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

24/25/03Carl Vance Purina Boiler Efficiency Team Members and Roles Members and Roles Ryan Cook Ryan Cook Documenter and Secretary Kofi Cobbinah Team Leader and Website Manager Carl Vance Communicator and Historian Matt Bishop Financial Officer and Mediator

34/25/03Carl Vance 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

44/25/03Carl Vance 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. 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.

54/25/03Carl Vance Our Design Philosophy Finish Design On Time and Under Budget. Satisfy the Client’s Requirements. Design for Safety. Act with Integrity.

64/25/03Carl Vance Client’s Requirements Client’s Needs Statement: Design of a combustion air preheater must be: Economically Feasible Economically Feasible Minimize Modifications to Existing Systems Minimize Modifications to Existing Systems Show an improvement in evaporation rate. Show an improvement in evaporation rate.

74/25/03Carl Vance 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.

84/25/03Carl Vance Basic Boiler Operation Source: Reducing Energy Costs, KEH Energy Engineering, 1990.

94/25/03Carl Vance 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.

104/25/03Carl Vance Source: Reducing Energy Costs, KEH Energy Engineering, 1990.

114/25/03Carl Vance Design Options What are the industry standards? Which design best meets our client’s requirements.

124/25/03Carl Vance Runaround System Source: Canadian Agriculture Library,

134/25/03Carl Vance Gas - to - Gas Plate Heat Exchanger Source: Canadian Agriculture Library,

144/25/03Ryan Cook Concentric Duct Design Source: Canadian Agriculture Library,

154/25/03Ryan Cook Design Choice Final Design Choice: Concentric Duct Design 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.

164/25/03Ryan Cook Why a Concentric Duct? Inexpensive No modifications to current system Simple Design that Works Passive System

174/25/03Ryan Cook Design Benefits Concentric Duct Design Will Provide: Relatively Low Installation Cost Relatively Low Installation Cost Low Material Costs Low Material Costs Low Impact on Existing Systems Low Impact on Existing Systems High Payback on Investment High Payback on Investment Low Maintenance Costs Low Maintenance Costs

184/25/03Ryan Cook Preheater Design Basics

194/25/03Ryan Cook Given Conditions Exhaust Stack Surface Temperature 399 K = 258 degrees Fahrenheit 399 K = 258 degrees Fahrenheit Inlet Air Temperature 305 K = 89 degrees Fahrenheit 305 K = 89 degrees Fahrenheit Exhaust Stack Height 4.3 meters 4.3 meters Exhaust Stack Diameter 3 feet = meters 3 feet = meters

204/25/03Ryan Cook 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 m/s.

214/25/03Ryan Cook Temperature Distribution

224/25/03Ryan Cook Our Design

234/25/03Ryan Cook Our Design

244/25/03Ryan Cook 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.

Mathematical Models Convection Model Heat Exchanger Model Drag Model Radiation Model Insulation Model

Known Values for Convection Volumetric Flow Rate = 2.84 m 3 /s Thermal Conductivity =.0263 W/(m*K) Kinematic Viscosity = 1.59E –05 m 2 /s Prandlt Number = T s – T a = 100 K Stack Surface Area = m 2 Stack Diameter = m

Convection Model

Convection Model Savings

Known Values for Heat Exchanger Cp,c = 1007 (J/kg*K) Cp,h = 1030 (J/kg*K) h i = (W/m 2 *K) h o = (W/m 2 *K) T c,I = (K) T h,I = (K) Mass Flow Rate = 4.52 kg/s

Heat Exchanger Model

Heat Exchanger Savings

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

Drag Model

Drag Model Costs

Known Values for Radiation Inner and Outer Diameters Emissivity of Steel Stack, ε 1 = 0.87 Emissivity of Aluminum Duct, ε 2 = 0.15 Stack Surface Area Stefan- Boltzmann Constant σ = 5.67E – 08 (W/(m2*K 4 )) Stack Temperature = K Duct Temperature = 322 K

Radiation Model

Radiation Model Savings

Known Values for Insulation (Modeled as Fiberglass) R – Values:  Preheated Air = (m 2* K)/W  Duct = 4.9E –04 (m 2* K)/W  Fiberglass Insulation = (m 2* K)/W (per inch) Average Temperature Difference

Insulation Model

Insulation Model Costs

444/25/03Kofi Cobbinah 5 Year Savings Summary Force Convection $ Radiation$ Drag Loss - $ Insulation Loss - $2.00 Total$

454/25/03Kofi Cobbinah Design Estimate Total implementation cost: Materials--- $350 Materials--- $350 Labor--- $1650 Labor--- $1650 Total of approximately: $2,000 Source: McGuire Construction Co.

464/25/03Kofi Cobbinah Energy Savings The energy added to the system was converted to kBtu’s per hour. 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.

474/25/03Kofi Cobbinah 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.

484/25/03Kofi Cobbinah Expenses Total Expenses: $ Printing/Binding ---$ Printing/Binding ---$ Photocopying --- $50.00 Photocopying --- $50.00

494/25/03Kofi Cobbinah Time Log Average individual Hours: Total Team Hours: 482.8

504/25/03Kofi Cobbinah 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.

514/25/03Kofi Cobbinah Project Website D4P/EGR486/ME/02- Projects/Heat/index.htm D4P/EGR486/ME/02- Projects/Heat/index.htm Or go to and click on “Design 4 Practice” and follow links to “Senior Project Websites” and click on our website

524/25/03Kofi Cobbinah 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.

Questions? Photo courtesy of David Pedersen