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Undersize balls do not clean as effectively and need to be removed regularly. The system needs
to be shut down to remove undersized balls and pass through a clearance check. An operator
sizes the balls at the clearance check and removes undersized or worn out balls, which can
require several hours of their time. Another option is to replace the entire ball stock without
sizing, based on average ball lifetime (Rice et al. 1993). Most manufacturers recommend
completely replacing a set of balls once a month, however past data indicates that complete
replacement frequency is actually higher (Rice et al. 1993).
Effective cleaning using sponge balls depends on even flow distribution in the condenser. If the
flow is uneven, the ballsmay not be uniformly distributed, which leads to inadequate cleaning or
excessive wear in some pipes. Over-cleaning may remove any protectant-coating while under-
cleaningmay leave a foulant film or othermaterials (Rice et al. 1993).
The sponge ball cleaning system can be negatively affected by debris. If the pipes or strainers
become cloggedwith debris, the sponge balls can also become stuck and further clog the system
making it useless (Rice et al. 1993, Perkins et al. 2009). Clogging will change the differential
pressure in the strainer section, so an automatic backwash system is recommended to clean the
screenwhen the differential pressure reaches a certain setpoint.
The strainer design is critical for proper operation. If the strainer fails, balls can escape (Perkins
et al. 2009, Rice et al. 1993). In 2003, Calvert Cliffs accidently discharged approximately 400
pounds of balls into theChesapeakeBay over a 75-d period andwas in violation of theirNPDES
permit (Nietmann 2003). Some strainerswithmultiple screens and linkages require an average of
15 hours per month to repair linkages and performance maintenance. Other strainers require
minimalmaintenance (Rice et al. 1993).
Ball cleaning systems are marginally effective. The ball systems assist in keeping the system
clean and greatly reduce, but do not eliminate the need formanual cleaning. Some facilitiesmust
backwash their system during heavy debris loading to clean debris from the filters and strainers.
The potential operating andmaintenance costs can be high (Perkins et al. 2009).
6.1.1.2. Cleaning process
Cooling water is first moved through a debris filter to remove coarse solids. The three steps
followed during cleaning are described below.
A.
Ball injection
Balls are inserted into circulatingwater upstream of the condenser inlet, against the direction of
the inlet coolingwater flow. The balls are the same density as the coolingwater when deaerated,
allowing the balls to enter the pipes randomly. A charge of balls equal to 5 – 15% of the number
of condenser pipes per pass shouldmaintain cleanliness.
B.
Pipe cleaning
Ball distribution is affected by the location of the ball injection and flow patterns in the inlet
waterbox. Backwashing starts automatically once the differential pressure across the debris filter
and strainer reaches a preset limit.
