Taking the High Road

IntroductionSandwich belt high angle conveyors are versatile systems for elevating or lowering bulk materials continuously at steep angles up to 90&deg;. A wide range of industries have adopted the system to handle coal, refuse, coarse copper ore, hot clinker, municipal sludge, wood chips, gypsum, slag, excavated earth, various grains, and refuse derived fuel (RDF), at throughput rates of 0.27 &ndash; 4000 tph, over elevating heights from 3.66 &ndash; 175 m. Installations at cement plantsThe first example of a sandwich belt high angle conveyor delivering raw products for cement manufacture was in an underground gypsum mine; the vertical system continuously elevated gypsum. The underground crusher reduced the size of the material to under 150 mm, and dropped it onto a reciprocating plate feeder to load the sandwich belt conveyor. At the surface, the conveyor discharged onto a plant conveyor that delivered the rock either to an outside storage pile, or directly to the plant. This completely vertical system replaced a horizontal feed conveyor and bucket elevator, considerably simplifying material transport and eliminating a high-maintenance transfer point.Closer to the cement-making process, the sandwich belt high angle conveyor, supplied to a steel cement company in Australia&rsquo;s Port of Melbourne, formed part of a complex, automated cement manufacturing plant. The raw products, steel mill slag, and gypsum were brought in by ship and stored in open stock piles. The slag, a byproduct of the steel-making process, was shipped in from Japan. As required, these were then delivered to separate holding bins, from which the sandwich high angle conveyor was fed at different load points. The critical blending process was achieved by metered feeding of the products onto the sandwich conveyor&rsquo;s lower infeed belt. The product was then elevated and discharged directly into the grinding mill, where it was reduced to a fine particle cement. No firing was required because the steel mill slag acts as a clinker. An additional installation for a cement plant in the southeastern US delivered various raw products to the storage bunkers, which ultimately fed the kiln. The most interesting aspect of this installation was the long approach with multiple feed points. The blending of the products (limestone, gypsum, sand, iron ore, etc.) was achieved by a crane-mounted clam shell, which stocks the materials above the respective apron feeders. This 90&deg; angle arrangement also replaced a previous system, composed of a horizontal feed conveyor and bucket elevator, thus, once again, eliminating a transfer point and reducing operation and maintenance costs.The sandwich belt high angle conveyor has also been used for the hot handling operations of a cement plant. Such a system replaced the typical arrangement of a long approach conveyor, linked to an elevating pan conveyor, and handled a range of materials from hot and powdery clinker, to gritty pozzolanic sand, to sharp, lumpy gypsum rock. This was not only more economical, but provided a system where material flowed continuously, with no intermediate transfer, until discharge.Advancing the technology for the environmentContinuing to prove the versatility of the sandwich belt high angle conveyor, Dos Santos International commissioned a DSI Sandwich belt high angle conveyor with Zanella Engenhaira e Industria de Maquinas of Curitiba, Parana, Brazil. The project is part of a cement plant in the municipality of Pitimbu for the Ricardo Brennand Group. Brennand Group is part of the Cimentos Nacional Co. The factory arrangement was laid out to accommodate protected areas, and therefore reduce the environmental impact. This request for a small footprint was easily achieved by the DSI Snake at Paraiba, elevating 720 tph of limestone, iron ore, sand, and clay at a 60&deg; incline. Brennand recognised the challenge of the raw materials it was transporting and sought a better handling of raw materials. This DSI Snake was the first to use a commercially designed DSI Wet Brush, a system that applies a minimal amount of moisture to mitigate side migration of the bulk material towards the edge of the belt sandwich. Most bulk materials do not need help from a wet brush, but some materials do have a tendency to migrate towards the belt&rsquo;s edges. The DSI Wet Brush uses precise water flow control and measurement that reacts to precise monitoring of the bulk material flow rate. A sonic, broad level sensor at the bulk material feed point, along with a belt speed monitor, provides all of the information required to control the wet brush system. System interlocking maintains a perfectly dry system when there is no bulk material or the feed belt speed is zero. Material flow is measured continuously, and the wet brush automatically adjusts moisture for optimal response.The DSI Snake at Paraiba features an extended loading zone, which is fed by five separate belt feeders and chutes. It includes a cross-belt magnet to remove any tramp iron, and a material analyser that ensures the correct raw mixture. Eventually, in production, the plant will have a capacity of 3000 tpd of clinker and 1.5 million tpy of cement. ConclusionThe sandwich belt high angle conveyor technology has been used in a wide range of industries to convey many different materials. The applications described here show the suitability of these systems for carrying the array of bulk materials that are the raw feed for cement manufacturing. This article was originally published in World Cement's BMHR supplement.

Taking the High Road

Introduction

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