The Measurement of Condenser Losses Due to Fouling and Those Due to Air Ingress

Putman, R.E. & Harpster, J.W.
“The Measurement of Condenser Losses Due to Fouling and Those Due to Air Ingress” EPRI Condenser Seminar and Conference, San Antonio, TX, Sept. 10-12, 2002.

Abstract

The performance of a steam surface condenser is negatively affected not only by tube fouling but also by the presence of excessive amounts of air within the shell side of the condenser. However, because they have similar effects, it has been the custom to lump their costs together. Clearly, if the contribution of each to operating cost could be estimated with some confidence, then maintenance decisions would become focused on whether it is more important to clean the condenser or to remove the source of an air in-leakage.

There are two general methods for distinguishing between these two sources of condenser performance degradation: (a) measure the resistance due to fouling and subtract this from the total increase in tube thermal resistance to obtain the increase due to air ingress and (b) estimate the change in tube thermal resistance due to air ingress and subtract this from the total increase in thermal resistance to obtain the increase due to fouling.

For both methods, the frame of reference is an estimate of the total apparent increase in single-tube heat transfer coefficientresulting from these two effects. This can be obtained by calculating the present single-tube heat transfer coefficient using the standard Fourier equation, and comparing it with the single-tube U-coefficient for a clean condenser operating under the same load and cooling water conditions. In both cases, the condenser Performance Factor needs to be applied.

One approach to measurement method (a) is outlined in the new ASME Power Test Code PTC.12.2-1998. A variation of this method is embodied in an EPRI/Bridger Scientific report in which the flow through one of the tubes in each pair is also measured.

Measurement method (b) involves calibrating the degradation in performance due to air ingress by injecting known quantities of air or nitrogen and also noting the reading of the flow meter measuring the air removal rate. Subsequently the flow meter can be used to infer the degradation due to air ingress based on the change in air removal rate. Interference with the precision of these methods from “air binding” and “zones of stagnation” are also discussed.