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32 / November 2020 powderbulk.com SOLIDS WEIGHING AND BATCHING OVERVIEW — PART II Whether you're manufacturing cement or seasonings, if you're in the powder and bulk solids industry, you're going to need to weigh and batch ingredients to come up with a consistent end product. This two-part article describes how to weigh and batch ingredients in an accurate and cost-effective manner. Part I, which appeared in the September issue of PBE, explained the different ways of how materials can be measured, while Part II explains how to incorporate the weighing and batching methods into your process. Todd Smith, K-State Bulk Solids Innovation Center dient source is the control device, and better accuracy will again be achieved if the feeder has a fast speed and a dribble speed. In addition, the conveying sys- tem's source feeder will require a quicker pre-act point for shutting off the feeder since there will be more material in flight between the source and the receiver. But fortunately, the in-flight quantity — the amount of material that's been discharged from the feeder but has not yet settled onto the scale — should be repeat- able from batch to batch with most materials. And the in-flight time is negligible since a typical dilute-phase system operates at a conveying speed of several thou- sand feet per minute. Is it possible to weigh multiple materials in the same filter-receiver? Yes, and a filter-receiver on load cells operates similar to how a gain-in-weight hopper does. This means that each ingredient must be conveyed and controlled one at a time. Sometimes, the gain-in-weight filter-receiver is used as the primary weighing device, as previously described. However, in other cases, the primary weigh- ing of each ingredient is done earlier in the process, such as at a bag-dump station. When this is the case, the filter-receiver's load cells are used as a "check- weigh" or verification point to make sure the material weight or amount is correct before dispensing it into the process. No matter where weighing takes place in the system, adding a gain-in-weight method to your process's material handling equipment can be done at a modest cost, resulting in a fairly inexpensive system. System 2. Another conveying and batch weighing system also uses a receiver on load cells as a gain-in- weight hopper but eliminates the hopper's filter section through the use of a special scale valve, as shown in Figure 2. The scale valve has two positions. When in the "fill" position, the valve directs material and air into the weigh hopper below. Most of the material is retained in the hopper, but the conveying air and Weighing and conveying Frequently, you can build gain-in-weight or loss-in- weight methods into equipment that'll be needed for processing your bulk solids. This reduces capital costs and the amount of equipment required for your ingre- dient handling system. System 1. A typical vacuum conveying system con- sists of one or more ingredient sources with piping to a filter-receiver, as shown in Figure 1. From pet food and plastics to chemical and pharmaceutical ingre- dients, the filter-receiver collects the material, and its self-cleaning filter media separates the dry material from the conveying air. If the receiver is mounted on load cells, then it can act as a gain-in-weight hopper and all of the previous considerations for a gain-in- weight hopper would still apply [Editor's Note: See "Solids Weighing and Batching Overview — Part I" in September's issue]. In this case, the feeder at the ingre- FIGURE 1 Vacuum conveying system with a filter-receiver on load cells Filter-receiver on load cells Clean air to vacuum pump Pneumatic conveying pipeline Load cell Small bag material sources Bulk bag material sources