Belt Type Sludge Dryer

Belt drying units are high efficiency sludge drying systems. The most obvious advantage of belt drying plant is that it produces a dust-free granular final product with low emissions and high dryness, and this process is carried out at low costs.

Process Description

Highly dewatered sludge is pumped to the granulation unit by spreading it to form a 7-9 mm diameter stick pasta by means of an eccentric monopump and spreading it homogeneously on the belt. The sludge sticks formed here are cut to certain lengths and laid on the belt. In this way, the sludge laid on the belt evenly ensures efficient air circulation and drying.

There is a set of nozzles in the granulation unit. The granulation unit can be washed with pressurized water when desired. Washing is required at certain intervals. In case the unit is completely clogged due to foreign substances in the sludge, it may be necessary to disassemble the unit and clean it mechanically. This process is a simple maintenance process of approximately 1.5 hours.

The sludge laid on the belt is carried forward in the tunnel by means of a conveyor belt. The conveyor belt is designed as perforated and hot air comes into contact with the sludge through these holes and dries the wet sludge. In this type of convective drying facilities, since the sludge heats up and dries very slowly in the first drying step, the structure of the product is dried without deterioration. The heat required for evaporation is taken from the hot air given into the system. For this reason, the hot air starts to cool.

The product falls onto the 2nd belt below after the first belt. With this belt, it travels the same distance to reach approximately 90% dryness towards the opposite side, i.e. the direction where the product is poured. During this period, the product maintains its homogeneous structure.

The belt width is 2500 or 4000 mm net. Belt speed can be adjusted between 0.2-0.7 m/min. Belt material is perforated stainless steel. The part of the upper belt that contacts the sludge is coated with PFA or PTFE. The perforation pattern is given below.

In addition, there are 1 or 2 product turning systems in the system to ensure more homogeneous drying of the product at points close to the middle of the belt. In this way, the product is both mixed and its adhesion and agglomeration are prevented.

When necessary, a water-cooled screw conveyor can be added to the drying plant outlet to reduce the output product below the desired temperature. The product coming out of the dryer has a structure and temperature suitable for pelletizing and has a structure that does not produce dust. The transportation of the final product can also be carried out without pelletizing.

PROCESS DESCRIPTION IN PARALLEL WITH THE FACILITY FLOW DIAGRAM

Mud Line

The sludge dewatered by belt filter presses in the treatment plant will be transferred to the sludge silo by monopump. The sludge cake taken from the bottom of the sludge silo by monopump will be pressurized and pressed to the granulation unit at the beginning of the belt drying plant.
The sludge cake, which is turned into thin and long pasta strips in the granulation unit, is laid on the 1st belt conveyor. The sludge that starts to dry on the 1st belt then falls on the 2nd belt.
At the end of the 2nd belt, the sludge that has reached the desired dryness is transferred to the dry sludge conveyor. The dry product is transferred to the dry product silo by this conveyor.
The product kept in the dry product silo will be transported to the final disposal point by trucks when the silo is full.

Hot Air Line

Some of the hot air used in the system is continuously circulated. Therefore, while some air is absorbed from the atmosphere as fresh air, the same amount of air is discharged from the system as flue gas.
Hot air will be produced by a directly heated air boiler. The main hot air flow, which reaches 280 oC at the air boiler outlet, is directly given to the bottom of the drying tunnel and from there it is distributed uniformly along the length and width of the entire drying tunnel with an internal duct system.
The hot air given to the drying tunnel is circulated approximately 4 times per hour in the drying tunnel, ensuring that the air is saturated with moisture and the water in the sludge evaporates and passes into the air phase.
The air saturated with moisture is drawn from the drying tunnel by the flue gas fan. This air flow, which contains moisture, will enter a condensation unit operating on the wet washing principle in order to both remove moisture and wash possible dust contaminants in it. In this unit, the air washed with clean water is then transmitted to the hot air boiler to be heated again.

SYSTEM MAIN UNITS

1 – Granulation Unit
2 – Drying Tunnel
3 – Belt Drive Group
4 – Recovery Fan
5 – Hot Air Fan
6 – Hot Air Boiler
7 – Heat Exchanger
8 – Wet Washing Unit
9 – Outlet Conveyors