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Alluvial Ensuring Survival of Traditional Mineral Dredge Designs and Techniques

Alluvial Dredges Limited (ADL) celebrated its 70th anniversary in 2005. Its founding in 1935 was a joint venture between Lobnitz & Co. of Renfrew Scotland, whose first hull was laid in 1848, and Yuba Manufacturing of California (YMC). At the time, both companies were world leaders in the dredge mining design field.

Shortly after the Second World War, YMC relinquished their interest in ADL, which continued to operate under the Lobnitz & Co stewardship until it was nationalized and made part of British Shipbuilders.

With the demise of the Clyde Shipyards in the late 1960’s, ADL re-established itself as a private company and moved their senior management team and design staff to nearby Paisley, where they continued the design and supply of mineral recovery dredges and equipment. During this period, ADL developed methods of building and assembling from sections at the mine site, as they no longer had manufacturing facilities in Paisley. Proprietary items were sourced globally and shipped to site where they would be assembled by a locally-recruited labor force operating under the guidance of an ADL team of engineers.

ADL still conducts its business from premises in Paisley, retaining the design records, detail drawings and calculations from a wide range of mineral recovery projects.

While in recent times there have been only a few new build mineral recovery dredges, the existing records, along with modern technology, ensure that the present staff have the knowledge and ability to design such equipment with confidence.

These records are also invaluable in conducting feasibility studies into the use of dredges, and upgrading existing dredges. Evidence of this was the recent refurbishment and upgrading of a dredge originally built by ADL in 1948. Much of the original dredge equipment was replaced by modern equipment and controls, which had to fit within the confines of the original design. The dredge is now fully operational and is pictured in this article.
The senior management of the company are experienced in the design and operation of mining dredges, and are able to pass that experience to younger members of staff through in-house seminars, which reference the design records. This is being conducted to ensure that the science of designing mineral recovery dredges does not become lost to the industry.

ADL has continually been at the forefront of innovative dredge design. One such project was the Delta One dredge for BHP’s Beenup Mineral Sands operation near Augusta, Australia, south of Perth. Due to the nature of the deposit, the dredge was equipped with both a spud system and a dual headline system. The spuds were used in the shallow upper bench where the material was consolidated, and the dual headline system operated to the remaining full dredging depth of 45 meters.

The control of the dual headline could maintain the dredge on a straight line across the cut, which improved the dredge output in comparison to a single headline system. With a displacement in excess of 3000 tonnes, the Delta One was the largest inland bucket wheel dredge, and the triangular formation of the hull and the ladder gave rise to the name Delta. The cutter ladder was a watertight structure with bucket wheel drive and slurry pump contained within. At the aft end of the ladder there was a holding tank for storing ballast water. This water was pumped to forward ballast tanks as the ladder was lowered, to destroy the ladder buoyancy and provide a predetermined downward force at the bucket wheel. Access to the equipment within the ladder was through port and starboard legs running from the ladder pump room to the ladder pivot, and could only be accessed when the ladder was raised.

Sadly, due to environmental problems resulting from the process plant associated with this dredge, Delta One closed down and was dismantled, after worked on the project from 1996 to 1999.

ADL is now conducting another particularly challenging mineral dredge design project. The dredge specification calls for a peak output of 8700 tonnes of dry solid material per hour from a very shallow deposit and feeding it to a separate treatment plant. The company is designing to fit very large rated and weighted equipment into a relatively compact hull platform. It has been stated in the past, that a mineral dredge design is simple and makes use of fairly basic equipment. However, the science of designing a mineral recovery dredge is the ability to bring together the correct equipment that will operate harmoniously, efficiently and profitably within the particular deposit for which it has been designed.

ADL has operated under the umbrella of named holding companies over the past 70 years, but latterly the holding company name became Lobnitz Marine Holdings Ltd., reuniting the company with the name of one of the founders. Retained within the group companies is the capability to design the full spectrum of dredges and dredging equipment as well as floating dry docks involved in ship repair.

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