Rolls-Royce Launches RB211-Gzero Power Upgrade
Power increase to 32 MW achieved with no increase in length and minimal change internally
Rolls-Royce unveiled its latest retrofit upgrade of the RB211 aeroderivative industrial gas turbine at the 41st Turbomachinery Symposium last September. Designated RB211- Gzero, it represents a 10% boost to 32 MW in power output for both mechanical drive and power generation.
The RB211-Gzero retrofit upgrade provides existing users of industrial RB211-C and RB211-G Gas generators, using respective RT-56 and RT62 power turbines, with a nominal 10% power increase, depending on ambient temperature. The RB211Gzero further enhances the productivity and customer value of these units.
Rolls-Royce engineers have designed the retrofit configuration to achieve power increase with minimal modification to the existing package design during routine unit overhaul. Scott DeWolfe, director of Sales and Marketing Support for the Rolls-Royce Energy business, said the cost-effective and simple retrofit approach ensures facility downtime is minimized, while performance, power and operator profitability are optimized. “The industrial RB211 has been refined through in-field experience, including remote and offshore operations, where availability and rugged reliability are of crucial importance,” DeWolfe said.
To the casual observer, the RB211Gzero appears the same as the RB211G. The length is the same, so that it will fit exactly into the original housing with the same footprint on the existing foundation. The RB211-Gzero upgrade is achieved with increased airflow featuring zero-staging, partial reblading of the intermediate pressure compressor and upgrading of the inlet vane of the power turbine to suit the higher flow.
The upgrade focuses on two of the five modules: the air intake and the intermediate pressure compressor. The remaining three modules remain unchanged and are taken from the donor engine during retrofit. The design process requires a comprehensive knowledge of materials and flow path design. The air intake casing has been redesigned and shortened to ensure identical engine interface length is maintained, compensating for the increased length of 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. The existing stage-one disc and blade row is removed and replaced with new stage-zero and stage-one discs and blade assembly. These are designed to mate with the existing stage-two to five-drum assembly.
Stage-zero and stage-one discs are in titanium and replace the existing stage-one steel disc. Blades on the new discs feature an elliptical leading edge design technology from the Rolls-Royce Trent engine family for 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 hot-day match. To accommodate greater flow, a new power-turbine thrust bearing package was installed. Bleed ducting to the RB211Gzero design was also installed.
The modular design allows the RB211-Gzero gas generator modules to be individually removed and replaced with new or leased modules at a service center, while the originals are being repaired or overhauled.
“Rolls-Royce has a proven track-record of applying systematic product enhancement and upgrade improvements to increase power output and enhance the efficiency and mission performance of equipment for owner operators,” DeWolfe said. “The first RB211 gas turbine went into service in 1974, rated at a nominal 20 MW,” DeWolfe said. “Year on year, our team of expert design and field-service engineers has applied fleet performance data insights from operating hours accumulated in the field to drive continuous RB211 unit performance improvements. These have included power and efficiency upgrades and improvements such as the RG211-GT, the RB211-H63 and now the RB211-Gzero.”
DeWolfe said the RB211-Gzero is engineered as a modular package, factory tested and ready for rapid, low-risk installation and commissioning. Its design incorporates engine accessory systems integral to the package, simplifying installation. But, the main advantage is the 10% power increase under ISO conditions.