Sustainable Development Goals
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 there is a large demand for energy. The approximately 125 million residents and large 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, as well as provide a partial solution to the country's need for energy.
An integrated waste recycling center with a gasification and ash melting plant built on top of the waste recycling center was chosen for the main 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 that is 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 steam of the boiler generates electricity of 12 megawatts (MW) and covers the electric power consumption of this facility and of the Recycle Plaza at the same location. Surplus electric power is sold to Tokyo Electric Power Corporation. Additionally, steam is supplied to the Recycle Plaza for heat utilization.
Performance test measurements at the Kawaguchi facility were carried through by a third-party test agency. After power supplies both for the facility and to the recycle 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, in the course of the performance test, the emergency shutdown test and test of failure of the electric supply were carried out. It was confirmed that the plant shuts down safely in the event of an emergency and starts 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 approximately 3.8 MW is sold to the local electric power company.
Since January 2003, the Kawaguchi facility ash recirculation ratio was increased step by step, while material balances were established and the quality of the slag was 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 with respect to 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, again reducing the amount of final residue to be landfilled.
The Kawaguchi facility has been in full-time, full-scale commercial operation since 2002, achieving more than 90% availability each year, processing as-received post-recycled curb side-collected solid waste, and recovering electricity, ferrous and non-ferrous metals. The gasification system is designed to combine 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.
Gasification and ash-melting system burn the syngas converted from MSW between 1,300°C to 1,450°C so that dioxins totally decompose and bottom ash melts to vitreous slag (artificial sand) which meets the most stringent elution standards of soil and is recycled.
The Asahi Clean Center is unique in that this facility has a community pool built on top of the gasification processing plant. This pool is heated by the utilization of 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, as well as in emergency situations, 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.