With annual output exceeding one million tons, HeidelbergCement AG subsidiary Lehigh Inland Cement in Edmonton, Canada, requires highest quality equipment and systems to ensure the consistency and accuracy critical to producing cement for its customers throughout Canada and the U.S. Accordingly, Lehigh Inland relies on Schenck Process weighing and feeding systems to maintain a consistent feed to its kiln and to meter fly ash into its finish grinding mill.

Providing accuracy in Lehigh's kiln feed system is the Schenck Process Multicor-S800 Coriolis Mass Flow Meter. Additionally, a Multicor-S80 Coriolis Mass Flow Meter has been installed for dispensing fly ash in the finish grinding mill to produce a new interground-type cement.

THE PROCESS

The cement-producing process for Lehigh Inland begins at a quarry 190 miles from Edmonton, where limestone is mined and crushed into 7.9-in. chunks. From the quarry, as many as 300 rail cars of limestone per week are transported to the Edmonton plant. After unloading and stockpiling, the raw material is fed into a hammermill crusher, along with clay mined at the plant site. The limestone and clay are mixed at a 3:1 ratio.

The mixture, known as preblend, is conveyed to the preblend dome, where it is stacked by a radial arm stacker in a continuous, circular pile up to 700 layers deep (equivalent to 40 ft.). Further mixing of the preblend occurs in this area before conveyance to the surge bin.

A temporary preblend holding station, the surge bin feeds the mixture to a conveyor system, where small amounts of sand, bottom ash, iron ore, and more limestone are added as needed to ensure that limestone and clay quantities exist in correction proportion to produce quality cement. From the surge bin, the preblend is conveyed to a roller mill.

The roller mill's three 27-ton steel wheels pulverize the preblend into a powder-like mixture, thereby producing more than 230 tons of kiln feed per hour. At this stage, the kiln feed is sampled multiple times to check for compliance with specification criteria. Correcting for deficiencies in any of the raw materials, adjustments are made from the additive silos to produce a suitable mixture. The kiln feed then is carried from the roller mill by high pressure air to the homogenizing and kiln feed silos, where continual mixing maintains a powdery consistency.

MULTICOR-S800 CORIOLIS MASS FLOW METER

After leaving the silos, the kiln feed enters a calibration bin and proceeds to the Schenck Process Multicor-S800 Coriolis Mass Flow Meter. Besides key features such as dust containment, compact design, and direct weighing technology, the S800 provides Lehigh improved accuracy and reliability as compared to the producer's previous kiln-feeding system, which involved pneumatics transporting materials into impact flow meters. Air slides were used to deliver kiln feed to and from the flow meters; and, the combination of impact flow meters, pneumatics, and air slides created pressure and ventilation differences from one side of the system to the other. The resulting sucking action on the flow meter paddle would cause it to go down, thus adversely affecting the system's overall accuracy.

Upon installation of the Multicor-S800 Coriolis Mass Flow Meter, Lehigh Cement Plant Engineering Superintendent Dave Moule observed, “For our particular application, the variation in pressures or ventilation did not affect the Schenck Process coriolis meter. We could count on the equipment to give us the same results regardless of any outside forces or plant disturbances.” Moreover, increased accuracies produced by the Schenck kiln feed system allowed Lehigh to run at a higher feed rate, which has led to greater production capacity. The Multicor-S800 Coriolis Mass Flow Meter is capable of feed rates up to 600 tons per hour with accuracies of ±1%.

After being metered from the S800, the kiln feed enters an air slide and then a high-pressure air pump, which conveys materials to the top of a preheater tower. Entering the tower at a temperature of 194°F, the material falls within 20 seconds through the tower and emerges from the bottom at a temperature of 1,562°F. From there, the feed enters the kiln, where it is heated to 2,552°F, resulting in the creation of clinker. Cooling, grinding, and milling of clinker into cement produces the finished product, which is stored in one of 24 on-site silos, awaiting shipment to customers in bags and bulk form, by rail or truck.

MULTICOR-S80 SOLIDS FLOW METER

As part of a separate process within the Edmonton plant, the Multicor-S80 Coriolis Mass Flow Meter was installed for introducing fly ash into the finish grinding mill to produce a new interground-type of cement. Lehigh's Moule explained, “This process allows us to reduce the clinker content in the cement product by substituting unclassified ash, which has cement-type properties, without compromising product quality. The result is a substantial energy savings.”

Traditionally, fly ash has been used in concrete at levels ranging from 15% to 25% by mass of the cementitious material component [Thomas 2007]. In view of the vital role that precise combination of constituent materials plays in cement production, the importance of accuracy provided by the Multicor-S80 cannot be overstated. Fly ash typically is provided to cement plants at little or no cost; yet, an inadequate amount of the material metered into the process due to inaccurate equipment reduces cost savings realized through the use of fly ash by the producer. An even more serious consequence is off-spec product.

Installing the Multicor-S80 for precise measurements in a dust-tight compact design enabled Lehigh to reach accuracies of ± 0.5% when metering over two tons per hour. Moule added, “A short pay-back period also made the equipment an excellent investment for Lehigh.”

CEMENTING SUCCESS

The Multicor-S800 Coriolis and Multicor-S80 mass flow meters have allowed Lehigh Inland Cement to increase kiln-feed and fly-ash metering accuracies, while providing the added advantages of dust containment and a compact design that suits plant space requirements. Moule affirmed, “With the coriolis meters in place, we obtained the reliability and accuracy we were seeking.”

Reference: Thomas, Michael (2007) “Optimizing the Use of Fly Ash in Concrete,” Portland Cement Association, Skokie, Ill.

This information was adapted from materials provided by Schenck Process, Whitewater, Wis., www.schenckamericas.com