Direct Fired Thermal Desorption System Configurations

There are two categories of direct fired thermal desorption systems: Counter flow and parallel flow. Both varieties consist of an inclined rotary desorber with a burner mounted at one end injecting an open flame. The difference between configurations is the direction of material flow in relation to the burner.

Counter Flow Thermal Desorbers

In a counter flow system, contaminated materials are introduced into the desorber and travel toward the burner mounted at the opposite end. Volatilized organics, entrained particulate and combustion gasses travel against the flow of material, exiting the desorber where the cold material enters. Mixing with the contaminated cold fed material reduces the temperature of the exiting gas to less than 500°F. This relatively low temperature allows the particulate laden gas stream to be routed directly to a fabric filter baghouse where greater than 99% of the entrained solids are separated from the gas. The particulate free gas is then typically routed to a thermal oxidizer where the organics are converted to carbon dioxide and water vapor. When treating chlorinated compounds, the oxidizer exhaust gases may be routed to a quench duct to reduce the gas temperature followed by a packed-bed scrubber where HCL formed in the oxidizer is neutralized with a caustic sodium hydroxide (NaOH) solution.

Counter flow thermal desorber diagram sm

 

 

Parallel Flow Thermal Desorbers

 In a parallel flow system, materials are introduced into the desorber at the same end the burner is mounted. Volatilized organics, entrained particulate, combustion gasses and the material being treated all flow in the same direction. All streams exit the desorber opposite the burner end.  Mixing with the heated solids reduces the temperature of the contaminated gasses exiting the desorber to a temperature slightly higher than the solids. This relatively hot gas stream which exceeds the temperature limitation of a baghouse is typically routed to a cyclone to remove the bulk of the solids. Following a cyclone, these configurations usually then route the gas to a thermal oxidizer followed by a heat exchanger. The heat exchanger reduces the temperature of the gas suitable for a baghouse where the remaining particulates are removed prior to the gases being discharged to atmosphere. As with counter flow systems, a parallel flow unit may also incorporate a scrubber that manages HCL formed while treating chlorinated compounds.

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