Column with energy input

Figure 6.7-7. Examples of different random packings 6.7.4.4 Columns with energy input...

In countercurrent columns with energy input, pulsation or agitation causes an improvement in the renewal of the droplets and the surface, and hence an improvement in the separation effect, particularly with systems having a large surface tension. 

Countercurrent columns with additional kinetic energy input have found a broad range of industrial applications [42-48]. Examples of extraction towers with energy input are pulsed towers, pulsed packed columns and pulsed perforated-plate towers. A number of units with some form of mechanical agitation are also used (Karr column, Scheibel column, Oldshue-Rushton column, Ktihni column, RZE extractor, RDC and ARD extractor, Graesser contactor). 

Liquid-Column Breakup Because of increased pressure at points of reduced diameter, the liquid column is inherently unstable. As a result, it breaks into small drops with no external energy input. Ideally, it forms a series of uniform drops with the size of the drops set by the fastest-growing wave. This yields a dominant droplet diameter... 

Alatiqi presented (I EC Process Design Dev. 1986, Vol. 25, p. 762) the transfer functions for a 4 X 4 multivariable complex distillation column with sidestream stripper for separating a ternary mixture into three products. There are four controlled variables purities of the three product streams (jCj, x, and Xjij) and a temperature difference AT to rninirnize energy consumptiou There are four manipulated variables reflux R, heat input to the reboiler, heat input to the stripper reboiler Qg, and flow rate of feed to the stripper Lj. The 4x4 matrix of openloop transfer functions relating controlled and manipulated variables is ... 

The bottoms stream from the stripper, substantially free of nonaromatic impurities, is sent to the recovery column (3) where the aromatic product is separated from the solvent. Because of the large difference in boiling point between the solvent and the heaviest aromatic component, this separation is accomplished easily, with minimal energy input. 

A hydrocarbon mixture is distilled, producing a liquid and a vapor stream, each with a known or calculable flow rate and composition. The energy input to the distillation column is provided by condensing saturated steam at a pressure of 15 bar. At what rate must steam be supplied to process 2000 mol/h of the feed mixture ... 

Coupling of a distillation column with a vapor permeation unit, the latter treating the vapor from the top of the column, is shown in Fig. 3.18. The distillation column may have to be operated imder pressure in order to allow the membrane system to be run at a temperature of around 100 °C. The permeate can be recycled to the inlet of the distillation column, which wiU result in nearly 100% recovery of the organic component. The only additional energy input in this scheme for the final dehydration of the predistilled product is that for the condensation of the permeate, as the dehydrated product would have to be con-... 

The other columns in Table 4.3 give results for columns with other total stages. If the number of stages is reduced to 24, which gives a shorter column, reboiler heat input increases. This increases column diameter and heat-exchanger areas. This results in an increase in both capital and energy costs. 

Stripper. Absorber bottoms at 322 K is preheated to 380 K in a heat exchanger using the hot stripper bottoms at 400 K and fed to the top of a stripping column with 10 stages and operating at 2 atm in the column and 1.5 atm in the reflux drum. Reboiler heat input is 54.12 MW to maintain a reflux-drum temperature of 363 K, as suggested by Desideri and Paolucci as a balance between stripper reboiler energy and water losses in the vapor from the reflux dmm. 

---