De Novo VOC From Regenerative Thermal Oxidizers

Regenerative thermal oxidizers are used extensively for the abatement of volatile organic compound (VOC) emissions from process vent streams. Due to the unique heat storage and convection properties of the ceramic packing utilized, they are especially well suited for applications with high flows and dilute concentrations of organic vapors. However, packed-bed devices such as these are known to be vulnerable to interstitial plugging when processing vent streams that contain particulate matter in addition to the VOC. In this paper, the authors postulate a new failure mode that involves relatively small concentrations of organic solids in the vent stream, and that may lead to serious performance deficiencies long before interstitial plugging becomes problematic. Specifically, we assert that “De Novo VOC” can be generated from organic particulate matter that adheres temporarily to the bed and is revaporized when the flow is reversed, causing a significant decrease in the apparent destruction efficiency of the abatement device. In this theoretical treatment, the spatial and temporal response of a hypothetical thermal bed is compared against the phase-change and combustion characteristics of a common organic solid, in order to estimate particle loading levels that may pose immediate compliance problems for users of these systems. Although experimental data are not available to corroborate the conclusions reached herein, the authors contend that routine carryover of small amounts of organic particles from a collection device (e.g., baghouse) to the thermal destruction system can create high exhaust VOC levels, and may eventually lead to hostile fires in the beds. As a means of mitigating against such failures, the authors recommend that an inlet particulate loading limit be implemented for all regenerative thermal oxidizer installations.