Proceedings of the 6th International Symposium on Marine Engineering
Tokyo, Japan, October 23rd to 27th, 2000
ISME2000-PD-34
DRAFT SUBMITTAL
FT8 PHASE II RELIABILITY IMPROVEMENT PROGRAM
Warren M. Boley Jr. & Thomas W. Prete
Pratt & Whitney/Turbo Power & Marine Systems, inc.
East Hartford, Connecticut, USA
Abstract
This paper describes the FT8 gas generator (GG8) development history, including required design modifications to the JT8D aircraft engine, initial field experience and the latest reliability improvements incorporated into the GG8. These include improvements to the bearing compartment operating temperature, improved bearing compartment seals, as well as increases to bearing life. Turbine durability improvements are also discussed. In house test results are correlated to over 100,000 hours of field service with the Phase II product to provide insight into the enhanced development process used to validate improvements prior to field incorporation.
The incorporation and control of a cold air buffer system to control bearing compartment oil coke formation is provided. Improvements to bearing compartment carbon seals are reviewed, and the benefits of this design are discussed. Rotor system thrust bearing life improvements are achieved through the incorporation of modified compressor seals and turbine aerodynamics.
Introduction
The GG8 Industrial gas generator is based on the Pratt & Whitney JT8D aircraft, which is the most widely-used turbofan in aviation history with over 13,000 produced and over 400 million flight hours. The GG8 development program was launched in August 1986 on the premise that the combination of a highly-proven aircraft engine, the latest Pratt & Whitney technology and lessons learned from Turbo Power & Marine's success with 1,200 FT4 industrial gas turbine systems would result in a reliable, highly efficient industrial gas generator. Once developed, the gas generator would be ideal for the numerous industrial applications such as : peaking/intermediate load, base load cogeneration/combined cycle, marine use, and mechanical drive operation. When combined with the PT8 power turbine, the FT8 has a simple cycle, nominal ISO rating of 25.4 MW and a heat rate of 8950 BTU/kW-hr (LHV) which is one of the highest efficiencies in its power class. The first FT8 commercial installation was at Pratt & Whitney Manufacturing Division in East Hartford, Connecticut where it began base load, cogeneration duty in 1993. Experience and lessons learned during initial commercial service identified durability and reliability improvement opportunities. After over 100,000 initial service hours, the Phase II reliability improvement package was defined, validated and released for commercial service in July, 1996.
Technical Description-The GG8 Gas Generator
The GG8 is a twin spool gas generator with an eight stage low pressure compressor and a five stage high pressure compressor. The first 3 stages of the low compressor have variable geometry. As shown in Figure 1, the GG8 low compressor results from removing the fan stage, fan ducts, and first stator from the JT8D-219 and adding two supercharging stages forward of the 1.5 stage. The new stages were designed as controlled diffusion airfoils, in which the aerodynamic blade shape controls the diffusion on the suction surface of the airfoil to avoid losses due to boundary layer separation. The entire rotor structure from stage 2 aft, the core static structure and stator vanes from stator 1.5 aft, and the #1 bearing compartment are existing JT8D-219 hardware. The inlet case and the outer main structural cases are unique to the FT8.
The high compressor is identical to that of the JT8D-219, except for some material and coatings incorporation for industrial and marine service, and changes to the casing.
The overall combustor configuration of the JT8D-219 was retained, consisting of nine combustion cans, each with a single fuel nozzle followed by an annular transition duct. The cans and fuel system have been modified for liquid and/or gas fuel operation with water injection for NOx control.
The gas generator turbine differs from the JT8 with the introduction of advanced aerodynamics, cooling system, and seal technology. A single-stage high pressure turbine drives the high compressor, while a two-stage low turbine drives the low compressor. Active clearance control is used in the low turbine where cooling air flow is controlled to maintain optimum case/blade clearances throughout the operating profile of the machine.
