A system generating electricity from wastewater biosolids is scheduled to be set up in the Truckee Meadows Water Reclamation Facility (Reno, Nev.) this summer. The demonstration-scale system is designed to process wastewater solids at a rate of 9 kg/h (20 lb/h). The system, which dries the solids into a solid fuel, is the product of a renewable energy research project at the University of Nevada (Reno), according to a university news release.
The university will study its patent-pending technology to see if the fuel generated is suitable for gasification and, ultimately, conversion to electricity. The researchers will investigate how dry the fuel becomes, what the material’s fuel value is, and what the metal content is, said Chuck Coronella, principal investigator for the research project and associate professor of chemical engineering at the university.
“Our innovation is a low-temperature fluidized bed, with inert solids serving as a very fast heat-transfer medium,” Coronella said. The continuous-feed demonstration system is the size of a refrigerator and will help researchers determine the optimum conditions for a commercial-size operation, the news release says.
For the current trial, wet solids are fed to a fluidized-bed dryer operating at 77°C (170°F), Coronella said. The fluidized bed is composed of inert solids, such as sand, that are agitated rapidly. The moving inert material breaks the wet solids into smaller pieces that dry quickly. The dried solids leave the bed as a fine powder entrained in the air. “The current trial will validate only the low-temperature dryer, not the generation of power,” Coronella explained.
The trial also will test drying solids continuously, which poses a challenge, even though the feed rate is extremely small compared to the needs of typical wastewater treatment facilities, Coronella said. After completing the small-scale test, the researchers plan to conduct a large-scale test capable of handling feed rates common to a small- or medium-size facility. “The next demonstration will be integrated and will include dewatering, drying, gasification, and power production,” Coronella said.
Truckee Meadows agreed to the trial after being approached by Coronella and setting up an interlocal agreement between the cities of Reno and Sparks, co-owners of the facility, explained Starlin Jones, operations and maintenance manager of the facility. To install the system at the facility, the researchers need to install a gasifier and some kind of combustion facility to convert the dried fuel to power, Coronella explained.
“The system that we are developing needs no additional fuel for drying,” Coronella said. “Most of the heat required for drying is provided from waste heat derived from combustion of the dried fuel.”
The major benefit of the new technology is that it enables complete solids management onsite. That change would reduce trucking costs and biosolids disposal fees while also potentially generating 14,000 kw•h per day to offset plant power needs, the news release says.
“The challenge has been developing a cost-effective means to convert de-watered sludge to a dry fuel,” Coronella said. Coronella estimates that plants generating more than 91 Mg/d (100 ton/d) will be able to justify the costs of installing this type of system.
University researchers began working on converting sludge to electric power in 2005 after being solicited by the California Energy Commission to study the topic and receiving the Energy Innovations Small Grant to fund the research, Coronella said. The newest phase of the project received funding from the Tech Transfer Office under a U.S. Department of Energy grant.
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