Last Week:Heat ExchangersRefrigeration
This Week:More on RefrigerationCombustion and SteamPasteurizationSteam Raising and Combustion
Refrigeration
Condenser
Evaporator
Compressor
Qout
Qin
Win
Refrigeration
Cond
Comp
Qout
Win
Fermenting Room
Lagering Cellar Cooler
Hop Storage Cooler
Flash Tank
EvaporatorSecondary Refrigerant
Storage Tank
Wort Cooler
Fermenting Vessels
Green Beer Chiller
Beer Chiller
Pasteurizer
Yeast Tanks
Air Conditioning
Primary RefrigerantsAmmonia, R-12, R-134aSaturation temp < Desired application temp
2 to 8C Maturation tanks0 to 1C Beer Chillers-15 to -20C CO2 liquefaction
Typically confined to small region of brewery
Secondary RefrigerantsWater with alcohol or salt solutionsMethanol/glycol, potassium carbonate, NaClLower freezing temperature of waterNon-toxic (heat exchange with product)Pumped long distances across brewery
Example 1
A maturation tank is maintained at 6C 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 18C 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 -10C, it exits the maturation tank at 2C and its specific heat is 3.5 kJ/kg.K. Determine the mass flow rate of secondary refrigerant required.
Example 2A brewery refrigeration unit has to meet the following
cooling duties simultaneusly.
1. Cool 800 hL of wort from 35 to 8C in two hours
2. Maintain two cold rooms at 0C – 40 kW ea.
3. Lager chiller cooling 50 m3/hr of product to 0C – 500 kW
4. Beer chiller cooling 50 m3/hr of product to 5C – 250 kW
5. 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, 20CCooling water temp to condenser, 15C
Wort BoilingImportance
• Flavor development• Trub formation• Wort stabilization• Wort concentration
Time and temperature – color, flavor, sterilization, etc.
Turbulence – trub formation and volatile removal
Rolling boil required.
Temperature above boiling (C)
Hea
t tr
ansf
er c
oef.
Interface Evaporation
(forced convection) <2C
Film Boiling >25C
Bubbles(nucleate boiling)
2C < T < 25C
Wort BoilingIn wort boiling it is important to maintain a temperature
difference below the critical difference between the wort and heating element surface (25C) If the wort is boiling at 105C, 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.
0.35 MPa 139.0C0.40 MPa 143.5C0.45 MPa 148.0C0.50 MPa 152.0C
0.55 MPa 155.5C0.60 MPa 159.0C0.65 MPa 162.0C
CombustionFuel + Oxidizer Heat + Products
Oxidizer: Air (79% N2, 21% O2 by Volume)
Fuels: Typically hydrocarbonsMethane CH4
Ethane C2H6 GasesPropane C3H8 Natural Gas = 95% CH4
Butane C4H10
C6 – C18 LiquidsGasoline (Average C8)Fuel Oil No. 1 (Kerosene)Fuel Oil No. 2 (Diesel)
Fuel Oil No. 3-6 (Heating Oils)
CombustionTo 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.
CombustionActual 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.
CombustionFlue 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
SteamHigh latent heat, cheap, non-toxic, available
Combustion/Steam ProblemA 5 m3 wort kettle is heated from 70C to 95C 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)
PasteurizationMicroorganisms growing in beer
• Wild yeast strains• Lactic acid bacteria
No – Homogeneous population of microbesN – Remaining number of microbest – time in minutesD – Decimal reduction time at temperature T
Time (min) Number of microbes per Liter
0 10,000
2 1,000
4 100
8 1
10 0.1
D
t
oN
N
10
min 260 D
PasteurizationTypically choose D value of most resistant organism1.0 P.U. = “one minute of heating at 60C”
An average Z value of 6.94C is used
Z
T
T DD60
6010
TLogDLogD
TZ
60
60
tPU TTotal
60394.1
Flash PasteurizationT
ime
(min
)0.
1
1
1
0
100
50 60 70Temperature (C)
Over Pasteurization
Under Pasteurization
Minimum Safe Pasteurization
5.6 min
PasteurizationFor the data given below, calculate the total number of
pasteurization units (PU). Assume a Z value of 6.94C.
What type of pasteurizer is this?
Minute Mean Temp (C)
PU’s
21 49.7
22 53.0
23 55.9
24 58.3
25 60.2
26 61.5
27 62.25
28 62.65
Minute Mean Temp (C)
PU’s
29-34 62.8
35 62.6
36 61.2
37 58.6
38 56
39 53.7
40 51.75
41 50
Total
Flash Pasteurization
Beer in = 0C
Pasteurizer60-70C30 sec - 2 min
90-96%regeneration
Flash PasteurizationP
ress
ure
(Bar
)
Tem
pera
ture
(C
)
Time (sec)
Pressure in Pasteurizer
CO2 equilibrium pressure
Temperature in Pasteurizer
Flash PasteurizationTypical Conditions:
Beer inlet: 3COutlet from regenerative heating: 66CHolding tube: 70COutlet from regenerative cooling: 8COutlet from cooling section: 3CHolding Time: 30 sec
Advantages
Little space required
Relatively inexpensive equipment and operation
Short time at “intermediate” temperatures where chemical changes occur without pasteurization
Tunnel PasteurizationPasteurized 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
Tunnel PasteurizationP
ress
ure
(Bar
)
Tem
pera
ture
(C
)
Time (min)
Spray water temperature
Product Temperature
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