Liquid feed points

Burghardt et al. (1995) studied, among others, the liquid distribution using needle-type distributors in trickle beds and found that the density of the liquid feed points does have an important effect on the value of the liquid holdup, and thus on the performance of the reactor. They concluded that for a density of more than 5000 feeding points per square meter, the liquid holdup was stabilized. 

At high liquid flow, die hydraulic gradient may become so large that the caps near the liquid feed point will stop bubbling, and the efficiency will... 

Packed Tower.—A conventional countercurrent packed tower is shown Tor comparison. When used Tor flue gas scrubbing, a short section of low-pressure-drop packing (e.g., 3 in. Intalox saddles) is employed with a mist eliminator above the liquid feed point. 

The optimum position of a liquid feed point is where the composition of the feed is the same as that of the liquid leaving the feed tray or, if the feed is a vapour, the vapour leaving the feed tray. 

Another approach is the simulated moving-bed system, which has large-volume appHcations in normal-paraffin separation andpara- s.yXen.e separation. Since its introduction in 1970, the simulated moving-bed system has largely displaced crystallisation ia xylene separations. The unique feature of the system is that, although the bed is fixed, the feed point shifts to simulate a moving bed (see Adsorption,liquid separation). 

Bubble point liquid feed, q = 1.0 (q-line vertical)... 

For columns in which there is a substantial flash of the feed liquid, or in which the feed is a vapor of a different composition than the internal vapor, a collector plate can be installed above the feed point. The purpose of this plate is to provide mixing of the vapor phase in the gas risers so that a more uniform vapor composition enters the rectifying section of the column. 

The condition of the feed as it enters the column has an effect on the number of trays, reflux requirements and heat duties for a given separation. Figure 8-15 illustrates the possible situations, i.e., sub-cooled liquid feed, feed at the boiling point of the column feed tray, part vapor and part liquid, all vapor but not superheated, and superheated vapor. The thermal condition is designated as q, and... 

Reading Figure 8-17 for (L/D)niin assuming a liquid feed at the boiling point, (L/D)niin = 1-2- This demonstrates the value of taking the thermal condition of the feed into account. 

To aid in solving the tedious Underwood equation to ultimately arrive at (L/D)niin, Frank [100] has developed Figure 8-47, which applies for liquid feed at its bubble point and whether the system is binary or multicomponent, but does require that the key components are adjacent. Otherwise, the system must be solved for two values of 0 [74]. To obtain the necessary parameters for Figure 8-47, Frank recommends using the same overhead con-... 

The liquid feed line is known as the submergence limb and the line carrying the aerated mixture as the rising main. The ratio of the submergence (hs) to the total height of rising main above the air injection point (hr + hs) is known as the submergence ratio. + hr/hs)]-K... 

A process liquid is pumped from a storage tank to a distillation column, using a centrifugal pump. The pipeline is 80 mm internal diameter commercial steel pipe, 100 m long. Miscellaneous losses are equivalent to 600 pipe diameters. The storage tank operates at atmospheric pressure and the column at 1.7 bara. The lowest liquid level in the tank will be 1.5 m above the pump inlet, and the feed point to the column is 3 m above the pump inlet. 

The separation of liquid mixtures by distillation depends on differences in volatility between the components. The greater the relative volatilities, the easier the separation. The basic equipment required for continuous distillation is shown in Figure 11.1. Vapour flows up the column and liquid counter-currently down the column. The vapour and liquid are brought into contact on plates, or packing. Part of the condensate from the condenser is returned to the top of the column to provide liquid flow above the feed point (reflux), and part of the liquid from the base of the column is vaporised in the reboiler and returned to provide the vapour flow. 

The precise location of the feed point will affect the number of stages required for a specified separation and the subsequent operation of the column. As a general rule, the feed should enter the column at the point that gives the best match between the feed composition (vapour and liquid if two phases) and the vapour and liquid streams in the column. In practice, it is wise to provide two or three feed-point nozzles located round the predicted feed point to allow for uncertainties in the design calculations and data, and possible changes in the feed composition after start-up. 

Bubble-point calculation, feed (liquid feed)... 

As the liquid and vapour flow-rates and compositions will vary up the column, plate designs should be made above and below the feed point. Only the bottom plate will be designed in detail in this example. 

A distillation column is fed with a mixture of benzene and toluene, in which the mole fraction of benzene is 0.35. The column is to yield a product in which the mole fraction of benzene is 0.95, when working with a reflux ratio of 3.2, and the waste from the column is not to exceed 0.05 mole fraction of benzene. If the plate efficiency is 60 per cent, estimate the number of plates required and the position of the feed point. The relation between the mole fraction of benzene in liquid and in vapour is given by ... 

For an all liquid feed at its boiling-point, r is equal to the ratio of the key components in the feed. Otherwise r/ is the ratio of the key components in the liquid part of the feed, Xfh is the mole fraction of each component in the liquid portion of feed heavier than the heavy key, and a is the volatility of the component relative to the heavy key. 

At any depth below the feed point, the upward liquid velocity must not exceed the settling velocity of the particles. (uc) Where the concentration is C, the required area is therefore given by ... 

In order to calculate the change in composition from one plate to the next, the equilibrium data are used to find the composition of the vapour above the liquid, and the enrichment line to calculate the composition of the liquid on the next plate. This method may then be repeated up the column, using equation 11.37 for sections below the feed point, and equation 11.35 for sections above the feed point. 

Below the feed-point, assuming the feed is liquid at its boiling point then ... 

If the plate efficiency is 60 per cent, estimate the number of plates required and the position of the feed point. The relation between the mole fraction of benzene in liquid and in vapour is given by ... 

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