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Burner Design, Combustion Analysis and its Emissions

Banner Burner Design, Combustion Analysis and its Emissions

Combustion systems are key to the generation of hot gases, heating in ovens and power generation in thermoelectric plants. Due to its peculiarity, Brazil produces very heavy fuels, which are more viscous at room temperature than those existing in markets abroad. Another thing is that the use of natural gas is a trend, as it does not produce SOx or particulates, which is an advantage for the environment. Other fuels such as biomass and hydrogen are being studied as an alternative to fossil fuels. To a lesser extent, fuels such as coke and charcoal or mineral are still used in some specific industrial processes.

The burners can be quite simple, like a lance, but they can have their own cooling system to reduce the temperature especially in areas exposed to radiation from the boiler or furnace. These systems use gases, water vapor or stagnant air mattresses. Higher temperatures can cause fuel to crack and even clog or change the discharge area. The turbulent mixing rate of the fuel with the oxidizer is critical to the development of the flame, where chemical reactions are generally faster than the turbulent mixing rate. Therefore the turbulent mixture controls the shape and length of the flame in the combustion chamber.

The CFD modeling of burners and combustion chambers is quite challenging as it involves the simultaneous presence of flows in a transonic flow in the boom (Mach between 0.7 and 1) with a low subsonic flow (Mach much below 0, 3) in the chamber, boiler or oven. This requires a robust and precise tool like CFD++, which has the same set of equations in different regimes. In addition to these two regimes, there is also low Reynolds number flow near the walls, where heat and momentum transfer occurs. CFD++ can use wall functions (10<y+<300), with or without roughness, or solve the flow to the wall by going to the beginning of the viscous sublayer (y+<1).

Regarding chemical kinetics, experimental coefficients found in open literature can be used, or a chemical kinetics tool such as KinTech Lab can be used. In this case, the evolution of local temperatures and pressures are considered to find the coefficients of the equation of Arrhenius in order to generate the appearance or disappearance rates of chemical components. KinTech Lab can also be used to find the reduced chemical reaction mechanism, which allows for use in conjunction with CFD++. A complete methane burning engine might have more than 300 reactions, but a reduced engine might have a few dozen reactions. It all depends on what purpose of the chemical analysis. For each reaction, there is the addition of one more equation to be solved by CFD++.

Studies and Analysis

ATS designed a burner for Vale’s pelletizing furnace in Vitória using the CFD++ tool. She considered a reduced chemical model to calculate thermal NOx emissions. This kinetic model was validated and compared with experimental data from the literature. Fifteen configurations and different strategies to reduce NOx emissions were studied for the flare design. From the simulations, a prototype was built based on the best configuration found with CFD++. A measuring easel was specified and constructed. Finally, a test is carried out to validate the results at the Vale Vitória plant.

For Braskem, Triunfo-RS, a vinyl-acetylene burner was designed to be installed in a tangential boiler that also burned oil and coal. Studies were carried out for the cooling of the burner and accurate calculation of the thermal load by radiation of the boiler, which required CFD++ analysis to calculate the form factors. Furthermore, ATS also studied the flow within the tangential boiler, with combustion, to represent the central fireball. The changes were implemented by Braskem and it was verified that the CFD++ forecasts were adequate and accurate.

Air quality analysis for large areas (~50km) is performed by AERMOD, a software created by the U.S. Environmental Protection Agency (US EPA) and widely accepted in Brazil. Its atmospheric emission modeling takes into account the industry’s pollutant flows, and if relevant, other emitting agents such as cars can also be allocated, it also takes into account the local relief, terrain and meteorological data recorded, these The last three are integrated by AERMET.
The simulation performed in AERMOD allows observing the places with the highest concentrations of pollutants over time (last years) and observing the local averages. With these data, it is possible to plan the best defined locations to perform the measurement of air quality in the communities surrounding the industry. It is also possible to observe how efficient a pollutant abatement mechanism is, if the expected result will be observed by the communities.

ATS has CTF/AIDA certificate and training to use AERMOD, AERMET and CALPUFF (~200km).

ATS carried out pollutant dispersion studies for the Viana and Linhares plants of TEVISA (Termelétrica Viana), in the State of Espírito Santo, and of Petrobras in the State of Rio de Janeiro. The report with the results was approved by Organs environmental agencies of each state.

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