Efficient Batching and Transfer of Food Ingredients
Introduction
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 using either vacuum 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.
PD Transfer
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 to remove 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 operation.
Pneumatic Transfer: Vacuum or Pressure?
As shown in the process flow diagram, 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 vacuum or pressure dilute phase conveying.
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 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
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. Alternatively, the station can include gravimetric feeding devices, such as screw or vibratory feeders, mounted on load cells or scales, 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.
Gain-in-Weight Batching Principle
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 below illustrates this 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.
Loss-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.
Multi Destination Majors Batching
When major ingredient batching requires a single ingredient to be delivered to multiple stations (see process diagram on bottom) or multiple ingredients delivered to a single destination, scale hoppers with specialty weighing switch valves mounted above the scale hopper can be used. After the fluidised material is discharged from a source such as a silo or bulk bag, it will typically drop through a rotary valve, through a sifter (if required), and is then metered into the conveying line by another rotary valve. Once in the convey line, it is then transported to the weighing switch valve, located above a scale hopper.
Weighing Switch Principle of Operation
The weighing switch valve operates on a diverter type principle and is ideal for diverting material directly into a hopper from a conveying line. Due to the valve’s low-clearance height, it is ideal when requiring inline diverters in tight spaces. As shown in the figure below, the valve includes an internal wafer type device which allows for the discharge of material into the hopper below when activated in the correct discharge position. When the scale hopper below indicates the batch is complete based on the weight signal, the weighing switch valve can be immediately shut. This allows for the transfer of the excess material in the conveying line either to the next process or scale hopper, or back into the original source. This closed loop design results in a more efficient method of product transfer with higher product yields.
Batch Weighing with Scale Hoppers
Scale hoppers are receiving hoppers suspended on load cells for ingredient batch weighing (see photo right and diagram on bottom). The material resides in the scale hopper until the precise weight and/or combination of materials is achieved. With the scale weighing system, weigh accuracies of +/- 0.5% of the full scale capacity can be expected. Once the desired weight has been achieved, the mixer then calls for material, a butterfly valve opens and the material in the scale hopper is discharged.
Options in Cleaning and Construction
Depending upon the ingredients to be batched and frequency of batching, a variety of design executions can be provided for the equipment to reduce the overall
cleaning or changeover steps. Stainless steel is generally used for the contact components, but sometimes FDA approved epoxys can also be used for large volume
scale hoppers or silos in order to reduce overall equipment costs. Conveying receivers can be designed with retractable spray balls for wash-in-place cleaning
to ensure quick changeover and minimal contamination between material runs.
In cases where minimal product contamination is desired, such as delivery of isolated minors like probiotics, a specialized glove box design bag dump station can be provided. This ensures protection of the product from the outside environment.
When designing for a batching system, it is important to discuss all aspects of the design requirements, including the expected changeover and cleaning times, as these options can greatly affect the overall system cost.
Conclusion
Properly weighing and accurately delivering the ingredients without manual intervention can result in a number of process advantages, including fewer mistakes, better accuracy, lower bulk costs, improved product quality and savings in manufacturing costs. In addition, utilizing devices and systems which involve highly accurate weighing and metering of precious and expensive ingredients such as probiotics and vitamins can result in lower overall ingredient costs. The highly experienced personnel of Colormax Systems can provide a wide variety of design and layout options in both ingredient transfer and delivery to help manufacturers to not only lower process costs but also to improve efficiency and product quality.
