Updated: July 2002

1. Outline of system

The amount of incinerated ashes is increasing year by year in recent years with the diffusion of sewerage systems. Consequently, the shortage of the land for disposing of incinerated ashes by coastal reclamation has become a serious problem to be solved. Meanwhile effective use of the ashes arising from incinerated sewage sludge has been required. Based on the basic concept titles "the control of resource consumption, volume reduction and effective use of wastes," we have materialized Mitsubishi ash melting furnace system for sewage sludge using advanced technologies.
Figure 1 shows the system outline. Incinerated ashes are transported in a high density by air, and blown into a melting furnace for the side in tangential direction. The ashes are melted in a reduced state i.e. at a temperature of approx. 1,400 to 1,600ºC, and discharged continuously from the bottom of the furnace. Melted slag is crystallized on a crystallizing conveyer and taken extracted as crystallized slag (high quality aggregate). On the other hand, incinerated exhaust gas is discharged from the top of the furnace. It is cooled down after secondary incineration, and released into the atmosphere after acid gas in removed.

Figure 1 Flow diagram of ash melting and Recycling system

2. Characteristics

(1) Reduced fuel consumption:
Oxygen-enriched incineration reduces the consumption of auxiliary fuel.
(2) Compacted exhaust gas treatment systems:
Oxygen-enriched incineration decreases the amount of exhaust gas, compacting exhaust gas treatment systems.
(3) Stabilized slag discharge from even high-temperature zone:
Even ash heating and melting provides stabilized slag discharge.
(4) Properly maintained swirling prevents ashes from being carried over.
Strong swirling force sticks and catches melted ashes securely on the surface of the furnace walls.
(5) Furnace protected by evenly water-cooled structure:
Slag self-coating protect inner walls of the furnace.
(6) Facilitated operation control, and quick starting:
The adoption of oxygen-enriched incineration enables quick responses to the changes in ash components.
(7)High-quality slag produced:
Produced slag is effectively usable as high-quality aggregate including base course materials and asphalt mixtures.

3. Performance

Table 1 shows the results of the effective use test applied to crystallized slag. As this table indicates, both highly polymerized slag and lime slag meet the standards JIS A 5001 applicable to the crushed stones for roads when they are used as base course materials or as asphalt mixtures. In addition, the results of the heavy metal elusion test applied to this slag also meet the Soil Environment Criteria (the Environment Agency Notice No. 46).

Table 1. Result of effective use test

*1: NP = Non Plastic

4. Applicability and objectives

(1) Applicability: ash treatment/effective use system
(2) Objectives: ashes produced by waste incineration (ashes produced by sewage sludge incineration)

Figure 2 Outside appearance of demonstration system (Capacity: 2.4tons per day)