To fluidize immobile cement, thereby eradicating ‘pack set’ — a perennial problem at cement plants and shipping terminals — Mitsubishi Cement Corp. installed Pneumatic Modulation Technology (PMT) earlier this year at its Long Beach shipping terminal and Lucerne Valley production facility. Technology Evaluations, Inc. (TEI), supplier of fluidizers using PMT, brings considerable expertise in process innovation, yet is relatively new to the cement industry; nonetheless, Mitsubishi Cement Vice President and Plant Manager H.O. “Bud” Biggs chose to take the risk that adopting new technology inherently entails. And, he's glad he did. “The TEI Fluidizers are working great, and we have just ordered additional units to gear up for next year's production,” Biggs reports.

THE FACILITIES

At Long Beach, Mitsubishi's shipping terminal has a storage capacity of 58,000 tons. Its 200-ft-square storage bunker is equipped with 30,000-plus sq ft of air-slides incorporating nine discharge ports and three blowers. Cement is transferred to truck silos using two-phase pneumatic conveying fed by Fuller-Kinyon style (screw-type, volumetric) pumps.

Like many other storage units that use air-slides, the last 10% to 15% of inventory at Long Beach has been difficult to extract, flowing slowly and erratically. The current cycle of high cement demand highlights the lost value of dead inventory — lost sales — and the significant flexibility in shipping logistics that a small increase in storage capacity affords. Accordingly, Mitsubishi constructed additional overhead storage capacity and applied PMT to improve its bottom line and throughput capacity.

Located about 100 miles from Los Angeles, Mitsubishi's Lucerne Valley plant brings on line cement and clinker production capacity of 1.6 million tpy. Storage capacity at the facility comprises a grouping of 12 silos, each 30 ft in diameter and 70 ft high. The storage silos are equipped with air-slide systems of varying configurations, some dating back 50 years. On occasion, cement in these silos has been difficult to withdraw.

The silos are uniquely designed to make use of additional storage capacity in the interstitial areas, called ‘star bins’. Also equipped with air-slides, these star bins have a history of problematic discharge — especially ‘Star Bin E’, which has resisted all attempts to discharge cement for 20 years.

THE TECHNOLOGY

Tony Witheridge, a principal of Technology Evaluations, Inc., invented the TEI Fluidizer in the course of investigating the root causes of problems associated with mobilizing Class C Fly Ash. Explaining PMT, he says, “Basically, our technology splits a single air flow into two streams, each modulated with multiple frequencies. By increasing the air-to-particle contact ratio, PMT doubles the effectiveness of air flow, providing fluidizing capacity equal to the original single flow for each of two streams. Each split flow requires connection to a separate airslide, as each modulated wave front is 180 degrees out of phase with the other. Recombining the two flows would simply yield continuous flow again.”

The benefits of improved particle-to-air contact are said to include a drastic decrease in energy requirements; reduced internal powder friction; and, improved overall fluidity. According to TEI, the end result compares favorably to traditional systems providing continuous air flow: PMT better fluidizes fine powders, improves overall transfer rate using less energy, and inhibits the formation of rat holes.

THE LONG BEACH TRIAL

While its track record in cement applications was limited to independent lab testing, the TEI Fluidizer using Pneumatic Modulation Technology prototype had been successfully field tested on Class C Fly Ash. Thus, given an understanding of process theory, plus the escalating pressures of market demand and the high cost of ship wait time, Mitsubishi agreed to a trial of the equipment at its shipping terminal.

To facilitate a field test, Mitsubishi removed and modified flanges to hook up the TEI Fluidizer trial unit via 4-in. cam locks and flexible hose connections. The 130-lb TEI trial unit is highly portable, a significant benefit due to limited space beneath the storage bunker. Under the direction of Terminal Manager Marty Marcum, responsible for overseeing the trial as well as maintaining full-bore terminal operations, pipework modification for the field test was completed within a couple of days.

Following pipework modification, baseline performance was established for a designated area using normal air-flow conditions. The area designated for observation exhibited erratic discharge and was located nearby a viewing hatch. As part of establishing baseline conditions, repeated attempts were made to empty that portion of the bunker using continuous air flow, and drop measurements were made to confirm stored cement depths. After determining that the cement would discharge no further, the TEI Fluidizer trial unit was put to the test.

Within an hour, the TEI trial unit was uncrated, connected to the existing blower, and put in operation. Soon apparent was clear evidence that PMT provided a less erratic cement flow and improved transfer rates, TEI specialists note, in part because the discharging cement contained less air volume. Increased fluidity also enabled smoother discharge, allowing further opening of the trim valve leading to the FK pump. Overall transfer rates were increased by an estimated 25% above normal flow conditions.

