Iryna Dobytchina via iStock via Getty Images Plus
By Gerard J. Lynch, P.E., Spiral Water Technologies
The hydroelectric power industry has long been an important source of low carbon energy. In 2019, the total U.S. conventional hydroelectricity generation capacity was 79,746 megawatts — or about 80 million kilowatts — according to the U.S. Energy Information Administration. About half the total U.S. utility-scale conventional hydroelectricity generation capacity is concentrated on the West Coast in Washington, California and Oregon.
Whether the cooling water source for these plants is an ocean, river, lake or pond, the need for filtration to remove incoming contaminants and protect the equipment is the same. For this reason, hydroelectric power plant operators often add automated self-cleaning filters to remove fish, quagga and zebra mussels as well as sediment and silts from incoming water sources. Automated water filtration allows them to protect their equipment.
When thinking about the use of raw natural waters for cooling systems, there are several considerations. For example, experienced raw-water filtration operators know one challenge is avoiding downtime and system failures due to high total suspended solids (TSS) or solids loading. One solution has been the use of self-cleaning filters. While self-cleaning filters are widely used, most cannot manage TSS above 500 ppm. Consequently, trouble can arise when seasonal or unexpected issues arise.
At many power plants, the traditional natural water-cooling system design includes a three-valve bypass and large, manually cleaned filters installed in parallel with the self-cleaning system. Many of the power plants that use river water for turbine bearing cooling and compressor cooling have utilized this design approach for more than 20 years. No matter what type of automatic filtration is used, the design should be configured with operational freedom in mind.
Operators also need robust filter systems to better manage natural water upset conditions. Being prepared requires a substantial solution.
Cooling water sources for hydroelectric power plant cooling include ocean, river, lake or pond water. Bag-clogging debris is filtered from the river water.
Developments in automatic water filtration make it possible to improve the operation of both micro- and large-scale hydroelectric power plants as well as other industrial applications that must work with high solids water processes. Many filters currently used in major facilities, however, date back to the 1960s. Scalable automatic filtration options that address industry-specific needs can be used to upgrade water filtration performance. Industry-specific needs include:
Conventional filters have limitations on micron retention. Finer filtration technologies like bag filters and cartridges have limited dirt-holding capability as well as higher operating costs for media, labor and disposal of spent media.
In the hydropower industry, research suggests that one optimal filtration option would be an automatic, self-cleaning filter that can accommodate concurrent demands for lower micron filtration such as 15- to 1,500-micron retention along with the ability to handle TSS loading higher than 500 ppm. This would address the challenge that the tighter the micron retention, the higher the TSS loading. (While many filters can achieve the desired micron retention, most cannot also meet the high solids-loading criterion. This limits the usefulness of some filters in challenging industrial applications.)
An automatic, single-pass, self-cleaning filter was developed to meet this criteria. The technology is designed to remove high levels of TSS or biological oxygen demand (BOD). Further, the filter is designed to process bulk-solids removal up to 15,000 mg/l TSS (15 percent by volume) while providing continuous 15- to 1,500-micron filtration. The filter does not use bags, cartridges and media filters, which reduces labor demands vs. filtration systems that do.
Also, because the filtration technology was developed as an algae-harvesting device under a government grant for the production of biofuels, it is not affected by algae and other deformable solids.
The experience of a micro-hydroelectric power facility in the Pacific Northwest illustrates the effectiveness of the automatic filtration in addressing problems associated with filtering natural water used to cool bearings and mechanical seals.
A filter bag is used to protect the cooling water system. Finer filtration technologies like bag filters and cartridges have limited dirt-holding capability.
A county utility in the Pacific Northwest operates a micro-hydroelectric plant that delivers power generated by local rivers and streams. This plant had relied on 200-micron bags to filter the water used to cool bearings and mechanical seals on the plant’s two system turbines. The bags were prone to clogging, however, due to fouling caused by the high turbidity (heavy particulate matter) of the nearby river that provided the plant’s water source. The river also is subject to seasonal upset when weather and environmental conditions increase its turbidity.
These conditions resulted in daily plant stoppages as employees halted operations in order to manually clean or replace filters. The conditions also required the availability of 24-hour, on-call maintenance staff to minimize hydroelectric downtime.
Another issue at the Pacific Northwest hydroelectric plant was that — like many industrial applications — the service-water requirements for removal of smaller particles like grit and sand were critical in the protection of the plant’s turbine bearings and pump seals. Heat exchangers used for lubricating oil cooling can offer better performance if the heat transfer surfaces are kept clean and silt free. A thin coating of silt is an insulator that cuts down on the performance of the heat exchanger.
Automatic self-cleaning filters were used to reduce maintenance, usually enlisting a backwashing principle, with the pore size of the element opened so as not to exceed the TSS they can handle. (Some automatic filters are limited to a maximum TSS of about 200 ppm. They can stay within this limitation by collecting only the largest particles, letting the majority of smaller particles pass through.)
The filtration equipment supplier assessed the operation at the facility and, after making recommendations, installed a 50-micron filter inline prior to the plant’s mechanical seal water delivery. The automatic, self-cleaning water filter was designed for ultra-high and variable total suspended solids (TSS) of up to 15,000 ppm. The filter has a proprietary helical action that makes it able to provide continuous 15- to 1,500-micron filtration while requiring less energy usage than traditional filtration systems. The installation took approximately four hours and did not require removal of the existing bag filters or any system overhaul.
In addition to providing low micron filtration, the new automatic filter system collects, condenses and purges solids. Because filter bags no longer needed to be removed and replaced regularly, the utility was able to improve employee efficiency and reduce operational downtime.
The hydroelectric plant’s experience demonstrates the ability of an automatic filtration system to improve facility efficiency through its ability to capture highly variable solids subject to seasonal extremes. After installation, the hydroelectric plant was able to run continuously without daily downtime for filtration maintenance. Moreover, the power plant operators determined that the filter delivered a notable return on investment, paying for itself in a single season by reducing consumables and lowering labor costs.
In conclusion, though this micro-hydroelectric plant was small in scope and volume, the same technology and design solution can be applied to larger hydroelectric power plants and industrial applications. This includes cooling tower water treatment systems as well as other difficult-to-treat waters. Effective water filtration allows plants to meet increasing demand for better operating efficiencies. PC
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