Proven Smart Flow Meter Technology achieves compelling high-rate feeding performance

Measuring and controlling the flow rate of high throughput bulk solids is a requirement frequently encountered in many different industries such as chemical, power, food, animal feed, grain, cement, coal, glass, aluminum and plastics compounding operations. Usually, high-capacity metering equipment is physically large, complex, expensive and cumbersome, and delivers only marginally accurate performance with questionable long term stability. With the development of drift-free digital flow metering technology, higher rate metering and feeding has become more accurate, reliable and economical, and Smart Flow Meters can even double as accurate high speed weigh feeders.

Features
The ideal solids flow measuring device not only features high performance accuracy, but also simplicity of design, long term operational stability, low or no maintenance, insensitivity to ambient conditions, durability and the ability to tare without interrupting production. The K-SFM Smart Flow Meter has no permanently moving parts, thereby ensuring gentle handling of the bulk material – a distinct advantage over other flow meter technologies. It employs two patented digital Smart Force Transducer load cells (SFT) to independently measure the weight and speed of the material flow. With these two readings known, flow rate is easily determined.

Operating principle
The Smart Flow Meter’s principle of operation is based on Newton’s second law of motion: F=ma (force = mass x acceleration). Bulk material flows by gravity into the upper measurement channel, an inclined chute mounted on an SFT. The force acting perpendicularly on the chute channel continuously generates a weight signal representing the material’s mass. The bulk material then flows into the lower, vertical channel with the second SFT, measuring the force of impact, thus enabling to determine velocity through a mathematical calculation based upon Newton’s law. Using the signals from both load cells, the flow rate is then determined per unit of time.

In practice, the two force measurements reflecting weight (chute channel) and speed (vertical channel) are combined with parameters of design geometry (upper measurement channel length and slope) to determine the flow rate, even though the material accelerates in transit through the device.

Taring option
The Smart Flow Meter is fitted with a bypass channel to enable taring at any time without interrupting the metering process. Taring may be called for when sticky materials cause build-up inside the device or when major changes in ambient temperature or the temperature of the bulk material occur during operation. The bypass flap built into the inlet allows the material flow to be diverted to a separate internal channel. Whilst the material flow is redirected, the new tare weight is determined and the zero value is reset. As soon as re-taring has been accomplished, the flap moves back to the standard position and the material flows down the regular metering path of the device. Re-taring can be done manually or by setting up the controller to periodically perform the operation.
 
High-accuracy digital weighing
The Smart Flow Meter employs the rugged Smart Force Transducer digital weighing technology that exploits the dependency of a vibrating wire’s resonant frequency on its tension to measure applied loads. Through mechanical means the applied load is transmitted to the wire, causing a change in its resonant frequency from which the value of the applied load is computed by an on-board microprocessor. A fully calibrated (linearized, spanned, and temperature compensated) signal is then transmitted via RS485 serial communication to the KCM feeder controller.
Used in this way, the SFT has practically no deflection. The SFT is dynamically responsive to the instantaneous changes in loading which are characteristic of any flow meter operation. A weighing resolution of 1:4,000,000 in 80 ms is achieved. Due to its fully digital design, the SFT features exceptional long-term measurement stability, eliminating the need for periodic load cell recalibration.

Design and construction
The Smart Flow Meter is available in two capacities: Model K-SFM-275 for bulk material flows from 2,000 to 36,000 kg/h (4,400 to 79,200 lb/h) and model K-SFM-350 from 5,000 to 120,000 kg/h (11,000 to 264,000 lb/h). A short and long term accuracy of <±1% can be achieved without calibration. A simple field calibration procedure is available which can increase accuracy even further. Both models are rated IP65 (NEMA 4) with all stainless steel construction 1.4404/1.4435 (AISI 316 L). A large access door is provided for easy cleaning. ATEX 3D and 2D versions are available for applications in hazardous locations.

Applications
The Smart Flow Meter excels as a high rate gravimetric feeder, or as a batcher or meter in a wide variety of industries. It can handle many types of free flowing bulk materials with particle sizes from 0.02 mm up to 10 mm. The bulk material’s angle of repose should be less than or equal to 40 degrees (measured from horizontal). Bulk material shapes easily handled by the Smart Flow Meter include granules, chips or fibers. Typical applications include feeding control at high rates with a rotary valve or similar device at the infeed, measuring batches into filling or other downstream equipment, or simple metering for materials management or data logging.
 
