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What is a Thermal Oxidizer?

Catalytic oxidizers can use rhodium as a catalyst.
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  • Written By: Michael Anissimov
  • Edited By: Niki Foster
  • Last Modified Date: 22 November 2014
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Thermal oxidizers are used as a method of pollution control for process air containing small particles of combustible solids or liquids. Exhaust air in industrial settings may be highly polluted, and it makes sense to oxidize (burn) as much of it as possible, so that the exhaust consists of little but non-toxic carbon (soot). Thermal oxidizers are sometimes divided into non-flame oxidizers, which use slow heating to incinerate pollutants, and direct flame thermal oxidizers, which use plumes of flame. Thermal oxidizers may also include a process called catalytic oxidization. In catalytic oxidization, organic compounds pass over a support material coated with a catalyst, commonly a noble metal such as platinum or rhodium, that encourages the pollutants in the air to burn. Catalytic oxidizers can break down pollutants at much lower temperatures than thermal oxidizers lacking catalytic action.

The most significant distinction between types of thermal oxidizers is whether they are regenerative or recuperative. Regenerative thermal oxidizers use ceramic heat transfer beds to recover as much energy as possible from the oxidization process -- often as much as 90% to 95%. These heat transfer beds act as heat exchangers, coupled to a retention chamber where the organics are oxidized. A recuperative thermal oxidizer uses a heat exchanger in the form of a plate, shell, or tube to heat intake air with the thermal energy from the oxidization process. These systems are less efficient than regenerative thermal oxidizers, only recovering about 50% to 75% of the generated heat.

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One technology used to increase the efficiency of thermal oxidizers is that of rotor concentrators. Rotor concentrators reduce the overall amount of air flowing through the system and increase the concentration of organics in the oxidization stream. The incoming polluted air flows through a continuously rotating wheel covered with an adsorbent agent. Clean air flows into the atmosphere. The wheel is cleaned by exposing it to a desorption gas, producing a small, highly concentrated stream of organics which can then be efficiently oxidized.

The most important parameter for thermal oxidizers and catalytic oxidizers is their destruction efficiency, which commonly ranges between 90% and 99%. The higher the destruction efficiency, the less pollutants are released into the atmosphere. The common unit for specifying destruction efficiency is in terms of milligrams per cubic meter of volatile organic compounds. To achieve these destruction efficiencies, catalytic oxidizers operate at 400 to 600°F (about 204-316°C), thermal oxidizers at 1000 to 1800°F (about 538-982°C).

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anon354575
Post 9

Speaking of platinum, there is a company in N.J. that buys used/spent catalysts and fuel cells. I have done business with them in the past and I remember how hard it was to find a company that was willing to pick up from my location. Hope this helps. --Trevor- Retired and loving it

anon264176
Post 8

By-products of combustion from thermal oxidizers in industrial applications are "washed out" in devices like wet fume scrubbers. Emissions are recorded and monitored by federal and state regulatory agencies.

The advancement of semi-conductor manufacturing processes and bio-technology are continuously refining the technology behind the process and organizations are sensitive to protecting and preserving the environment.

anon250106
Post 7

CO2 is plant food. The globe has warmed and cooled over time well before any humans stepped foot on the planet. How could we be so arrogant to think we have that much influence over something we cannot control? If the world is warming, it has nothing to do with man.

everetra
Post 6

@SkyWhisperer - My only wish is that more of the general public understood what chemical and oil plants actually did to clean up their exhausts rather than have this knee-jerk reaction to “pollution” exhausts from industrial facilities.

It would help to elevate any debates we do have about global warming or air pollution in general.

MrMoody
Post 5

I’m surprised to learn that thermal oxidation is a similar process as the one that takes place in my car’s catalytic converter.

In my converter the bad exhaust fumes flow over the oxidized metals to emit clean exhausts. Every now and then my check engine light will come on if the converter or CO2 sensor goes bad; in that case I need to have repairs done.

Actually in my state, we don’t have emissions testing, so it’s not something that I’m terribly concerned about, but I know how the technology works. I didn’t realize that they used it on a mass scale in the industrial plants.

SkyWhisperer
Post 4

@allenJo - I don’t think it changes the dynamics of the debate at all. My understanding is that regenerative thermal oxidation converts the bad stuff into CO2. It’s CO2 that everyone’s complaining about.

Sure, the exhausts that make it into the atmosphere are cleaner, but as long as they are in the form of CO2, they could potentially contribute to global warming, if you accept the global warming hypothesis as it relates to man-made CO2 emissions.

I’m personally on the fence about the whole issue, but as a matter of principle, I think the less junk we send up into the atmosphere the better. Whether it contributes to global warming or not is not the point for me. The point is that we need to reduce air pollution. That’s why I prefer alternative energy sources.

allenJo
Post 3

We used to live in Kentucky near an oil refinery. I remember watching the plumes of white soot ascend from the refineries.

I was concerned about my health but my dad, who worked in the refinery, explained to me that they were basically cleaning up the exhaust. The white plumes were nowhere near as harmful as the original exhaust fumes and he explained that in fact the exhausts were not toxic, causing almost no air pollution.

In my young, pliable mind I didn’t know the technicalities of the process; I only believed that the white plumes looked cleaner than the dark ones, and so bought into the explanation.

I guess it does work, I just wonder how this ultimately affects the ongoing debate over carbon emissions. Are these oxidized plumes less harmful to the environment than those that have not been “cleaned” in this manner?

cdeclerk
Post 1

Can naturally occurring trivalent chromium be converted to hexavalent chromium in a thermal oxidizer?

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