MERCER02-14
17
5.3.
Summary
Coatings based on foul-release paints are effective and limit initial settlement and attachment.
However, these systems are mechanically weak and subject to failure due to detachment and
abrasion. Biocide-based coatings are effective and strong, but release toxins into the surrounding
environment, whichmay impact surrounding organisms.
All of the coatings need to be applied to clean, dry substrates. The piping systemmust be shut
down for a minimum of four days to accomplish coating application. Both types of coating
systems require the pipes to be cleaned periodically in order tomaintain a low level of fouling.
Also, the coatings require periodic reapplication, which can take several days depending on the
coating type and degree ofwear or damage.
6. MechanicalApproaches
Mechanical cleaning of intake pipes consists of two primary categories: online and offline. On-
line techniques clean the systemwithout removing it from service. Examples of this technique
include ball systems, metal scrappers, and brush and cage systems (Nair 1999, Rice et al. 1993).
Offline techniques clean the system during scheduled outages. Examples of this technique
involve shooting or lancing (Rice et al. 1993). This cleaning procedure and frequency varies
greatly depending on debris type and loading.
6.1. Online
The method used for a given site depends on the level of biofouling, space available for filters,
ball strainers or cages for brushes, and availability of reverse-flow capability. This method
typically removes a thin layer of the foulant with each cleaning, so foulants are not able to build
up (Rice et al. 1993). This cleaningmethod is able to take placewhile the plant is in operation.
6.1.1. Ball Systems
6.1.1.1. Overview
Ball systems operate by using the coolingwater flow to push or force slightly oversized sponge
rubber balls through the condenser pipes, continuously wiping the inner pipe walls (Rice et al.
1993). After flowing through the pipes, the sponge balls are captured by special strainers or
filters (Cristiani 2004). Some plants use the ball cleaning system continuously while others
prefer to use it a few times a week or during an emergency. Cleaningwith sponge balls reduces
or eliminates the need for chemicals.
Different balls are available to remove different foulant types. Standard balls are used in general
applications and come in a variety of sizes and hardnesses. Extended life balls are made of
standard balls coatedwith a smooth skinwhichwears out over time, resulting in an extended life.
However, the smoothness reduces cleaning efficiency, so they are only recommended for mild
fouling issues. Abrasive balls are recommended for harsh conditions or pipes with strongly
attached foulants. They are made by coating or blending the standard balls with an abrasive
material (Leung et al. 2002, Rice et al. 1993).
