|Different Types of Thermal Oxidizers
Recuperative Thermal Oxidizers
A Recuperative Oxidizer utilizes two heat transfer systems; a primary and / or secondary heat air by
recovering heat from the exhausting clean process air. Typically this is accomplished by a shell and tube
heat exchanger and sometimes by a plate-type exchanger. As the process waste-gas passes on one side of
the metal tube or plate the preheated recuperative exhaust from the combustion area exits on the opposite
side of the shell tube or plate exchanger at that material as the conducting heat transfer medium. The
second heat exchanger is essentially the same as the first, but utilizes the recuperative super heated exhaust
stream to pre-heat clean plant air to be used somewhere in the plant process.
Regenerative Thermal Oxidizers
A Regenerative Thermal Oxidizer operates on the principal of thermal oxidation and the use of two or three
heat recovery beds or chambers. These heat recovery chambers use a heat sink material within the bed
area. The heat sink media is usually made of ceramic material, the best technology today is the use of
structured ceramic blocks with a certain number of perforations according to the heat retention and pressure
drop requirements. The ceramic heat recovery media acts as a heat exchanger for the system. The heat
recovery beds or chambers function under a "swing bed" heat recovery or absorptive principle in which the
transfer of heat takes place by means of process flow through two beds by reversal.
When the waste-gas process stream travels through the first heat recovery ceramic media bed, the
waste-gas process stream adsorbs the radiant energy stored in the structured ceramic media bed; this
process assists in preheating the waste-gas process stream. The pre heated waste-gas process stream then
enters the reaction chamber where the burner or temperature is held at the required system operating
temperature. After the temperature has been elevated and retained for the appropriate retention time, the
waste-gas is cleaned and the cleaned process stream passes through the second heat recovery bed or
The cleaned process stream passes through the heat recovery chamber; the cold structured ceramic media
absorbs the BTU energy of the super heated process exhaust stream, and retains the heat energy for the
reversal of the thermal system. Once the radiant heat energy of the first heat recovery bed has been
depleted through the absorption of the incoming air stream, the process flow system is then rotated, so the
incoming waste-gas process stream is then directed through the previous heat recovery chamber, with the
clean waste gas stream going through the previous directed chamber.
The exhaust flow reversal minimizes the amount of supplemental fuel needed by using the radiant heat
energy from the structured ceramic media beds or chambers. A well designed heat recovery bed will be able
to operate on as much as 90% thermal efficiency saving thousands of dollars annually.
A catalytic thermal oxidizer system usually operates in the temperature range of 550°F - 650°F (275ºC to
350ºC). The operating temperature is substantially lower than most the forms of thermal oxidation, many
manufactures now have designed catalyst that is more durable and can operate at higher temperatures
without damage. Some catalyst temperatures may reach up to 900°F - 1100°F (482 ºC - 593 ºC) without
There is a chemical reaction which takes place between the use of the metals and the volatile organic
hydrocarbon, this chemical substrate accelerates the destruction process at a much lower temperature
ranges. Catalytic thermal oxidizer systems are used with low level VOC waste gas process streams. Catalytic
monolith structured cells types may be used in the other types of thermal oxidizers such as regenerative
thermal oxidizers and recuperative systems.
Direct Fired Thermal Oxidizer (Afterburner)
The DFTO is an well utilized technology for process streams heavily laden with VOC pollutants and
intermittent batch processes where the oxidizer can come be prepared to process streams relatively quickly.
Direct fired thermal oxidizer uses a specially designed burner to raise the temperature of a pollutant laden air
stream to a predetermined combustion temperature. In the equipment operation, the contaminated process
exhaust is ducted into a burner chamber. Heat applied by the burner oxidizes the VOC's and HAP's creating
harmless products of combustion (water and carbon dioxide). The clean, heated exhaust gas can then be
discharged to the atmosphere or processed by a optional heat recovery system.
Direct Fired Thermal Oxidizers achieve over 99% hydrocarbon destruction rate efficiency. To achieve this the
heated air is kept in the combustion chamber for a specified amount of time, called the residence time. At the
inlet to the combustion chamber turbulence is generated to mix the pollutants and oxygen molecules. Proper
mixing of the combustion air and process streams provides higher destruction efficiencies in a safe manner.
Systems should be designed to minimize the risk of explosion and takes complete advantage of the VOC
laden exhaust stream to minimize auxiliary fuel needs. On process that are rich in BTU values a burner
system should be designed to use process streams directly into the burner as fuel. After burners can be
designed to operate on small tank vents to the largest of industrial plant applications. Special designed
systems can be designed to process streams that contain acids such as carbonic, hydrochloric or sulfuric
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