Rock Products

OCT 2014

Rock Products is the aggregates industry's leading source for market analysis and technology solutions, delivering critical content focusing on aggregates-processing equipment; operational efficiencies; management best practices; comprehensive market

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ROCK products • OCTOBER 2014 60 Air Cannons Hammer Preheater Buildup at Nebraska Plant Ash Grove Cement has solved a buildup problem in the precal‐ ciner of its Louisville, Neb., plant by installing a network of high‐ performance air cannons, improving material flow and drastically reducing the need to hydro‐lance. The series of 25 air cannons from Martin Engineering fires a powerful discharge of compressed air in a prescribed pattern to remove material that becomes adhered to the vessel walls. The solution helps the plant avoid downtime and eliminate the potential for water blasting to cause lumps of material to fall into the kiln feed and interfere with production. When system operators began noticing material buildup in the pre‐ calciner, they found that it was impeding the flow through the pre‐ heater and into the kiln. The staff used the common technique of water lancing to remove blockages, particularly from the preheater tower's riser duct. But the time‐consuming process had to be re‐ peated twice daily, when maintenance personnel would open ac‐ cess doors into the tower and remove the accumulation with a high‐pressure spray. "Efficient material flow is a critical element of dry‐process ce‐ ment manufacturing, and accumulation or blockages can take a big bite out of a plant's profitability," explained Martin Engi‐ neering's Andy Marti. "Although many plants still use manual techniques to remove build‐up, the cost of labor and periodic shutdowns has led many producers to investigate more effec‐ tive methods for dealing with this type of maintenance." Air-Powered Solution In order to prevent the loss of efficiency and clinker quality at Ash Grove Louisville, 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 network of Martin XHV Air Cannons Air Can‐ nons for the main production line. Martin Engineering technicians installed the air cannons dur‐ ing a scheduled maintenance outage, starting where the accu‐ mulation appeared most severe: below the riser orifice, where the duct is reduced in size to increase velocity. The unique can‐ non 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. 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 high‐temper‐ ature applications. The negative pressure‐firing valve was de‐ veloped to provide reliable operation and long service life in challenging applications. The cannons discharge in a timed sequence that moves in an upward spiral around the tower firing about 20 seconds apart, with the entire cycle taking just over eight minutes to complete. Control room operators can alter the schedule to accommodate a range of kiln pressures and operating conditions, extending the sequence to as much as 45 minutes. A crew from Martin Services installed the entire system, in‐ cluding cannons, air lines and controls, as well as the com‐ pany's Thermo Safety Shields on each unit. Operating like trap doors, the sliding shields bolt in between the air cannon valve and mounting flange, helping to protect workers from exposure to severe heat, gases and high‐temperature mate‐ rials. Stage II Based on its success with the initial air cannon system, Ash Grove started planning a similar system for the plant's second production line. For that operation, engineers designed a net‐ work of 15 additional air cannons, equipped with Martin Tor‐ nado Exhaust Valves. Described as the latest advancement in air cannon valve design, the patent‐pending Tornado fires in re‐ sponse to a positive air pressure surge delivered by a solenoid valve, which can be located as far as 200 ft. away. The unique design improves air cannon safety, since the dis‐ charge sequence requires a positive signal. Unlike negative pres‐ sure‐firing designs, a cannon equipped with the Tornado valve will not discharge accidentally in response to a pressure drop, so an air supply failure or broken line won't trigger its firing. In ad‐ dition, this positive‐acting valve amplifies the discharge force, delivering up to 20 percent greater force than a standard XHV‐ equipped air cannon of the same size. With the new air cannon network in place, the Louisville plant has been able to significantly reduce the need for water blasting. Material now flows more efficiently, and maintenance personnel have drastically reduced the man‐hours that were spent on manual removal.

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