Using side stream filters for cooling water is multi-path filtration, so the water is filtered multiple times, allowing for fine particle sizes to be removed and provides effective filtration even with 20-100 micron.
Here are some other benefits of cooling tower water filtration:
- Improved efficiency of heat transfer
- Improved chemical efficiency, lower chemical usage and better protection from Legionnaires disease
- Reduced operation failure/down-time
- Reduced operating, maintenance & labor costs
- Increased equipment lifetime
What is Side Stream Filtration?
Side stream filtration systems reduce the amount of suspended solids, organics and silt particles by continuously filtering a percentage of the cooling tower water (5-15%). Left untreated, this will lead to scaling, fouling and microbiological activity and eventually the cooling system will suffer from reduced efficiency. The filtered water is then returned to the cooling water system for reuse. Side stream filtration is typically used in high-flow cooling towers.
Side Stream Water Filtration:
A percentage (5-15%) of the recirculating cooling water volume flows through a water loop, reducing the overall load of solids. This loop then passes through a filtration system.
When to Consider Side Stream Filters
There are some key parameters indicating that a side stream filtration system is needed:
- The source of makeup water contains high levels of suspended solids, iron, biological and/or organic contamination.
- Biological growth is an issue although biocide treatment is used.
- The need to clean chillers and heat exchangers more than every 12-16 months.
- High corrosion rates in the water loop, including its components.
- The cooling tower system shows signs of diminished heat transfer and efficiency.
- The cooling tower sump and/or fill has a high accumulation of solids.
Benefits of Using Side Stream Filters
There are numerous benefits that can yield a high ROI by implementing side stream filtration. It is worth mentioning that not all benefits are applicable for all systems or environments and understanding the water quality and contaminants present is recommended before making a commitment.
- The corrosion inhibitor will be protecting cleaner surfaces given that solids have been filtered out of the system. This reduces corrosion rates and increases equipment lifetime.
- Side stream filtration, when paired with chemical treatment, will maintain a cleaner system, thus reducing the need to mechanically clean sumps and exchangers. This in turn lowers maintenance costs.
- Side stream filters keep the system clean for better heat transfer rates, for longer periods, lowering operational costs.
- Removing suspended solids from circulating water can in some cases deliver higher cycles, reducing the need to replace membranes and lowering maintenance costs.
Applications for Side Stream Filters
A side stream filtration system can improve the water quality and the efficient use of energy in these applications, usually in systems where the flow is more than 60 m3/h:
- When the primary source of makeup water is either surface water or other unclarified source, such as, rivers, streams, lakes, etc., it may contain biological and/or environmental contaminants. These contaminants are too small to be caught by the grate or screen protecting the piping at the inlet, but they will be trapped by a side stream filter.
- When systems have challenging biological issues and biocide programs are implemented, the number of dead organisms increases. A side stream filter will trap and remove them.
- Cooling tower systems are prone to fouling even when an anti-foulant program is implemented. A side stream industrial water filter will reduce the fouling.
- Scaling deposits are a cause of heat transfer loss. By reducing fouling, side stream filtration can help keep the heat transfer surfaces scale free.
- Cooling tower sumps can contain high levels of airborne particles (dust, debris, etc.) which can lead to high dirt loads. A side stream filter will trap these particles that otherwise would contaminate the cooling supply.
- In instances where the heat exchangers need frequent mechanical cleaning, side stream filters, by continually filtering a percentage of the cooling tower water, can reduce the frequency of mechanical cleaning.
System Implementation Considerations
The following factors should be examined carefully when considering installing a side stream filter to verify that the system is suitable for the application. Consulting with an expert to help choose the most suitable side stream filter is essential.
- Particle removal analysis: Lab and visual tests will indicate how clean the system is. A side stream filtration system that is correctly chosen and sized will effectively reduce fouling and clogging.
