Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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drocarbons. A natural gas burner system is provided and utilized for system pre-heat. Once the heat exchange media is saturated and hot enough to elevate the airstream above autoignition levels, the burner and combustion blower is turned off, and natural gas or methane is safely injected into the incoming airstream, enriching it to the concen- tration levels necessary for self-sustaining operation. NGI actually im- proves the thermal efficiency of an RTO because it eliminates the re- quirement for combustion air being introduced, and thereby mitigates the mass imbalance in airflow between the regenerator bed that is on inlet and the bed that is on outlet. In commercial application, NGI im- proves an RTO's thermal efficiency by approximately 1% or more over- all. Another advantage to NGI is an improvement in NOx emissions from an RTO. The burner is the single biggest contributor of NOx to the exhaust stream of an RTO, due to the high flame temperatures. Eliminating the burner from operating significantly decreases the NOx levels seen in operating RTOs. Due to the lower combustion tempera- tures of an RCO, NGI is not a tool that is utilized in conjunction with catalyst. However, many existing systems could see a decrease in operat- ing fuel usage, by a simple, low cost retrofit that would install a Natur- al Gas Injection system to the RTO, especially those airstreams not conducive to catalyst usage. ADSORPTION TECHNOLOGY Concentrators Rotary concentrators are a continuous adsorption technology commonly ap- plied to very dilute airstreams with relatively low hydrocarbon concentrations. Classified as a capture device, Rotary adsorbers can be used to concentrate the emissions into smaller airstreams with much higher concentrations (typically by a factor of 10 or higher) that can be handled by a smaller oxidation or destruc- tion device much more economically. Continuous adsorption is achieved through the use of rotating media, a section of which is simultaneously desorbed. This de- sign eliminates the need for dual running and stand-by fixed adsorption beds. The hydrocarbon-laden air passes through the rotary adsorption unit where the hydrocarbons are adsorbed onto an adsorbent media such as activated car- bon or hydrophobic zeolite. The large volume of incoming air, now purified by the adsorption process, is exhausted to atmosphere. The hydrocarbons which were adsorbed are then continuously removed from the media by desorption with a higher-temperature, low-volume airstream. This high concentration desorption air is delivered to an oxidation device for destruction. Concentration of hydrocarbons into a smaller airstream is a significant ben- efit to operating costs to a destruction device. By decreasing the airflow, the de- vice is inherently smaller and less costly to purchase. By increasing the concen- tration, the auxiliary fuel benefit of the hydrocarbons is increased, in many cas- es, almost to the level of self-sustaining operation, where the customer's natur- al gas requirements are virtually eliminated. Traditionally, concentrators were ap- plied and justified on very large airstream volumes, but recent commercial ap- plications have been on airstreams of 30,000 scfm and smaller. 240

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