Flash Distillation

Question 1

How many phases should you have leaving the heater to enter the flash drum?

Answer 1

Two

Question 2

Having a demister effects what of a flash drum?

Answer 2

size

Question 3

You need space for what to leave the liquid phase before they reach the pump

Answer 3

bubbles

Question 4

What is the purpose of a deflector?

Answer 4

To break up turbulent flow and make sure no drops spray up

Question 5

What is a disadvantage to deflectors?

Answer 5

They can force bubbles into the liquid possibly leading to entrainment

Question 6

What is the cap size of drops?

Answer 6

200 microns

Question 7

What is the average percentage of liquid that goes into the vapor without a demister?

Answer 7

5%

Question 8

Using mesh is common because it is what?

Answer 8

Cheaper than using a vane

Question 9

Weeping occurs from the what?

Answer 9

Demister

Question 10

Simulator allows for a fixed what?

Answer 10

temperature (heat duty)

Question 11

Always use what kind of device in simulation?

Answer 11

adiabatic

Question 12

The thickness of the walls depend on what?

Answer 12

diameter and pressure

Question 13

When designing a flash drum one should consider what clearance for transporting materials to the factory site?

Answer 13

bridge

Question 14

What is the formula for total height of the flash drum?

Answer 14

hT=hv+hf+hL

Question 15

You should have the liquid and vapor flow rates and the density and temperature set before you calculate for what?

Answer 15

Flash drum design

Question 16

Which equation do you used to find vapor and liquid fractions?

Answer 16

Ratchford Rice Equation

Question 17

The diameter of a flash drum is related to what?

Answer 17

vapor velocity

Question 18

The height of the vapor is related to what?

Answer 18

vapor velocity

Question 19

The height of the liquid is related to what?

Answer 19

level control (usually not always)

Question 20

The height of the feed inlet is related to what?

Answer 20

flooding

Question 21

The force of viscosity depends on what equation?

Answer 21

Stokes

Question 22

How does the viscosity force impact a flash drum?

Answer 22

Force that prevents a drop from falling

Question 23

What causes drag force?

Answer 23

The kinetic energy of vapor going up

Question 24

The gravity force is often grouped with what force?

Answer 24

Buoyancy

Question 25

F drag is equal to what?

Answer 25

F of gravity and buoyancy

Question 26

In the dimensional analysis for drag, force is dependent on what 4 things?

Answer 26

velocity, cross sectional area, density, and viscosity

Question 27

What are two important nondimensional numbers required?

Answer 27

Re, Cd

Question 28

Cd is a function of what?

Answer 28

Particle Reynolds Number

Question 29

What Rd, drop radius should be used?

Answer 29

can find with an expected distribution of drop size chart that plots vapor velocity to droplet diameter

Question 30

What order to you solve equations to find the height of a flash drum?

Answer 30

Solve for K Solve for D Solve for H

Question 31

If a demister is present what does K equal?

Answer 31

0.15

Question 32

hL can be find either by knowing the volume of the pool or approximating that residence time is what value?

Answer 32

2 min

Question 33

If L/D < 3 what should you do?

Answer 33

increase V pool

Question 34

If L/D > 5 what should you do?

Answer 34

use a horizontal drum

Question 35

The feed that is separated by distillation is not necessarily what?

Answer 35

pure

Question 36

Why dont we use heat integrated distillation columns?

Answer 36

not significant difference and difficult to control, also we are a conservative industry

Question 37

In petrolium fractionation the feed furnace does not go over what temperature?

Answer 37

650 F

Question 38

A three component separation needs how many columns?

Answer 38

2

Question 39

If you have 4 components how many components can be separated at a time?

Answer 39

1

Question 40

What is the difference between a direct and indirect sequence of distillation columns?

Answer 40

direct, the bottom feed flows to the second column | indirect, the top feed flows to the second column

Question 41

When do we use pressure swing distillation

Answer 41

to break azeotropes

Question 42

In double effect we go from a low pressure column to a high pressure column and then the vapor from the hig pressure column is used to heat the reboiler for the low pressure column. True or False?

Answer 42

True

Question 43

When is double effect used?

Answer 43

In C3 splitting

Question 44

Absorbers and strippers typically remove what?

Answer 44

CO2 and H2S

Question 45

CO2 dissolves into what to form carbonic acid?

Answer 45

water

Question 46

The stripper and absorber are operated at the same what?

Answer 46

pressure

Question 47

What is better than water at stripping?

Answer 47

Monethanol amines glycols

Question 48

What do you have to worry about in absorber stripper arrangements?

Answer 48

SOx (SO2 or SO3)

Question 49

What are problems with working with absorbers and strippers?

Answer 49

``` Mercury volatile compounds cancer promoting volatiles IOC incenerator money matters ```

Question 50

What is expensive in absorbtion/stripping?

Answer 50

solvent

Question 51

Never do what? It won't work most of the time

Answer 51

blindly try specs and number of trays

Question 52

If you have many components what should you do in distillation absorption?

Answer 52

Start with a few of the most abundant components

Question 53

Where should you put your components first?

Answer 53

Adiabatic flash

Question 54

Use an isothermal flash when?

Answer 54

the feed is not two phase at the desired pressure and then change the temperature until you get some separation in the direction you want

Question 55

List your components in increasing what and determine key compounds

Answer 55

boiling point

Question 56

Light key goes mostly where?

Answer 56

to the top

Question 57

Heavy key goes mostly where?

Answer 57

to the bottom

Question 58

After trying a flash what should you try?

Answer 58

Replacing the flash by a three plate column with similar specs as those given by the flash outlet streams

Question 59

Once you have a three plate column what should you do?

Answer 59

Add the compounds that are missing. Do it slowly, increasing their concentration until you reach the desired values

Question 60

What is the last thing you should do when you know nothing, not even the number of trays needed?

Answer 60

keep tightening the specs and increasing the number of plates accordingly so that you meet the separation you want.

Question 61

What direction does a bubble cap tray force vapor?

Answer 61

up then down then up and out

Question 62

What direction does a valve tray force vapor?

Answer 62

Up and out

Question 63

What are some examples of distillation trays?

Answer 63

Sieve Valve Bubble cap Specialized

Question 64

What are some operational limits for trays?

Answer 64

Vapor going up the downcomer (high entrainment) weeping downcomer flooding (phase maldistribution) flooding

Question 65

What are the extremes of entrainment?

Answer 65

dumping and blowing

Question 66

Blowing occurs if what gets too high?

Answer 66

vapor velocity

Question 67

If the vapor velocity gets too low what can happen?

Answer 67

dumping

Question 68

What increases as liquid flow increases?

Answer 68

the potential for downcomer flooding

Question 69

Flooding is more likely as what increases?

Answer 69

vapor velocity

Question 70

Weeping is likely to happen if what is too low?

Answer 70

vapor velocity

Question 71

the design point of column tray design should be what percentage away from the top line

Answer 71

80%

Question 72

The design point falls along what line?

Answer 72

The line produced at constant L/V

Question 73

Use what percent of flooding velocity?

Answer 73

80%

Question 74

The diameter of the tray holes is a function of what?

Answer 74

the Net area An

Question 75

What is the first think to consider with the tray design?

Answer 75

diameter of hole

Question 76

How do you find net area?

Answer 76

Qv/(0.8*Un,f)

Question 77

How do you find the area needed to calculate the diameter?

Answer 77

A=An/0.8

Question 78

Once you have A how do you find the diameter?

Answer 78

D=sqrt(4A/pi)