Question

1. explain how the temperature and pressure affect extraction process

2. List and explain advantages of using plate columns in gas absorption tower

3. explain the importance of material of construction in the evaporation process

4. explain types of multiple effect evaporators and list their advantages

5. distinguish between the total condenser and partial condenser

Answer 1

Answer :

(1)

Effect of temperature on extraction process:

• At high temperature solubility of most material is increase in Solvent.
• Increasing temperature is results Increase in Viscosity.
• Diffusion Co-effcient is propotional to Temperature.
• Vapor pressure of Solvent is increased with temperature.
• At very high temperature, Chemical deterioration of some material take place.

Effect of pressure on extraction process.

• Density in increase with pressure, So At high pressure extraction yield will be high.

(2)

Advantages of plate column in Gas absorption tower:

• it can be handle wider range of gas & liquid flow rate than packing tower.
• it can handle Solid content present in Gas or liquid.
• Gas/liquid Contact in Cross-flow in plate column is highly effcient than counter flow in packed column.
• it can handle liquid with high viscosity.
• it can be used for non-foaming system.
• inter stage cooling / Heating can be provided in plate coloumn.

(3)

importance of MOC in evaporation process.

• Evaoparator mostly work at High temerature and Very Low pressure (Vaccum). Hence Material of construction used for evaporation have ability to withstand it.
• Material used for construction Must have Corrosion resistence.
• Selection of material based on our process material that may be contain chloride, acidic agent. or caustic chemical..( Eg. Cast iron never used in NaOH production).

(4)

Types of Multiple effect evaporator and their advantages:

There are four types :

(A) Forward feed

In forward feed type feed is introduced in first effect. partly concentrated liquor flows to theseconf effect and Fully concentrated Product draws from last effect. Steam/Heating fluid eneters to first effect.Vapor generated in first effect is used in second effect and so on.

the arrangement for forward feed as shown in fig.

Advantages:

• It is Easy to operate.
• It is Less expensive.

the liquor from one effect to next is transffered by pressure gradient.because last effect has lowest pressure.So no pump required for transporting liquor.

very low chance of deteriotation of heat sensitive material because of highly concentrated fluid at low temperature.

(B) Backward feed.

The feed is introduced to the last effect Partly concentrated liquor feed to the second last effect and Concentrated product withdraw from last effect. Steam / heating fluid eneters in first effect.

the arrangement for Backward feed as shown in fig.

Advantages:

• High Heat transfer rate because most concentrated solution contact with high temperature so its lower viscosity.
• Steam economy will be high.

(C) Mixed Feed

in this type, Feed eneters in intermediate effect and flows to the next high effect umtill it reaches the last effect. in this section flows occur in forward feed mode. then liquor pumped to effect just before feed enetered then it flows to the first effect and product wuthdraw from first effect.

the arrangement for mixed feed as shown in fig.

Advantages:

• it has combination of forward feed and Backward feed So, it has a high economy and Simple in operation.
• It is used for high viscosity Fluid.

(D).Parallel feed.

Fresh feed enters in all effect and Thick liquor withdraw from all effect.

the arrangement for parallel feed as shown in fig.

Advantages:

• it allows better control.

(5)

Difference between total condenser and partial condenser

• In total condenser All vapor entered will be condensed to liquid.
• In partial condenser Vapor is partially Condensed.