Metal Finishing Guide Book

2012-2013

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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 ceramic media in the RTO���s combustion chamber will allow the combustion chamber operating temperature to be lowered to roughly 800��F. In large air volume systems, this fuel savings can be significant. 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, arsenic 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 discuss the properties of individual air streams before making any decisions on the applicability of catalyst in an RCO, but for many, the potential 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 required 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 selfsustaining condition in an airstream with a low concentration of hydrocarbons. 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 concentration levels necessary for self-sustaining operation. NGI actually improves the thermal efficiency of an RTO because it eliminates the requirement 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 improves an RTO���s thermal efficiency by approximately 1% or more overall. 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 temperatures of an RCO, NGI is not a tool that is utilized in conjunction with catalyst. However, many existing systems could see a decrease in operating fuel usage, by a simple, low cost retrofit that would install a Natural Gas Injection system to the RTO, especially those airstreams not conducive to catalyst usage. 697

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