Sludge is the solid waste generated in the process of sewage disposal. with the development of domestic sewage treatment, sewage treatment and water treatment plant will continue to expand and improve, sludge quantity is increasing, at present in the domestic sewage treatment plant in the general infrastructure and operating costs accounted for about 20% of the infrastructure and operating costs to 50%. in addition to sewage sludge contains a lot of organic matter and rich in nitrogen, phosphorus and other nutrients, there are heavy metals, pathogens and parasites and other toxic and harmful ingredients. For the normal operation and the treatment effect of the two pollution and ensure that the sewage treatment plant to prevent caused by the sludge treatment and disposal of sewage sludge, sewage treatment in China occupy the position has been increasingly prominent.
1. Principle

Sludge fluid dryer is composed of three parts from the bottom to top:

A. Air chest: located at the bottom of dryer; for the recycle gas distributed to different areas of the fluidized bed device, the bottom is equipped with a special gas distribution plate, used to distribute inert fluidizing gas. The board has strong advantages, the pressure drop can be adjusted, to ensure the gas circulation can evenly to guide the dryer.
B. Middle part: The segment, heat exchanger built here. The sludge dehydration water evaporation of all energy through the heat exchanger into. Usually steam or hot oil can as a heat exchange heat medium.
C. Suction hood: As the first step, used to make the flow of dry particles from gas circulation, while the circular gas with a fine sludge and evaporation of water leaving the dryer through the bellows of the lower part of the fluid bed, circulating gas into a fluid bed. Particles in the bed fluidization and mixing. By cyclic gas continuous flow through the material layer to dry objective.
D. Process flow chart 
   Fluid bed dehydration system——process flow chart 
   Fluid bed dehydration system——process flow chart
2. Comparison between advantages of fluid bed dehydration and characteristics of sludge
  A. Advantages
1.Send sludge directly to fluid bed：no need for circulating of dry particles and mixing of wet and dry materials
2.Final products： without dust; solid content is over 90% of dry solid
3.Low dehydration temperature： 85 degree centigrade
4.Heat exchange installed in fluid bed： no indirect heat supplying
5.Low emission： no pollution to environment
6.Inert gas ： oxygen content lower than 3 VOL; safe
7.High environmental level： manufacture is carried out in a closed environment; less residual gas in dehydration process; less odors;
8.Running time: 24 hours a day
9.It has been proved that it is a reliable system： it can be run for 800 hours a year;
10.Automatic control system： no need to be on duty
11.Good quality of sludge