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

Last Week: Heat Exchangers Refrigeration This Week: More on Refrigeration Combustion and Steam Pasteurization Steam Raising and Combustion. Refrigeration. Q out. Condenser. Compressor. W in. Evaporator. Q in. Refrigeration. Q out. Hop Storage Cooler. Cond. Air Conditioning.

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

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  1. Last Week: Heat Exchangers Refrigeration This Week: More on Refrigeration Combustion and Steam Pasteurization Steam Raising and Combustion

  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 1 • 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 -10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. Example 2 • A brewery refrigeration unit has to meet the following cooling duties simultaneusly. • Cool 800 hL of wort from 35 to 8C in two hours • Maintain two cold rooms at 0C – 40 kW ea. • Lager chiller cooling 50 m3/hr of product to 0C – 500 kW • Beer chiller cooling 50 m3/hr of product to 5C – 250 kW • Air conditioning, hop stores and yeast tanks – 100 kW • If the primary circuit uses R-134a and the secondary circuit uses 22.5% sodium chloride, estimate, stating all assumptions that you make, the maximum flow rates of R-134a and brine and the refrigerant compressor power. • Specific heat of brine – 3.7 kJ/kg.K. • Min temp diff in evap and condenser, 20C • Cooling water temp to condenser, 15C

  7. 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)

  8. 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.

  9. 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)

  10. 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.

  11. 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.

  12. 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 LHV = H2O vapor in products, HHV = liquid

  13. Steam High latent heat, cheap, non-toxic, available

  14. Combustion/Steam Problem A 5 m3 wort kettle is heated from 70C to 95C with steam at 3 bar (gauge) in an external heating jacket. The steam enters as saturated vapor and it exits as saturated liquid. Natural gas (LHV = 40 MJ/kg). a. Calculate the total mass of steam required for the heating process. b. What mass of fuel is required and what will the fuel cost be if natural gas can be purchased for $1.00/Therm (1 Therm = 100,000 BTU)

  15. 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

  16. 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

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

  18. 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?

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

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

  21. 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

  22. 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

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

  24. 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

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