Description of Thermal Oxidizers

Transcription

1 Description of Thermal Oxidizers NESTEC, Inc. is a full service equipment supplier specializing in solutions for plant emission problems. The benefit in working with NESTEC, Inc. is we bring 25+ years of experience in the environmental field to every project. Furthermore, NESTEC, Inc. has developed a team of contractors and suppliers with similar experience to ensure every aspect of a project goes smoothly. When the project is complete the system is maintained and serviced by experience NESTEC, Inc. technician s familiar with your process, equipment and training requirements. Corporate Office: 21 Unionville Road P.O. Box 568 Douglasville, PA Bus Fax Represented in Ontario by:

2 DESCRIPTION OF EQUIPMENT Regenerative Thermal Oxidizer (RTO): The Regenerative Thermal Oxidizer (RTO) converts Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) to carbon dioxide and water vapor through thermal oxidation. RTOs use regenerative heat transfer to achieve very high thermal efficiencies, which results in very low fuel cost. Through flow reversal, process gas is alternately heated then cooled in the thermal energy recovery chambers prior to being exhausted to atmosphere. Exhaust gas containing VOC and HAP compounds is directed past the inlet isolation valve, into the exhaust fan and discharged into the inlet manifold where the gas is directed into one of two thermal energy recovery chambers that is on inlet at that time. Valves designed to alternate flow from one chamber to the next insure the exhaust gas is directed to the proper chamber. As the gas passes through the thermal energy recovery media it gradually increases in temperature until is it very close to the combustion temperature (usually 1,500 Deg F). During this period, the VOCs and HAPs are heated above the respective ignition temperature and thermal oxidation begins. After the gas exits the heat recovery media it passes through the combustion chamber to insure total conversion of the contaminants have occurred. At this point, a burner will add heat, if required, to maintain set point temperature. The newly purified exhaust gas exits the oxidation chamber and enters a heat recovery chamber, which is on outlet at that time. Similar to the inlet, the exhaust gas passes through the heat recovery media, but this time, gradually decreasing in temperature until it is very close to the inlet temperature. The cleaned exhaust gas is collected in the exhaust manifold, directed to the exhaust stack and discharged to atmosphere. Exhaust gas will continue to flow in an alternating pattern from one chamber to the next, exiting from the opposing chamber. The sequence is then reversed every 2 to 5 minutes to provide equal heating and cooling within each heat recovery chamber. Recuperative Thermal Oxidizer The Recuperative Thermal Oxidizer converts Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) to carbon dioxide and water vapor through thermal oxidation. Recuperative thermal oxidizers use high efficiency metal, air-to-air heat exchangers designed to recover thermal energy from the oxidizer exhaust, preheating the incoming process stream.

3 Exhaust gas containing VOC and HAP compounds from the process is directed through the inlet isolation damper, exhaust fan, and directed to the inlet side of the heat exchanger. As the gas passes though the cool side of the heat exchanger, it gradually increases in temperature until is it near the combustion chamber temperature. As the gas exits the heat exchanger, it passes through the combustion chamber where the gas is increased and held at a preset temperature (usually 1,400 F). The combustion chamber is designed to hold the contaminants for at least one-second to insure total conversion occurred. A burner will add heat, if required, to maintain set-point temperature at the discharge of the heat exchanger. The newly purified exhaust gas exits the oxidation chamber and enters the hot side of the heat exchanger. Similar to the inlet side, the exhaust gas passes through the hot side of the heat exchanger, but this time, it gradually decreases in temperature until it is very close to the inlet temperature. The cleaned exhaust gas is then directed to the exhaust stack and discharged to atmosphere. Direct Fired Thermal Oxidizer The NESTEC Thermal Oxidizer (TO) converts Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) to carbon dioxide, water vapor, and non-combustibles through thermal oxidation. When required, the thermal oxidizer can be provided with a waste heat boiler or some other heat recovery device, increasing the overall energy efficiency of the plant. Through proper design and control, this system will maximize conversion of organic compounds while minimizing operating costs and product of combustion, such as carbon monoxide and oxidizes of nitrogen (NOx) Exhaust gas containing VOC and HAP compounds is directed through a process isolation valve, then into the inlet side of the thermal oxidizer. The gas then passes through a mixing nozzle where it combines with natural gas, forming a combustible mixture. In this configuration, the process gas stream is used as combustion air. The gas is heated to approximately 1,450 F and held at that temperature for 1 second. During high solvent conditions, the fresh air / purge damper will open to control the combustion chamber temperature to approximately 1,500 F. In this manner, the oxidizer is assured of having enough oxygen to support the combustion of VOCs and CO. The newly purified exhaust gas exits the oxidation chamber and is directed through the draft inducer, which simultaneously cools the exhaust air and creates a draft in the combustion chamber by air induction. The cooled exhaust gas exits the draft inducer, is directed through the exhaust stack and discharged to atmosphere.

