ch15 distillation review

Water boils at?

212 degrees F, 100 degrees C

Ternary Mixture -

3 components in a mixture.

Distillation columns can have how many feed lines?

3 or more feed lines.

Water changes from a solid to a liquid at?

32 degrees F, 0 degrees C

Problem in a distillation column include:

Feed composition changes, puking, flooding, and equipment or instrumentation failure.

Stacked packing -

Is uniformly arranged inside a distillation column.

What does the overhead outlet do?

It is the vapor exit point for vapor in the distillation column. Also allows hot vapors to pass through into the condenser.

What is done with condensed liquid from the overhead system?

It is used as reflux or sent to the tank farm as product.

In a binary mixture (2 component mixture) where the major component is water, __________ or ________ __________ of steam is a sustainable alternative to using a reboiler.

Open, Direct Injection.

Overloading-

Operating a column at maximum conditions.

Reboilers are used for what?

Restore heat balance and add additional heat for the separation process.

It is easier and cheaper to do what in a distillation column?

Run the tower on total reflux than to shut it down and then restart it.

Feed system is designed to do what?

Safely store, blend , and transport raw feed stock.

Sensible heat. can be...

Sensed and measured.

The heat that produces state changes consists of...

Sensible and latent heat.

Plate columns are not as ________ to liquid feed distribution as packed columns are.

Sensitive.

Vacuum distillation is used to safely do what?

Separate azeotropic mixtures.

Fractional Distillation

Separation of 2 or more components through distillation.

Flooding causes what in a column?

Severe pressure differences between sections in the column.

Sieve Tray -

Simplest type of tray. A metal plate with holes in it. The holes range from 1 inch - 1/8 th inch in diameter.

Vacuum towers are an excellent option in what situation?

Situation that require high temperatures.

What has the lowest boiling point?

Smaller and lighter components in a tower.

What is the section of the tower located directly below the feed tray called?

Stripping section.

Kettle Reboilers do what?

Take suction off the bottom of the column and heat it up until a part of it vaporizes and is sent back to the column. The liquid that does not vaporize is sent to another system for further processing.

Feed system is composed of what?

Tanks, pipes, valves, instrumentation, and pumps.

Vapor Pressure -

The outward force exerted by the molecules suspended in vapor state above a liquid at a given temperature; when the rate of liquefaction is equal to the rate of vaporization (equilibrium).

Entrainment

The upward movement of high-velocity, large-vapor droplets in a distillation column.

3 distinct operations are?

Batch, continuous batch, and fractional distillation.

Stripping section is located where?

Below the feed tray.

Feed inlets located where?

Between the rectifying and stripping section.

Substance has a low vapor pressure, it has a high ___________ _____________.

Boiling Point.

Flow leaves the tower through one of three paths:

Bottom, sidestream, or top.

Bubble-cap trays -

Bubble cap tops on top of risers that rise when the vapor pressure increases.

The top of the riser usually has what attached to it?

Bubble-cap or valve attached.

Name 3 types of trays found in a distillation plate column.

Bubble-cap tray, sieve tray, valve tray.

Heat balance is maintained inside a packed column with one or more of the following systems:

-Kettle or thermosyphon reboiler system -Direct injection of steam -Electric heaters on the column -Steam tracing on the column -Furnace system

Packed columns are designed for pressure drops between ________ and __________ inch of water per foot of packing.

0.20, 0.60

What 6 conditions can effect the temperature in a distillation column?

1. Pressure 2. Flow rate 3. Fluid levels 4. Feed composition 5. Reflux rate 6. Equipment problems

What does open or direct injection allow?

100 % conversion of Btus into the liquid and helps reduce effective partial pressure of different components.

At sea level atmospheric pressure equals what?

14.7 psi

what is a thermosyphon reboiler?

A fixed head, single-pass heat exchanger hooker up on the side of a tower to add additional heat to the process.

Sieve Tray -

A flat, thin plate with small holes in it mounted on a horizontal tray designed to enhance vapor-liquid contact in a plate column.

Feed Distributor

A device used in a packed distillation column to evenly distribute the liquid feed.

Packed Tower-

A distillation column (tower) that is filled with specialized packing material instead of trays.

Bubble-cap Trays

A fixed cylindrical tube (riser) and cap mounted vertically to a horizontal tray designed to enhance vapor-liquid contact in a plate column.

Total Condenser -

A heat exchanger that is used to convert the entire overhead vapor to liquid.

The rectifying section of a tower has what?

A higher concentration of light components than the stripping section has, so it is said to be enriched.

Total Reflux -

A process where the feed to the column is stopped and the total amount leaving the column from the top, sides, or bottom is returned to the column.

What can be used to heat a packed distillation column?

A series of electric plate heaters.

Feed preheater is usually what?

A shell. and tube heat. exchanger or a fired furnace.

