52 PRODUCTION/PROCESSING/HANDLING
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towards refinement (and, possibly, optimisation) of the separation systems, concentrating on reducing size and weight, while attempting to enhance performance and reliability.
A mix of physical laws and empirical data, together with a good deal of prior experience, forms the background to the process and mechanical design procedures. Unfortunately, the close confines in which the internals operate means that some interaction between the internals should be expected. The operator may be able to observe the overall influence of these effects but it will usually be impossible to measure the performance of the individual separators, directly.
In operation, the rates of separation of the fluid components are typically governed by the rates at which oil droplets rise through water to form the oil layer, or settle out of the gas phase, under gravity or in a cyclonic device. These fundamental physical processes therefore determine both the maximum flow rate through the pressure vessel, and the dimensions of each separation device. Furthermore, it is evident that the flow conditions will show large spatial variations across the diameter and length of the vessel, because of the evolving separation processes and the changes in fluid composition. This complexity implies that the internals should (ideally) be considered in sequence, from the flow diverters and distribution devices at inlet to the liquid/liquid separation and gas cleaning systems downstream. Such detailed understanding of the flow behaviour is not easily achieved but both the client and the supplier, despite their different standpoints, must ultimately recognise the need for this understanding if satisfactory reliability and performance is to be achieved. The reducing output from established centres of
production, coupled with sharply rising demand from developing nations, has dramatically increased the value of all petrochemical reserves. Consequently, there is emphasis on increasing the recovery from
maturing fields and on re-assessing fields that were once considered to be marginal. As one consequence of the growing economic and geo-political pressures on energy supplies, the plans to exploit deep water resources by means of sub-sea operations must, surely, present one of the most exciting challenges ever to face the industry. The intention is to transfer process control and separation devices to the sea bed, thereby dispensing with the need for a rigid or floating platform to provide support and access to the well-head. Among the many benefits claimed, sub-sea processing offers the opportunity to re-inject bulk water back into the well, thereby increasing the yield and delivery rate, delivers a significant reduction in the capital and operating costs, and provides much greater operational flexibility over the life of the field. However, taking the decision to locate the pressure vessel and separation systems, together with pumps and valves, and the associated instrumentation and control equipment, on the sea bed, places extra demands on the designer in terms of size, weight, reliability and performance. The assembly of this equipment at depths up to 3000m, coupled with greater demands for efficient and automatic operation, brings fresh technical challenges that will require a great deal of ingenuity for solution. However, the enormous potential of hitherto untapped sub-sea gas and oil reserves off the coast of West Australia and West Africa, together with the chance to enhance maturing or marginal fields in the North Sea and off the East Coast of South America, makes it certain that all related suppliers, including those specialising in separation equipment, will move towards even greater design sophistication over the next few years. This is the route chosen by Zeta-pdm. o
Enter 52 or ✔ at
www.engineerlive.com/iog
Dr John Turner is Technical Director, Zeta-pdm, Newport, Isle of Wight.
www.zeta-pdm.com
TRIPLE ECCENTRIC VALVES FOR GAS-TO-LIQUID PROJECT
yco Flow Control has announced details of the order it is now completing with Vanessa triple eccentric valves for the Shell Pearl (gas-to-liquid) GTL project at the Ras Laffan Industrial Park in Qatar, estimated at over $100 million in value.
T
The size of the project led to the involvement of several major EPCs located in various countries and continents, but such was the strength of Tyco global capabilities and its handling of the extremely challenging SGSI (Shell Global Solutions International) Type Approval Test (TAT) programme that it resulted in a truly outstanding result. Initial contact was established with Shell in The Netherlands in 2005 to discuss the Pearl GTL project and the necessary TAT programme for valves. There followed
eighteen months of technical discussions to define the applicability of the Vanessa zero leakage triple offset rotary process valve range, the acceptance criteria and the scope of the TAT programme. During the very severe testing regime the entire Vanessa valve range was qualified up to 72-in class 600 and 48-in class 900 in basic, cryogenic and high temperature configuration and witnessed by Shell. The Tyco Valves and Controls UK project group worked closely with JGC Corporation (JGC) and Kellogg Brown & Root LLC (KBR) throughout the engineering phases of the project to reinforce the activities that had been carried out in conjunction with SGSI. o
For more information, visit
www.tycoflowcontrol.com www.engineerlive.com
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