Section 3
Setting Up the Mill for Fortification
Required Equipment and Premix Addition Options
Anti-bridging and Outlet Covers
Feeder Controls
Mechanical Principles
Types of Premix Feeders
Hopper Size and Discharge Rates
Premix Delivery Systems
Adequate Mixing
Recommendations and costs
Required Equipment
Premix Feeder
• Measures correct
amount of premix
• Position at
appropriate place
in production line
• Size based on
mill’s rated
capacity
Mixing Mechanism
• Can be done
during normal flour
transport or with
special equipment
• Assures that
premix is uniformly
added to flour
Premix Addition
Premix is usually added to
flour using one of two
procedures:
• Continuous
• Batch
The gravity-based system such as the one
pictured here is an example of premix being added
to flour continuously as it is produced at the mill.
Premix Addition: Continuous
• Premix is continuously
added to the flour
stream using a feeder
feeder
• Premix addition is
proportional to the rate
of flour production
• Validation is required to
confirm that the mixing
process is uniform
conveyor
Premix can be continuously added into a collection
conveyor such as the one shown here.
Premix Addition: Batch
• Premix is generally added
to a batch of flour via a
gravity spout and blended
in a mixer
• Premix addition is based
on flour batch size
• Operation can be manual
or automatic
• Validation of mixing
uniformity is required
Batch mixer photo courtesy of Buhler
Company
All Feeders Require Anti-bridging
With continuous or batch, use feeders with anti-bridging
devices to provide consistent premix flow.
Two product flow issues resulting in flow stoppage include:
• Bridging occurs when product discharges above the outlet but no
premix flows in to fill the void. Looking into the top of the feeder
hopper, it appears to contain premix across the entire hopper.
• Tunneling is a form of bridging where the product falls directly
through the outlet but premix remains on the sides of the hopper.
Looking into the feeder hopper, the discharge point is visible but the
sides of the hopper remain covered with a wall of premix.
See the troubleshooting pages of section 4, Operations,
for more information.
Feeder Outlet Requirements
• Cover the feeder’s
outlet spout for product
safety
• The cover can be part
of the feeder design or
it can be addressed in
installation
• Locate the outlet spout
for easy opening for
inspection and check
weighing
At left, a screw feeder discharge spout is
covered. At right, the cover opens to
allow for easy inspection and check
weighing.
Photos by Jeff Gwirtz
Control Systems for Premix Addition
• Control systems selected should match the
technical capability of the plant operation and
maintenance program.
• Systems range from manual systems to those with
basic and advanced interlocking to fully automated
systems.
• All systems presented achieve the basic needs of a
fortification program.
Controlling the Feeder Manually
• In a manual system,
the feeder is started
and stopped by the mill
operator.
• Feeder settings are
controlled and
monitored by the mill
operator.
• This is the least
expensive approach to
install requiring no
sensors or electronic
controls.
Flour
Streams
Premix
Feeder
In manual operation,
the feeder control is
near the premix
feeder. The control
model pictured can be
operated manually or
automatically.
Photo by Jeff Gwirtz
Flour
Out
Controlling the Feeder Using Basic
Sensors and Interlocking
Sensors:
• Monitor for incoming
flour
• Switch the premix
feeder on and off as
needed
• Monitor premix level
and flow
• Warn operator of
problems
• Reduce mill operator
workload
• Are inexpensive
Flour
Streams
Flow
Sensor
Premix
Feeder
Mill/Control
Room Warning
Flow or Level
Sensor
Flour
Out
Controlling the Feeder Using
Advanced Sensors and Interlocking
• Loss in weight feeder
makes feeder setting
and monitoring easier
for the operator
• An online flour scale
more accurately starts
and stops the feeder
using a baseline flow
rate
• These system
improvements are
needed to develop an
automated system
Flour
Streams
Flow
Sensor
Premix Feeder
Loss-in-weight
Mill/Control
Room Warning
Flow or Level
Sensor
Flour
Out
Controlling Feeder with Automation
• Programmable logic
controller continuously
matches the addition rate
of premix to the
measured flow rate of
flour
• Requires appropriate
human machine interface
• Most accurate method of
flour fortification and
exceeds minimal
requirements
• Easily retrofitted into mills
using existing automation
Flour
Streams
Flow
Sensor
Premix Feeder
Loss-in-weight
Mill/Control Room Warning
Programmable Logic Controller
Flow or Level
Sensor
Flour
Scale
Controlling the Feeder-Summary
Control Point
Control System
Level
Manual
Basic
Advanced
Automation
1
Manual
Feeder
On/Off
X
X
X
X
X
X
X
2
Automatic
Feeder
On/Off
3
Premix
Hopper
Level
X
X
X
X
X
X
X
X
4
Premix
Flow
Sensor
X
X
X
X
X
5
Premix
Rate Set
Manual
X
X
X
X
6
Premix
Loss-InWeight
X
X
X
X
X
X
X
7
Warning
System
X
X
X
X
X
X
8
Flour
Flow
Sensor
9
Flour
Production
Scale
10
Programable
Controler or
Computer
X
X
X
X
X
X
X
X
X
Mechanical Principles
Two ways feeders control amount of premix added to flour:
Gravimetric
Volumetric
• Also known as “loss in
weight”
• Continuously weighs premix
• Requires greater volume of
premix than generally used
• More complex and expensive
than required in most cereal
milling
• More precise than volumetric
• Most commonly
used by screw
feeders
• Similar to using a
measuring cup
• Minimum error of
measurement is
+2%
Feeder Mechanical Information
Electrical interlock system
prevents flow of premix
when flour flow stops.