Valve Trays -

A small round metal disc with 3 or 4 legs called risers that allow the valve to lift as hot vapors push through the horizontal trays. Designed to enhance vapor-liquid contact in a plate column.

What is a thermosyphon reboiler?

A vertical, shell and tube heat exchanger mounted near the bottom of the column. Steam us used to reheat the bottom product.

Rectifying section if located where?

Above the feed tray.

The system pressure in the accumulator and the liquid feed temperature, combined with the liquid height above the reflux pump provide what?

Adequate pressure to the suction side of the pump.

As heat transfers to a liquid, the molecules begin to speed up and move farther _______ and the liquid _______.

Apart, Expands.

Partial Condensers -

Are designed to return all of the condensed liquid back to the top tray of the tower and to function as an external top tray for the tower.

Condensers are located where?

At the top of most distillation column.

What does heating the feed do?

Avoids thermal shock and matches the temperature set point of the feed tray.

Boil-up Rate

Balance of the products (vapor and liquid) returned to the column from the kettle reboiler.

How does vacuum effect molecules?

Causes them to move apart.

What is one of the most common methods of troubleshooting?

Check the difference between the set point and the process variable.

Liquids are composed with molecules ___________ together than the molecules of gases.

Closer.

"Warm end process" consist of this equipment:

Compressor, piping, valves, receiver, chiller, instrumentation, filter, and redundant absorber drums.

DCS(distributed control system) -

Computer-automated system used to operate process equipment from a remote location.

Reflux-

Condensed distillation column product that. is pumped back to increase product purity and control temperature.

As hot vapors exit the top of the column, a __________ is used to partially or totally condense the vapors.

Condenser.

Binary Mixture

Contains two or more components.

Steam tracing uses?

Copper tubing that can easily be wrapped around the outside of a distillation column and insulated.

What is it called when vapor flows up the column and liquid falls down the column?

Counter current.

Explain how to break a flood on a distillation column.

Decrease feed rate, decrease reflux rate, or decrease the bottoms temperature.

How do technicians typically break a flood?

Decreasing the feed rate, reflux rate, or the bottom temperature.

Bottoms System -

Designed to allow liquids to boil and roll freely.

Equilibrium curves are used to?

Determine the vapor composition above a boiling liquid and how one mixture differs from another. The larger the difference between boiling points, the easier it is to separate the fraction by boiling point.

Tray Columns ( Plate Columns) -

Devices located on a tray in a column that allow vapors to come into contact with condensed liquids; 3 basic designs are bubble-cap, sieve, and valve.

The upper rectifying trays, middle feed tray, and lower stripping trays have what?

Different temperatures and different products on them.

Downcomers -

Directional devices integrated into the tray design to funnel liquid from upper trays to lower trays in a distillation column.

The reflux pump is designed to do what?

Discharge product to storage and to the top tray of the column.

Packed distillation columns use liquid distributors to do what?

Disperse fluid evenly over the top of the packing. (located under the reflux line)

Condensate also known as.

Distillate.

2 most complex operating areas?

Distillation and Reactor technology.

What involves boiling liquids and condensing the vapors?

Distillation.

Downcomers

Downspouts that allow liquid to drop down to lower trays in a column.

Kettle reboils do what?

Draw feed from the bottom section of the column by gravity flow.

Jet flooding -

Excess vapor flow up column and prevents fluid flow down column.

Local Flooding

Excessive liquid flowing down a column blocks vapor flow up the column in one section.

Having to add pressure to a distillation column could force you to?

Expend more energy , limit tower efficiency, and stop vaporization in severe cases.

Basic components of a plate column include:

Feed inlet, feed tray, rectifying or enriching section, stripping section, bottom outlet, overhead outlet, reflux line, reboiler, condenser, feed preheater, sidestream outlets, downcomer, weir, riser, control loops, pipes, pumps, valves, instrumentation, and computers.

Primary subsystems in a plate distillation system.

Feed system, preheat system, distillation column, overhead system, and bottom system.

Distillation process includes what?

Feed system, preheat system, distillation column, overhead system, and bottoms system.

Packing supports come in the following designs:

Flat sieve plates, gas-injection support plates, grid supports, cone supports, and corrugated supports.

Dry tray -

Flow down the column is restricted, caused by lack of sufficient. feed.

Pressure is defined as what?

Force or weight per unit area.

System -

Frequently used to describe the various equipment arrangements associated with distillation.

Flow rate measured in?

Gallons per minute.

Structured packing -

Has specific geometric shapes, like a mesh.

Valve Trays -

Have moveable plates. Plate movement depends on process flow. More efficient than the sieve tray. Each valve is a metal strip or a small metal disc that lifts under pressure.

What 2 components does a distillation column balance?

Heat and material.

What heat transfer devices are available for the process?

Heat exchangers or furnace system.

