Rto

Reg en erati ve an d Re cu pe rati ve T he rm al Ox idi zer s Thermal oxidizers destroy air toxics and Volatile Organic Compounds (VOCs) that are discharged in industrial process exhausts. Thermal oxidizers achieve VOC destruction through the process of high temperature thermal oxidation, converting the VOCs to carbon dioxide and water vapor, recycling released energy to reduce operating costs. Most thermal oxidizers capture heat from the outgoing air stream to preheat incoming air and reduce operating costs. The two most common methods of reclaiming heat are regeneration and recuperation. Regeneration refers to regenerating the heat of a large thermal mass; thermal oxidizers employing this method are called Regenerative Thermal Oxidizers. Recuperation refers to transferring heat directly from the outgoing air stream to the incoming air stream; thermal oxidizers employing this method are called Recuperative Thermal Oxidizers. Ho w a Re ge ne rati ve Th erm al Ox idi zer Wor ks Process gas with VOC contaminants enters the Twin Bed RTO through an inlet manifold. A flow control valve directs this gas into an energy recovery chamber, which preheats the process stream. The process gas and contaminants are progressively heated in the stoneware bed as they move toward the combustion chamber. The VOCs are then oxidized, releasing energy in the second stoneware bed. The stoneware bed is heated and the gas is cooled so that the outlet gas temperature is only slightly higher than the inlet temperature. The flow control valve switches and alternates the stoneware beds so each is in inlet and outlet mode. If the process gas contains enough VOCs, the energy released from their combustion allows self-sustained operation. For example, at 95% thermal energy recovery, the outlet temperature may be only 77° (25°) higher than the inlet process gas temperature. PLC-based electronics automatically control all aspects of the RTO operation from start-up to shutdown so that minimal operator interface is required. Re ge ner ativ e S yst em Co mp on ent s Regenerative Thermal Oxidizer Systems include system fan, motor, burner, heat exchange media, flow control valves, PLC based system controls, temperature recorder and exhaust stack. The system has a ceramic fiber-lined, steel outer skin and an access platform for servicing burner components.

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Regenerative Thermal Oxidizer System Schematic

Ho w a Th erm al R ec up er ativ e O xidi ze r Wor ks The Thermal Oxidizer is designed based on volume of airflow, organic vapor concentrations and desired destruction efficiency. During operation, VOC-laden air is drawn into the system fan and is discharged into the system's heat exchanger. The air is preheated through the tube side of the heat exchanger and then passes the burner, where the contaminated air is raised to the thermal oxidation temperature (1,200-1,800ºF or 650-1,000ºC). When the VOC-laden air is raised to the thermal oxidation temperature for the specified residence time (0.5 - 2.0 seconds), an exothermic reaction takes place. The VOCs in the air stream are converted to carbon dioxide and water vapor. The hot, purified air then passes on the shell side of the heat exchanger where the energy released by the reaction is used to preheat the incoming air. The heat exchanger minimizes the system's fuel consumption with the system being self-sustaining at moderate LEL levels. Finally, the contaminant-free air is exhausted into the atmosphere. Re cu pe rati ve Sy st em C om po ne nts Thermal Oxidizer Systems include a system fan, motor, heat exchanger, modulating burner, fuel train, ceramic-lined reactor, fresh air start-up valves, system controls, temperature recorder, first-out shutdown detector and exhaust stack. The system has a weatherproof, ceramic-lined steel outer skin with access doors that allow service to all internal parts. Re ge ner ativ e T he rmal Ox idi zer ( RTO) 1. O utli ne o f s yst em This equipment has three heat storing towers filled with ceramic heat storing material and the combustion room with burner on top of them. There is a control valve for gas passage in the lower part of each heat storing tower. 2

Each heat storing tower has the pre-heating process, radiation process and purge process, each of which is selected by the timer. In the pre-heating process, the VOC gas is pre-heated by passing it through the heat storing material which stores heat from the exhaust gas in the radiation process. Then, the solvent and VOC are combusted, oxidized and decomposed in the combustion room. In the radiation process, the exhaust gas from the combustion room gives heat to the heat storing material, and discharged to the atmosphere from the chimney. In the purge process, the uncombusted gas pooled at the lower part of the heat storing tower in the pre-heating process is replaced with the exhaust gas from the combustion room so that any smell may be prevented when the pre-heating process is switched to the radiation process. The burner installed in the combustion room is used in the initial temp rise, or in case the decomposition temp (800ºC-900ºC) cannot be obtained only by the heat generated by solvent and VOC in the raw gas. 2. C ha ra cteri stic s 1) High performance The solvent and VOC are oxidized and decomposed at the high temp 800ºC-900ºC in the combustion room, so most part can be eliminated. This can be regarded as the best way to treat the solvent of multi-components and VOC gas. 2) High efficiency & low NOx Since the heat recovery rate is as high as 85%-95%, it doesn't need so much amount of combustion fuel as compared with other method (direct combustion system, catalytic combustion system). Even if the solvent (VOC) concentration is 1000 ppm or lower, self-burning is available. Since less of combustion fuel , less of NOx is generated. 3) High-concentration treatment is available. In case any highly concentrated solvent/VOC exceeding self-burning area is treated in the RTO, the inside of the combustion room may be heated to a temp above 1000ºC, possibly damaging the units. In this case, a direct bypass line from the combustion room to the chimney helps exhaust gas bypass the heat storing material to prevent the inside of the combustion room from being heated abnormally. There is another way to prevent abnormal temp rise by sucking atmospheric air. By each of these ways or by their combination, it is possible to control the inside of the combustion room into normal temp. 4) Countermeasures for substances of high boiling point Various impurities that may be used for raw materials could be trapped in the raw gas. These substances could come flying as mist at high boiling point, and could be deposited on the units (mainly at the lower part of heat storing material and control valve), thus eventually causing the system to fail in operation. For the countermeasures, the following methods are available. We apply each of the methods or any combination of them to maintain a lasting and stable operation. - Select heat storing materials in a way that the gas passage may not be clogged even when any impurity sticks. - Adopt "Bake out"(the tar-burning cycle) so that any stuck impurities can be removed. 3

