Are your heat exchangers losing transfer efficiency? Is your cooling tower filling up with dirt and silt? Are you plugging nozzles in your process cooling system? If so, it might be time to install or upgrade your filtration system.
Cooling water systems are an integral part of any facility, and the overall value of this equipment relies on an effective, efficient cooling water system. For optimal facility operations, it is important to protect the equipment throughout the cooling system. When cooling systems are not running efficiently, the entire system suffers due to extra wear and tear on process equipment. In addition, maintenance costs increase, as do downtime and operating costs.
One key component to achieving optimal performance of your cooling system is good filtration. Here are seven factors to consider when buying a filtration system for your facility.
1. Continuous vs. Intermittent Flow
Will the filter be installed in a location with continuous flow, or will you be able to stop the flow to the filter to clean or replace the filter media? Over time, filters become dirty as they remove the contaminants in the system. This means the filter media must be cleaned or replaced. If the flow can be stopped or the filter can be bypassed for a short period of time, then a simple filter will suffice.
If continuous flow is needed downstream of the filter, then a duplex-style filter or an automatic filter is needed. In these designs, all or most of the flow continues even as the dirty filter media is cleaned.
2. Manual vs. Automatic Filter
Based on plant operation and personnel availability, consider whether the filter will be cleaned manually or automatically. Manually cleaning filters may entail replacing disposable media or flushing and cleaning re-cleanable filters. An automatic filter will clean itself based on either a set timer or a high differential pressure across the filter.
While the capital cost of the automatic filter is higher usually, the benefits of unattended operation and more consistent -differential pressure provide the advantages of around-the-clock equipment -protection and lower operating costs.
3. Backflushing Filter vs. Self-Cleaning Filter
While the terms backflushing and self-cleaning sometimes are used interchangeably, there is actually a difference between them. More importantly, that difference may determine which type of filter will work works best in a system.
A backflushing filter uses a portion of the clean water that was just filtered, or an external source of clean water, to backflush the dirt off the filter media and down the drain. This normally means that a portion of the clean water does not go downstream to where it is potentially needed for equipment.
A self-cleaning filter uses a moving disc or rotating blade to wipe the screen clean and push the solids to the bottom of the filter vessel. From there, the solids are purged out on a timed basis. In this type of filter, a smaller amount of fluid is lost with the removed solids.
In a particular application, if there is nowhere to send the backflush water, or sending it down the drain is not an option, then a self-cleaning filter might be a better solution.
4. Cleanable vs. Disposable Filter Media
Another consideration, based on plant goals and operation, is whether to use disposable or cleanable filter media.
Disposable media usually are bag filters or cartridge filters that are disposed of and replaced with new filters when they become dirty. Cleanable media are filter mediums — ranging from stainless steel baskets to granular media — that can be backflushed or removed and cleaned and then replaced in the housing.
Systems with disposable media usually have a lower cost for the initial equipment. The long-term operating costs — disposing of the dirty filters and purchasing new filters — can drive the overall costs higher than cleanable media.
With cleanable media, higher initial capital cost and any ongoing costs that might be associated with the manual filter cleaning must be considered.
5. Understand and Plan for Your Particle Size Distribution
The particle size range — from very small to relatively large particles, or relatively uniform particle sizes throughout — of the dirt in the system significantly affects the filtration efficiency and cost to operate. Therefore, before buying a filtration system, it is important to analyze your cooling water for its particle size distribution.
Without a particle size distribution analysis, prospective filtration system buyers can only guess at what micron size filter is needed to properly protect equipment or spray nozzles. While knowing the maximum particle permitted into any process equipment is a good starting point, if a buyer knows the particle size range, it is possible to evaluate whether a series of filters can better protect the equipment and provide the longest filter life. Usually, smaller micron filters are more expensive, so if a wide range of differently sized solids is present in the water flow, a multi-stage filtration system should be considered. These systems use cleanable, larger particle removal filters to protect the finer micron polishing filters.
6. Total Percent Solids Loading
The total solids loading for your water flow is another important value to know before buying a water filtration system. Knowing this value and selecting a system that takes it into account helps avoid overloading the filters. Most filters, strainers and media filters are not designed to handle more than 200 ppm of solids. If your total solids loading value exceeds 200 ppm, filters that can handle the higher solids load can be used. But, it is important to know that information before purchasing equipment.
One caveat: most particle size distribution and loading numbers are determined with a grab sample; therefore, they represent a “snapshot” in time of what the filter might see over the course of its use. You can overcome this limitation by taking multiple samples at different times of the day, week and month. Analyzing and comparing all of the samples’ results can help you obtain a more precise picture of your system and its specific parameters.
7. Process Application Data
And finally, don’t overlook “all that other stuff.” When deciding on any filter, it is important to know the operating and maximum temperatures, operating and maximum pressures, what chemicals are in the system, and maximum, average and minimum flow rates. The more data you have — and the more accurate it is — the better the filter will work in your application.
The more care and attention that is put into choosing the optimal filtration system, the better the system will work for the operation and the facility. The proper filter can provide years of trouble-free operation and protect valuable equipment while at the same time increasing energy efficiency and lowering operating costs.
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