Rolls-Royce launches major power upgrade for the RB211

Staff report

Rolls-Royce has launched its RB211-Gzero upgrade in the form of an engineered modular package. It is aimed at operators of the 440-plus worldwide installed fleet of RB211-C and RB211-G variant gas generators coupled to RT-56 or RT-62 power turbines. The modular format, which also ensures that unit length and footprint remain virtually unchanged, is intended to make retrofitting and maintenance easier.
The advertised power increase can be achieved during routine gas turbine overhaul by retrofitting the package to applicable RB211 units. The main effect is achieved by increasing the flow of air through the engine. This increases power availability at ISO conditions by 10 % for the RB211-G, and up to 31 % for the RB211-C, depending on the existing package configuration and site conditions, mainly ambient temperature. This retrofit approach, which R-R describes as a simple, minimal modification, requires very few changes to the existing gas turbine and also ensures that down time of the power generation facility, or in some cases the oil and gas production platform, is kept to a minimum.

Historical development
This is the third major upgrade of the RB211 since it first went into service in 1974. The industrial machine itself has been refined through in-the-field experience, including remote and offshore operations where availability and rugged reliability are of great importance. There are over 700 units altogether in the field, recording over 30 million operating hours. It is available in a power range of 29 to 44 MW and is aimed mainly at onshore and offshore power generation and oil and gas industry applications.
R-R has a good track record in applying systematic product enhancement and upgrade improvements to increase power output and enhance the efficiency and emissions performance of these engines. The first RB211 was rated at 26 418 horsepower. Year on year, says R-R, the company has been able to drive a series of RB211 unit performance improvements by applying fleet performance data from operating hours accumulated in the field. These include power and efficiency upgrades such as the RB211-GT, RB211-H63 and now the RB211-Gzero.

Upgrading retrofit
The RB211-Gzero gas generator power increase is achieved with increased air flow, together with zero-stage addition, partial re-blading of the intermediate pressure compressor and upgrading of the inlet vane of the power turbine to suit the higher flow.
For existing RB211-C engines, the conversion, which can be implemented during the overhaul cycle in one of the company's own or approved repair and overhaul bases worldwide, combines the existing C to G turbine refit with the RB211-Gzero compressor upgrade to create the RB211-Gzero gas generator. The new RB211-Gzero engine is interchangeable with the current G engine, with similar dimensions and interfaces.
Ease of gas generator refit is a key element of the upgrade alongside minimal package alteration in the cause of achieving a cost-effective modification in the field with minimal downtime.

Retrofit changes
The upgrade (Figures 2 and 3) focuses on two of the five RB211 modules: air intake and intermediate pressure compressor. The remaining three modules remain unchanged and are taken from the donor engine during retrofit.
Module 1, the air intake casing, has been redesigned and shortened to ensure that identical engine interface length is maintained, compensating for the increased length of module 2, the intermediate pressure compressor. A redesigned elliptically-profiled nose bullet extends further forward in the air stream and achieves ideal airflow entry to the compressor.
Core elements of the upgrade focus on the intermediate pressure compressor module. Here the existing stage one disc and blade row is removed and replaced with a new stage zero, and stage one discs and blade assembly, designed to mate with the existing stage two-to-five drum assembly.
The new stage zero and stage one discs are manufactured in titanium and replace the existing stage one steel disc. Blades on the new discs feature an elliptical leading edge design for improved efficiency. High wedge-angle and 3D tangentially-bowed vane technology from the Rolls-Royce Trent aero family contribute to improved compressor efficiency across the widest operating range. The total number of variable-geometry stages increases from one on the RB211-G to three: one row of variable inlet guide vanes and two stages of variable stator vanes. New power-turbine nozzles were installed for better hot-day performance. To accommodate greater flow, a new power-turbine thrust bearing package was installed. Bleed ducting to the RB211Gzero design was also installed.

Modular package
The RB211-Gero modular package is sold as factory tested and ready for rapid installation and commissioning. The unit design incorporates most engine accessory systems integral to the package, which simplifies installation. The gas generator modules can be removed and replaced individually, with new or leased modules at a service centre, while the originals are being repaired or overhauled.
An integrated suite of routine repair, service and maintenance processes is also available including 'TotalCare' service agreements, remote monitoring and diagnostics, and technical training.

Captions

Figure 1. Cutaway of the Gzero modified RB211 aeroderivative
Figure 2. Side by side comparison of RB211 and RB211-Gzero
Figure 3. Principal modifications to the power unit
Figure 4. Power curve comparisons - RB211-C62, RB211-G62 and RB211-Gzero