Question

Which is the suitable contacting equipment for gas-liquid operations involving liquids with dispersed solids?

• A. Packed columns
• B. Bubble columns
• C. Plate columns
• D. Spray columns

Hint:

Think about what happens when you try to pour a liquid with sand in it through a sponge (packed column) versus letting it flow over a series of perforated plates (plate column). The plates are less likely to get completely blocked.

Answer 1

The Correct Option is C

Step 1: Understand the characteristics of gas-liquid operations involving liquids with dispersed solids. 
These operations involve the contact between a gas and a liquid that contains solid particles suspended within it. The presence of these dispersed solids can pose challenges for the contacting equipment, particularly regarding clogging, fouling, and efficient mass transfer. 
Step 2: Consider the operational aspects and limitations of each type of contacting equipment. 
Packed columns: These columns contain inert solid packings that provide a large surface area for gas-liquid contact. However, dispersed solids in the liquid can easily get trapped within the packing, leading to clogging and increased pressure drop, and reducing efficiency. Cleaning a clogged packed column can also be difficult. Bubble columns: These are vertical vessels where gas is introduced at the bottom and rises as bubbles through the liquid. While they offer relatively simple construction and can handle some suspended solids, high concentrations of solids can still lead to issues with settling at the bottom or affecting the gas-liquid interfacial area and mass transfer. Plate columns (or tray columns): These columns consist of a series of trays or plates stacked vertically within a shell. Gas flows upwards through openings in the trays, contacting the liquid flowing across the trays. Plate columns offer several advantages for liquids with dispersed solids. The flow paths are relatively open compared to packed columns, reducing the risk of clogging. They can also be designed with features that help handle solids, and they are easier to clean than packed columns. Different tray designs (e.g., sieve trays, valve trays) can be selected based on the concentration and properties of the dispersed solids. Spray columns: In these columns, the liquid is dispersed as droplets into a continuous gas phase. While they can handle some solids, the nozzles used to create the spray can become clogged if the solid concentration is high or if the particle size is significant. 
Step 3: Evaluate the suitability of each equipment for the given conditions. 
Considering the potential for clogging and the need for relatively unobstructed flow, plate columns are generally more suitable for gas-liquid operations involving liquids with dispersed solids compared to packed columns or spray columns. While bubble columns can handle some solids, plate columns offer better control over flow patterns and can be designed to minimize issues related to suspended particles. 
Step 4: Select the most appropriate contacting equipment. 
Plate columns are the most suitable contacting equipment for gas-liquid operations involving liquids with dispersed solids due to their relatively open flow paths and ease of handling and cleaning compared to packed columns, and lower risk of clogging compared to spray columns. They also offer better control over gas-liquid contact than simple bubble columns in the presence of solids.