Impacts Of Drying On Aquafeed

Transcription

Impacts Of
Drying On
Aquafeed
Prepared For:
Horizons Conference
Bangkok, Thailand
8 April 2014
1 | Impact of Drying Parameters on Aquafeed | Process Engineering | © Buhler Aeroglide
Welcome!
Presenting:
Justin Hamm, Applications Engineer
- Buhler Aeroglide – Cary, NC USA
- direct phone: +1 919 278 2841
- mobile phone: +1 919 802 7432
- email: [email protected]
2 | © Bühler | 1 | Impact of Drying Parameters on Aquafeed | Process Engineering | © Buhler Aeroglide
Discussion Topics
Drying Basics: Extruded Aquafeed
Aquafeed Properties Affected By Drying
Drying Basics:
Extruded
Aquafeed
Typical Dry Aquafeed - Production Line
Raw Ingredient
Storage
Grinding and
Mixing
Packaging
Cooking and
Extrusion
Drying (and
Cooling)
Cooling
Fat Application
(enrobing or
vacuum)
Typical Aquafeed Dryers & Coolers
Conveyor Dryers &
Coolers
Rotary Dryers &Coolers
Vertical Dryers & Coolers
Why “Dry” Aquafeed?
Primary Objective: Improve Product Shelf Life
Other Objectives:
Change material performance (floating & sinking)
Improve rigidity & crush strength
Improve absorption of product coatings
The Typical Drying Cycle
Process air is
heated (or reheated)
Fresh makeup air is
brought in to
replace the
exhausted air
Heated air
pulled into
recirculation
fan
Part of the
recirculation
air is
exhausted
Water vapor
is taken away
via the
recirculation
air
Heated air
passes
across
product bed
The heat from
the air
vaporizes
surface
moisture in
the product
Heated air
transfers its
energy to the
product
Step 1: Evaporation from the Product
It takes heat to evaporate water. Air is the medium for heat transfer in the dryer.
Step 2: Vapor Transfer to Air
Air is like a sponge. The drier the air is, and the better contact it has with the product,
the faster it will absorb the vapor.
Step 3: Diffusion of Water to the Surface of the product
Water diffusion is a function of product composition, size and moisture content.
Constant Rate
Controlled by Evaporation & Transfer to Air
Product Temperature
Falling Rate:
Diffusion Controlled
Critical Moisture
Content
Retention Time
Temperature
% Moisture
Typical Extruded Extruded Feed Drying Curve
Product Characteristics That Affect Drying
Nature of the Product
- Size/Shape (Surface Area)
- Solid Type (Porosity, Moisture Binding)
- Product Components (i.e., Starches, Oils, Fats, etc.)
- Product Bulk Density & “Packing Characteristics”
- Moisture Content (In/Out)
Aquafeed
Properties
Affected By
Drying
Are These Properties Important For You?
1. Shelf
Stability
6. Crush
Strength
2. Coating
Absorption
Your
Product
5. Vitamins
& Pigment
3. Bulk
Density
4. Buoyancy
(Float/Sink)
These properties are impacted by Drying and Cooling
1. How Does Drying Affect Shelf Stability?
The ability for the product to maintain its quality while being stored for extended
periods. This can be within sealed packaging or silos.
Dryer Impact
1.2
1
0.8
0.6
0.4
0.2
0
<Curve is different for each product>
80%
60%
40%
20%
Moisture (%)
0%
Water Activity
1. Drying to final moisture target for water activity goal
a. What’s your products correlation of water activity & moisture content?
2. Moisture uniformity of finished product
aw limits
Micro-organism
0.91
Gram Negative Bacteria
0.88
Gram Positive Bacteria
0.86
Yeast
0.80
Mycotoxins
0.70
Molds
0.62
Osmophillic Yeast
0.61
Xerophellic Molds
0.60
Absolute Limit For Growth
1. How Does Cooling Affect Shelf Stability?
Cooling product before packaging or entering silos/bins can reduce the potential
for condensation within the container from moisture flash-off.
Cooler Impact
Fully cool product before it enters packaging & storage
product temperature
ambient +10ºC
