A processor of aluminum silicate minerals (i.e. clay) was experiencing inefficiencies in its particle reduction process. The inefficiencies were so severe that the corporate office began to inquire.

At this facility raw materials are brought in and stockpiled both in indoor and outdoor areas. The processing of the material involves drying and particle size reduction milling. Some of its customers require course granular materials and others require the minerals to be reduced to a very fine powder. The finer powders are primarily used in porcelain and ceramic markets, where the largest demand is. The main issue was that the company could not achieve efficient processing of the finer powder. The final step in the process consists of passing the milled powder through a screening classifier. The product that is successfully reduced to the desired particle size passes through the screening classifier. If the material has not been reduced to the desired particle size it will not pass through the screeners. This out-of-specification material is ejected and re-directed back to into the milling process using a pneumatic (pressure) conveying line. The diameter of the conveying line (metal pipe) is approximately 8 in.

Investigation indicated that a significant amount of material was not being milled to the desired particle specification (the finer powder) on the first pass through the mill. The classification screeners were catching the out-of-spec material and re-directing it back into the mill. Of course, this re-direction took capacity, time, and energy away from the ability to process additional new material entering the mill. The mill itself was properly designed and maintained to mill to any size particle in one pass.

Additional examination revealed the moisture content of the raw stock was directly proportional to the ratio of the amount of material being re-directed back into the mill. The moister the material, the more difficult it was to produce the fine powders to specifications. It was tough to control the moisture level of the raw material since it arrived from different sources and was stored in various indoor and outdoor areas of the facility. One answer was to increase the temperature of the dryer. However that resulted in inefficiencies in the drying process since the moisture content of the feedstock varied. The dryer had to be set at a temperature that would sufficiently dry the worst-case damp feedstock. When relatively dry feedstock was processed, the hotter dryer setting was simply wasting energy.

Solution

As a solution the mineral processor implemented a QuantiMass ultra mass flow measurement system, which was installed on the pneumatic conveying line that redirected the out-of-spec material back into the mill. The QuantiMass would provide real-time measurements of the quantity of material passing back into the mill. An increase in the flow rate reported by the QuantiMass system indicated the mill efficiency was decreasing. Adjustments could then be made to increase the dryer temperature to ultimately restore efficiency.

The company felt an in-line (also referred to as on-line), continuous solids flow measurement sensor would help them achieve its goals. The real-time monitoring of the flow-rate for the actual amount of feedstock being ejected and re-directed from the screener to the mill would allow them to determine quickly that the material was too moist and the process was becoming inefficient, which would allow them to make appropriate adjustments to the dryer. They could easily install the sensor into their process. Plus, the company connected the solids flow measurement sensor to the optional controller to have immediate on-site visibility to the flow data.

Considerations

In order to achieve maximum accuracy from this type of solids flow measurement sensor, a few factors should be taken into consideration:

Compact, in-line solids flow measurement sensors are commonly based off of microwave technology. The measurement process of the sensor is centered on the Doppler effect. The mass flow-rate is determined by evaluating the frequency and amplitude changes during the measurement process. Reproducible measurements can be made for most powders, dust, pellets and granules, usually up to the size of 0.75 in.

Common reasons for operating these types of sensors include obtaining in-line, continuous solids flow measurements for accurate validation of material quantities, measuring for proper mixing (blending) of additives in specific recipes, and monitoring for variable flow quantities due to disturbances like different densities.

Key Criteria

Some of the key criteria that the company was looking at when it chose the QuantiMass system were:

Summary

In summary, an in-line solids flow measurement sensor can be an easy way to incorporate a system that helps automate and verify the quantity of material being conveyed in a process. It can usually be added without requiring major changes to existing processes.

For more information, contact Monitor Technologies LLC at 630-365-9403, [email protected], or www.monitortech.com.