Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 240 of 331

in incoming airflow capacity with the existing motor and fan, while providing better thermal performance, lowering the natural gas con- sumption of the RTO. • Regenerative Catalytic Oxidation (RCO): RCO's are a recent hybrid VOC abatement technology that is gaining acceptance in plants where energy cost are high and the hours of operation are long. An RCO combines the benefits of an RTO with the benefits of catalysis. By adding a precious metal catalyst to the combustion chamber of an RTO system, the catalyst provides hydrocarbon conversion at a much lower operating temperature than an RTO, typically 600°F to 1000°F, which thereby reduces the auxiliary fuel requirements. The precious metal catalyst, like all catalysts, is a substance which acceler- ates the rate of a chemical reaction, i.e. oxidation, without the cata- lyst or the substance being consumed. Another benefit of a precious metal catalyst is its ability to eliminate not only VOCs, but also sec- ondary products, notably CO and NOx. In addition, a precious met- al-based catalyst is much more resistant to poisoning and fouling than base metal catalysts. Like structured packing, converting an ex- isting RTO to an RCO is possible, and often beneficial depending on the operating and energy consumption conditions in the plant. Adding a layer of proprietary precious metal catalyst on top of the ce- ramic media in the RTO's combustion chamber will allow the com- bustion chamber operating temperature to be lowered to roughly 800°F. In large air volume systems, this fuel savings can be signifi- cant. The proprietary catalyst in Durr systems is impregnated in the ceramic media of choice, either saddles or structured packing. In some instances, an RCO system may not be a beneficial choice. These exceptions result from either the presence of a stream that contains organometallic or inhibiting compounds that will cause degradation of catalyst performance. Each VOC stream needs to be examined to ensure there are no catalyst poisons such as silicon, phosphorus, ar- senic or other heavy metals. In addition, the catalyst performance could be masked or fouled by particulate in the air stream. However, the catalyst can be recharged relatively easily. It is important to dis- cuss the properties of individual air streams before making any deci- sions on the applicability of catalyst in an RCO, but for many, the po- tential for operating cost savings is large. • Natural Gas Injection (NGI): Typically a natural gas burner system is used to provide the energy required to make-up the heat that is not recovered by a regenerative oxidizer (around 5% of the energy re- quired to reach setpoint). An incoming airstream with a high enough concentration of hydrocarbons, would provide enough energy from auto-ignition of the hydrocarbons for the oxidation process to be self-sustaining, i.e. require no burner operation for make-up energy. Natural Gas Injection (NGI) is a means of artificially creating a self- sustaining condition in an airstream with a low concentration of hy- 239

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