Mammoet completed the replacement of a matured exhaust silencer for a gas turbine, at a gas-fired power station in Victoria. Removal of this 305t exhaust silencer was completed in a single lift reducing the amount of time the client, an Australian energy company, needed for their operations to be suspended to allow replacement to take place.
There were several challenges on site, which included the space available, how to interface with other activity crucial to the lift procedure, and the technical complexity of the lift itself – which needed to be very precise, despite the weights involved. The challenge lay in creating a methodology that was both strong enough to lift the loads and fast enough to keep delays to a minimum.
So, the lift was meticulously planned, as every aspect of the lift was engineered weeks in advance. The crane’s position, boom laydown and location of the superlift tray were all marked out ahead of its arrival on site, ensuring engineering checks could be made that significantly optimized its setup time.
Mammoet proposed to use the Liebherr LG1750, because its suspended ballast system allowed the center 125t ballast tray to be disconnected from the outer 400t capacity ballast tray, once the load had been raised to the installation radius. This cut down on any delay so that the crane’s counterweight could be adjusted by auxiliary cranes and allowed the team to execute the project both efficiently and meticulously.
Secondly, the team faced the challenge of having to deal with the gas turbine’s tight shutdown schedule. Mechanical preparations could not start until the gas turbine was switched off and there was a narrow timeframe to complete lifting lug welding, so that the LG1750 crane could be assembled and be ready for lifting.
Liebherr developed a completely new boom system with the designation SX for its 750-tonne lattice boom cranes LR 1750/2 and LG 1750. This has proved invaluable for erecting the latest generation of wind turbines where turbines with a hub height of up to 165 metres and component weights of up to 120 tonnes.
The new SX system has already been tested and is available now. It differs from previous boom systems by the fact that 3.5 metre wide lattice sections are used in the bottom area of the boom rather than sections measuring just 3 metres wide. The extended lattice sections increase the lateral stability of the boom and therefore deliver a higher load capacity. Furthermore, the weight of the lattice sections has been reduced. This means that the boom length can now be raised up to 165 metres comprising the main boom plus the fixed lattice jib.
An additional increase in lifting capacity is achieved by a particularly innovative extension to the SX system: instead of 3.5 metre wide lattice sections, two lattice sections each 14 metres in length (SX2 system) or three lattice sections each 14 metres in length (SX3 system) with a width of 6 metres are installed in the lowest area of the main boom. This provides additional rigidity to the boom system, thus increasing its load capacity.
In order to install the six metre wide lattice sections in the boom, there is an extension adapter from 3 metres to 6 metres on the pivot section for the turntable. At the top the width of six metres is reduced to 3.5 metres by a second adapter. When designing this system extension, Liebherr focused on ensuring it was highly economical. This means that crane operators only have to buy the 6 metre wide sections and the adapters in addition to the SX system.
The challenge for the development of the six metre wide lattice sections, however, was the question of how they could be transported economically on public roads. Liebherr created something completely new to solve this problem: the wide boom sections made up of two halves which can be bolted together in the centre and separated again very quickly. To transport them, the individual halves are slightly offset longitudinally and then joined so that they mesh together like teeth. This means that a practical transport width of 3.5 metres can be achieved.
The complete SX system can be interchanged between the LR 1750/2 crawler crane and the LG 1750 mobile crane. To enable the higher lifting capacities of the SX system to be used, Liebherr has also developed a new fixed jib specially enhanced for this system. A runner is included, and the head sheaves and a new hook block are designed so as to prevent the hook block becoming twisted.
Mammoet overcame the above challenge by carrying out detailed site surveys in advance and planning an accelerated mobilization schedule. The LG1750 could then be brought onto site and set up quickly to minimize the required shut down period for the gas power plant.
Once the 205t used silencer had been removed, a new silencer was be fitted, comprising two pieces: a 168t base module and a 159t top module.
Throughout the project, Mammoet ensured the highest levels of operational efficiency, so that disruptions to day-to-day work were minimal, and that downtime for the power station was kept low. Furthermore, Mammoet was able to provide right equipment and expertise to efficiently setup and operate the LG1750 SX despite significant space restrictions on-site.
Completion of this replacement will see the gas-fired power station continue with full operation for power generation. The power station’s two generating turbines have an overall capacity of 566 Megawatts.