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Hood Air Systems & Steam Sizing for Paper Machine Dryer Hoods

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1. The purpose of this project was to look at the problems of hood leakage and hood condensation on a Paper Board Machine in Naheola Alabama. Enclosed you will find a computer analysis (Program called HOOD) of the 4 types of Hoods. Based on the evaporation rate into the hood the program calculates the amount of supply air required (ACFM, SCFM, lbs/hr) and the amount of exhaust air (ACFM, SCFM, lbs/hr) and determines the motor BHP to move the air. If the engineer inputs the energy cost factors for steam (to heat the supply air) and electricity (for fans), the program will calculate the annual cost for electricity and steam.
a. TAPPI- Open Hood Design
b. TAPPI - Partially Enclosed Hood Design
c. TAPPI - Closed Hood Design
d. TAPPI – High Humidity Closed Hood Design

Water Vapor Escaping from Main Hood

Main Hood Drippage Onto Operating Floor

#3 Board Machine Production Info (PDF)

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Example #1 - Sizing Paper Machine Cylinder Dryer Hoods Program Input Data

1. Paper Machine Production Data: 40,743 lbs bone dry/hour
2. Evaporation into The Hood: 57,718 lbs water/hour
3. Electricity Price: $0.0388/kwh
4. Mill Steam Price: $3.00/million Btu
5. Make-up Air Ambient Temperature: 85 F
6. Supply Fan Discharge Air Temperature Into The Hood: 180 F
7. Pocket Humidity Ratio: 0.20 lbs w.v./lb dry air
8. Steam Pressure For Heating The Supply Air: 50.00 Psig
9. Steam Temperature For Heating The Supply Air: Saturated Steam
10. Mill Steam Cost: $3.00/million Btu
11. Barometric Pressure: Sea Level
12. Intake Duct Pressure: 0.00 inches w.c.
13. Exhaust Fan Differential Static Pressure: 1.75 inches w.c.
14. Exhaust Air Dry Bulb Temperature: 130 F
15. Exhaust Fan Static Efficiency: 60 %
16. Exhaust Fan Motor Efficiency: 92 %
17. Exhaust Fan Motor Drive Efficiency: 95 %
18. Operating Hours Per year: 8400 hours/year
19. Supply Fan Differential Static Pressure: 15.00 inches w.c.
20. Supply Fan Static Efficiency: 60 %
21. Supply Fan Motor Efficiency: 92 %
22. Supply Fan Drive Efficiency: 95 %

Hood Air Systems Summary - Open Hood (PDF)
Hood Air Systems Summary - Partial Enclosed Hood (PDF)
Hood Air Systems Summary - Closed Hood (PDF)
Hood Air Systems Summary - High Humidity Closed Hood (PDF)

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