Introduction

Eliminating pollutants by heat means to raise their temperature until the following reaction of organics decomposition is possible:

VOC + O₂ => CO₂ + H₂O + heat

The reaction occurs naturally starting with 500-600°C and it is completed only over 720-800°C. We can also depurate flows containing halogen, silicon or sulphur compounds. It also exists a regenerative version of the plant, in which the pre-heating occurs through two or more thermal masses accumulating and giving in heat.

Regenerative thermal oxidizers (RTO)

For the efficient and cost-effective VOC removal we offer regenerative thermal oxidizers (RTO) equipped with high-efficiency heat recovery systems, projected thanks to our Italian partners' Brofind S.p.A experience in this field.

Through a specific fan, a part of the dilution air will be sucked together with the process air (which can be close to the LEL). The installation of the third tower is the safest technical solution to ensure the removal of VOCs which cannot be treated when the waste air stream changes direction, thus obtaining the highest removal efficiency in order to respect the lowest concentration limit. The three tower unit is also the technology that can reach the maximum removal efficiency and admit the maximum inlet VOC concentration.

This solution eliminates the presence of peaks of pollutants in the emission and is preferable when more restrictive limits at the emission are required. Each regenerative tower contains a ceramic matrix layer serving as heat accumulator, which is either heated or cooled down - depending on the direction of the gas flow passing through it. The ceramic matrix considered can allow low pressure drops and high heat recovery efficiency.

Process description

Initially, the incoming process gas passes through a ceramic heat-recovery bed before entering the combustion chamber. It is during this step that the gas is preheated to within 5% of the combustion chamber temperature. After the process stream exits the ceramic bed, the already hot gases are further heated to the desired combustion chamber temperature. These gases are then sent through another heat-exchange bed where energy is absorbed and stored to heat the next cycle of contaminated air. Up to 95% of heat energy can be recovered with this multiple-bed approach. Low-VOC concentrations can be processed in a self-sustaining mode without burning extra fuel.

The oxidation temperature is achieved either by using addition fuel or by auto-ignition of the contaminants in the waste air when these contain a sufficient concentration of volatile organic compounds. The average duration of these process intervals is automatically regulated by fitted software and is typically between 90 and 120 seconds, depending on some process parameters such as concentration and nature of pollutants. As already mentioned, the third tower allows a further treatment of the waste air volume not completely treated, which during flow inversion could be envoyed directly to the stack.

A tele-remote control system fitted with PC software and graphic pages for a simple and easier running and diagnosis of the state of the plant can also be added.
An optional burn out system that consists in a pyrolysis of the organic compounds, in case of their deposit on the ceramic mass, should be added in case of presence of polymerizing compounds, such as styrene.