Mechanical Operations - Chemo Concept

Every chemical industry deals with chemicals in the solid state. For example for Sulphuric acid is produced from solid sulfur, Phosphoric acid is produced from phosphate rock, Sodium hydroxide is produced from sodium chloride.

And the solid materials used in chemical industries are not found in the phase in which we wanted.

What is Mechanical Operations?

Mechanical operation is a set of operations that are carried out on solid materials to get them in the desired phase.

Mechanical operations involve size reduction of solid, separation of solids, purification of solids, and much more.

List of Mechanical Operations

Here is a list of mechanical operations generally used in industries:

1. Transportation
2. Screening
3. Size reduction
4. Filtration
5. Clarification
6. Mixing

Let's learn about all one by one

1. Transportation

Before any processing is done on solid materials, it is necessary to transport them to the different sections and equipment.

Transportation not just involves horizontal movement of solids but also solids are transported to heights to feed into equipment.

It is easier to transport free-flowing solids and transportation becomes harder as it becomes sticky.

Equipment for transportation of solids

• Belt conveyor
• Bucket conveyor
• Screw conveyor
• Pneumatic transport
• Hydraulic transport
• Hopper

2. Screening

Screening is an operation of solid-solid separation based on size.

Screening basically is an operation of separation of bigger size particles from smaller size particles.

Using particles having nearly the same size helps in easier control and study of any process.

In screening one screen or a perforated metal sheet is used.

A solid feed of different sizes is introduced on-screen or perforated metal plate. The undersize particle gets passed from holes called underflow and oversize particles get trapped on the plate or screen which can be taken out called overflow.

A screen can be used in a single quantity to get particles lower than the diameter of holes.

Multiple screens are used in many cases to separate a mixture of solids of different sizes into a group of the size range.

There are many types of screening equipment used in industries.
The capacity and Efficiency of a screen is one important factor that is to be measured to find the effectiveness of screens.

Some of them are

• Grizzly
• Trommel
• Gyratory screen
• Vibrating Screen
• Centrifugal Screen

3. Size Reduction

Size reduction involves as the name suggests reduction of the size of the particles of bigger size to a smaller size by applying some type of force on them and breaking them into smaller size particles.

In industries, many solid operations depend on the outer surface area of the solid. Smaller size particles of the same amount will have a higher surface area than bigger particles.

Size reduction is also called commutation.

Types of forces involved in size reduction are compression, attrition, impact, shear actions, etc.

Size reduction equipment which is common in industries are classified as:

(I) For Course Particles

• Jaw crusher
• Crushing rolls
• Gyratory crusher

(II) For intermediate size particles

• Hammermill (Impactor)
• Roller Mill

(III) For Small Size Particles

• Ball mill
• Tube mill
• Rod mill

(IV) For ultrafine size crushing

• Fluid energy mill
• Agitated mill
• Colloid mill

(VI) By mills based on cutting action

• Slicer
• Dicer
• Cutter

(VII) By mills based on attrition action

• Attrition mill

4. Filtration

Filtration is a liquid-solid separation operation in which filter media is used which allows only liquid to pass through it and retains solid on its surface.

Sometimes filter aids are added to the feed to make filtration easier.

It is necessary to apply pressure on the feed to remove more amount of liquid from solid cake generated on filter media.

As time passes solid gets deposited on filter media which results in higher pressure of filtration pressure.

Sometimes negative pressure is applied on another side for easier separation.

An industrial example of filtration operation is the separation of sodium hydroxide flakes from its solution.
Widely used filtration equipment are

• Filter press
• Rotary filter
• Belt filter
• Membrane filter

5. Clarification

Clarification is one of the important solid-liquid separation processes in which gravity plays a major role.

In clarification operation feed containing both solid and liquid is taken in settling tank or clarifier.

Solids having higher density sink down to the bottom and water floats over them.

After a specified time we get layers of both solid and liquid which can be taken out separately.

Sometimes flocculating agents are also added for agglomeration of particles which helps in settling.

An industrial example of clarification operation is in the production of caustic soda sodium chloride is used as raw materials which contain some amount of other salts which are treated chemically and settled down in a clarifier for initial impurity removal.

6. Mixing

In industries many times it is necessary to mix two solids to make a homogenous mixture. There are different types of mixing equipment used according to the type of solids are being mixed.

Mixers used for Cohesive Solids

• Change can mixer
• Kneader
• Disperser
• Masticator
• Mixing rolls
• Muller mixer
• Mixer extruder
• Pugmill

Mixers used for free-flowing solids are

• Ribbon blender
• Internal screw mixer
• Tumbling mixer
• Impact wheels