Selection of Media

Before sizing any filtration vessel – either diameter, or cylinder height it is important to know and understand the operational requirements and performance characteristics of the media being used. 

Selection of media should be done in conjunction with a process engineer and the filter media supplier, to ensure the correct media is selected for the desired treatment outcomes. The recommendations on the filter media datasheet need to be implemented into the filter vessel design, to ensure the filter vessel selected can hold the correct amount of media at the required depth whilst the desired filtration rate is achieved. It is also very important to review and confirm that the internal distribution is suitable for the filter media, ensuring optimum performance when in service and backwash functions.

Flow Rate/Filtration Velocity

There are two types of calculations in order to determine the vessel diameter to be used: 

1. Superficial Velocity. The speed at which the water passes through the media in m³/hr flow rate/m² media bed surface area.
2. Empty bed Contact Time (EBCT) – The time in minutes the water is in physical contact with the media bed. 

Therefore it is important to know the target filtration velocity in m³/m²/hr needed for the specific filtration media selected (or EBCT if using GAC/Calcite etc). 

For e.g. 

Flow Rate                                        ÷                                      Filtration Velocity                           =                             Filter Surface Area

   20m³/h                                                                                     10m³/hr/m²                                                                            2m²

Media Bed Depth/Backwash Expansion

To calculate the cylindrical height of a vessel it is critical to know what the media bed depth and backwash expansion requirements are. 

The common 2 step calculation used to calculate the height of the cylindrical section of a filter vessel: 

1. Operational Media Bed Depth. What is the depth of media needed to meet the performance outcomes?
2. What is the expansion percentage to perform an effective backwash?

These 2 factors determine the actual effective cylindrical height of a filter vessel in order to house the media when in service mode and in addition allows enough room to expand the media during a backwash cycle.

For E.g.

Media Bed Depth                            x                                      Backwash Expansion                 =               Cylindrical Height

1000mm                                                                                    50% (1.5)                                                                1500mm

Pressure

Once the hydraulic engineer has calculated the maximum operating pressure requirements of the plant, the vessels should then be selected, so the maximum design pressure of the vessels is higher than the maximum operating pressure of the plant.

For e.g. if the operating pressure of the plant is 4 bar, then the vessels should be selected with a 6 bar design pressure. This provides some contingency if there were pressure spikes and water hammer causing pressure to rise above 4 bar.

When the pump is selected, the dead head of the pump must never exceed the maximum design pressure of the vessel. It is recommended the design pressure of the vessel be at least 20% higher than the maximum dead head pressure of the pump.

Chemicals Used

If chemicals are intended to be used in the process it’s important to inform us.

It is critical to check the compatibility of the internal liner against these chemicals, at times it may mean a different liner is selected to avoid premature degradation or failure. If aggressive or harmful chemicals are used in the process this may also mean the vessel is subject to a higher hazard rating under AS4343 and therefore require design registration. Glacier Filtration offers assistance with design registration applications and approval. 

Differential Pressure

Differential pressure is very important to consider when designing the treatment system, in order to avoid high differential pressures between inlet/outlet of filter vessels. High differential pressure can cause serious damage to the filter vessels (especially those with nozzle plate floor internals).

High differential pressures between inlet/outlets of filters usually point to a blocked media bed which will mean the filtered water quality is poor and will decrease over time. It is important to initiate regular backwashes of the media bed to ensure the bed does not become blocked. It is also important to ensure there is sufficient pre-treatment to remove particles or organics that could block internal nozzles in the filters, which is a big contributor to high differential pressure inside the filter. It is recommended to initiate a backwash cycle when the differential pressure between inlet and outlet is between 0.4 – 0.6 Bar maximum. In filters with nozzle plate floor internals,  the differential pressure between inlet and outlet should never exceed 0.8 Bar.

Internal Configuration 

Choosing the correct collector nozzle for a media filter is crucial to ensure optimal filtration performance and prevent issues like channeling, clogging, or uneven flow distribution.

Key factors to consider when selecting a collector nozzle for a media filter:

Sand size and type: The nozzle size and aperture of the slot should be compatible with the sand/carbon/resin size and type to prevent clogging, channeling or even media escaping the vessel during operation if the slot aperture is too large.

Collector Nozzle Material and Design: It is important to choose a nozzle material that’s resistant to corrosion and compatible with the filter’s operating conditions such as pressure, temperature and chemicals. Different nozzle shapes and designs can affect flow distribution, pressure drop, and clogging tendencies.

Filtration Process: The Filtration process is important to consider as this impacts the internal distribution configuration. Systems where air scour is required, nozzle plate floor or air scour lateral system can be installed, whereas standard slotted lateral collectors are suitable for GAC, resins and filter applications where air scour is not required. 

