AP C2G2 C1007520FpG1p

Figure 5 presents a family of pressure drop-lines at constant liquid flow as a function of the vapour flow. The constant liquid rate lines start parallel to the

Figure 5 Bed AP vs. rates. (Permission from Gulf Publishing Company.)

dry-column line (which is a function of the drag only). Equation [3] allows calculation of the packing factor, Fp, by measuring the slope of the dry-packing pressure-drop data. As the vapour rate increases, the slope of the constant liquid rate lines increase; this increase is also proportional to the liquid rate. The initial departure from the dry-line slope indicates interaction between the vapour and liquid, and represents a loading point. Efficient mass-transfer operations can be achieved only above the loading

Table 2 Packing selection guidelines (trays included as a reference)

Application in distillation

Random packing

Structured packing

Traditional trays

High-capacity trays

Pressure drop/theoretical stage

2

1

3

3

Maximum capacitya

2

1

3

2

Efficiency at high pressure

2

4

2

1

Efficiency at low pressure

2

1

2

3

Efficiency at low liquid ratec

2

1

3

4

Efficiency at high liquid rated

3

4

2

1

Low residence time

2

1

4

4

High residence time

3

4

1

1

Heat transfer

2

1

2

2

Foaming systems

2

2

3

3

Non-metallic services^

1

2

4

4

Fouling systems

4f

2f

1e

1e

Efficiency in high 3 systems

2

4

1

1

Inspection and maintenance

3

4

1

1

Low cost

2

4

1

3

Application rating: 1, best; 2, good; 3, fair; 4, poor. aEfficiency may be reduced at high capacities.

bAs may be required based on corrosion protection considerations, such as ceramic. cSystems below 5 gallons min- fT2. dSystems over 15 gallons min- ft~2.

"Applies to sieve trays, specially dual-flow, not to valve trays.

It would require a fouling-resistant distributor, which may result in reduced efficiency.

point. For any given liquid rate, as the vapour rate further increases, the pressure-drop line slope increases rapidly until the line becomes near vertical. At this point the flow and AP are unstable, and the bed is flooded; the vapour flow does not allow the liquid to flow down the bed and there is massive entrainment of liquid in the vapour phase and mass transfer is no longer viable.

For most packings, bed flooding occurs between 1 and 2 inches of water-pressure drop per foot of packing. Pressure drop at flooding seems to be a function of the packing size. Kister cited Zenz and later Strigle and Rukovena observations indicating that flooding (APfl) is higher for smaller size packings, and proposed a correlation to determine the pressure drop at flooding as a function of the packing factor.

We also obtained by regression from data published by Strigle:

led antifoam injection is known to aggravate foaming problems. Filtration of liquids and adsorption of contaminants on activated carbon has proven valuable to control foaming in some systems such as amines.

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Solar Panel Basics

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