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AN INCREASING NUMBER OF UTILITY COMPANIES ARE USING CHEMICAL FOAM TO CLEAN THEIR STEAM TURBINES as a valuable tool in their maintenance mix. Since the procedure is done in a few days-without disassembling the turbine-it offers dramatic cost savings over conventional cleaning methods. While the technique has become recognized as a cost-effective cleaning method during a scheduled outage, recently its benefits are also being realized to restore full load between outages. This approach allows considerable flexibility in maintenance scheduling by extending time between outages or enabling potentially instant load recovery without waiting for a major outage (Table 1).
Deregulation demands efficient, cost-conscious operations. Forced to stretch the time between major outages, utilities must juggle critical maintenance decisions to achieve maximum power output. A load decline of 20 to 30 MW can run into millions of dollars in lost generation in just a matter of months. Generation capacity needs to be restored economically without waiting months or years for the next scheduled outage. When a drop-off is attributed to turbine inefficiency-if monitoring does not indicate mechanical failure-the decline is often due to deposit problems on the turbine steam path components. The traditional solution means a complete turbine teardown requiring a major outage, rotor removal, grit-blasting and reassembly. However, for a load loss related to deposits, chemical foam cleaning can offer a 100 percent success rate and 100 percent load recovery in a matter of days.
TEXAS QUICK DECISION
At the Welsh Power Plant in East Texas, Southwestern Electric Power Co. (SWEPCO) saw the output on Unit #2 dropping off at a noticeable rate in early 1998. As the scheduled spring outage for Unit #3 approached, the risk of having two units down at the same time continued to increase. Since the load decline had been gradual and vibration had not changed significantly, plant and engineering support concluded that steam path mechanical failure was not likely. Turbine pressure readings indicated a problem in the high-pressure section between the first stage and the cold reheat. While there was no history of abnormal turbine deposits, the evidence provided by low vibration levels, the gradual loss of output and the fact that the capacity factor of the three Welsh units had increased 30 percent over the past three years,...