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For the purposes of the prevention of global warming and the multiplication of electric power sources, the Bureau of Sewerage, The Tokyo Metropolitan Government, has addressed itself to the project of power generation using digestion gases and the acquisition of new power sources utilizing the techniques of small-head hydraulic power generation. As one of its undertakings, sodium-sulfur batteries (NaS batteries hereafter) or the so-called secondary batteries were delivered to the Kasai Wastewater Treatment Plant in December 2001. In the past years, the NaS batteries have been practically used by the Tokyo Electric Power Company, Inc., which has long been a power generation undertaker and a developer. However, this introduction was the first achievement for a sewerage project undertaker or a power consumer.

The NaS battery system introduced to the Kasai Wastewater Treatment Plant has a scale with a battery capacity of 7,200kWh and an inverter output of 1,200kW, in consideration of cost effect and actual operating conditions. The advantages resulting from the facility introduction are the acquisition of a power source in case of a service interruption, the curtailment of electricity rates, and the reduction of the environmental load. Since December 2001, verification by the use of actual loads has been continued. Primarily, the combined efficiency of the NaS batteries on the design base was 73%, but in the verification running, this efficiency showed a great variation between 65% and 75% according to the operation mode of the NaS batteries. This was due to the great effect of the power consumption by the warm-up heaters for the NaS batteries. Under some operating conditions, the heater power changed widely. Since the combined efficiency was lower than expected, the goal value of about 1.5 tons annually in CO2–based conversion was substantially lowered for the reduction of the environmental load. In regard to the curtailment of the electricity rates on the one hand, a goal value of 40 million yen could be saved because of the successful peak-cut operation and favorable day-night management of the NaS batteries.

This paper reports the principle of the NaS batteries, the introduction processes, the concrete operation at the Kasai Wastewater Treatment Plant, and the result.

Document Type: Research Article


Publication date: January 1, 2003

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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