Updated: July 2002

1. Advantages of Sludge Melting

1) Volume of slag is about 1/25 of that of dewatered cake and ½-1/3 of that of incineration ash.
2) Stabilization
Slag is not odorous, not disturbed by wind and easy to handle.
No elution of such components as heavy metals is observed.
3) Utilization of slag
Slag can be used as construction materials such as concrete aggregate.

2. Sludge Melting Process Flow

Dewatered cake from Receiver (1) is loaded into Multi Stage Sludge Dryer (2), in which the dewatered cake directly contacts steam of 350 to 400ºC and is dried to have a moisture content of less than 10%.
The cake or sludge thus dried is temporarily stored in Dried Sludge Bin (4) and then fed to Mill (5). The sludge is ground into fine particles of an average of 200 to 500 microns and, together with the combustion air, is then sent by Dried Sludge Feeder (6) to Melting Furnace (7).
The sludge burns in the furnace while it swirls intensely with combustion gas, and ash components of the sludge melt and are liquidized. The liquidized ash flows down over the inner wall of the cyclone furnace and comes out of the bottom section of Second Combustion Chamber (8) into Slag Receiver (9).
The temperature in the cyclone furnace is maintained at about 1,400ºC by heat generated by sludge combustion. On the other hand, steam used for sludge drying circulated between the dryer and Steam Heater (12). In the steam heater, steam (150ºC) from the dryer is heated up to 350 to 400ºC by the flue gas from the furnace. Malodorous components coming out of the drying process, together with surplus steam - water evaporated from sludge being dewatered -, are mixed with the high temperature flue gas of the second combustion chamber and oxidized.
Pressure in the sludge dryer is kept slightly lower than the atmospheric pressure, thereby preventing odor leakage.
Flue gas (combustion gas + surplus steam) is sent to Combustion Air Pre-heater (10) and the steam heater to recover heat, then stripped of dust and sulfur oxides and discharged to the atmosphere.
Auxiliary Furnace (11) supplements heat for sludge drying.

3. Advantage of the system

1)Operation is very stable due to the supreme range ability of the dryer and the easily controllable melting furnace.

2)The combustion heat of the sludge can cover most of heat requirement for the melting system:

a. Because of the the melting furnace equips no forced cooling furnace well, heat loss through the furnace wall is extremely small.
b. Since the required heat of the sludge dryer is recovered from the flue gas from the melting furnace, for average sewage sludge case, no auxiliary fuel is required.

3)Odor free circumference can be kept depend on the negatively pressurized drying system, and the combustion air intake which is placed at the sludge pit.

4)There are no hazardous materials like as dioxin included in the effluent, since all discharges from the system are treated in the high temperature furnace.