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Distillation
A process in which heat is used to separate a mixture of hydrocarbons into two or more relatively pure products (or fractions) by the difference in their respective boiling points or boiling ranges. When a mixture of hydrocarbons is heated, the light components are the first to boil and go into a vaporized state. These vapors are cooled and condensed to form a fraction that is enriched in light hydrocarbon molecules. The liquid that doesn't vaporize forms a heavy fraction.
The desired value for a process variable.
Distillation
A process in which heat is used to separate a mixture of hydrocarbons into two or more relatively pure products (or fractions) by the difference in their respective boiling points or boiling ranges. When a mixture of hydrocarbons is heated, the light components are the first to boil and go into a vaporized state. These vapors are cooled and condensed to form a fraction that is enriched in light hydrocarbon molecules. The liquid that doesn't vaporize forms a heavy fraction.
Hydrocarbon
A molecule made up of hydrogen and carbon atoms.
Physical Change
A change that does not involve the breakdown or restructuring of a substance's molecules.
Chemical Change
A change that involves a chemical reaction in which a substance's molecules are rearranged.
Sensible Heat
Heat that actually increases the temperature of a substance.
Latent Heat
Heat that is added to vaporize a substance already at boiling temperature.
Vapor Pressure
Pressure exerted by the molecules in a liquid as they attempt to escape from a liquid to a vaporized state.
Partial Pressure
The amount of pressure exerted by each component in a mixture of gases. The total pressure inside a closed vessel is equal to the sum of the partial pressures exerted by each gas.
Reflux
A liquid formed by cooling and condensing overhead vapors from a distillation column. This liquid is returned to the tower to remove heat from hot, rising vapors that are contacted on each tray. The exchange between cool reflux and hot vapors keeps each tray in the tower operating at a slightly different temperature.
Stripping Section
The part of the column below the feed tray where light components are vaporized out of the liquid.
Rectifying Section
The part of the column above the feed tray where heavy components are condensed out of the vapors.
Atmospheric Column
A column that operates at or slightly above atmospheric pressure (14.7 psi or above).
Vacuum Column
A column that operates under a partial vacuum (under 14.7 psi).
Tray
A plate inside a distillation column where vapor-liquid contact takes place. Different types of hardware can be used to create this contact.
Feed Tray
The tray on which feed is introduced into the tower.
Down comers
Passageways for the downward flow of liquid through the tower.
Initial Boiling Point
The temperature at which the first drop of condensate falls from the condenser into the receiver in a laboratory distillation test. Abbreviated IBP.
End Boiling Point
The highest temperature reached during a laboratory distillation test, or the temperature at which the last drop of liquid in the sample vaporizes during the test. Abbreviated as End Point - EP.
Boiling Range
The range of temperatures from a sample's initial boiling point to its end boiling point. A boiling range test identifies both light and heavy hydrocarbons over a product's entire boiling range.
Flash Point
The temperature at which a petroleum product generates ignitable vapors.
API Gravity
A measure of the "lightness" or "heaviness" of a product. An API gravity of 10° means that a product is exactly the same weight as water. Products that are heavier than water have API gravity less than 10°. Petroleum products that are lighter than water have an API gravity that is greater than 10°.
Heat Balance
All the heat that goes into a distillation column must be taken out. If we adjust the amount of heat put into a tower or the amount removed, the composition and quantity of the products that are formed will also change.
Cut Point
The product separation temperature that is used in a distillation column to obtain a product that contains the desired mixture of hydrocarbons. Altering the heat balance in a column to produce more or less of a particular product is called changing the cut point.
Material Balance
The input of material to a distillation column equals the output of material from that column. Whatever material enters a tower as feed leaves the tower as products.
Process Variable
A process condition that can change during the process operation. The four most common process variables are temperature, pressure, liquid level, and flow rate.
Primary Element or Sensor
A device that senses the condition of a process variable, or causes a change in the variable that makes a measurement possible.
Control Loop
A combination of instruments that works to keep a process variable at a set value. The instruments will vary according to the process being controlled.
Measuring Means
The instrument in a control loop that senses and measures the condition of a process variable and transmits this measurement.
Controller
The instrument in a control loop that continuously compares a measurement of the process variable with set point. The controller continuously transmits a signal to the final control element and adjusts this signal when necessary to make a process correction.
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