District Energy - 2007 Third Quarter

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.