4 Concentrator System with Thermal Oxidizer The concentrator system offers cost effective technology for industrial applications with high volume, low concentration flows of VOC's. This system can easily achieve flow volume reduction ratios of 1000:1 to as high as 10,000:1, allowing for several highly economical final treatment options. The high volume reduction translates into low capital and operating costs compared with standard concentrator systems, or direct treatment. A proven technology, the systems are currently treating exhaust streams at facilities for semiconductor manufacturing, painting/finishing, and printing. Systems range in size from 200 cfm to over 100,000 cfm with final treatment being either condensation for solvent recovery, or thermal oxidation for VOC destruction. Removal or recovery rates of 95% - 99% are achievable. Because of the high turn-down ratio, these "back end" systems are significantly smaller than stand-alone systems, saving on capital expenditures. The adsorber section of the fluid bed system includes a series of perforated plate adsorption trays. Contaminated process exhaust enters from the bottom, passing upward through the adsorption trays, fluidizing the adsorbent and adsorbing the VOCs. VOC saturated adsorbent flows to the bottom of the adsorber vessel, from which it is removed at a slow, steady rate and transferred to the desorber. Meanwhile, regenerated adsorbent is continuously fed into the top of the adsorber vessel, providing counter-current VOC removal. In the desorber, the temperature of the adsorbent material is increased, causing it to release the VOC contaminants into a low volume, inert carrier gas stream. The cleaned adsorbent material is then returned to the top of the adsorber vessel for reuse. The concentrated contaminant stream is so small that it can often be easily treated with a simple afterburner or recovered for reuse or disposal through condensation. The condensation process is shown below. One key to achieving high performance levels is the beaded activated carbon adsorbent material. The small, spherical "beads" have a high surface area for adsorption and are ideal for treating a wide range of solvents at high or high concentrations. With an attrition rate of less than 1% per year, operating and maintenance costs are extremely low.

5 VALUE ADDED FEATURES OF THE NESTEC SYSTEM Non-Proprietary Design: All NESTEC thermal oxidizers utilize readily available, off the shelf components making it easy to obtain stare parts. Although the systems are designed by NESTEC, Inc, all of the components can be obtained locally. NESTEC Inc will provide drawings on any component should you need to have something fabricated quickly by a locally shop. We won t hold you hostage! Keep It Simple Philosophy: All NESTEC employees have worked for other oxidizer companies where complicated systems were the norm. Our field exposure, working on these systems, enlightened us to taken a different approach - to keeping the design as simple as possible with the fewest number of moving parts without sacrificing performance. NESTEC's systems have achieved this goal. Not only did this simplistic approach work by removing many parts, it also makes them more cost effective, reliable, and easier to maintain. Ground Access: One of the most underrated features, but much appreciated when service is required. All of the major components are located at ground level. No need to climb a ladder with tools in hand this is a real time saver. Inspection Ports: There are several inspection doors located at various points on NESTEC systems. The most notable is the hinged access door with easy opening davits at the burner chamber. It allows for visual of the burner tile, heat recovery media or heat exchanger, and internal insulation. Doors are also located at several other key areas of the oxidizer. RTO Specific Value Added Features: Heated Valves: The poppet valves on the NESTEC, Inc RTO are configured such that the valve blade is always hotter than the incoming air stream. This makes them perfect for applications containing particulate or condensable material, greatly reducing condensate onto the valve which can cause a reduction in destruction efficiency and valve life. Bake-Out Feature: The system acts like a self-cleaning oven to remove any organic material than may get entrained in the heat recovery media. Puff/Pressure Reduction Control Technology: Many RTOs require the addition of extra chambers, valves, fans and motors to eliminate the puff associated with valve switching, but not so with the NESTEC RTO. Through careful engineering, the NESTEC RTO minimizes the size and frequency of the puff before it becomes a problem. This feature also enhances the flow of the process into and out of the unit, thereby reducing pressure fluctuations and increasing performance. Cushioned Valve Stops: The NESTEC RTO uses two vertical, fast acting poppet valves designed and manufactured by NESTEC, Inc. Our valve provides the tightest seal of any RTO valve, always providing high destruction efficiency. The pneumatically operated valve moves very quickly, but does not slam into its seat. Just prior to the valve seating, the cushioned stops engaged, the valve slows down and seals tightly. Maintenance on the valve is extremely low. Fewest moving parts: Less parts = less maintenance: The valves on the NESTEC RTO have the fewest number of components when compared to a three chamber RTO or a rotary (valve less) oxidizer (which could total over 124 internal, hidden parts).