Quality straining deals with rigours of fast flowing water source

To enable its use as cooling water, industrial facilities such as power, processing, and manufacturing plants prefilter raw water from rivers, lakes, gulfs, and coastlines to remove organic, aquatic, and other solids.  However, because the cooling water originates from bodies of water, it can be dirty, with considerable debris, weeds, and trash.  

As a result, strainers are required to remove the waste from the cooling water before it goes into heat exchangers and cooling systems, and to prevent spray nozzles from clogging.

The challenge is that natural bodies of water such as rivers and lakes are typically rife with both large solids and small particulate (i.e.-debris, dirt, and other suspended solids) as well as larger organic matter.  Since many filters are designed to handle either smaller particulate or larger debris, but not both, the result can be unscheduled downtime, excessive maintenance, and costly, premature replacement.  

When a power plant was providing energy as a backup for a Kansas City power provider,the plant used river water for cooling, utilizing large basket strainers.  The plant is now part of an energy solution partner with multiple district energy networks nationwide, and sought more efficient operation and maintenance from a downtown steam loop that produced chilled water.  

“To provide condensing water for steam production as well as cooling water to the chillers and condensers, they take water from the Missouri River and put it through a once-through cooling system,” says Keith Williams, PE, who was involved with the project, and is a manufacturer's representative at Lenexa, KS-based Associated Equipment Sales.  

According to Williams, the river’s fast flow along with high tide complicated the straining of river water for the plant.  “The Missouri River is the fastest river in North America, so high tide is when it is ripping everything off its banks: grass, weeds, twigs, and debris.  All of that has to be filtered to keep from clogging the condenser tubes in the heat exchangers,” says Williams.

He adds that the power plant’s previous basket strainers required manual cleaning every shift, three times a day during high tide.  

“It was a very dirty, disgusting job that no one wanted to do. I advised using an automatic scraper strainer from Acme Engineering that is capable of very fine straining while still passing very large debris,” commented Williams.

The automatic scraper strainer from Acme Engineering, a North American manufacturer of industrial self-cleaning strainers, is a motorised unit 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 system, managed by a fully automatic control system.  

The four scraper brushes rotate at 8 RPM, resulting in a cleaning rate of 32 times 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 large solids and high solids concentration.  It ensures a complete cleaning and is very effective against biofouling.  

Blowdown occurs only at the end of the intermittent scraping cycle when a valve is opened for a few seconds to remove solids from the collector area.  Liquid loss is well below 1% of total flow.

Photo: Acme Strainers scraper inside screen