Packed Columns in Chemical Engineering

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Questions and Answers

What is the purpose of the trays (plates) in tray towers?

To provide intimate contact of liquid with vapor to promote rapid mass transfer (correct)

To reduce the interfacial surface area for mass transfer

To prevent the vapor and liquid from contacting each other

To create a froth that hinders mass transfer

What is the main function of sieve trays in tray towers?

To provide a large interfacial surface area for mass transfer

To create a hindrance in the flow of liquid

To allow vapor to bubble up through simple holes to contact the flowing liquid (correct)

To block the flow of vapor through the tray

In what way do gas and liquid flow in absorption, stripping, and distillation operations in vertical towers?

Concurrently

Counter-currently (correct)

Parallelly

Intermittently

What are the common types of Tray Towers mentioned in the text?

Sieve Trays and Valve Trays Signup and view all the answers

What is the main advantage of a valve tray over a sieve tray?

Ability to operate at a greater range of flow rates Signup and view all the answers

Why have bubble-cap trays been generally superseded by sieve-type or valve trays since 1950?

Almost double the cost of sieve-type trays Signup and view all the answers

What is the reported operational flexibility of tray towers in terms of?

Turn-down ratio Signup and view all the answers

What happens when the vapor rate is too low in a tray tower?

Liquid-droplet entrainment becomes excessive Signup and view all the answers

What is the relationship between the maximum value of $x_1$ and the minimum of $L'$?

They are inversely proportional Signup and view all the answers

Under what condition does the operating line reach the minimum value of $L$ when the equilibrium line is concavely downward?

By becoming tangent to the equilibrium line Signup and view all the answers

What is the approximation for the optimum liquid flow rate for absorption in terms of the limiting rate, $L'_{min}$?

1.2–1.5 times $L'_{min}$ Signup and view all the answers

In the example of separating a paraffin hydrocarbon from a non-volatile organic compound, what is used for stripping?

Steam Signup and view all the answers

What is the purpose of packed columns in absorption processes?

To provide a large area of intimate contact between the liquid and gas Signup and view all the answers

What is the characteristic of good packings for tower columns?

High void spaces Signup and view all the answers

How does the liquid flow through the packed sections in a column?

Downward through the packing Signup and view all the answers

What materials are commonly used for tower packings?

Clay, porcelain, graphite, or plastic Signup and view all the answers

Study Notes

Tray Towers

The trays (plates) in tray towers serve to promote contact and separation between gas and liquid streams.
The main function of sieve trays in tray towers is to provide a large surface area for mass transfer between the phases.

Flow in Vertical Towers

In absorption, stripping, and distillation operations, gas flows upward, while liquid flows downward, in vertical towers.

Types of Tray Towers

Common types of tray towers mentioned in the text include sieve trays, valve trays, and bubble-cap trays.

Valve Trays vs Sieve Trays

The main advantage of a valve tray over a sieve tray is its ability to self-correct and maintain a consistent liquid seal, even with changes in vapor flow.

Superseding of Bubble-Cap Trays

Bubble-cap trays have been generally superseded by sieve-type or valve trays since 1950 due to their higher efficiency and lower costs.

Operational Flexibility of Tray Towers

Tray towers have reported operational flexibility in terms of turndown ratio, allowing them to adapt to changes in flow rates.

Low Vapor Rate in Tray Tower

When the vapor rate is too low in a tray tower, the tray may become flooded, leading to reduced efficiency and performance.

Equilibrium Line and Operating Line

The maximum value of $x_1$ is related to the minimum value of $L'$.
The operating line reaches the minimum value of $L$ when the equilibrium line is concavely downward.

Optimum Liquid Flow Rate for Absorption

The approximation for the optimum liquid flow rate for absorption is in terms of the limiting rate, $L'_{min}$.

Separation of Paraffin Hydrocarbon and Non-Volatile Organic Compound

Steam is used for stripping in the example of separating a paraffin hydrocarbon from a non-volatile organic compound.

Packed Columns in Absorption Processes

The purpose of packed columns in absorption processes is to provide a large surface area for mass transfer between the phases.

Characteristics of Good Packings

Good packings for tower columns should have a high surface area, low pressure drop, and high mass transfer efficiency.

Liquid Flow through Packed Sections

Liquid flows through the packed sections in a column by trickling down through the packing, creating a large surface area for mass transfer.

Common Materials for Tower Packings

Common materials used for tower packings include ceramic, metal, and plastic materials.

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Description

Test your knowledge of packed columns in chemical engineering with this quiz. Learn about the vertical, cylindrical vessels containing packing sections through which liquids and gases flow for mass transfer processes.