Rotary Dryer for Sludge Dewatering

In the process of urban sewage and industrial wastewater treatment of sediment substances, including sewage contained in solid matter, suspended matter, colloidal substances and the sediment separated from the water, collectively referred to as sludge.
The amount of water contained in the sludge is called the water content, usually expressed as the percentage of the ratio of the mass of the water contained in the sludge to the total mass of the sludge. Sewage treatment process of sludge moisture content is generally high, the initial settling tank of sludge water 96% ~ 98%, the chemical precipitation of sludge water content of 98%, secondary sedimentation tank sludge is often more than 99%.
Sludge water content is high, bulky, difficult to direct treatment and disposal, generally have to concentrate, digestion, dehydration treatment, dehydration sludge moisture content is usually 65% to 80%, and the volume can be greatly reduced. And then further drying to 15% to 20% moisture.
In different water content of sludge show different state, in general, the water content of 70% to 75%, the sludge was soft state, not easy to flow; usually dehydration can only be reduced to 70% to 65%, almost become solid; water content as low as 35% to 40%, into a dispersed state (the above is semi-dry state); further as low as 10% to 15% into a powder.
The sludge drying method can be divided into direct drying and indirect drying. Direct drying is the introduction of high temperature flue gas directly into the dryer, through the gas and wet material contact, convection heat exchange. Direct drying will increase the amount of contaminating gases.
Indirect drying is the heat of high temperature flue gas through the heat exchanger, to the steam, steam in a closed loop in circulation, and no contact with the sludge. Indirect drying there is a certain heat loss, but need to deal with the amount of flue gas is small, does not produce secondary pollution.