Bottoms product contains __________ molecules than the side stream, or top.

Heavier.

Temperature in the stripping section is usually much ____________ than in the rectifying section.

Higher.

Packing supports are designed to do what?

Hold up the combined weight of the packing and liquid under a variety of abnormal conditions.

Random packing -

Includes discrete pieces of packing that are randomly dumped or poured into a packed column.

Overlap

Incomplete separation of a mixture.

Increased pressure results in-

Increased temperature.

As pressure ___________, the boiling point ___________.

Increases,Increases.

Continuous Batch -

Is a continuous of the batch operation. Product quality from still to still is relatively consistent.

Bubble Point Curve

Is the lower curve on a Vapor Liquid Equilibrium Curve and identifies the specific temperature where the mixture first produces vapor.

Dew Point Curve

Is the upper curve on a Vapor Liquid equilibrium Curve and is defined as the temperature where the first drop of liquid forms.

Bed limiters and hold-down plates are engineered to do what?

Keep fixed bed packing from migrating or fluidizing out of the section.

Bed limiters and hold down plates do what?

Keep the internal components of the column stable and in operating conditions.

What kind of energy do molecules in motion have?

Kinetic energy.

Liquid distributor designs in a packed column:

Ladder pipe, spray distributor, perforated ring distributor, notched-trough distributor, tunnel orifice distributor, weir-riser distributor, and orifice pan distributor.

What do furnace systems provide?

Large-scale temperature control where flow rates into the column are high.

What is the heat called that cannot be measured?

Latent heat.

What is carefully controlled in the bottoms system?

Liquid level, temperature, and composition.

Overall Flooding

Local flooding expands to the entire column.

It is possible for a packed column to experience ________ and ________ _________ as the voids between packing and stages fill up.

Local, Overall flooding.

Azeotropic Mixture

Mixture of 2 or more components that boil at similar temperatures and at a certain concentration.The liquid and vapor concentrations of an ___________ are equal.

Fractional Distillation -

Modern and most common operation.

What determines how a chemical reacts during separation?

Molecular weight.

Tray Drying -

Occurs due to low feed rates, low reflux rates, or high upward vapor flow rates from tray to tray.

Downcomer Flooding

Occurs when the liquid flow rate in the tower is so great that liquid backs up in the downcomer and overflows to the upper tray. Liquid accumulates in tower, differential pressure increases, and product separation is reduced.

Puking-

Occurs when the vapor is so great that it forces liquid up the column or out the overhead line.

Weeping -

Occurs when the vapor velocity is too low to prevent liquid from flowing through the holes in the tray instead of across the tray. Differential pressure is reduced and product separation is reduced.

Initial Boiling Point

Often described as the temperature where the mixture first starts to boil or evolve vapors.

Foaming

Often the result of too much heat, impurities in the feed, or active turbulence on the trays above undersized downcomers.

Cryogenic Distillation

Often used to separate oxygen and nitrogen from our atmosphere by using low-temperature drying and distillation methods.

Batch -

Oldest distillation process. Product quality was very poor, waist of time, and money.

Sidestream can be located where?

On every tray or stage a column.

Hold down plates rest where?

On top of the packing.

What usually has overlap?

Overhead, side stream, and bottoms product.

Reboiler help control what?

Overlap and heat balance.

Name 2 types of distillation columns?

Packed column, plate column.

The packing in a distillation column is supported by what?

Packing supports.

The tank farms has a complex system of:

Piping, valves and pumps.

Feed Tray

Point of entry of process fluid in a distillation column, under the feed line.

Basic components of a distillation column include:

Preheaters, pumps, the condenser and drum, and the reboiler.

What is designed to raise the temperature of the raw feedstock before it enters the distillation column?

Preheating systems.

Vacuum effect the boiling point in the opposite way of positive ___________.

Pressure

What are the abnormal conditions packing supports withstand?

Pressure surges, localized flooding, and temperature and flow variations.

Temperature in a tower can be affected by:

Pressure, flow rates, fluid levels, feed composition, reflux rate, and equipment problems.

Temperature in a tower can be affected by:

Pressure, flow, level, feed composition, reflux rate, and upset trays.

Each section of packed and plate columns have it's own individual characteristics:

Pressure, temperature, composition, velocity, and performance.

Basic elements of a control loop?

Primary element and sensors, transmitter, controller, converter, and a final control element.

Heat Balance

Principle that heat in equals heat out.

Material Balance

Principle that the sum of the products leaving equals the the feed entering the distillation column.

Atmospheric Pressure -

Produced by the weight of the atmosphere as it presses down on an object resting on the surface of the earth.

Packing supports are designed to do what?

Provide sufficient air-liquid passage and to prevent the packing from migrating into the lower sections of the column.

Name 3 types of packing used in a packed column.

Random, structured, and stacked.

