Industrial facilities that rely on process cooling water drawn from natural sources such as rivers, lakes and oceans face “strainer danger” when both small particles (sand, silt, suspended solids) and larger debris (aquatic life, trash, vegetation) must be removed at the risk of fouled processes and production downtime.
In once-through process cooling systems, the water circulates through pipes, absorbing system heat and is then returned to its original source.
The problem is that most available strainers do not filter out debris at both ends of the fine-to-large size spectrum. Although multiple strainers can be used in sequence to filter out a range of debris sizes, this requires extra capital, equipment, space and labour.
“If a facility draws raw water from a natural source for process cooling, it must be sufficiently strained; but, manual cleaning can become excessive after storms or high tides introduce bigger debris at higher volume that must be removed,” says Keith Williams, President, Associated Equipment Sales, which represents North American manufacturers of heating, cooling and hydronic equipment.
In response, the industry has developed automatic self-cleaning scrapers that filter out both tiny particles and large debris.
This virtually eliminates manual maintenance as well as equipment clogging and downstream fouling issues, which helps to minimise production downtime.
“For industrial plant using naturally sourced cooling water, I recommend using an automatic scraper strainer that’s designed to remove particles down to the micron level … while still allowing you to pass surprisingly large debris. I’ve found that this is usually not possible with traditional equipment,” says Williams.
The automatic scraper strainer from Acme Engineering is a motorised unit that’s designed to continually remove both very large and very small, suspended solids from cooling water. Cleaning is accomplished by a spring-loaded blade and brush arrangement, and managed by a fully automatic control system.
Four scraper brushes rotate at 8 RPM, resulting in a cleaning rate of 32 strokes per minute. The scraper brushes get into wedge-wire slots and dislodge resistant particulates and solids.
This approach enables the scraper strainers to resist clogging and fouling when faced with high concentrations of large solids. It ensures complete cleaning and is very effective against organic matter “biofouling.”
Blowdown occurs only at the end of the intermittent scraping cycle when a valve is opened for a few seconds to the remove solids from the collector area. Liquid loss is well below 1% of total flow. According to Williams, the scraper basket also allows the strainer to bypass extremely large particles and debris automatically.
“Unlike a manual strainer, you don’t have to open and clean it. No one has to manually blow down solids and, as it’s automatic, it’s essentially a set and forget type of system that lets you walk away and focus on other aspects of your facility,” adds Williams.
And, whereas the automatic strainer is primarily used to remove particles and debris from natural water sources for cooling water, it can also be used to strain various liquid products that must be filtered for a wide range of residues and detritus.
“When a facility has both small particles and large debris in its cooling water or process stream, using an automatic strainer minimises the required maintenance to keep it operational and helps to maximise production uptime. The larger the facility, the greater the benefit,” concludes Williams.
