Fine particulate additives such as cement, fly ash, lime and bentonite are pneumatically transferred from bulk tankers and stored in the AccuMix™ 750XB’s 1180 cubic foot self erecting silo. If more than one type of additive is required, an optional self erecting auxiliary silo may be set up next to the plant which is controlled and powered by the AccuMix™ 750XB. The silos are equipped with negative pressure DCE Dalamatic DLM V10/10F dust control systems, which filter and evacuate the pressurized air entering the silo. This process maintains constant silo pressure so as not to affect the consistency of the feeder.
Additives enter the feeder via a specially designed cone, which has been optimized to prevent bridging and designed to maintain a constant and consistent supply of material regardless of the level of the material in the silo. This is accomplished without the need for an aeration system, which will vary the materials consistency. Additives then enter a Gears Inc. designed screw feeder through a 24”x32” opening. The size of this opening combined with oversized half-pitched double flighting and material baffles provide a smooth and consistent flow without the concern of bridging. The maximum capacity of the feeder is 40 tons per hour for most cement. This will vary with the unit weights of different materials. It should be noted that experience has shown the limiting factor with this feeder will be the ability of the pneumatic tanker to off load the fine particulate additive into the AccuMix™ 750XB’s silo.
A Ramsey Granumet DE 10 Impact Flow Meter then weighs the additive. Unlike other forms of inline weighing devices, the impact flow meter is maintenance free, has very few moving parts and it’s calibration and zero will not change once established. The Ramsey Granumet DE 10 is unique in that it measures only the horizontal aspect of the flow force making it immune to zero drift due to material buildup. It has no wear parts or adjustments. Measurement is also not affected by changing impact points or pulsating and surging flows. Force is measured by a Precision Linear Differential Variable Transformer, which is non-contacting and therefore cannot be damaged by shock or overload. The output is sent by means of a noise immune Pulse Frequency Modulated digital signal to the Ramsey Micro-Tech 2106 Integrator. This Integrator provides automatic zeroing, multiple machine directed calibration options, flow rate and total to the plants computer. Accuracy will depend on the type of additive, flow rate, variations in production rate and stability of site. In most situations the manufacturers stated accuracy of better than ± 1/2 % can be achieved (manufacturer’s specifications available upon request).
The computer constantly verifies calibration of the Impact flow meter. The computer compares product load tickets, which are entered by the operator, and silo inventory that is measured by an Endress+Hauser Levelflex FMP 232. Using patented MicroImpulse time domain reflectometry (MiTDR) technology, the Levelflex measures the level of product in the silo to within 1%. This measurement is unaffected by pneumatic filling, moisture, temperature or vibration and requires no calibration or maintenance. The computer uses the silo level to estimate the remaining inventory and compares this to product delivered and used.