Refurbishing Large Scale Media Filters [read more]

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Industries

Principal Applications

Refurbishing Large Scale Media Filters : Steel Works

Large Scale Media Filter Refurbishment

Any large scale industrial and manufacturing plant will have substantial media filters to service and maintain which for a multitude of reasons may need extensive refurbishment in order to bring them back to optimum performance.

Recently, water filtration specialist engineering firm 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.

This case study gives an interesting breakdown of the refurbishment process and the reasons why particular works took place

The Project

The project was to refurbish the 5 existing sand filters. The filters were located outside and comprised of 5 off steel fabricated vessels each approximately 3 metre in diameter. They had 600 mm (approximately) inspection manholes located at the uppermost and lowermost levels to enable works to be carried out.

The system was last refurbished approximately 8 years ago when the control valves, filter bed nozzles (560 per vessel) and sand were replaced.

Following an inspection, IPS identified that 3 of the 5 vessels were fundamentally void of filter media and 2 vessels had very little media remaining (approximately 500 mm). Therefore a total overhaul of the sand filters was required.

The refurbishment project also included the conversion of the operation of the filters to filter glass to improve water quality.

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

Scope of works

The following works were initially anticipated per vessel

Additional works

  1. It was believed the existing media was missing due to a number of reasons, one reason being that the backwash water flow was too high. To address this issue the following was carried out 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 locking off at a mid-set point.

  3. It was agreed that, due to the filter system having been removed from service and continuous works being viable, that the work required 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 utilising the latest in electronic components. 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 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.

  Installation of all the cleaned/replacement nozzles

Media loading process commences

In total, 830 new nozzles were procured by IPS to replace damaged/ broken nozzles resulting from removal and the 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 including the manufacture of additional support brackets.

Vessel internal showing installed nozzles and pea gravel prior to levelling

 

The second stage comprised 9 m2 of a 6-3mm grade

Final layer of 7 m2 was loaded with a grade of 3-1mm plus a smaller added fraction specified by IPS to match the original media blend. A 20% freeboard was left to allow for expansion of the filter glass during backwash

A flow control valve was added to the backwash line so the backwash flow could be metered to prevent wash out of the top glass layer.

 

Commissioning

The 5 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 5 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 system was brought back into service.

System settings

1.       Differential pressure                     Clean 0.4 barge : Trigger 0.8 barg

2.       Backwash valve setting                 5 complete turns form fully open

3.       Blower setting                                  Locked on outlet valves and relating to individual blower performance

Service and Maintenance Recommendation

1.       At six months check levels of upper media( media supplied ready)

2.       Recheck backwash flow rate

3.       Recheck blower settings

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