Abstract
The objective of this study was to develop an understanding of the relationships between biofouling, heat transfer, and to assess the technical feasibility of the targeted chlorination (TC) concept as an alternative to conventional chlorination in once-through seawater cooling systems. A shell and tube type heat exchanger was designed and constructed. The test facility monitored biofouling growth by measuring heat transfer resistance (thermal performance), pressure drop (hydraulic performance), and biomass deposit. Biocide effectiveness was determined by triplicates' average residual biomass.Tests were run to evaluate 18 treatment scenarios. Preliminary tests were done to determine variabilities between shells and among tubes, effect of heating, very high dose chlorine burn out and regrowth behavior. LOGIT, a software package by the National Bureau of Standards (NBS) for sigmoidal fit, was used for the preliminary test data.The other three tests studied effect of chlorine dosage (low, high), contact time, and frequency. To minimize variability in results, triplicates for each chlorination scheme were used. The total amount of chlorine applied (flow rate Q x C x T x F) ranged from about 400 to 4000 pounds per million gallons per day (an equivalent to a CTF range of 6 to 60 ppm.min/day). With respect to efficiency of biofouling control, it was found by regression analysis that among four variables C, T, (CT) and F, F was most significant and C, T, and (CT) were relatively equal in ranking. The results of this study have large ramifications with respect to technical feasibility of TC concept, i.e., pulse injection of higher chlorine into sections of the condenser can improve condenser performance while reducing chlorine usage to regulatory acceptance levels. Suspected corrosion problems associated with the high levels of chlorine were absent for the chlorination levels (0.5 to 20 ppm) studied.This study, in addition to verifying the TC concept, has also broadly limited the effective dose (5 ppm maximum), frequency (twice per day), and contact time (15 minutes). The difference between targeted chlorination, conventional chlorination and no chlorination was also demonstrated with respect to biofouling of AL-6X condenser tubes for once-through cooling with seawater.