• The on/off switch, speed
controller, and low- level
indicator light can be
located near the feeder or
at a remote location.
• Some installations may
need a voltage regulator
to ensure proper
performance of the feeder
and controller.
Controller
Feeder
Feeder Mechanical Information
• The electrical interlock system is installed between the
feeder motor and the motor driving the flour collection
conveyor.
• In pneumatic delivery systems, an interlock should be
made between the feeder and the blower to ensure that
the feeder cannot be turned on without the blower
operating. This prevents buildup of premix in pneumatic
lines followed by over-treatment of flour once the blower
is turned on.
• An alternative is an automatic shut-off switch on the
feeder that is hooked up to a flour flow indicator or a
pressure indicator in a pneumatic system.
Premix Feeders
Feeders are required for automated batch and continuous
addition. Three main types of premix feeders are used to
fortify flour.
1.Screw Feeder
2. Revolving Disk
3. Drum / Roller
Premix Feeders: Screw Feeders
• Dispense fixed volume of
premix per revolution
• Size of feed screw
determines the feed rate
volume of premix
dispensed per revolution
• Variable speed controls the
number of revolutions per
unit of time
• Weight of premix
dispensed is determined by
product density
Size of the feed screw varies such
as the small ones above and the
larger one below.
Premix Feeder: Revolving Disk
•
•
•
•
Slide mechanism controls rate of premix addition
Powered by either an AC or DC motor
Small hopper must be refilled frequently
More mechanical components than the screw feeder
Hopper
Gate Adjustment
Rotating Spring
Rotating Disc
Premix Feeder: Drum or Roll Type
Premix passes between two closely set revolving cylinders
Floating Fill Container
Flexible Hopper
with Agitation
Guide Veins
Feed Rate Slide
Bar Adjustment
Roll Scraper
Feed Rolls
Motor
Premix Feeder: Drum or Roll Type
• Used for decades and many are still in use
• Can be volumetric, gravimetric or loss of weight feeders
• Either a DC or AC motor for power
• Pulley system controls the rotation speed
• Pulleys and wheels of differing diameters make gross adjustments in
the feed rate. An adjustable gate is used to make fine adjustments
• Require more parts and more maintenance
• Shear pins in the drive mechanism break if large objects (bolts,
plastic) get stuck between the rolls
• In some newer models, a variable speed DC drive motor allows
addition rate to be adjusted electronically rather than mechanically
• Variable speed AC drive motors are also available
Feeder Hopper Size
• Choose a feeder with a large enough hopper that it does not have to
be filled frequently
• Regardless of type of feeder used, the size and number of feeders
needed will depend on:
– Number of production lines
– Hourly production of respective production line
This feeder bank has
feeders with different
size hoppers for different
additives.
Photo courtesy of Research Products
Company
Feeder Premix Discharge Rates
All types of premix
feeders are available with
different discharge rates
• A small feeder may
discharge premix at
levels as low as 25 g
per hour (0.4 g/min)
• The largest can
discharge up to 32 kg
per hour (533 g/min)
Estimated premix discharge rate
Mill
Capacity
(MT/day)
Flour flow
rate*
(kg/min)
Premix**
Discharge rate
(g/min)
5
2.5
0.4
20
10
1.5
50
25
3.8
100
50
7.5
200
100
15
400
200
30
* At 72% extraction rate
** At 150 grams premix per metric ton of flour
5 MT daily capacity mills require smaller feeders
than discussed in this tool kit
Continuous Premix Delivery Systems
With continuous feeding, two types of premix delivery are
possible. Location of the feeder depends on the type used.
