Updated: July 2002

1. Purpose

The Meltox system is a sludge melting system where the sludge furnace generates high temperatures exceeding 1300ºC by burning the sludge. This system can reduce sludge volume and stabilize toxic matter such as heavy metals in stable slag, which be then used in construction materials.

2. System Outline

The Meltox system consists of sludge drying, sludge melting, and flue gas treatment (Fig .1) systems.
1) Sludge Drying System
A pulverizing mechanism in a flash dryer yields fine-sized dried sludge with low moisture content. Low exit gas temperature enables high thermal efficiency. Adoption of the flash dryer can omit boilers, secondary dryers or pulverizers, bringing easy operation and less maintenance compared with other drying processes.
2) Melting Process
A uniquely designed sludge furnace (Fig. 2) is the hub of the system. The furnace comprises a vertical primary combustion chamber, an inclined secondary combustion chamber, and a slag outlet section with a radiation plate. Sludge is blown into the furnace with compressed air, where it is incinerated and melted during its spiral descent. The radiation plate maintains a steady flow of slag, which is cooled by water or air before discharge.
Dual stage combustion, in which reducing incineration with an air ratio of 0.8 to 0.9, and complete combustion are carried out in the primary and secondary combustion chambers respectively, reducing NOx production.
Fused mist in flue gas is separated in the furnace by centrifusion, followed by separation at the slag outlet section. Those processes contribute high slag yield. The combustion in the furnace is controlled by a fuzzy logic system, achieving energy savings, reduced NOx production, and stable operation without specialized operators.
3) Flue Gas Treatment Process
The flue gas goes through a heat exchanger for heat recovery, a bag filter for dust removal, and a desulfurizer for SOx removal and to avoid secondary pollution. The dryer air is recirculated to reduce the total amount of flue gas, and a part of the drying gas is led to the furnace where odor elements are decomposed through combustion.

3. Performance and Features

- Reduction in Sludge Volume: the volume of the slag is thirty-fold less than that of the original sludge.
- Stabilization and Containment: heavy metals are solidified in the slag.
- Slag as a Byproduct: the slag can be used as a byproduct.
- Energy and Space Saving: complete combustion with the low air ratio and heat recovery saves energy, while the compact furnace and the simple system design save space.
- Fuzzy Logic Control: the fuzzy logic control for combustion achieves labor-saving, and stable and effective operation.
- Low NOx Generation: the dual-stage combustion system minimizes the generation of NOx in the furnace.

4. Slag as a Byproduct

The slag can have various configurations depending on cooling methods, such as water cooling or air cooling. The slag can be utilized in various ways, such as for filling material, tiles for pavement and roads, interlocking blocks, terrazzo tiles, and other construction materials. Other value-added applications are now in the R&D stage.

Fig. 1

Fig. 2 Cross Section of Melting Furnace