That invariably translates to diminish product quality, process interruptions and/or exorbitant maintenance costs.
Moulded plastics, food and beverage processing, paper manufacturing, metal working, energy, countless process industries depend on filtered fresh water for no-contact cooling or as an integral product component.
'Since no two waters are the same, and all processes differ to varying degrees, those tasked with designing or modifying water treatment systems can only be successful if they balance the requirements of the system that will use the water against the physical and chemical analysis of the water to be treated', advises Phil D'Angelo, Vice President of Technical Development for Jodan Technologies (Glen Mills, Pennsylvania).
'There are a lot of conditions and requirements to consider: the turbidity of the water, hardness, system pressures, process purity requirements, volume demands, filter backwashes and system maintenance'.
'Certainly, in a process filtration system, minimising downtime for maintenance is a major consideration'.
As opposed to sidestream water filtration used in cooling towers, many process water systems require pretreatment of the water taken from surface or ground water sources.
Post filtration process water is often used in combination with other water treatment technologies such as softeners, demineralisers or membranes in a continuous flow mode, feeding process equipment.
For many of those applications Jodan Technologies, a consulting firm that works with industrial and utility clients to resolve water related problems, considers the 'centrifugal' sand filtration system a valuable technology.
A centrifugal filtration system uses a combination of in-situ fine sand centrifugal separation combined with down-flow sand filtration, which ensures greater filtration efficiency than traditional down-flow sand filters.
Centrifugal filtration systems such as the Vortisand from Sonitec are widely used for various process water polishing applications.
This fully automated, unusually compact system provides removal of solids to a miniscule 0.45um with filtration up to 820 litre/min/m2.
A dramatic example of the advantages of centrifugal water filtration for process applications can be found in a recent Jodan project at an electric power generation facility located in the northeastern USA.
A relatively small plant that generates 100MWe from landfill (methane) gas, the plant generates approximately $100,000 worth of electricity per hour during summer peak periods, and therefore could afford little or no downtime.
The power plant uses two 55bar boilers that run on softened water from large pack bed softeners, which require very clean influent water.
Previously the plant had used a large clarifier, to which ferric chloride, sodium hypochlorite and caustic were added to flocculate the suspended materials, control biologicals, and add some alkalinity for boiler water chemistry control.
The clarified water then passed through existing pack bed softeners at about 946 litre/min.
'The system was not only supplying water for producing electricity, it was also supplying process steam to a local steel mill', D'Angelo explains.
'The steel mill dropped its requirement for steam, so the flow rates dropped from 946 litre/min to approximately 189 litre/min total'.
'Consequently, the system they had in place was hydraulically too large for the flow requirements'.
For an optimal solution, Jodan put together a filtration and softener package that would use the utility's existing pack bed softeners in an intermittent process mode.
However, instead of using the clarifiers in front of the softeners, a Vortisand sand filter was proposed.
'We proposed a 567 litre/min centrigugal sand filter composed of three vessels, used in processing mode', says D'Angelo.
'Although the vessels only needed to be 30in in diameter, because of our experience with water treatment equipment, we decided to be on the conservative side and made them 36in in diameter'.
'This approach increased the available filtration surface area which optimised the linear velocity and maximised particle loading to a differential pressure end point, which is clearly the correct approach for any filter design'.
Now, based on the soft-water storage tank level (SWST), river water comes into the plant where it is pretreated with chemicals before going into the Vortisand filtration system.
The filtered water then flows into a 272.5kl filtered water storage reservoir.
Before entering the boiler, the water passes through a 1um absolute pleated filter as well as KDF redox media to remove chlorine, and then into the packed bed water softeners and, finally, into the SWST at 567 litre/min.
When the SWST is full, the system shuts down until the SWST levels are two-thirds full and the process starts over again.
'When the Vortisand system reaches about a 9 to 10 lb/in2 differential, each of the three Vortisand vessels automatically backwashes in sequence', says D'Angelo.
'One of the benefits of this filtration technology is that even while a given filter vessel is backwashing, two filter vessels are online'.
'Because they are sized at 36-inch diameter, they can easily handle the 567 litre/min demand'.
'As a result, the power plant has no downtime, which is of vital importance in any process application'.
D'Angelo adds that the filter vessels are backwashed using chlorinated soft water, which controls biologicals.
'When you backwash a sand filter, you backwash from the bottom up', he says 'It is advantageous to add chlorine or bromine upflow through the filter sand bed in order to avoid any buildup of biological materials'.
'By doing it this way, we're keeping that sand clean all of the time and reducing maintenance requirements and costs'.
The new utility plant water treatment system has been running consistently since May 2006.
'It has performed extremely well since startup', D'Angelo says.
With its microbial filtering capabilities and high flow rates, the Vortisand filter system is used in a myriad of process applications.
Mike Assimus, National Sales Manager at MSC Liquid Filtration Technologies (Enfield, Connecticut), says the system is used to clean water that is used by a major paper manufacturer in the process of making paper wipes used in industrial and medical applications.
'The plant is using well water that is fairly turbid', says Assimus.
'They are using 12 Vortisand vessels in a variable-flow system that can handle 2270-3785 litre/min, depending on the process requirements'.
Filtering the water at a 0.45-2um nominal level is vital because the water flows through high-pressure pumps that impel it to the paper machine, where it is used to form the product.
'The water has to be clean to protect the pump and spray nozzles at the water application point, and also must be pure to create a product that is suitable for medical applications', Assimus says.
'The spray nozzles have very fine orifices, and if there are any contaminants in them, then the spray will be uneven'.
'Also, impure water under high pressure could cause erosion of the nozzle, also excessive wear and tear on the pumps'.
Assimus notes that any downtime due to water system interruptions would be highly problematic because the paper plant has to run fulltime to barely keep up with orders.
'They have noticed a decrease in the wear on these nozzles since the Vortisand system was installed', he says.
'Not only is that a maintenance time-saver, but a significant money saver as well'.
Other design features of the vortexing sand filter system save on process uptime and maintenance costs as well.
