This presentation on maize drying in Ghana was given at the 2nd All Africa Post-Harvest Congress & Exhibition. The lead researchers from KNUST, who prepared this presentation, are making it available via the Consortium for Innovation in Post-Harvest Loss and Food Waste Reduction slideshare account. KNUST is a member of the Consortium.

1. Te c h n o - e c o n o m i c e v a l u a t i o n o f
a C ro s s f l o w C o l u m n D r y e r f o r
M a i z e D r y i n g i n G h a n a
1
2nd All Africa Postharvest Congress and Exhibition
ADDIS ABABA, ETHIOPIA
SEPTEMBER 17-21, 2019
George Obeng-Akrofi, Joseph O. Akowuah, Ahmad Addo, Dirk Maier
Department of Agricultural and Biosystems Engineering,
Kwame Nkrumah University of Science and Technology, Kumasi-Ghana
Iowa State University, USA

2. INTRODUCTION
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Grain drying: The case of maize in
Ghana
• Production of maize is dominated
by smallholder farmers (SHF) in
sub-Saharan Africa (Cairns et al.,
2013 ).
• However, these farmers continue to
record high postharvest losses due
to lack of proper drying and storage
facilities.
Activity % Loss
Field (Over-Maturity, Harvesting, Heaping) 5.0
Shelling or Threshing 1.5
Drying 0.5
Storage (mould) 15.0
Storage (Insect and Pest) 8.0
Total 30.0
Table 1: Major Season Maize Postharvest Losses in the
Middle Belt of Ghana (Akowuah et al., 2015)
Drying and storage are among the key areas along the maize value chain that
is of critical importance to smallholder farmers/traders in Africa.

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Open sun drying in Ghana
Germination of grains due to humid conditions
Grain drying
is a
challenge in
Ghana
Unreliability in drying
Quantitative losses
Contamination by animals

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Commercial dryers
Few installed in Ghana but rarely
patronized due to:
• High drying cost associated
with use of LPG or diesel as
source of fuel.
• Not in proximity to farmers.
• Low prospect for acceptance,
adaptation and adoption.

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Need for study
 Low-cost drying systems are suitable for
smallholder farmers in developing countries
(Chua and Chou, 2003).
 Technical and economic performance assessment
of such drying systems will give confidence to:
o farmers who use these drying systems
o investors who wish to invest in their development
and commercialisation.

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Focus of study
 This study sought to assess the performance of a
500 kg capacity crossflow column dryer with a
biomass burner heat source.
 The economic viability of the drying system for
scale-up was also appraised.

8. MATERIALS AND METHODS
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9. 9
Experimental Procedure
 Dryer description
 Inner and outer bins
 Drying air pipe
 Blower
 Biomass burner
 Experimental Set-up
 Maize
 Bamboo
Fig 1: CAD model of column drying showing all
components
Fig 2: Pictorial view of experimental set-up

10.  Data collection points
 Temperature and
relative humidity
profile in the drying
chamber
 Moisture content
variation of maize
at different sections
in the drying
chamber
Tinytag Data
Loggers
Tinytag Data
Loggers
LEVEL 2
LEVEL 1
Drying
Chamber
Plenum
Fig 3: Longitudinal Cross-section showing
positions of data loggers
LEVEL 3

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Dryer performance evaluation
 Burner Efficiency, BE
𝐵𝐸 =
𝑀 𝑎𝑖𝑟 × 𝐶 𝑃𝑎𝑖𝑟 × ( 𝑇 𝑎𝑖𝑟 – 𝑇 𝑎𝑚𝑏)
𝑀 𝑏𝑐 × 𝐻 𝑉
× 100 (1)
 Drying Rate, DR
𝐷𝑅 =
𝑀𝐶 𝑖− 𝑀𝐶 𝑑
t
(2)
 Drying Efficiency, DE
DE =
𝑀 𝑤 𝐿 𝑣
𝑀 𝑎𝑖𝑟 𝐶𝑝 𝑎𝑖𝑟∆𝑇
(3)

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A smallholder
Ghanaian
farmer
2 ha maize
farmland
Column
drying system
Premium
price for
dried maize
Revenue
from drying
services
Model scenario for economic appraisal

