8/11/2019 Sand Filter Design Guide

1/2

28| May/June 2011|ME28| May/June 2013|ME

Large Scale

Media FilterRefurbishment

INTRODUCTION

Any large scale industrial and manufacturing plant

will have a substantial number of media filters to

service and maintain which, for a multitude of rea-

sons, may need extensive refurbishment in order

to bring them back to optimum performance.Recently, water filtration engineering specialist

Industrial Purification Systems (IPS) was called upon to

evaluate the media filters installed in a large scale steel

works - which were inexplicably void of filter media - and to

instigate a planned schedule of refurbishment works. The

following case study describes the refurbishment process

and explains why particular works were carried out.

THE PROJECTThe project was to refurbish the steel works five

existing sand filters, which were located outside and

comprised five steel fabricated vessels, each approximately

three metres in diameter. They were equipped with 600mm

(approximately) inspection manholes located at the

uppermost and lowermost levels to enable maintenance

work to be carried out. The system was last refurbished

approximately eight years ago when the control valves, filter

bed nozzles (560 per vessel) and sand were replaced.

Following an inspection, three of the five vessels were

found to be void of filter media and two vessels had very

little media remaining (approximately 500mm). Therefore a

total overhaul of the sand filters was required.

The refurbishment also included the conversion of the

operation of the filters to filter glass to improve water quality,and it was decided that the conversion process should

entail removing all the filters from service so that this work

could be undertaken.

SCOPEThe following works were initially scheduled for each

vessel:

It was anticipated that industrial cleaners would be in

attendance to remove the 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 inone of the vessels (named vessel 4).

One day to fill each vessel with water (for cushioning)

and load the filter glass (three layers) and seal the

hatches.

Carry out fabrication repairs to one of the vessels

(named vessel 4) where the air discharge pipe had

failed and dropped from its location damaging the

backwash inlet valve

F I LT E R M A I N T E N A N C E

Continued on page 30

Figure 1 Following final installation of all the cleaned o rreplacement nozzles

Figure 2 the media loading process commenced

8/11/2019 Sand Filter Design Guide

2/2

30| May/June 2011|ME30| May/June 2013|ME

Wish to Comment?Find this article at maintenanceonline.co.ukand at the end of the editorial thereis the option to add a comment eg Was it relevant? Can you add to it?

Continued from page 28

F I LT E R M A I N T E N A N C E

ADDITIONAL WORKSIt 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 issue the following was carried out1. 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

2. 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 lo cking off at a mid-set point.

3. It was agreed that, due to the filter system

having been removed from service andcontinuous works being viable, that the

work required to repair vessel 4 would be

considered part of the refurbishment program.

DIFFERENTIAL PRESSURE SWITCH

This had ceased to function on the existing

system and was replaced by a custom made

controller (manufactured by IPS) utilising the latest

in electronic components. Feed lines and isolation

valves were also replaced.

REFURBISHMENT WORKSOn inspection of the empty vessels a

number of undamaged nozzles were removed anddestroyed to test for aging and brittleness. The

nozzles integral strength was discovered to be

acceptable however it was found that they were

extremely 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 the

nozzles (totalling 2800) for manual cleaning. This

meant additional working hours so the project could

be delivered on time.

In total, 830 new nozzles were needed to

replace the damaged or broken nozzles resulting

from the removal and cleaning process.The air release pipework in vessel 4 was

repaired by firstly removing the backwash in valve,

jacking the pipework back into place and fixing

Figure 3 Vessel internal showing installed noz zles and peagravel prior to le velling

Figure 4 The second stage comprised 9 m2of a 6-3mm grade

Figure 5 Final layer of 7 m2 was loadedwith a grade of 3-1mm plus a smaller added

fract ion specified by IPS t o match the or iginalmedia blend. A 20% freeboard was left toallow for expansion of the filter glass duringbackwash

Figure 6 A flow control valve wa s addedto the backwash line so the backwash flowcould be metered to prevent wash out of thetop glass layer.

including the manufacture of additional

support brackets.

COMMISSIONINGThe five vessels were individually

commissioned with the upper lids off so the

backwash and air scour process could be

observed. The backwash control valves wereset at five complete turns from fully open to

achieve the required flow rate.

When the air scour was checked it was

found to be far too vigorous so blower volume

was adjusted on the flow valves located on

the blower outlets so a more controlled scour

was achieved.

The vessels were finally brought

back into service with the following system

settings:

differential pressure clean 0.4 barge :

Trigger 0.8 barg,

backwash valve setting five complete

turns form fully open, blower setting locked on outlet

valves and relating to individual blower

performance.

And it was also recommended that the

following service and maintenance

procedures be carried out at six monthly

intervals:

check levels of upper media (media

supplied ready),

recheck backwash flow rate,

recheck blower settings.

t: +44 (0)1744 811652 industria l-purification.co.uk