Updated: July 2002

1. Outline of device

This device consists of vertical pelletizing drier and inner combustion type rotary kiln which has function of pelletization, drying and carbonization of dehydrated cake.

2. Feature

1. Pelletizing Drier
Pelletizing drier forms sludge pellets taking advantage of the adhesive characteristics of sludge itself, while drying.
Dehydrated sludge is injected from the bottom of the device by cake pump and dried with the hot air blown into the drier.
Supplied sludge will be coated on the surface of dried pellets with the effect of mixing blades to make the pellets larger and larger.
Dried sludge overflows from the top of the casing and is discharged.
The amount of cake to be supplied into the device is controlled by the torque of mixing blade, thus water content of pellet is kept within designed range.
2. Carbonization Kiln
Inner combustion type rotary kiln is used as carbonization device.
Dried sludge supplied into the rotary kiln continuously, is carbonized with low oxygen condition, while travelling inside the kiln axial direction by rotating movement and slight inclination.
Carbonized sludge is led to outer shell to be put out, cooled and discharged.
Exhaust gas from the device is combustion deodorized by deodorizing furnace and the excess heat is transferred to the drying exhaust gas with heat exchanger. This reheated gas is used as hot air for dryer again.

3. Performance

Example of test plant
1. Test sample: sewage sludge
2. Material balance
Dehydrated sludge: 130 kg/h (water content 80%)
Dried sludge: 40 kg/h (water content 30%)
Carbonized sludge: 15 kg/h
3. Carbonization temperature: 400ºC

4. Adjustment field and processing object

This device can be applied to those listed below. Sewage sludge, Nightsoil treatment sludge, Septic tank sludge, Rural sewage sludge, Domestic animal excreta, Sludge from food industries, etc.
Carbonized sludge has those features.
(1) Its weight and volume is reduced largely by 1/10 and 1/8 respectively compared to dehydrated sludge.
(2) Compared to sludge compost, it has lower nitrogen content, higher phosphorus and potassium content which enables to use as fertilizer or soil developing agent.
(3) Since organic substances included in sludge are decomposed by heat treatment, it has no foul odor, no possibility of rotting, so that it can be stored long period.