What is it worth to maintain design clearances in a steam turbine? Would 1% efficiency improvement be worth the cost of new seals? The two primary causes of efficiency loss in a steam turbine are leakage and steam surface roughness. During a recent maintenance inspection, Macek Power was asked if old worn shaft seals should be replaced in favor of new seals available in the customer warehouse. Replacing the seals in this relatively small 9-stage, 20 MW, machine after all, would cost at least, US$30,000.
To help the customer, a small utility, decide on the expense of seal replacement, Macek Power employed thermodynamic performance simulation techniques to analyze the steam path and determined that the difference in turbine mechanical efficiency between excessive clearance old seals and new seals was 1.4%. For the same maximum possible steam flow into the turbine, calculations showed that new seals with in-range design clearances would equate to a difference in production of 360 kW.
At an electrical energy selling price of $0.05 per kWh, the difference in annual revenue at this location between old and new seals was shown as approximately US$158,000. Not surprisingly, the customer decided to replace the seals. This is one example of how Macek Power engineering and analysis can benefit the end-user.