This paper describes in detail ALSTOM’s steam path upgrade of JK Spruce Unit 1 GE ‘G2’ HP-IP turbine cylinder. The retrofit features high performance impulse technology three dimensional blade designs for short height turbine stages. Performance improvement was achieved through improved aerodynamic design and increased stage count in the HP expansion (the number of stages in the IP remained unchanged in order to maintain the steam conditions in an extraction part-way down the steam path). The unit was also converted from partial arc to full arc steam admission during the retrofit which resulted in additional performance improvement at full load conditions. Performance guarantees for the retrofit were given in the form of absolute values for HP and IP cylinder adiabatic efficiency and a guarantee on absolute post-retrofit output power. The guarantee levels were based on in-house performance prediction method for turbine cylinders employing the Company’s low reaction technology blading. The code is based on the method first described by Craig and Cox [1], which has been continuously updated and developed to correctly account for advances in the company’s steam path technology over time. The guarantee for the HP cylinder efficiency (excluding the effect of inlet valve pressure drop) was 93.0%, the IP cylinder was guaranteed to achieve an efficiency of 92.8% excluding valves. The retrofit performance achieved was verified by enthalpy drop tests on the HP and IP expansions and the guaranteed performance levels were achieved in both cases. The centre-gland leakage was also measured as part of the performance guarantee testing. A novel method using the centre-gland blowdown pipe was employed, as an alternative to the temperature variation method. This alternative approach is described in the paper. The retrofit has now been in operation for a period of approximately two years and following the initial guarantee testing, additional performance tests have taken place at various points during this period. The data allows any degradation in the performance of the retrofit cylinder over time to be assessed. This is also discussed in the paper.

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