GLOBAL INDEX 2011 KUBOTA CORPORATE COMMUNICATION MAGAZINE

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3435With that objective in mind, city officials took note of the sewage sludge incinerator at its Chubu Sewage Treatment Center, which was responsible for the largest amount of CO2 emissions among the facilities managed by the city (9,356 t/year in FY2005, or 9.2% of the total of all city facilities). At sewage treatment plants, sewage is separated into water and sludge, the latter of which is burned up by a sewage sludge incinerator after the condensation and dewatering processes. The sewage treatment process at the facility in Hamamatsu – and every facility of its kind, for that matter – emits a large amount of CO2 throughout the treatment process. With the spread of sewage systems, this discharge increased by some 54% between 1990 and 2006, making reduction of CO2 discharged from sewage treatment a policy agenda on the national level. As such, the Japanese government took up reduction of CO2 and other greenhouse gases through promotion of energy conservation and introduction of new energy sources for sewage systems, and included it in the Kyoto Protocol Target Achievement Plan.The origins of this ambitious project to reduce CO2 emissions at Hamamatsu City’s sewage sludge incinerator can be traced back to 2005, when Kubota’s circulating fluidized bed incinerator was introduced. In the early 2000s, a new trend was developing in the sewage sludge incinerator market − the development and introduction of circulating fluidized bed incinerators, which feature improvements over conventional incinerators.The impetus behind this trend was a change in the nature of raw sludge. Primarily owing to the split-flow treatment of rainwater drainage and domestic wastewater in recent years, the ratio of organic substances coming from inflow sources has increased, thus creating “calorie-rich” wastewater. In addition, the shift from lime to polymer coagulant as a dewatering aid has tended to add more calories to dewatered sludge. In response, demand was high for an incinerator capable of burning up such sludge with greater speed, using less energy, and generating less CO2.The circulating fluidized bed incinerator uses high-temperature circulating sand as a heat medium for the instant dispersal and drying of sludge for incineration. This incinerator is characterized by improved efficiency, energy conservation, and compact size. Because its combustion efficiency is higher than that of conventional incinerators and a higher combustion load (calorific value within the combustion chamber) may be tolerated, the incinerator can be made more compact. Also, thanks to the low air power requirements necessary for sand circulation, flow power requirements have been substantially reduced. High fuel efficiency has also been achieved by collecting high-temperature combustion air from the incinerator exhaust gas.At the time, sewage sludge incinerators in Hamamatsu City were undergoing a replacement period. Due to the need to respond to higher-calorie sludge, the introduction of circulating fluidized bed incinerators was considered. In fact, however, there were some who questioned the adoption of such incinerators. There were still only a few local governments across the country that had introduced them, thus giving rise to serious concerns over the risk of 05,00010,00015,00020,00025,000(1,000 kg)4,53221,00016,18610,81710,7122,2954,5325,8674,7833,1336,5581,48110,071Chubu Sewage Treatment Center9,356Annual CO2 Emissions from Energy Consumption in Buildings, etc. in Hamamatsu City (By facility type, FY2005)Action Plan of the Hamamatsu Municipal Government to Prevent Global Warming(Phase II)Circulating fluidized bed incinerator (Incinerator No. 2)Administrative facilitiesWater supply and sewage facilitiesPublic cleansing facilitiesFirefighting facilitiesSchool facilitiesLife-long learning facilitiesCommunity hallsGymnasiumsFarming/fishing facilitiesSocial welfare facilitiesMedical/healthcare facilitiesCommercial/industrial facilitiesOther facilities

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