Sustainable Development Goals
Organizations Involved:
Kawaguchi City, Tokyo Electric Power, Orix, Shimizu Corp
Services:
Design & Engineering, Consulting, Due Diligence Services, Component Supply
The Challenge:
Kawaguchi City, just outside of Tokyo, needed additional waste treatment capacity to serve the rapidly growing population. In addition, there was a lack of recycling facilities for source-separated materials and the ash of the existing stoker grate incineration plants needed to be diverted from landfills.
Japan is densely populated and has a significant energy demand. The approximately 125 million residents and sizeable industrial base demand sustainable solutions to its waste management problems. Efficient and state-of-the-art technologies are needed on an immense scale to solve the waste disposal issue and partially solve the country's energy needs.
The Solution:
An integrated waste recycling center with a gasification and ash melting plant built on top of the waste recycling center was chosen for the primary process of the new "Asahi Clean Center." The facility receives municipal solid waste ("MSW") from Kawaguchi City and adjacent to Hatogaya City. The facility incorporates efficient and safe operations. The performance test demonstrated the fulfillment of all guarantee values, including below 50 pg I-TEQ/m3 of Dioxin and Furan.
The plant has a capacity of 420 metric tonnes per day (TPD) of MSW in three process lines, plus 37 TPD of bottom ash received from other less efficient waste incineration facilities within the city. The monthly average of MSW processed is within variations of 10% above or below the design capacity in the daily operation. Thermal energy recovered from the boiler's steam generates 12 megawatts (MW). It covers this facility's electric power consumption and the Recycle Plaza at the exact location. Surplus electric power is sold to Tokyo Electric Power Corporation. Additionally, steam is supplied to the Recycle Plaza for heat utilization.
A third-party test agency carried out performance test measurements at the Kawaguchi facility. After power supplies both for the facility and the recycling plaza nearby, the efficiency ratio of surplus power was 9.0 %. During the performance test, city gas was only used several times per day for the short-time operation of the slag outlet burner. Therefore, the gasification and vitrification by the energy content of the waste itself were confirmed. Furthermore, during the performance test, the emergency shutdown test and test of failure of the electric supply were carried out. It was confirmed that the plant shut down safely in the event of an emergency and started up without hindrance again afterward.
The average CO content is 1.8 ppm, and the CO guarantee value of 10 ppm was safely fulfilled each day. The operation is carried out continuously, and the fly ash vitrification ratio is 90%. During the operation of all three lines, approximately 8.3 MW of electric power is generated. It covers the self-consumption of the facility, which is supplied to the recycling center, and the residual of roughly 3.8 MW is sold to the local electric power company.
Since January 2003, the Kawaguchi facility ash recirculation ratio has increased step by step, while material balances have been established, and the slag quality has been analyzed. It can be concluded, that the overall vitrification ratio increases with higher ash recirculation ratio and reaches values of more than 90%. The slag quality itself remains stable and allows for efficient recycling of the slag in the building industry. Furthermore, the facility is also optimized concerning the non-combustibles discharged from the bottom of the fluidized bed: ferrous and aluminum are recovered as valuable metals in the first step. Afterward, the remaining fraction is shredded, ground, and returned to the gasifier. From there, it is carried to the ash melter and becomes part of the vitrified slag, reducing the amount of final residue that must be landfilled.
The Outcome:
The Kawaguchi facility has been in full-time, full-scale commercial operation since 2002, achieving more than 90% availability each year. It processes as-received post-recycled curb-side-collected solid waste and recovers electricity and ferrous and non-ferrous metals. The gasification system combines material recycling (metals, mineral components, ash) with energy recovery. This concept fits ideally with the goals set by the EU Directive and exceeds the EU's stringent processing requirements.
The gasification and ash-melting systems burn the syngas converted from MSW between 1,300°C and 1,450°C, so dioxins totally decompose. Bottom ash melts to vitreous slag (artificial sand), which meets the most stringent soil elution standards and is recycled.
The Asahi Clean Center is unique in that it has a community pool built on top of the gasification processing plant. This pool is heated by using waste heat from the gasification plant. Bathrooms for men and women, health bathrooms, resting rooms, lounge, and kiosks all utilize the remaining heat of the waste gasification facility. The water used in the bathrooms and kitchens and emergencies is drinking water quality. Only domestic sewage is discharged into the municipal sewer. The plant's throughput, including emissions, is also posted publically via a digital sign above the sidewalk for everyone to observe 24/7/365.
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