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FLEXO Magazine : March 2009
TECHNOLOGIES & TECHNIQUES Concentrators reduce the air volume being sent to an oxidizer, increasing the capacity and efficiency of an existing oxidizer system. Large air volumes with low VOC concentrations are absorbed into a concentrator then desorbed in a condensed, smaller volume before being sent to the oxidizer. Maximizing internal thermal energy recovery. system. In many cases this has lead to the installation of addi- tional capture hoods or enclosures and increased the amount of air to be treated by a particular oxidizer system. A concen- trator can take exhaust air at or near ambient temperatures and concentrate it so that what is actually sent over to the oxi- dizer system is reduced by a factor of eight to 15 times. This greatly reduced airflow is typically fuel-rich with VOCs and much less of an operating cost burden on the oxidizer system. 7. FOCUS ON COMBUSTION AIR. Combustion air, both in your oxidizer system or in your process burners, is often overlooked as a potential area for operating cost savings. Next to main oxidizer system fans, the smaller combustion fan supplying high-pressure air across the oxidizer burner can seem insignificant. However, these small- er fans, more often than not, are supplying fresh air at out- door temperatures directly into the oxidation chamber where it must be heated to full oxidation chamber temperature. At a temperature difference usually over 1,400 0 F, it does not take much airflow over the course of a year to add up to significant operating cost dollars. Making sure burners are tuned properly and not firing on excess combustion air can make a big difference. With RTOs, there is the additional opportunity to install a flameless fuel injection system where combustion air is not needed at all. Finally, even with a perfectly tuned burner, combustion air can be preheated using a heat exchanger or a blend with stack air. 8. IMPROVE PRIMARY HEAT RECOVER'f. Oxidizers are typically designed with some form of internal heat recovery. Usually the hot purified gases leaving the com- bustion chamber are used to pre-heat the incoming solvent laden airstream. This is referred to as the primary heat recov- ery of an oxidizer system. Projects that improve the primary heat recovery of an oxidizer system often offer the quickest payback because they provide additional heat recovery at all times the oxidizer is in service. For recuperative thermal and catalytic units this typically consists of adding additional passes to the internal air-to-air heat exchanger. For RTOs and RCOs this would be handled with increasing or changing the Secondary heat recovery installation. type of ceramic heat recovery media or changing the control scheme that dictates how often beds are switched from inlet to outlet. 9. CONSIDER SECONDARY HEAT RECOVER'f. If improving primary heat recovery is not cost effective-or oxidizer operating conditions do not allow it-secondary heat recovery may be the best option for conserving the heat input to an oxidizer system. Heat exchangers can be added to the exhaust stack of an existing oxidizer to capture excess stack heat in air, water, or even steam. There is a wide variety of low back-pressure designs that can be added to an oxidizer's stack without requiring a replacement of the oxidizer system fan. Payback for these projects is greatly improved if the cap- tured heat can be used back in the exhaust generating process itself, because again-it is assumed that the process is operat- ing at all times the oxidizer is operating. For example: fresh air is passed through a secondary heat exchanger in an oxi- dizer exhaust stack and supplied back as base loading for the oven zones the oxidizer is treating. Every time the oxidizer is on the oven zones require heat, so this heat recovery project pays back all year long. If the same fresh air was supplied back to the plant as tempered makeup air, this may only provide payback during the heating season. Following this logic, in the past comfort heat applications may have been ignored. But considering today's unstable and rising fuel costs, coupled with the energy recovery grants available to facilities, these projects deserve attention. 10. PROPERLY MAINTAIN EXISTING SYSTEMS. Finally, no matter how well an overall system is designed, it cannot continue to operate at a high efficiency level with- out proper maintenance. A handful of small inefficiencies in system operation can lead to large operating cost bill over the course of a year. At today's energy prices, regular calibration of feedback instruments and control loops can pay for itself many times over. All too often, production facilities take the "no news is good news" approach to their air pollution control equipment when they really should be chasing the benefits of "Company Stays Green and Saves Green" headlines instead. MARCH 2009 - www.flexography.org FLEXO
Sustainable Winter 2009