Asahi Clean Centre: One of the World's Cleanest Energy-from-Waste Gasification Facilities

Organisations Involved: Kawaguchi City, Tokyo Electric Power, Orix, Shimizu Corp

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 needed to be diverted from landfill.

Japan is densely populated and there is a large demand for energy. The approximately 127 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.

The Solution: 

A gasification and ash melting was chosen for the main process of the new "Asahi Clean Center". The facility receives municipal solid waste ("MSW") from Kawaguchi City and adjacent Hatogaya City. The facility incorporates efficient and safe operation. The performance test demonstrated the fulfillment of all guarantee values, including below 50 pg I-TEQ/m3 of Dioxin and Furan. The monthly average of MSW processed is 141.5 t/d, with variations of 10% above or below the design capacity in the daily operation. 

The plant has a capacity of 420 t/d of MSW in three process lines, plus 37 t/d of bottom ash from an external source. Thermal energy recovered from the steam of the boiler generates electricity of max.12'000 kW 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 thirdparty 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 short time operation of the slag outlet burner. Therefore, the gasification and vitrification by the energy content of the waste itself was confirmed. Furthermore, in the course of the performance test, emergency shutdown test and test of failure of 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 afterwards. 

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 operation of all three lines approx.8300 kW electric power is generated. It covers the self-consumption of the facility, is supplied to the recycle center and the residual approx.3800 kW are 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 an 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 a first step. Afterwards, 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 land filled.

The Outcome:

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 to the goals set by the EU Directive and exceeds the EU stringent processing requirements.

Gasification and ash-melting system burns 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 build 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 woman, health bathroom, resting room, lounge, kiosk, all utilize the remaining heat of the waste gasification facility. The water used in the bathrooms and kitchens, as well as in emergency situations, and is drinking water quality. Only the domestic sewage of is discharged into the municipal sewer.