Distillation is defined as: a process in which a liquid or vapor mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat.
Although many people have a fair idea what “distillation” means, the important aspects that seem to be missed from the manufacturing point of view are that:
Distillation is the most common seperation technique
It consumes enormous amounts of energy, both in terms of heating and cooling requirements
It can contribute to as much as 50% of the plant's operating costs
The best way to reduce operating costs of existing units, is to improve their efficiency and operation and control. To achieve this improvement, a thorough understanding of distillation principles and how distillation systems are designed is essential.
Types of Columns Columns can initially be divided into two Groups:
Batch Columns
In batch operation, the feed to the column is introduced batch-wise. That is, the column is charged with a 'batch' and then the distillation process is carried out. When the desired task is achieved, a next batch of feed is introduced.
Continuous Columns
In contrast, continuous columns process a continuous feed stream. No interruptions occur unless there is a problem with the column or surrounding process units. They are capable of handling high throughputs and are the most common of the two types. We shall concentrate only on this class of columns.
Continuous Columns can further be catagorized by: The nature of the feed being processed:
-Multiple components - feed contains more than two components
-Binary - feed only contains 2 components
Column Interals: - Packed column - "packings" are used to increase contact between vapor and liquid streams
- Tray Column - Engineered tray designs are used to hold liquid (weirs) to promote better contact between vapor and liquid streams
Bubble Cap
Valved
Sieve
Factors that affect Distillation Operations -State of feed to tower -Compostion of Feed -Condition of Column internals - Weather Conditions - Flow conditions within the column - VLE (Vapor to Liquid Equalibrium)
Foaming - Expansion of a liquid as gas passes through it. Excessive foaming can contaminated tray above. However, foaming is desired for distillation seperation. tray spacing, properties of solution (entrainment)
Flooding - too much vapor pressure forcing liquid to become entrained = limits flow of liquid through downcomers.
Dumping/Weeping - vapor pressure is too low to hold liquid on trays = liquid begins to leak through perforations of plates
- Column Diameter - The above conditions are all directly correlated to the Velocity (or Flow) of the gas stream. The DIAMETER of the column directly affects this FLOW RATE
Weeping - would be the point of lowest desired flow rate of vapor
Flooding - would represent the point of highest flow rate of vapor
The process of distillation ia a basic concept is that we can separate a mixture of two pure liquids with different boiling points by heating the mixture to a temperature between their respective boiling points. For example, water boils at 100°C and ethanol boils at around 83°C at atmospheric pressure. If we heat the mixture to say 92°C, the ethanol will boil and be transformed into vapor (which is collected and condensed) while the water will remain as a liquid. This phenomenon is usually quantified by the relative volatility of the two components.A distillation column is used to make this process more efficient. A schematic diagram of a distillation column (with Trays) is shown below.
The distillation column itself is made up of a series of stacked plates. A liquid feed containing the mixture of both liquids enters the column at one or more points. The liquid flows over the plates, and vapor bubbles up through the liquid via holes in the plates. As liquid travels down the column, vapor comes in contact with it many times (due to the multiple plates). This is the critical process in distillation columns. The liquid and vapor phases are brought into contact because as one molecule of higher boiling material converts from vapor to liquid phase by energy release, another molecule of the low boiling material utilises the free energy to convert from liquid to vapor phase.
You guys are going to do some of the research and learning. Below you will find the description of your presentation and also a grading rubric for the project.
a process in which a liquid or vapor mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat.
Although many people have a fair idea what “distillation” means, the important aspects that seem to be missed from the manufacturing point of view are that:
Types of Columns
Columns can initially be divided into two Groups:
The nature of the feed being processed:
Column Interals:
- Packed column - "packings" are used to increase contact between vapor and liquid streams
- Tray Column - Engineered tray designs are used to hold liquid (weirs) to promote better contact between vapor and liquid streams
Factors that affect Distillation Operations
-State of feed to tower
-Compostion of Feed
-Condition of Column internals
- Weather Conditions
- Flow conditions within the column - VLE (Vapor to Liquid Equalibrium)
- Foaming - Expansion of a liquid as gas passes through it. Excessive foaming can contaminated tray above. However, foaming is desired for distillation seperation. tray spacing, properties of solution (entrainment)
- Flooding - too much vapor pressure forcing liquid to become entrained = limits flow of liquid through downcomers.
- Dumping/Weeping - vapor pressure is too low to hold liquid on trays = liquid begins to leak through perforations of plates
- Column Diameter - The above conditions are all directly correlated to the Velocity (or Flow) of the gas stream. The DIAMETER of the column directly affects this FLOW RATEThe process of distillation ia a basic concept is that we can separate a mixture of two pure liquids with different boiling points by heating the mixture to a temperature between their respective boiling points.
For example, water boils at 100°C and ethanol boils at around 83°C at atmospheric pressure. If we heat the mixture to say 92°C, the ethanol will boil and be transformed into vapor (which is collected and condensed) while the water will remain as a liquid. This phenomenon is usually quantified by the relative volatility of the two components.A distillation column is used to make this process more efficient. A schematic diagram of a distillation column (with Trays) is shown below.
The distillation column itself is made up of a series of stacked plates. A liquid feed containing the mixture of both liquids enters the column at one or more points. The liquid flows over the plates, and vapor bubbles up through the liquid via holes in the plates. As liquid travels down the column, vapor comes in contact with it many times (due to the multiple plates). This is the critical process in distillation columns. The liquid and vapor phases are brought into contact because as one molecule of higher boiling material converts from vapor to liquid phase by energy release, another molecule of the low boiling material utilises the free energy to convert from liquid to vapor phase.
You guys are going to do some of the research and learning. Below you will find the description of your presentation and also a grading rubric for the project.