Updated: July 2002

1. Preface

For the purpose of stabilization and volume reduction in the treatment and the disposal of sewage sludge, a drying-incineration treatment, a drying-pyrolysis treatment, a drying-melting treatment, compositing and an incineration treatment together with municipal solid waste have been practiced. Application of a dryer to these processes has a very important position in the energy saving and the enhancement in efficiency of the total process. Thus, the drying process becomes essential considering each processes.
A hot air dryer, an air stream dryer and an indirect steam dryer, etc. have been practically used as the dryer for sewage sludge. Among them, the indirect steam dryer has been most widely used. The main reasons are:
1) It can adjust the moisture content of dried sludge over a wide range.
2) It has a high thermal efficiency (saving energy).
3) The amount of exhaust gas to be treated is small.
Among them, the fact that the moisture content of dried sludge is not limited shows that an efficient drying to a required moisture for the succeeding processes such as incineration, pyrolysis and melting can be made. It has result in a high adoption of the indirect steam dryer.
Here, the N.G.K. S.S. Dryer will be introduced which has many practical results since adopted in 1979 as follows.

2. Features

1) Heated and self-cleaning agitator paddles on multiple shafts provide a high evaporating capacity.
2) The moisture content of dried sludge can be adjusted over a wide range.
3) Applicable to a wide range of sludge

3. Outline

It is constituted by (1) a hollow paddle blade, (2) a rotary shaft equipped by the blade, (3) a casing, (4) an upper cover and (5) a jacket. Four rotary shafts (2) (two for a small device) are arranged along the casing (3) and supported by the bearing units (6) and rotated respectively to reversed direction by driving motors (7).
Steam is supplied to the rotary shaft (2), the hollow paddle blade (1) and the jacket (5). The sludge is fed from the inlet (8) and filled between the hollow paddle blade (1) and the casing (8) and mixed and stirred and the moisture in the sludge is evaporated by repeated contact of sludge with the heaters (1), (2) and (5). Thus, the dried sludge is successively discharged from the outlet (10) through the gap of the notch (9).
The gas containing evaporated moisture is discharged from the exhaust gas outlet (11) and the moisture is dried in the scrubber and the gas is partly discarded out of the system (boiler and furnace, etc.) and recycled for use.

4. Practical Application

Drying --- Incinerator 30 equipments
Drying --- Pyrolysis equipment 8
Drying --- Melting equipment 4
Drying --- Compost equipment 1
Drying --- Mixed incineration of sludge and municipal solid waste 5