Home 
Air Pollution Control Equipment
Air Pollution Control Equipment
Thermal Oxidation Principles
Oxidation is a process which would naturally occur in the general environment over thousands of years, resulting in the breakdown of hydrocarbons in the presence of air to form carbon dioxide and water vapour. Thermal oxidizers allow for this natural reaction to occur in a matter of seconds within the unit by means of operating at increased temperatures. As this thermal oxidation process occurs, there is an exothermic heat release due to the breakdown of hydrocarbon hydrogen bonds. This heat can be reused in the oxidation process such that at even low inlet fume concentrations, the process is self-sustaining.Various oxidizer types used to control VOC emissions streams include direct thermal systems, recuperative thermal systems, regenerative thermal systems, recuperative catalytic systems and regenerative catalytic systems. The Regenerative Thermal Oxidizer (RTO) is by far the most widely used system (accounting for more than about 85% of installations).
Regenerative thermal oxidizers (RTO) offer superior heat recovery characteristics versus other oxidation systems, as recovered energy is effectively used to preheat incoming process air to oxidation temperatures, which significantly lowers overall operating costs. The typical Regenerative Thermal Oxidizer consists of two to three reinforced, refractory-lined chambers filled with high temperature high heat capacity heat exchange (ceramic) media. The ceramic beds allow for the retention of heat generated by the exothermic oxidation reaction, which can be reused in the fume preheating and oxidation process, allowing for a self-sustainable process requiring little or no additional energy input. The RTO operates at temperatures between 800 and 900oC. At these temperatures, due to its operation below the adiabatic flame temperature, the formation of harmful NOx and CO byproducts is extremely low.
Catalytic Oxidisers are also suitable for specific applications. Catalytic materials enhance the chemical reactions that convert VOCs into carbon dioxide and water. A catalyst does not take part in the reaction, but lowers the temperature required to destroy pollutants, with the result being lower operating costs and reduced equipment stress.
To date, thousands of Thermal Oxidizers have been installed by MEGTEC in a number of industries worldwide:
- Abrasives
- Automotive Painting and Parts Processes
- Baking & Food Processes
- Coating Processes
- Chemical / Petrochemical
- Coal Mine Ventilation Air Methane
- Coffee Roasting
- Commercial Printing
- Composite Wood Products
- Converting Applications
- Electronic Components
- Ethanol
- Fiberglass Processes
- Flexible Packaging
- Flooring
- Insulation Manufacturing
- Landfill, Biogas
- Latex Materials
- Odour Abatement
- Particleboard, Plywood, Veneer
- Painting & Finishing
- Pharmaceuticals
- Spice Manufacturing
- Structural Composites
- Wall Coverings
- Wastewater Treatment
- Wire Coating
- Wood Finishing
Regenerative Thermal Oxidisers
Scion Technologies offers a range of MEGTEC Regenerative Thermal Oxidisers, suitable for meeting Client’s varying application needs. Operating costs and footprint are both minimized while high destruction rates ensure that the most stringent compliance targets are met.Megtec offers a range of Regenerative Thermal Oxidiser models which, among others, include:
-
VOCSIDIZER® – a cost-effective & energy efficient single-bed thermal oxidizer, which achieves destruction efficiencies of between 98% and 99.7% (
-
This technology is an advance on the standard multiple bed RTO design. The RTO has the option of being electrically heated and operated and thus has the advantage of not requiring a burner for either start-up or operation. The unit consists of a single heat transfer bed filled with ceramic media. Plenums (located above and below the bed) can serve either as the inlet or outlet route for process or cleaned air. The direction of air flow from the forced draft fan is controlled by pneumatically operated valves. The dampers will periodically switch position to reverse air flow and allow thermal regeneration of the bed.
Download VOCSIDIZER brochure
The bed is initially heated to 1100oC by a grid of electrical heating coils only during a first start-up. Thereafter, the sufficient energy is generated and sustained within the ceramic bed to ensure that the process is almost completely autothermal. These units are so energy efficient (over 95%) resulting in exhaust temperatures from the RTO being only about 20 to 50°C higher than the incoming fume stream temperature.
