DESIGN AND TESTING OF CASHEW NUT SHELL GASIFIER STOVE
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Transcript of DESIGN AND TESTING OF CASHEW NUT SHELL GASIFIER STOVE
DESIGN AND TESTING OF CASHEW NUT SHELL GASIFIER STOVE
Miguel M. Uamusse, Jonas Matsinhe
Universidade Eduardo Mondlane, Mozambique
ABSTRACT
Biomass has already emerged in the renewable energy area as one of the promising
candidates for the future energy source(Basu, 2010). Historically, biomass has been a
major source of fuel from the existence of making rapid urbanization, but widespread
use of fossil fuels in the industrialization has relegated it to a minor source of energy
The CNS Gasifier Stove developed has a thermal efficiency of 35.5 % and an energy
output of 2.19 kW. The corresponding values for LPG stove and Kerosene stove are
53.53 % (0.69 kW) and 39.3 % (0.6 kW), respectively. Though the use of CNS gasifier
as a fuel is less efficient than the aforementioned, with the rising oil prices and the
search for alternatives to contemporary cooking fuels, it is still a viable alternative in this
comparison.
LIST OF ABBREVIATIONS
ASTM American Society for Testing and Materials
CNS Cashew Nut Shell
FAO Food and Agriculture Organization of the United Nations
GHG Greenhouse Gases
HHV Higher Heating Value
IEA International Energy Agency
LHV Lower Heating Value
LPG Liquefied Petroleum Gas
MC Moisture Content
NBCB North Bank of Cahora Bassa
NOMA NORAD’s Program for Master Studies
Pi, Po Power input and out put
Qs,Ql Sensible and Latent Heat
TGA Thermal Gravimetric Analysis
UNEP United Nation Environmental Programe
VM Volatile Matter
WBT Water Boiling Test
WHO World Health Organization
1. INTRODUCTION
Energy is a basic necessity for human activity, economic and social development. But global
strategies to meet this basic need for the world's rapidly growing population are lacking. The
major sources of energy to supply such a scenario are oil, coal, natural gas, hydro energy, nuclear
energy, renewable combustible wastes and other sources. The global energy supply in 2010 was
estimated to 11,500 mtoe (million tons of oil equivalent) and Projected to be 13,700 mtoe in the
year 2020. Under the 2010 scenario, the global energy mix was: oil 35.1 %, Coal 23.5 %, Natural
gas 20.7 %, Renewable combustible wastes 11.1 %, Nuclear 6.8 %, Hydro 2.3 %, other sources
0.5 % (Economy Watch, 2010).
Energy is a basic necessity for human activity, economic and social development. But global
strategies to meet this basic need for the world's rapidly growing population are lacking. The
major sources of energy to supply such a scenario are oil, coal, natural gas, hydro energy, nuclear
energy, renewable combustible wastes and other sources (Wilson et a,.l 2010). The global energy
supply in 2010 was estimated to 11,500 mtoe (million tons of oil equivalent) and Projected to be
13,700 mtoe in the year 2020. Under the 2010 scenario, the global energy mix was: oil 35.1 %,
Coal 23.5 %, Natural gas 20.7 %, Renewable combustible wastes 11.1 %, Nuclear 6.8 %, Hydro
2.3 %, other sources 0.5 % (Economy Watch, 2010).
1.1.Biomass Energy Technologies
Biomass to energy routes are numerous and can mainly be divided in three groups, as shown in
Figure 2.1: thermochemical, biochemical conversion routes and physical or mechanical
extraction route (Tsamba, 2008). The first group includes combustion, gasification, and
pyrolysis. The second group incorporates digestion and fermentation. Only thermochemical
technologies are discussed in the following section.
Figure 1.1 Thermochemical Conversion Routes (Tsamba, 2008)
1.2. Gasification
Gasification is thermo-chemical process at high temperature that converts carbon containing
fuels, such as coal and biomass, into a combustible gas containing mainly carbon monoxide,
hydrogen, methane and inert gases, through incomplete combustion and reduction. At the
beginning of 1812’s, gasifiers were used for industrial power and heating applications until in the
1920’s, when oil-fueled systems gradually took over the systems fueled by producer gas (Quaak
et al., 1999). It is also noted that unreliable supplies of petroleum gas revitalized gasifiers during
World War II and it was intensively used in transportation and on farm systems (Rajvanshi,
1986). Gasification is found to be appealing for the reasons listed below (Quaak et al., 1999;
Rajvanshi, 1986):
i. The combustible gas can be used in internal combustion engines or gas turbines (enabling
high efficient power generation), burned directly or used in the production of methanol or
hydrogen.
ii. A gaseous fuel needs little excess air in combustion and has low levels of contaminants.
iii. It enables solid fuels to replace oil, considering the rising oil price and climate change
effect.
Eventually, gasification technology is currently identified as a sustainable renewable alternative
for energy generation with zero impact to the environment.
