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Optimisation & Design
Challenges of splash baffles:
• Placement sensitivity: Improper positioning can restrict flow or reduce effectiveness, requiring careful design to avoid interference with the tube bundle.
• Potential fouling: Poorly designed baffles may accumulate debris over time, necessitating periodic maintenance.
• Limited fine droplet capture: Splash baffles are less effective at removing smaller mist particles, which may still escape with the vapor.
Applications Splash baffles are commonly used in kettle-type heat exchangers in industries such as oil and gas, where bulk liquid separation is sufficient to maintain system performance. Their simplicity makes them suitable for processes prioritizing low cost and minimal pressure drop.
Demisters: Functionality and applications
How demisters work Demisters, or mist eliminators, are specialized devices installed at the gas outlet of heat exchangers or separators to capture fine liquid droplets. They operate through three primary mechanisms:
• Inertial Impaction: Heavier droplets impact and adhere to surfaces( e. g., wires or vanes) due to their momentum.
• Interception: Droplets are captured when they pass close to solid surfaces within the demister.
• Brownian Diffusion: Very small droplets(< 1 micron) are removed through random motion, though this is less significant in industrial settings.
Captured droplets coalesce into larger drops, which drain back into the liquid phase due to gravity. Demisters are typically constructed as wire mesh pads, vane-type separators, or fiber beds, each suited to specific droplet sizes and process conditions.
Figure 2. Diagram of a perforated triangular splash baffle in a kettle-type heat exchanger, showing vapor passing through perforations and liquid collecting in the pool below.
Challenges of demisters:
• Pressure drop: The resistance to vapor flow can reduce system efficiency, particularly in highvelocity applications.
• Maintenance needs: Mesh-type demisters require regular cleaning or replacement to prevent clogging, especially in fouling-prone environments.
• Higher initial cost: Compared to splash baffles, demisters involve more complex designs and materials, increasing upfront costs.
Applications Demisters are indispensable in chemical plants for recovering valuable solvents, preventing downstream contamination, and controlling emissions. They are also used in refining of hydrocarbon separation, in food processing for steam stripping, and in environmental applications for capturing acid or oil mists.
Types of demisters:
• Wire mesh demisters: Made of knitted stainless steel or plastic, these are cost-effective and suitable for droplets larger than 5 microns. They offer low pressure drop and are widely used in chemical processing.
• Vane-type demisters: Featuring parallel plates with zigzag paths, these are ideal for larger droplets(> 8 – 10 microns) and high-capacity operations, particularly in fouling-prone services.
• Fiber bed demisters: Composed of densely packed fibers, these capture very fine mists( 0.1 – 3 microns) and are used in aerosol collection and pollution control.
Advantages of demisters:
• High separation efficiency: Demisters excel at capturing fine droplets, ensuring high vapor purity for stringent applications.
• Versatile applications: They are used across industries, including petrochemicals, refining, and air pollution control, for processes requiring minimal liquid carryover.
• Robust design options: Different types cater to diverse droplet sizes and operating conditions, offering flexibility in system design.
Figure 3: Schematic of a Vane-Type demister in a separator, capturing fine liquid droplets to ensure high vapor purity. www. heat-exchanger-world. com Heat Exchanger World July 2025
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