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“How To Get The Most Out of Your Oven” Energy Consumption and Air Flow Focus

“How To Get The Most Out of Your Oven” Energy Consumption and Air Flow Focus. Larry Scher Mondelēz International North America Snacks Regional Manager of Project Engineering, Process & Ovens B&CMA Technical Conference May 2016. Agenda. Introduction Oven Energy Consumption Overview

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“How To Get The Most Out of Your Oven” Energy Consumption and Air Flow Focus

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  1. “How To Get The Most Out of Your Oven”Energy Consumption and Air Flow Focus Larry Scher Mondelēz International North America Snacks Regional Manager of Project Engineering, Process & Ovens B&CMA Technical ConferenceMay 2016

  2. Agenda • Introduction • Oven Energy Consumption Overview • Oven Air Flow Overview • Q & A

  3. Biscuit Baking Oven Thermal Efficiency • Definition: {Product Related Heat, Sensible (+) Latent}/{Total Heat Input} X 100 • Typical Ranking of Thermal Efficiency for Different Oven Types: • Convection Impingement > Convection Recirculating >Ribbon Burner Oven > Cyclotherm Oven • Thermal Efficiency Dependent on: • Heat Transfer Means (Convection vs. Radiant); • Oven Exhausting Set-up (Extent of Over-Exhausting); • Oven Band System Design (Band Run-Out, Return Band Chamber Design); • External Oven Design & Condition (Surface Heat Losses)

  4. Typical Steps to Conduct an Oven Mass & Energy Balance • Use Standard Oven Energy Balance Model: • Total Oven Energy Input = Heat to product, sensible (+) Heat to Product, latent (+) Heat to Exhaust (+) Band Loss Heat (+) Surface Loss Heat • Collect oven design/process information/product related information in order to compute all terms of the oven energy balance model: • Typical oven design information: oven surface areas for surface losses calculation; band physical dimensions, type, density • Typical process information: exhausting rates, temperatures; band temperatures in/out of bake chamber; oven external skin temperatures; band speed/time bake • Typical product related information: dough throughput, dry biscuit throughput, product moisture evaporation rate; dough, biscuit product temperatures

  5. Typical oven mass balance for a Biscuit Baking Oven Evaporated moisturefrom dough/biscuits Exhaust Gases Evaporated moisturefrom dough/biscuits Dough In Baked BiscuitsOut Oven Oven Burnercombustionproducts(Direct Ovens only) In-leakage& excess air • Uses: • Calculate evaporated moisture rate for energy balance use • Calculate ideal oven exhausting rate & % excess air of actual exhausting • Calculate oven exhaust absolute humidity • Useful for oven heat & mass transfer / drying analysis

  6. Typical oven energy balance for a Biscuit Baking Oven Exhaust heat • Product Related Heat: • Sensible • Latent • Energy Input: • Gas Related • Electricity Related Oven Oven Band heat • Oven Skin/Surface heat • Convection • Radiation • Uses: • Determine oven energy input requirements • Quantify oven energy utilization by category • Compute analysis of opportunities for oven optimization/energy consumption reduction/oven thermal eficiency • Support analysis of opportunities for oven optimization/energy consumption reduction

  7. Typical oven energy balance breakdown for different biscuit types for DGF Ribbon Burner Oven

  8. Opportunities for Oven Energy Consumption Reduction • Exhausting rate optimization to an ideal excess air level • Exhaust heat recovery: e.g., pre-heat make-up air and/or combustion air • Band System Optimization/Alternatives: • Minimize band run-out lengths by design, as feasible • Cover, insulate the oven band run-outs, when feasible • Employ a covered return chamber, insulated preferred, when possible • Consider alternative, lighter weight bands, as feasible • Eliminate obvious external oven surface heat losses: • Ensure proper insulation coverage/good condition • Minimize oven bake chamber openings • Insulate well doors & idler roller bearing blocks to minimize heat loss • Tune/ensure properly operating burners