- Filtration sizing: To get the best performance, the side stream filter needs to be sized. The 2 key factors when sizing the system are flow rate and filtration efficiency. The flow rate should reach a percentage of the full recirculation flow rate, depending upon the chosen filtration technology’s ability to eliminate particles from the recirculation water with more efficient technologies requiring less of the recirculation flow due to their ability to remove a greater number of particles.
- Installation: There are 2 typical ways of installing cooling system side stream filters:
- On a tap off the water flow line: a percentage of the flow downstream of the pumps is filtered and then returned to the full flow stream by using a booster pump or sent back to the basin (no additional pumps required). The downstream effect on cooling capacity may influence the cooling water flow rate pressure sent to the heat source and this should be taken into consideration.
- Off basin/sump: the side stream filter takes tower sump suction and then the treated water is returned to the basin. A dedicated pump rated at the necessary flow rate, a control valve and a controller are required for this type of installation. The filtration system’s operating pressure, as recommended by the manufacturer, is also required. This would be the preferred option for process towers.
- Design features: Will the side stream filtration system be automatic? Is electricity needed? Backwash water? Footprint? Ease of operation? Upgrade options? All of these features should be taken into consideration.
- Finances: An ROI analysis of the different cooling tower water side stream filtration systems will provide the costs and the savings that can be expected. One of the expenses is the filtration system and each system is priced differently, with each using a distinct technology providing varying performance levels. Assessing the costs vs the filtration requirements is advised. Other expenses to calculate assess are installation and the peripherals (pumps, piping, etc.).
Choosing the Right Side Stream Filtration System
There are several filtration technologies for side stream systems and having information regarding the general requirements of the application is important. Each technology has advantages / disadvantages and system costs differ. Understanding all of this will help when determining which side stream filtration system is right for your cooling tower needs. Answering the following will help you choose which side stream filtration system is best for your requirements:
- What is the makeup water quality?
- What contaminants are present in the system?
- Is there an existing chemical treatment program in place?
- What are the maintenance and operational requirements?
- What is the budget?
Last but not least, consulting filtration experts, before a decision is made, is essential.
Amiad’s Technologies and Solutions for Side Stream Filtration
Amiad’s technologies and filtration solutions and its full range of filters for side stream filtration help improve heat transfer efficiency, maintain good water quality and reduce operating costs.
Centrifugal Separators
Amiad’s hydrocyclone sand separator and sand separator batteries are effective and efficient, with flow rate consistency and design adaptability, and when flushed regularly, require minimal maintenance.
- For removal of large heavy particles
- Small footprint
- Filtration degree: 70 – 150 micron
Media Technology
Media filters provide depth filtration technology by filtering water through a thick layer of graded granular particles. Suspended solids are trapped and attach to the filtration media. Available in a wide range of media types – sand, crushed glass, active carbon, anthracite, basalt, etc. The filter vessels are available in various tank construction materials, meeting international drinking water standards.
- For removal of low density particles (≥1)
- Filtration degree: down to 1 micron (depending on filter-bed type and raw water quality)
Screen Technology
Suction-scanning screen technology combines focused flush with automation to provide 100% cleaning of the screen area. The sophisticated screen is the optimal combination of material strength, filtration efficiency and cleanability, allowing the accumulating filter cake to be rapidly and totally removed.
- For removal of high and low density particles (≥10)
- Small footprint
- Economical
- Filtration degree: 10 – 1,000 micron
Disc Technology
Spin KlinTM disc technology uses thin, color-coded polymeric discs that are diagonally grooved on both sides to a specific micron size. A series of these discs are stacked and compressed on a specially designed spine, with the top groove in the opposite to the groove below. This creates a filtration element with a significant series of channels, effectively trapping the solids. The disc stack is enclosed in corrosion and pressure resistant housing.
- For removal of high and low density particles (≥10)
- Polymeric system for corrosive environments
- Good filtration performance for organic loads
- Filtration degree: 10 – 400 micron
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