Gas Turbine and Combined Cycle Generator Dewpoints: Worse Than Expected

Many hydrogen cooled generators operate with no hydrogen dryer. Plant personnel offer a variety of reasons: • The OEM didn’t supply a dryer to begin with. • Manual Reactivations are too labor intensive. • Don’t think their generator is wet. • Because they have a Gas Turbine (no steam), they don’t think there is anywhere for the hydrogen to pick up moisture. • Don’t think moisture matters. • Purity is good so everything must be fine. • They employ “Bleed and Feed” or “Scavenging” to deal with purity / moisture issues. Generator manufacturers recommend keeping the hydrogen dry. We had a theory that many generators were much wetter than was realized or recommended by the manufacturers. We took portable dewpoint analyzers to the plants to test the actual dewpoint of the hydrogen. This paper presents our results. Over 90% of the generators tested were found to have hydrogen dewpoints higher than the generator manufacturer’s recommendation.