Air cannons hammer preheater build-up at Ash Grove Nebraska cement plant

Efficient material flow is a critical element of dry-process cement manufacturing, and accumulation or blockages can take a big bite out of a plant’s profitability. Hang-ups in storage systems and accumulations in process vessels can choke material flow, while bottlenecks create costly reductions in equipment and process performance. Poor material flow raises maintenance expenses and drags profits down. If they become severe, flow problems can bring production to a complete stop. Although many plants still use manual techniques to remove build-up, the cost of labor and periodic shutdowns has led some producers to investigate more effective methods for dealing with this inevitable maintenance.

Ash Grove Cement is the largest American-owned cement manufacturer and the sixth-largest in the nation. The company’s network includes nine cement plants, two deep-water import terminals and a major quarry operation in Blubber Bay, British Columbia, as well as subsidiar ies consisting of ready-mix companies, aggregate suppliers, packaged materials companies and a paving firm. In all, Ash Grove has a total annual capacity of nearly 9 million short tons of cement, including a wide range of specialty products for difficult service environments. The company has a reputation stretching back to 1882 for running some of the most efficient and best maintained plants in the country.

The facility in Louisville, Nebraska has an annual output of about 1 million ST per year of Portland and blended cement. Located on the south bank of the Platte River between Omaha and Lincoln, the plant was originally opened in 1929 with an annual capacity of 240,000 ST per year, and the operation has been expanded and updated continuously throughout its life.

Among the issues the plant has confronted is material buildup in the precalciner, which interfered with operating efficiency by impeding the flow through the preheater and into the kiln. The staff used the common technique of water lancing to remove blockages, particularly from the preheater tower’s riser duct. Twice daily maintenance personnel opened access doors into the tower and removed the accumulation with a high-pressure spray. The work was time-consuming, and the water blasting had a tendency to cause lumps of material to fall into the kiln feed, interfering with production.
 

An air-powered solution

In order to prevent the resulting loss of efficiency and clinker quality, a group led by process engineer Mark Junkins investigated possible solutions. They met with material handling experts from Martin Engineering, and together the group designed a system that uses high-performance air cannons to control material buildup and enhance the flow.

The system is based on 25 Big Blaster® XHV Air Cannons, which fire a powerful discharge of compressed air in a prescribed pattern to remove material that becomes adhered to the vessel walls. Introduced by Martin Engineering in 1974, the technology has since developed a proven track record around the world for relieving bottlenecks caused by material buildup in high-capacity storage and process vessels.

Martin Engineering technicians installed the air cannons during a scheduled maintenance outage, starting where the accumulation appeared most severe: below the riser orifice, where the duct is reduced in size to increase velocity. The unique cannon design requires no high-temperature discharge pipes or special mounting plates, and discharge nozzles are embedded directly in the refractory lining of the preheater tower.

Valve performance and timing

All of the air cannons in the main production line network are equipped with the Martin Engineering XHV Valve, designed specifically to deliver premium performance and long service life in preheater towers, clinker coolers and other hightemperature applications. The negative pressure-firing valve was developed to provide reliable operation and long service life in challenging applications.

The XHV valve is constructed with a rugged, short-stroke piston that features a high-temperature polymer seal for dependability and low maintenance requirements. The advanced design delivers high output force and excellent sealing to reduce air loss, as well as rapid discharge and filling. All XHV valves are guaranteed for 200,000 firings, and a removable piston seat simplifies service.

Available in 2-, 4- and 6-inch models and ten different tank sizes, the XHV Valve Assembly features an aluminum piston with a high-temperature polymer face. Because of the short piston stroke (just 5/8″ or 16mm), the design minimizes wear on the piston and cylinder. A return spring snaps the piston quickly back into firing position and prevents dust entry.

The company also offers a retrofit kit that allows as imple performance upgrade of air cannons f r om v i r t u a l l y a n y manufacturer. A simple, bolt-on attachment allows the XHV Assembly to be installed on existing Martin Engineering internal- and external-valve air cannons, as well as onto competitive models.

Andy Marti, Martin Engineering, Neponset, IL, USA
Edition: Edition 50

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