Many manufacturers across nearly every industrial sector blend or batch products together using predetermined recipes. In fact, any process with more than a single ingredient will likely batch or blend at some point within that process. The key to accurate and repeatable batch/blending is to control the flow rate of the individual products and to measure them as they are batched or blended. Although there are many ways to accomplish this, finding an accurate and repeatable batch blending system will assist in maximizing profits and minimizing costs associated with product loss or waste.

Typical problems with volumetric and loss in weight batch/blend systems

While there are likely just as many ways to batch/blend as there are manufacturers who utilize them, two that are often employed, especially for the blending of flowable solids, are volumetric devices and loss-in-weight gravimetric devices. Unfortunately, there are some drawbacks to using these types of devices and when these drawbacks turn into problems, these problems can lead to the entire batch/blend system working improperly. With improper batch/blend systems, customers may begin to see variations in product quality from batch to batch. Even within batches, some ingredients may be over applied or under applied, leaving an end-product with serious quality issues. The result is, at best, a waste of one or more individual ingredients, and at worst, it may cause an end-product to be completely unusable.

Figure 1: Batch blending. Source: Eastern InstrumentsFigure 1: Batch blending. Source: Eastern Instruments

Volumetric devices deliver products based on an assumed volume (determined by opening a valve, for instance, or rotating a screw at a certain RPM). Using a volumetric batch blend system, means that customers are not actually measuring any of their ingredients, but are rather assuming their flow rates and thus, their batch size. Unfortunately, if the density of the ingredients shifts or changes at all, these devices will not be able to react, making it very easy to over apply or under apply an ingredient. When this happens, the batch/blend will most assuredly be impacted.

Loss-in-weight batch/blend systems are typically designated by a hopper on loadcells that delivers or doses products from the hopper. They are typically more accurate and repeatable than volumetric systems as they are gravimetrically weighing each of the ingredients rather than assuming their flow rates/batches. The accuracy of these devices, however, is hampered by their very design. At some point, the hopper will need to be refilled and when it does, the device will have to run “blind” while their hopper refills, meaning they will no longer be measuring the flow/total. Also, these devices tend to “dribble” fill the final amount of the product as they approach their target during dosing, which greatly reduces the flow rate of the material coming out of the hopper and greatly increases batch times. This “dribble fill” feature increases this device’s accuracy, but if “time is money” then these devices can be costly.

The CentriFeeder: The solution to batch/blending needs

The solution to accurate batch/blending is to gravimetrically measure the flow rate and total of each of the individual ingredients being batched/blended and to do so without the device being affected by refilling hoppers or bins. The device should also quickly start and stop the flow rather than “dribble fill” for an extended period. The solution is Eastern Instruments’ newest line of solids feeders, the CentriFeeder MCV. The CentriFeeder MCV is a solids feeder that is specifically designed to both measure and control the flow of granular or pelleted products. By integrating a flow measurement device along with the flow control capabilities of an integrated slide gate, the CentriFeeder MCV can output an extremely accurate and easily maintained consistent flow that can be used for batching, blending, ratio control or even bulk density measurement.

For both batching and blending applications, the CentriFeeder MCV provides an accurate, real-time flow signal, as well as near perfect control of the flow rate or total. For recipe-based blending applications, control the flow rate of individual ingredients or combine several CentriFeeders for near perfect recipe control. For controlling ingredients entering a batching process, or for filling, use the CentriFeeder to control the total of one or more ingredients included in the batch/fill.

How it works

The CentriFeeder MCV is a gravimetric device that builds upon the patented flow measurement accuracy of the CentriFlow Meter by integrating the flow controlling capabilities of an integrated slide gate. Combined into a single, multifunctioning weight feeder, the MCV measures the flow rate and total product as it passes through the feeder, but also controls the flow rate and total to a predetermined setpoint. As product flows through the MCV and over the curved measurement pan, the instantaneous flow rate is measured and sent to the included digital electronics where an internal PID control loop is established. This PID control loop modulates the integrated control valve in order to maintain a flow rate. The CentriFeeder MCV is able to respond to changes in flow rate within 100 ms and can typically be within +/-1.00% of the flow set point within one second. Because it only measures the product that passes through it, it does not rely on weighing entire hoppers and so is impervious to accuracy errors due to refilling, making it a perfect alternative to conventional loss-in-weight feeders. The result is an extremely easy and accurate way to batch/blend any granular product including plastic pellets, sand, seeds, grains, fertilizers and more.

Capacity of the CentriFeeder MCV

With three feeder sizes, the MCV can accommodate a wide range of flows. The smallest feeder, the CentriFeeder MCV 1.5, can measure and control flows down to 200 lb/hr, while the CentriFeeder MCV 6.0, the largest feeder, can measure and control flows up to 16,000 lb/hr or more. When used for dosing or filling, the CentriFeeder MCV can quickly fill containers as small as 1 kg.

Using the CentriFeeder MCV for flow rate control

One of the important uses of the CentriFeeder MCV is to maintain a consistent and accurate flow rate for blending or for continuous operations. To set up the feeder for continuous operating or for blending applications, simply enter a flow rate set point into the feeder’s electronics. The feeder will automatically measure the flow rate of the product as it crosses the measurement pan. The flow signal is sent back to the electronics, where it is compared against the desired set point. The integral slide gate is then modulated appropriately, using position information provided by the blade’s position sensor to reach and then maintain the set point.

Figure 2: The CentriFeeder MCV. Source: Eastern InstrumentsFigure 2: The CentriFeeder MCV. Source: Eastern Instruments

Using the CentriFeeder MCV for batching or filling

The CentriFeeder MCV is also used to either dispense discrete batches, or to fill containers as small as 1 kg. Using a predictive algorithm, the feeder’s microprocessor determines the target value required to compensate for the weight of in-flight material and is thus able to stop flow before the set point has been reached, making for extremely accurate fills.

Using the CentriFeeder MCV to blend products

When used in conjunction, multiple CentriFeeders can blend products together. The flow rates of each product are set in their respective electronics in order to maintain the proper ratio of the different products based on a predetermined recipe. The recipe can either be entered via the CentriFeeder’s touch screen HMI or through PLC communication.

Summary

The CentriFeeder MCV solids feeder from Eastern Instruments is a unique and extremely versatile device that can be used for flow rate control and blending as well as for batching or filling. Its extreme accuracy ensures batches or blends to within +/- 0.5% and its response time — reaching set point within one second — means better control of a process. Moreover, its compact design ensures that it will fit anywhere. When batch/blend systems work correctly, end-products will be perfectly proportioned, and it will be consistent and reproduceable every time. Eastern Instruments can help. Visit their website today.