Packing is usually ___________ or ____________, typically a combination of both is used in a packed column.

Random, structured.

What is connected to the bottoms system/ stripping section to maintain and add heat energy in to the liquid?

Reboiler

What device is designed to maintain the heat in a column?

Reboiler.

What is the section of the tower located above the feed tray called?

Rectifying or enriching section.

In most packed columns, the downward flow of liquid is occasionally ____________.

Redistributed.

Vacuum system benefits:

Reduce energy cost, reduce. molecular damage by over heating, and reduce equipment damage.

Bottoms outlet is used to do what?

Remove residue from the distillation column and and to feed the reboiler.

Latent heat -

Required to change liquid to vapor, cannot be sensed or measured.

Liquid that does not vaporize in a column is called.

Residue

What is the bottoms product on a distillation column called?

Residue, or heavy components of the process.

Bottoms Product

Residue; the heavier components of a distillation process fall to the bottom the tower and are removed.

Column Loading

The amount of material fed continuously into a distillation column.

Partial Pressures-

The amount of pressure per volume exerted by the various fractions in a mixture of gases.

Reflux Ratio-

The amount of reflux returned to the tower divided by the amount of overhead product sent to storage. For example, 120 GPM reflux divided by 60 GPM overhead to product tank = 2:1 reflux ratio.

Relative Volatility -

The characteristics associated with a liquid's tendency to change state or vaporize inside a distillation system.

Distillate

The condensate taken from a distillation column.

Pressure is proportional to height ;

The higher the atmosphere, gas, or liquid the greater the pressure.

Overhead Product

The lighter components in a distillation column, which rise through the column and go out the overhead line, where they are condensed.

What does open injection replace?

The need for a reboiler.

The composition and condition of feed stock sit enters the tower effects what?

The number of trays needed, reflux rate, level, pressure, and temperature.

Temperature Gradient -

The progressively rising temperature from the Botton of a distillation column to the top.

Boiling Range

The range of temperatures from when the lightest component boils (initial boiling point) to when the heaviest component boils (final boiling point).

Stripping Section -

The section of a distillation column below the feed line, where heavier components are located.

What is based off the difference in volatility and boiling point?

The separation of components in a distillation column.

Distillation

The separation of components in a mixture by their boiling points.

Rectification-

The separation of different substances from a solution by use of fractionating tower.

McCabe Thiele

The simplest method used in the analysis of binary distillation. The composition of the mixture on each theoretical tray can be determined by the mole fraction of one of the components.

Bubble Point

The temperature at which a liquid mixture begins to boil and produce vapor.

Boiling Point

The temperature at which a liquid turns to a vapor.

Dew Point

The temperature at which a mixture produces the first drop of liquid on a Vapor Liquid Equilibrium Curve.

Final Boiling Point

The temperature at which the heaviest component boils.

Basic components of a overhead system are:

The top of the column, the overhead condenser, a drum, two pumps, and a series of control loops.

Rectifying Section-

The upper section of a distillation column (above the feed line), where the higher concentration of lighter molecules is located.

Reflux is used for what?

To control both temperature in the rectifying section and product purity.

What are pressure gauges used for?

To provide valuable information about conditions inside a distillation column.

What are thermocouples used for?

To sense temperature changes on a process.

Bed limiters are attached where?

To the inside wall of the column.

What are condensers?

Typically tube and shell heat exchangers used to condense hot vapors into liquid.

Overhead System -

Used to cool off the hot overhead vapors.

Vapor-Liquid-Equilibrium Diagram -

Used to help a technician understand phase behavior of a 2 component mixture.

Any pressure below atmospheric pressure is referred to as?

Vacuum

Stronger the bonds, or molecular attraction, the lower the _________ _________ .

Vapor Pressure.

How will the liquid and vapor product on each tray in a tower run counter current to each other?

Vapor moving up the column while liquid moves down the column.

3 types of pressure are important to the vaporization process:

Vapor pressure, Control pressure and Vacuum.

Distillation involves -

Vaporization and condensation.

3-phase approach to cryogenic distillation operation:

Warm end section, a cold box, and liquid oxygen or nitrogen storage.

Channeling-

Will cause uneven distribution of the wetting process and will unbalance the internal vapor-liquid flow. (caused by tower slanting)

Is shifting of the towers alignment bad?

Yes can severely decrease efficiency in a tower.

Pressure changes affect what?

boiling points.

5 process variables being controlled?

flow, level,pressure,temperature, analytical.

"coldbox" equipment consist of:

heat exchangers, turbines, and a packed distillation column.

Heat added to distillation system =

molecular activity increase and pressure increase.

Jet Flooding

occurs when the vapor velocity is so high that liquid down flow in the tower is restricted. Liquid accumulates in the tower, differential pressure increases, and product separation is reduced.

Pressure is measured in what?

psi ( pounds per square inch)