Convective Thermal Dryer Helps Clearwater Cogeneration WRF Save Energy By Turning Up the Heat

Challenge

In 2001, the city of Corona, Calif., built a state-of-the-art biosolids drying facility that uses 500ºF of waste heat from its then-new combined-cycle cogeneration plant, to pre-heat the biosolids dryer’s combustion air and to supply the low-grade heat required to promote biological growth in the water reclamation facility (WRF)’s digesters.  Waste heat from the power plant is also beneficially used to produce Class A biosolids.  Combining the facilities saved energy as well as construction and operating costs, with some of the same personnel operating both systems. 

Corona’s Clearwater Cogeneration WRF needed help processing 110 wet tons per day (9,167 pounds per hour) of municipal biosolids with a dry solids content of 14%. 

 

Solution

Evoqua Water Technologies supplied a Sernagiotto convective thermal dryer that can be fueled by either natural gas or digester gas.  Using digester gas, when possible, saves the city an extra 2.3 million btus per hour of natural gas.

 

The energy-efficient biosolids dryer produces an end-product that complies with USEPA 40 CFR Part 503 Rule for heat-dried Class A biosolids.  The tested heat value of the dried product is similar to a low-grade coal – around 6,500 btus per pound of product. 

 

Results

After years of continuous operations, the facility is meeting its designed performance.  Special attention was paid to the abrasive nature of the material during the design phase to ensure the appropriate metal alloys and equipment were used to extend equipment life.  Additionally, Corona’s top-notch operating staff, coupled with intrinsic computer-controlled automation specifically designed for plant requirements, has helped the drying system run efficiently. 

 

The Sernagiotto dryer has reduced the normal wet cake handling by 80% of the former production volume, saving the city money in hauling costs and also the worry of land application limitations, both associated with the Class B biosolids that Corona produces.  And the dryer has also helped prevent odors that could otherwise be a major problem because of the plant’s location within city limits. 

 

All of the biosolids, Class A or B, are sent to a facility where they are composted with biosolids from other agencies.  Corona currently has arrangements that will allow them to participate in the beneficial reuse of the Class A biosolids produced at the dryer.  These arrangements for a “direct partnership” include supplying dried biosolids to the cement industry alternative fuels operations in the Southern California area. 

 

Additionally, the dryer allows Corona to recover a significant amount of water from the biosolids during processing, with the added benefit of recycling that water for use toward the recycled water system within the city.

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