Spray, Rotary & Flash Sludge Dryers

In industrial wastewater treatment plant, there are 3 common processes applicable which involve use of heat for the purpose of sludge drying. Sludge Dryers are needed to ensure that the sludge are subjected to moisture removal before sent for further processing. Among all available methods, the flash dryers are the most common whereby it employs the most efficient mode of operation for use in wastewater treatment plants.

Flash Dryers
Sludge cakes in flash drying system are usually pounded and grind in a cage mill or by another route using atomized suspension technique surrounded by the presence of hot gases. The equipment design is made in such a way that the particles will always stay in contact with the turbulent hot gases so that maximum heat transfer of moisture from sludge to the gases can be achieved. Flash dryers can assist in the removal of water up to 8 to 10 percent and typical design usually has a cage mill that receives input of wet sludge from feed system. Inside the cage, hot gases together with the sludge are forced through a narrow ducting so that drying can occur and these will then be transferred to a cyclone in order to remove the vapor solids. The dried sludge has commercial application either as soil conditioner or it can also be incinerated in the furnace to retrieve heat or steam.

Rotary Dryers
Rotary dryers are normally used for drying sludge and other municipal industrial waste solid. Basically there are two different systems for the rotary dryers whereby in the direct-heating method, the material will always be in contact with hot gases while in indirect-heating dryers, steam is used instead. The processed municipal solid wastes or the dried sludge can be later sold or turned into burning fuel. Mechanically, plows can be installed to facilitate lifting and then assist to agitate the material to achieve better drying operation.

Spray Dryers
A spray dryer employs the use of a high-speed centrifugal bowl to get a good separation between the moisture and the sludge. Centrifugal force serves to atomize the sludge into small tiny particles with wide surface area and then spray on top a drying chamber. Inside this compartment, hot gases will be introduced so that moisture can be removed efficiently.

Other options which can be employed for dewatering purpose: sand drying beds and sludge filter press.

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