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Economic appraisal
 Economic Indicators
 Net Present Value
 Internal Rate of Return
 Payback Period
 Benefit-Cost Ratio
 Sensitivity Analysis
 Investment cost
 Price for drying maize
 Discount rate
𝑵𝑷𝑽 = 𝑡=0
𝑛
𝑎 𝑡𝑆𝑡
=
𝑆0
1+𝑖 0 +
𝑆1
1+𝑖 1 +
𝑆 𝑛
1+𝑖 𝑛 (4)
𝑁𝑃𝑉 𝑆 =
𝑆𝑡
1+𝑰𝑹𝑹 𝑡 = 0 (5)
𝑷𝑩𝑷 =
𝐶 𝑖
𝑆
(6)
𝑩𝑪𝑹 = ( 𝐵 𝑖
(1+𝑑) 𝑖) ÷ ( 𝐶 𝑖
(1+𝑑) 𝑖)
(7)

14. RESULTS AND DISCUSSION
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Temperature vs time during drying
20
25
30
35
40
45
50
55
60
Temperature(˚C)
Drying period (h)
Drying Chamber Plenum Ambient
0 1 2 3 4 5
51.53 ± 2.4 ˚C
38.47 ± 2.8 ˚C
28.47 ± 2.1 ˚C

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Moisture content vs. time
10
12
14
16
18
20
22
24
0 1 2 3 4 5
Moisturecontent(%)
Drying period (h)
Inner Outer Average
Safe moisture
content for
storage (13 %)

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Tab 2: Summary of dryer technical performance
Parameter/Item Value/Description
Trial Date 22nd December, 2018
Initial Mass of maize 250 kg
Initial Moisture Content 20.70 %
Final Average Moisture content 13.25 %
Average Drying Time 5 hrs
Average Drying Rate 1.81% / h
Drying Efficiency 64.65 %
Average Drying Temperature 39 ˚C
Average MER 5.1 kg/h

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Parameter Value
Capacity of drier (t) 0.5
Number of batches per day 2
Number of hours required per batch of drying 5
Number of operational months per year 3
Operational hours per year 720
Weight of bag maize from farm gate (kg) 130
Number of bags of maize dried per day 8
Number of bags of maize dried per week 46
Quantity of maize dried per year (t) 72
Number of bags of produce dried per year 554
Assumed average amount of maize produced per year in a district (t) 20,000
Number of dyers required to process the total available maize 278
Price charged for drying a bag of maize (USD) 0.94
Cost of drying system (USD) 604.00
Tab 3: Technical and financial parameters
from the study

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Economic appraisal of business model
NPV = $1,633
IRR = 71 %
PBP = 1.41 yrs
BCR = 2. 83
Fig 5: Variation of NPV and IRR over a 10 yr operation period
-0.4
-0.2
0
0.2
0.4
0.6
0.8
-1.00
-0.50
0.00
0.50
1.00
1.50
2.00
0 1 2 3 4 5 6 7 8 9 10
IRRx100(%)
NPVx103(USD)
Time (year)
Net Present value (NPV) Internal Rate of Returns (IRR)
Discount rate of 14 % as at February, 2019 was used for the analysis

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Sensitivity Analysis on variation of drying charges
Drying Charge (USD/bag of maize) NPV (USD) IRR (%) PBP (yrs) BCR
0.75 1,084 53 1.86 2.26
0.94 1,633 71 1.41 2.83
1.13 2,174 88 1.13 3.39
1.32 2,723 106 0.95 3.96
Tab 4: Variation of NPV, IRR, PBP and BCR in relation to price charged for drying
maize per bag (130 kg)

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Discount Rate (%) NPV (USD) IRR (%) PBP (yrs) BCR
7 2,409 71 1.41 3.47
14 1,633 71 1.41 2.83
21 1,135 71 1.41 2.34
28 798 71 1.41 1.98
Tab 5: Variation of NPV, IRR, PBP and BCR in relation to discount rate
Sensitivity Analysis on variation of discount rate

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Estimated Investment Cost (USD) NPV (USD) IRR (%) PBP (yrs) BCR
604 (base cost) 1,633 71 1.41 2.83
725 (20 % more) 1,500 58 1.70 2.54
906 (50 % more) 1,300 46 2.14 2.21
1,089(80 % more) 1,100 37 2.59 1.95
Tab 6: Variation of NPV, IRR, PBP and BCR in relation to dryer investment cost
*Discount rate of 14 % (as at February, 2019) was used for the analysis
Sensitivity analysis on variation in cost of dryer

23. KEY FINDINGS
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The average drying rate recorded during the study
was 1.81 %/h with a drying efficiency of 64.65 %.
With a positive NPV of USD 1,633 and IRR 71%
greater than the discount rate used, the business
model is proven to be viable. A PBP of 1.41 yrs is
expected with a BCR of 2.83.

25. ACKNOWLEDGMENT
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Thank you
for your
attention !!!