Vicky WilsonFollowing a fourth successful order for its GT35 gas turbine compressor units from BP last year, ABB Stal recently gained a further order for a unit to be installed on a new UK sector FPSO. This follows several other orders last year for GT35s from fast ferry operators.
ABB Stal market communications manager Bo Svensson believes this recent success is due to the many similarities in the requirements for the two types of vessels. "Obviously the operating profiles of the two applications are very different, but both need to operate within certain pitch and roll parameters together with the ability to withstand G-forces higher than those required for fixed platforms and onshore applications."
Although gas turbine technology is well established in the offshore sector, the changing environment has seen more stringent requirements including lower size and weight, low life-cycle costs, high reliability, low maintenance and cost-effective environmental standards. As a result, ABB Stal has seen a growing interest in its light, high-efficiency industrial GT35 and GT10 gas turbines for both power generation and mechanical drive applications.
ABB Stal's light industrial range combines many of the advantages of ero-derivative and heavy-frame industrial machines. The GT35, originally developed as a jet engine for the Swedish Air Force and transformed into an industrial unit, has easy service access and a rapid starting capability.
Although slightly heavier than ero-derivative turbines, the GT35 and GT10 are as compact as an ero engine and use a common mineral oil lubrication system which can also provide oil to the drive machine, thus avoiding the need for expensive synthetic oil for the gas generator.
The units also have lower firing temperatures: 850?C for the GT35 and 1,112?C for the GT10. (For ero-derivatives typical temperatures are around 1,200!C). Also, due to the lower firing temperatures, good fuel flexibility is achieved.
While the GT10 requires some simple blade cooling, the GT35 does not need any. Both types have a low power degradation. As an example, the GT10 has been certified by KEMA in The Netherlands to have only 1.5% power degradation over 15,000 hours, and three GT35 units on the BP Norge Ula platform had power degradation rates of less than 2% after around 40,000 hours operation each.
In response to the drive for low NOx emissions, both the GT35 and GT10 can also be equipped with ABB's dry, low NOx EV burner, enabling operation with 25ppm NOx to be achieved.
For high speed marine propulsion and FPSO applications, the GT35 and GT10 have been adapted to operate under pitch and roll situations. "We see a particular area of opportunity in the FPSO market," says Svensson. "Rather than the 30,000b/d capacities seen in the past, FPSOs are now being built to handle around 100,000b/d and our medium-sized gas turbines are ideally suited to meet the larger mechanical drives and generating sets required by these vessels."
Combined cycle system
ABB is also working with a Norwegian oil company to study combined cycle installations in order to reduce CO2 emissions. The company has developed a compact combined cycle system.
In the combined cycle system, gas turbine exhausts are fed into a waste heat recovery boiler to produce steam which then drives the steam turbine. Since most of the fuel energy used in a gas turbine disappears with the exhaust gases, the addition of a steam cycle greatly increases the efficiency of the system as a whole. Specific fuel consumption will also improve: the result is a reduced CO2 tax. For example, a marine combined-cycle system based on the GT10 turbine uses 190g/kWh, compared with 240g/kWh for a GT10 used in a simple cycle, a reduction of more than 20% in specific fuel consumption.
With a system involving 3 x 25MW gas turbines, the user would pay approximately NKr30 million per turbine per year in CO2 tax. One gas turbine could be replaced with one steam turbine, giving the same amount of power, but with a saving of NK30 million in CO2 tax.
"We see many advantages in introducing combined cycle technology offshore," says Svensson. "The system has good fuel economy, a more environmentally-friendly profile and a space/weight advantage, together with lower maintenance requirements resulting in higher levels of availability."
ABB Stal is the only company manufacturing steam turbines in Scandinavia and has a long tradition of supplying such turbines to the shipping industry.
For more information contact Bo Svensson, ABB Stal: telephone +46 122 81000, fax +46 122 18684, Email: bo.svensson(a)sesta.mail.abb.se or http://www.abb.se/stal/index.htm.