Air cannons prevent clogging
The common practice followed in cement plants and concrete block production facilities to clear the build-ups in hoppers is by mechanical means. This is time consuming and unsafe practice. The clogging seriously affects the production rate.
Clogging and solution
CRH Road Stone is one of the oldest producers of cement and concrete products in Ireland. They had a problem at storage bins with shallow base slopes and sharp corners in the pyramid hopper and a tendency to accumulate damp material. Over a period of time, the material use to get hardened, adding to the problem, as the weight can compromise the balance and structural integrity of the hopper, becoming a potential hazard to the work area. The problem used to aggravate with seasonal fluctuations in climatic conditions. In order to find a long lasting solution, CRH approached a distributor of Martin Engineering products. They came up with an innovative approach that set two 100-ltr Martin® XHV air cannons at the back of the bin. These work in tandem with a single, larger 150-ltr XHV air cannon fitted to a split blowpipe manifold, which is connected to fan jet nozzles on the front sloping side of the bin. All three units are fitted with a 4-inch (102 mm) quick exhaust valve (QEV) connected to the on-site compressor system 35 ft away. Plimley, a distributor for Martin Engineering, also supplied and installed a new airline to feed the air cannons.
The right solution
"This is the first application of the split manifold system on heavy, sticky material that I know of," observes Dave Harasym, UK Sales Manager for Martin Engineering. "Generally, this technology is used on light material such as fly ash. "Proper flow from a square bin typically requires four cannons, one on each side firing simultaneously," Harasym adds. "We were losing one side to a retaining wall, so figuring out how to do it with three cannons was a challenge."The XHV features a rugged 5/8-inch (16-mm) stroke piston with a high-temperature polymer seal for long life. Working from one side of the tank, the complete valve assembly can be removed in one easy step and replaced within minutes, eliminating the need to ever remove the tank from the vessel for service. Each unit is activated with a new type of 110 V, negative-firing solenoid, which provides the power, efficiency and easy maintenance of an advanced internal valve with the single-line plumbing of a traditional valve design. Installers also devised a mechanism by which the discharge volume from the bin determines the firing sequence for the system.
"On the block side outlet, the flow of material is controlled by a swinging door that drops the material into a weigh hopper," explains Hugh McGee, Plant Operations Manager, CRH Roadstone. He further adds, "When the door opens, the air cannon discharges the compressed air into the bin. This happens every time the door opens and keeps the material flowing."
Martin Engineering has been an innovator of air cannon technology since the 1970s, designing a number of advancements that have improved its commercial viability, many of them protected by patents in the US and elsewhere. The company´s contributions have included faster-acting valves to improve performance, retractable nozzles to facilitate longer service life, quick-change nozzles to reduce maintenance time and components to enhance safety. Using proprietary software to design and predict the performance of new nozzle configurations, the firm continues to develop new solutions that deliver greater efficiency and safety.