AgendaPasteurizationProcess ControlMaterialsHeat Transfer Test
Next WeekCumulative “Final” Test
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
Microbiological Load Reduction – LRVSterile 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)
Outletat Organisms of No.Inletat Organisms of No.Reduction Titre
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.”
Factors effecting flow rate and life:
• Pressure Drop• Surface Area
P increases as dirtblocks pores
Increased surfacearea has greatincrease on dirtcapacity
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
(120C, 20 min)
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%
Pasteurization Units• Measure of effect of heat and time on
microorganisms• 1.0 PU corresponds to 1 minute at 60C• PU = t * 1.393(T-60C) (t in minutes)
Rules of Thumb• Increase T by 2C, double PU’s for same time• Increase T by 10C, PU’s increase 10x• 20 PU’s indicates that 1 in 10 Billion
microorganisms surviveEffect of PU’s on specific microorganisms needed
Plate/Flash PasteurizationTypical plates: Stainless steel, 0.6 mm thicknessCan withstand 20 bar pressure
Design Factors for Plate Pasteurizer• Product Flow Rate and Properties of Liquid• Temperature Program and Pressure Drop• Hygiene and Cleaning
Plate Pasteurizer Design• 95% Heat Recovery in regenerator• Product enters Pasteurizer at 4C• Holding temperature 72C• Holding time 25 seconds• Hot water typically used for heating, 2C
warmer than holding temperature
Level of Regeneration
Plate Pasteurizer Control• 0.15C corresponds to 1 PU
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
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)
Tunnel Pasteurization
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
Typical temperature regime
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
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?
Stable vs. Unstable Variable• Goal: Boil Water in an Open Pot at 1 atm• Control Variables: Amount of Water, Rate of Heat• Given Quantity of Water, Sufficient Heat = Boiling• While Boiling: Temp is Stable (or Self-Regulating)• Water Level is Un-Stable, Requires Control
Pressure Cooker Example• No Pressure Relief – Temp and Press Unstable• With Pressure Relief – Temp and Press Stable• Level Unstable in Both• Weight = Inherent Control Scheme
Process Control – A system of measurements and actions within a process intended to insure that the output of the process conforms with pertinent specs
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
Definitions• Controlled Variable• Setpoint• Measured Variable• Manipulated Variable
Example
Disturbance?
VariablesControlled?Measured?Manipulated?
More AccurateMore Complicated
On/Off Control• Valve Open or Closed, Heater On or Off• Inexpensive and Simple• Oscillatory, Wear on Switching Device
Sequence Control• Series of Events (Washing Machine)• CIP Sequence, Fermentation Temperature, Keg
Washing and Filling• Achieved with PLC, Pegged Drum (Mechanical)
Closed-Loop Control
Open-Loop Control• Controlled Variable Measured Prior to
Intervention by Manipulated Variable
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
Control Example
Proportional Control
Proportional + Integral Control
Proportional + Integral + Derivative Control
Feedback vs. Feedforward Control
Carbon and Low Alloy Steels• Carbon Steel – Iron alloys with 0.05 to 1% C• Low Carbon Steel – aka mild steel• Low Alloy Steels – alloying elements with <2%
Advantages• Inexpensive and readily available• Easily worked and welded• Good tensile strength and ductility
Disadvantages• Corrosion• Protective coatings often required
Copper• Pure copper traditionally used• Brass – alloyed with zink• Bronze – alloyed with tin
Advantages• Soft and easily worked• Readily available for small pipes/tubes• Resists corrosion well• Resistant to caustic and organic acids/salts
Disadvantages• Strong acids and oxidizing acids attack• Cost
Stainless Steel• Considered stainless if chromium > 11%• Typical values 11-30% chromium• Cr2O3 oxidation layer gives ss it’s passivity
General Corrosion• Covers entire surface• “Best” kind of corrosion to have• Measurable and predictable (design for)
Galvanic Corrosion• Two metals in contact in same electrolyte• Less noble, less passive, more active metal
corroded, other metal protectedErosion and Cavitation
• Abrasive particles and/or high velocity• Cavitation corrosion (bubbles near pumps)
Sensitisation – Inter-grainal corrosion (415-825C)Pitting – Occurs below surface, chloride ion
Localized weak points in passive surface