Deaerating condenser boosts combined-cycle plant efficiency
Anew system of steam condenser dissolved oxygen control has found favor in the combined-cycle cogeneration market. Savings in equipment, a reduction in building size (and plant height), and the ability to deaerate large quantities of makeup water using only turbine exhaust steam are the reasons.
In earlier days, no condenser manufacturer guaranteed condensate oxygen levels of 7 parts per billion (ppb) under any operating condition. Instead, guarantees were limited to Heat Exchange Institute (HEI) standards.
HEI standards promise 0.005 cc/I (7 ppb) dissolved oxygen (DO) in the condensate only if (1) the air leakage is reduced to a fraction of the tabulated leakage rates; (2) the condenser makeup is limited to 3%; or (3) the condenser is operated at or near full load and with design cooling water conditions.
Condition (3) is not stated as a DO limitation by HEI. It is a limitation on the condenser vacuum and the condensing temperature approach, both of which affect condensate dissolved oxygen levels. HEI standards for steam surface condensers indicate that these limits can only be achieved as follows: at or near full load:
