Last Week: Heat Exchangers Refrigeration This Week: More on Refrigeration Combustion

1. Last Week: Heat Exchangers Refrigeration This Week: More on Refrigeration Combustion Pasteurization Process Control Materials

2. Refrigeration Qout Condenser Compressor Win Evaporator Qin

3. Refrigeration Qout Hop Storage Cooler Cond Air Conditioning Lagering Cellar Cooler Comp Win Yeast Tanks Flash Tank Fermenting Room Pasteurizer Beer Chiller Green Beer Chiller Fermenting Vessels Wort Cooler Secondary Refrigerant Storage Tank Evaporator

4. Primary Refrigerants • Ammonia, R-12, R-134a • Saturation temp < Desired application temp • 2 to 8C Maturation tanks • 0 to 1C Beer Chillers • -15 to -20C CO2 liquefaction • Typically confined to small region of brewery • Secondary Refrigerants • Water with alcohol or salt solutions • Methanol/glycol, potassium carbonate, NaCl • Lower freezing temperature of water • Non-toxic (heat exchange with product) • Pumped long distances across brewery

5. Example • A maturation tank is maintained at 6C using a secondary refrigerant (glycol/water solution). The cylindrical tank has a diameter of 3 m and a length of 6 m. The air temperature in the room is 18C and the overall heat transfer coefficient between the maturation tank and surroundings is 12 W/m2K. Determine the rate of heat gain to the maturation tank. • The glycol water solution is supplied from a storage tank at -5C, it exits the maturation tank at 2C and its specific heat is 3.5 kJ/kg.K. Determine the mass flow rate of secondary refrigerant required.

6. Wort Boiling • Importance • Flavor development • Trub formation • Wort stabilization • Wort concentration • Time and temperature – color, flavor, sterilization, etc. • Turbulence – trub formation and volatile removal • Rolling boil required. Interface Evaporation (forced convection) <2C Film Boiling >25C Heat transfer coef. Bubbles (nucleate boiling) 2C < T < 25C Temperature above boiling (C)

7. Wort Boiling In wort boiling it is important to maintain a temperature difference below the critical difference between the wort and heating element surface (25C) If the wort is boiling at 105C, calculate the maximum operational steam pressure you would recommend for an indirect steam heated wort boiler. The wall of the steam heating element is 1.0 mm thick and has a thermal conductivity of 15 W/m.K. The condensing steam’s heat transfer coefficient is 12,000 W/m2.K and the maximum heat flux is 160,000 W/m2.

8. Combustion Fuel + Oxidizer  Heat + Products Oxidizer: Air (79% N2, 21% O2 by Volume) Fuels: Typically hydrocarbons Methane CH4 Ethane C2H6 Gases Propane C3H8 Natural Gas = 95% CH4 Butane C4H10 C6 – C18 Liquids Gasoline (Average C8) Fuel Oil No. 1 (Kerosene) Fuel Oil No. 2 (Diesel) Fuel Oil No. 3-6 (Heating Oils)

9. Combustion To Balance Stoichiometric Combustion Reaction: 1. Balance Carbon (CO2 in products) 2. Balance Hydrogen (H2O in products) 3. Balance Oxygen (O2 in reactants) 4. Balance Nitrogen (N2 in products) Example: (a) Determine the theoretical quantity of air required for combustion of natural gas. Give results in kg of air per kg of natural gas. Assume that natural gas is 100% CH4. (b) Determine the mass of CO2 emitted per kg of natural gas burned.

10. Combustion Actual combustion process  Excess air Complete combustion (reduce CO, UHC) Reduce flame temperature (reduce NOx) Example: Determine the composition of CH4 combustion products with 25% excess air.