  9. Overview of Air Flow in a Biscuit Baking Oven • Types of Air Flow in a biscuit oven bake chamber: • Air Flow promoted by the oven return air or exhausting • Recirculating air flow (for certain oven types only such as Forced Convection) with varying air flow pattern relative to the band/product • Typical Air Flow Patterns relative to the band/product include: • Impingement Air Flow • “Sweeping”, parallel air flow • Indirect radiant heating of oven surfaces: air flow typically circulates within duct work or plenums heating inner surfaces of the bake chamber • Natural Convection Air flows promoted by differences in bake chamber temperatures, air densities • Air flow promoted by the moving oven band, higher as time bake decreases/band speed increases

  10. Overview of Air Flow in a Biscuit Baking Oven • Air Flow Design dictates the range of biscuit baking rates of oven: • Impingement Air Flow Forced Convection Oven: • High maximum air velocities enable high biscuit baking rates when desired • Use of higher air velocities help enable lower baking temperatures • Most suitable for shorter time bake cracker baking • “Sweeping”, parallel air flow forced convection oven: • Typically lower to moderate air velocities with lower to moderate biscuit baking rates • Normally most suitable for cookies & cakes baking • Indirect radiant heating of bake chamber inner surfaces: • Often included as an operating feature of the Forced Convection oven • Favors reduced heat transfer/biscuit baking rates • Most suitable for baking cookies & cakes in a Forced Convection oven • DGF ribbon burner ovens most often do not have a recirculating air flow pattern: • Bake chamber air flow generated by exhausting, band travel, in-leakage air, air flow inter-change between adjacent zones, & heated walls • Requires high operating temperatures with major use of radiant heating

  11. Air flow in a DGF Ribbon Burner Oven Bake Chamber Cross-Section: Exhaust gases Top Burner Product EvaporatedMoisture Vapor Fuel Gas Band Bottom Burner In-Leakage Air Combustion Airto Burners • DGF bake chamber air flow magnitude is typically lower than 500 feet/minute.Air flow is relatively low in magnitude but complex air flow is promoted by: • Exhausting pattern/rates • Band travel/magnitude • Air inleakage at mouths & between individual zones • Heated surfaces contact with air/gases (natural convection) • Strive for uniform air flow in bake chamber by: • Tracking/Centering band in bake chamber • Ensuring burners are properly centered in bake chamber and are level • Centered/distributed exhaust gases extraction positioning • Properly sized exhaust flows • Non-uniform air flow in bake chamber promotes: • Baking rate differences Typical air flow pattern in bake chamber

  12. Air flow in a direct heated forced convectionAir Impingement Biscuit Baking Oven Fresh make-up air Exhaustgases Bake Chamber Cross-Section: • Comb air B • Fuel gas Top Air Plenum with Nozzles • Recirculating air Band • Product evaporatedmoisture vapor In-leakage air Bottom Air Plenum with Nozzles • Typical air velocity range is 300 to 3000+ linear feet per minute • Maximize air velocities when possible enabling lower oven temperatures • Biscuit baking rate is function of air velocity & temperature (i.e., heat flux): • Control top vs bottom air velocity to control top vs. bottom baking • Uniform air velocities per zone is critical to attain uniform biscuit baking • Versatile biscuit baking by properly setting air velocity magnitudes per zone top/bottom • Cracker baking: Higher air velocities • Cookie baking: Lower air velocities

  13. Opportunities for Oven Air Flow Related Improvements for a Biscuit Baking Oven • High Air Flow uniformity with zone/oven length and oven side to side is ESSENTIAL for uniform biscuit baking • Employ oven data logging tools & oven instrumentation to monitor & help ensure air flow uniformity per oven zone • Oven convective and radiant heat flux profiling • Air velocity profiling when available • Permanent measurement of pressurized plenums pressures to help monitor air velocity • Periodic hand held measurements of nozzle, bake chamber air velocity using tools such as hot wire & vane anemometers and pitot tubes • Essential to have capability to increase convection air velocity w/o constraints on recirculating air blower & air heating burner • Challenging to measure bake chamber air velocity for lower air velocity bake chambers such as a DGF ribbon burner oven: • Permanent instrumentation, hand held tools, & data logging tools

  14. Wrap-up/Summary “How To Get The Most Out of Your Oven” Energy Consumption and Air Flow Focus • Performing an oven mass & energy balance computation is essential for process analysis of the biscuit baking operation & pursuit of optimization & energy savings opportunities • Knowledge & mastery of the air flow of a biscuit baking operation is essential for optimization

  15. Thank You!

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