- Let the high-temp exhaust gas return to the raw gas line to prevent any impurity from becoming mist, and from sticking to anything. 5) Others Ceramic wool is used for fire-resistant material in this equipment, it is free of cracks in the event of sudden thermal changes as compared with the conventional castor, and can be used for a longer time with no repair. The switching control valve is selected so strictly that it may be used for a long time with less work for maintenance/repair.

3. P erf orma nc e 1) Treating capacity Up to 1000m3/H - 6000m3/H can be dealt with the 3-tower type. For more, increase the number of towers or units. 2) Performance - VOC Removal rate -99% - Thermal recovery rate 85-95% 4. A pp lic abilit y a nd o bj ecti ve s Solvents and VOC are used in various industries of painting, printing, tape, rubber, paper, packing and texture, and the fields related to electronics. Various solvents are used for various purposes. All of these exhaust gases from production system can be treated by this equipment. This is also used as the deodorizers at the night soil treatment plant and sewage water treatment plant. 5. O th ers 4

If coupled with any solvent gas (VOC) thickener for the lower concentration gas than starting self-burning and a large-volume exhaust gas, the gas volume will be reduced, and if the solvent concentration is raised, economic treatment is available Thermal Recuperative Oxidizer System Schematic

Ca se St ud y A flexographic converter needed to expand its business by adding an 8-color CI printing press to its existing press lines, and planned to add a second press later. The increase in emissions and flow from the new press was beyond the capacity of the existing 10-year old catalytic oxidizer. The customer needed a way to maintain compliance at an affordable cost. After analyzing the customer's process, Anguil recommended a 12,000 SCFM (18,925 NM3/Hr) Anguil Twin Bed Regenerative Thermal Oxidizer engineered for 98% destruction efficiency. This system is designed for heat recovery of over 95% and is self-sustaining, requiring no auxiliary fuel addition even with low VOC loadings. Anguil's innovative system utilizes advanced, high-temperature structured ceramic media in the energy recovery chambers to provide higher airflow capacity than traditional saddle packing. The structured media and Anguil's unique energy recovery chamber design were essential to providing an extremely low pressure drop through the oxidation system; the low pressure drop means the system will have lower horsepower consumption and operating costs. In a key move, Anguil's application engineers designed process modifications that allowed over 50% of the exhaust air from the presses to be re-circulated back into the press supply fans. By recirculating the air, Anguil reduced the volume of air that needed to be treated and, therefore, was able to reduce the size and capital and operating cost of the RTO.

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A major concern for printers is capturing fugitive emissions from their printing process. Anguil was able to greatly improve the capture of fugitive emissions for this customer by addressing two major sources of emissions: the last color deck and the overhead tunnel dryer. Anguil improved the ink pan covers to reduce fugitive vapors coming off the ink roll and enclosed the open web lead between the last print deck and tunnel dryer to capture the fugitive vapors. Anguil designed a 100% Permanent Total Enclosure (PTE) for the printing area, to be constructed at a later date. The PTE will automatically improve the volume of controlled emissions and provide the customer with emission credits that can be applied toward the installation of a future press. Re fere nc es This description, with only a few modifications, is directly from the Anquil Environmental Systems web site at http://www.anguil.com/prregthe.php.

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Thermal oxidation has benefited from a series of steady improvements over its life. This evolution has been driven by industry's need to control increasingly larger dilute streams while reducing operating costs. Now, the 1990 Clean Air Act Amendments (CAAA) and its Title V Operating Permit Program place even greater importance on thermal oxidation. Thermal oxidation offers a breadth of proven applications, destruction efficiency, low operating cost and simple monitoring for compliance. Because of this and the CAAA requiring all major sources of regulated air emissions to demonstrate "continuous" control reflecting maximum achievable control technology (MACT) or best available control technology (BACT), thermal oxidation needs to be a top consideration for end-of-pipe control. The cost of monitoring a control technology can be as high as $500,000; however, a continuous emission monitoring system (CEMS) for a thermal oxidizer can be as little as a thermocouple and a simple indication of flow, like fan speed or load. Additionally, new developments in catalytic oxidation greatly reduce the operating cost of these devices while delivering the same reliable high-destruction efficiency. The first oxidizers were straight thermal units without any heat recovery. They provided effective control, but were far too expensive for large sources. Next were recuperative oxidizers with shell-and-tube heat exchangers capable of recovering up to 70 pct of the energy of oxidation. However, these units still consumed a great deal of energy and recuperative units soon gave way to regenerative thermal oxidation (RTOs). These units have ceramic beds capable of delivering up to 95 pct thermal efficiency. RTO technology successfully met industry's broad need for reliable control of high-volume dilute emissions.

FL OW D IAG RAM o f i nd ustri al o xi diz er

Yet, if the global market has taught us anything, it is that industry needs to continue its relentless attack on operating costs. Since RTOs operate with high temperatures and large gas volumes, there is still significant 7

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