Lonestar Industries, Greencastle, Ind., a large US cement producer, has made cement since 1919. Besides six cement plants, the company operates several ready mix and aggregate plants throughout the US.

At the Greencastle cement plant Lonestar mines most of the raw materials for Portland cement, Portland lime and masonry cement. The cement is made through a wet process that combines calcium, silica, alumina, and iron oxides with water to form a slurry with 34 percent moisture content. The slurry is burned in kiln at 2,700° to form clinker, which is ground with gypsum to produce the gray powdered cement. The energy intensive wet process uses coal as the primary fuel source and post-consumer and manufacturer waste solvents as the secondary fuel.

The Greencastle plant annually produces 720,000 tons of cement. The cement is packaged in 94 and 70 pound paper bags or shipped in bulk by truck or railcar. Cement awaiting packaging or shipment is stored in 36 outdoor silos. Because cement is vulnerable to compaction, explains assistant plant manager David Puzan, "it's critical to keep your product dry and rotated as you move it and ship it to customers."

Cement compacts in silo bank: capacity down 25 percent

Last winter Lonestar had compaction problems with one of their silo banks. The bank includes eight silos with five storage interstices, for a total of 13 storage spaces. The silos, erected in 1928, were covered by a single roof that had a slow leak. Cement in the eight silos was flowing with increasing difficulty. The silos had been built with flat bottoms, which contributed to the flow problems. The five interstices held a discontinued product line including build-up on the walls, which had to be removed to increase plant storage capacity. Engineers estimated the unuseable space was 25 percent of the plant's storage capacity.

"During the winter, construction slows, and that's when we fill up for heavy spring shipments." Puzan says. "All the other available silos were approaching capacity. The silos in this bank had ratholed, and the compacted cement plugged the feeder openings. Our goal was to retrieve lost capacity so we could restock for the busy season, and there was some urgency." The plant decided to re-roof the silo bank, clean out the silos and interstices, and reclaim lost storage before spring. Lonestar wanted to salvage as much dead inventory as possible.

Cement plant considers cleaning options

"We knew silo cleaning wasn't work we could do ourselves," Puzan says. "Years ago it was common practice for plant workers to enter silos and try to clean them. It's very dangerous and can be fatal. I don't approve of our workers entering silos; I won't allow it. We contacted several silo cleaning services for competitive bids on the project. These services are professional; they know what they're doing, and they have the equipment to do it efficiently."

Puzan considered a few silo cleaning companies he knew from prior experience. "I've worked with three different cleaning services over the years at various plants," he says. He picked one with which he had a good prior experience. The selected company gave Lonestar a detailed proposal estimating the time to remove the cement buildup. "Their bid was a little higher than others, but they offered a turnkey cleanout. Some services had lower bids but then had associated costs that were job dependent. The service I chose was up front with their proposal."

Cleaning service reclaims lost storage capacity

Lonestar hired the cleaning service, which sent out a crew of three to clear the 13 storage spaces and feeders. The service makes several variations of a proprietary cleaning device called a mole for cleaning service use and for sale. The device is remotely controlled and monitored from the silo roof, eliminating worker entry. The device's cutting heads are made of various materials to suit each particular job. Construction materials include steel, aluminum, stainless steel, and several durable plastic resins. The device can be powered pneumatically or hydraulically.

At the cement plant the service company used the Arch•Master vertical auger device to drill through bridged cement and create a flow channel to the feeder. Next, their Big Mole system enlarged the flow channel outward to the silo walls.

The crew worked between January and March. "We weren't sure how long it would take because each silo had different compaction problems." Puzan says. "Compacted cement ranged from 200 to 2,000 tons per silo."

"The crew was very flexible. They'd work with us if we needed to transfer cement. If there was a bottleneck, they would move on to another silo. They gave us constant updates on their progress. They worked long days and worked some nights when needed. Their flexibility helped us to minimize costs."

"The weather was not the best through January and February. First we had torrential rain, then we had record snowfall. Two blizzards hit: we had subzero temperatures and over 50 inches of snow in 2 months. Sometimes the weather was so bad we didn't want the crew working, so we sent them home. But there was very little downtime on the project. They stuck with the job and worked well with our people. These guys became part of our team for 3 months."

The cleaning service cleaned the 13 storage areas and freed up the feeders. Some silos had to be cleaner than others. The discontinued product line had to be completely removed from the interstices because Lonestar didn't want to contaminate the incoming fresh cement. After the bulk of the removal was done, the crew used shovels and then brooms to clean down to the floor. "Those silos were cleaned so well that you could sit down and eat a lunch in there," Puzan says.

The compacted Portland cement was reprocessed and reused, returning valuable inventory. Because of the silos' flat bottoms, the cleaning crew left some of the hardened cement in place to create an angle of repose rather than clear it to the floor. "We get a cone effect to funnel the cement into the feeder," Puzan says. "And we don't have to worry about that cement contaminating our product because we're continuing to store the same type of cement in those silos."

Lonestar regained lost storage in time for their busy season. "The crew opened up 25,000 to 30,000 tons of capacity by March." Puzan says. "It enabled us to keep our cement production rate on target and service our customers." Asked whether Lonestar would use the silo cleaning service again if needed. Puzan replied, "Definitely. That's an easy question."

Technical profile features technical articles contributed by writers in which new technology, new products, specific applications or proprietary concepts are discussed. This technical profile was written by Rudolph John Lehman, Mole Master Services, Inc., Marietta, Ohio, U.S.

