 12. As a result, the average moisture content value of those samples
was used to calculate the LHV. According to this, the average moisture
content, percentage of each feed stock was less than 9 %, as indicated in
Table 1, which is more suitable for any gasification process.
In order to calculate the moisture content on dry basis the following
formula is used (Simpson 1997)(PCIA &Global Alliance 2013).
Mcdb ¼Wwet Wdry
Wdry *100 (5)
where:
Mcdb ¼Moisture content on dry Basis.
Wwet ¼Wet weight (Initial Weight), gm.
Wdry ¼Dry weight (Oven dry), gm.
Figure 11. (a) Firing of the feed stock in the gasifier stove (b) Test set up for water boiling test.
Table 2. Higher and lower heating values of feed stocks.
Feed Stocks Fuel Ratio Higher Heating Value
(HHV) MJ/kg
Mcdb Moisture contents
on dry basis (%)
Mcwb Moisture contents
on wet basis (%)
Lower Heating
Value (LHV)
4
MJ/kg
Eucalyptus 1 18.640 8.51 7.84 15.772
Bamboo 1 17.657 9.59 8.75 14.698
MSCD Dung 0.277 17.16 18.13 8.23 7.60 15.349
Eucalyptus Saw dust 0.723 18.50
A. Hailu Heliyon 8 (2022) e10163
8
And, the moisture content on the wet basis can calculated using the
ratio of moisture with the initial weight. It can also be derived from
moisture content on dry basis, and it can be calculated as follow (PCIA &
Global Alliance 2013).
Mcwb ¼Wwet Wdry
Wwet *100 ¼Mcdb
1þMcdb*100 (6)
where.
M
cwb
¼Moisture content on wet basis.
M
cdb
¼Moisture content on dry basis out of 100%
The net heating values of wood
LHVf¼18;648 210*Mcdb (7)
LHV
f
¼is the lower heating value of moist wood (kJ/kg) and M
cdb
¼
is the moisture content of wood on dried basis (wt. %) (Gebreegziabher
et al. 2013)or(Gebreegziabher et al. 2013), using Eq. (5)
LHVf¼ð1McwbÞ*½HHV LT25 *ðMcdb þ9HÞ (8)
LHV
f
¼Lower Heating Value of the fuel (MJ/kg).
Figure 12. (a) Furnace for drying the samples (b) Three samples (bamboo, eucalyptus and MSCD).
Figure 13. Temperature profile of water boiling test (a) using eucalyptus as a feed stock (b) using bamboo as a feed stock (c) using mixture of sawdust and cow dung.
A. Hailu Heliyon 8 (2022) e10163
9
H¼gravimetric fraction of hydrogen in the fuel (
1
6 % typical value
for wood) (PCIA &Global Alliance 2013).
L
T25
¼Latent heat of water at constant pressure and 25 C(¼2.44
MJ/kg) or.
LHV –Lower Heating Value is reduced (also called net heating value).
This is the theoretical maximum amount of energy that can be recovered
from the burning of a moisture-free fuel if the combustion products are
cooled to room temperature, but the water generated by the reaction of
the fuel-bound hydrogen stays in the gas phase. LHV differs from HHV by
1.32 MJ/kg in the case of wood fuels (PCIA &Global Alliance 2013).
%Yield of Charcoal ¼Wchar
Wfeedstock
(9)
Sfc ¼fcd
Pci Pcf
(10)
where;
W
char
¼Total Weight of Charcoal.
W
feedstoc
k¼Total weight of feed stock.
S
fc
¼Specific fuel consumption.
P
ci
¼weight of Pot with water before test (grams).
P
cf
¼weight of pot with water after test (grams).
f
cd
¼equivalent dry wood consumed (grams).
4. Results and discussion
The first consideration in the construction of this gasifier stove is to
optimize the high of the stove to ensure that the flame high from the
feed stock to the pot would burn in such a way that heat loss to the
external environment is minimal. The second one is, the secondary air,
which runs from the bottom of the outer cylinder to the top of the inner
cylinder to combust the volatile gas that comes due to the gasification
process inside the inner cylinder, will be heated up before combustion
by the heat emitted by the inner cylinder owing to the gasification
process. And, the last one is the inner hollow cylinder that have a
perforated wall (with maximum diameter as it goes from the bottom to
the top) and floor are the design consideration that improves the stove's
performance.
4.1. Lower heating value of the feedstocks
The MC of the three feed stocks is shown in Table 1 below, with a
moisture content of 7–9% on average, for the wet basis and dry basis
using Equation (6) and Equation (5) respectively.
We can simply compute the LHV of those feed stocks using Eq. (7) or
using all of the moisture content values from Table 1 and value of HHV
from literature (Parikh et al. 2005)(Kumar and Chandrashekar 2014)
(Rusch et al., 2021)(Szymajda and Łaska 2019)(Szymajda et al. 2021),
using Eq. (8) as shown in Table 2.
