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Abstract—High quality cured tobacco is one of the most foreign
currency generators in Zimbabwe. Currently curing process within
the small to medium scale farmers is through curer’s experience. In
order to reduce this dependency and achieve high quality the curing
process requires a well-designed temperature control system. A
biomass fired flue curing tobacco barn design for small-medium scale
farmers in Zimbabwe with a clear objective to control temperature
and humidity is the focal point of this paper. The designed barn
accommodates capacity of small-medium tobacco farmers with a
provision to use firewood, coal or dung in as source of energy. To
reduce curer experience dependency a furnace with seized fuel trays,
which are charged into the furnace as per calculated frequency for
every curing stage basing on heat content and type of fuel was
incorporated. The designed barn system that, have an outside control
box contains a combination of heat extraction fans, cold air blowers
and humidifiers that regulate temperatures and humidity levels to
required levels for every curing stage under the instruction from
16F887 microcontroller. This has replaced the primitive way to check
thermometers inside the barn even at high temperatures of about
80°C. Commendable energy efficiency was realized in various system
performance simulations through different techniques.
Keywords—Humidity, Microcontroller, Stability, Temperature
Control System, Transient.
I. STATEMENT OF THE PROBLEM
OW quality tobacco with high curing costs is currently
produced by small-medium scale farmers in Zimbabwe.
A. Aim
To design a temperature-humidity control system of flue-
curing tobacco barns for small-medium scale farmers in
Zimbabwe.
B. Justification of the proposal
Cases of under and overheating tobacco are generally
tarnishing its quality and sale value at Auction floors, hence
they is need to find and commercialise innovative ideas of how
Portia Mupfumira is with the Harare Institute of Technology, Harare,
Zimbabwe BE 277 Belvedere (phone: +263 777 037 263; fax: +263 4
7414106; e-mail: [email protected], [email protected] ).
Webster. T. Rukweza, is an undergraduate student at Harare Institute of
Technology, Harare, (e-mail: [email protected] ).
best to control temperatures and humidity levels in a barn
with minimum use of fuel. Energy efficiency of the barn will
mean a significant reduction of the current alarming rates of
deforestation. Efforts to provide tobacco farmers with better
curing technology is needed as Zim-Asset identifies tobacco as
one of the major pillar of economic revival. [8]
C. Scope of the study
The main goal is to have temperature controllable system
hence, area of focus will be maintenance of the required
temperatures and humidity levels of the barn at different curing
stages with minimum fuel consumption.
D. Definitions of terms
Quality Function Deployment : the process of removing
lids from any container after the contents have been processed.
[7]
Semi Automated : When some processes in the production
or design of a product are done by machines but other
processes are still performed by humans. [1]
Finite Element Analysis : A type of computer program
that uses the finite element method to analyse a material or
object and find how applied stresses will
II. BACKGROUND
Successful tobacco production involves an energy intensive
curing process, which determines the final quality of the
tobacco leaf and ultimately the selling price of the leaf. The
sole objective of curing is to dry the green leaf in such a way
that the final leaf has required colour, texture and aroma. [2]
The golden leaf is passed through three stages of curing
requiring different temperatures, a range which varies between
32-80 degrees Celsius.
The process is usually done manually by controlling the
amount of firewood in the fireplace to suit the temperature
requirement of every stage. This requires high skilled labour to
produce a better quality. They are also reported cases of
accidents whereby the barn overheats and burn the produce.
According to the research done by Tobacco Research Board,
curing is one of the key determinants responsible for the
quality of tobacco which is being produced by small-medium
scale farmers.
The existing barns with temperature-humidity control
Design of a Microcontroller Based
Temperature-Humidity Control System of Bio-
mass Fired Tobacco Curing Barn for Small to
Medium Scale Farmers in Zimbabwe
Portia Mupfumira, and Webster. T. Rukweza
L
International Conference on Mechanical and Industrial Engineering (ICMIE'15) July 14-15, 2015 Harare (Zimbabwe)
16
technology largely depend on electricity as the source of fuel.
This is beyond the reach of many small-medium scale farmers
since they do not afford this technology.
By using firewood an approximated value of 43m3 of fuel
wood (15 000kg)/ year produces an average of 1400kg of
cured tobacco. This translates to a Specific Fuel
Consumption(SFC) of 10.7kg/kg of tobacco which is
approximately a third of the farmers’ income [5].This indicates
a loss of 98.5% of energy during curing because of the current
system’s inefficiencies.
Fig. 1 Traditional Barn fuel feeding mechanism
III. METHODOLOGY
A. Introduction
Primary data were collected through informal interviews,
field observations and questionnaires. Microsoft Equation
Engineering tools such as Failure Mode Effect Analysis,
Quality Function deployment and Simulation packages were
used to analyse and design the system. The researchers
designed a comprehensive design of the barn control system.
