Atritor Ltd is a world leader in the simultaneous drying & de-agglomeration of slurries & liquors (up to 95% water), sludges & filter cakes to fine powders with the added option of integral dispersant coating and classification. Systems are for continuous operation and vary in energy intensity from the Air Swept Turbo AST dryer, through the Atritor Dryer-Pulveriser to the high energy superfine Cell Mill-Dryer used by the world's leading mineral fillers producers. Waste sludges and slurries from most industrial sources can be handled. Atritor has a fully comprehensive Test Facility at their Coventry base in middle England with a wealth of reference installations for customer confidence.

For futher information please contact

Atritor Limited

PO Box 101

Edwick Park Estate

Coventry

CV6 5RD

UK

tel: +44 2476 662266

fax: +44 2476 665751

e-mail: sales@atritor.com

web: www.atritor.com ■

The introduce to new sludge drying system

There are several companies, such as Andritz Group, Baker/Rullman, Swiss Combi, Berlie Technologies Inc, etc. adopting rotary dryer to dry sludge in the world. For the conventional rotary dryer, it can only be used to dry granular materials. The wet sludge is sticky lumpy, so it is impossible to dry wet sludge directly with conventional rotary dryer. The wet sludge has to be mixed with a quantity of (fine) dry sludge so as to yield a certain concentration of solid before drying with conventional rotary dryer. It then goes to a rotary dryer. Therefore, this system needs vibrating screener, crusher and mixer.

The new type sludge drying system

According to the sludge drying process and its drying characteristic, we put forward a new type of sludge drying system. Its drying process is as following:

Stage one

The wet materials directly being fed into rotary dryer with disintegrator are carried forward and broken into small pieces by the smash device during falling process. Heat and mass transfer is taken place between hot gas and wet material surface. Large blocks of wet material are broken into small pieces during repeating processes of carrying and falling in order to increase the surface area of wet material. The small particles are dried by hot air, and discharged until desired water content is achieved. The fine powder carried by air is collected by dust catcher.

Because of the disintegrator inside the rotary dryer, the length of rotary dryer is between 5 meters to 7.5 meter. So the outlet temperature of rotary dryer is about 200C/400F for the inlet temperature for rotary dryer is about 850C/1560F. The outlet water content of dried material is about 15% --40%, it can varies according to the process requirement.

Stage two

The dried material discharged from rotary dryer is fed into vibrating fluid bed dryer, fluid bed dryer or single pass rotary dryer and continued to dry to the required water content. Vibrating fluid bed dryer or fluid bed dryer also has cooling area to cool down the dried material if necessary. The temperature of dried material in this stage is about 90C/195F. The heat resource for this stage dryer utilizes the exhaust from rotary dryer. The inlet temperature is about 180 --190C/360 ¨C380F and outlet temperature is about 80 -- 100C/175 ¨C210F.

The advantages of this new drying system:

1, Rotary dryer works as the first stage dryer and smashing device at the same time. It completely replaces the mixer in the other system, for most of sludge are sticky and need to mix with dried material before drying in the other drying system;

2, Vibrating fluid bed dryer, fluid bed dryer or single pass rotary dryer works as the second stage dryer, heat recovery device and cooler at the same time. It also prolong drying time, for the drying time in rotary dryer is not long enough for high water content material because of the length of rotary dryer with unique structure;

3, This system does not need vibrating screener, crusher, mixer and cooler. The dried sludge can be cooled down in vibrating fluid bed dryer/fluid bed dryer. About 80 -- 90% of dried sludge is about 1 to 4 mm in diameter, and the fine powder of dried sludge can be recycled to the wet sludge.

4, 70% of exhaust from second dryer can be recycled to the first stage dryer. It reduces the load for off gas treatment equipment;

5, only need fluid bed incinerator, rotary dryer with disintegrator and off gas treatment equipment are needed for sludge incinerating system. For the size of dried sludge from rotary dryer is about 1 to 4 mm in diameter, it is the suitable size for fluid bed combustor.

6, The lowest investment. The reasons are as follows:

1), simple structure and short length for rotary dryer;

2), no vibrating screener, crusher, mixer and cooler;

7, High efficiency in energy utilization. Its efficiency is higher than Andritz¡¯s rotary dryer. Besides, we do not need a lot of ancillary equipment in this system; ■