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Flexo Sustainable : Year End 2011
to humans and animals, as well as damaging to crops. VOCs are a major ingredient in smog. Furthermore, even though carbon dioxide has developed quite a reputation as a leading greenhouse gas, certain un- treated hydrocarbons have many times the greenhouse gas potential as carbon dioxide. Methane, for example, has been reported to have up to 20 times the greenhouse gas potential of carbon dioxide. So, the treatment of VOCs prior to release is certainly necessary, and one of the end products is carbon dioxide. Given today ’s media climate, it is therefore understand- ably tempting to think of VOC oxidizers as a “necessary evil.” This label is certainly under- standable, but not entirely fair. When one considers the quantity of carbon dioxide generated by the treatment of VOCs, one can break up the end product CO2 into two categories. For this discus- sion, these will be termed the Process Exhaust CO2 and the Energy Input CO2. Process Exhaust CO2 refers to the CO2 formed from the carbon in the process exhaust VOC. For instance, if the process exhaust contains 75 lb/hour of Isopropyl alcohol (C3H7OH), after treatment this converts to about 165 lb/hour of CO2. This resultant quantity of CO2 will be similar, whether the treatment occurs in a biofilter, oxidizer, or by atmospheric degradation. Short of solvent recovery—almost all of the cur- rent treatment options end up converting the process exhaust carbon to Process Exhaust CO2. Now, for any of the treatment methods described above, a certain amount of energy input is required to facilitate treat- ment of the VOC. This energy, in turn, typically comes with its own carbon penalty, resulting in a second quantity of CO2 – here called the Energy Input CO2. It may seem intuitive that of all the choices for treatment technology, oxidizers—with operating temperatures typically greater than 1400 degrees Fahrenheit—would rank the worst in regard to Energy Input CO2. Indeed, a direct-fired thermal oxidizer with no heat recovery treating a process exhaust of 10,000 standard cubic feet per minute (SCFM) with the same 75 lbs/hour of Isopropyl Alcohol mentioned earlier would result in: • About 165 lb/hour of Process Exhaust CO2 • Over 2,800 lb/hour of Energy Input CO2 Fortunately, there are very few applications where a 10,000 SCFM process exhaust would be controlled with an oxidizer that uses no heat recovery. However, catalytic oxidizers have been used in many printing applications and these installa- tions will consume auxiliary gas and result in: • About 165 lbs/hr of Process Exhaust CO2 • Almost 125 lbs/hr of Energy Input CO2 Even in the case of catalytic oxidation, the CO2 generation from energy input is approaching the same value as the CO2 from the carbon in the process exhaust. But, there are ways to minimize the energy input by using highly efficient oxidation equipment that operate in a ther- mally self-sustaining way—meaning no additional fuel input is CO2 Emission Comparison: Typical CO2 emissions from the various oxidizer technologies. Anguil RTO on Package Printing: This RTO is installed on a package printing operation. It is self-sustaining, which means there are minimal CO2 emissions generated during the destruction of VOCs. 8 Sustainable FLEXO YeaR-end 2011 www.flexomag.com