Compact, equipment does not require a central vapor collection system; work was awarded in the USA
Volatile organic compounds (VOCs), widely used in industries, mainly as solvents and fuels, originating from various emission sources, are extremely harmful to health and cannot be released into the atmosphere. With the aim of proposing an efficient solution for the treatment of organic vapors in small and medium-sized industrial emissions sources, even in conditions of reduced flow rates, chemical engineer Bárbara Maria Borges Ribeiro developed compact catalytic incineration equipment that does not require a system vapor collection center. The work, carried out with the Process Engineering Department of the Faculty of Chemical Engineering (FEQ) at Unicamp, was supervised by Professor Edson Tomaz and collaborated by Professor Jefferson Ferreira Pinto.
The importance of the work is highlighted when it is known that these compounds released into the atmosphere, in addition to accentuating the greenhouse effect, react with nitrogen oxides to form ozone in the troposphere, a pollutant harmful to health and the environment. They also cause harm to humans such as respiratory, liver, kidney and neurological problems. Some of them have mutagenic and/or carcinogenic characteristics. Therefore, VOCs cannot be released into the atmosphere and must be transformed into carbon dioxide and water through oxidation.
The work was presented at the "Air and Waste Management Association's 110th Annual Conference & Exhibition", which took place from June 5th to 8th in Pittsburgh, Pennsylvania, United States, and received the award for best poster in the master's degree category.
Thermal and catalytic processes
When burning VOCs, thermal incineration is common, which, although efficient, has a high energy cost, coming from auxiliary fuel – liquefied petroleum gas, LPG or methane gas – to maintain the high temperatures necessary for the volatile reaction to occur with the oxygen from the air, which transforms them into carbon dioxide and water. In this process, unwanted compounds are also formed, such as nitrogen oxides. (NOx), considered important atmospheric pollutants, due to the high quantities of fuel required and high operating temperatures. The large amount of energy consumed and the dimensions of this incinerator are justified as long as there is a considerable volume of volatiles. Therefore, the different emission sources are directed in the industry to a central vapor collector before processing.
The researcher then developed work thinking about a catalytic incinerator that could be used with small amounts of VOCs and that no longer used the burning of fuels as a heat source, but the energy released by electrical resistances. Catalytic incineration is an alternative to this treatment, as it allows operation at lower temperatures, with energy savings, due to the use of a catalyst, in addition to minimizing the formation of NOx and other unwanted compounds.
The equipment developed in the research can be used in areas classified as risk, as the oxidation of organic vapors occurs without the formation of a flame due to the presence of the catalyst. The gaseous mixture consisting of volatiles and air is initially heated in the incinerator before passing through a commercial automotive catalytic honeycomb, which facilitates equipment maintenance as the catalytic bed can be found on the market. The product resulting from the catalytic transformation is then released into the atmosphere.
Different operating conditions were studied in this process, varying the gas entry temperature into the incinerator, the flow rate and the concentration of toluene - used to evaluate the efficiency of the process because it is a solvent widely used industrially and because it has a more resistant structure to degradation. Different combinations of these variables were considered, aiming for high VOC conversion efficiency. Efficiency greater than 99% was obtained for different operating conditions, with temperatures ranging from 270 °C to 360 °C, well below the 800 °C of thermal systems, which reduces emissions of volatile organic pollutants to very small values.
Conclusions
Bárbara considers that the study, by exploring different operating conditions, indicated the parameters necessary to obtain high conversions of VOCs, enabling the catalytic incinerator developed to be applied to the treatment and control of industrial effluents containing these compounds.
It clarifies that temperature was the main parameter for obtaining high toluene conversions. Thus, it was found that the lower its concentration, the higher the temperature must be and that, otherwise, a very high flow rate also requires an increase in temperature. On the other hand, when concentrations are high, the system can operate at lower temperatures since the combustion of the volatiles itself is responsible for maintaining the bed at the temperature necessary for the transformation.
In addition to operating at lower flow rates, the catalytic incinerator can be used in a decentralized manner, that is, it does not depend on collecting emissions from various sources, allowing the treatment of its volatile components in isolation.
The researcher clarifies that the technology is available for industrial application. The sizing of the equipment, which is simple and safe to operate, depends on the flow rate. It can be used in classified risk areas, as there is no formation of flames during combustion, and it consumes much less energy than the thermal incinerator commonly used today.
In the catalytic incineration process, the volatile organic compound (VOC) meets atmospheric air and the mixture is heated by resistances. The reaction between VOC and oxygen, coming from atmospheric air, occurs in the presence of the catalyst, with the formation of carbon dioxide (CO2) and water (H2O).