On its own, the single bed bi-directional RTO achieves a destruction efficiency of 98%, however with a residual air cleaner, efficiencies of up to 99.7% can be achieved. The residual air cleaner is an accumulator vessel which captures the small quantities of VOCs emitted during a poppet valve changeover (i.e. when the flow direction to the bed is reversed). These captured VOCs are then purged back to the inlet of the RTO to ensure complete oxidation.
One of the main advantages of the single bed RTO is simplicity, compact modular design, high degree of pre-assembly and therefore minimised installation time. The single-bed RTO units are ideal for chemical industries where there is limited or no fuel gas supply. These RTO units are extremely cost effective in terms of both capital and operating costs.
Although this technology does not on its own achieve destruction efficiencies quite as high as the three-chamber Regenerative Thermal Oxidizer, it is an extremely competitive and cost-efficient thermal oxidizer for a number of industrial applications
-
CLEANSWITCH® - a two-bed thermal oxidizer, for destruction efficiencies of >99%; treats exhaust flows up to 142,000 Nm3/h.
-
The CLEANSWITCH is a cost-effective, two-bed Regenerative Thermal Oxidiser. It takes its name from MEGTEC’s patented valve that keeps the cleaned air totally separate from the process exhaust. The valve’s double gas seal has no metal to metal contact, which means that the valve has a high integrity. The CLEANSWITCH valve allows for the elimination of pressure spikes which are normally associated with the opening and closing of poppet valves in the more traditional thermal oxidizer designs, therefore this RTO is suitable for use in the most pressure-sensitive processes.
download CLEANSWITCH brochure
The CLEANSWITCH provides the cost benefits of a modular design, with improved performance. The CLEANSWITCH achieves destruction efficiencies of greater than 99%, in line with the US EPA point source emissions limits. Thermal efficiencies of up to 95% are obtained, which minimizes supplemental fuel costs.
-
EPSILON® – a multiple-bed thermal oxidizer, suitable for meeting emission limits of LEL).
-
The EPSILON is a 2,3,4,5 or more can system (as per customer’s needs), suitable for treating 5,000 to 200,000 Nm3/h vapour (at a maximum of 25% LEL). It is designed to meet stringent emissions limits of <20 mg C/Nm³ or lower and achieves a thermal efficiency of between 92 and 98%. The EPSILON has been widely installed in Europe and countries where >99.7% destruction efficiency is required. The EPSILON is therefore also highly suitable for use in the South African market place, where new legislation for total hydrocarbon point source emission limits is expected to be fairly stringent.
download EPSILON brochure
The typical EPSILON consists of two, three (or more) reinforced, refractory-lined chambers filled with high temperature high heat capacity heat exchange (ceramic) media. The ceramic beds allow for the retention of heat generated by the exothermic oxidation reaction, which can be reused in the fume preheating and oxidation process, allowing for a self-sustainable process requiring little or no additional energy input.
The ceramic beds are separated by a central combustion chamber, which includes a burner to bring the process stream to its final oxidation temperature and which is also used for control purposes. Below each media bed, an air plenum is provided to direct the flow through the beds. As the flow travels through the first bed, heat is transferred from the media to the incoming air to preheat it, and then it is directed into the combustion chamber where the combustion process is completed. The air then enters the second bed where it releases heat back into the media. At controlled intervals, the flow direction through the oxidizer is changed by the action of the two pneumatic poppet valves in order to maintain a stable temperature profile.
When the hydrocarbon laden process gas passes through the media bed and approaches the combustion chamber, its temperature rapidly increases. Due to the abundant excess oxygen content of the process gas, complete combustion readily occurs when the ignition point is reached in the combustion chamber, which is typically in the 800°C to 900°C range (below the adiabatic flame temperature). With a sufficient concentration of VOC in the incoming process stream, the heat energy of the VOC may be enough so that the destruction of hydrocarbons will be self-sustaining with no additional heat energy required.
