Metal Finishing Guide Book


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are composed of ceramic saddles, randomly packed into an insulated chamber. The airflow through the saddles is forced to make many changes in direction and velocity. Due to the turbulent nature of the airflow, the pressure drop across the bed increases with the square of the airflow. Dürr's investigations into the fundamental principles of RTO operation led to the development and application of a structured heat transfer media. These investigations indicated that a heat transfer media having straight airflow passages of constant cross-section offer significantly improved performance over traditional saddles by providing more laminar airflow characteristics. The improved performance can be seen in a lower pressure drop across the packed beds of an RTO. Structured packing is a ceramic monolithic block, composed of silica alumna ceramic. Each block is approximately 12" tall, 6" wide and 6" long, and has hundreds of parallel passages, each approximately 1/8" square, extending from top to bottom. It's physical and performance characteristics allow for a higher airflow velocity through a packed bed, resulting in a more compact RTO which is attractive to land-locked plants that may not have the normal space required for an RTO. This higher bed velocity also allows for a unique solution to plants that have existing RTO equipment that may require additional airstream treatment capacity. Increased flow in a traditional saddle packed bed requires an exponential increase in pressure drop and motor horsepower, quickly overloading existing handling capacity. Replacement of an existing saddle bed with ceramic monolith can not only reduce the pressure drop for existing capacity, but also provide almost a 40% increase in incoming airflow capacity with the existing motor and fan, while providing better thermal performance, lowering the natural gas consumption 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 accelerates the rate of a chemical reaction, i.e. oxidation, without the catalyst or the substance being consumed. Another benefit of a precious metal catalyst is its ability to eliminate not only VOCs, but also secondary products, notably CO and NOx. In addition, a precious metal-based catalyst is much more resistant to poisoning and fouling than base metal catalysts. Like structured packing, converting an existing 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 653

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