2. How Does Drying/Cooling Affect Coating Absorption?
The uniform application of liquid or powder additives to the pellets surface. The
coating is absorbed into the surface pores.
Dryer Impact
1. Moisture uniformity of pellet surfaces
2. Product temperature affects absorption rate
a. Warm product absorbs more quickly & completely
b. Optimal temperatures for most products are between 45ºC-55ºC
3. Case hardening seals the pellet surface reducing the absorption rate
Possible Solutions
Improve moisture uniformity
Partial cooling between dryer and coating/enrobing process
Avoid case hardening
3. How Does Drying/Cooling Affect Bulk Density?
The ratio of the products weight by cubic volume. Value used to determine
product consistency. Primarily controlled by pre-conditioner & extrusion process.
Dryer Impact
1. Drying to final moisture specification
a. Over drying reduces wet weight basis percentage
Possible Solutions
Routine moisture samples
Advanced process control functions (moisture control)
4. How Does Drying/Cooling Affect Pellet Buoyancy?
The rate at which a pellet sinks when placed in fresh or salt water.
Dryer Impact
1. Moisture uniformity
2. Drying to final moisture target
3. Case hardening seals the pellet surface increasing buoyancy
4. Coating absorption changes surface porosity & bulk density
Possible Solution
Advanced process control functions (humidity, evaporation)
Avoid case hardening
5. How Does Drying/Cooling Affect Vitamins & Pigments?
Certain specialty products contain added vitamins essential for the animal
nutrition. Sometimes pigments are also added to alter the tissue coloring.
Many vitamins & pigments have temperature limitations
Dryer Impact
Over heating product can degrade these important/expensive ingredients
Example: Salmon feed is temperature limited due to degradation of astaxanthin
ingredient which gives fish a pink color. Astaxathin limit approx. 70ºC (160ºF)
Possible Solution
Sequential heat zones
Lower operating temperatures and increased retention times
6. How Does Drying Affect Pellet Hardness & Crush Strength?
The ability of the product to withstand pressure from stacking in bulk silos/bins as
well as in consumer packaging. Also the ability for the animal to breakdown and
process the food.
Dryer Impact
1. Drying to final moisture targets
2. Moisture uniformity of individual
pellets (Not only composite sample!)
Possible Solution
Advanced process control functions (moisture, humidity)
Adjust process air temperature profiles
Common Issues Affecting Pellet Properties?
1. Poor Moisture Uniformity
2. Case Hardening
3. Dryer Control
Why is Moisture Uniformity Important?
Shelf Stability
Example Cost of Over-drying
The higher moisture product can
exceed
maximum
safe water activity 5,867
levelkg
Hourly
feed ratethe
at 25%
moisture
5,000 kg
and mold/bacteria can occur Hourly output at 12% moisture (A)
Hourly output at 11% moisture (B)
Difference in hourly production (A - B=C)
Coating Absorption & Bouyancy
Annual hours of dryer operation (D)
Annual
lost production
from over-drying
(C product
x D = E)
Non-uniform moisture can affect
downstream
processing
and
performance properties
4,944 kg
56 kg
7,800
436,800 kg
Annual cost of lost production (E/1000 x $500 US = F)* USD $218,400
Energy expended per kg of water removal (G)
3,300 kj
Vitamins, Pigment & Crush Strength
Annual excess energy used in over-drying (E x G = H)
1,441 MM kj
Non-uniform moisture can alsoEnergy
mean
non-uniform
flavor,
color,
hardness,
etc.
cost per kJ (I)
USD $0.0000035
Additional cost of excess energy consumption (H x I = J) USD $5,045
Bulk Density
Over-drying means lost production
Total annual cost of over-drying (F + J) USD
