A recent project for Industrial Purification Systems (IPS) was
to evaluate the media filters in a large scale steel works
which were inexplicably void of filter media and to instigate
a planned schedule of refurbishment works

The project was to refurbish the five
existing sand filters. These were
located outside and comprised five
off steel fabricated vessels each about 3m in
diameter. They had 600mm inspection
manholes at the uppermost and lowermost
levels to enable works to be carried out.

The system was last refurbished eight
years ago when the control valves, filter bed
nozzles (560/vessel) and sand were
replaced. IPS identified that three of the
five vessels were void of filter media and
two had very little media remaining (about
500mm). A total overhaul of the sand filters
was required. The project also included the
conversion of the operation of the filters to
filter glass.

It was decided that the conversion
process would remove all filters from
service for work to be undertaken and that
work should be completed in 2.5 weeks.

Scope of works During the works it was anticipated that
industrial cleaners would be in attendance
to remove existing media and clean out
the filter vessels prior to inspection
Replacement of any damaged plastic
nozzles and their close inspection
Redesign of the filter bed to incorporate
filter glass
Approximately one day to remove existing
spades in one of the vessels (named vessel 4)
One day to fill each vessel with water (for
cushioning) and load the filter glass (3
layers) and seal hatches.

Carry out fabrication repairs to vessel 4
where the air discharge pipe had failed
and dropped from its location damaging
the backwash inlet valve
It was believed the existing media was
missing due to a number of reasons, one
being that the backwash water flow was too
high. To address this, the following action
was taken:
Installation of a line sized valve to control
the backwash flow from the backwash
pump. The valve was installed in a
location to serve all the pumps associated
with the backwash flow and was of the
type suitable for this application (not
butterfly) The valve was installed in a
location adjacent to the existing platform
next to the backwash discharge pit
The line was installed in a straight run of
pipe with approximately 1 metre of pipe
either side with the valve used being
suitable for setting and locking off at a
mid-set point.

It was agreed that, due to the filter system
having been removed from service and
continuous works being viable, work needed
to repair vessel 4 would be considered part
of the refurbishment program.

Differential pressure switch This function had failed on the existing
system and the equipment was replaced by a
custom controller manufactured by IPS. Feed
lines and isolation valves were also replaced
as part of the project.

Refurbishment works On inspection of the empty vessels a number
of undamaged nozzles were removed and
destroyed to test for aging and brittleness. The
nozzles integral strength was discovered to
be acceptable however it was found that they
were contaminated with a scale-like material
and nozzle slots predominately blocked. Later
analysis identified the material as Calcium
Fluoride. Identification of other nozzles in a
similar condition resulted in a decision to
remove all 2800 nozzles for manual cleaning.

This meant additional working hours so the
project could be delivered on time. In total,
830 new nozzles were procured by IPS to
replace damaged/broken nozzles.

The air release pipework in vessel 4 was
repaired by firstly removing the backwash in
valve, jacking the pipework back into place
and fixing, including the manufacture of
additional support brackets.

Commissioning The five vessels were individually
commissioned with the upper lids off so the
backwash and air scour process could be
observed. The backwash control valves were
set at five complete turns from fully open to
achieve the required flow rate.

When the air scour was checked it was
found to be too vigorous so blower volume
was adjusted on the flow valves located on
the blower outlets so a more controlled scour
was achieved.