Adsorption Columns & Equipment - How do they Work? (Lec127)

Summary

This lecture delves into various absorption equipment types, including stirred tanks, fixed beds, and pressure and temperature swing adsorption. It explains how these methods operate, their applications, and the factors influencing their efficiency. Stirred tanks are ideal for batch processes, while fixed beds, also known as percolation columns, are commonly used for gas and liquid separation. Pressure swing adsorption (PSA) and temperature swing adsorption (TSA) are highlighted for their effectiveness in regenerating adsorbents by manipulating pressure and temperature, respectively. The lecture also touches on displacement purge adsorption, which uses a preferential adsorbate to displace contaminants from the adsorbent surface.

Takeaways

• 🔬 **Absorption Equipment Types**: The lecture discusses various types of equipment used in absorption processes including stirred tanks, fixed beds, pressure swing adsorption, temperature swing adsorption, and displacement purge adsorption.
• 🧪 **Stirred Tank Operation**: Stirred tanks operate in batch mode where a slurry is formed for mass transfer, and the residence time is determined by the approach to equilibrium.
• 🌡️ **Fixed Bed Adsorption**: Fixed beds, also known as percolation columns, are used for gas and liquid phase separation and operate in a cyclic batch mode with at least two types of beds for absorption and reverse sorption.
• ⏱️ **Mass Transfer Zone (MTZ)**: In fixed bed adsorption, mass transfer occurs in a specific region known as the MTZ, which moves through the bed as the adsorbent becomes saturated.
• 🔄 **Bed Configuration**: The number and arrangement of fixed beds depend on factors like feed flow rate, pressure drops, energy requirements, and the method of adsorbent regeneration.
• 🌀 **Pressure Swing Adsorption (PSA)**: PSA involves reducing the partial pressure of the adsorbate to regenerate the adsorbent, which can be achieved by decreasing the system's total pressure or adding inert gas.
• 🔥 **Temperature Swing Adsorption (TSA)**: TSA uses temperature changes, typically an increase, to favor desorption by shifting the adsorption equilibrium.
• 🌡️ **Effect of Temperature**: An increase in temperature generally leads to a decrease in the quantity of adsorbate being adsorbed, which is useful for desorption.
• 💧 **Displacement Purge Adsorption (DBA)**: DBA removes adsorbate from the adsorbent surface by displacement with a more preferential adsorbate species, which can lead to product contamination.
• ⚖️ **Heat Considerations**: In DBA, the net heat generated or consumed is typically zero due to the similarity in the heat of adsorption between the displacement fluid and the original adsorbate.

Q & A

What are the main types of equipment used in absorption processes?

The main types of equipment used in absorption processes include stirred tanks, fixed beds, pressure swing adsorption, temperature swing adsorption, and displacement purge adsorption.

How does a stirred tank operate in the context of absorption?

A stirred tank operates at batch conditions where the adsorbent is added as a powder, and the liquid via a solvent is added to remove. The mixture is stirred to form a slurry in which mass transfer occurs.

What determines the required residence time in a stirred tank absorption process?

The required residence time in a stirred tank absorption process is mainly determined by how fast the adsorbent approaches equilibrium.

What is a fixed bed adsorption process, and what is its common application?

A fixed bed adsorption process, also known as a percolation column, involves a stationary bed of adsorbent through which the fluid flows. It is commonly used for gas and liquid phase separation.

How does the rate of interaction change in a fixed bed adsorption process over time?

In a fixed bed adsorption process, the rate of interaction typically increases initially but decreases over time as the adsorbent becomes saturated.

What are the factors that determine the number and arrangement of fixed beds in an adsorption process?

The factors that determine the number and arrangement of fixed beds in an adsorption process include feed flow rate, pressure drops, energy requirements, length of the mass transfer zone, method of adsorbent regeneration, and capital investment.

What is pressure swing adsorption, and how is regeneration achieved in this process?

Pressure swing adsorption is a process where adsorption and desorption are favored by changing the pressure conditions. Regeneration is achieved by reducing the partial pressure of the adsorbate, either by reducing the system's total pressure or by adding an inert gas.

How does temperature swing adsorption differ from pressure swing adsorption?

Temperature swing adsorption differs from pressure swing adsorption in that it uses changes in temperature, typically an increase, to favor desorption of the adsorbate from the adsorbent.

What is the effect of temperature on the adsorption equilibrium in temperature swing adsorption?

In temperature swing adsorption, an increase in temperature leads to a decrease in the quantity of adsorbate being adsorbed, favoring desorption.

What is displacement purge adsorption, and how does it work?

Displacement purge adsorption is a process where adsorbed species are removed from the adsorbent surface by replacing them with a more preferential adsorbate species, which can be a gas, liquid, or vapor.

What is a potential drawback of using displacement purge adsorption?

A potential drawback of displacement purge adsorption is that the displacement fluid can contaminate the product stream, as the displaced adsorbate is released back into the fluid.