Combustion Air Pre-heater

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Combustion Air Pre-heater
Combustion Air Pre-heater
Final Design Presentation

• ME 486
• 4/25/03

ME 486 4/25/03
Photo courtesy of David Pedersen
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Purina Boiler Efficiency Team

• Members and Roles
• Ryan Cook
• Documenter and Secretary
• Kofi Cobbinah
• Team Leader and Website Manager

• Carl Vance
• Communicator and Historian
• Matt Bishop
• Financial Officer and Mediator

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Our Client Nestlé Purina

• Client Contact John Cain
• Manager of Engineering at the Flagstaff Plant.
• NAU Graduate in Mechanical Engineering
• Purina as a company
• Flagstaff Plant opened in 1975
• Employs 180 people
• Purina is now a division of Nestlé Foods

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Project Description

• Problem Definition
• Nestlé Purina has requested a design for a
  combustion air pre-heater. The goal of the
  project is to provide savings for the plant by
  reducing energy costs and improving efficiency in
  the steam system.

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Our Design Philosophy

• Finish Design On Time and Under Budget.
• Satisfy the Clients Requirements.
• Design for Safety.
• Act with Integrity.

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Clients Requirements

• Clients Needs Statement
• Design of a combustion air preheater must be
• Economically Feasible
• Minimize Modifications to Existing Systems
• Show an improvement in evaporation rate.

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Purina Steam System

• The boiler produces approximately 500,000 lbm
  of steam per day.
• 40 cooking products.
• 50 drying products.
• 10 miscellaneous areas air and water
  heating systems.
• Steam production is 2/3 of the plant's total
  energy use.

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Basic Boiler Operation
Source Reducing Energy Costs, KEH Energy
Engineering, 1990.
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What is a Combustion Air Preheater

• Device or system that heats the boiler intake air
  before it enters the combustion chamber.
• Uses recaptured waste heat that would normally
  leave the boiler to the atmosphere.

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Source Reducing Energy Costs, KEH Energy
Engineering, 1990.
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Design Options

• What are the industry standards?
• Which design best meets our clients
  requirements.

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Runaround System

• Source Canadian Agriculture Library,
  http//www.agr.gc.ca/cal/calweb_e.html

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Gas - to - Gas Plate Heat Exchanger

• Source Canadian Agriculture Library,
  http//www.agr.gc.ca/cal/calweb_e.html

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Concentric Duct Design
Source Canadian Agriculture Library,
http//www.agr.gc.ca/cal/calweb_e.html
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Design Choice

• Final Design Choice
• Concentric Duct Design
• Air enters into a duct that surrounds the stack.
• The stack transfers heat to the air by convection
  and radiation.
• The air enters into the boiler at a higher
  temperature.

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Why a Concentric Duct?

• Inexpensive
• No modifications to current system
• Simple Design that Works
• Passive System

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Design Benefits

• Concentric Duct Design Will Provide
• Relatively Low Installation Cost
• Low Material Costs
• Low Impact on Existing Systems
• High Payback on Investment
• Low Maintenance Costs

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Preheater Design Basics
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Given Conditions

• Exhaust Stack Surface Temperature
• 399 K 258 degrees Fahrenheit
• Inlet Air Temperature
• 305 K 89 degrees Fahrenheit
• Exhaust Stack Height
• 4.3 meters
• Exhaust Stack Diameter
• 3 feet 0.9144 meters

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Specifications to date

• The exhaust stack height is 4.3 meters, which
  fixes our duct height and will provide the
  surface area for heat transfer.
• Duct diameter will be 1.05 meters to optimize
  forced convection.
• Mass flow rate of air through duct will be 4.52
  kg/s. This gives an air velocity of 13.56 m/s.

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Temperature Distribution
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Our Design
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Our Design
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Installation

• Two half tubes that will be welded together
  around the stack.
• Spacers will be inserted along the bottom to to
  keep the duct steady.
• Will be hung by threaded rod supports from the
  ceiling.

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Mathematical Models

• Convection Model
• Heat Exchanger Model
• Drag Model
• Radiation Model
• Insulation Model

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Known Values for Convection

• Volumetric Flow Rate 2.84 m3/s
• Thermal Conductivity .0263 W/(mK)
• Kinematic Viscosity 1.59E 05 m2/s
• Prandlt Number 0.707
• Ts Ta 100 K
• Stack Surface Area 12.26 m2
• Stack Diameter 0.9144 m

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Convection Model
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Convection Model
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Convection Model Savings
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Known Values for Heat Exchanger

• Cp,c 1007 (J/kgK)
• Cp,h 1030 (J/kgK)
• hi 17.31 (W/m2K)
• ho 25.05 (W/m2K)
• Tc,I 305.4 (K)
• Th,I 509.1 (K)
• Mass Flow Rate 4.52 kg/s

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Heat Exchanger Model
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Heat Exchanger Model
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Heat Exchanger Savings
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Known Values for Drag Model

• Mass Flow Rate
• a O.D. / 2
• b I.D. / 2

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Drag Model
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Drag Model
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Drag Model Costs
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Known Values for Radiation

• Inner and Outer Diameters
• Emissivity of Steel Stack, e1 0.87
• Emissivity of Aluminum Duct, e2 0.15
• Stack Surface Area
• Stefan- Boltzmann Constant
  s 5.67E 08 (W/(m2K4))
• Stack Temperature 399.7 K
• Duct Temperature 322 K

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Radiation Model
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Radiation Model Savings
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Known Values for Insulation(Modeled as
Fiberglass)

• R Values
• Preheated Air 0.559 (m2K)/W
• Duct 4.9E 04 (m2K)/W
• Fiberglass Insulation 16.78 (m2K)/W (per inch)
• Average Temperature Difference

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Insulation Model
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Insulation Model Costs
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5 Year Savings Summary
Force Convection 7980.00
Radiation 540.00
Drag Loss - 270.00
Insulation Loss - 2.00
Total 8250.00
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Design Estimate

• Total implementation cost
• Materials--- 350
• Labor--- 1650
• Total of approximately 2,000
• Source McGuire Construction Co.

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Energy Savings

• The energy added to the system was converted to
  kBtus per hour.
• Total kBtus per year saved 553,000
• The evaporation rate will improve 1 for a daily
  average.

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Financial Savings

• The Financial Savings were based on fuel oil at
  0.46 per gallon and 150 kBtu/gallon.
• This provides a 5 year savings of 8,248.
• Simple payback for the project is 1.3 years.

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Expenses

• Total Expenses 150.00
• Printing/Binding ---100.00
• Photocopying --- 50.00

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Time Log

• Average individual Hours 120.7
• Total Team Hours 482.8

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Our Appreciation Goes To

• Nestle Purina Company at Flagstaff.
• Mr. John Cain Client Contact.
• Dr Peter Vadasz Advisor.
• Dr. David Hartman ME 486 Professor.
• Everyone at our presentation today.

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Project Website

• http//www.cet.nau.edu/Academic/Design/D4P/EGR486/
  ME/02-Projects/Heat/index.htm
• Or go to www.cet.nau.edu and click on Design 4
  Practice and follow links to Senior Project
  Websites and click on our website

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Conclusion

• The team has been able to prove that adequate
  heat transfer is available to pay for the design,
  reduce energy costs, and improve the efficiency
  of the boiler.

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Questions?
Photo courtesy of David Pedersen