Thermal desorption is an environmental remediation technology that utilizes heat to increase the volatility of contaminants such that they can be removed (separated) from the solid matrix (typically soil, sludge or filter cake).
In spite of incineration treatments, functioning conditions (temperature levels, residence time) are able to guarantee the only volatilization of pollutants, without oxidizing nor destroying them. Once volatilized, organic pollutes can be treated in many ways, in a secondary phase. Process operational temperatures go from 90 to 650 °C and for the further removal of polluted elements combustion air itself or inert gas is used as a transportation fluid.
Thermal desorption unit is composed of the following components:
• Thermal desorber;
• Solid materials cooling unit;
• Gas thermal oxidator;
• Gas cooling unit;
Treating phases can be summarized as follows:
|Loading belt, storage hopper with extractor belt|
Material to treat is fed, through a conveyors’ system, in the hopper that is the initial storage of the waste. The solid, stored in the bin above the hopper, is extracted in the lower part of the machine through a conveyor with metal blades which feeds the next one installed under the hopper.
|System for solids conditioning in input|
Before being introduced in the thermal desorber, if necessary, a conditioning system provides the treatment of the solid portion with chemical products.
|Loading belt to thermal desorber|
A belt “launches” the material previously conditioned, inside the rotating drum. The waste enters from the opposite side of the burner (in counter-current) in order to create a temperature gradient which climbs along the drum until the highest service temperature near to the flame. The drum is slightly inclined to allow the advancing of the fed waste.
Flue gas is extracted from the higher part near waste entry in the drum and passes through the primary cyclone. This is used for dust separation from the air drawn by the rotating drum. Then, through two screws, dust is transferred again in the drum, specifically in the hotter part to avoid it winds up again inside the cyclone.
|Reheating and oxidator|
Air extracted by the rotating drum, after separation of dust in the cyclone, crosses gas thermal oxidator for the combustion of organic pollutes on a temperature between 850 and 900 °C. Separation of the particulate gathered on the bottom of the reheating system is done through automatic screws and valves.
Air coming from the thermal oxidator is cooled in order to be suitable for further treatments in the filter and in the scrubber.
Heat exchange is realized between air coming from the thermal oxidator and air coming fro the heating muff.
|Bag filter and scrubber|
Flue gas flow, deprived of dampness, passes inside the baghouse. It is equipped with pressure switch for the monitoring of pressure before and after the filter and automatic system for dust shaking with screw for their gathering.
Air drew by the baghouse is gathered in the scrubber. It is essentially composed of Venturi tube, where gas current to be washed and absorber liquid are put in, and of a packed column where gas, climbing back up, lefts the liquid drew.