Regenerative Thermal Oxidizers

 

Regenerative Thermal Oxidizers (RTO) destroy toxic particulates in the air and volatile organic compounds often emitted in industrial process exhausts. They typically do this by capturing heat from an outgoing air stream to preheat incoming air. This often has the effect of reducing operating costs. 

Regenerative Thermal Oxidizers are a highly energy efficient and effective means to reducing and controlling air pollution.

rtoThe two most typical methods of reclaiming heat are: 

  1. Regeneration
  2. Recuperation

When the heat contained within a large thermal mass is regenerated, a thermal oxidizer employing this method is called a Regenerative Thermal Oxidizer.

Recuperation implies more of a direct heat transfer from the outgoing to the incoming air stream. When this method is used, the system is called a Recuperative Thermal Oxidizer.

The regeneration principle operates around multiple energy recovery chambers in use on the system, which are the housings for the ceramic heat recovery media. The ceramic heat recovery media acts as a heat exchanger for the system. The multiple chambers operate under a "swing bed" absorption principle: which is the principle of transfer through multiple beds by the use of flow reversal. In the use of this principle with ceramic stoneware, the process is called regeneration.

RTOAs the dirty exhaust stream travels through the first bed of ceramic media, the exhaust stream adsorbs the heat energy stored in the ceramic media mass, which pre-heats the exhaust stream. The exhaust stream then enters the burner reactor chamber, where heat energy is added from the burner to reach the system operating temperature. After the temperature has been elevated, the clean exhaust stream then passes through the second energy recovery chamber.

As the exhaust stream passes through the chamber, the cold ceramic media mass absorbs the heat energy of the exhaust stream, and stores the heat energy for the reverse flow of the system. Once the heat energy of the first chamber has been depleted through the absorption of the incoming air stream, the flow through the system is rotated, so the incoming dirty air stream is then directed through the previous absorption chamber, with the clean waste gas now going through the previously purged chamber.

By using the reversal of exhaust flow through the ceramic beds, a minimal amount of heat energy needs to be added to the incoming exhaust stream to maintain the systems minimum operating temperature. The sizing of the ceramic media beds is such that a 95%+ heat recovery efficiency is possible through the regenerating, reversal flow process.  

What happens with a Regenerative Thermal Oxidizer is intriguing. Gas laden with volatile organic contaminants enters a Twin Bed RTO via an inlet manifold. The gas is directed by a flow control valve as it spews into an energy recovery chamber; work that takes place within this chamber is primarily preheating. Heating of the process gas and contaminants continues in a place called the stoneware bed as the gas stream moves toward a combustion chamber.

It's in the combustion chamber where the most exciting part of the entire process occurs:

The volatile organic compounds, or VOCs, are oxidized.

RTO oxidizerThis oxidation releases a surprising amount of energy into a second stoneware bed. This stoneware bed is in turn heated while the gas, a bit less volatile, is cooled until the outlet gas temperature is only slightly higher than the inlet temperature. The flow control valve switches and alternates stoneware beds so that each is in inlet and outlet mode. Depending upon the amount of VOCs contained in the process gas, the energy released from the combustion can be self-sustaining. At 96% thermal energy recovery, the outlet temperature may be only 74 degrees F. (23 degrees C.) higher than the inlet gas temperature.  

Components of a traditional RTO (Regenerative Thermal Oxidizer) include a system fan, motor, burner, heat exchange media, flow control valves, electronic & automatic system controls, temperature recorder, and exhaust stack. The system's outer skin is typically ceramic and fiver-lined, but comprised primarily of steel.

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