Photo courtesy of David Pedersen

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 4/25/03 Carl Vance 2

4/25/03 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 3

4/25/03 Project Description Problem Definition  Nestl é 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 4

4/25/03 Our Design Philosophy Finish Design On Time and Under Budget.

Satisfy the Client’s Requirements.

Design for Safety.

Act with Integrity.

Carl Vance 5

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.

4/25/03 Carl Vance 6

4/25/03 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 7

Basic Boiler Operation Source:

Reducing Energy Costs

, KEH Energy Engineering, 1990.

4/25/03 Carl Vance 8

4/25/03 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 9

Source:

Reducing Energy Costs

, KEH Energy Engineering, 1990.

4/25/03 Carl Vance 10

4/25/03 Design Options What are the industry standards?

Which design best meets our client’s requirements.

Carl Vance 11

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

4/25/03 Carl Vance 12

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

4/25/03 Carl Vance 13

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

4/25/03 Ryan Cook 14

4/25/03 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 15

Why a Concentric Duct?

Inexpensive No modifications to current system Simple Design that Works Passive System 4/25/03 Ryan Cook 16

4/25/03 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 17

Preheater Design Basics 4/25/03 Ryan Cook 18

4/25/03 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 19

4/25/03 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 20

Temperature Distribution 4/25/03 Ryan Cook 21

Our Design 4/25/03 Ryan Cook 22

Our Design 4/25/03 Ryan Cook 23

4/25/03 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 24

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 = 0.707

T s – T a = 100 K Stack Surface Area = 12.26 m 2 Stack Diameter = 0.9144 m

Convection Model variable

O.D. (D 2 ) I.D. (D 1 ) hydraulic diameter X section area (m^2) airspeed (m/s) Re

1 0.9144

0.086

0.13

22.04

59300 1.05

1.1

1.15

1.2

0.136

0.186

0.236

0.286

0.21

0.29

0.38

0.47

13.56

9.66

7.43

5.98

57800 56400 55000 53700

Convection Model

Pr Nu h (W/(m^2 K)) Ts - Ta (K) q" stack S.A (m^2) Energy transfer (W)

0.707 131.8

40.49

100 4050 12.26

49700 129.1

126.6

124.1

121.8

25.04

17.94

13.85

11.22

2500 1790 1390 1120 30700 21900 17000 13700

Convection Model Savings

Estimate Btu/h Yearly Btu Savings Gallons per year saved Yearly monetary savings 5- year savings

169600 1.038E+09 6920 $3,180 $15,900 104800 74700 58000 46700 6.410E+08 4.570E+08 3.550E+08 2.860E+08 4270 3050 2370 1910 $1,960 $1,400 $1,090 $880 $9,800 $7,000 $5,450 $4,400

Known Values for Heat Exchanger Cp,c = 1007 (J/kg*K) Cp,h = 1030 (J/kg*K) h i

h o

= 17.31 (W/m 2 *K)

= 25.05 (W/m 2 *K)

T c,I T h,I = 305.4 (K) = 509.1 (K) Mass Flow Rate = 4.52 kg/s

variable T h,o (K)

503.72

503.73

503.74

503.75

503.76

503.77

503.78

Heat Exchanger Model

T h,I (K)

509.10

m dot h (kg/s) m dot c (kg/s) q (Watts)

4.52

4.52

25050 25000 24950 24910 24860 24810 24770

Heat Exchanger Model

result check T c,I (K) T c,o (K) Delta T lm (K) U (W/m^2*K) Area (heat transfer)

305.40 310.90

198.26

10.24

12.34

310.89

310.88

310.87

198.27

198.28

198.29

12.32

12.29

12.27

310.86

310.85

310.84

198.30

198.31

198.32

12.25

12.22

12.20

Heat Exchanger Savings

Btu/h Yearly Btu Savings Gallons per year saved Yearly monetary savings 5- year savings

85500 85300 85100 85000 84800 84700 84500 5.23E+08 5.22E+08 5.21E+08 5.20E+08 5.19E+08 5.18E+08 5.17E+08 3490 3480 3470 3470 3460 3450 3450 $1,610 $1,600 $1,600 $1,600 $1,590 $1,590 $1,590 $8,050 $8,000 $8,000 $8,000 $7,950 $7,950 $7,950

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

Drag Model

a (O.D./2) b (I.D./2)

0.5

0.4572

0.525

0.55

0.575

0.6

0.4572

0.4572

0.4572

0.4572



f

1.500 1.619E-03

duct friction head loss h f

2.000

1.500 1.660E-03 1.499 1.701E-03 1.499 1.744E-03 1.498 1.786E-03 0.490

0.186

0.089

0.049

Drag Model

Sum of K values minor losses h m

0.25

6.191

0.3

0.31

0.35

0.37

2.812

1.475

0.984

0.675

Drag Model Costs

specific energy loss (J/kg) power loss (W) kWh per year cost per year 5 year cost

80.3

363 2220 $133.2

$666 32.4

16.3

10.5

7.1

146 74 47 32 890 450 290 200 $53.4

$27.0

$17.4

$12.0

$267 $135 $87 $60

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 = 399.7 K Duct Temperature = 322 K

Radiation Model variable

O.D.

1 1.05

1.1

1.15

I.D.

ε 1 ε 2 σ (W/(m2*K

0.9144 0.87 0.15 5.67E-08

4 )) stack surface area (m^2)

12.26

T 1

399.7

T 2

322

Radiation Model Savings

q (W) Btu/h Yearly Btu Savings Gallons per year saved Yearly monetary savings 5- year savings

1620 5530 1690 5770 1750 5970 1820 6210 3.38E+07 3.53E+07 3.65E+07 3.80E+07 225 235 243 253 $104 $108 $112 $116 $520 $540 $560 $580

   Known Values for Insulation (Modeled as Fiberglass) R – Values: Preheated Air = 0.559 (m 2* K)/W Duct = 4.9E –04 (m 2* K)/W Fiberglass Insulation = 16.78 (m 2* K)/W (per inch) Average Temperature Difference

Insulation Model

insulation thickness (inches) 0

6 1 2 4

R value preheated air duct insulation

0.559

0.00041

0.00

0.559

0.559

0.559

0.559

0.00041

9.27

0.00041 18.53

0.00041 37.06

0.00041 55.59

Insulation Model Costs

insulation thickness (inches) q (watts) Btu/h yearly cost 5 year cost 0

1

5.36

0.31

18.30

1.04

$0.34

$0.02

$1.72

$0.10

6 2 4

0.16

0.08

0.05

0.54

0.27

0.18

$0.01

$0.01

$0.00

$0.05

$0.03

$0.02

5 Year Savings Summary 4/25/03 Force Convection Radiation Drag Loss Insulation Loss

Total

Kofi Cobbinah $7980.00

$540.00

- $270.00

- $2.00

$8250.00

44

Design Estimate Total implementation cost:  Materials--- $350  Labor--- $1650 4/25/03 Total of approximately: $2,000 Source: McGuire Construction Co.

Kofi Cobbinah 45

4/25/03 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 46

4/25/03 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 47

4/25/03 Expenses Total Expenses: $150.00

 Printing/Binding ---$100.00

 Photocopying --- $50.00

Kofi Cobbinah 48

4/25/03 Time Log Average individual Hours: 120.7

Total Team Hours: 482.8

Kofi Cobbinah 49

4/25/03 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 50

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 4/25/03 Kofi Cobbinah 51

4/25/03 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.

Kofi Cobbinah 52

Photo courtesy of David Pedersen Questions?