The action of the poppet valves (when one valve opens and the other closes) would normally result in a small purge of the raw feed gas to the atmosphere. In order to achieve more stringent emissions specifications (e.g. EU directive), this purge gas is captured and routed to a third media-filled chamber. This purge gas is then slowly bled back into the main feed gas to the RTO. The three chambers cycle constantly, with one in heating mode, one in cooling mode, and one in purge mode.
Two chamber RTO’s are also available where emissions standards are less stringent, for example in the USA, where a destruction efficiency of 98% is required.
For details on additional MEGTEC RTO models, visit Megtec’s Website - www.megtec.com
Catalytic Oxidisers
 |
| download MAGNUM brochure |
Scion Technologies offers a range of MEGTEC Catalytic Oxidisers for various flow ranges, with the MEGTEC MAGNUM being the most suitable for higher air/fume flowrates.
The MEGTEC MAGNUM is suitable for exhaust flows up to 51,000 Nm3/h. The MEGTEC MAGNUM uses and efficient inline burner and maintenance-free exterior to deliver years of dependable operation. Extra economy is obtained through a stainless steel heat exchanger with a nominal 70% heat efficiency.
For details on additional Catalytic Oxidiser models, visit Megtec’s Website - www.megtec.com
Secondary Energy Recovery
 |
| download VOCSIDIZER using VAM brochure |
| download global warming & carbon credits |
| download VAM to thermal energy |
| download useful energy from VAM |
Both the single-bed thermal oxidizer and the traditional Regenerative Thermal Oxidizer can be used for the generation of steam, boiler feedwater preheat, hot oil systems or the generation of power from steam from the Secondary Energy produced by the Thermal Oxidizer. When running at higher inlet solvent loads, Thermal Oxidizers produce more energy than can be recovered within the ceramic beds. This excess energy, instead of being “dumped” to atmosphere, can be successfully utilised.
This has proven to be very successful on a commercial scale for the generation of power from methane-laden ventilation air from coal mines using single bed Regenerative Thermal Oxidizers. Only 0.2% methane concentration is required to maintain the oxidizing energy of system. At higher concentrations, the energy of methane exceeding this level can be recovered and utilized.
To this effect, MEGTEC Systems recently announced the inauguration of the first power plant in the world to use MEGTEC's technology to generate electrical power by using coal mine ventilation air methane (VAM) as its primary fuel. The power plant is now in full operation in Australia at the West Cliff Colliery of BHP Billiton, the world's largest diversified resources company.
Innovative Technology for Coal Mine Ventilation
The system is based on a patented combination of emission control and steam-cycle technologies. By using the compact and flameless VOCSIDIZER® regenerative thermal oxidizer (RTO) as an energy source, MEGTEC has made it possible to generate high grade, super-heated steam from a fuel with 0.9% methane content. The steam has the same quality as used at traditional power plants. It is used to drive a conventional steam turbine, which generates electricity that can be delivered to the state grid or directly to the mine.
Each hour, the installation is treating 0.9 % of methane content in 150,000 scfm (250,000 m3) of ventilation air. The energy produced from the methane is utilized to generate steam suitable for running a conventional 6 Megawatt turbine, resulting in this first power plant of its kind. The volume of ventilation air treated amounts to only 20 % of the total volume of ventilation air available from the ventilation shaft.
Methane as a Green House Gas
When coal is formed, so is methane. When the coal is excavated, methane is released. Since methane in air is explosive in concentrations between 5 and 15%, ventilation air is used to dilute the methane to levels below 1 % - well below the explosion limit. This safety measure leads to very large volumes of air with extremely low methane content being released to atmosphere.
Since methane emissions are a green house gas driving the global warming more than 20 times more potent than CO2, BHP Billiton can convert the emission reduction to carbon credits corresponding to 250,000 tons of CO2e (CO2-equivalents). A VAM Power Plant treating the full volume of ventilation air can generate approximately one million carbon credits.