1.3. Type of Gasifiers and Process
Due to the interaction of air or oxygen and biomass in the gasifier, gasifiers are classified
according to the way air or oxygen is introduced in it. There are three types of gasifiers,
Downdraft, Updraft, and Crossdraft . As the classification implies updraft gasifier has air passing
through the biomass from bottom and the combustible gases come out from the top of the
gasifier. Similarly in the downdraft gasifier the air is passed from the tubers in the downdraft
direction.
Table 1.1 Advantages and Disadvantages of Gasifiers (Quaak, 1999; Rajvanshi, 1986
Gasifier type Advantages Disadvantage
Updraft (i) Small pressure drop.
(ii) Little tendency towards slag formation
and simplicity in construction.
(iii) High charcoal burnout with internal
heat exchange leading to low gas exit
temperature and high gasification
efficiencies.
(iv) Can run on wide range of moisture
content and some size variation in feed
stock.
(i) Moisture Content of fuel.
(ii) Relatively long time required for
start up of engine utilizing syngas
(iii) Poor reaction capability with
heavy gas load.
(iv) High amounts of tar and
pyrolysis products.
(v) Demanding excessive cleaning
for the case of engine application
Downdraft (i) Flexible adaptation of gas production to
load.
(ii) Low sensitivity to charcoal dust and tar
content of fuel.
(iii) Produces gas with low tar content
suitable for internal combustion engine
(i) Needs uniform and not very
small particle size of fuel 1 – 2
mm.
(ii) High amount of ash and dust
particles remain in gas
(iii) The relatively high temperature
of exit flue gas
(iv) Results in lower gasification
efficiency biomass moisture
content must be less than 25 %
on dry basis
Crossdraft (i) Fast response time to load.
(ii) Flexible gas production.
(iii) Can be operated in small scale
(i) High sensitivity to slag formation
(ii) Demanding clean charcoal
(iii) High pressure drop.
(iv) Charcoal gasification results in
extremely high temperature.
2. DESIGN OF THE GASIFIER STOVE
2.1. Development Process
The development of Cashew Nut Shells gasifier stove was executed in accordance to the
calculation done in section 3. The size of the reactor was scaled down to 0.15 m reactor diameter,
0.60 m height of reactor and 2.1 kW power output, just enough for a family with 3 to 4 members.
However for the ultimate analysis the chemical formula for the CNS was determine as; From
ultimate amalysis, C = 63.2 %, H = 6.74 and O = 21.9 %. For the purpose determining the
amount of air for combustion of the biomass, empirical formulae was deployed as stated in
Equation 4.1
OHbCOaAirNOCH 2201.023.02.1 +⇒+ ………………………………… (4.1)
BiomassofkgperAirofkgTotal
NONOAir
wOW
zyX
ZYMrmXc
N
OH
47.4:
47.379.021.0:
0085.0267.5041.0041.0.
1463.
23.0267.5369.12.1
267.574.61
267.5267.5
369.116
9.2174.6174.6267.5
122.63
2222 +⇒+
====
======
=======
The schematic configuration diagram of the said gasifier stove is depicted in Figure and its main
dimension given in Figure .
Fig.2.1. Gasifier Reactor
2.2. The Major Parts of the CNS Gas Stove.
i. The Gasifier Stove Reactor
The gasifier stove reactor is shown schematically Figure 4.1. The reactor is cylindrical in shape
having a diameter of 0.15 m and a height of 0.60 m. The cylinder is made from a galvanized
iron sheet gauge 1.8 mm, thickness on the outside and of a stainless steel sheet gauge 2.0 mm
thickness in the inside. This cylinder is provided with an annular space of 2 cm, where the
burned CNS or any other materials is placed to serve as insulation in order to prevent heat loss in
the gasifier..
Fan assembly
Ash chamber
Reactor
Port support
ii. The Ash Chamber
The ash chamber (Figure 4.1) serves as the storage for ash produced after each operation. It is
located beneath the reactor to easily catch the ash that is falling from the reactor. This chamber is
provided with a door that can be opened for easy disposal of ash and it must be kept always
closed when operating the gasifier. The ash chamber is tightly fitted in all sides to prevent the air
given off by the fan from escaping the chamber hence, minimizing excessive loss of draft in the
system in gasifying the fuel.
iii. The Fan Assembly
The fan assembly is the component of the stove that provides the air needed by the fuel during
gasification. It is fastened on door of the chamber directly push the air into the column of CNS in
the reactor. The fan used for the standard model is a 76.2 mm (3 inch) diameter axial-type fan
that is used in computers. It has a rated power input of 16 W using a 220 volt AC. A manually
operated rotary switch is used to control the speed of the fan which, in turn, controls the flow of
gas to the burner during operation
iv. The Burner
The burner converts the gas coming out from the reactor to a bluish flame, where combustible
gas is allowed to pass through. The secondary holes located at the periphery of the burner are
used to supply the air necessary for the combustion of gases. On top of the burner is a pot
support that holds the pot in place during cooking. The burner is removable for easy loading of
fuel into the reactor and is set in place during operation.
