Destroying solvents by oxidation is a process that uses heat and oxygen to convert organic, hydrocarbon solvents to carbon dioxide and water vapor.
There are two oxidation techniques appropriate for compliance: thermal and catalytic oxidation.
Thermal oxidation relies on the combination of high temperature (typically 1350 to 1600 °F), sufficient residence time (0.6 to 1.0 second) and effective gas phase mixing to achieve VOC destruction in the target range of 98-99%.
Because fuel is so expensive, virtually all thermal oxidizers come equipped with some capacity for heat recovery to minimize fuel consumption. When the heat exchanger is an integral part of the oxidizer, the hot, clean exhaust preheats the incoming, solvent laden air. This is known as primary heat recovery. The closer the preheated air temperature from the exchanger is to the final oxidation temperature, the less fuel is used.
Best Management Practices & Pollution Prevention
Because each source and facility is unique, choosing the right oxidation technology for any given application will require a thorough analysis of applicable regulations, the types and concentrations of VOCs, the air volume being treated, energy costs, as well as the typical plant operating parameters. Some generalizations can be made. For instance, capital cost and operating cost are closely tied to the air volume processed and the solvent concentration within the air stream. Therefore, airflow reductions through dryer recirculation loops should be considered, since this will reduce the total volume of air processed while proportionately increasing the solvent concentration.
Oxidizers can be sized to treat the emissions from one or more presses with the latter configuration providing multiple benefits to the flexographic printer. When multiple presses are connected to a single oxidizer, the overall operating cost is reduced as the unit spends much less time idling at zero solvent load. In addition, heat exchanger efficiency is improved when operating at any flow condition less than maximum due to the higher heat transfer within the exchanger. The majority of oxidizers being sold at this time are for multiple press applications. Any vendor of oxidizer equipment should provide an evaluation of the various options addressing the variables listed above.
Finally, the oxidation process results in the discharge of warm clean air into the atmosphere. Flexographic printers should consider directing this energy back to their process, either through a secondary heat exchanger or thermostatically controlled mixing boxes. Properly designed, a secondary heat recovery system may reduce operating costs enough to provide an economic payback on the initial investment.
For access to vendors who may supply alternative materials and equipment, see the PNEAC Vendor Directory.