Gravity
• Feeder is placed above
the flour collection
conveyor
• Premix drops directly into
flour as it flows through
the conveyor
Pneumatic
• Can be located at several
places in the mill
• Premix drops into a
venturi tube
• Premix is blown into the
flour collection conveyor
Premix Delivery System: Gravity Feed
Things to consider:
• Feeder is installed
above the flour
collection conveyor
• Premix is delivered via
a nearly vertical gravity
spout
• Install spout away from
general suction system
Gravity Method of Premix Delivery
Premix Feeder
Flour In
Mixing Conveyor
Flour Out
Premix Delivery System: Pneumatic
Things to Consider:
• Requires equipment
such as blowers,
valves and piping
• Conveying lines
should have minimal
length and directional
changes
• Make the venturi tube
accessible for
Flour
monitoring
Pneumatic Method of Premix Delivery
Feeder
Air
Blower
Venturi
Tube
Premix Delivery System: Pneumatic
1
2
1. Venturi tube with air flow
restriction and product inlet
2. Attaching venturi tube to
premix hopper transition
3. Completed assembly
3
Ensuring Adequate Mixing in the Mill
Proper addition point for premix on the flour collection
conveyor is essential for effective flour fortification.
•
•
•
Locate the feeder at the front half of collection conveyor, above the
blades of the mixing screw
At least 3 meters of conveyor length is normally needed to ensure
adequate blending
Introduce premix away from general suction system
Poor
To Little Flour
Good
Mixing
Poor
To Little Mixing
Flour
Level
Flour Flow
Flour
Outlet
Ensure Adequate Mixing In Packaging
If premix addition cannot be accomplished in mill,
consider this option:
• Install mixing conveyor between holding bin and
packout bin
• The premix is discharged into the start of this special
conveyor
• At least 3 meters of conveyor length is normally
needed to ensure adequate blending
• Introduce premix away from general suction system
Equipment Recommendations
When considering equipment, look for these specifications:
• Directions for installation and maintenance in desired language or
can be translated
• All surfaces in contact with premix are food-grade and non-corrosive
• Adjustable delivery control, calibrated from 0 to 100% of feeder
capacity
• 220 volt ± 10% 50/60 Hz single phase power
• Anti-bridging design to prevent bridging or tunneling of premix in
hopper
• Capable of delivering from 0.04 to 8 L/hr with ± 5% accuracy over
full range
• Hopper capacity of 8 liter minimum
• Easy accessibility for operator to check hopper and flow rate
System Recommendations
When considering equipment, look for these specifications:
• Directions for installation, maintenance, and system operation
available in desired language or can be translated
• Automatic shut off / warning capability
-
Feeder shuts off when flour flow stops
-
Warning if feeder is empty or premix fails to discharge
• Place feeder on load cells to aid in monitoring premix usage or use
loss-in-weight feeder
• If possible, use electronic control loop to balance feeder discharge to
flour production scales
Vendor Expectations
Millers should expect the following from equipment and system
vendors:
• At least two references from mills where equipment and
systems have been in operation for at least one year
• Installation and operating instruction manual that explains in
words and diagrams the installation, calibration and
maintenance of the equipment and system
• Technical support for installation, training, calibration, and
maintenance
• Recommended spare parts inventory for items with life span of
less than three years
• Identified lead time for parts delivery and commitment to
maintain parts inventory support
Equipment Costs
• Cost of feeders
varies with the
capacity of the
production line and
optional equipment.
• Cost of blending
equipment, if
needed, varies with
capacity of
production line.
• Costs shown do
not include
shipping, import
duties, value added
tax or installation.
Equipment
Cost Range (USD)
Feeders
Volumetric Feeder
$1,000 - $8,000
Gravimetric Feeder
$5,000 - $20,000
Loss-of-weight Feeder
$10,000 - $21,000
Powder Feeder
$1,000 - $25,000
Scales
Electronic
$100 - $2,000
Blenders / Mixers
Screw-Ribbon
/Paddle/Cut Flight
$10,000 - $25,000
Rotary Batch Blender
$35,000 - $170,000
Vertical Batch Mixer
$15,000 - $200,000
More Information About Mill Set-up
Contact FFI at info@ffinetwork.org
Compare videos of premix flow rate of a mill grinding:
•
500 metric tons of wheat a day, at 75% extraction, and
premix addition of 150 grams per metric ton of flour
•
100 metric tons of wheat a day, at 75% extraction, and
premix addition of 150 grams per metric ton of flour