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Comparison of High Efficiency Heat Exchanger Retrofits for the
Powell Star Bulk Barn
Stephen Barts and T. David ReedVirginia Tech
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Background• The Powell Star CB-9 barns is the most
predominant bulk curing barn in Virginia
– Very good curing characteristics
– Has a unique heat exchanger that was designed specifically for the barn
– Has a relatively high level of energy consumption(fuel and electricity) resulting in comparatively high curing costs
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Background• Original heat exchanger manufactured 15-20
years ago
• Little consideration give at that time to efficiency
• Aging heat exchangers now warrant replacement
• Greater emphasis should be given to efficiency of replacement units
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Objective
Evaluate new high efficiency heat exchanger retrofits for the Powell Star CB-9 curing barn
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Test Barns at Lazy C Farms 201
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Test Barns at Lazy C Farms
Heat exchangers evaluated
1. Original Powell Star unit (Powermatic burner)2. DeCloet SLR (existing Powermatic burner)3. Tytun (new Reillo burner)
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Tobacco Barn Heat Exchanger Testing Procedure
1. Burner setup – set output to 400K Btu and optimize efficiency (O2, CO, excess air, etc.)
2. Use a calibrate combustion gas analyzer to measure stack temperature and provide calculated combustion efficiency value
3. Record combustion efficiency after a set firing schedule
Presented at the 47th TWC (Reed)
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Testing Protocol
1. Initial 2 minute warm-up
2. 2 minute off cycle
3. Run three (3) burner cycles of 6 minutes on and 2 minutes off
4. Record combustion efficiency at end of third cycle as heat exchanger efficiency
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Length of burn (minutes)
2 2 4 6 2 4 6 2 4 6Ef
ficie
ncy
(%)
70
75
80
85
90
Tytun
Star
DeCloet
Length of burn (minutes)
2 2 4 6 2 4 6 2 4 6
Stac
k te
mpe
ratu
re (F
)
100
150
200
250
300
350
400
450
500
Tytun
Star
Decloet
Heat Exchanger Efficiency TestingLazy C Farms, 2017
Powell Star CB-9 barns
89.0%
76.2%
74.4%
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Length of burn (minutes)
2 2 4 6 2 4 6 2 4 6
Stac
k te
mpe
ratu
re (F
)
100
150
200
250
300
350
400
450
500
Length of burn (minutes)
2 2 4 6 2 4 6 2 4 6Ef
ficie
ncy
(%)
70
75
80
85
90
Heat Exchanger Efficiency TestingLazy C Farms, 2017
Original Star heat exchanger
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Length of burn (minutes)
2 2 4 6 2 4 6 2 4 6
Stac
k te
mpe
ratu
re (F
)
150
200
250
300
350
400
450
500
Length of burn (minutes)
2 2 4 6 2 4 6 2 4 6
Effic
ienc
y (%
)
70
75
80
85
90
Heat Exchanger Efficiency TestingLazy C Farms, 2017
DeCloet SLR
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Length of burn (minutes)
2 2 4 6 2 4 6 2 4 6
Stac
k te
mpe
ratu
re (F
)
100
150
200
250
300
350
400
450
Length of burn (minutes)
2 2 4 6 2 4 6 2 4 6Ef
ficie
ncy
(%)
70
75
80
85
90
Heat Exchanger Efficiency TestingLazy C Farms, 2017
Tytun
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High Efficiency Condensing Heat Exchanger
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Air Flow Issues• Standard Powell Star CB-9 experiences airflow
issues related to the burner placement
– Heat exchanger is mounted low in relation to the fans
– Offset burner results in uneven heat distribution
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Front Box Pin TemperaturesLazy C Farms, 2017
Original Star barn – front box pin temperatures
Curing Time (hrs)12 24 36 48 60 72 84 96 108 120 132 144 156 168 180 192 204 216
Tem
pert
ure
(F)
70
80
90
100
110
120
130
140
150
160
170
Upper leftUpper rightLower leftLower right
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Front Box Pin TemperaturesLazy C Farms, 2017
DeCloet – front box pin temperatures
Curing Time (hrs)12 24 36 48 60 72 84 96 108 120 132 144 156 168 180 192 204 216
Tem
pert
ure
(F)
70
80
90
100
110
120
130
140
150
160
170
Upper leftUpper rightLower leftLower right
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Front Box Pin TemperaturesLazy C Farms, 2017
Tytun – front box pin temperatures
Curing Time (hrs)
12 24 36 48 60 72 84 96 108 120 132 144 156 168 180 192 204 216
Tem
pert
ure
(F)
70
80
90
100
110
120
130
140
150
160
170
Upper leftUpper rightLower leftLower right
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Curing Efficiency Results
Heat Exchanger Fuel consumption Curing efficiency
(Gal. per cure) (Lbs tobacco per gal.)
Original Star barn 517 a 7.1 b
DeCloet heat exchanger 450 a 7.9 b
Tytun retrofit 346 b 10.1 a
Averaged results of 6 cures
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Summary
• The DeCloet SLR heat exchanger increased curing efficiency by 11% and had a positive impact on air-flow
• The Tytun retrofit with a high efficiency heat exchanger and burner resulted in a 42% increase in curing efficiency
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Cost of Tobacco Curing
• Prices can fluctuate making budgeting difficult
• Bulk LPG and the use of natural gas addresses the cost of curing fuel
• Retrofitting barns with high efficiency heat exchanger addresses reducing fuel consumption
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