The heart of a ballast water treatment system is the disinfection stage. This is the part of the system that takes filtered seawater and sanitizes it to prevent the spread of microbes, microorganisms, and viruses that cannot otherwise be removed by a filter. Ballast Water treatment systems are designed to prevent the spread of invasive species and what better way to prevent their spread than to deny them access to your vessel?
Selecting a Filter
There are four types of ballast water filters:
- Basket-type: uses a central basket filter element, located inside the body of the unit, and a rotary indexing arm circulates around the dirty side of the filter to draw fouling from the filter element out the drain line by pressure differential from the filter’s clean side to the drainDo you want to protect your crew from having to handle dangerous chemicals?
- Candle-type: uses numerous candles-shaped filter elements that are closed off during flushing and clean water moves back across the element to remove fouling. This water is typically led out the drain line by the pressure differential between the filter’s clean side to the drain
- Disc-type: use numerous stacked discs, each etched with a ripple pattern so that when the discs are compressed together they form a three-dimensional filtration grade across their entire face. For cleaning, the disc stacks are opened by a spring and pressurized water from the clean side of the filter is injected backward across the disc faces and led out the drain line. Pressure is provided by a backwash pump.
- Canister-type: similar to the basket-type, canister-type filters are a large, circular filter element, but this element is typically much larger and is cleaned through a series of nozzles attached to an indexing arm. These nozzles open to allow water to move backward across the filter element and draw fouling to the drain line by the pressure differential from the filter’s clean side to the drain.
Hyde Marine uses two different types of filters, each tailored to the application and needs of your vessel. For smaller vessels, where space is a premium, we utilize the Filtrex basket-type filter. This premium filter matches a corrosion-resistant body with one of the best 20-micron filter meshes in the industry to give it an unmatched cleaning efficiency for its size.
For larger vessels, where UV power becomes more prominent and often ports are located in deeper water, Hyde Marine uses the Hydac candle-type filter. This filter is unique among candle-type filters in that it uses special chambers in the lid of the filter to direct dirty-side water pressure through the candle to improve cleaning efficiency. Using the pressure from the upstream side of the filter means that as the filter gets dirtier, the upstream pressure increases and all of this power is available to clean the filter. Traditional filters that rely solely on clean side pressure lose that pressure as the filter loads.
With every Filtrex filter installation, Hyde Marine recommends the installation of a backflush pump to help ensure that clean side pressure is not adversely impacted and the filter can always clean itself. Due to the use of upstream pressure, the Hydac filter does not need these pumps.
Keeping It Clean
For a ballast water filter, cleanliness is the key to a long, trouble-free life. That is why Hyde Marine takes a leading role in making sure our filters are always cleaned to their peak efficiency every time.
The starting point for ballast water filter cleaning is to create enough differential pressure from the cleaning side of the filter (the filter discharge on a Filtrex filter and the filter inlet on a Hydac filter) to the overboard of the filter drain line. It is this pressure differential that creates the cleaning force necessary to remove organisms and debris that is caught in the fine mesh filters For GUARDIAN systems that use a Filtrex filter, Hyde Marine strongly recommends using a backflushing pump to generate suction pressure across the filter element. This eliminates the degradation of pressure gradient due to a clogging filter. For systems that use a Hydac filter, the backflushing pump is not needed because the inlet pressure increases as the filter becomes fouled. For deck-mounted systems or systems with a high-pressure ballast pump, the backflush pump may be specially considered on a case-by-case basis.
What to Watch For
For ballast water filters, there are three critical factors for ensuring a successful installation.
- Mind Your Drains: ballast water backflush drain lines are often installed with excessive discharge head or are led below the waterline where the discharge head is added to the line by the draft of the vessel. Adding discharge head to the drain line increases the inlet pressure needed for proper cleaning
- Clean Early, Clean Often: Hyde Marine is a strong believer that filters should be cleaned as often as practical. We institute both warm-up and cool-down cleaning cycles, and if a filter is backflushing often due to heavy loading, we institute heavy-duty continuous backflushing to reduce component wear.
- Check Your Curves: ballast water treatment systems will invariably increase the discharge head on the ballast pump. Make sure you check the curves for your pump to make sure you know how this increased head will affect pump flow rates and head requirements. Early identification of these losses can either impact what size system you choose or can often be mitigated by changing out the impeller on the pump during the retrofit project.
It has been said that failing to plan equates to planning to fail. For ballast water treatment systems, and particularly for the filters attached to them, there is a clear correlation between a successful installation and the planning and engineering that went into the project.
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