Pressure readings at the FK Pump showed the Fluidizer maintained a near constant pressure in the range of 10 to 15 psi throughout its application. After pressure readings reached zero during the third day of trial unit operation — and the cement dust was allowed to settle overnight — both Mitsubishi and TEI were eager to observe the effects of the Fluidizer inside the storage bunker as the inspection port was removed. The TEI Fluidizer trial unit extracted over 12 feet of immobile cement, clearing powder down to the air-slide cloth.

THE LUCERNE VALLEY TRIAL

The success of the Fluidizer trial at its shipping terminal prompted Mitsubishi to implement a second trial at its cement facility. To that end, plant personnel selected a transition silo that had resisted discharging the bottom 20 feet for several years. Pipe modifications to connect the trial unit via cam-locks and flexible hoses were effected, separating the external air manifolds into two fluidization zones. Besides supplying twice the air-slide coverage, system developers affirm, the two-flow split provides the benefit of eliminating backpressure waves upstream.

On the first day of using the trial unit, the silo's discharge opening was continually plugged with large cement chunks, blocking the flow of cement. Once the rocks were removed after the first day, unimpeded flow was achieved. Initial changing hues of discharged material attested to the Fluidizer's ability to mobilize stagnant, stratified cement. Previous records indicated a maximum depth to cement in the silo of 57 feet. Using the trial unit, depths of 67 feet were recorded, indicating about 15% added storage capacity.

The effects of PMT were tested also on a 60-ft section of a closed-type air-slide chute bearing the marks of a substantial number of hammer impacts. The internal condition of the cloth and walls showed significant encrustation that impaired flow and allowed cement lumps to accumulate, further impeding withdrawal. A few minutes of PMT air effectively reconditioned the chute by removing the encrustation and blockages. A dramatic increase in cement flow was accomplished in the chute due to more fluid cement and the mere 4 degree working angle that PMT requires.

APPLICATION: INSTALLATION AND OPERATION

Following the success of the TEI Fluidizer trials, Mitsubishi purchased 6-in. units for both the shipping terminal and cement plant. Though the models are the same, each site uses the Fluidizer differently in application.

At Long Beach, the shipping terminal air-slide design and operation called for a fixed installation. The site's existing air manifold is fairly complex, as each of nine discharge stations has a tight array of 34 pneumatically controlled air-slide control valves. While installation proved a challenge due to limited working space for manifold modifications, TEI provided support by generating 3D-CAD illustrations of the new manifolds using off-the-shelf components. Once manifold connections were fabricated and installed, commissioning the TEI Fluidizer at the terminal required simply turning on the switch to start material flowing.

Installation of a production unit at Long Beach prompted the purchase of two more units, installed in early 2007. The three units are connected to manifolds associated with each of three main cement reclaim lines to improve systemwide discharge rates during low inventory and to increase shipping throughput.

At Mitsubishi's Lucerne Valley plant, one TEI Fluidizer was set to work on Star Bin E, where cement had been stuck for about 20 years. By means of flexible hoses, the Fluidizer was connected to Star Bin E on a Friday and left to run continuously through the weekend, loosening up the cement before any flow commenced; once it started flowing, the silo was emptied.

Since then, the Fluidizer has been used to empty other star bins, which are now used as transition silos for Type III and block cement. Also emptied by the Fluidizer was a silo previously used for transition and now available for finished product storage. The net result of this application is recovered inventory, increased capacity, and improved operating flexibility, TEI engineers affirm.

The plant intends to use the TEI Fluidizer as a mobile unit to address problems that may arise. For example, when the plant experiences a problem withdrawing cement from a silo, or when a silo needs to be emptied, the Fluidizer is used to extract the cement, avoiding confined space entry. When repair of an air-slide is required, the plant employs vacuum equipment to complete the clean out; this material needs to be recycled back into the finish mill, whereas cement recovered by the TEI Fluidizer is saved as product.

THE FUTURE

Technology Evaluations anticipates continued success in the cement industry by improving the performance of cement discharge from large storage units equipped with air-slides. Because the trials demonstrated a dramatic improvement in flow for chutes using closed-type air-slides, efforts are underway to design smaller PMT equipment optimized for such applications. Since implementing the Fluidizer, TEI affirms, Mitsubishi has achieved better flow, higher throughput, and safer operations. Adds Bud Biggs, “Anytime we can improve operations and safety at the same time, we have a winner.”

This article was adapted from a report provided by Bernard Smith, senior plant process engineer, Mitsubishi Cement Corp., and Jane Witheridge, president, Technology Evaluations, Inc.