1. 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

2. 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

3. 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.

4. Premix Addition: Continuous
Premix is continuously added to the flour stream using a feeder
Premix addition is proportional to the rate of flour production
Validation is required to confirm that the mixing process is uniform
feeder
Validation is achieved by quantitative analysis of a representative micronutrient like iron of samples at different times during the process. The results of the tests on the samples should be consistent. Measuring process capability is discussed in section 5 on Quality.
conveyor
Premix can be continuously added into a collection conveyor such as the one shown here.

5. 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

6. 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.

7. 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

8. 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. 8

9. 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.
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
Streams
Out
Premix Feeder
Controlling the feeder manually is only recommended for small-capacity mills.

10. Controlling the Feeder Using Basic Sensors and Interlocking
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
Out
Premix Feeder
Mill/Control
Room Warning
Flow
Sensor
Flow or Level
Sensor

11. 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
Premix Feeder Loss-in-weight
Flour
Streams
Out
Mill/Control
Room Warning
Flow
Sensor
Flow or Level
Sensor
Loss in weight feeder is a different style of feeder.

12. 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
Mill/Control Room Warning
Programmable Logic Controller
Premix Feeder Loss-in-weight
Flour
Streams
Flow
Sensor
Flow or Level
Sensor
Programmable logic controller and appropriate human machine interface in an automated system can continuously match the addition rate of premix to the measured flow rate of flour.
Flour Scale

13. Controlling the Feeder-Summary
In this summary, the numbers in the top diagram correspond to the column numbers in the bottom table. In each column, an X marks the options available for controlling the feeder at that point. The four levels of control are Manual, Basic, Advanced and Automated as described in the previous slides.
Within Basic control there are varying combinations of interlocking and control. These different levels of interlock and control can be used and tailored to the type of premix addition system and milling site capabilities. A mill without automation can properly manufacture fortified flour with a manual system provided the correct policy and procedures are established and followed explicitly.

14. 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% 14

15. 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

16. 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. 16

17. 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

18. 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.

19. 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

20. Premix Feeder: Drum or Roll Type Premix passes between two closely set revolving cylinders

21. 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

22. 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

23. 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
7.5
200 15
400 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

24. Continuous Premix Delivery Systems With continuous feeding, two types of premix delivery are possible. Location of the feeder depends on the type used.
Gravity
Pneumatic
Feeder is placed above the flour collection conveyor
Premix drops directly into flour as it flows through the conveyor
Can be located at several places in the mill
Premix drops into a venturi tube
Premix is blown into the flour collection conveyor

25. 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

26. 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 monitoring
Pneumatic Method of Premix Delivery

27. Premix Delivery System: Pneumatic1 2
Venturi tube with air flow restriction and product inlet
Attaching venturi tube to premix hopper transition
Completed assembly
Venturi Tubes
A venturi tube is a simple piece of equipment that connects the premix feeder and the pneumatic delivery pipes.
Venturi tubes are used to deliver the premix into the flour stream in an entirely closed pneumatic system. 3

28. 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

29. 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

30. 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

31. 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

32. 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

33. Equipment Costs
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
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. 33

34. More Information About Mill Set-up
Contact FFI at
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