Harnessing Heat and Making Power with Recycled Water at UCONN
- David Witte - Hazen and Sawyer
Water reuse can be an important component of a comprehensive watershed management program and water supply plan. Removing wastewater streams from surface water bodies can reduce pollutant loads to receiving waters including nutrients, heavy metals, pharmaceuticals and endocrine disrupting compounds. Another important advantage is that wastewater reuse also reduces water demands that potable supplies would otherwise have to satisfy. But recently an increasing number of energy related uses are being found for reclaimed water. In particular, recycled water is now being used for its heat value and used as a water source for steam production in power plants. These benefits of recycled water are a true example of the energy water nexus and are being implemented at the University of Connecticut as it embarks upon the first-of-its-kind water reclamation project for the region.
In addition to quenching the water needs of the University, the recycled water will also be used as a heat source for the entire recycled water complex. The thermal energy from the recycled water will be extracted by use of a heat pump system and used to heat the new facility. Heat pumps are the same technology that is used for geothermal heating in homes, schools, and commercial facilities. The recycled water heat pump system is more cost competitive in this application because the up-front costs associated with drilling and installing the ground-loop piping for geothermal installations are eliminated.
Three heat pumps were designed for extracting heat from the recycled water in the University of Connecticut Reuse project. At the average low air temperature of 25?F for the heating season, a total electrical input of 24kW for running the heat pump compressors will extract 117kW of heat from the water; this totals to a rate of 141kW of heat delivered to the facility. In other words, an additional 488% of free heating power will be harnessed from the water that would have otherwise gone untapped. The system is projected to save over $60,000 per year in operating costs as compared to electrical heating. The capital costs are slightly higher for the heat pump system, but the payback period is very short.
This new 1mgd reuse facility will provide water to the University’s power plant. This water will be used for cooling tower make-up, boiler feed water, and limited site irrigation. The treatment technology will include microfiltration membranes and in-vessel LPHO UV disinfection system. Also, the boiler water treatment system uses reverse osmosis technology to further treat the reclaimed water. The overall program is estimated to cost on the order of $17,000,000.
This paper will review the University’s progressive new program and summarize key decision factors and program components that will help other utilities in evaluating such progressive and sustainable new energy systems. The review will include how the recycled water will be used for multiple purposes including heating, cooling, and energy production. This paper will be timely and informative considering today’s focus on sustainable energy management, renewable energy and the water energy nexus.
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Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.