Literature review was done on tobacco curing, electronic
design and software development on temperature and humidity
control systems. Raw data was retrieved from the native
farmers.
Interviews, questionnaires and direct observation provided
insight into the lid removal process and areas which could be
improved.
B. Instrumentation
The following instruments were used f or collecting data:
• Informal Interviews
• Field Observations
• Questionnaires
• Engineering Tools
C. Current scenario
Environmental impacts of Tobacco production
According to [3] by 2016 if the current trend shown in
Figure 4 do not change major tobacco areas will have no trees.
This is supported by high fuel usage of firewood shown in
Figure 3. An interview with a farmer in Mutare indicated that
deforestation is leading to major siltation of the rivers and long
term damage of soil, a scenario which is catastrophic. Besides
land degradation, tobacco farming has come under
international scrutiny as deforestation is causing global
warming. It is estimated that, on average, it takes about 20
cubic meters(approximately 6.6 tonnes of wood), cleared from
a hectare of wood to produce a tonne of flue cured tobacco[6].
High levels of deforestation have resulted in EMA imposing
barn of commercial firewood usage.
90%
8% 2%
Fuel usage
Firewood
Coal
Biomass
Fig. 2 Fuel usage distribution
0
20
40
60
80
100
2009
2010
2011
2012
2013
2014
TOBACCO PRODUCTION TREND(2009-2014)(in million kgs)
TOBACCO PRODUCTION TREND(2009-2014)(in million kgs)
Fig. 3 Tobacco production trend
The below graph shows that there is an exponential growth
of deforestation as new farmers enters the business every year
[4].
2009 2010 2011 2012 2013 2014
RATE OF DEFORESTATION
Fig. 4 Deforestation rate
IV. MODELING
A. System Model Design
This model has also been designed with the help of the
reviewed literature on the farmer requirements using QFD
basing on correlation between farmer requirements and
International Conference on Mechanical and Industrial Engineering (ICMIE'15) July 14-15, 2015 Harare (Zimbabwe)
17
engineering characteristics. Product Design Specifications
(PDS) was used for conceptualisation.
Fig. 5 Quality Function Deployment (QFD)
Fig. 6 Humidification Mechanism
Fig. 7 Blower wind pipe and chimney
Fig. 8 Flue pipe arrangement
Fig. 9 Furnace tray for optimum fuel consumption
Use either SI (MKS) or CGS as primary units. (SI units are
strongly encouraged.) English units may be used as secondary
units (in parentheses). This applies to papers in data storage.
For example
V. RESULTS
The designed system operates under the instruction of a
computer program. It utilizes a microcontroller as the brain
with the cold-air fan, heat extraction fan furnace fan and
solenoid valve as the actuators. The program controls two
variables, humidity and temperature at required levels of
different curing stages. Figures below shows the system setup
and simulation using Proteus and temperature flow and control
in the barn.
Fig. 10 Designed system setup
Fig. 11 System simulation using Proteus
International Conference on Mechanical and Industrial Engineering (ICMIE'15) July 14-15, 2015 Harare (Zimbabwe)
18
Fig. 12 Barn heat flow
Fig. 13 Barn temperature regulation
VI. RECOMMENDATIONS
It is recommended here that the following aspects be taken
into consideration for the improvement and full operational
performance of the tobacco barn.
• Maintenance of the fans as per the requirements of
the maintenance and reliability strategies outlined.
• Use of Eucalyptus grandis or some firewood
alternatives with almost similar heating value so as to
maintain stability of the system.
VII. CONCLUSION
The fire control system is cost effective , key in
environmental degradation reduction and seeks to
commercialise the technological idea in product quality
improvement that plays a critical role in the overall nation’s
revenue.
REFERENCES
[1] Angeles, J., 2007, Fundamentals of Robotic Mechanical Systems, Third
Edition Springer, New York
[2] Boyle P, Gray N, Henningfield J, Seffrin J, Zatonski W. A.(2010).
Tobacco: Science, Policy and Public Health, Second Edition. New
York: Oxford University Press
[3] Environmental Management Agency, (2016)
[4] Forest Commission of Zimbabwe, (2014)
[5] Scott P.( 2006). Development of Tobacco Rocket Barn for Small Holder
Farmers in Malawi
[6] Tobacco Research Board, (2012)
[7] www.wikipedia.com
[8] Zim-Asset Chapter 3 section12
International Conference on Mechanical and Industrial Engineering (ICMIE'15) July 14-15, 2015 Harare (Zimbabwe)
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