Application Examples
1) In detergent manufacture the liquid base detergent is fed to a spray tower where it is converted into a powder. The nature of the process makes it difficult to regulate the spray tower output. Nevertheless, additives such as powdered enzymes and liquid perfume require to be accurately proportioned to the wild flow of the powdered detergent.

A Smart Flow Meter positioned at the discharge of the spray tower provides for very precise regulation and metering of the detergent flow. With the additive feeders downstream slaved to the mass flow output signal of the Smart Flow Meter, the additives can be accurately fed to the production process, resulting in a more consistent quality of the end product as well as savings on costly additives.

The Smart Flow Meter as well as the additive feeders are each equipped with a KCM control module that seamlessly integrates with the SmartConnex control environment, capable of controlling up to 24 feeding and metering devices simultaneously.

2) In large-scale coffee production, the proportions of the actual coffee beans and the skins in the coffee fruit are of concern to coffee processors. The waste skins are removed either by dry or wet methods, resulting in the naked coffee beans which are then ready for further processing. A low bean-to-skin weight ratio means that less coffee can be produced from each unit of purchased coffee fruit. Coffee processors therefore require a means of identifying supplies of coffee fruit with thin skins.

In order to determine the weight of the bean skins in a production process, two Smart Flow Meters are employed: one immediately preceding the skin removal section and the second one at the skinned bean discharge. The difference in weight between the two flows represents the weight of the skins.

3) In powdered sugar production, large amounts of crystallized sugar are fed from a storage hopper into a hammer mill while adding a small proportion of starch or calcium phosphate. Because of the high throughput rate of the crystallized sugar, as well as its abrasive nature, a standard loss-in-weight feeder is an unnecessarily expensive solution for the main ingredient.

A Smart Flow Meter installed below the storage hopper is the better choice. A conveyor screw feeds the crystallized sugar from the hopper into the Smart Flow Meter which then measures the mass flow of the sugar and regulates the speed of the conveyor screw in order to maintain the desired throughput rate. A small loss-in-weight feeder slaved to the sugar’s flow rate accurately proportions the additive by weight.

Because the Smart Flow Meter has no moving parts in permanent contact with the product, better efficiency is attained and there is less need for maintenance or cleaning.

4) In polyethylene compounding systems, Smart Flow Meters offer significant advantages over traditional weigh belt feeders for handling the main components. The Smart Flow Meter is easy to operate, can handle large feeding capacities, offers high long-term accuracy and requires only minimal maintenance. Furthermore, change-over to alternative raw material sources is easily done. The automatic taring option enables to compensate for any material build-up inside the device without interruption of the production process.

Depending on the recipe, a number of raw materials can be fed to the process by Smart Flow Meters. Feed rates often range between 10,000 and 20,000 kg/h [22,000 to 44,000 lb/h] but can also be significantly higher. Material supply to the flow meters can be accomplished by screw feeders or rotary valves, for example. In addition, additives can be fed into the extruder by weigh belt feeders and loss-in-weight feeders.

Compared to the weigh belt feeder solution, the Smart Flow Meter offers considerable savings on raw materials, and with maintenance costs around nil, it also contributes to substantially reduce operational costs.
 
5) In raw meal kiln feeding in cement manufacture, closed-loop control typically uses a metering feed gate to control flow rate. Both Smart Flow Meter models can be used to precisely regulate raw meal to the kiln preheater.

Due to the necessity for long, uninterrupted periods of continuous operation, a weighing hopper with load cells is normally used. This allows for periodic automatic checks and adjustments based on the loss-in-weight principle. Should on-line calibration corrections be required, the controller will automatically apply that correction over time to avoid destabilization of the kiln.

6) In feeding pulverized coal in a cement kiln firing application, the Smart Flow Meter is used in closed-loop control with a rotary valve or screw prefeeder. Model K-SFM-275 with a 10-bar rated jacket controls flows of pulverized coal, and is fully compatible with pump or injector feeding systems. Multiple Smart Flow Meters may be connected to a single coal storage silo to simultaneously feed the main burner, precalciner and other preheating positions. When the coal storage silo is mounted on load cells, regulation of the silo filling level and automatic feeding precision checks are possible.

The combination of an appropriate feeding device with the Smart Flow Meter results in the ability to proportion the introduction of additives to the finished cement, or to accurately measure loading of the final product.

Conclusion
By combining stable, high-resolution digital weighing with an innovative approach to continuous flow meter design, reliably accurate flow measurement and control is available, without the complexities, cost, or performance limitations of traditional technologies. The application of smart digital weighing technology to high capacity solids metering and feeding brings quality-conscious processors in a wide range of industries the ability to improve their processes and simplify their operations.