agenda pasteurization process control materials heat transfer test next week

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