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CHEN 4470 – Process Design Practice

Distillation Modeling. CHEN 4470 – Process Design Practice Dr. Mario Richard Eden Department of Chemical Engineering Auburn University Lecture No. 13 – Design of Overhead Condensers and Air-cooled HX February 16, 2012 Material Developed by Dr. Jeffrey R. Seay, University of Kentucky - Paducah.

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CHEN 4470 – Process Design Practice

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  1. Distillation Modeling CHEN 4470 – Process Design Practice Dr. Mario Richard EdenDepartment of Chemical EngineeringAuburn University Lecture No. 13 – Design of Overhead Condensers and Air-cooled HX February 16, 2012 Material Developed by Dr. Jeffrey R. Seay, University of Kentucky - Paducah

  2. Overview • Purpose of Overhead Condensers • Provide reflux flow to the top of a column and acts as an additional theoretical stage above the trays/packing • Types of Condensers • Knock-back reflux • Total condenser • Partial condenser Proper condenser design is critical to the optimum operation of a column!

  3. Knock-Back Condenser • This design is easy to operate, but difficult to achieve precise control. • Condenser will be larger due to the bi-directional traffic on the process side. • Condenser can be in the vertical or horizontal position. • Elevation is critical. 2-Phase Flow Region • Horizontal – Process on the shell side. • Vertical – Process is on the tube side.

  4. Partial Condenser Vapor Distillate • Used when vapor product is required, or if non-condensible gases are present in the overhead product. • Controlling the vapor stream split can be challenging. • Condenser can be in the vertical or horizontal position. • Horizontal – Process on the shell side. • Vertical – Process is on the tube side. • Elevation is not critical. Liquid Distillate

  5. Total Condenser • Total condensers are used when no non-condensable gases are present. • As with other condensers, vertical or horizontal operation is possible. • Elevation is not critical for a total condenser. • Subcooling of the reflux can be a problem with overhead condensers, especially with vertical designs. Liquid Distillate

  6. Condenser Design • Considerations • The overhead condenser is often a critical part of the control concept of a column • Because distillation is based on VLE principles, the overhead condenser can be used to control the temperature and pressure in the column • A later lecture will present some control concepts and strategies for overhead condensers • Condensers in series can also be used to optimize utility consumption

  7. Condensers in ASPEN Plus

  8. Air-Cooled Heat Exchangers • Typical Air-Cooled Condenser Tube Detail Design Equations: Air-cooled HX are primarily used when no other cooling utilities are available on site Note: The surface area, A, includes the area of the fins! C and m are parameters based on the size of the fin.

  9. Air-Cooled HX Design • Design Considerations • Natural convection in turndown cases • Changing ambient air conditions • Effect of precipitation on operation of unit • Possibility of water-hammer inside tubes • Possible Control Parameters • Air flow across the tube bank • Position of louvers on top of the unit • Liquid level inside the tubes

  10. Other Business • Next Lecture – February 21 • Equipment sizing and pinch analysis

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