4.2. Temperature profile
The entire time taken for those three tests was determined by the
flame characteristics of the gasification process; for example, a 40-minute
flame stayed in the first test with eucalyptus, the other tests with bamboo
and MSCD (Mixture of Sawdust and Cow Dung) waited only 30 min with
flame.
The quantity of eucalyptus, bamboo, and a combination of saw dust
and cow dung feed stock utilized ranged from 536 - 558 gm, 409–501.25
gm, and 400–425 gm (eucalyptus sawdust to cow dung ratio was
72.27%–27.73%), respectively. The maximum temperature for euca-
lyptus was 94.2 C–94.4 C, which lasted 15 min, 84 C–86 C for
bamboo, and 88.5 C–94.4 C for saw dust and cow dung, which lasted
just 5 min.
4.3. Utilized feedstock, charcoal produced and amount of water
evaporated
When using ecaluptus as a feed stock, the gasification process is
started by closing the primary air inlet gate, resulting in a complete py-
rolysis reaction that is extinguished when the feed stock has been
completely converted to charcoal. Whereas other feed stocks are started
by half-opening the primary air inlet gate. In addition, unlike the other
two feed stocks, eucalyptus feed stock did not result in intermittent fires.
The quantity of wet feed stock used for water boiling is displayed on Fig
14; it was calculated by subtracting the charcoal generated from the total
feed stock used, and it is presented at the bottom of the stacked column
below the charcoal figure. One thing to note is that bamboo charcoal
output was higher than the other feed stocks.
Figure 14. Feed stocks utilized for water boiling and charcoals production.
A. Hailu Heliyon 8 (2022) e10163
10
Figure 15. Water evaporated from and remains in the pot.
Table 3. Parameter for thermal calculation and thermal efficiency of the stove.
S.N
Parameters Units Eucalyptus Bamboo Mixture of Sawdust &Cow Dung
ST-E1 ST-E2 ST-E3 ST-B1 ST-B2 ST-B3 ST-SCD1 ST-SCD2 ST-SCD3
1 Initial Temp of water
0
C 21.8 21.7 22.8 19.3 19.4 24.8 21.6 19.2 20.3
2 Final Temp of water
0
C 94.2 94.4 94.4 85 86 84.6 92.4 91.2 94.4
3 Biomass used for water boiling gm 452.8 461.9 460.1 400 407.8 392.1 333.7 324.5 341.6
4 Initial volume of water gm 2500 2500.1 2499.9 2499.9 2500.5 2500.5 2500.5 2498.3 2499.1
5 Moisture content % 7.84 7.84 7.84 8.74 8.74 8.74 7.60 7.60 7.60
6 Equivalent dry fuel burned gm 417.3 425.7 424.0 365.0 372.1 357.8 308.3 299.8 315.6
7 Water vaporized gm 614.5 630.6 615.4 318.9 317.7 327.9 324.8 309.6 343.5
8 Specific heat of water kJ/kg
0
C 4.186 4.186 4.1 86 4.186 4.186 4.186 4.186 4.186 4.186
9 Latent heat of evaporation of water kJ/kg 2260 2260 2260 2260 2260 2260 2260 2260 2260
10 Lower heating value kJ/kg 15772 15772 15772 14696 14696 14696 15349 15349 15349
11 Thermal Efficiency*% 32.61 32.56 32.00 26.25 26. 52 26.00 31.17 31.56 32.02
*
Thermal Efficiency is calculated using Equation (1)
Figure 16. Thermal efficiency of the gasifier stove using different feed stocks.
A. Hailu Heliyon 8 (2022) e10163
11
During the test, the quantity of water evaporated using bamboo waste
and MSCD briquette was almost same, but it was much less than the
amount of water evaporated using eucalyptus feedstock, as indicated at
the bottom front side of Fig 15 's column diagram. The largest amount of
water evaporated during this experiment was 630.56 gm and the lowest
amount was 309.56 gm out of a total of 2500 gm using eucalyptus slice
log and bamboo residues as feed stocks.
4.4. Thermal efficiency
For the thermal efficiency using Eq. (1), after gasification, the ulti-
mate by product (charcoal) in the gasifier was not considered as it is
illustrated on Table 3, i.e., the energy in the charcoal, but this must be
considered in order to determine the overall thermal efficiency. Eq. (2)
will be used to compute the exact value of the gasifier over all conversion
efficiency. The thermal efficiency of the stove is ranges from 26% to 33%
as it shown in Fig 16.
4.5. Overall thermal efficiency
In contrast to thermal efficiency, the quantity of energy in the end
product of the feed stocks (charcoal) is taken into account in the total
overall thermal efficiency calculation. Only, overall thermal efficiency of
the eucalyptus gasifier stock was included in our calculations.
