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when used with another type of pipe cleaning system (Stone and Webster Engineering Corp.
1992).
6.4. Summary
Online systems clean a thin layer of foulantwith each pass, so organisms are not able to build up.
There is limited maintenance and operator attention required and service is usually not
interrupted during cleaning. Constant movement of the balls in the pipes can deteriorate pipe
wall material and brushes can scrape away thewallmaterial aswell. Ballsmust be inspected and
replaced frequently. Debris can stop ball movement, causing the pipes to clog, resulting in a
system shutdown.
Offline systems provide a variety of options to deal with either soft foulants, or harder and
tighter foulants. The water lance system is the only method that does not require periodic
replacement. All offline systems require an operator during cleaning. Some equipment poses
safety hazards due to the highwater or air/water pressures that are used tomove themechanism
through the pipe. The cleaning materials used can damage pipe walls if used aggressively or
incorrectly (Rice et al. 1993).
Pipe cleanliness may begin to deteriorate as soon as the cleaning is complete. If a hard fouler is
attached in the pipe, the mechanismmay not be able to adequately remove it (Rice et al. 1993).
There is a loss of production if the system requires the plant to be shut down. Once the plant is
brought back into operation, the foulants will continue to grow back, decreasing the plant’s
efficiency.
7. CombinationApproaches
The descriptions of biofouling control options provided above include approaches that that can
be considered combinations (e.g., use of sodium hypochlorite plus sodium bromide) and the case
studies below provide additional examples (e.g., copper and chlorine). Beyond simple chemical
mixtures, combinations of a targeted mechanical, coating, or water treatment strategy have the
potential to enhance or optimize cooling system fouling control. For example, as described in
Section 2, a combination of heat and acetic acid has been proposed to specifically control
hydroids. However, all potential combination strategies require careful consideration of the
benefits gained from multiple approaches against the added costs and logistical constraints
associatedwithmore than one controlmeasure.
A combination strategy employed by some power plants is to install debris filters to remove
coarse solids and large organisms and water treatment (e.g., chlorination) or an anti-fouling
coating. However, very little information is available on the performance and costs of these
combined approaches. CCNPP has decided against debris filters as a control strategy but has
applied a silicon-based anti-fouling coating, which appears effective at limiting the growth of
many macro-organisms but does little to control
G. franciscana
. Additionally, the aging,
maintenance and reapplication of the coating has become a concern. The addition of a water
treatment and/or onlinemechanical approach to the existing anti-fouling coating strategymay be
