Tip of the Week
Stop by each week for a useful tip from the engineers at Koch-Glitsch.

Tip of the Week graphic

April 2010
Will reducing the operating pressure of your column increase the capacity?
by Eric Cole
 
Yes ..... and No.  Reducing the operating pressure of a column increases the relative volatility but decreases the vapor density. 
 
For the same feedstock and products, increasing the relative volatility will reduce the required reflux and boil-up rates. However, at the same actual vapor rates, the decreased gas density means less mass will be produced.  It is system dependent as to which of these two properties is dominant.  In some cases, a reduced operating pressure will result in higher product rates, but it can also result in lower product rates.
 
 
 
Internal vs. external reflux
by Pamela Tokerud
 
“External reflux” is the measured liquid flow to the top of a distillation column. 
 
“Internal reflux” is the unmeasured liquid flow leaving the top equilibrium stage. 
 
The purity of the top product is more a function of the internal, rather than the external, reflux rate.
 
 
 
Isolating inlet activity in
horizontal liquid-liquid coalescers
by Sam L. Mitchell

Introducing liquid-liquid coalescing media into an empty drum can dramatically increase removal efficiency of one phase from another.  However, it is equally important to provide an optimal environment for the new media installation to perform the separation. 
 
The size and type of device on the two or three phase inlet should be addressed first, insuring inlet velocity and orientation of flow allows for the smoothest transition possible into the bulk current of the drum.
 
 
 
Verify demethanizer surface tensions to
produce correct hydraulic designs
by John Einwich
 
The fluid properties in demethanizers present several challenges when designing  distillation equipment for optimum performance: 
  • Some demethanizers can employ as many as six feeds, as well as a “hip” reboiler. 
  • The presence of hydrogen in the feed, especially near the top of the column, can easily create thermodynamic and simulator convergence problems.
  • In terms of equipment hydraulics, the vapor densities in demethanizers are extremely high.  Density differences and surface tensions are extremely low.
 
Therefore, some hydraulic rating methodologies that key on surface tension must be closely monitored.
 
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