Monthly Archives for June 2013
Dead Band in Process Control
The range through which an input signal can be varied, upon reversal of direction, without initiating an observable change in the output signal. Dead band is the name given to a general phenomenon that can apply to any device. For … Continue reading
Vapor-Liquid Equilibria
What we know about vapor-liquid equilibria is mainly based on experimental data. There are of course predictive methods, but they are based on the results of measurements for the determination of the parameters they involve and the control of their … Continue reading
Membrane Separations
Membrane separation operations are still seldom used in refining today. The potential applications of the different ultrafiltration, pervaporation and gaseous permeation technologies are described in the other section. Since selectivity is kinetic, a membrane separation module separates a mixture into … Continue reading
Fixed Bed Adsorption Operations
In an adsorption operation the movement of the solid phase gives rise to serious problems (solid phase displacement devices, mechanical resistance of the adsorbent, etc.). As a result, the adsorbent is generally implemented in a fixed bed. The adsorption-desorption operation … Continue reading
Thermodynamic Equilibrium and Kinetic Factors
Table 1.1 shows that the most common separation operations are based on equilibrium selectivity, also termed thermodynamic selectivity. This selectivity is due to the fact that at thermodynamic equilibrium, the distribution of the component(s) to be separated out is different … Continue reading
Membrane Separation
Separation can also be based on kinetic selectivity, i.e. on a difference in migration velocity of the relevant components. This principle is used in a membrane separation operation as represented schematically in Figure 1.5 for a binary mixture of two … Continue reading
Equilibrium Based Separation
Separation operations based on equilibrium selectivity can be classified according to the separating agent that is used (matter or energy) and the nature of the phases in contact: Distillation is the most commonly used basic operation. The feed is normally … Continue reading
Function of Separation Operations in Refining
A crude oil is made up of a complex mixture of a very large number of components, most of which are hydrocarbons. In order to get petroleum products that meet given specifications, it is first necessary to separate out the … Continue reading
Differential Pressure in Distillation Tower
The tower differential pressure is the difference between the pressures at the bottom of the tower and the pressures at top of the tower. This difference in pressure is caused by the flow of vapor in the tower. Without vapor … Continue reading
Temperature Control in Distillation Tower
The temperature decreases as the material move higher in the tower. The gradual decrease in temperature from the bottom of the distillation tower to the top is called the temperature gradient. The temperature gradient is measured in term of difference … Continue reading