Resource Recovery from Waste Using the Input Flexibility of Waste Gasification Technology
Nowadays, gasification of waste or biomass is becoming the great interest all over the world. Especially, gasification of municipal solid waste (MSW) has been well-researched in Japan. The development of MSW gasification technology was started in the 1970s in Japan because of oil crisis. Several technologies have been researched and developed. The Direct Melting System (DMS), which is the gasification and melting technology developed by Nippon Steel & Sumikin Engineering Co., Ltd ., is one of the developed waste gasification technologies in this era. This technology was introduced for commercial use in Kamaishi City, Japan in 1979. As well as this waste technology, other gasification technologies have been developed for commercial use and installed.
A detailed description of the DMS has already been given previously. Waste is charged into the gasifier without any pre-treatment, which is different from other gasification technologies, such as fluidized bed gasifiers. Waste is directly charged into the gasifier from the top with coke and limestone. The gasifier consists of three mainparts: a drying and preheating zone, a thermal decomposition zone and a combustion and melting zone. Waste is gradually dried and preheated in the upper section (the drying and preheating zone). Combustible waste is thermally decomposed in the second zone and syngas is discharged from the top of the gasifier. The syngas, which mainly contains carbon monoxide, carbon dioxide, hydrogen, methane, hydrocarbons andnitrogen, is transferred to the combustion chamber in the downstream of the gasifier and then completely burned. Incombustibles descend to the combustion and melting zone (1,000 to 1,800 ºC) at the bottom and are melted with the heat generated by coke burning. Molten materials are intermittently discharged from a tap hole, quenched with water and magnetically separated into slag and metal. The sensible heat in the flue gas discharged from the combustion chamber is recovered by a boiler and power is generated by a steam turbine.