Central Exhaust Duct
CED
The CED • Central Exhaust Duct is a critical component in a Volatile Organic Compound (VOC) abatement system. Its primary function is to collect and convey the Solvent-Laden Air (SLA) from various emission points within an industrial facility to the VOC abatement unit.
Critical Role in System Efficiency • CED
The CED's performance directly impacts the overall effectiveness and efficiency of the entire VOC abatement operation. Its design and construction are essential for several reasons:
Efficient Collection: the ductwork must be correctly sized and installed to ensure adequate suction and capture velocity at every emission point. If the air volume or velocity is too low, fugitive emissions can escape, rendering the abatement system partially ineffective;
Leakage and Dilution: uncontrolled leakage poses a threat. The system's negative pressure draws surrounding fresh air into the duct. This influx significantly dilutes the solvent concentration, which can negatively impact the thermal efficiency or destruction rate of the downstream abatement technology and unnecessarily increase the system's operational fuel costs;
Pressure Drop and Energy Costs: excessive pressure drop is a measure of the frictional resistance to airflow within the ductwork. High pressure drop forces the system's fans to work harder, demanding significantly more power and thus increasing energy consumption and overall operational costs (OpEx). Minimizing pressure drop is key to maximizing the system's energy efficiency;
Uniform Delivery: the CED often helps to mix the various solvent-laden streams (acting as a plenum), providing a relatively uniform concentration of VOCs and a steady flow rate to the abatement unit. This uniformity is crucial for the abatement equipment to operate within its optimal design parameters, maximizing abatement efficiency.
Design Considerations • CED
Due to the nature of the air it conveys, which can be corrosive, high-temperature, or contain particulates, the CED requires specific engineering considerations:
Material Selection
The materials used for the CED must be carefully selected based on the specific chemicals and conditions of the SLA. Common materials include:
Galvanized or Carbon Steel: suitable for non-corrosive, lower-temperature applications.
Stainless Steel (304 or 316): often necessary when dealing with corrosive solvents or extra-low or higher temperatures.
FRP (Fiberglass Reinforced Plastic): used in highly corrosive environments where metal would quickly degrade.
Airflow Dynamics • CED
The ductwork must be sized using precise airflow calculations to maintain the necessary transport velocity for any particulates present and ensure consistent velocity head across all branches. Poor airflow design can lead to:
Settling: heavy particulates can drop out and accumulate within the ductwork, requiring frequent and costly cleanouts and potentially restricting flow.
Imbalance: unequal airflow distribution, meaning some emission sources are under-captured while others are over-captured, wasting energy.
Safety and Access • CED
The CED must incorporate safety features such as explosion panels or dampers where combustible solvent concentrations are possible. Furthermore, adequate access ports may be engineered for future internal inspection, cleaning, and maintenance, ensuring the long-term integrity and functionality of the conveyance system.
Contact DEC!
For more information on DEC's VOC sustainable emission control solutions, interfaced with CED • Central Exhaust Duct, please contact DEC.
