Today, we’re about to go back to class, exploring the basics of combustion, what it takes to achieve complete combustion, and why all of this is important to VOC abatement at manufacturing organizations.
What is Combustion?
In chemistry, combustion is a basic equation meaning “the reaction of oxygen with anything.” When applied to propulsion (internal combustion engines), heat generation, or pollution control, combustion is understood to be the reaction of oxygen with a compound containing carbon and hydrogen.
Basic Chemistry of Combustion
Also known as “burning,” the combustion process occurs when the initial bonds of a carbon-based chemical are destroyed and bond with oxygen to form carbon dioxide and water. This is shown using the equation CxHy + O2 –> CO2 + H2O. In turn, when applied to volatile organic compounds, these compounds would burn following this formula:
- Benzene (C6H6): 2C6H6 + 15O2 –> 12CO2 + 6H2O
- Butyraldehyde/butanal (CH3(CH2)2CHO): C4H10O + 6O2 –> 4CO2 + 5H2O
- Toluene (C7H8): C7H8 + 7O2 –> 7CO2 + 4H2O
Whether the VOCs are simple, like the examples above, or more complex, the equation remains relatively simple: Organic Compound + Oxygen = Carbon Dioxide + Water.
The Three T’s of Combustion and VOC Abatement
However, if VOC abatement was as simple as “mix oxygen with your emissions,” we wouldn’t be in business, and millions of organic chemists, climatologists, and former Vice Presidents would be out of a job. With regards to VOC Abatement, combustion relies on the right combination of three specific elements: Time, Temperature, and Turbulence.
Think of this process like a recipe. You need the proper mix of ingredients, you need to cook at the right temperature and for the right amount of time in order for the end result to turn out properly. In the combustion process, you need to make sure that:
- There is a proper amount of oxygen mixed into the combustion chamber,
- The pollutant and the oxygen stay in the chamber for the right amount of time
- The pollutant and oxygen are held in the chamber at the right temperature
Without the proper mix of these three elements, combustion is not completed. If temperatures are too low, the bonds aren’t able to break apart. If the temperature is too high, the result of the combustion is Carbon Monoxide (CO) as opposed to CO2, which poses its own hazards to people and the environment.
The goal is to burn as much of a VOC as possible, with special focus on destruction efficiency, thermal efficiency, and cost efficiency as possible. This is all done in an oxidizer—a piece of equipment that will take in exhaust emissions, allow combustion to take place, reducing emissions to water vapor, carbon dioxide, waste (waste is 0.001%-5% of emissions, depending on input, industry-specific regulations, and design), and heat.
In order to completely destroy a VOC, the compound needs to stay in the combustion chamber for a specific amount of time, usually 0.5-1 second, with more time needed for complex, hard to burn hydrocarbons like those found in pesticides.
Temperature is the second element of combustion, and refers to the chamber/furnace temperature (as opposed to stack temperature). Often, the temperature required to destroy a hydrocarbon in a thermal oxidizer ranges from 1,400-1,600 Degrees Fahrenheit.
This depends on the contents of your emissions, with some compounds breaking apart at lower temperatures and some at higher temperatures. Additionally, finding the right temperature may require the addition of fuel or modification of turbulence to ensure consistency and complete destruction.
These higher temperatures will require different design considerations, as different components may be needed. Additionally, as temperatures reach extremes, chemicals in the waste begin to react with the oxygen. For instance, at 2,800°F (1,540 °C) and up, NOx species, as well as CO begin to appear in significant amounts.
Turbulence, the third element of combustion, is used to define the proper air flow needed to mix oxygen with hydrocarbons. While oxygen content is an important factor (ranging from as little as 2% to over 21% of the volume), the proper mixture of hydrocarbon and oxygen is just as important. This is where turbulence comes into play.
Fans will circulate the mixture to ensure that the oxygen and hydrocarbons to provide a balanced chemical equation at the end of combustion. Improper mixing results in hydrocarbons escaping without being combusted. Too much oxygen could also result in inconsistent temperatures or undesirable reactions (the creation of NOx in nitrogen-based combustion).
Conclusion: The 3 T’s Are Only One Part of VOC Abatement
The chemistry of combustion is relatively simple, but the real science comes in when you want to maximize efficiency. Just as different industries have different emissions standards set forth by the EPA, they also have different ways to optimize the destruction of these emissions.
The CMM Group is skilled at helping you not only maximize destruction efficiency, but prevent the oxidizer project from turning into a money pit by optimizing thermal recovery efficiency as well. No matter the industry, it’s likely we’ve worked with a company in it to design, build, implement and service a thermal or catalytic oxidizer that meets their needs.
We would like to invite you to learn more about VOC Abatement and selecting a solution by downloading our VOC Abatement System Specification Checklist below. Additionally, by signing up to get the checklist, you will also be among the first to receive our new VOC Abatement Guide.