Decom
The controllable buoyancy system could drive down the costs of
decommissioning
Controllable buoyancy
W
ith more than 600 installa- tions in the North Sea
alone, the energy industry faces a daunting and hugely costly task in terms of decom- missioning, with some putting the figure at £30 billion. With this in mind, Deep
The controllable buoyancy system undergoing testing
Sea Recovery has developed its Controllable Buoyancy System (CBS) to help tackle many of the issues associated with de- commissioning and other sub- sea tasks requiring movement of heavy loads through the water column such as renew- able energy device installation. When working at great depths, challenges include in- creasing pressures and de- creasing capacity of compressed gas, shortfall in heavy lift vessel (HLV) capac- ity, remote operation, and in- creasing cost per tonne. CBS technology is a variable buoy- ancy system, which uses liq- uid nitrogen as a subsurface
buoyancy gas source, and as the system is reusable, it has the potential to save operators significant costs. At present, the only tech-
nology available for raising and lowering heavy loads is the HLV crane. CBS could provide a viable alternative, or comple- mentary, technology to assist in cutting costs and improving safety for operators to utilise. Having successfully trialled their first prototype at the Na- tional Hyperbaric Centre in Ab- erdeen, Scotland, Deep Sea Recovery has proven the ability to control the ascent, descent and hover of the CBS system using liquid nitrogen. CBS uses an integrated cryogenic gas gen- erator within a lifting structure which makes extensive use of advanced composite materials that are both strong and light. CBS said: “The modular and scalable design of CBS en- ables the safe handling of loads of unlimited magnitude from less than one tonne right up to tens of thousands of tonnes. For small loads, one CBS unit is likely to suffice whereas for very large loads, multiple, large scale CBS units are likely to be deployed, with links across CBS units to en- able the computerised control and management system to monitor and exercise control over the whole ascent or de- scent operation.” Full autonomy and remote actuation is achieved using its computerised control and man- agement system which enables CBS to generate accurately
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monitored volumes of gas for buoyancy, in order to facilitate the precisely controlled raising and lowering of loads subsea. A shipboard operator is
present to monitor the pre-pro- grammed operation of CBS and, if the situation were to de- mand, has the capability of manually overriding au- tonomous operation. Compre- hensive, real-time telemetric data will be transmitted via datalink to the operator in- cluding remaining liquid cryo- gen reserve, depth, pressure, temperature, physical location, rate of ascent/descent, ton- nage, etc.
This telemetric data will be further supplemented with live video links. If total remote op- eration is demanded, sonar could be used to replace the physical datalink.
Duncan Bates, mechanical engineer and project manager at Deep Sea Recovery, explains: “The industry is inundated with literature detailing the supposed costs of decommis- sioning and there is a constant drive to find cheaper methods of achieving each and every step of the process.
“If the industry sticks with
the current equipment on the market, spiraling costs will be unavoidable. By providing an alternative to the industry in the form of our CBS technol- ogy, we can save organisations money, time, and provide a buoyancy system that is clean, scalable and most importantly reusable, significantly driving down operational cost.”
November/December 2012 Offshore Technology
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