In the Tama area of the Tokyo Metropolitan Area, an eco-cement production plant that processes and recycles incineration residues and melting fly ash produced in municipal garbage incineration plants into eco-cement is in operation. (Fig. 2-41)

## (4) Waste into energy

When it is difficult to recycle waste into materials it must be processed by other means such as incineration. Thermal energy produced in such a process can be recovered in the form of power energy or water vapor, a process called thermal recycling. Technology to convert biomass waste such as food waste, livestock manure, and wood waste from construction into methane for use as energy is also being used with increasing frequency.

Today, the reduction of emission of greenhouse-effect gases such as $ CO_{2} $ is an important issue related to controlling global warming. Thermal recycling converts thermal energy produced by waste incineration into electric power and other forms of energy. Since it replaces fossil fuels it reduces $ CO_{2} $ emissions. In addition, in view of the fact that biomass contains $ CO_{2} $ that is fixed from the atmosphere, the $ CO_{2} $ produced by burning biomass is considered as reintroducing $ CO_{2} $ that originally existed in the air (the carbon neutral concept). Accordingly, these $ CO_{2} $ emissions are not included with artificial $ CO_{2} $ emissions, and substituting biomass for fossil fuel results in a reduction of $ CO_{2} $ emissions.

## a) Waste power generation

Waste power generation involves recovering high-temperature thermal energy produced by incinerating waste by means of a boiler and using the water vapor thus generated to rotate a power generation turbine. It is an effective means of using the heat produced by incinerating plants. The first waste power generation plant in Japan was probably the Nishiyodo Plant of Osaka City established in 1965. Since then, the national government has encouraged waste power generation, by, for example, granting subsidies to construct new incineration plants and equipment for the use of extra heat added to existing incineration plants. As a result, many waste power generation facilities have been constructed around the country. As of the end of fiscal 2004, of the waste incineration plants in operation or under construction, 281 plants are generating or will generate electric power. These power generation plants have a total capacity of 1,491 MW and account for about 20% of all waste incineration plants. (Fig. 2-42)

Waste may contain plastics or vinyl chloride, which produce hydrogen chloride when incinerated. Along with hydrogen chloride, iron chloride and alkali iron sulfate is produced on the surface of metals, which decomposes with dust on the surface. The metal surfaces subsequently rapidly corrode when the surface temperature rise to $ 350^{\circ} $ C- $ 400^{\circ} $ C. As a result, waste incineration plants in Japan are designed so that the temperature of water vapor does not exceed $ 300^{\circ} $ C. As a result, the power generation efficiency of waste power generation plants is 10%-15% at the most. More recent plants, however, have an efficiency exceeding 15%. Nevertheless, this rate is

Fig. 2-43 Example of super waste power generation

Source: Kitakyushu City

Fig. 2-42 Outline of waste power generation