When do we use partial condenser

You can confirm flooding by measuring exchanger pressure drop while reducing unit capacity. When flooding stops, pressure drop suddenly decreases. Flooded tubes can create many problems, including high pressure drop in the tubes, entrainment of liquid in the vapor outlet, and vibration or other issues from cyclic filling and dumping of liquid from the tubes. Allowing the tubes to extend slightly from the tubesheet and cutting their ends at an angle helps liquid drain from the tubes. The tube extension increases vapor pressure drop entering the tube — but this rarely is significant.

Even with angle-cut tubes, there is a prudent limit to upper vapor velocity entering the tube. So, you should check the actual velocity, V actual , against flooding velocity, V flood , particularly when problems arise. You also need a second correlating factor, F 2 , which is based on the mass flow rates of vapor, G , and liquid, L , in consistent units:. Then, you can calculate a flooding factor, P , to account for the drag force of the gas based on its density and the tendency of surface tension to bridge the tube:.

This allows calculating the flooding velocity, V flood , which is based on a mixed phase mass density at the bottom of the tube:. All the distillation columns considered up to this point in the book have used total condensers, where the distillate product is a liquid. However, many industrial columns have partial condensers in which the distillate product is removed as a vapor stream.

This is commonly employed when there are very light components in the feed to the column that would require a high column pressure or a low condenser temperature to completely condense these very volatile components. The use of a partial condenser can avoid the use of costly refrigeration in the condenser. The control of partial condenser columns is more complex because of the interaction among the pressure, reflux drum level, and tray temperature control loops.

Both pressure and level in the reflux drum need to be controlled, and there are several manipulated variables available. The obvious are reflux flow, distillate flow, and condenser heat removal, but even reboiler heat input can be used. In this section, we explore three alternative control structures for this type of system, under two different design conditions: 1 a high vapor distillate flowrate moderate reflux ratio and 2 a very low vapor distillate flowrate high reflux ratio.

As the dynamic simulation results will show, the preferred control structure depends on the control objectives of the entire process. A reflux apparatus allows for facile heating of a solution, but without the loss of solvent that would result from heating in an open vessel. In a reflux setup, solvent vapors are trapped by the condenser, and the concentration of reactants remains constant throughout the process. A condenser is a vessel or stage which turns a vapor into a liquid.

A compressor is used to pump that vapor to a condenser, where the vapor turns back into a liquid, ready for reuse. Total condenser condenses all the vapors. Some of liquid is diverted back into column as reflux and rest is obtained as final product. So the main purpose of using total condenser is to condense all the vapors from top of the column.

There are three main types: air-cooled, evaporative, and water-cooled condensers. Skip to content Helpful tips. March 27, Joe Ford.