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Backflushing Description
Backflushing, simply defined, is a process used to clean filters by reversing the flow of fluid through the system. Effective, economical backflushing can be difficult to achieve since no two filtration operations are alike and the amount and type of contaminant pressures, pumps,
housing, etc. all vary. System design and backflush principles are predominantly the same, but operational parameters must be tailored to the application by field trials (at a pilot plant, side stream or full operation).
Backflushing is a potentially powerful sales tool in virtually all filtration markets. Unfortunately, most filtration systems are not set up for backflushing. Since most of the currently used filters are not effectively
backflushed, most operators of the most popular filtration devices and systems are unfamiliar with how to implement backflushing; and therefore, unaware of the potential advantages of this technique.
Existing filter hardware can be used for backflushing in many applications. Though not always the most effective method, existing filter hardware can prove economical either as a permanent solution or for trial to show the
economics of a more effective process.
Types of Filters Used
Current Backflush Systems – Typically, sintered stainless steel, stainless steel mesh, wedge wire screen or ceramic cartridges
Non-Backflush Systems – Bags, depth cartridges, pleated cartridges and others
Purpose of Backflushing
The purpose of backflushing is to remove accumulated particulate from the filter to extend its life, recover filter cake and/or reduce operational costs.
Potential Customers
- All customers who have a valuable product, either filter cake or filtrate
- High cost or hazardous waste filter disposal
- High solids liquid filtration
- Economics of backflushing are less than the cost of filter replacement, disposal and labor
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Backflush Operation Variables:
- Hardware and System Design – Standard hardware or backflush specific hardware
- Backflush Fluid – Air, water or clean filtrate
- Backflush Program – Maximum differential pressure, reverse pressure/flow rate, duration, speed, frequency, acceptable recovery, manual or automatic
- Filter Type – Ceramic, metallic, Porex, or others; Surface, classification, layers
- Contaminant Concentrate – Reuse, dispose, wet, dry, further concentration
Common Backflushing-Related Problems:
- Current System Design – Not originally designed for backflushing, but most can be adapted
- Ineffective Cleaning – Differential pressure too high prior to backflush, multiple layer filter, inaccessible pleats, poor reverse flow, insufficient duration
- Backflush Solids – Volume, wetness, transportation, hazardous materials
- On Restart, Filters Plug Quickly – Ineffective backflush did not get contaminant out of the system
- Operator Intensity or Dependence – Automate the system
- Economics Visualization – Field trial with pilot (side stream or existing system)
- Cartridges Dislodge from Seal Plate – Install a hold down device or locking mechanism to keep cartridges in place
Recommended Backflush Parameters:
- Pressure Differential for Backflush Initiation – 5 to 10 psid (over clean pressure differential)
- Air Reservoir Pressure – No more than 50 psi
- Backflush Rate – 1.5 to 2.0 times forward flow rate
- Backflush Valve Open Rate (Trial and Error) – The faster the better without damaging or dislodging cartridges
- Backflush Time – Sufficient to remove all upstream fluid volume
- Maximum Clean Water Pressure Differential – Starting differential plus 50% or when time between cycles is too short
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