“Bottom-up” terminal upgrade boosts productivity
Introduction
With commodity prices soaring, and the price of copper approaching an all time high, Minera Escondida Ltda. port was faced with a dilemma. How could the port be further upgraded to load larger vessels at a faster rate without stopping production for the upgrade? The existing marine structures were already stressed to the limit, and the shiploader was operating at maximum capacity.
Upgrade Requirements
The obvious solution of building a new port with appropriate facilities was carefully considered, but was impossible within the given time and cost constraints. Instead, an innovative system was required that would allow the existing infrastructure to accommodate the higher demands.
The onerous demands included:
- designing a fender system that would accommodate the larger vessels, without imposing higher loads on the berthing dolphins or shiploader platform;
- increasing the stand-off distance to allow loading in rougher seas, while not compromising trimming;
- increasing the outreach of the boom to accommodate the larger fenders, larger stand-off and wider vessel beam, without increasing the stresses on the shiploader support tower or foundation;
- improving the average loading rate;
- improving trimming without additional vessel movements;
- reducing dust emission;
- improving operational safety, and,
- most importantly, implementing these modifications within an annual 14 day maintenance shutdown period.
Meeting the Challenge
These demands are common in today’s competitive, fast-moving environment. Meeting them is a challenge that demands a combination of skills – creative, analytical and practical – and resourcefulness, to do what has never been done before.
The owner of the port was quick to realize that they could not be the best by following others … they had to take lead. They had to surround themselves with competent engineers, get the best advice, and then act quickly and decisively.
Shiploader
The shiploader presented the greatest challenge. The effective outreach had to be increased from 30m to 42m, but, because of geometrical constraints at the berth, the boom itself could not be increased beyond 36m. This left 6m for a trimmer, flinger or other device to achieve the balance of the outreach.
Copper concentrate, a very sticky or dusty commodity, presents numerous problems for conventional trimmers and flingers. To overcome these difficulties, Sandwell, a Vancouver based engineering company, specifically developed the so called ‘banana spout’ to gently direct the concentrate under the wings of the hatch coamings, a minimum of 6m from the centre of discharge. The spout was manufactured in Canada, and installed on the new boom during the short shutdown. It has proved to be such a success that it has subsequently been used in a number of projects around the world handling both concentrate and coal.
Increasing the boom length from 30m to 36m was a structural engineer’s version of a diabolical Sudoku puzzle. It goes without saying that even if the longer boom had the same mass as the shorter boom; the foundation loading would increase because of the forward location of its centre of gravity. So, to keep the overall loading on the foundation the same, the longer boom had to be made much lighter than the old boom, which meant that the weight per meter had to very much less than the original. This required numerous unique solutions, including ‘borrowing’ ideas from other high-tech mining and offshore equipment.
Patricio Industrial was commissioned to fabricate the high-tech tubular boom. To complete the work they purchased sophisticated computer controlled plasma profiling equipment for the project, and fabricated the boom in a shop in Antofagasta, just 20km north of the port. The end result was so good that it prompted the engineer inspecting the work to comment that it was ‘some of the finest workmanship seen worldwide’, a real tribute to this relatively small Chilean company.
Other weight saving measures on the boom included such innovations as; using water and hydraulic lines to double-up as handrails and knee-rails, integrating conveyor supports with spill trays and the supports for the fibreglass walkways, a high-speed conveyor belt, optimised transfer points, integrated headbox and deflector, auto-levelling integrated transfer chute and spout support frame, and dual shaft-mounted tail drive integrated with take-up pulley. Each node on the tubular boom was designed using thicker walled ‘can sections’ more typical of offshore platforms than mobile equipment, and the entire tubular system was pressured and monitored for cracks.
Since the end of new longer boom projected beyond the end of the wharf it could not be reached for maintenance. To overcome this difficulty, Sandwell developed a self powered retractable platform that effectively extends the wharf by 6m for maintenance purposes.
Figure 3 - Wharf extension platform, shown in retracted positionMarine Facilities
Addressing the shiploader was only half the problem. Berthing the larger vessels and operating them in higher waves had to be addressed.
The wave issue was solved by increasing the standoff of the vessel from the berth face to 6m, and installing a new gangway with the required outreach. Retrofitting the fenders was more problematic. Generally larger fenders produce larger reactions, but since the marine structures were already stressed to the limit, this option was not feasible on the shiploader platform. Sandwell worked closely with Metso to produce a fender system that would allow the existing marine structure to be maintained. Since the energy absorbed by a fender is the product of the average force and the displacement, the ideal fender, from a structural perspective, is one that has a constant force at all displacements and at all speeds. The solution was a dual buckling system that would absorb twice the energy without any additional loading on the marine structures.
A prime safety concern was addressed by changing the boom hoist from a single rope to a dual rope system that would allow the boom to be safely supported by either rope in the event of failure of the other system. Wire ropes with a plastic impregnated core were used to improve the factor of safety of the remaining rope following such an event.
Outcome
The end result of this project is that Minera Escondida Ltda. lost no time in upgrading its port facilities, and is now successfully shipping its copper concentrate at a higher rate in larger vessels more safely.
Authors,
David Frykberg,
Shiploading Specialist
Ports, Marine and Offshore Division
and
Shashi M. Shrivastava,
Vice President and General Manager
Ports, Marine and Offshore Division
