FIG. 11.14.8 Wet oxidation process.

exceed the critical temperature of water (705°F), because the continuous presence of a liquid water phase is essential (Liptak 1974).

A consequence of high operating temperature is the need to run the process at high pressure (300-3000 psig) to keep water from vaporizing. The static pressure energy of the exhaust gases can drive an air compressor or gen erate electric power, while the thermal energy of the reactor effluent can be used for steam generation.

Detoxified priority pollutants and products stay in the aqueous phase. Materials such as sulfur compounds, chlorinated hydrocarbons, or heavy metals end up in their highest oxidation state, i.e., sulfates, hydrochloric acid, or salt. Air pollutants are controlled because oxidation takes place in water at low temperatures and no fly ash, dust, sulfur dioxide or nitrogen oxide is formed.

Typically, 80% of the organic substances will be completely oxidized. The system can accommodate some partially halogenated compounds, but highly chlorinated species such as PCBs are too stable for complete destruction without adding a catalyst or very high pressure and temperature (Kiang & Metry 1982).

Control of a wet air oxidation system is relatively simple, as the system is self-regulating. Oxidation occurs in a massive amount of water, which provides an effective heat sink and prevents the reaction from running away. Should a surge of organic material enter the reactor, the air would be depleted, or the heat liberated by additional oxidation would form more steam.

Was this article helpful?

0 0

Post a comment