Based on the lower heating value of eucalyptus charcoal, the overall
thermal efficiency of the gasifier stove can be calculated using Eq. (2).
Using the amount of charcoal produced by eucalyptus feed stocks from
Table 4 and higher heating value of eucalyptus charcoal 28 MJ/kg
(Berrueta et al. 2008), (Abasiryu et al. 2015) and finally by making all
other value similar to the one that was used for thermal efficiency of the
stove using eucalyptus feed stokes in Eq. (2), we obtained the values
which is described on Fig 17.
4.6. Charcoal production versus thermal efficiency
The percentage yield of charcoal was determined using the weight of
the charcoal produced during gasification divided by the weight of the
original feed stock, see Eq. (9). And, the specific fuel consumption is
calculated using Eq. (10), which is the ratio of dry fuel calculated having
Eq. (3) and quantity of evaporated water as shown it is in Fig 15, all the
results are explicitly shown in Table 4.
The charcoal generated by the gasifier stove is shown in Fig 18. To get
a good amount of charcoal, we need to get the charcoal out of the gasifier
stove as soon as the flames goes down and put it inside the closing cane.
Otherwise, the charcoal will burn and react with the oxygen in the air,
resulting in the formation of ash.
The percentage yield of bamboo tree charcoal was higher than that of
eucalyptus and MSCD briquettes, as shown in Fig 19, but the thermal
efficiency of the gasifier stove was lower with this feed stock, which can
be compensated on the overall thermal efficiency while using this
bamboo charcoal on other charcoal stoves.
When the relationship between the percentage yield of charcoal and
thermal efficiency is linearized, it can be expressed with the linear
equation Y ¼- 0.7956Xþ22.766 and the radius of curvature R
2
¼0.92,
indicating that the linear equation and the real graph are extremely close,
as shown in Fig 20. In other words, depending on thermal efficiency, this
Table 4. Percentage Yield of Charcoals and Specific fuel Consumption.
S. N
Parameters Units ST-E1 ST-E2 ST-E3 ST-B1 ST-B2 ST-B3 ST-SCD1 ST-SCD2 ST-SCD3
1 Initial weight of feed stocks gm 536.0 556.9 555.3 498.0 501.3 501.2 421.0 400.5 409.3
2 Final weight of feed stocks gm 83.2 95.0 95.2 103.0 103.5 109.2 87.3 76.0 67.7
3 Percentage yield of charcoal*% 15.52 17.6 17.14 20.68 18.65 21.79 20.74 18.98 16.54
4 Specific fuel consumption** 0.469 0.431 0.444 0.647 0.717 0.579 0.537 0.591 0.614
*
Percentage yield of charcoal using Eq. (9).
**
Using Equation (10)
Figure 17. Overall thermal efficiency of the gasifier when eucalyptus is used.
A. Hailu Heliyon 8 (2022) e10163
12
linear equation may be used to calculate the percentage of charcoal
yields.
The main benefit of this association is that feed stocks with low
thermal efficiency and a high percentage of charcoal production can be
applied in charcoal burners for further energy use. While the total overall
efficiency is determined, this will compensate for the decreases in their
thermal efficiency.
4.7. Comparisons with other stoves
This gasifier stove was compared to two other gasifier stoves to see
how they differed in terms of overall efficiency, as well as one other
charcoal cook stove to compare thermal efficiency. When comparing the
overall efficiency of those three stoves, the formula utilized is compa-
rable. In comparison to the Novel Biomass stove by (Shaisundaram et al.,
2021), Improved cook stove (ICS) by (Mohammadreza Rasoulkhani and
Mohammad Hossein Abbaspour-Fard 2018) and metal charcoal stove by
(Abasiryu et al. 2015), the over efficiency as well as the thermal effi-
ciency of this Top-lit up draft, Natural Draft gasifier has a surprising
result, as shown in Table 5. The reason for this was a proper removal of
the charcoal at the end of the gasification process in addition of the
optimal design of the stove. As the flame was switched off, the charcoal
was collected from the gasifier, and the process of air starvation was
correctly carried out, ensuring that the ash was not production.
Figure 18. Charcoal produced using the gasifier stove after gasification process.
Figure 19. Percentage yield of charcoal.
A. Hailu Heliyon 8 (2022) e10163
13
The charcoal generated throughout the procedure, particularly the
eucalyptus charcoal, was comparable to charcoal available on the local
market. This will allow us to use that high-calorie carbonized wood in
other charcoal stoves, maximizing the efficiency of the process.
