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Despatch VOC Thermal Oxidizer
Despatch’s patent-pending VOC Thermal Oxidizer is a point of generation abatement system designed to eliminate over 99% of Volatile Organic Compounds (VOCs) from gasses exhausted during the drying step of solar cell manufacturing with virtually no maintenance. The solar cell manufacturing process creates unwanted environmental pollutants which are byproducts of the drying process and contain the nonmetallic ingredients found in the paste material, such as ethanol, Texanol™ and Terpineol. These pollutants can condense inside facility ductwork and create hazardous conditions. Destroying the VOCs using the Oxidizer eliminates the need to collect and dispose of this waste in a separate process. Despatch’s Thermal Oxidizer attaches directly to the furnace, removing any chance of condensation. VOCs are incinerated, releasing only small amounts of CO2 and water. This solution meets legal and environmental requirements regarding the capture and destruction of organic materials.
DESCRIPTION
Despatch patent-pending VOC Thermal Oxidizers mount directly to each end of the dryer chamber. This connection eliminates any risk of condensation and allows the system to be maintenance free. By locating a VOC Thermal Oxidizer at the entrance and exit of the dryer, operators are able to achieve more effective abatement with faster belt speeds. Functionally, the VOC Oxidizer is comprised of three components: a heating element, an exhaust venturi and a facility hood connection. During the oxidation process, solvent-laden air is drawn from the furnace by a natural chimney effect and assisted by the venturi. The mixture then enters the heating element – a heater comprised of a framed array of open heating coils, extending through multiple levels. VOCs are heated and combusted in this section. Operating temperature of the Oxidizer is 760-800°C. The CO2 and H2O exit the heater array via the venturi-assisted exhaust and move into the exhaust hood. The exhaust hood connects to the main facility exhaust and contains a pressure switch to ensure that the hot exhaust does not enter the ambient atmosphere. At elevated temperatures, certain organic compounds will react with oxygen (i.e. combust or oxidize) and produce only CO2 and H2O. Ethanol, for example, in the presence of oxygen will automatically ignite at 425°C and will react according to the equation: 1 CH3CH2OH + 3 O2 ----> 2 CO2 + 3 H2O Although thermal destruction of most organic compounds takes place at 350°C to 450°C, thermal oxidizers typically maintain a temperature of 760°C (1400°F) to ensure destruction of all VOCs. The oxidation process releases heat and thereby contributes to maintaining the temperature of the oxidizer. Destruction of VOCs is determined by a time/temperature relationship. Time in the destructive environment is determined by the design of the path through the heater/destruction chamber and the expected volume of gas. Temperature is monitored to ensure the destruction temperature is maintained. Proper temperature and airflow is actively monitored to maximize performance and guarantee safety.
BENEFITS
During solar cell manufacturing, the pastes used in the metallization process generate harmful byproducts containing VOCs that vaporize into the atmosphere, entering the air we breathe. Due to their classification as environmental pollutants, strict legal restrictions for handling and disposal apply. Issues with incinerators and condensers: Incinerators (also known as Oxidizers or Scrubbers) are usually larger in size and configured to handle the effluent of multiple machines or lines and as a result are remotely located near the ceiling or on the facility rooftop. While remote incinerators may meet legal emissions requirements, solvents can condense inside facility ductwork before reaching the system, creating issues with hazardous waste, odor and cleaning. VOC condensers cool exhaust to the point where the contaminants change into a liquid state (condense) and are separated from the exhausted gas flow to be collected. Condensers are located closer to the point of origination of the solvents, but are not completely effective, so there is a solvent condensation risk both before and after the active condensing coil. Primary problems with these abatement methods include the condensing of the VOCs in facility ductwork prior to the condenser or incinerator, which creates maintenance issues and hazardous conditions. The condensing of VOC’s in undesirable locations can result in: •Clogging of facility ductwork •Dripping of condensate back into the dryer •A fire hazard due to contaminated ductwork •Significant maintenance to keep the ductwork clean and safe •Exposure risk to handling of hazardous material •Hazardous waste disposal fees •Odor •Reduced uptime due to high level of cleaning maintenance Despatch patent-pending VOC Thermal Oxidizers mount directly to each end of the dryer chamber. This connection eliminates any risk of condensation and allows the system to be maintenance-free. By locating a VOC Thermal Oxidizer at the entrance and exit of the dryer, operators are able to achieve more effective abatement with faster belt speeds. Additional features include: •The VOC Oxidizer is capable of abatement of up to 352.5 Kg (84.5 gallons) of Volatile Organic Compounds on each 1200 wph line (when back side aluminum processed last). •Costs related to proper disposal of hazardous VOCs are completely eliminated. •A 53% reduction in annual cost can be realized when a VOC Oxidizer is employed in place of a local condenser.
INNOVATIVE ASPECT
Despatch’s VOC Thermal Oxidizer eliminates over 99% of Volatile Organic Compounds (VOCs) from gasses exhausted during the drying step of solar cell manufacturing with virtually no maintenance. The Despatch VOC Thermal Oxidizer is unique in the following ways: 1. It is located at the point of generation. Its location immediately at the dryer exit prevents fouling of ductwork that needs to be cleaned and can become a hazard. 2. Unlike other oxidizers/incinerators, there are no moving parts to fail. 3. Unlike other oxidizers/incinerators, it does not require a combustible gas. 4. It is designed to be facility-friendly. The air exiting the Oxidizer is diluted with room air to allow utilization of standard ductwork. 5. Runs off of electric furnace power, therefore no separate power drop is necessary.
