Good results – better than for the OEM supplied equipment – have been reported for a new gas turbine compressor washing system installed at Cleco’s Evangeline power plant. Keeping the compressors clean is a particular issue for this plant because of its agricultural location.
Cleco’s Evangeline combined cycle power plant, an intermediate load following facility, is located in St. Landry, central Louisiana, USA. It is the fleet leader for Siemens SGT6-5000F (W501F) class engines in terms of operational hours. It was also Cleco’s first unregulated power plant.
Due to the agricultural location the engines experience compressor fouling from such sources as pollen and prescribed burning of local sugar cane and cotton fields, resulting in loss of performance.
Compressor washing problems
The plant has three SGT6-5000F machines, two in a 2-on-1 combined cycle configuration. All three engines burn natural gas and are only used for power production. The engines run heavily during peak times and are generally shut down at night. Cleco has experienced intermittent problems with the OEM compressor wash system. Therefore, on-line washing was performed prior to shutdowns or during non-peak hours for risk mitigation and avoidance of potential penalties and on-crank washes were performed during scheduled outages.
Prior to installation of the GTE system described here, Cleco used the OEM-supplied gas turbine compressor water wash system for both on-line and off-line washing of all three engines.
To address the washing issues, GTE started a rigorous R&D programme with Cleco that encompassed a two year testing period. GTE investigated on-line and on-crank nozzle spray patterns for different nozzle sets, engine performance data, system reliability data and operator feedback, with the aim of achieving an optimised design.
GTE washing system
The GTE washing system was installed on unit 7-1, which is part of the 2-on-1 power block. Cleco evenly splits the loads between the engines, so it was possible to collect meaningful comparative performance data for both the GTE and the OEM supplied compressor water wash systems.
The GTE installation employs an automated multi-stage nozzle cleaning system for both on line and on crank washing. It achieves full inlet throat coverage and optimised blade wetting for engine loads from 60 to 100%, providing operational flexibility. The system incorporates GTE’s patented water wash technology and seamlessly integrates into the Siemens WDPF control system to facilitate regular on-line washing by the operators.
The semi-automatic on-crank water wash process reduces the need for operator involvement and decreases turbine downtime. Operator involvement is only required to open the drain valves, initiate the wash, and determine adequate engine rinsing.
Daily use of the GTE on-line washing system has cut the engine power degradation rate in half. In comparison with the OEM water wash system, the GTE system demonstrates an average power benefit of 1.18% and an average increase in engine efficiency of 0.42% over a four month span, between on-crank water washes.
The on-crank wash provides improved degradation recovery better than the OEM water wash system. This is primarily due to the complete intake coverage, use of heated and highly atomised water, and precision controlled injection of the OEM approved additive.
The payback period is estimated to be less than six months.
Mike Bishoff, the Cleco O&M supervisor, says he found the system valuable because it was easy to use and low maintenance, it maintains power output, it reduces fuel and parts costs, and it has added operational flexibility.
Cleco plans to install the GTE system, which is now commercially available, on their two other SGT6-5000F engines at Evangeline.