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Combustion Air Pre-heater

Combustion Air Pre-heater. Final Design Presentation. Combustion Air Pre-heater. ME 486 4/25/03. ME 486 4/25/03. Photo courtesy of David Pedersen. Purina Boiler Efficiency Team. Members and Roles Ryan Cook Documenter and Secretary Kofi Cobbinah

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Combustion Air Pre-heater

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  1. Combustion Air Pre-heater Final Design Presentation Combustion Air Pre-heater ME 486 4/25/03 ME 486 4/25/03 Photo courtesy of David Pedersen

  2. 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 Carl Vance

  3. 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 Carl Vance

  4. 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. Carl Vance

  5. Our Design Philosophy • Finish Design On Time and Under Budget. • Satisfy the Client’s Requirements. • Design for Safety. • Act with Integrity. Carl Vance

  6. Client’s Requirements Client’s Needs Statement: • Design of a combustion air preheater must be: • Economically Feasible • Minimize Modifications to Existing Systems • Show an improvement in evaporation rate. Carl Vance

  7. 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. Carl Vance

  8. Basic Boiler Operation Source: Reducing Energy Costs, KEH Energy Engineering, 1990. Carl Vance

  9. 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. Carl Vance

  10. Source: Reducing Energy Costs, KEH Energy Engineering, 1990. Carl Vance

  11. Design Options • What are the industry standards? • Which design best meets our client’s requirements. Carl Vance

  12. Source: Canadian Agriculture Library, http://www.agr.gc.ca/cal/calweb_e.html Runaround System Carl Vance

  13. Source: Canadian Agriculture Library, http://www.agr.gc.ca/cal/calweb_e.html Gas - to - Gas Plate Heat Exchanger Carl Vance

  14. Concentric Duct Design Source: Canadian Agriculture Library, http://www.agr.gc.ca/cal/calweb_e.html Ryan Cook

  15. 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. Ryan Cook

  16. Why a Concentric Duct? • Inexpensive • No modifications to current system • Simple Design that Works • Passive System Ryan Cook

  17. 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 Ryan Cook

  18. Preheater Design Basics Ryan Cook

  19. 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 Ryan Cook

  20. 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. Ryan Cook

  21. Temperature Distribution Ryan Cook

  22. Our Design Ryan Cook

  23. Our Design Ryan Cook

  24. 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. Ryan Cook

  25. Mathematical Models • Convection Model • Heat Exchanger Model • Drag Model • Radiation Model • Insulation Model

  26. Known Values for Convection • Volumetric Flow Rate = 2.84 m3/s • Thermal Conductivity = .0263 W/(m*K) • 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

  27. Convection Model

  28. Convection Model

  29. Convection Model Savings

  30. Known Values for Heat Exchanger • Cp,c = 1007 (J/kg*K) • Cp,h = 1030 (J/kg*K) • hi = 17.31 (W/m2*K) • ho= 25.05 (W/m2*K) • Tc,I = 305.4 (K) • Th,I = 509.1 (K) • Mass Flow Rate = 4.52 kg/s

  31. Heat Exchanger Model

  32. Heat Exchanger Model

  33. Heat Exchanger Savings

  34. Known Values for Drag Model • Mass Flow Rate • “a” = O.D. / 2 • “b” = I.D. / 2

  35. Drag Model

  36. Drag Model

  37. Drag Model Costs

  38. Known Values for Radiation • Inner and Outer Diameters • Emissivity of Steel Stack, ε1 = 0.87 • Emissivity of Aluminum Duct, ε2 = 0.15 • Stack Surface Area • Stefan- Boltzmann Constant σ = 5.67E –08 (W/(m2*K4)) • Stack Temperature = 399.7 K • Duct Temperature = 322 K

  39. Radiation Model

  40. Radiation Model Savings

  41. Known Values for Insulation(Modeled as Fiberglass) • R – Values: • Preheated Air = 0.559 (m2*K)/W • Duct = 4.9E –04 (m2*K)/W • Fiberglass Insulation = 16.78 (m2*K)/W (per inch) • Average Temperature Difference

  42. Insulation Model

  43. Insulation Model Costs

  44. 5 Year Savings Summary Kofi Cobbinah

  45. Design Estimate • Total implementation cost: • Materials--- $350 • Labor--- $1650 Total of approximately: $2,000 Source: McGuire Construction Co. Kofi Cobbinah

  46. Energy Savings • The energy added to the system was converted to kBtu’s per hour. • Total kBtu’s per year saved = 553,000 • The evaporation rate will improve 1% for a daily average. Kofi Cobbinah

  47. 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. Kofi Cobbinah

  48. Expenses • Total Expenses: $150.00 • Printing/Binding ---$100.00 • Photocopying --- $50.00 Kofi Cobbinah

  49. Time Log • Average individual Hours: 120.7 • Total Team Hours: 482.8 Kofi Cobbinah

  50. 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. Kofi Cobbinah

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