3. METHODOLOGY
the methodology used for this work was first study the raw material use( CNS)and calculation
the size of stove suitable to supply a power output of 2.1 kw for household cooking. The required
time to operate the stove was set at 40 minutes, before discharging char and reloading Cashew
Nut Shells.
1. Power Input (Pi):The amount of power to supply the energy needed by the stove,
considering a thermal efficiency for the stove of 30 %, will be
ηPoutPi =
where: Pout-power output, kW; Pi-power in put, kW; η-efficiency of stove
2. Fuel Consumption Rate:(FCR) Based on the power input, the amount of Cashew Nut
Shells to be burned per hour will be
HVFPiFCR×
=0012.0
where: FCR -fuel consumption rate, kg /hr Po -power output, kW HVF-heating value of
cashew nut shell, kJ/kg.
3. Cross-Sectional Area of the Reactor (Ar) assuming a specific gasification rate of 87
kg/hr-m2 , the cross-sectional area for the CNSG stove will be
SGRFCRA =
Where: FCR - fuel consumption rate, kg/hr, SGR-specific gasification rate of Cashew
Nut Shells,
4. Height of Reactor (Hr)
In order to attain the 40-minute operating time required, considering a 1.5 cm per min
fire zone rate for the stove, the height of the reactor will be
FZRTH or ×=
Where: Hr-Height of reactor, m; To-operating time, FZR-fire zone rate.
5. Diameter of Reactor (Dr)
Using the computed Ar, the diameter of the reactor inner cylinder will be
5.04
=πADR
Where: D - diameter of reactor, m FCR - fuel consumption rate, kg/hr, SGR-specific
gasification rate of Cashew Nut Shell
6. Airflow Requirement (Ar)
The amount of air needed to gasify the fuel, considering an equivalence ratio for the stove
of 0.35 m/s, will be
Rr ESAFCRA ××=
where: AFR - air flow rate, m3/hr, FCR - rate of consumption of Cashew Nut Shells, kg/hr, SA-
stoichiometric air of Cashew Nut Shells, 4.5 kg air per kg cashew nut shells
Table 4.1 gives the summary of empirically parameter of gasifier. The values were calculated
using the correlation as introduced in above.
4. RESULTS AND DISCUSSIONS
During the entire operation, the quality of gas varied from the start to the end. In the initial stage,
the flame color was yellowish to pink; in the middle stage, the flame turned pinkish-to bluish;
and towards the end of operation, the flame became bluish. The color of the flame is affected by
the moisture and hydrocarbon present in cashew nut shells being burned in the fire zone
Figure 4.1 Table 2.2 Advantages and Disadvantages of Gasifiers (Quaak, 1999; Rajvanshi,
1986 Color of Flame in CNSG
Table 4.1. result of design parameter.
Parameter Calculation result
Power input 6.1 kW
Fuel Consumption Rate 1.35 kg/hr
Cross-Sectional Area of the Reactor 0.0154 m2
Height of Reactor (Hr) 0.60 m
Diameter of Reactor (Dr) 0.130 m
Airflow Requirement (Ar) 0.20 m3/min
The power imput is around 6,1kW and Fuel consumption rate are good for this
gasification, and the CNS gas stove emits a flammable and poisonous gas. It is thus
recommended that the gas produced during operation is properly burned. It is
recommended that inhalation of the gas emitted from the stove is prohibited since it is
toxic and injurious to health.
5.CONCLUSIONS AND RECOMMENDATIONS
a) The fuel properties of the cashew nut shell waste revealed its suitability for gasification.
The sampled cashew nut shell had a moisture content (4.2 %), low ash content (7.5 %),
and a heating value of 24.2 MJ/kg against the recommended values 6.7%, 26.2%,
21.5MJ/kg respectively.
b) The proper utilization of the cashew nut shell waste through gasification route will
conserve the biomass fuel and make its use self-sustainable for thermal energy. They can
be used for domestic cooking, heating and for keeping the surrounding warm, instead of
relying on depleting fossil fuel, highly cost gas and electricity.
REFERENCES
Basu, P (2010), Biomass Gasification and Pyrolysis ,Piratical design and Theory,
Elsevier USA
Economy Watch (2010), World Energy Consumption, http://www.economywatch.com/energy-
economy/scenario.html retrieved on Tuesday, 13th September, 2011
Quaak, P, Knoef, H and Stassen, H, (1999), Energy from Biomass: A Review of
Combustion and Gasification Technologies, Energy Series: World BankTechnical Paper
No. 422.
Rajvanshi, A.K (1986), “Biomass Gasification”, in Goswami, D. Y Alternative Energyin
Agriculture Vol. II, Ed. CRC Press, pp. 83-102
Tsamba, A. J (2008). Fundamental study of two Selected Tropical Biomass for
Energy: Coconut and cashew nut shells. Stockholm: KTH Industrial Engineering and
management.
Wilson, L, Yang, W, Blasiak, W, W, Geoffrey R. J and Mhilu, C. F (2010), Thermal
characterization of tropical biomass feedstocks, Energy Conversion and Management.
Volume 52, pp. 191–198.