11. Combustion Flue gas analysis – Work backwards to find % excess air. Example: Determine the excess air used for CH4 combustion when the O2 concentration in the products is 5.5% volume. (Note, for ideal gas mixtures, volume fraction = mole fraction). Calorific Value of Fuels (= Heating Value) Solids, Liquid: MJ/kg Gases: MJ/m3 (at STP) or “Therms” LHV = H2O vapor in products, HHV = liquid

12. Sterile Filtration • Alternative to pasteurization for microbiological stabilization • Avoid heat treatment, flavor deterioration • Occurs before packaging (could be contaminated after filtration, before package) • Process Requirements • Feedstock microbiological and non-mb loads (concentration and particle size) • Filtrate concentration, product spoilage concentration allowed • Product viscosity, density, flow characteristics

13. Microbiological Load Reduction – LRV • Sterile Filters = 99.9999999999% LRV • Filtration Mechanisms • Direct Interception – Pore smaller than particle • Charge Effects – Particles (-), so filter (+) • Inertial Impactation – Particles want straight path, fluid curves (different densities required) • Diffusional Impactation – Random motion (gas)

14. Key Features Effecting Filter Performance • Pore geometry • Membrane thickness • Surface Charge • Removal Ratings • Nominal – “An arbitrary micron value assigned by the filter manufacturer, based upon removal of some percentage of a given size or larger.” • Absolute – “The diameter of the largest hard spherical particle that will pass through the filter under a specified test condition.”

15. Factors effecting • flow rate and life: • Pressure Drop • Surface Area • P increases as dirt • blocks pores • Increased surface • area has great • increase on dirt • capacity

16. Surface area • can be increased • with pleats • Filter sizes: • Pre-filter: 1.5 m • Sterile: 0.45 m • Cleaning • Backwash (high V) • Hot Liquor • Sodium Hydroxide • Steam Sanitized • (120C, 20 min)

17. Pasteurization • Inactivate all microorganisms • Inactivate undesired enzymes (chem. changes) • Five Key Factors for Effective Pasteurization • Temperature • Time • Types of microorganisms present • Concentration of microorganisms present • Chemical composition of the product • Pasteurization Level • Decimal reduction time, D – Time required to inactivate 90% of microorganisms present • Temperature dependence value, Z – Increase in temp. require to increase D value by 90%

18. Pasteurization Units • Measure of effect of heat and time on microorganisms • 1.0 PU corresponds to 1 minute at 60C • PU = t * 1.393(T-60C) (t in minutes) • Rules of Thumb • Increase T by 2C, double PU’s for same time • Increase T by 10C, PU’s increase 10x • 20 PU’s indicates that 1 in 10 Billion microorganisms survive • Effect of PU’s on specific microorganisms needed

19. Pasteurization • Microorganisms growing in beer • Wild yeast strains • Lactic acid bacteria • No – Homogeneous population of microbes • N – Remaining number of microbes • t – time in minutes • D – Decimal reduction time at temperature T

20. Pasteurization Typically choose D value of most resistant organism 1.0 P.U. = “one minute of heating at 60C” An average Z value of 6.94C is used

21. Pasteurization For the data given below, calculate the total number of pasteurization units (PU). Assume a Z value of 6.94C. What type of pasteurizer is this?

22. Flash Pasteurization Minimum Safe Pasteurization Over Pasteurization 5.6 min Time (min) 0.1 1 10 100 Under Pasteurization 50 60 70 Temperature (C)

23. Flash Pasteurization Beer in = 0C Pasteurizer 60-70C 30 sec - 2 min 90-96% regeneration

24. Flash Pasteurization Pressure in Pasteurizer CO2 equilibrium pressure Pressure (Bar) Temperature (C) Temperature in Pasteurizer Time (sec)

25. Flash Pasteurization Typical Conditions: Beer inlet: 3C Outlet from regenerative heating: 66C Holding tube: 70C Outlet from regenerative cooling: 8C Outlet from cooling section: 3C Holding Time: 30 sec Advantages Little space required Relatively inexpensive equipment and operation Short time at “intermediate” temperatures where chemical changes occur without pasteurization

26. Plate/Flash Pasteurization • Typical plates: Stainless steel, 0.6 mm thickness • Can withstand 20 bar pressure

27. Plate Pasteurizer Design • 95% Heat Recovery in regenerator • Product enters Pasteurizer at  4C • Holding temperature  72C • Holding time  25 seconds • Hot water typically used for heating, 2C warmer than holding temperature • Level of Regeneration

