Figure 1. A Typical Centrifugal Sand Filtration System.
also shut down. There is also a dry contact
available on the filtration system panel that
enables monitoring of the backwash float.
Particle Counts Down
The new filtration system was installed
in September 2005. To evaluate the system’s
performance for Enwave, XLB conducted
a series of laser particle analyses and
ultraviolet transmission tests on collected
chilled-water samples, drawn from the
cooling system at an in-line recirculating
pump. During this period, Enwave’s water
treatment supplier was also monitoring the
system and reporting the improvements.
With the sand filtration system,
total particle count (all micron
sizes) had been reduced by 89.6
percent and total suspended
solids by 96.5 percent.
Source: Sonitec Inc.
of the contamination, the thickness of the
fouling on metal surfaces, recirculation
flow, the chemicals used, etc.
As an optional feature, the filtration
system software was modified so that if
the filtrate valve downstream of the filter
remains closed when it should be open,
then the filter system automatically shuts
down. Although not a standard operating
parameter on this particular filtration
system, this feature was an advisable
addition. Since the Enwave system pushes
550 gallons per minute, it was determined
that if a downstream valve on the filtration system would stick for any reason
after backwashing, then the filter pump
would automatically shut down.
The filtration system’s operator interface unit (OIU) is programmable, with the
capability to automatically feed a chemical
for media cleaning, after a predetermined
number of backwashes. The OIU is pass-word-protected. The duration of the backwash is also adjustable by accessing the
OIU. The system has alarms on the OIU
that tell when prescheduled maintenance
is required. Alarms are also generated
when high backwash frequency occurs
(above a predetermined frequency), or if
the filter system sand trap should become
plugged. An alarm is generated if there
is a pressure increase beyond the factory
setting for the sand trap; the system will
The evaluations showed that with the
sand filtration system, total particle count
(all micron sizes) had been reduced by
89.6 percent and total suspended solids
by 96.5 percent. Ultraviolet light absorption testing was equally impressive. Prior
to installation of the new filtration system,
the average reading was 92 percent, which
meant that 8 percent of the light was being
partially absorbed by suspended impurities
in the water. After the new system was
installed, that number went up to 95 percent.
A comparison of particle sizes in
Enwave’s system before and after filtration
Figure 2. Enwave’s Chilled-Water Loop Particle Count.
Particle Count (#/ml)
Prior to filtration
After 2 months
< 1 1-2 3-8 9-16
Particle Sizes (micron)
Source: Sonitec Inc., with information from XLB Water Solutions.