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C.
Ball collection and return for inspection
The balls are collected at the outlet by a strainer then redirected by a recirculating pump to the
ball collector. At the collector unit, operators must then visually inspect the balls, manually size
them and replace any undersize balls. Balls flow from collector unit to the injection location at
the inletwater boxwhere cycle begins anew (Leung et al. 2002, Rice et al. 1993).
6.1.1.3. Retrofit considerations
When installing a ball cleaning system into an existing piping system, space and outlet piping
configurations can impact the retrofit. If a debris filter has not already been installed, this should
be considered, as it can be costly to install. The ball collection strainer requires accessible
exposed piping of one pipe diameter at the outlet, therefore the outlet pipe’s location and design
can affect the ball collection strainer and the retrofit costs. The remaining system components
(valves, pumps, etc.) can be installed where space is available. The location and number of ball
injectors required to achieve uniform ball distribution in the pipes is affected by inlet piping and
waterboxdesign, and the resultant hydrodynamics (Rice et al. 1993).
The start-up costs for using the ball cleaning system are lower than other online options as it only
requires a ball addition and ball collection system. However, the piping systems require
adjustments to the mechanized control system components and controls. Space and piping
configurations can also influence the retrofit (Rice et al. 1993).
6.1.2. Brush andCageSystems
This system is used primarily by smaller power plants, although some large power plants do use
it. This system uses a flow-reversal mechanism to shuttle a captive brush back and forth through
each pipe by reversing the flow direction. The cleaning brushes are caught by nylon cages
attached to the end of the pipeswith epoxy and screws.
The brush and cage system requires limited maintenance or operator attendance. The only
moving parts are the flow reversal valves and brushes, so the worn cleaning elements do not
need to be replaced frequently. The lifetime of the brushes is approximately 5 years. The system
provides continuous cleaningwithout the need for chemicals (Rice et al. 1993).
The flow-reversal system is expensive and can increase back pressure, reduce generator output
and hydraulic transients in the system. The systemmust be shut down during brush and cage
replacement. The cages obstruct the ends, making it difficult to detect pipe leaks and conducting
eddy current tests. The cages can become clogged with debris if a filter isn’t installed. The
brushes may over-clean the pipes, remove pipe material, or can become bent or damaged thus
restricting pipe flow (Rice et al. 1993).
6.2. Offline
Offline pipe cleaning involves shooting or lancing. Shooting propels a tube-cleaning projectile
(plastic pig) through each pipe using pressure, while lancing pushes and pulls a flexible lance or
rotating shaft with an attached cleaning device (water head, brush, scraper, drill bit or cutter)
through each pipe. Shooting requiresmoving an object through the pipes at speeds of 10-20 ft s
-1
and is faster than lancing. Lancing requires manual feeding and withdrawal of the lance. The
