What is a Regenerative Thermal Oxidiser?

What are the benefits of an RTO?

Because of its high level of heat recovery, an RTO needs only a tiny fraction of the fuel needed by a traditional or recuperative oxidiser. In fact, in many cases, the heat generated by the oxidation of the pollutants can equal the heat needed to run the oxidiser. At this point the oxidiser is said to be 'autothermal'. Where the heat available from the pollutants exceeds the heat input added by the RTO, not only is no fuel required, surplus heat can be available for recovery from the pollutants themselves.

RTO’s are well suited for continuous operation generally at average concentrations in the range of 2 to 4 g/Nm³. The CTP Autotherm RTO operates within a wider concentration range, both on the lower and higher end of the scale. While conventional RTO systems reach their autothermal point between 2.5 to 3.5 g/Nm³, the Autotherm will operate without additional heating from approximately 1 g/Nm³.

How does a Regenerative Thermal Oxidiser work?

After an initial heat up period, the contaminated gas enters the bottom of bed A and passes up through the bed being heated and is oxidised as it goes. It then passes through the combustion chamber and into bed B.

As it passes down through bed B, the hot gas transfers its heat to this colder bed. The now oxidised waste gas stream exits the RTO at the bottom of bed B.

Over time, bed A cools down as it transfers heat to the incoming waste gas stream, and bed B heats up. At this point, the flow in the RTO is reversed. The waste gas now enters through the bottom of bed B and passes out of bed A. Once again the waste gas is heated by the hot bed and cooled down by the cooler bed.

Heat in the beds is obtained from the oxidation of the incoming VOC’s, with additional heat being provided by a burner in the combustion chamber (when needed).

The heat exchanger beds keep the heat within the oxidiser limiting the amount of additional heat input required, resulting in a lower fuel usage than a traditional thermal oxidiser.

Why have more than two beds?

There are a few reasons for having more than two beds. The first is that in the case of sticky and/or dust-laden waste gases, an additional bed allows one bed to be cleaned, through 'burnout', while the other two beds continue handling the waste stream.

The second reason is to provide improved cleanup with no momentary spikes. In a two bed system, when the flow is reversed, a small quantity of waste gas that has only just entered the RTO, but has not passed through it, is reversed and sent to stack having missed the RTO. For many industries this is not a problem as the waste release is so small that it is well within the local environmental emission requirements. In some cases however, particularly for highly odorous or potentially harmful streams, it is essential that these spikes do not occur. For this reason, CTP has developed the three bed system.

How does the three bed system work

The images below show how a three bed system operates. It can be seen that only two beds are actually used for the oxidation process at any one time, and that the third bed is purged with either fresh air or stack gas.

Stage 1

Waste gas is introduced in bed A and passes out of bed B

Stage 2

Waste gas now enters into bed B and passes out of bed C
Stack gas/fresh air is introduced into bed A to purge any remaining waste gases out through bed C

Stage 3

Waste gas now enters into bed C and passes out of bed A
Stack gas/fresh air is introduced into bed B.

Back to stage 1

With stack gas/fresh air introduced into bed C.

Benefits over other RTO’s on the market