Dealing with sewage sludge is a problem which is mounting year by year. To counter this problem, Osaka Gas has implemented a melting treatment which draws on our long-standing proprietary technologies and expertise. This Coke Bed Sludge Melting Process transforms sewage sludge waste into slag by incinerating it in a cupola-type melting furnace. The volumes of resultant slag are reduced to levels 1/10th to 1/30th the initial sludge volumes, and noxious materials are stabilized allowing the slag to be used effectively in construction and as road-paving aggregates.

2. Major Line Flow Sheet for Coke Bed Sludge Melting Process

3. Outline of the Process

(1) Feeding sludge and coke

Dewatered cake is fed using a continuous feeder into the drier, where it is dried to a water content of about 40%. The dried sludge is then conveyed to the top of the melting furnace together with the weighed coke and slag conditioning material, and charged into the melting furnace through the charge hopper.

(2) Burning and melting sludge in the melting furnace

At the bottom of the furnace a coke bed is provided which is heated to a temperature higher than 1500deg.C. The sludge is dried and heated, and the combustibles in the sludge are decomposed and burned. The non-combustibles(ash) in the sludge are melted down to form slag.

(3) Treatment of molten slag

Molten slag of 1300 to 1500deg.C discharged from the melting furnace is either cooled by water or cooled by air.

4. Basic Construction of the Melting Furnace

The cupola melting technology generally used for production of castings is applied to the melting furnace, the heart of this process .

Generally, the unprocessed metal corresponds to the dried sludge, the slag making material to the basicity conditioner (crushed stone or lime stone), and the casting to the molten slag recovered from the inorganic materials contained in the sludge.

(Sludge decomposition reaction on the coke bed)

CnHm -> nC+ (m/ 2) H₂ (Thermal decomposition)
C+CO₂-> 2CO (Boudauard reaction)
C+H₂O-> CO+H₂ (Water gas reaction)

5. Features of the Process

(1) Easy to operation and maintenance
(2) Less susceptibility to load variations
(3) Low NOx exhaust gas
(4) Using long-term stable supply fuel (coke)
(5) Stable properties of slag
(6) Safety of the produced slag

6. Applications of Molten slag

7. Achievements of Coke Bed Sludge Melting Process