HEAT-RATE IMPROVEMENTS OBTAINED BY RETUBING CONDENSERS WITH NEW, ENHANCED TUBE TYPES

Significant fuel savings can be achieved at power plants by retubing t he condensers with enhanced tubes. Because of the higher overall heat- transfer coefficient, the exhaust steam is condensed at a lower pressu re and the plant efficiency is therefore increased or plant heat rate is reduced Only the spirally indented type of enhanced tube is current ly being used in the U.S. and most other countries; however, different types of enhanced tubes have been proposed for power-plant condensers , each with their own set of attributes. This paper determines what at tributes and their magnitudes of enhanced tubes lead to the most energ y savings as measured by reduction of the plant heat rate. The particu lar attributes considered are the inside and outside enhancement level s, the inside efficiency index (inside enhancement level divided by pr essure-drop increase), and the enhanced-tube fouling-rate multiplier. This generic investigation showed that the outside enhancement level i s the most important attribute, and a value of about 1.5 can lead to h eat-rate savings of about 20 to 40 Btu/kW-hr. Increasing the inside en hancement is less effective because of the increased pressure drop tha t leads to a reduction of the coolant how rate and velocity. The effic iency index, which is a measure of the pressure drop increase, is only important if the outside enhancement level is close to unity. However , the authors strongly recommend that an economic evaluation be perfor med at each site to determine the energy savings and payback time.