The dimensions of those gasifier stoves are comparable; for example,
the Novel biomass and Improve cook stoves stand 30 cm tall and have a
diameter of 20–25 cm, while the Gasifier Stove Natural Draft stands 36
cm tall and has a diameter of 19 cm. The only reason for the increase in
overall and thermal efficiency is the design of this stove, which includes
an additional secondary cylinder that directs secondary air from the
bottom of the stove to the top, allowing time for the secondary air to heat
up before reaching the top point of combustion, and a second reason is
the interior hallow cylinder, which we don't see in the other two gasifier
stoves.
The gasifier cylinder's interior hollow cylinder will allow primary air
to be distributed to each point section. Also, once the gasification process
has begun, the gas produced at each section of the gasifier cylinder has
the opportunity to easily move up for combustion.
5. Conclusion
This gasifier stove had two advantages: it could be used as a good-
performing cooking stove by capturing the energy released during the
carbonization process, and it could also be used as a carbonizing ma-
chine, converting the feedstock into appropriated charcoal that could be
used directly or converted into briquettes using a pressing machine. This
also eliminates the unburden gas emitted during the carbonization pro-
cess, helping to maintain a stable climate.
Eucalyptus feed stocks were shown to be a more suitable feedstock in
the investigation. Thus, it burnt for around 40–45 min with a gentle, non-
stop flame. This was not the only reason; the thermal efficiency of these
feed stocks was greater 32.30 0.30%, and the amount of smoke pro-
duced was virtually non-existent when compared to the other two feed
stocks. The greatest temperature reached with this feed stock was 94.4
C. The percentage production of charcoal of this gasifier stove is indi-
rectly connected to the thermal efficiency, Y ¼-0.7956Xþ22.766, which
is a more convenient correlation ship for those who use a charcoal stove
Figure 20. Percentage yield of charcoal versus thermal efficiency.
Table 5. Comparison of the research parameter with other research.
S.N
Parameters Units Own Research (Shaisundaram
et al., 2021)
(Mohammadreza Rasoulkhani and
Mohammad Hossein Abbaspour-Fard 2018)
(Abasiryu et al. 2015)
Gasifier Stove
Natural Draft
Novel Biomass Stove ICS (Improved Cook Stove),
Natural Draft
Metal charcoal stove
1 Initial Temp of water
0
C 21.7 25 23 27
2 Final Temp of water
0
C 94.4 99 96.6 99
3 Biomass used for water boiling gm 461.9 500 350 600
4 Moisture Content % 7.84 15 5 -
5 Equivalent dry fuel burned gm 425.7 425 332. 5 -
6 Initial volume of water ml 2500.1 1300 3000 2000
7 Water vaporized ml 630.6 1300 - 100
8 Specific heat of water kJ/kg
0
C 4.186 4.186 4.186 4.186
9 Latent heat of evaporation of water kJ/kg 2260 2260 2260 2260
10 Lower heating value kJ/kg 15772 20,000 17540 27600
11 Amount of char remaining gm 95 200 - -
12 Lower heating value of charcoal kJ/kg 28,000 30,000 - -
13 Over all Efficiency % 55.18 38.6 34.6 20.02
*Over all Efficiency is calculated using Equation (2)
A. Hailu Heliyon 8 (2022) e10163
14
parallel with this stove, based on data received from nine stove tests.
Considering the lower heating value of charcoal, the total overall thermal
efficiency was 53 2%.
In comparison to other contemporary gasifier technologies, the
overall efficiency of this gasifier is amazing, and when compared to the
development of cooking stoves in Ethiopia, the performance of this
gasifier is among the best. Finally, heat losses on the stove bodies are
significant, i.e., around 70% of the energy contained in the feed stock was
wasted on the stove and pot, with the remaining energy recovered as
charcoal. Only 29 3% of the energy in the feed stock transfer for boiling
of water excluding the energy content in the char. This is evident because
a significant quantity of energy was lost as heat through various heat
transfer mechanisms. As a consequence, significant heat was generated
on the surface of the gasifier stove, indicating that the stove requires a
strong body insulating material to improve its performance.
Delcaration
Author contribution statement
Arkbom Hailu: Conceived and designed the experiments; Performed
the experiments; Analyzed and interpreted the data; Contributed, mate-
rials, analysis tools or data; Wrote the paper.
Funding statement
This work is supported financially by Mekelle University EiT - M as
part of the EnPe Project (NORAD's Master Program in the Energy and
Petroleum Sector) at the Department of Mechanical Engineering.
Data availability statement
Data included in article/supplementary material/referenced in
article.
Declaration of interest statement
The authors declare no conflict of interest.
Additional information
No additional information is available for this paper.
Acknowledgements
I would like to express my gratitude to Dr. Mulu Bayray and Mr.
Mussie Tesfaye a staff member of Mekelle University EiT-M, Mechanical
Engineering Department, for their assistance.
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