“We Bring

Engineering

to Life”

Biological and Agricultural Engineering

Reducing Curing Costs and

Alternative Fuel Sources for

U.S. Flue-Cured Tobacco

Production

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Flue-Cured Energy Sustainability • Modern U.S. agriculture is heavily dependent on nonrenewable energy

sources

• Curing energy is still a substantial production input

• Significant increase in the cost of petroleum fuels in recent years and

continued uncertainty of future prices

• More growers continue to make energy efficiency improvements to

existing infrastructure and replacing older barns

• Any significant increase in U.S. production will require new curing

barns – 5 manufacturers made barns for 2013 season

• Energy efficiency improvements and energy conservation is the

quickest and cheapest new energy source

• Research continues to explore energy efficiency improvements and

renewable energy technologies that are economically feasible

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Efficient Grower Average Energy Use per Cure (10-box barn, 10 hp (7.5 kW) fan motor)

(Assumptions: $1.10/gal LP, $0.10/kWh, 3500 lb per cure season average)

Fuel

(gal)

Fuel Cost

($/barn)

Electricity

(kWh)

Electrical Cost

($/barn)

Total

$/Cure $/lb ($/kg)

300 (1,140 L) $330 1,500 $150 $480 0.14 (0.31)

• Curing energy efficiency is affected by many variables

− barn and heating system efficiency

− green leaf loading rate

− curing management

− weather

− quality of the green tobacco

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LP Gas and Natural Gas Price History

Source: U.S. Energy Information Administration (LP Gas – Wholesale/Resale; N.G. – Commercial)

*>80% of NC Producers use LP gas

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Source: U.S. Energy Information Administration (LP Gas – Wholesale/Resale; N.G. – Commercial)

LP and Natural Gas Present and Future Cost Comparison

Currently, NG provides a 30% cost savings

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Automatic Ventilation Control – Improving

Management and Energy Efficiency

Many automatic systems now

measure relative humidity directly,

but display dry-bulb and wet-bulb

temperature.

10-15% Fuel Savings

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Real-time Continuous Monitoring of the Curing

Environment

• Significant time management tool for growers

• Web-based monitoring system

• Audible alarm conditions to help minimize leaf damage during

equipment failures or power loss

• Capacity to store curing data (temperature, humidity, burner on

time) the entire season to assist with maximizing cured leaf quality

and other diagnostics

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2012 NC County Agent Survey Data (50% of total acreage reported) 20

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Fuel Cost ($/unit)

0.80 1.00 1.20 1.40 1.60 1.80 2.00

lb/gal $ / lb Cured

7 0.114 0.143 0.171 0.200 0.229 0.257 0.286

8 0.100 0.125 0.150 0.175 0.200 0.225 0.250

9 0.089 0.111 0.133 0.156 0.178 0.200 0.222

10 0.080 0.100 0.120 0.140 0.160 0.180 0.200

11 0.073 0.091 0.109 0.127 0.145 0.164 0.182

12 0.067 0.083 0.100 0.117 0.133 0.150 0.167

13 0.062 0.077 0.092 0.108 0.123 0.138 0.154

System Energy Efficiency and Estimated

Cost per Pound Cured Leaf (fuel only)

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On-Farm Energy Evaluation of New Curing Barns

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Energy Content and Cost Comparison of Fuels

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Hurst Boiler Biomass Fired Hot Water Heating System – 2012 20

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Woodchip Biomass System

and Automated Controls

Water to Air Heat

Exchanger mounted

in Return Air Plenum

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Hurst System Specifications

• System rated @ 3.4 MMBTU/hr (996 kW)

• Heat on demand modulating system

• PLC touch screen controller with real-time performance information

• 1000 gallon water storage

• Emission controls

• Manual ash removal

• Burns a wide variety of wood waste (fine saw dust to 2” chips)

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System Performance – 2012 Season • 300,000 to 350,000 BTU/hr (88 to 103 kW) @ 70 gpm

• 195 to 200oF (91 to 93oC) water temperature at the barn

• No change in cure duration

• 17 barns and 131 cures

• 250 tons @ $30/ton

• Primary fuel source chipped pallets (< 10% m.c.)

• 1.2 lb wood chips per lb cured leaf

• Fuel cost $55 to $65 per cure or 1.5 – 2.5¢ per lb cured (3.3 – 5.5¢/kg)

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Greenhouse Heating Applications w/Biomass Unit

Curing Barns and Greenhouse

Applications

Result in Extending System

Operation from July - March

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Max Ox Smaller Capacity Biomass Heating System –

10 Barns and 200’ Greenhouse Application (900,000 Btu/hr (264 kW))

2013

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Automated Biomass Fired System • Advantages

– Reduced fuel cost (70 to 90%)

– Abundant renewable fuel

– High combustion and thermal efficiency

– Automated system (combustion controls, emissions, ash removal)

– TSNA NOx mechanism eliminated

• Disadvantages

– High initial investment

– More equipment maintenance

– Increased management

– Limited local service technicians

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Additional Technologies Evaluated to Improve

Barn Energy Efficiency

• Thermal and electrical energy load vary with time during curing

• Variable rate technologies can potentially improve load matching and

therefore decrease total energy usage

• Variable Frequency Drive (VFD) or Adjustable Speed Drive

technology utilized to change the speed of an electric motor

– Strategically reduce the fan electric motor speed and decrease electrical

energy usage

• Variable firing rate burner or modulating burner utilized to decrease

fuel consumption and heat exchanger thermal cycling

– Burner heat output adjusted automatically based on thermal load

– Reduction in thermal cycling to extend the heat exchanger longevity and

minimize TSNAs in the cured leaf

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VFD unit and Controller

Utilized to Automate the

Change in Fan Speed

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VFD Application Summary • Limited, if any, decrease in cured leaf quality observed

• Limited increase in curing time associated with fan speed reduction

• Typical seasonal electrical energy savings range 20% to 25% (300 to

400 kWh)

• Cost savings will depend on the electrical rate ($/kWh) and motor size

• At 25% energy savings simple payback is 4 to 5 years (10 hp)

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Modulating Burner Technology Summary

• Marginal fuel savings obtained at two locations

• Application may not be possible with all heat exchanger designs

• Some heat exchangers will not operate very efficiently at low firing rates

• Approximately a 35% reduction in the number of burner cycles compared

to a conventional burner

2013

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Questions??

2013

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