Efficient Batching and Transfer of Food Ingredients to Mixers: Majors, Minors and Micros
Introduction: Food Manufacturing
The manufacture of any blended food product typically involves the intermediate process steps of transfer and weighing or “batching” of individual ingredients based upon their weight percentage in a blend.
Depending on this percentage, materials are usually categorized as majors, minors and micros. In many cases, the transfer and weighing of these majors, minors, and micros to the blending step can be a manual and labor intensive process.
In an effort to improve process efficiency and product quality, the complete batching process can be automated.
This includes the automated transfer of the raw ingredients to the batching system and the use of Gain-in-Weight (GIW) or Loss-in-Weight (LIW) batch devices to accurately and efficiently deliver the individual raw ingredients to the process.
By utilizing automated transfer conveying methods for the raw ingredients by either positive or negative pressure, and also highly accurate means of batching, the manufacturer can realize lower overall manufacturing costs, inclusive of lower time required for manufacture as well as more savings on individual ingredients.
Ingredient Transfer: What Method is Best?
The transfer of ingredients is dependent upon a wide variety of process parameters, including material characteristics, distance to be transferred, required rate of transfer, and the type of container in which the ingredient is originally received.
For example, majors such as flour, sugar and salt are often received by truck or railcar and then stored in silos prior to usage. Pressure Differential (PD) trucks and railcars use positive pressure to unload material, whereas other types of delivery to the batching step of process can often be done by either positive pressure or negative pressure pneumatic conveying.
Upon the arrival of the PD truck at the plant, a flexible hose is connected from a pressure blower to the PD truck and another from the PD truck to the conveying line. The system operator selects the desired destination (for example, silo 1 for starch or silo 2/3 for flour on the truck unload control panel.)
When the system is started, the blower pressurizes the PD truck and conveys material via positive pressure from the truck through the conveying line and directly into the silo. Many times, an inline magnet installed in the conveying line typically removes any metal particles which may be present in the conveyed material.
When the high level sensor in the silo is activated, the operator closes the material flow gate on the truck and allows the system to purge the conveying line before finally stopping the system.
Dilute Pneumatic Transfer – Positive or Negative Pressure?
Other possible sources of ingredient delivery include bulk bags or super sacks, boxes, sacks and drums. In all of the ingredient transfer steps, pneumatic conveying systems can be used to transfer these ingredients. These systems can utilize either positive or negative pressure dilute phase conveying.
Positive pressure conveying systems are typically used to transport product over long distances and at high throughputs. Applications which involve pressure conveying often include loading and unloading of large volume vessels such as silos, cyclones, railcars, trucks, and bulk bags.
Conversely, vacuum (negative pressure) systems are often used for lower volumes and shorter distances. One of the advantages of vacuum systems is the inward suction created by the vacuum blower and reduction of any outward leakage of dust. This is one of the reasons why vacuum systems are often used in higher sanitary or dust containment applications.
Another advantage of vacuum systems is the simple design for multiple pickup points. It should be noted, however, that the distances and throughputs possible with a vacuum system are limited due to the finite level of vacuum that can be generated.
Often a combination of pressure and vacuum conveying designs are used for a system, as shown in the process flow diagrams, taking full advantage of the process and efficiencies of each technology.
Batch Weighing Principles
Alternatively, the station can include gravimetric feeding devices, such as screw or vibratory feeders, mounted on load cells or scales (see photo on page 3), which deliver the product to the process by means of Loss-in- Weight (LIW) feeding. As outlined below, in some cases where small amounts of micro ingredients are required for a total overall batch, both methods are employed: LIW feeders for the micros and minors, and GIW batchers for the major ingredients.
Photo: The main ingredient is fed directly from the big bag to the batch weigh receiver while minor ingredients are added via loss-in-weight feeders for higher accuracy
Gain-in-Weight Batching Principle
LIW batching is used when the accuracy of individual ingredient weights in the completed batch is critical or when the batch cycle times need to be very short. Gravimetric feeders operating in batch mode simulaneously feed multiple ingredients into a collection hopper. Adjustment of the delivery speed (on/off, fast/slow) lies with the LIW feeder controls and the smaller weighing systems deliver highly accurate batches for each ingredient.
Once all the ingredients have been delivered, the batch is complete and the mixture is delivered to the process below. Since all ingredients are being delivered at the same time, the overall batch time as well as further processing times downstream are greatly reduced.
This method of batching is often used for micros, (such as trace elements and probiotics) due to the highly accurate requirement of their weight in the mix as well as their ingredient cost. In some cases the LIW feeder for the probiotic material can even be located within a protected enclosure or glove box, in order to ensure no contamination from the environment and a completely contained delivery of the ingredient to the process below.
In GIW batching volumetric metering devices sequentially feed multiple ingredients into a collection hopper mounted on load cells. Each feeder delivers approximately 90% of the ingredient weight at high speed, slowing down towards the end of the cycle to deliver the last 10% at a reduced rate to ensure higher accuracy. The GIW controller monitors the weight of each ingredient and signals each volumetric feeder to start, increase or reduce speed, or stop accordingly. Once all the ingredients have been delivered, the batch is complete and the mixture is discharged into the process below.
The photo to the right illustrates a type of batching station.
It should be noted that this type of batching method is sequential for each ingredient, and therefore generally results in a longer overall batching time than with LIW batching (outlined below) if the number of ingredients is high.After transfer from the material source, the ingredients are usually delivered to the batching station.
This station can include volumetric metering devices, such as a screw feeders or valves, which deliver the product to a hopper on load cells. This method is called Gain-in-Weight (GIW) batching.
As shown in the process flow diagram on page 2, other possible sources of ingredient delivery include bulk bags or super sacks, boxes, sacks and drums. In all of the ingredient transfer steps, pneumatic conveying systems can be used to transfer these ingredients. These systems can utilize either positive or negative pressure dilute phase conveying. The transfer of ingredients is dependent upon a wide variety of process parameters, including material characteristics, distance to be transferred, required rate of transfer, and the type of container in which the ingredient is originally received.