Aperture of Collectors: Sizing the aperture of a lateral collector correctly is crucial for efficient filtration and backwash process. The aperture should be sized to avoid media loss during operation. 

Glacier Filtration can also help and assist you to ensure you choose the correct collector nozzle for your specific pressure filter application.

External Configuration 

Inlet/Outlet Nozzle Connections: 

• Nozzle location: The location of the inlet/outlet nozzles is mainly in the standard position for all new water treatment plants, however Glacier Filtration can customise the nozzle location.  Where replacement of old vessels is required, Glacier can usually match the nozzle location to the existing pipework infrastructure. The location of the inlet/outlet nozzles on the vessel should be carefully considered to prevent structural problems and ensure that the nozzles are properly aligned with the existing pipework.
• Nozzle size: The size of the nozzles should be carefully selected to ensure that they are compatible with the flow and pressure requirements of the water treatment plant. 
• Nozzle orientation: The orientation of the nozzles should be carefully considered to ensure that they are properly aligned with the existing pipework. The nozzles should be oriented in a way that minimizes the amount of stress on the pipework and ensures that the pipework is properly supported.
• Code requirements: The location and orientation of the nozzles must comply with all applicable codes and standards. These codes and standards may specify the minimum size, location, and orientation of the nozzles, as well as any other requirements that must be met.
  

Manway Location: The location of a manway in a pressure vessel is an important design consideration that affects several factors, including:

• Structural integrity: The manway should be located in an area of the vessel that is not subject to high stresses. This will help to prevent the manway from becoming a weak point in the vessel and failing under pressure.
• Accessibility: The manway should be located in an area that is easy to access for maintenance and inspection purposes. This will help to ensure that the vessel can be properly maintained and that any problems can be identified and repaired quickly.
• Flow distribution: The manway should be located in an area that does not disrupt the flow of water inside the vessel. This will help to prevent problems such as cavitation and erosion.
• Safety: The manway should be located in an area that is safe for personnel to enter and exit. This will help to prevent accidents and injuries.
• Code requirements: The location of the manway must comply with all applicable codes and standards. These codes and standards may specify the minimum size and location of the manway, as well as any other requirements that must be met

Sight Glass: Glacier Filtration offers the option to include sight glass on your vessels. Sight glass provides real time monitoring by allowing operators to visually inspect inside the vessel. Sight glass facilitate maintenance activities by enabling visual inspection of the water condition and the internal components of the vessel. Glacier can customise the position of the sight glass dependent on the customers requests, as well as the quantity of sight glass to be installed into each vessel. 

Filtration Plant Design and Maintenance 

Vessels should be designed with maintenance and accessibility in mind.  Maintenance access must be considered for media inspection and replacement, so its important vessels include features such as manways, inlet/outlet nozzles, drains, and sight glass. Glacier provides the ability to customise the locations of these important components, to ensure it adequately suits the space the vessels are being installed into and allow the operator to perform regular and routine maintenance duties. 

Pressure Filter Vessel Internal Liner 

It’s important to select a liner material that is suitable for the intended application and water treatment process. It’s important to also check the compatibility of internal liner materials against chemicals that will be used in the process or present in the water. Glacier Filtration offers different polyester resins to suit different applications. 

Location and Installation Factors 

UV: It’s essential to consider UV effects when selecting FRP vessels, especially those intended for outdoor use or exposure to sunlight. Glacier Filtration offers a UV resistant layer to the exterior of the vessel where requested. 

Seismic risks: If vessels are to be installed in an area with high seismic risk or exposure to high winds, it may be necessary to anchor the filter to the floor. Glacier Filtration provides seismic calculations and approved seismic rated anchor brackets suited to the location. 

Mobile Structure: If vessels are to be installed in a mobile structure, it may be necessary to anchor the filter to the structure. Glacier filtration provides anchor brackets upon request. 

Orientation & Space Constrains: In areas where space is limited, vertical vessels are more suitable. Glacier Filtration can provide different sized vessels and customise manway access points, inlet/outlet nozzles, site glass to suit small spaces, and ensure easy maintenance. 

Design Codes

It is important to understand that different regions globally have different manufacturing standards for pressure filter vessels. All of Glacier Filtration’s pressure filter vessels are manufactured to globally recognised pressure filter vessel standards. 

Many water treatment projects and organisations require design certification to particular codes or standards, so it’s important to adhere to these requirements. If you require third party design registration and certification to any of the globally recognised standards for manufacturing, chemical usage, or specific applications such as potable water usage, Glacier provides assistance with applications and approval.