28. Plate Pasteurizer Control • 0.15C corresponds to 1 PU

29. Flow Control Options • Fixed Flow • Range of Pre-set Flows • Fully Variable Flow • Most Suitable Option Depends Upon • Size of Outlet Buffer Tank • Importance of No Recirculation of Product • PU Variation Desired • Product Quality • Type of Filler • Minimum Flow typically 1/3 of maximum • Pressure drop 1/9 of max flow (must be adjusted downstream to avoid overpressure) • Heat transfer coefficient decreases, residence time increases

30. Best Practice - Full flow to 1/3 of full in 15 min while maintaining PU’s within 2.0 • Control Loops • Holding Cell Temperature • Critical for PU Control • Must be varied with changes in flow • Final Product Outlet • Flow – Upstream and downstream influences • Pressure – Varied with changes in flow • Interrelationships of many variables requires use of sophisticated control (PLC)

31. Tunnel Pasteurization Simpler system than flash pasteurization Slow process (may take up to 40 minutes) Energy intensive process Beer near outside of can/bottle over pasteurized Mechanical failure, other stoppage could cause over pasteurization, effecting beer flavor

32. Tunnel Pasteurization Pasteurized after bottled or canned Bottles or cans move slowly down conveyer system Hot water sprays heat beer to pasteurization temperature Cool water sprays cool beer after pasteurization is complete Pressure builds in headspace - Volume of headspace - CO2 concentration in beer Bottles could break (Typical 1 in 500) CO2 could leak if bottles are not sealed well

33. Typical temperature regime

34. Tunnel Pasteurization Spray water temperature Pressure (Bar) Temperature (C) Product Temperature Time (min)

35. Factors Effecting Tunnel Pasteurization • Materials of Construction • Structure and weight – lighter stronger matl • Corrosion – chemical attack metal, cracking • Transport System – typically conveyor • Spray System – Votex or spray pan • Temperature • Heating • PU Control

37. Plate/Flash vs. Tunnel Pasteurization • Plate uses significantly less floor space • 15% reduction in operating cost • Reduced capitol costs • Beer tastes fresher (approx 92% less TIU) • Cleaning and contamination downstream

38. Why is Process Control Needed? • Safety • Quality Specifications, Consistency • Environmental Regulation, Environmental Impact • Optimum Operation of Equipment • Cost Effectiveness • Aims of Control System • Suppress Influence of External Disturbances • Ensure Stability of a Process • Example: External Disturbance on Shower • Flow rate of hot water increases? • Temperature of hot water decreases? • Flow rate of hot water decreases?

39. Basic Control Elements • Sensor – Receives Stimulus, Outputs Signal • Controller – Receives Signal, Compares to Desired Value, Sends Control Signal • Actuator – Receives Control Signal, Makes Corrective Action on Process • Process – “The Organized Method of Converting Inputs to Outputs • Functions of Control System • Measure • Compare to Desired Value • Compute Error • Corrective Action

40. Definitions • Controlled Variable • Setpoint • Measured Variable • Manipulated Variable • Example • Disturbance? • Variables • Controlled? • Measured? • Manipulated?

42. More Accurate More Complicated

43. On/Off Control • Valve Open or Closed, Heater On or Off • Inexpensive and Simple • Oscillatory, Wear on Switching Device

44. Sequence Control • Series of Events (Washing Machine) • CIP Sequence, Fermentation Temperature, Keg Washing and Filling • Achieved with PLC, Pegged Drum (Mechanical) • Closed-Loop Control

45. Open-Loop Control • Controlled Variable Measured Prior to Intervention by Manipulated Variable

46. Definitions • Overshoot – Ratio of maximum amount by which response exceeds steady state to final steady state value • Rise Time – Time required for response to reach final value for first time • Response Time – Time it takes for response to settle at its new steady state value

47. Control Example

48. Proportional Control

49. Proportional + Integral Control

50. Proportional + Integral + Derivative Control