Presentation on theme: "Section 3 Setting Up the Mill for Fortification"— Presentation transcript:
1 Section 3 Setting Up the Mill for Fortification Required Equipment and Premix Addition OptionsAnti-bridging and Outlet CoversFeeder ControlsMechanical PrinciplesTypes of Premix FeedersHopper Size and Discharge RatesPremix Delivery SystemsAdequate MixingRecommendations and costs
2 Required Equipment Premix Feeder Measures correct amount of premix Position at appropriate place in production lineSize based on mill’s rated capacityMixing MechanismCan be done during normal flour transport or with special equipmentAssures that premix is uniformly added to flour
3 Premix AdditionPremix is usually added to flour using one of two procedures:ContinuousBatchThe 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 feederPremix addition is proportional to the rate of flour productionValidation is required to confirm that the mixing process is uniformfeederValidation 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.conveyorPremix 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 mixerPremix addition is based on flour batch sizeOperation can be manual or automaticValidation of mixing uniformity is requiredBatch 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 safetyThe cover can be part of the feeder design or it can be addressed in installationLocate the outlet spout for easy opening for inspection and check weighingAt 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 GwirtzFlourStreamsOutPremix FeederControlling the feeder manually is only recommended for small-capacity mills.
10 Controlling the Feeder Using Basic Sensors and Interlocking Monitor for incoming flourSwitch the premix feeder on and off as neededMonitor premix level and flowWarn operator of problemsReduce mill operator workloadAre inexpensiveFlourStreamsOutPremix FeederMill/ControlRoom WarningFlowSensorFlow or LevelSensor
11 Controlling the Feeder Using Advanced Sensors and Interlocking Loss in weight feeder makes feeder setting and monitoring easier for the operatorAn online flour scale more accurately starts and stops the feeder using a baseline flow rateThese system improvements are needed to develop an automated systemPremix Feeder Loss-in-weightFlourStreamsOutMill/ControlRoom WarningFlowSensorFlow or LevelSensorLoss 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 flourRequires appropriate human machine interfaceMost accurate method of flour fortification and exceeds minimal requirementsEasily retrofitted into mills using existing automationMill/Control Room WarningProgrammable Logic ControllerPremix Feeder Loss-in-weightFlourStreamsFlowSensorFlow or LevelSensorProgrammable 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:GravimetricVolumetricAlso known as “loss in weight”Continuously weighs premixRequires greater volume of premix than generally usedMore complex and expensive than required in most cereal millingMore precise than volumetricMost commonly used by screw feedersSimilar to using a measuring cupMinimum 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.ControllerFeeder
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 FeedersFeeders are required for automated batch and continuous addition. Three main types of premix feeders are used to fortify flour.1.Screw Feeder2. Revolving Disk3. Drum / Roller
18 Premix Feeders: Screw Feeders Dispense fixed volume of premix per revolutionSize of feed screw determines the feed rate volume of premix dispensed per revolutionVariable speed controls the number of revolutions per unit of timeWeight of premix dispensed is determined by product densitySize 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 additionPowered by either an AC or DC motorSmall hopper must be refilled frequentlyMore 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 useCan be volumetric, gravimetric or loss of weight feedersEither a DC or AC motor for powerPulley system controls the rotation speedPulleys and wheels of differing diameters make gross adjustments in the feed rate. An adjustable gate is used to make fine adjustmentsRequire more parts and more maintenanceShear pins in the drive mechanism break if large objects (bolts, plastic) get stuck between the rollsIn some newer models, a variable speed DC drive motor allows addition rate to be adjusted electronically rather than mechanicallyVariable speed AC drive motors are also available
22 Feeder Hopper SizeChoose a feeder with a large enough hopper that it does not have to be filled frequentlyRegardless of type of feeder used, the size and number of feeders needed will depend on:Number of production linesHourly production of respective production lineThis 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 ratesA 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 rateMill Capacity(MT/day)Flour flow rate*(kg/min)Premix**Discharge rate(g/min)52.50.420101.550253.81007.52001540030* At 72% extraction rate** At 150 grams premix per metric ton of flour5 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.GravityPneumaticFeeder is placed above the flour collection conveyorPremix drops directly into flour as it flows through the conveyorCan be located at several places in the millPremix drops into a venturi tubePremix is blown into the flour collection conveyor
25 Premix Delivery System: Gravity Feed Things to consider:Feeder is installed above the flour collection conveyorPremix is delivered via a nearly vertical gravity spoutInstall spout away from general suction systemGravity Method of Premix Delivery
26 Premix Delivery System: Pneumatic Things to Consider:Requires equipment such as blowers, valves and pipingConveying lines should have minimal length and directional changesMake the venturi tube accessible for monitoringPneumatic Method of Premix Delivery
27 Premix Delivery System: Pneumatic 12Venturi tube with air flow restriction and product inletAttaching venturi tube to premix hopper transitionCompleted assemblyVenturi TubesA 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 screwAt least 3 meters of conveyor length is normally needed to ensure adequate blendingIntroduce 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 binThe premix is discharged into the start of this special conveyorAt least 3 meters of conveyor length is normally needed to ensure adequate blendingIntroduce 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 translatedAll surfaces in contact with premix are food-grade and non-corrosiveAdjustable delivery control, calibrated from 0 to 100% of feeder capacity220 volt ± 10% 50/60 Hz single phase powerAnti-bridging design to prevent bridging or tunneling of premix in hopperCapable of delivering from 0.04 to 8 L/hr with ± 5% accuracy over full rangeHopper capacity of 8 liter minimumEasy 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 translatedAutomatic shut off / warning capabilityFeeder shuts off when flour flow stopsWarning if feeder is empty or premix fails to dischargePlace feeder on load cells to aid in monitoring premix usage or use loss-in-weight feederIf possible, use electronic control loop to balance feeder discharge to flour production scales
32 Vendor ExpectationsMillers 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 yearInstallation and operating instruction manual that explains in words and diagrams the installation, calibration and maintenance of the equipment and systemTechnical support for installation, training, calibration, and maintenanceRecommended spare parts inventory for items with life span of less than three yearsIdentified lead time for parts delivery and commitment to maintain parts inventory support
33 Equipment CostsEquipmentCost Range (USD)FeedersVolumetric Feeder$1,000 - $8,000Gravimetric Feeder$5,000 - $20,000Loss-of-weight Feeder$10,000 - $21,000Powder Feeder$1,000 - $25,000ScalesElectronic$100 - $2,000Blenders / MixersScrew-Ribbon /Paddle/Cut Flight$10,000 - $25,000Rotary Batch Blender$35,000 - $170,000Vertical Batch Mixer$15,000 - $200,000Cost 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 atCompare 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 flour100 metric tons of wheat a day, at 75% extraction, and premix addition of 150 grams per metric ton of flour