IN PURSUIT OF GREENER CURING

METHODS:USE OF THE ROCKET

BARN FOR TOBACCO CURING IN

ZIMBABWE

CORESTA CONGRESS 2014

TOBACCO RESEARCH BOARD

KUTSAGA

Wisdom Munanga

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OUTLINE

• Background

• Common types of barns in Zimbabwe

• Objectives

• Materials and Methods

• Results and Discussion

• Summary and Conclusion

• Recommendations

• Acknowledgement

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BACKGROUND • Tobacco production in Africa has

increased from approximately 250 m

kg - 500 m kg in 2012 (ZTA, 2013).

• Currently, 90 % of flue-cured tobacco

production - in SADC region (Malawi,

Tanzania and Zimbabwe).

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BACKGROUND cont.

• Wood is the major curing fuel .

• In Southern Africa alone, an estimated

140 000 hectares of woodlands cleared

annually for tobacco curing (12 % of

the annual deforestation).

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BACKGROUND cont. • In Zimbabwe, the number of tobacco

growers increased to 106 000 in 2013.

• 80 % of these growers are small scale

farmers.

• most of the small scale growers rely on

wood for curing and most of them do not

have woodlots.

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BACKGROUND cont.

• Thus tobacco related deforestation

estimated at 15.9 % of the total annual

deforestation in 2003 has since

increased.

• Over 138 million m3 of firewood cured

part of the 127 m kg of tobacco in 2010-2011 season.

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BACKGROUND cont.

• To curb this problem, there is therefore

need to develop more efficient tobacco

curing systems.

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Common types of barns in Zimbabwe

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Common types of barns in Zimbabwe cont.

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Common types of barns in Zimbabwe

cont.

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Common types of barns in

Zimbabwe cont.

• Require ~ 9 kg wood to produce 1 kg of

cured leaf .

• To address this problem, the TRB

embarked on a programme aimed at

developing more efficient curing systems.

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Common types of barns in

Zimbabwe cont. One of the promising design was the rocket barn,

originally developed in Malawi.

Advantages

• reduced wood consumption.

• reduced turnaround time.

• Improved quality.

• More suitable for the small holder grower.

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OBJECTIVE

• To evaluate the curing efficiency of the

modifications of the rocket barn under

Zimbabwean conditions.

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MATERIALS AND METHODS The rocket barn

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MATERIALS AND METHODS

• Experimental site: Kutsaga Research

Station (Longitude 31° 13′ E, Latitude

17 ° 91′ S, Altitude 1480 m from 2011

– 2013).

• Two types of modifications

evaluated.

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The modified rocket barn

QD = kA/L.ΔT12

Qv = hv(Tb-Ta)

QR = eQ(Tm4-Ta

4)

MATERIALS AND METHODS Mod 1

Mod 2

Original

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•Design: RCBD, 6 treatments, 4 replications

MATERIALS AND METHODS

BARN TYPE DESCRIPTION

1 Rocket 1 Brick fire boxes

2 Rocket 2 Flue- pipes

3 Rocket 3 Brick fire boxes

4 Rocket 4 Brick fire boxes

5 Conventional 1 Updraft with brick firebox

6 Conventional 2 Updraft with flue-pipes

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Procedure

• Freshly harvested tobacco leaves from the

same field plot were used.

• Tobacco leaves were packed on clips that

were loaded into the barn at the same time.

• All barns were loaded with 350 clips (42

leaves/clip).

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Procedure cont.

• Wood from the blue gum at 12 % moisture

content used.

• The barns were fired at the same time.

• The time taken and amount of fuel consumed

to complete each curing cycle was recorded.

• Mean energy utilization index was calculated

as a ratio of fuel mass to mass of dried

tobacco leaves.

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Measurements

• Time taken to complete each stage

of the curing process.

• Fuel consumption.

• Vertical Temperature profiles.

• Cured leaf quality.

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RESULTS AND DISCUSSION

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Time taken to complete each stage of

curing and total barn turnaround time

(hours).

0

50

100

150

200

250

300

Rocket 1 Rocket 2 Rocket 3 Rocket 4 Conv. 1-test

Conv. 2-std

Tim

e ta

ke

n (

ho

urs

)

Treatment Barns

Colouring

Lamina Drying

Midrib Driyng

Total time

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Amount of fuel consumed during each

curing stage and the total fuel

consumption (kg).

0

500

1000

1500

2000

Rocket 1 Rocket 2 Rocket 3 Rocket 4 Conv. 1-test

Conv.2-std

Fu

el co

nsu

me

d (

kg

)

Treatments/ Barns

Colouring

Lamina drying

Midrib drying

Total

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Mean Energy Utilization Indices (MEUIs)

0

2

4

6

8

10

12

14

Rocket1

Rocket2

Rocket3

Rocket4

Conv.1- test

Conv.2- std

Mean e

nerg

y u

tiliz

ation

indic

es (

kg o

f w

ood/k

g o

f

tobacco)

Treatments/ Barns

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Mean vertical temperature profiles (oC).

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Cured leaf quality

0

10

20

30

40

50

60

70

Rocket1

Rocket2

Rocket3

Rocket4

Conv.Test

Conv.Std.

Gra

de

In

de

x (

%)

Treatments/ Barns

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SUMMARY OF RESULTS Turn around time

• In new rocket barn designs 5 – 6 days

• Conv. Barns 7 – 12 days.

Fuel Consumption

• Rocket barns ~ 800 kg and

• Conventional barns ~1700 kg.

Grade Index

• Similar for all barn types

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CONCLUSIONS

Results showed that the modifications

resulted in:

• Reduced turnaround time.

• 50 % wood fuel saving.

• No adverse effect on leaf quality.

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CONCLUSIONS cont.

• The brick fire exchange system - more

stable temperatures.

• The rocket barn is an efficient curing system.

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RECOMMENDATIONS

• The capacity of the barns currently in use

in Zimbabwe, is small (1 – 2 ha).

• Only ideal for the small - scale growers.

• Thus, further research on bigger energy

efficient barns is currently underway at

TRB.

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ACKNOWLEDGEMENT

• TRB management and staff

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Thank you all!!!

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