Liebherr-Components has developed a gear ring rope winch for the RL-K 7500 offshore crane, which is specially designed for heavy lifting tasks at sea. With a tare weight of 180 tonnes the ZSW 2400 is the largest and heaviest rope winch offered by Liebherr. It is particularly noted for its high availability and long service life, which is reached by a redundant drive system and an innovative winding mechanism that protects the rope. The Liebherr Pactronic® system makes it extremely energy-efficient. Integrated in the complete system with hydraulic drives and control system, the rope winch enables active heave compensation (AHC) for the subsea crane.
Oil and gas extraction systems are being installed directly on the sea floor more and more often, which increases the requirement for high-performance subsea cranes. This was why Liebherr-Components decided to develop a rope winch for heavy loads and extreme depths. The winch for the new Liebherr RL-K 7500 subsea crane should also be designed for a long service life and its mechanical principle of operation should be simple and robust.
Proven rope winch design with innovative features
During the development period of about one year, the designers at Biberach an der Riß, Germany, were able to draw on decades of experience in the field of large rope winches. They decided to use a conventional rope winch design without additional winders, because this rope winch design can raise and lower the full load in any position.
The rope drum with a diameter of 2.9 m is hydraulically driven on both sides by gear rings. A total of eight Liebherr DMVA 165/165 double motors on the primary drive side and eight DPVO 165/DMVA 165 pump motors and 16 DAT 500 slewing drives on the storage side is required to exert the high rope pull force of 270 tonnes with single reeving and to manage the active heave compensation. The drum with Lebus grooving holds eight rope layers with a rope diameter of 100 mm. The rope winch can therefore move loads up to 200 tonnes at depths up to 2,000 m and loads up to 95 tonnes at depths up to 3,400 m.
High availability and energy efficiency with redundant drive system
The redundant drive design with two load paths can still lift the load in the event of failure of one drive side. This guarantees maximum safety and very high overall availability of the crane in any operating condition of the rope winch. The secondary drive side acts as an energy recovery system while a load is being lowered. The pump motors, developed and manufactured by Liebherr, are designed to operate as hydraulic motor while lifting a load and to operate as pumps during lowering or while idling to charge an energy accumulator (gas pressure tank). The innovative Liebherr Pactronic® system was originally developed for the mobile harbour cranes manufactured at Nenzing, Austria by the Liebherr division Maritime Cranes, and has been specially adapted for active heave compensation (AHC) in subsea cranes. The Pactronic® system allows up to 60% of the power required for AHC operation to be taken from stored energy. The resulting energy efficiency of the system is unparalleled in the market.
Wide range of applications in the modular system
Another advantage is that the new rope winch is based on a modular system. The Lebus half shells on the rope drum and the insertion plates, which are available in different sizes, can be replaced. This allows exactly the same winch to use ropes with different diameters (to a maximum of 100 mm), and it makes applications as deep as 3,400 m possible. This greatly increases the range of possible applications of the rope winch. It is suitable for a very wide range of lowering and lifting operations in subsea applications, such as subsea mining or oil and gas drilling.
Active heave compensation – refined technology
Because subsea lifting and underwater work is possible only when the sea is quiet, only very small time windows are available for such operations. This can be optimised by decoupling the load from the vertical motion of the ship. The Liebherr maritime crane division has developed a control for offshore cranes to meet the requirement for active heave compensation (AHC). During development, the AHC control and the rope winch, which compensates for the wave motion by accurately calculated counter-motions, were precisely calibrated together.
Traditional AHC systems that compensate for the motion with hydraulic cylinders lead to high wear on the winch and there is also the risk that the system may become blocked. The newly developed deep-sea winch from Liebherr-Components has innovative winding mechanisms that protect the rope. The rope drum was designed with an increased number of windings to reduce the number of rope layers. The winding behaviour with reference to a diagonal pull in the required range of 0.8 to 1.5 degrees is maintained by an axial motion of the winch. This ensures that the rope is seamlessly wound on the special grooves and the winding capacity is fully used. The reduced material requirements for the end plates and the drum mantle saves up to 50% in weight compared to other designs with fewer windings and more rope layers. The innovative design of the winch significantly increases the rope service life and availability, which contributes to a great reduction in operating costs.
Press Release, September 04, 2012