$223,445
*Assumes
value that
of USD3%
$500of
peryour
metric product
ton
- example: over-drying by 3%
means
goes out the
exhaust stack
How Does Bed Loading Affect Moisture Uniformity?
“Good Conveyor Drying Begins
With Good Bed Uniformity”
Uneven Bed Loading
8.3%
9.1%
7.9%
4.2%
Example : (+/-) 2.45%
6.6%
Uniform Bed Loading
7.8%
7.9%
8.1%
8.1%
8.0%
8.4%
8.2%
7.6%
8.3%
Example : (+/-) 0.42%
How Can You Improve Your Bed Loading?
Feeder Adjustments
Oscillation speed
- Effects waves in product
bed
Stroke Centering
- Even loading left to right
Sweep angle
- Complete & level fill from
edge to edge
Programmable Sweep Speed
- Reduce dwell time on bed
edges for changes in depth
How Does Bed Depth Affect Moisture Uniformity?
Time and bed depth are related in most dryers
Set your dryer’s bed depths as deep as possible, without experiencing
- uneven moisture results
- blinding over the bed perforations
- creating clusters/lumps
Advantages of maintaining maximum bed depth:
- retention time is maximized, which reduces energy consumption
How Does Airflow Affect Moisture Uniformity?
Airflow Direction
Reverse up & down through bed to balance moisture from top to bottom of bed
Airflow Distribution
Maintain uniform air velocity & temperature across bed width to balance
moisture from side to side of bed
How Does Airflow Direction Affect Moisture Uniformity?
Alternating
Only Up-Airflow
Airflow
80
150
85
95
125
95
125
85
150
80
Only Up-flow
8.0%
8.5%
8.2%
6.8%
7.2%
7.0%
5.9%
6.2%
6.1%
Example : (+/-) 1.3%
Moisture Uniformity - Air Flow Direction
Single Plenum, Two Pass
Up & Down Flow
7.8%
7.9%
8.1%
8.1%
8.0%
8.4%
8.2%
7.6%
8.3%
Example : (+/-) 0.42%
How Does Air Flow Distribution Affect Moisture Uniformity?
Dryer Symmetry Is Critical For Uniform Distribution!
Single Plenum, Dual Pass
2. Case Hardening
3. Dryer Control
What is Case Hardening?
The formation of a dry, external layer that resists the passage of moisture from
the pellet interior to the surface
Cause:
A combination of very high process air temperatures and very low air humidity
levels. The hot, dry process air dries the readily available surface moisture
quickly creating an impermeable surface.
Effect :
1. Reduces evaporation rate and decreases dryer performance
2. Pellets are more likely to float when placed in water
Why Is Case Hardening A Problem?
Shelf Stability
Evaporation rate is reduced making it difficult for the dryer to reach moisture
targets
Coating Absorption
The hardened surface makes uniform absorption more difficult.
Bouyancy
Sealed pellet surfaces can contribute to floating characteristics
Crush Strength
The pellet exterior can be brittle while the core is soft and moist
2. Case Hardening
3. Dryer Controls
How Can Advanced Dryer Controls Improve Your Process?
Shelf Stability & Bulk Density
- Moisture Control automates temperature set points to maintain moisture
target
- Evaporation Control automates temperature adjustment preventing
over/under drying
Coating Absorption, Bouyancy, & Crush Strength
- Humidity Control automates exhaust to eliminate risk of case hardening
- Bed Depth Tracking provides operator feedback to maintain optimal bed
depth
Advanced
Controls
Process Feedback & Automation
Depth Sensing
Humidity Sensing
Damper Modulation
Temperature Sensing
1
3
Moisture Sensing
2
PLC Automation
HMI Visualization
1
3
2
1
3
2
Are These Properties Causing You Problems?
Review your process for ways to improve :
Moisture Uniformity
Dryer Controls
Cooling
Questions ?
Thank You for attending Bühler Aeroglide’s
“Impacts of Drying on Aquafeed”

Impacts Of Drying On Aquafeed

Transcription

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