Mole•Master Services' silo cleanout service removes unwanted material build-up and clogs from all types of storage silos and bins, regardless of their construction or the type of material stored. The system can be used to correct build-up situations including, but not limited to lumping, bridging, ratholing and scaling problems.

Mole•Master's cutting machines, referred to as "moles," can be powered either pneumatically or hydraulically and are manufactured by Mole•Master according to several different configurations. Each is designed for a particular type of bulk stored material and for specific operating conditions.

The process is completely automated, allowing cleanout to take place without human entry into the silo or bin. It is a dry process; no water or other liquids are used. Therefore there is no water damage to the facility or surrounding areas; cleanup is easy and material within the silo is recoverable for further processing or load out. There is no contamination of the material; often the value of the freed material pays for a significant portion of the cleanout project.

Storage vessels are restored to 100% of planned storage capacity. In addition, clogged hopper outlets are opened for faster, more efficient material flow. Because Mole•Master's equipment is extremely efficient, cleanout is accomplished quickly. Downtime of storage facilities using Mole•Master's silo cleanout service is a fraction of the downtime required when cleanout is accomplished using traditional methods.

Mole•Master utilizes unique non-sparking equipment in hazardous environments such as grain storage facilities. Technicians first purge grain storage vessels of oxygen using carbon dioxide. During the purging process, the oxygen content of the silo's or bin's interior is lowered from the 21% composition found in nature to a range of 11%-12%. Lowering the oxygen content eliminates the possibility of explosion by removing the oxygen necessary to sustain a spark hot enough to cause an ignition or explosion. Mole•Master technicians continuously monitor the oxygen level of air within the silo or bin as well as that in the headhouse and/or basement, as required. Through the use of a portable manifold with pressure, flow and temperature gauges, Mole•Master technicians also continuously meter for carbon dioxide and other poisonous gases. An additional benefit from the purging of oxygen is a "fumigant" effect; fungal life cannot exist at the low levels of oxygen after purging. The company has recently developed a new cleanout device called the Maxi-Mold, which has proved effective in solving the unique problem encountered in the unclogging of bridged grain storage silos and bins.

The first step in the Mole•Master silo cleanout process is visual inspection and review of the particular material build-up problem. Pneumatic equipment is actuated by a compressor set up near the base of the silo. Air hose is run from the compressor to the top of the silo where a manifold distributes various other hoses, which are then connected to the cleanout/unclogging equipment and moles. The pneumatic equipment operates much like a continuous mining machine or industrial tiller. The hydraulic system works similarly. Hydraulic fluid is stored in a tank which is permanently mounted on Mole•Master trucks. From the trucks, the hydraulic hose is run to the silo's roof. The hydraulic machine is then assembled on the silo's roof on aluminum I-beams which distribute its weight over a large area to minimize loading pressures on the roof.

Once the machinery has been set up, inspection of the vessel takes place, either through existing access holes or through 17-cm to 20-cm diameter access holes drilled or cut by Mole•Master's technicians. Explosion-proof, high-intensity electric lights are lowered into the silo or bin so that the vessel's interior can be examined to evaluate material build-up. Technicians take measurements to determine the precise placement of the moles.

Mole•Master can remove materials ranging from those which have set up extremely hard to materials that are simply de-aerated or that have a higher than normal moisture content and, therefore, will not flow. Different types of moles are used according to the condition and location of the material to be removed.

Technicians continuously monitor the equipment's progress from the silo roof. Rate of flow of the freed material as it exits the storage vessel is also monitored in order to evaluate the effectiveness of the equipment in use. Mole placement and changeouts are based on this monitoring.

After cleanout has been completed, Mole•Master's technicians seal any access holes which have been created. Mole•Master will install cleanout ports for subsequent cleanout projects if desired. Openings can also be regrouted or sealed with a recessed steel plate coated with roof tar.

For safety reasons - the use of high pressure equipment and the existence of open holes on the silo roof present potential hazards to untrained persons - and because of the proprietary nature of the equipment, the company asks to work without direct supervision. Progress reports and visual inspection by the client can be arranged at the beginning of the project.

Mole•Master recently completed a silo cleanout project for Cargill, Inc., at the company's export facility at Reserve, Louisiana, in the U.S. During the project Mole•Master removed more than 1,800 tons of stagnant, hardened soybean material from six of the storage silos. The length of time required to clean out any given silo depends on silo size, the amount of material build-up and the hardness of the build-up. This operation took place over a total of 20 service days, an average of three days per silo. Brian Butz, plant manager at the facility, estimated the cleanout time with the previously used hand methods was five to 10 times longer than the time required by Mole•Master.

Cleared out a 20-year build-up

A Cargill plant at Port Allen, Louisiana, was the site of another storage bin cleanout operation. According to Stephen Szykulski, head of the electrical department, the specific problem involved the build-up of grain materials in the bottoms of storage bins. The materials had been building gradually over a period of 15 to 20 years. Build-up ranged from a material with a consistency approaching that of concrete to a loose, gummy product. The bins' storage capacity and flow rates had been reduced by the build-up.

Prior to the Mole•Master cleanout, the bins had never been cleaned. "We had tried to do it by hand, essentially with picks and shovels, but that's a long drawn out affair with a very slow progress rate," Mr. Szykulski said. Mole•Master's cleanout crew retured the bins to 100% of planned storage capacity and a normal flow rate. Average cleanout time per bin was 2 days. 

Mole•Master also provides complete storage silo maintenance programs. Other services include structural repairs and retrofit, roof repairs, waterproofing and sealing, epoxy injection and rust transformation, hopper modifications and structural inspections.

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