Down the Rathole

Discharge Aids

Down the Rathole

A Hopper Flow Solution for a Concrete Plant
A cement and concrete manufacturer faced a problem with their storage bins for the raw material, which accumulated in the hopper forming a rathole seriously affecting production. To keep the whole of the material flowing they installed an air cannon system with some interesting specifications.
(ed. WoMaMarcel - 09/10/2015)
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Three air cannons keep the material flowing in a pyramid hopper construction .

Although technology for industrial concrete production has made great strides, the hopper’s basic funnel design still tends to accumulate build-up in cement manufacturing operations, which can eventually lead to clogging and process downtime. That was the problem CRH Roadstone Limited, a cement and concrete block production firm located in Waterford, Ireland, was experiencing. The company found that the limestone dust extracted from the quarry, once screened and loaded into the dust bin, built up until it left just a center hole for discharge, seriously affecting production.

Regular clearing of obstructions required the time-consuming use of a mechanical digger, which scooped material out of the open mouth of the hopper from the loading area located above it. Fed up with the downtime and maintenance costs, CRH Roadstone contacted a local engineering firm, Plimley Trading Limited of Newbridge, Ireland, which specializes in metal fabrication and customized engineering solutions for concrete manufacturers. As a distributor of Martin Engineering products, Plimley also invited the flow products manufacturer into the process to help devise a cost effective solution.

“We [Plimley together with Martin Engineering] carried out a material flow project for the same customer at a different location in 2012 and it was a complete success,” explained Shane Dunne, Senior Engineer for Plimley. “Based on that, the manager asked us to have a look at the hopper in question with a view to resolving the material build-up problem.”

The Hopper and the Rathole

CRH Roadstone is one of the oldest producers of cement and concrete products in Ireland. It is part of Cement-Roadstone Holdings (CRH), the largest building materials provider in North America and a regional leader in Europe, with an emerging presence in major Asian economies. The Waterford, Ireland quarry location is a core facility for the company’s regional production. At the Waterford facility, front loaders transport screened limestone dust and sand from the quarry to the tiered loading area secured by a tall retaining wall. Next to the wall, the 24 ft high (7.31 m) split pyramid hopper is comprised of two square bins with inverted pyramid-shaped discharge points at the bottom, which unload onto separate conveyors leading to either the concrete block production facility or the cement processing plant.

At the front side of the hopper, a split blowpipe manifold is used.

With shallow base slopes and sharp corners, the bins in the pyramid hopper have a tendency to accumulate damp material. After the front loader was done dumping and discharge would stop flowing onto the conveyors, operators assumed the bin was empty, but material remained within, forming a rathole that got smaller as more material collected. Seasonal fluctuations in production caused raw material to sit dormant, exposed to the moist Irish climate. The material hardened over time, 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.

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