Dismantling of Kone Continuous Ship Unloader (CSU) 2

As the Bristol Port Company continued its diversification into the renewable energies market, it’s once world-renowned coal import terminal needed to be decommissioned to make way for the latest in state of the art equipment with increased efficiency and capabilities. The terminal decommissioning had been split into a number of different phases which had previously saw the disposal of one CSU, three Stacker Reclaimers and some 4km of conveyor gantries. One of the final phases of the terminal decommissioning was the disposal of the final Continuous Ship Unloader (CSU2) from within Royal Portbury Dock.

The CSU machines were at the very heart of the coal terminal, each with the means to discharge 2,000ton of coal per hour from vessels as large as 130,000te deadweight. The use of these vast CSU machines ensures total efficiently and the minimum risk of dust and spillage during vessel unloading allowing the terminal to maintain high levels of environmental standards.

As O’Brien Specialist Crane Services had already successfully completed the extremely complex dismantling and disposal of CSU1, the sister unloader of CSU2, with zero incidents and on schedule, it was a straightforward decision for the Bristol Port Company to reengage O’Brien SCS for the disposal of CSU2.

Despite initial appearances, it quickly became apparent that CSU2 was of a totally different structural design than the previously dismantled CSU1. After further investigation, it was found that CSU2 had been delivered to Royal Portbury Docks several years later then CSU1, as it was a replacement machine for the original CSU2 that had been written off due to fire during the 1990’s.

These variations in structural design meant that the tried and tested disposal procedure would need to be altered and all engineering verified. In spite of significant engineering work performed during the planning stage of the CSU1 project, the O’Brien SCS team opted to treat the CSU2 project as totally standalone, starting all engineering from scratch. This would ensure that nothing was missed or left to chance, guaranteeing that all structural variations were considered.

The very first task for the engineers was to carry out investigation works to determine the counterweight material within the raised ballast box. As was the same as CSU1, there was a discrepancy between the stated mass of the CSU’s raised counterweight and its actual volume. After extensive testing, the counterweight material was determined to be a MagnaDense mix as assumed. MagnaDense mix counterweight has double the density of standard concrete which explained the discrepancy and how the weight of the raised ballast box was some 500ton. The O’Brien SCS inhouse engineers continued by carrying out a robust desktop review of the as build information followed by a detailed onsite structural survey to obtain all information required to develop a dismantling methodology.

As per the previous project, a controlled collapse, explosive demolition or traditional piecemeal dismantling techniques could not be utilised due to site and structural constraints. The raised luffing boom structure was of a cantilever design, supported at only one single pivoted point, about which it was able to freely rotate, this was then connected to the raised ballast box via an A-frame tower and bracing members, which ensured the raised structures were perfectly balanced. This meant that removing any sections from the CSU boom or counterweight would lead to imbalance and instability. Also, the removal of the A-frame or any bracing members would lead to an uncontrolled collapse as the structure would no longer be self-supporting. In addition to these challenges, it was apparent that lifting the entire 500te in-situ poured MagnaDense counterweight was not practical or financially viable.

A method was proposed that would utilise the O’Brien Specialist Crane Services’ own temporary support towers. This method would utilise the towers to independently support the luffing boom and raised ballast box during the dismantling operation, this would ensure total stability and remove any risk of uncontrolled collapse. In total four support towers were used and secured at strategic locations below the cantilever structures, each supporting weights of up to 280ton as calculated by the engineers. Consideration was also given to the support points on the CSU structure to ensure these had suitable strength to withstand the loads imposed.

As the CSU structure would now be fully supported, the engineers could turn to the next task in developing an actual dismantling procedure. The site constraints remained the same as CSU1, this meant that no heavy lift cranes could be rigged or operated on the quay edge, instead all dismantling cranes had to be located on an area of made-up ground land side of the CSU. This had the effect of significantly increasing the lifting radius of the heavy lift mobile crane to as high as 38m. As loads being lifted were as high as 89tons, this demanded a large capacity mobile crane. A Demag AC1000 1,200ton capacity mobile telescopic crane complete with sideways superlift was selected for the dismantling works, supported by a smaller 300ton capacity support crane.

Following the completion of the planning phase, the O’Brien SCS site team mobilised to site in a very short space of time to reflect the client’s urgency to free up the quay side area. The initial task carried out was the assembly of the four support towers by the in-house team of steel erectors, completing this in record time of only four days.

This then allowed the longest phase of the project to commence, the breaking out of the 500ton MagnaDense mix counterweight using a remote-controlled demolition excavator with breaker attachment and then removing this from the 36m high counterweight box. Only following the removal of the 500ton MagnaDense mix counterweight could the main dismantling operation commence. The total piecemeal dismantling of the 1,300ton structure took the onsite team only 45 hours across 5 days, including the rigging and de-rigging of the 1,200ton mobile crane along with the dismantling of the support towers, to the total astonishment of all stakeholders.

Once at ground level, the scrap processing procedure began segregating the different waste streams throughout. On this project O’Brien SCS achieved a >99% reuse and recycling rate with a 100% non-hazardous waste diversion from landfill inline with our ambitious sustainability targets.

The O’Brien SCS team carried out all aspects of this project in-house including;

  • Initial site survey & feasibility study,
  • Calculations of the imposed loads on the support towers,
  • Design and engineering for support towers including wind loading,
  • Assessment on support points on the CSU machine to ensure structural strength,
  • Stability and C of G calculations for each stage of the dismantling operation,
  • Design of dismantling sequence, including calculation of individual load weights and C of G’s
  • Design and installation of crane pad,
  • Provision of risk analysis,
  • Implementation of environmental control measures,
  • Design & installation of temporary bracing system,
  • All onsite workings required to remove the CSU machine including tower assembly, ballast removal, piecemeal dismantling and scrap processing,
  • Planning, supervision and execution of all works,

All O’Brien SCS calculations were independently Cat III checked and verified prior to implementation by an external engineering consultant.

The project featured many risks including working at heights, complex lifting operation, operation of heavy plant, working in a live port, hot works around coal dust residue, working over/near water and working in close proximity of operational conveyor belts. However, the project was seamlessly completed to the total satisfaction of the Bristol Port Company and other key stakeholders, with zero health, safety, or environmental incidents.

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